Ball screw drives are commonly used to provide linear motion in machine tools. And stiffness is one of the most important performance indexes. However, stiffness of nuts with different preloads is difficult to be calculated precisely because of complex structures. In order to improve the calculating accuracy, a new model is proposed with the consideration of geometry errors of grooves and balls based on the existing theoretical model. The influence of geometry errors on axial deformation of double-nut is analyzed and modeled. Meanwhile, a preload-adjustable ball screw drive is constructed on the basis of a modified double-nut mechanism. A novel loading mechanism is designed to apply axial load on the working table and test the force in real time. Two laser displacement sensors are adopted to test axial deformation of the double-nut. The axial stiffness of the double-nut is analyzed based on the axial load and the axial deformation. Stiffness simulations of the new improved model, the theoretical model, and the empirical model are also analyzed. The contrastive analysis shows that the experimental results agree much better with the axial stiffness calculated by the new improved model. This study provides a more accurate model to calculate the stiffness of the double-nut with preloads for preloaded ball screw drives.
A theoretical investigation of dynamic behaviors of helical geared multishaft rotor systems is performed in this paper. A modal synthesis is developed to calculate free and forced vibrations for geared rotor systems including more than two shafts and gears. Degrees of freedom can be reduced to save the computing time in this method. Results of reduced model are compared with those of full degrees of freedom model, to obtain the acceptable reduction of degrees of freedom without significant loss of accuracy in predicting free and forced vibrations. Then, with the help of this method, dynamic behaviors of helical geared multishaft rotor systems are investigated. Parametric studies are conducted to reveal the effects of several system parameters on the vibration characteristics. Results show the reliability and accuracy of the modal synthesis as well as its limitations of calculating responses due to high-frequency excitations, and provide some references to designers attempting to obtain desirable dynamic behaviors.
Constrained optimization problems constitute an important fraction of optimization problems in the mechanical engineering domain. It is not uncommon for these problems to be highly-constrained where a specialized approach that aims to improve constraint satisfaction level of the whole population as well as finding the optimum is deemed useful especially when the objective functions are very costly. A new algorithm called Feasibility Enhanced Particle Swarm Optimization (FEPSO), which treats feasible and infeasible particles differently, is introduced. Infeasible particles in FEPSO do not need to evaluate objective functions and fly only based on social attraction depending on a single violated constraint, called the activated constraint, which is selected at each iteration based on constraint priorities and flight occurs only along dimensions of the search space to which the activated constraint is sensitive. To ensure progressive improvement of constraint satisfaction, particles are not allowed to violate a satisfied constraint in FEPSO. The highly-constrained four-stage gear train problem and its two variants introduced in this paper are used to assess the effectiveness of FEPSO. The results suggest that FEPSO is effective and consistent in obtaining feasible points, finding good solutions, and improving the constraint satisfaction level of the swarm as a whole.
This paper deals with the modeling and control of rail vehicle suspensions. The analytical models of the quarter rail vehicle with a passenger seat, describing the vertical dynamic, are presented for passive and active suspensions. Three controllers, i.e. PID-ZN, LQR and a PID-LQR are designed in order to improve the passenger comfort. This comfort is evaluated in terms of the passenger displacement, acceleration and frequency as a response of a two types of rail imperfection excitations. Results show that passenger comfort can be improved up to 98%. The obtained results prove that the active suspension with a PID- LQR controller yields the best results by regrouping the advantage of both PID and LQR controllers.
In this work, a novel optimization approach is used to define the shape of a flywheel for energy storage. The procedure acts on a two-dimensional axisymmetric finite element method model, in which many parameters are used to describe the geometry. The optimization is performed by an evolutive system method, whereby the population’s genome is described with statistical quantities. An accurate definition of the fitness function allows for a broad spectrum of objectives. The evolution of the fitness value during population generation is discussed. The procedure does not benefit from parallelization: an alternative way of parallelizing the optimization process is presented, where the population is equally divided among the cores and calculated independently, allowing for an approximately linear performance scaling with the number of cores. The method is applied to the minimization of the mass in a flywheel for energy storage application, displaying great flexibility to the variation of the parameters describing the rotational speed, geometry constraints, and material properties. The true potential of the evolutive method is then demonstrated by optimizing an asymmetrical flywheel, where a mechanical interface lies on one side only. Usually additional parts are added manually on the optimized shape, increasing the thickness where necessary; this method permits to directly optimize to the final shape. The script used in this work is available upon request. Matlab and Ansys APDL software are needed.
Composite fibre-reinforced materials, under low velocity impacts, can experience simultaneous interacting failure phenomena, such as intra-laminar damage, fibre breakage and matrix cracking, and inter-laminar damage such as delaminations. These failure mechanisms are usually the subject of extensive investigations because they can cause a significant reduction in strength of composites structures leading to premature failure. In the present work, composite plates under low velocity impact are investigated. Experimental data, such as experimental curves and images from non-destructive inspections, are used to characterise the low velocity impacts-induced damage in conjunction with a non-linear explicit Finite element numerical model. The adopted numerical model, implemented in the FE code (Abaqus/Explicit) by a user-defined material subroutine (VUMAT), has been demonstrated to be very effective in predicting the damage onset and evolution and, in general, able to correctly integrate the experimental data by providing useful information about the impact damage localisation and evolution.
As worldwide wind energy generation capacity grows, there is an increasing demand to ensure structural integrity of the turbine blades to maintain efficient and safe energy generation. Currently, traditional non-destructive testing methods and visual inspections are employed which require the turbine to be out-of-operation during the inspection periods, resulting in costly and lengthy downtime. This study experimentally investigates the potential for using Lamb waves to monitor the structural integrity of a composite wind turbine blade that has been subject to an impact representative of damage which occurs in service. 3D scanning laser vibrometry was used to measure Lamb waves excited at three different frequencies both prior to, and after, impact to identify settings for an optimal system. Signal processing techniques were applied to the datasets to successfully locate the damage and highlight regions on the structure where the Lamb wave was significantly influenced by the presence of the impact damage. Damage size resulting from the impact was found to correlate well with the laser vibrometry results. The study concluded that acousto-ultrasonic-based structural health monitoring systems have great potential for monitoring the structural integrity of wind turbine blades.
The fault diagnosis of rotating machinery is quite important for the security and reliability of the overall mechanical equipment. As the main components in rotating machinery, the gear and the bearing are the most vulnerable to faults. In actual working conditions, there are two common types of faults in rotating machinery: the single fault and the compound fault. However, both of them are difficult to detect in the incipient stage because the weak fault characteristic signals are usually submerged by strong background noise, thus increasing the difficulty of the weak fault feature extraction. In this paper, a novel decomposition method, optimal resonance-based signal spares decomposition, is applied for the detection of those two types of faults in the rotating machinery. This method is based on the resonance-based signal spares decomposition, which can nonlinearly decompose vibration signals of rotating machinery into the high and the low resonance components. To extract the weak fault characteristic signals in the presence of strong noise effectively, the genetic algorithm is used to obtain the optimal decomposition parameters. Then, the optimal high and low resonance components, which include the fault characteristic signals of rotating machinery, can be obtained by using the resonance-based signal spares decomposition method with the optimal decomposition parameters. Finally, the high and the low resonance components are subject to the Hilbert transform demodulation analysis; the faults of rotating machinery can be diagnosed based on the obtained envelop spectra. The optimal resonance-based signal spares decomposition method is successfully applied to the analysis of the simulation and experiment vibration signals. The analysis results demonstrate that the proposed method can successfully extract the fault features in rotating machinery.
In order to accurately measure and control high-frequency grinding force in the process of grinding, a novel measurement method of three-dimensional grinding force with mutual perpendicular and independent elastic elements is proposed in this paper. To detect the high frequency grinding force, a resistance strain-type three-dimensional grinding force measurement platform was designed and developed. The key performance indicators of the measurement platform were investigated via finite element simulation. In addition, the detection performance of the measurement platform was researched and verified through natural frequency measurement experiments, static calibration experiments, and grinding experiments. The results show that the proposed method can effectively alleviate the inherent contradiction between natural frequency and sensitivity in the traditional dynamometer; the measurement platform as-established fully meets the performance requirements of three-dimensional dynamic grinding force detection. To this effect, the results discussed here provide technical support for achieving accurate detection of high frequency grinding force, monitoring grinding processes, optimizing grinding parameters, and improving grinding quality.
This paper describes a global optimization of a recirculation flow type casing treatment in centrifugal compressors of turbochargers. The global optimization for the recirculating flow type casing treatment has been performed based on the existing casing treatment. The optimization approach to the recirculation flow type casing treatment for the centrifugal compressor, incorporating meta-model assisted evolutionary algorithm, computational fluid dynamics analysis technique, artificial neural network, and genetic algorithms has been presented. For the baseline design of the casing treatment, numerical approach is validated with an experimental result from a test rig. The technical issue of the casing treatment is found to be the dropping of the adiabatic efficiency at smaller flow rate condition. In this study, the objective of the optimization is to improve adiabatic efficiency under multipoint mass flow rate conditions. The shape of the casing treatment has been parameterized by six parameters. The numerical optimization result gives the optimized recirculation casing shape, which has a possibility to improve the efficiency not only at design flow rate but also at smaller flow rate. The improvement in adiabatic efficiency at off-design point is discussed by means of the improved flow incidence at the inlet of the rotating impeller. The influence on adiabatic efficiencies at both design and off-design conditions is discussed by the sensitivity of the recirculation flow rate. It is found that the optimized design of the casing treatment provides optimized recirculation flow rate.
This paper is aimed at the solution of the driving actuator of the reversing valve, which is the core component of CNC die forging hammer. The proposed electromagnetic drive method contributes to a precise control of the valve spool position and eliminates the transmission mechanism and hydraulic circuits. The complete structure and the topology structure of the electromagnetic part are designed to guarantee its high controllability and robustness. The structure parameters of the electromagnetic part are calculated based on the driving requirement of the reversing valve. With the finite element analysis of the direct driving part, saturation phenomenon of the magnetic circuit is eliminated and optimization of the output force ripple is performed. The output force of the electromagnetic part is simulated to reach 1000 N with a rated speed of 0.55 m/s, which satisfies the drive demand of the reversing valve spool and the ripple amplitude of the output force is reduced by 43.9%. The operational test of the electromagnetic direct drive component is conducted to verify the finite element method simulation method and shows an expected performance.
Rotary ultrasonic applications are being widely used in machining hard and brittle materials. Conventional conducting ring used as power transmission part limits the ultrasonic applications from rotating at high speed. A high efficiency power transmission system is defined in this article to solve this problem. It consists of a contactless transformer, which was made up of two hollow copper coils, ultrasonic power supply and compensation capacitors. Four compensation methods are proposed and their properties are analyzed through simulations and experiments. The simulations show that S-S compensation is superior to others on the performance of transient and steady circuit parameters and the max transmit efficiency can reach about 97.2% when appropriate compensation method and capacitance are used. Rotary experiments show that speed has little effect on the property of the system.
In this study, path modification strategy is used to improve the accuracy of the die corner produced in wire electrical discharge machining process. Based on Taguchi’s L18 array, experiments are performed on Monel 400 alloy. The influence of the machine-controllable factors such as wire tension, open-circuit voltage, pulse-on time, pulse-off time and additional travel and uncontrollable factors namely corner angles and flushing nozzle height on the performance measures such as surface roughness, cutting speed, and corner error are studied. The outcome of this study reveals that the path modification value in terms of additional travel of 0.5 mm improves the corner accuracy of the profile by 35% as compared to the profile machined without adopting path modification strategy. The analyses of scanning electron micrographs are carried out. Finally, an optimal technological guideline is reported for ready industrial use.
Ultra-precision raster milling induces external stress to cause phase changes of Zn–Al alloy at a thin surface layer, which further degrade surface integrity of high-precision components. This study focuses on discussing phase changes at the surfaces of the alloy after ultra-precision raster milling under the high cutting speeds of 680 m/min, 1120 m/min, and 1360 m/min. Along with the penetration depth at the machined surfaces, phase changes and surface hardening rapidly declined to vanish with crystal orientation shift back to its standard Bragg angle. As the cutting speeds increased, phase changes, crystal orientation shift, and surface hardening obviously decreased with phase change thicknesses from 323 nm, 241 nm to 87 nm. It is worth noticing that at a high cutting speed phase changes at the machined surface can be greatly reduced to a significant degree.
This work develops an analytical method to estimate the natural frequency splitting and principal instability of the rotating cyclic ring structures. An elastic model is built up under the ring-fixed frame by using the energy method. The modeling leads to a partial differential equation with time-variant coefficient. The eigenvalue is formulated to estimate the natural frequency splitting, principal instability and their relationships. The dependence of the basic parameters on the natural frequency splitting and principal instability is demonstrated. The principal instability can occur at the splitting natural frequencies but cannot at the repeating ones. A classical problem regarding the parametric instability of the rotating ring with stationary supports and the inverse problem are examined. The results verify that the natural frequency splitting does not mean unstable for the former problem, but for the latter the splitting implies unstable. Besides, the model is transformed into the support-fixed frame and thus an equivalent time-invariant model is obtained, which is solved by using the general vibration theory. The analytical method is validated through the comparisons with the results in the open literature and especially the comparisons between the results from the two types of frames.
In this work, the modal damping of multilayered, fiber-reinforced polymer composite laminates with an arbitrary geometry have been computed using a mixed finite element-meshless method. The meshless node distribution scheme is used in conjunction with the Lagrangian quadrilateral interpolating functions to ensure the continuity of interelemental displacements. Furthermore, since the distribution of the elements is not confined to the geometry of the problem, any arbitrary geometry can be readily analyzed by using the same node and element distributions. Using the classical plate theory, together with a structural damping model, modal response results have been produced for a number of multilayer fiber-reinforced polymer plate geometries, including triangular and circular as well as rectangular plates with different combinations of free and clamped edges. Comparison of these results with those reported in the literature shows that the proposed method can predict the modal properties of fiber-reinforced polymer laminates with arbitrary geometries and boundary conditions with a good degree of accuracy.
Optimal axisymmetric penetrator nose shapes that result in most penetration under the effect of pressure-dependent Coulomb Friction are presented. The nose shapes were determined by dividing a circular cylinder into line segments and iteratively updating the combination of line segment slopes to generate the nose geometries that result in the most penetration. Analysis was conducted for five different penetrator velocities,
During the operation process of a gearbox, the vibration signals can reflect the dynamic states of the gearbox. The feature extraction of the vibration signal will directly influence the accuracy and effectiveness of fault diagnosis. One major challenge associated with the extraction process is the mode mixing, especially under such circumstance of intensive frequency. A novel fault diagnosis method based on frequency-modulated empirical mode decomposition is proposed in this paper. Firstly, several stationary intrinsic mode functions can be obtained after the initial vibration signal is processed using frequency-modulated empirical mode decomposition method. Using the method, the vibration signal feature can be extracted in unworkable region of the empirical mode decomposition. The method has the ability to separate such close frequency components, which overcomes the major drawback of the conventional methods. Numerical simulation results showed the validity of the developed signal processing method. Secondly, energy entropy was calculated to reflect the changes in vibration signals in relation to faults. At last, the energy distribution could serve as eigenvector of support vector machine to recognize the dynamic state and fault type of the gearbox. The analysis results from the gearbox signals demonstrate the effectiveness and veracity of the diagnosis approach.
The flexibility of the guiding rope and the tension difference between two guiding ropes cause the lateral and torsional vibrations of the hoisting conveyance in the rope-guided hoisting system, respectively, which are theoretically investigated with two different cases in this paper. The assumed modes method is used to discretize the hoisting rope and two guiding ropes, and Lagrange equations of the first kind is adopted to derive the equations of motion, while the geometric matching conditions at the interfaces of the ropes are accounted for by the Lagrangian multiplier. Considering all the geometric matching conditions are approximately linear, the differential algebraic equations are transformed to a system of ordinary differential equations. The current method can obtain not only the accurate lateral displacements of two guiding ropes, but also the constraint forces between the hoisting conveyance and two guiding ropes. Further, the current method is verified by the ADAMS simulation. Finally, the effects of various parameters on the lateral and torsional vibrations of the hoisting conveyance are analyzed and results indicate that the appropriate tension difference and distance difference could decrease the maximum lateral displacement, which is useful to design super deep rope-guided hoisting system for the decrease of the vibration.
The effect of hardness of grey cast iron flat specimen on its wear and friction on the contact were characterised with the presence of vegetable oil as biolubricant. Prior to the tribological test, the as-received grey cast iron flat specimen hardness was characterised. Friction and wear tests were then conducted using a ball-on-flat reciprocating sliding contact. The one-way analysis of variance (ANOVA) was used to determine the significance of friction and wear data with a 95% significance level. The wear scars after the test were then characterised by surface roughness and wear mechanism. The microstructure and elemental analysis were also reported. The average value of hardness was 210 HV with a large difference between minimum (185 HV) and maximum (250 HV) values. The friction and wear performance of grey cast iron specimens with soybean oil varied with its hardness. The specimens with higher hardness gave lower friction coefficient and greater wear resistance than the lower hardness specimens. The difference in coefficient of friction produced between high hardness specimens (COF = 0.122) and low hardness specimens (COF = 0.140) was 17%. In terms of mass loss, the low hardness specimens (mass loss = 50.38 mg) and the high hardness specimens (mass loss = 12.90 mg) produced a difference of 74%. It is shown that, with soybean oil lubricant, the grey cast iron specimen can produce wide range of tribological data especially on mass loss due to its hardness distribution. The influence of soybean oil lubrication in this work is less in improving the wear resistance (about 7%), but greater for friction reduction (about 24%) compared to an unlubricated grey cast iron surface. The hardness of grey cast iron specimen is an important parameter that needs to be specifically measured and controlled on the contact due to wide hardness distribution of grey cast iron may produce variation in tribological data.
Intelligent fault-diagnosis methods using machine learning techniques like support vector machines and artificial neural networks have been widely used to distinguish bearings’ health condition. However, though these methods generally work well, they still have two potential drawbacks when facing massive fault data: (1) the feature extraction process needs prior domain knowledge, and therefore lacks a universal extraction method for various diagnosis issues, and (2) much training time is generally needed by the traditional intelligent diagnosis methods and by the newly presented deep learning methods. In this research, inspired by the feature extraction capability of auto-encoders and the high training speed of extreme learning machines (ELMs), an auto-encoder-ELM-based diagnosis method is proposed for diagnosing faults in bearings to overcome the aforementioned deficiencies. This paper performs a comparative analysis of the proposed method and some state-of-the-art methods, and the experimental results on the rolling element bearings data set show the effectiveness of the proposed method not only with adaptive mining of the discriminative fault characteristic but also at high diagnosis speed.
The dynamic analysis of a gear transmission system for electric vehicle is analyzed by means of a multibody approach. The architecture of the transmission is constituted of one gear ratio, with the differential integrated in the same gear box. The multibody model of the complete transmission has been created and optimized in order to get the dynamic response of the system. In particular, the frequency response function of the system in terms of rotational speed and loading forces has been determined. Furthermore, the dynamic transmission error has also been determined.
The work described in this paper is an evaluation of the contact characteristics of bi-metallic gears forged through a novel bi-metallic gear forging process. Finite element analysis of the contact characteristics of single material gears was first performed to validate the tooth contact and tooth root stresses with empirical American Gear Manufacturers Association and British Standard standards. Having verified the validity of the model, simulations were performed for gears comprising lightweight cores with teeth bounded by steel bands of uniform thicknesses, 1 mm, 2 mm, 4 mm, and 6 mm to evaluate the differences in stress distribution and compare to single material gear teeth. The forged profiles obtained experimentally by utilising 2 mm, 4 mm, and 6 mm thickness bands via the bi-metallic gear forging process are also discussed. The uniform thickness model is subsequently adapted to incorporate the experimental forged profiles in order to estimate the contact stress, root stress, and stress distribution within the teeth to identify performance differences between bi-metallic forged gears and traditional single material gears.
This paper deals with the sensitivity analysis and the prediction of the orientation error limits of a three-DoF translational parallel manipulator (3-TPM). An analytical model relating the robot accuracy to the design parameters uncertainties, the joints clearances, the nominal pose, and the external load is developed. Based on this model, an analytical sensitivity analysis is performed to show the influence of each parameter on the orientation error. An algorithm based on the interval analysis is used to predict the bounds of the translator orientation error. Using the RAF robot as an example, it is shown that the pin length of the revolute joint, the width of the parallelogram structure and the radial clearance in the revolute joints are the most influential parameters on the orientation error of the manipulator. Moreover, one of the main results of this analysis is that an increase of the tolerances on certain parameters does not necessarily lead to an increase of the orientation error of the robot, for this specific example.
Saturation is an undesired event in trajectory tracking control of mechanical systems. When the actuators of a robotic device saturate, the solution of the inverse dynamics problem cannot fully be realized, which results in deviations from the desired trajectory and loss of performance. It is generally hard to consider the limited actuator torques and the corresponding nonlinear effects in the control design. The most common way to handle the problem is recalculating the control forces and trying to adjust the desired trajectory such that saturation will not happen. In contrast we propose a switched control approach, where, upon saturation, different sets of inputs are varied periodically to keep the reference point of the robot on the desired trajectory. For this, the desired motion is formulated by means of servo-constraints, and the periodic switching of these constraints is adjusted according to the variation of a new, manipulability type performance measure. It is demonstrated that the proposed controller can effectively reduce the trajectory following error due to actuator saturation. A typical robotic benchmark example is provided to show the application of the method, and to compare it with other approaches taken from the literature.
The paper deals with investigations about mechanical properties of Iroko, a hardwood species used for structures in shipbuilding as glued laminated timber. Experimental tests have been carried out to assess strength, stiffness and density of Iroko in accordance with current EN Standards. All the results obtained by tensile and three-point bending tests, along with the statistical analyses performed to define the characteristics values of some mechanical properties, are reported in the paper. These values allowed to assign the strength class, reported in EN 338 Standard, to the investigated Iroko wood population. The experiments have taken into account both solid timber strips and scarf-jointed strips, in order to evaluate the influence of such a type of joint, which is widely used in wooden shipbuilding on strength and stiffness. Eventually, peculiar investigations have been carried out to analyse the failure mode of some test pieces through special experimental techniques: three-dimensional computed tomography and infrared thermography.
This article examines the application of nonlocal strain gradient elasticity theory to wave dispersion behavior of a size-dependent functionally graded nanoplate in thermal environments. The theory contains two scale parameters corresponding to nonlocal and strain gradient effects. A quasi-3D plate theory considering shear and normal deformations is employed to present the formulation. Mori–Tanaka micromechanical model is used to describe functionally graded material properties. Hamilton’s principle is employed to obtain the governing equations of nanoplate accounting for thickness stretching effect. These equations are solved analytically to find wave frequencies and phase velocities of functionally graded nanoplate. It is indicated that wave dispersion behavior of functionally graded nanoplates is significantly affected by temperature rise, nonlocality, length scale parameter, and material composition.
Experimental and numerical investigations were carried out to study the temperature effect on the stiffness, strength, and failure behaviors of carbon/polyimide composite laminates. Both unnotched laminates and open-hole laminates were tested under tension load at three temperatures (room temperature, 200 ℃, and 250 ℃). A three-dimensional finite element analysis was carried out to study the thermomechanical coupling behavior in the notched laminate. The model considers each layer and interface as a single element in the thickness direction so that in-plane stress and interlaminar stress could be analyzed in the model. The stresses around the open-hole changing characteristics with the temperature and tensile loading have been discussed in detail. Failure analysis was carried out to predict the residual strength of the notched laminates at different temperatures. Compared to the experimental data, the numerical results have an excellent agreement.
To improve the maneuverability, stability, and reliability of the steer-by-wire system, a two-way H control method with a fault-tolerant module is proposed in this paper. First, a two-way H control scheme is proposed. Two controllers are designed in this scheme: one is used as a feedback controller as a general practice to stabilize the system and detect the tracking error; the other is used as a feed forward controller to make the output of the system follow the driver’s steering intention rapidly and precisely. Second, a fault-tolerant module aiming at front wheel angle sensor which is an important feedback signal to the system is added to improve the reliability of the system. A revised Kalman filter is applied in the fault-tolerant module to reconfigure the front wheel angle as a reference value and a substitute when the sensor fails, thus replacing hardware redundancy by software redundancy in a cost-effective way. Lastly, simulations by Matlab/Simulink and CarSim software and hardware-in-the-loop experiments are conducted and effectiveness of the proposed control method is demonstrated by simulation and experimental results and numerical analyses.
A fully framed system consisting of four beams and a rectangular plate has been investigated in terms of the energy transfer between the beams and the plate when a force is applied to one of the beams. This configuration, which is a mixture of stiff and flexible elements, is a particularly important example in the industrial area, as it is widely used. A modal model based on interface basis functions is used. A wave model, which is an approximate method, has also been developed in which the plate, acting as a wave impedance, is separately attached to each beam. Experimental studies have been carried out for validation. The investigation with respect to power flow and energy shows the validity of both models in the mid-frequency region. The results show that most energy is dissipated by the flexible plate. The physical phenomena and limitations of the wave method for this particular structural configuration are discussed. Even though it is an approximate method, the wave approach can describe the dynamic characteristics of the excited beam and the plate in terms of the ratios of power and energy of each component. The comparison of the two methods shows that the plate rather than the beams plays a crucial role in transferring the energy from the excited beam to the parallel opposite beam in the beam-framed structure when these two beams have identical properties, whereas the energy transfer is reduced when the beams have dissimilar properties.
The aim of this study is to investigate the effect of carbon nanotube reinforcement in conventional carbon fiber reinforced composite on the buckling and postbuckling behavior of the laminated nanocomposite plate made of carbon nanotube and carbon fiber reinforcements in a matrix material. The method of representative volume element is utilized to perform the multiscale modeling of the problem. Initially, Boolean-based random sequential adsorption algorithm is utilized to model a nanoscale representative volume element of nanocomposite material to mimic the effect of randomly distributed (i.e. having random orientation and position) carbon nanotubes in a matrix material. After estimating the elastic properties of the nanocomposite material using representative volume element, another microscale representative volume element of carbon fiber reinforced in the nanocomposite (i.e. carbon nanotube reinforced matrix material) is modeled to evaluate the stiffness properties of the lamina formed of carbon nanotube–carbon fiber reinforced nanocomposite. The laminae are further stacked in the sequence of (45°/–45°/–45°/45°) to model a laminate. Thereafter, the evaluated stiffness properties of the lamina are employed to predict the effect of carbon nanotube reinforcement on buckling and postbuckling behavior of the laminated plates through nonlinear finite element method formulation based on the first-order shear deformation theory and von Karman’s assumptions. It is established that carbon nanotube reinforcement in carbon fiber reinforced composite lamina results in the enhancement of stiffness properties of the resulting carbon nanotube–fiber nanocomposite lamina, with more prevalent effect on the matrix-dominated properties—transverse and shear moduli—than the axial modulus. The increased stiffness properties result in the substantial improvement in the buckling load and postbuckling strength of the laminated plate made of carbon nanotube–carbon fiber nanocomposite material, for all volume fractions of carbon nanotube, loading and boundary conditions, geometric parameters (i.e. aspect ratio and width-to-thickness ratio), and matrix materials.
This paper proposes a new extension of the Growing Neural Gas Network, called the Progressive Growing Neural Gas Network (PGNGN), for the application of kinematic investigation of parallel mechanisms, with more emphasis on the singularity-free workspace determination. In fact, PGNGN leads to a general approach in order to obtain the topology of the workspace. In this algorithm, the network starts to grow by taking into account new data points close to its border neurons by resorting to the so-called boundary data generation procedure. By considering singularity loci expression, the separated parts are detected and each part will pursue learning, adding units and connections, until a given performance criterion will be reached. Finally, after finding cavities, if any exists, the maximal circle for each part of the workspace is found. A graphical user interface (GUI) is developed providing the users with easy access to the important parameters in which the singularity-free workspace of three planar three-degree-of-freedom (3-DOF) parallel mechanisms are investigated in which two of them, namely, 3-
Stress concentration is one of the disadvantages of flexure hinges. It limits the range of motion and reduces the fatigue life of mechanisms. This article designs flexure hinges by using stress-constrained topology optimization. A weighted-sum method is used for converting the multi-objective topology optimization of flexure hinges into a single-objective problem. The objective function is presented by considering the compliance factors of flexure hinges in the desired and other directions. The stress constraint and other constraint conditions are developed. An adaptive normalization of the P-norm of the effective von Mises stresses is adopted to approximate the maximum stress, and a global stress measure is used to control the stress level of flexure hinges. Several numerical examples are performed to indicate the validity of the method. The stress levels of flexure hinges without and with stress constraints are compared. In addition, the effects of mesh refinement and output spring stiffness on the topology results are investigated. The stress constraint effectively eliminates the sharp corners and reduces the stress concentration.
This paper proposes a simple single variable shear deformation theory for an isotropic beam of rectangular cross-section. The theory involves only one fourth-order governing differential equation. For beam bending problems, the governing equation and the expressions for the bending moment and shear force of the theory are strikingly similar to those of Euler–Bernoulli beam theory. For vibration and buckling problems, the Euler–Bernoulli beam theory governing equation comes out as a special case when terms pertaining to the effects of shear deformation are ignored from the governing equation of present theory. The chosen displacement functions of the theory give rise to a realistic parabolic distribution of transverse shear stress across the beam cross-section. The theory does not require a shear correction factor. Efficacy of the proposed theory is demonstrated through illustrative examples for bending, free vibrations and buckling of isotropic beams of rectangular cross-section. The numerical results obtained are compared with those of exact theory (two-dimensional theory of elasticity) and other first-order and higher-order shear deformation beam theory results. The results obtained are found to be accurate.
Development of complex customized machine tools with low manufacturing costs is a challenging problem for many machine tool manufacturers in today’s competitive marketplace. In this research, a novel design method based on axiomatic design and sensitivity design structure matrix is introduced for identification of adaptable product platform. In order to identify the adaptable product platform, customer requirements are first classified into different groups based on K-means clustering method through genetic algorithm. axiomatic design is used to build the mathematical model for identification of the non-adaptable platform parameters, and sensitivity design structure matrix is employed to separate non-adaptable parameters in non-adaptable platform modules and adaptable parameters in adaptable platform modules. A bridge-type double-gantry boring–milling machining center, XXX-2890, is developed based on the existing heavy-duty gantry milling machines to demonstrate the effectiveness of the developed method.
Geometric interference can occur in cylindrical worm gear set that makes use of oversized hob to cut the worm gear. In particular, the interference occurs easily in the design with high lead and low pressure angles. The interference results in a corner contact. In this study, we examined the influence of the machine tool setting errors of the worm gear hobbing and the influence of the shaft misalignments of the worm gear set on the interference. To determine the interference, we used the surface separation topology based on differential geometry. In addition, we also examined the hob oversize range required to avoid the interference under the condition of the machine tool setting errors and shaft misalignments. This study found that the interference can be avoided not only when the hob oversize is larger than the upper limit, but also when the hob oversize is smaller than the lower limit. This study also found that the interference can be avoided by applying the intended errors on the machine tool setting and shaft alignment, without manipulating the hob oversize.
Milling head and rotary table are the key components in five-axis CNC machine tools. However, tracking and positioning precision of these rotary axes based on worm gear mechanisms are affected by the backlash, friction, elastic deformation, and other nonlinearities. Therefore, finding out a simple and universal principle to predict the tooth deformation in an initial design is quite significant. A novel deformation calculation and compensation method with finite element analysis and circular plate theory is proposed for the worm gear transmissions. When the relationship (form factor) between the solutions of circular plate theory and finite element analysis is derived, deformation calculation with finite element analysis can be replaced by multiplying the solution of circular plate theory and the form factor. Analysis and calculation results show that the presented method can provide a reference for the compensation control of the positioning errors.
Some adaptive sampling approaches have been developed to efficiently and accurately build global metamodels for the deterministic single-response problems. Most complex engineering problems, however, yield multiple responses during one simulation. This article adjusts the framework of the CV-Voronoi adaptive sampling approach for a multi-response system. In the proposed multi-response CV-Voronoi (mCV-Voronoi) sampling approach, a new strategy that combines a weighted-sum term and an extreme term is presented to properly estimate the cell errors by simultaneously considering the characteristics of multiple responses. The performance of this approach is investigated on 57 multi-response systems and two engineering design problems. The results show that mCV-Voronoi is very promising for global metamodeling of deterministic multi-response systems.
In this study, theoretical analysis is performed in order to investigate the nonlinear vibration response of the two-stage spur and straight bevel gears transmitting system. The system dynamic model of the transmitting system is considered in detail. The tooth contact analysis results are obtained through calculation and the dynamic model with time-varying stiffness, and backlash for both gear pair is built. The natural frequencies, mode shapes, and critical speed for the transmitting system with gyroscopic effects are calculated. The results show that the whirling motion due to the second shaft may be the main factor of vibration for the transmitting system and the lateral–torsional–axial vibration dominate the overall system vibration. Many critical characteristics cannot be represented in the transmission error, especially when the rocking and other freedoms are considered in the gear transmitting system. The rocking motion will be excited due to the coupled effect of bevel gear pair, which may be also the reason for the catastrophic damage of the thin web spur gear.
This paper investigates the hardness distribution in cold upsetting operation of the aged billets. Three sets of cylindrical billets were solutionized at 504 ℃ and then each set of billets were aged at 150 ℃ for a period of 9 h, 13 h, and 18 h, respectively. The billets were upset to different levels of strain and flow stress equation was evaluated for all the aging conditions. The flow stress equation was given as input to the finite element software and simulated to the same level of strain as in the case of experiments. An attempt to predict metal hardness was made by correlating the equivalent strain with the hardness. The hardness measurements predicted were in good agreement with the experimental results. The demand for producing billets with more hardness on the surface and softness inside encourages this investigation to measure hardness experimentally and theoretically.
For a parallel hip joint manipulator, the unified kinematics and stiffness model are established based on a novel unified theory, and then the bifurcation and stability are analyzed under the same unified theory framework. In bifurcation analysis, a chaos method is first applied to solve the non-linear bifurcation equations in order to get the full configuration of the parallel hip joint manipulator, which improves the convergence rate and accuracy. Based on the full-configuration solution, the single-parameter and double-parameter simulation for the bifurcation and stability of the parallel hip joint manipulator is performed. The bifurcation simulation results show that the configuration only changes along the corresponding path but cannot change to other paths when the configuration of the parallel hip joint manipulator is at a certain path. The stability simulation results show that when the parallel hip joint manipulator enters into an uncontrolled domain of a bifurcation posture along different paths, the posture component which changes dramatically will lose control first, and the other posture components will move along the changed configuration. In this paper, the kinematics, stiffness, bifurcation and stability of the parallel hip joint manipulator are solved under the same theory framework, which improves the solving efficiency and enriches the mechanical theory for the parallel manipulators.
Increasing demands for high-performance screw pumps in oil and gas as well as other applications require deep understanding of the fluid flow field inside the machine. Important effects on the performance such as dynamic losses, influence of the leakage gaps and presence and extent of cavitation are difficult to observe by experiments. However, it is possible to study such effects using well-validated computational fluid dynamics models. The novel-structured numerical mesh consisting of a single-computational domain for moving screw pump rotors was developed to allow three-dimensional computational fluid dynamics simulation of such machine possible. Based on finite volume method, the instantaneous mass flow rates, rotor torque, local pressure field, velocity field and other performance indicators including the indicated power were predicted. A calculation model for the bearing friction losses was introduced to account for mechanical losses. The geometry of the inlet and outlet passages and piping system are taken into consideration to evaluate their influences on the pressure distribution and shaft power. The paper also shows the influence of rotor clearances on the pump performance. The computational fluid dynamics model was validated by comparing the numerical results with the measured performance obtained in the experimental test rig through the comprehensive experiment performed for a set of discharge pressures and rotational speeds. Validation includes comparison of mass flow rates, shaft power and efficiency under variety of speeds and discharge pressure. It has been found that the predicted results match well with the measurements. The results also showed that the radial clearances have larger influence on the mass flow rate than the interlobe clearance. The correct design of the flow passages within the screw pump plays significant role in minimizing required power consumption. The analysis presented in this paper contributes to better understanding of the working process inside the screw pump and offers a good reference to improve design and optimize such machines in terms of clearance selection, shape of the ports, piping system, etc. In future, this model will be used for analysis of cavitating flows and determining performance of other multiphase screw pumps.
The determination of the isentropic turbine efficiency under adiabatic and SAE boundary conditions is studied in this paper. The study is structured into two parts. The first part describes the possibility of measuring the isentropic turbine efficiency directly. Normally this is not possible in measurements conducted following the SAE J922 guidelines. Therefore, the experiments have been carried out under adiabatic conditions, and combined with improved measuring equipment. The results were compared with adiabatic computational fluid dynamics simulations of this turbocharger. In the second part, a new criterion is defined in order to evaluate the quality of the adiabatic measurements and compare them with standard measurements. The investigation has been carried out with multiple turbochargers ranging from very small to medium passenger car size turbochargers. In the end, a possible application for the criterion is given.
Water condensation in aircraft fuel tank vent systems can run off to the fuel systems, where it can freeze to ice or support microbial growth in the fuel tanks. A laboratory scale test has been designed to investigate the ingress and runoff of water in the aircraft fuel tank vent pipes. The experiments are to determine the dual effects of air flow shear and hydrophobicity on water condensation in the vent pipes during descent from cruising altitudes. Results show only downslope runoff occurs and for large drop volumes where the height of the water drop is comparable with the height of the air flow boundary layer. Runoff is much more sensitive to drop volume and vent pipe inclination angle than air flow since the drops are within the air flow boundary layer. Downslope air flow has little effect on the runoff speeds. Downslope runoff speeds, where there is upslope air flow, exhibit large variations, when compared to those where there is downslope air flow. Upslope air flow can slow downslope runoff speeds of large volume drops by up to 400%. Runoff speeds may be up to 100 times greater with a hydrophobic coating than on the current inner vent pipe surface of anodised aluminium.
A coupling dynamic model of a rotating cantilever beam is established by considering the effect of steady-state axial deformation on transverse bending deformation. The present method uses fully nonlinear Green strain–displacement relationship to derive the coupling terms in the equations of motion. The steady-state axial deformation is derived by analysing the equation of axial motion. An expression of the rotational speed limit is also obtained. The numerical results indicate that the steady-state axial deformation has a considerable effect on the transverse bending frequencies. A comparison of the present model with the absolute nodal coordinate formulation indicates that the two models are in good agreement, which proves the effectiveness and rationality of the present model.
In order to meet the requirements of large downward force and high stiffness performance for the friction stir welding process, this paper proposes a 5 degree-of-freedom hybrid manipulator as friction stir welding robot. It is composed of a 3 degree-of-freedom redundant parallel module and a 2 degree-of-freedom rotating head. Semi-analytical stiffness model of the hybrid manipulator is firstly established by compliance models of the two substructures. Virtual work principle, deformation superposition principle and twist/wrench mapping model are applied to this compliance modeling process. A novel instantaneous stiffness performance index is then proposed on the basis of instantaneous energy defined by reciprocal product of external payload screw and corresponding deformation screw. It solves the problems of inconsistent physical unit of linear/angular stiffness and is able to evaluate overall and worst-case stiffness performance. Next, stiffness/compliance experiments are carried out to verify the stiffness model and the novel instantaneous stiffness performance index. Finally, stiffness performance of 5 degree-of-freedom hybrid manipulator is thoroughly discussed in terms of engineering requirements, worst-case stiffness performance and stiffness singularities. It can be summarized that the semi-analytical stiffness model and the novel instantaneous stiffness index are effective in analyzing and evaluating stiffness performance of the 5 degree-of-freedom hybrid manipulator.
To achieve the heat generation of an angular contact ball bearing, especially when confronted with a difficult challenge, is a complexity of numerical and analytical models of bearings. A combination method of the Kriging model and particle swarm optimization algorithm is proposed for optimizing structure parameters of the bearing to obtain the minimum heat generation of the bearing. Therefore, the heat generation and stiffness of the angular contact ball bearing, which are acquired based on pseudo statics analysis and raceway control theory of the bearing, are the optimization goal and constraint condition, respectively, that are used in particle swarm optimization. Taking the angular contact ball bearing NSK-7016A5 as an example, the results show that the total heat generation of the bearing is decreased and that the axial stiffness of the bearing is increased by optimizing the structure parameters of the bearing. In the end, the combination method that uses both Kriging and particle swarm optimization to optimize the structure parameters of the bearing could obtain satisfactory design results and increased bearing design efficiency; it also bears the potential for the design parameter optimization of other mechanical structures, which may lead to better design results.
This paper presents design imaginary skew rack cutters having teeth of two parabolic coefficients to generate spur and helical gears. First, a mathematical model of the imaginary rack cutter having teeth of two parabolic coefficients is derived using geometric relations and coordinate transformation. After the relationship between the coordinate system of the imaginary rack cutter and that of the helical gear pair is set up, a family of imaginary rack cutter surfaces is obtained using the homogeneous coordinate transformation matrix to transfer the coordinate system of the rack cutters to that of the helical gear. Based on the gear theory, the equations of meshing between the rack cutter and the helical gear are determined. Substituting the equations of meshing into the family of imaginary rack cutter surfaces, a pinion and a gear are generated and their geometries are plotted using an in-house software package. Based on the assembly errors, tooth contact analysis is performed to determine the influences of kinematic assembly errors and the parabolic coefficients. Results show that maximum parabolic coefficient value of the imaginary skew rack cutter exists in order to avoid undercutting and it can be determined.
The applications of robotics and automation technology to the therapies of neuromuscular and orthopedic impairments have received increasing attention due to their promising prospects. In this paper, we present an actuated upper extremity exoskeleton aimed to facilitate the rehabilitation training of the disable patients. A modified sliding mode control strategy incorporating a proportional-integral-derivative sliding surface and a fuzzy hitting control law is developed to ensure robust and optimal position control performance. Dynamic modeling of the exoskeleton as well as the human arm is presented and then applied to the development of the fuzzy sliding mode control algorithm. A theoretical proof of the stability and convergence of the closed-loop system is presented using the Lyapunov theorem. Three typical real-time position control experiments are conducted with the aim of evaluating the effectiveness of the proposed control scheme. The performances of the fuzzy sliding mode control algorithm are compared to those of conventional proportional-integral-derivative controller and conventional sliding mode control algorithm. The experimental results indicate that the position control with fuzzy sliding mode control algorithm has a bandwidth about 4 Hz during operation. Furthermore, this control approach can guarantee the best control performances in term of tracking accuracy, response speed, and robustness against external disturbances.
An adaptive hybrid simulated annealing technique with ANSYS parametric design language is developed to optimize hydrodynamic deep drawing assisted by radial pressure process. This work aims to determine an optimal pressure path by redefinition of simulated annealing parameters and creating an adaptive finite element code using ANSYS parametric design language for any cylindrical, conical, and conical–cylindrical cups. The simulated annealing algorithm is developed adaptively with respect to hydrodynamic deep drawing with radial pressure process to link with ANSYS parametric design language code using a script in MATLAB. Parametric definition of process parameters enables the optimization algorithm to change the finite element model configuration in each iteration. Defective product is detected by definition of two failure criteria based on thinning and wrinkling occurrence during the optimization process. The proposed optimization method is employed in fractional factorial design of experiment to investigate the effective parameters on final product quality. Also, a regression model is derived to predict the final product quality based on the maximum thinning percentage under the optimal pressure path. Reliability of the optimization procedure and regression model is validated by experiments.
Aero-engine spline couplings are widely used in the aero-industry to transfer torque and power. They are often subjected to fretting wear damage which results in reduced equipment life and early replacement. This work focuses on experimental investigation to be used as a basis for predicting fretting wear in spline couplings working in a misaligned condition. For this purpose tests have been performed on spline couplings under varying conditions of torque and misalignment angles. The experimental data has been used to develop empirical relations and neural-network-based approximations for the prediction of fretting wear. Though the tests have been performed specifically on spline couplings of nitrogen-hardened 42CrMo4, the findings of this work are fairly general and may be used as a quick and early design tool for spline couplings of any material owing to their straightforward and simple application.
In this paper, size-dependent free vibration analysis of curved functionally graded nanobeams embedded in Winkler–Pasternak elastic medium is carried out via an analytical solution method. Three kinds of boundary condition namely, simply supported-simply supported, simply supported-clamped and clamped-clamped are investigated. Material properties of curved functionally graded beam change in thickness direction according to the Mori–Tanaka model. Nonlocal strain gradient elasticity theory is adopted to capture the size effects in which the stress is considered for not only the nonlocal stress field but also the strain gradients stress field. Nonlocal governing equations of curved functionally graded nanobeam are obtained from Hamilton’s principle based on Euler–Bernoulli beam model. Finally, the influences of length scale parameter, nonlocal parameter, opening angle, elastic medium, material composition, slenderness ratio and boundary conditions on the vibrational characteristics of nanosize curved functionally graded beams are explored.
A piezoelectric dynamometer can produce thermal forces because of temperature fluctuations, thus affecting measurement precision. To investigate the influence of the thermal force on the dynamometer, this article proposes a hypothesis of decreasing the conduction power and establishes the function of a thermal force over time in an ordinary dynamometer based on the heat conduction differential equation. A novel double-sensor thermal compensation dynamometer is designed, with static calibration in constant temperature and force/heat coupling experiments, to solve the problem of the thermal force. The experimental results indicate that the nonlinearity and repeatability of the double-sensor thermal compensation dynamometer are less than 1% full scale (FS) of the static calibration at a constant temperature; in the force/heat coupling experiments, at a heating rate of 0.4 ℃/s to 110 ℃ with a loading force of 500 N, the maximal output deviation is less than 1.06% (FS), realizing the unidirectional thermal force compensation of the structure. The double-sensor thermal compensation dynamometer can be utilized in sharp temperature fluctuations environment, like rocket engine forces measurement.
Stress shielding is a mechanical phenomenon usually found in load-bearing bone implants. Difference in mechanical properties between the natural bone and the artificial implant leads to stress shielding problem. In the present work, polymethyl methacrylate and commercial pure titanium were selected to design laminate and particulate composites. Optimum composition was theoretically obtained that exhibits mechanical properties close to that of natural human bone. Bone fixing plate was designed for femur bone using computer-aided design. Finite element analysis was adopted to analyze the stress distribution in the bone and implant under static load conditions. Fixing plate with three screws was modeled and simulated using finite element analysis to investigate the stress distribution. Simulation was also done considering 316 L stainless steel as fixing implant and compared with the present optimized composition. Laminate composite with 0.3 volume fraction of titanium has shown mechanical properties close to the bone compared with other combinations. The results have clearly shown that the von-Mises stress induced in the bone with polymethyl methacrylate-titanium laminate composite plates was increased compared with the bone implanted with 316 L steel. Interestingly, laminate composites exhibited higher stresses in the bone compared with particulate composites. From the present design and simulation, it is clearly demonstrated that the laminate composites of polymethyl methacrylate–30% titanium can be an optimum choice for load-bearing implant materials with reduced stress shielding effect.
In this study, a new method for the simulation of the time-dependent behavior of actin cytoskeleton during cell shape change is proposed. For this purpose, a three-dimensional model of endothelial cell consisting of cell membrane, nucleus membrane, and main components of cytoskeleton, namely actin filaments, microtubules, and intermediate filaments is utilized. Actin binding proteins, which play a key role in regulating actin cytoskeleton behavior, are also simulated by using a novel technique. The actin cytoskeleton in this model is more dynamic and adoptable during cell deformation in comparison to previous models. The proposed model is subjected to compressive force between parallel micro plates in order to investigate actin cytoskeleton role in cell stiffening behavior, nucleus deformation, and cell shape change. The validity of the model is examined through the comparison of the obtained results with the data presented in previous literature. Not only does the model force deformation curve lie within a range of the experimental data, but also the elastic modulus of the cell model is in accordance with former studies. Our findings demonstrate that augmentation of actin filaments concentration within the cell reduces force transmission from cell membrane to the nucleus. Furthermore, actin binding proteins concentration increases by the enhancement of cell deformation and it is also indicated that cell stiffening with an increase in applied force is significantly affected by actin filaments reorientation, actin binding proteins reorganization and actin binding proteins augmentation.
Former research has proved that the design knowledge involved in the conceptual design stage has multiple attributes/perspectives, which can be further abstracted into the concepts with different abstract/granularity levels, from coarse to fine. Based on this, we believe that it is necessary to use multiple attributes to describe design knowledge during the knowledge retrieval process. Firstly, an attribute ontology with multi-perspective and multi-granularity is built in the new retrieval model. Therefore, the knowledge documents can be abstracted by the concepts of the ontology. Based on the correlation of the concepts, the clustering theory is introduced into the new model to cluster knowledge documents, and the combined keyword concepts of the clusters are generated as well. The keyword concepts of the clusters, rather than the keyword concepts of documents, are used as the index of the retrieval. During the knowledge matching process, the keywords and their semantic extension of design problems are extracted, and the similarity between the abstract descriptions of the knowledge clusters and design problems is calculated, so the best cluster can be found by the calculated results. Based on the granularity levels of the keywords (concepts) the design problems, finally the documents in the selected cluster are ranked in the order of granularity levels. The selected document by the model is that with the highest relevance and most suitable granularity level about the design problem. In the last section of the paper, we used a simple real case to evaluate the new model, and also develop the scheme of the whole design knowledge retrieval system for the future work.
The traditional load-sensing hydraulic system is an energy-saving fluid power transmission, which supply "on-demand" flow at a prescribed pressure margin greater than the highest load pressure of the system. In this paper, a novel load-sensing system that has a variable pressure margin through overriding differential pressure control via integrating an electro-proportional three-way type pressure reducing valve into the hydro-mechanical load-sensing valve is proposed. Also, a bond graph model taking into account the dynamic characteristics of load-sensing valve and load-sensing path is constructed, and three group experiments are performed to verify the validation of the model. Based on the bond graph model, a series of theoretical simulations are carried out to prove that the proposed Load-Sensing system enables a satisfactory balance between energy efficiency and rapid dynamic response over a wide range of operating conditions. In addition, due to overriding differential pressure control, mode selection and power limit regulation can also be achieved.
Machining fixtures play inevitable role in manufacturing to ensure the machining accuracy and workpiece quality. The layout of fixture elements, clamping forces, and machining forces significantly affect the workpiece elastic deformation during machining. The clamping and machining forces are necessary to immobilize and machine the workpiece, respectively. Finding the appropriate layout of fixture elements is the other possible way to reduce the workpiece deformation, which in turn improves the machining accuracy. The finite element method interfaced with evolutionary techniques is normally used for fixture layout optimization. In the finite element method, the workpiece is discretized into a number of small elements and fixture elements are placed only on the nodes. Hence, evolutionary techniques are capable of searching the optimal fixture layout from those discrete nodal points than from the entire area on the locating and clamping face. To overcome these limitations, in this research paper, response surface methodology is employed to establish a quadratic model between the position of fixture elements and maximum workpiece deformation. This enables the optimization techniques to search for the optimal solution in the continuous domain of the solution space. Then, the real-coded genetic algorithm based discrete optimization, continuous optimization based on binary-coded genetic algorithm and particle swarm optimization are employed to optimize the developed quadratic model and their performances are compared. The result clearly shows that the integration of finite element method, response surface methodology with particle swarm optimization is better than the integration with genetic algorithm to optimize the machining fixture layout and also reduces the computational complexity and time to a greater extent.
With the increase of the customer demands for the products, multidisciplinary products are gradually becoming more competitive than the traditional products. Considering conceptual design synthesis is the core phase of the product design and its result is the starting point of the next detail design works, if the rich resources in multiple disciplinary domains can be fully used during this phase, the efficiency of multidisciplinary product design will be largely promoted. Therefore, we proposed a novel conceptual design synthesis system for multidisciplinary products, which consists of three parts, i.e. basic framework, complex-number-domain-based mathematical model, and achieving approach. In the framework, three groups of concepts were defined and the conceptual design synthesis was concluded into three steps. The model can completely describe and modularize the function units which are the basic components of a design scheme. Based on the model, the achieving approach can automatically generate stable objective function unit chains which can directly construct the design scheme. Finally, the design of a multifunctional agricultural hydroelectric power system was taken as an illustration to prove the practicability of this proposed system.
Gas foil bearings are a smart green technology and suitable for the next generation of small turbo machinery e.g. turbochargers, micro gas turbines, range extenders and compressors of fuel cells. A combination of low power loss, high speed operation and the omission of an oil system are the major advantages. To enable access to this technology, it is essential to evaluate critical speeds and onset speeds of subharmonic vibration of the rotor system in the first design stage. Hence, robust and valid models are necessary, which correctly describe the fluid structure interaction between the lubrication film and the elastic bearing structure. In the past three decades several experimental and numerical investigations of bearing parameters have been published. But the number of sophisticated models is small and there is still a lack of validation towards experimental works. To make it easy for designers dealing with this issue, the bearing parameters are often linearised about certain operating points. In this paper a method for calculating linearised bearing parameters (stiffness and damping) of gas foil bearing is presented. Experimental data are used for validation of the model. The linearised stiffness and damping values are calculated using a perturbation method. The pressure field is coupled with a two-dimensional plate model, while the non-linear bump structure is simplified by a link-spring model. It includes Coulomb friction effects inside the elastic corrugated structure and captures the interaction between the single bumps. For solving the separated perturbed Reynolds equation a static stiffness is used for the 0. order equation (stationary case) and a dynamic stiffness is applied for 1. order equation (dynamic case). Therefore, an additional dynamic structural model is applied to calculate the dynamic stiffness. The results depend on the load level and friction state of each bump. Different case studies including the impact of clearance, frictional contacts and the comparison of a linear and non-linear structure are carried out for infinitesimal perturbations. The results show, that the linear structure underestimates main and cross-coupling effects. The impact of the clearance is notable, while the impact of the overall frictional contacts is small due to relatively small loadings. The infinitely small perturbation model is adapted to the experimental setup by using a superposition of two resulting bearing parameters identifications of two total loadings including shaker forces. Due to this adaptation a good correlation with the experimental results of the bearing parameters is achieved.
This paper describes an inverse design method for calculating the shape of meridional plane of centrifugal impeller. This design method permits the shroud and hub contours to be indirectly calculated by medial axis contour and constraint equations. The design process is computationally inexpensive and can conveniently modify the shroud and hub shapes as the design’s demand. Based on this design method, new constraint equations are used for a new shape design of meridional plane that lead to a uniform velocity distribution in the inlet of impeller. Numerical simulations are employed to investigate the fluid flows of centrifugal fan. After validation of the numerical strategy, the pressure and velocity distributions in centrifugal fan are illustrated. The numerical results show that the inlet performance is improved and the velocity distribution is more uniform. Furthermore, in order to understand the flow mechanism inside the centrifugal fan, the secondary flow in the blade passage and velocity distribution at the shroud and hub have been carried out a detailed investigation and study.
In this paper, two alternative numerical approaches for the simulation of Gerotor units are compared: a fast lumped parameter approach for the fluid dynamics through the unit that permits the co-simulation of the radial micro-motion of the rotors, and a computational fluid dynamics approach that puts emphasis on the description of the detailed features of the flow through the unit. Each approach provides unique insights on the unit operation, although with different assumptions and level of result details. For an objective comparison of these two state-of-art models, the authors compared their results with experiments. A commercial pump taken as reference, and tests focused on steady-state volumetric performance as well as the transient features of the outlet port pressure oscillations. The results presented in the paper permit to gain a high level of understanding of the operation of the unit and of the critical aspects that a designer should consider while analyzing such design of positive displacement machines. While comparing the two simulation approaches, the paper highlights the limits and the strengths of each one of the two approaches. In particular, it is shown how both models can match the experimental results considering proper assumptions, in terms of technological clearances and rotors’ micro-motions.
The paper constitutes a unique contribution in the field of numerical simulation of Gerotor units and represents a useful reference to the designers looking for suitable methods for simulating existing or novel design solutions.
Product service system is a new kind of manufacturing system paradigm, in which product and service are highly integrated and fully optimized. Supplier involvement in product service system development will greatly raise the productivity. Service planning of product service system development with supplier involvement is one of the critical steps in product service system development. The necessity of product service system development with supplier involvement in CNC (Computer Numerical Control) machine tool product service system is decided by the complexity of CNC machine tool product service system. The process model of CNC machine tool product service system development with supplier involvement is built in this paper first. Then, the maintenance service model is determined based on service blueprint, and the maintenance service planning is implemented. Next, the mode of recycling and remanufacturing is analyzed. And the feasibility of recycling and remanufacturing of parts is judged finally.
Due to light weight and high strength, industrial applications of ultra-fined grain materials are becoming prevalent. Ultra-fined grain materials are produced by severe plastic deformation techniques such as equal channel angular pressing, which impose large strains on ultra-fined grain microstructure, resulting in accumulation of the lattice defects and dislocations and consequently increasing the stored energy. Due to high stored energy of ultra-fined grain materials, they are thermodynamically unstable and prone to microstructural evolutions. In order to manufacture industrials parts, applying machining methods such as electrical discharge machining is necessary. Electrical discharge machining is a thermo-electrical process that erodes the surface of the workpiece by high temperature sparks. The surface of the workpiece is melted and then suddenly quenched into dielectric, and eventually a very hard and brittle layer, known as recast layer, is formed. The recast layer and heat-affected zone are the source of microstructural changes that affect the special properties of the ultra-fined grain materials and their stored energy. In this study, the bulk and local stored energy of electrical discharge machined ultra-fined grain aluminum samples are measured via differential scanning calorimetry technique and micro-hardness test. In the following, the effects of the electrical discharge machining process on ultra-fined grain aluminum are investigated. The results show that electrical discharge machining process alters the stored energy of the ultra-fined grain materials.
Shape memory alloy wire actuators can be used in combination with compliant structures to attain desired force and displacement capabilities. The wires can be placed inside a matrix, as in composite, or outside the material connected at different points on the structure. In the latter case, the offset of the wire and the location of the points decides the overall deformation of the structure. In this article we study the effects of offset distance, and the number of points, called attachments, where the shape memory alloy wire is connected to a host beam. First the characteristic curve of the shape memory alloy wire actuator is derived from a constrained recovery model. Then the response of a beam model, undergoing large deflection due to follower forces, is superposed with the characteristic curve to obtain the maximum beam deformation. It is found that there exists a particular offset, called optimum offset, for which the deformation of the host is maximum. Moreover, the ratio of stress and change in strain in the shape memory alloy corresponding to the optimum offset, attains a particular value, irrespective of the flexural rigidities of the beam. Furthermore, it has been observed that for a set of beams that have flexural rigidity less than a particular value, the deformation increases with number of attachments. However, for the beams that have flexural rigidity more than that particular value, the deformation remains almost unaltered with number of attachments. These numerical results are also supported qualitatively by the experimental observations.
The helical spring is a widely used element in suspension systems. Traditionally, the springs have been wound from solid round wire. Significant weight savings can be achieved by fabricating helical springs from hollow tubing. For suspension systems, weight savings result in significant transportation fuel savings. This paper uses previously published equations to calculate the maximum shear stress and deflection of the hollow helical spring. Since the equations are complex, solving them on a computer or spreadsheet would require a trial-and-error method. As a design aid to avoid this problem, this paper gives nomograms for the design of lightweight hollow helical springs. The nomograms are graphical solutions to the maximum stress and deflection equations. Example suspension spring designs show that significant weight savings (of the order of 50% or more) can be achieved using hollow springs. Hollow springs could also be used in extreme temperature situations. Heating or cooling fluids can be circulated through the hollow spring.
Despite the fact that the use of eye drops preparations is a simple task for most of the people for certain patients (i.e. for elderlies or for those suffering by musculoskeletal or neurological diseases) can make the eye drop insertion rather problematic. Given that most of the ocular diseases are associated with age, the poor patient compliance with the treatment is a common issue. Thus, for the design of the eye drop vials, the aforementioned issue should be taken into account and reliable methods for the description of their squeezability behavior should be developed. The present study aims both to develop prototype instrumentation and to fully determine the squeezability behavior of five different pharmaceutical eye-droplets vials. The correlation between the force required to deliver each droplet and the time is also investigated. Five different eye drops vials (containing different commercial available ophthalmic preparations) were selected to be investigated. Squeezability tests were performed using prototype instrumentation. A linear correlation between the applied force and the time was proven; a sudden decrease in the required force when each drop released was observed. The squeezability factor in all cases is below the typical range for the human squeezability requirements and is a combination of the liquid and the vial parameters.
Woodworking industry is increasingly characterized by processing complex spatial forms with high accuracy and high speeds. The use of parallel robot platforms with six degrees of freedom gains more significance. Due to stricter requirements regarding energy consumption, easy maintenance and environmental safety, parallel platforms with pneumatic drives become more and more interesting. However, the high precision tracking control of such systems represents a serious challenge for designers. The reason is found in complex dynamics of the mechanical system and strong nonlinearity of the pneumatic system. This paper presents an optimal control design for a pneumatically driven parallel robot platform. The Proportional-Integral-Derivative (PID) algorithm with feedback linearization is used for control. The parameter search method is based on a firefly algorithm due to the empirical evidence of its superiority in solving various nonconvex problems. The simulation results show that the proposed optimal tuned cascade control is effective and efficient. These results clearly demonstrate that the proposed control techniques exhibit significant performance improvement over classical and widely used control techniques.
Vehicular tailpipe emissions have one of the largest impacts on urban air quality. One way to reduce these hazardous emissions is to reduce the amount of fuel consumed by on-road vehicles. In this research, we consider both vehicle design and driver behavior as crucial elements in evaluating the environmental impact of two-wheel vehicles. Any redesign of vehicle specifications, results in different driving patterns that need to be re-evaluated in a realistic environment with traffic simulation. Therefore we developed traffic simulations with mixed fleets to model scooter/driver behaviors to reflect urban driving scenarios. Based on the results, a 31-variable continuous variable transmission (CVT) design and a 14-parameter cellular automata traffic model are integrated. Simultaneous redesign of CVT with traffic simulation can reduce the fuel consumption by 16.2% in our case study. This promising outcome demonstrates the need for multi-discipline integration of real-world traffic impact assessments and improvements.
In this paper, a relatively new strategy known as unified optimization is applied to the cam profile optimization for the delivery system of an offset press by integrating the procedure of single objective optimization with ADAMS software. The proposed approach mainly consists of two parts that includes a single objective optimization procedure and a multibody dynamic model of cam–follower mechanism. For the procedure of single objective optimization, the design process starts from defining the follower acceleration profile by using a modified trapezoidal curve, then genetic algorithm is adopted to determine the evaluating indexes for the kinematic behavior of cam–follower mechanism in multiobjective optimization. Subsequently, sequential quadratic programming, which deals well with equality and inequality constrains, is selected as single objective optimized algorithm in this part. On the other hand, the dynamic simulation developed by ADAMS software is carried out to investigate the dynamic characteristics of cam–follower mechanism. Finally, an optimization cycle, also known as iterative process, is proposed to implement the procedure of single objective optimization and dynamic simulation alternately to improve the kinematic and dynamic characteristics of cam–follower mechanism fully. The cam profile optimization method presented in this paper provides a new tool for cam designers to avoid the undesirable impact and follower jump.
Polycrystalline diamond layer peel-off is a hot topic in oil and gas drilling engineering. When an integrated polycrystalline diamond compact cutter suffers overload, there is a rapid decline in its rock-breaking performance and drilling rate of penetration. To modify the comprehensive performance of polycrystalline diamond compact, we innovatively propose a new embedded polycrystalline diamond compact. According to geometric analysis theory combined with the linear combination rule, the three typical embedded design schemes – the imitation palm-shaped, imitation Z-shaped and ring-embedded designs – are discussed. The influences of the number, size, location and combination of the embedded polycrystalline diamond layer on the polycrystalline diamond compact wear mechanism and rock-breaking performance are analysed. The results show that the embedded element and carbide matrix are combined by brazing welding, which not only exerts high abrasion resistance on the polycrystalline diamond layer but also combines with the good impact performance of carbide matrix. Compared with ordinary polycrystalline diamond compact, the intake amount of a single-embedded polycrystalline diamond compact is smaller, and it wears more evenly during the rock-breaking process. Comparing the results from before and after drilling, it effectively prevents the ordinary polycrystalline diamond compact from easily peeling off when suffering overload. The unique wear analysis model can be applied to other types of polycrystalline diamond compact by adjusting the embedding method. The research conclusions provide useful insights into the study of the polycrystalline diamond compact wear mechanism and rock-breaking performance.
Electromagnetic harvesters need to be designed with a mechanism to amplify the coil relative velocity to ensure compact size and lower weight. This paper discusses a novel technique to use fluid link for velocity amplification in an electromagnetic shock absorber. Incorporation of the fluid amplification significantly improves harvested power, without affecting the system dynamics. Numerical modelling and experimentation of a prototype shock absorber comprising of high energy rare earth magnets have been presented. Peak coil voltage of 0.60–24.2 V was recorded during experimentation on the prototype. Experimental and simulation results validate that incorporation of the fluid amplification link improves the harvested electric power by 9702%. Comprehensive design procedure for better harvesting efficiency and vibration isolation has been discussed. Lastly incorporation of the shock absorber in McPherson strut suspension is illustrated. The real size version will be able to harvest peak power of 18–227 W for the suspension velocities of 0.15–0.4 m/s.
A novel multifractal detrended fluctuation analysis based on improved empirical mode decomposition for the non-linear and non-stationary vibration signal of machinery is proposed. As the intrinsic mode functions selection and Kolmogorov–Smirnov test are utilized in the detrending procedure, the present approach is quite available for contaminated data sets. The intrinsic mode functions selection is employed to deal with the undesired intrinsic mode functions named pseudocomponents, and the two-sample Kolmogorov–Smirnov test works on each intrinsic mode function and Gaussian noise to detect the noise-like intrinsic mode functions. The proposed method is adaptive to the signal and weakens the effect of noise, which makes this approach work well for vibration signals collected from poor working conditions. We assess the performance of the proposed procedure through the classic multiplicative cascading process. For the pure simulation signal, our results agree with the theoretical results, and for the contaminated time series, the proposed method outperforms the traditional multifractal detrended fluctuation analysis methods. In addition, we analyze the vibration signals of rolling bearing with different fault types, and the presence of multifractality is confirmed.
To obtain good performance in the conventional energy regeneration system which has worse dynamic actuator performance than traditional orifice control systems, an energy regeneration system that employs a proportional throttle valve and a proportional directional valve to avail a hydraulic motor controlling the boom is proposed. The control model is constructed and the control properties are analyzed. Based on the proposed energy regeneration system, the new operation mode of the boom system with an energy regeneration system is characterized by the status of the joystick and the pressure of the boom cylinder. Considering the performance under the bad control in the low rotational speed, the total power loss of the hydraulic motor and the generator, a dynamic-working-points control strategy of the generator is discussed. Then, as the displacement and velocity sensors cannot be easily assembled in a hydraulic excavator, a compound control that consists of throttle control and volume control is presented. Finally, a test rig is constructed, the recovery efficiency of the proposed energy regeneration system is approximately 35% and it is also shown that the proposed energy regeneration system had better control performance than the conventional energy regeneration system.
The mobility of a whole parallel manipulator and the relative degree-of-freedom are the key points in mechanism synthesis and analysis, which often can be used to verify the existence of mechanisms. In this paper, the difference between the mobility of a parallel manipulator and the relative degree-of-freedom is discussed. First, a novel relative degree-of-freedom criterion is proposed based on the principle of determining the moving platform by N point positions, which is suitable for a kind of parallel manipulator with spherical joints attached to the moving platform. Next, the relative degree-of-freedom criterion is used to calculate the independent motions of the moving platform compared with the modified Kutzbach–Grübler criterion. The proposed relative degree-of-freedom criterion is different from the modified Kutzbach–Grübler criterion in result value and physical meaning. Finally, the type synthesis of such parallel manipulator with open-loop limbs or closed-loop limbs is performed based on the proposed relative degree-of-freedom criterion.
In traditional studies of linear motion roller guide, the static stiffness is a main indicator to evaluate the mechanical behavior. However, the local contact profile between the roller and raceway surface, although very important to the precision maintenance, cannot be reflected in the measured value of static stiffness. In this article, a new indicator, named the real contact total length (RCTL), is proposed based on the Greenwood–Williamson model and the Hertz contact theory. In particular, an electric contact model is presented where the RCTL of linear motion roller guide without preload is expressed in terms of the measured electric resistances. To verify the model, an experiment is conducted to measure the electric resistances under different vertical loads by a designed load test bench and a digital, direct-current, high-resolution electric resistance meter (DRRM). The test results show good agreement with the model. Based on the electric contact model, the main parameters that affect the RCTL value are roughness Ra and the length of roller, which are directly related to the mechanical behavior of linear motion roller guide in the design and manufacture stages.
A flexible hose that is unwound along with fiber-optic cables from a mother ship helps prevent interference with the mother ship during the unwinding of the fiber-optic cable. Because the density of fiber-optic cables is close to the fluid density, if there is no flexible hose, the fiber-optic cable is more likely to interfere with the mother ship because of the motion of underwater vehicles or mother ships. Hence, it is necessary to prevent the interference of fiber-optic cables by using flexible hoses made of stainless steel. Flexible hoses unwound as an underwater vehicle moves are coupled to the vehicle by shear pins, and once all flexible hoses are unwound, the underwater vehicle continues to move forward as the pins fracture. Here, a dynamic load applied on the shear pin for connection in the early stages of the unwinding of the flexible hose is an important factor that controls the position, which should be accurately predicted, prior to the motion of the underwater vehicle. Further, it is essential that the shear pin of the connection part be designed to fracture under the selected load so that underwater vehicle can continue to move forward as the pin breaks. In this study, analysis results based on loading information measured in real experiments were compared and verified, and based on the findings, an analytical model that can predict loads applied on the shear pin was developed.
Achieving a precise fault diagnosis for rolling bearings under variable conditions is a problematic challenge. In order to enhance the classification and achieves a higher precision for diagnosing rolling bearing degradation, a hybrid method is proposed. The method combines wavelet packet transform, singular value decomposition and support vector machine. The first step of the method is the decomposition of the signal using wavelet packet transform and then instantaneous amplitudes and energy are computed for each component. The Second step is to apply the singular value decomposition to the matrix constructed by the instantaneous amplitudes and energy in order to reduce the matrix dimension and obtaining the fault feature unaffected by the operating condition. The features extracted by singular value decomposition are then used as an input to the support vector machine in order to recognize the fault mode of rolling bearings. The method is applied to a bearing with faults created using electro-discharge machining under laboratory conditions. Test results show that the proposed methodology is effective to classify rolling bearing faults with high accuracy.
This paper presents a mathematical model of a machine tool rotary table with backlash to describe the dynamic behavior of the mechanical system and the motion controller. The accuracy of this model is verified by experiments. The steady-state vibration under different conditions is simulated to investigate its mechanism and change rule. The results show that the steady-state vibration is attributed to the alternate impact of transmission components. Based on the different performances of the steady-state vibration for different control gains and different motion directions, the concept of stability region in the plane of control gains is presented. In the critical region, the steady-state vibration only occurs when the table moves toward backlash. The complex contact regimes may lead to a significant increase in the amplitude of the steady-state vibration. Besides, the influences of the load and the magnitude of backlash on the steady-state vibration and the stability region are also discussed.
The primary goal of this article is to propose a new analysis tool that estimates the asymptotic trends in the time-varying oscillatory period of a non-linear mechanical system. The scope is limited to the step-response of a torsional oscillator containing a dry friction element and dual-staged spring. Prior work on the stochastic linearization techniques is extended and modified for application in time domain. Subsequently, an instantaneous expected value operator and the concept of instantaneous effective stiffness are proposed. The non-linear system is approximated at some instant during the step-response by a linear time-invariant mechanical system that utilizes the instantaneous effective stiffness concept. The oscillatory period of the non-linear step-response at that instant is then approximated by the natural period of the corresponding linear system. The proposed method is rigorously illustrated via two computational example cases (a near backlash and near pre-load non-linearities), and the necessary digital signal processing parameters for time domain analysis are investigated. Finally, the feasibility and applicability of the proposed method is demonstrated by estimating the softening and hardening trends in the time-varying oscillatory period of the measured response for two laboratory experiments that contain clearance elements and multi-staged torsional springs.
Structural health monitoring is essential for ensuring the structural safety performance during the service life. The process is of paramount importance in the case of the Pelamis wave energy converter due to the structural parts being subjected to the marine environmental risky conditions and consequently, power take-off system damage. In this paper, a fuzzy-based damage detection method using the dynamic response of the Pelamis type P1 is proposed. Accurate modeling of a dynamic system with simple dynamic equations is one of the important steps of damage detection process; for this purpose, the equations of the motion of the Pelamis system is derived using the Lagrangian method for creating a discrete model of the Pelamis in the first step. For validating the obtained model, scaled experimental model of the Pelamis is provided, and modal analysis is carried out. Then, the features in the frequency spectrum of the structure response in each degree of freedom as a result of power take-off damaged conditions are considered as inputs to the fuzzy system. Also, the fuzzy system is trained based on calibrating the membership functions by defining the damage classes appropriately. For validating the proposed method, noise with different signal to noise ratios is inserted to the measured features and the success rate of the damage detection is calculated. The results show that the proposed method is able to identify the damage classes with acceptable success rate.
Surface texture is one of the most promising methods to achieve friction reduction in the mechanical components, and it has been rapidly developed in the last decade. The friction reduction mechanism of regularly patterned surface texture is widely considered to be lubricant retention and debris entrapment. There are many ways to manufacture micro surface texture, among which deformed-based micro-surface texturing is the least studied. However, it has many unique advantages that cannot be surpassed by the rest, such as high production efficiency, fine geometrical fidelity and smooth surface finishing. Therefore, this study aims at developing a deformation-based low-cost micro form-rolling machine to create micro surface texture on the cylindrical component. A new demonstrator for examining the friction reduction efficiency of the micro surface texture has also been built and tested. Results show that the shaft with micro surface texture is able to reach a maximum of 48.1% friction reduction at rotation speed 400 r/min with lubricant SAE30 compared to the non-textured workpiece with the same condition.
The low-cycle fatigue behavior of a direct-quenched ultra-high-strength steel was experimentally characterized and numerically modeled. Fatigue and cyclic parameters were obtained by conducting strain-controlled low-cycle fatigue tests on uniform-gage specimens. Surface residual stresses were minimized and axial deflection eliminated by optimization of machining parameters and post-machining electro-polishing. The steel material showed cyclic softening and decrease in yield strength. Cyclic softening, stabilized response, and the cyclic stress–strain curve were numerically simulated using finite element analysis with a model capable of describing nonlinear kinematic-isotropic hardening. The results showed good agreement with experimental values and validated the model’s ability to simulate the softening and cyclic stabilization of the material under investigation. The same numerical method was then used in elasto-plastic stress–strain analysis of notched specimens made of the same material to make fatigue life predictions. Estimated lives were compared with predictions made by analytical approximations such as the linear rule, Neuber’s rule, and the strain energy density method and verified by experimental data. Finite element analysis using stabilized cyclic response yields the most accurate predictions and, thus, provides an effective tool for the fatigue analysis of this material.
In the present research, the intermetallic layer situation and bond strength of square tubes produced by shape rolling of Al–Cu bimetallic pipes has been investigated. The explosive welding process was used for the production of bimetallic circular pipes. The macro- and microscopic features of explosive-welded pipes and shape-rolled specimens at various stages were experimentally measured by using shear and hardness testing and optical metallography. Moreover, scanning electron microscopy was used for fractography of the fracture surfaces after the last stage of forming. The experimental results showed that the shear strength variation is dependent on the intermetallic layer thickness and its continuity. Also, continuity in Al–Cu interfaces that have a thick intermetallic layer intensifies the microcrack propagation, while due to discontinuity in the thin intermetallic layer, the retardation of catastrophic crack propagation was observed in the early passes of the shape-rolling process. However, the results of the present study showed that as the passes proceed in the rolling process, the crack propagation phenomenon, which is the cause of a decrease in shear strength, is expected.
A new information-localization strategy for machining large thin-walled parts is presented in this paper. This strategy uses sub-areas and fiducials calibration methods to improve processing precision of large thin-walled parts, which are of poor machinability, low rigidity, and poor deformation coupling. In our experiments, the large thin-walled part is firstly divided into several sub-areas based on the actual state of the workpiece sampled by a binocular vision sensor. And then each divided sub-area is calibrated by the machining benchmark fiducials. Finally, the machining error of each sub-area is automatically compensated based on the measurement results of fiducials in each sub-area by the touch probe. Two verification experiments show that the proposed strategy is feasible and efficient.
Due to the importance of geometrical design of clinching tools, the clinching process with extensible dies was investigated numerically and experimentally to seek for optimal parameters of clinching tools in this study. The joining parameters, including punch corner radius, sliding distance, die depth and bottom thickness, were optimized using the orthogonal experimental design simulation method based on the evaluation of tensile strength. The simulation results were validated through an experimental setup testing on material aluminum alloy Al5052. The orthogonal experimental design simulation results showed reasonably good agreement with the experimental results. To further investigate the validation of the simulation model, the different bottom thicknesses within a reasonable range of value were studied. The results also indicated that the simulation model could be employed to predict the joint forming by the clinching process with extensible dies.
Owing to the importance of geometrical design of clinching tools, the flat-clinching were investigated numerically and experimentally to determine the optimal geometrical parameters in this study. The geometrical parameters in flat-clinching, including punch corner radius, draft angle of the punch, blank holder corner radius, blank holder radius, and punch velocity, were optimized using the orthogonal experimental design simulation method based on the evaluation of interlocking. The simulation results show that the punch corner radius and the blank holder radius have a significant impact on the clinched joint, whereas the draft angle of the punch and blank holder corner radius have little influence on the clinched joint. The simulation results were validated through an experimental setup testing on material aluminum alloy Al5052. The experimental results have a good agreement with the orthogonal experimental design simulation.
A novel model is developed for a vibrating single-conductor transmission line carrying Stockbridge dampers. Experiments are performed to determine the equivalent viscous damping of the damper. This damper is then reduced to an equivalent discrete mass-spring-mass and viscous damping system. The equations of motion of the model are derived using Hamilton’s principle and explicit expressions are determined for the frequency equation, and mode shapes. The proposed model is verified using experimental and finite element results from the literature. This proposed model excellently captures free vibration characteristics of the system and the vibration level of the conductor, but performs poorly in regard to the vibration of the counterweights.
The wheel–rail contact can be found in two patterns. In the first pattern, the treads of both wheels are in contact with the two top surfaces of the -shaped guide rail; in the second pattern, the treads of both wheels are in contact with the two top surfaces of the -shaped guide rail, and the wheel edge is in contact with the guide rail web on one side. Based on these findings, an equivalent mechanical model with four unilateral springs is proposed to describe the wheel–rail contact. Additionally, a dynamic model of the Translohr tramway is established using Matlab/Simulink. The wheel–rail contact in a tramway moving along curves with different radii is calculated using simulation, and the results obtained are consistent with the observations and results of field measurements. The effects of various factors, including curve radius, tram speed, guide rail pre-pressure, and guide rod length, on the side wear of the guide rail were investigated. The results revealed that curve radius and tram speed are the critical factors affecting rail track side wear. These two factors can qualitatively determine rail track side wear, while other factors can only quantitatively affect the degree of rail track side wear.
Seawater axial piston pump is a critical power component in seawater fluid power system. As the properties of high bulk modulus and low viscosity of seawater, the pressure and vibration characteristics of the seawater axial piston pump will be getting poorer than the traditional oil pump. In this study, the pressure, flow, and vibration characteristics for a seawater axial piston pump are investigated. The three-dimensional computational fluid dynamics simulations for the port plate with non-grooved, U-shaped, and triangle-based pyramid silencing groove designs have been conducted over a range of operating conditions, which consider the fluid compressibility effect and cavitation damage. Measurements of pressure ripple and pump vibration are carried out at various loading conditions to verify the results of simulation. The experiment turned out that the well-designed port plate can mitigate both pressure ripples as well as vibrations of the pump. This research will lay the foundation for the further development of a low fluid noise seawater axial piston pump.
The stiffness of the cable-driven parallel manipulator is usually poor because of the cable flexibility, and the existing methods on trajectory planning mainly take the minimum time and the optimal energy into account, not the stiffness. To solve it, the effects of different trajectories on stiffness are studied for a six degree-of-freedom cable-driven parallel manipulator, according to the kinematic model and the dynamic model. The condition number and the minimum eigenvalue of the dimensionally homogeneous stiffness matrix are selected as performance indices to analyze the stiffness changes during the motion. The simulation experiments are implemented on a six degree-of-freedom cable-driven parallel manipulator, to study the stiffness of three different trajectory planning approaches such as S-type velocity profile, quintic polynomial, and trigonometric function. The accelerations of different methods are analyzed, and the stiffness performances for the methods are compared after planning the point-to-point straight and the curved trajectories. The simulation results indicate that the quintic polynomial and S-type velocity profile have the optimal performance to keep the stiffness stable during the motion control and the travel time of the quintic polynomial can be optimized sufficiently while keeping stable.
The service life of mud pump pistons may be extended by imitating the body surface morphology of earthworms. To achieve this solution, bionic strip structures of various sizes are processed on the working surface of a BW-160 mud pump piston. The service lives of standard and bionic pistons are compared under experimental conditions. Results show that the bionic strip structure clearly improves the service life of mud pump pistons. The influence of the width of a bionic piston strip is greater than that of strip spacing. The bionic strip should not be too small or large because size could have negligible or deleterious effects on service life, respectively. The optimal structure parameters of a bionic strip piston when the optimal contact area between the piston and the cylinder liner is 73.5% are a strip width of 3 mm, strip spacing of 3 mm, and strip number of 3. These parameters improve piston service life by 81.5%. Finite element analysis simulations of wear demonstrate that the bionic strip can change the stress state on the working surface of the piston, increase lubricant storage space, improve the wear resistance of the piston, reduce extrusion injuries on the root, and prolong piston service life.
Nanocomposite ceramics possess beneficial mechanical and physical characteristics over traditional engineering ceramics; however, there is currently no effective method of machining nanocomposites ceramics. This paper proposes a new ultrasound-aided electrolytic in-process dressing machining method. There are many factors influencing the material removal rate in the ultrasound-aided electrolytic in-process dressing grinding. In order to optimize the processing parameters and guide practice, the material removal models are developed to simulate the material removal process based on ductile failure and brittle rupture models, and the influence of grinding parameters on material removal rates is obtained. With the model, the influence of grinding parameters on the material removal rate is analyzed by MATLAB. The analysis results are verified by the ultrasound-aided electrolytic in-process dressing grinding test: the material removal rate increases with the increase of grinding parameters; depth of cut significantly improves material removal rate, followed by axial feeding speed, wheel speed, and workpiece speed that are less important; considering the comprehensive processing effect, depth of cut is the key parameter with the optimal setting at about 3.73 µm. The ultrasound-aided electrolytic in-process dressing grinding test not only proves the reliability of the model, but also proves that the ultrasound-aided electrolytic in-process dressing grinding can improve the ductile machining effect, when compared to electrolytic in-process dressing grinding, which is suitable for mirror machining of the nanocomposite materials.
Rotating shafts often experience undesirable large-amplitude whirling oscillations associated with resonance at critical speeds. This paper further develops a nondestructive technique in which measured information about the growing nature of the response is used to predict an incipient critical speed. A number of models of varying degrees of sophistication are developed and tested using the new approach, but the main advantage of the method is that it is model-free and thus possesses considerable practical utility. In addition, further experimental results are presented for the case of two disks mounted on a shaft, and the technique is successfully demonstrated in predicting a critical speed associated with a higher mode.
The Blossoming Flower Clock is an ingenious timepiece made in the 18th century and now preserved in Beijing Palace Museum, China. It generally cannot be disassembled and examined due to its historical value, and hence the inner mechanisms of the clock are unknown. This study provides a systematic design approach for reconstructing the five automata in the clock, namely time keeping, music playing, ducks swimming, flowers blossoming, and figures posturing. For the first two automata, practicable mechanical structures are inferred based on a classification and analysis of known technological customs and practice at the time. A total of seven feasible mechanisms are proposed for the time-keeping automaton, while three possible mechanisms are presented for the music-playing automaton. For the remaining automata, the structural characteristics and design constraints of the associated mechanisms are derived by means of a systematic motion analysis. By applying the concepts of generalization and specialization, a total of seven feasible mechanisms are synthesized for the ducks-swimming automaton, while six mechanisms are presented for the flowers-blossoming automaton and figures-posturing automaton. The proposed methodology is formalized in the form of a flow chart. Overall, the present results suggest that the proposed method provides a useful approach for reconstructing the unknown internal workings of mechanical devices.
Cavitation frequently appears in high pressure water hydraulic components and leads to serious hydraulic erosions and horrible hydrodynamic noises. In this paper, a novel approach of suppressing cavitation was proposed, inducing the outlet pressure back to the orifice to improve the pressure distribution of throttle valves. In order to realize this approach, an optimized throttle valve chamber structure was designed. After that, the anticavitation performance of the valve was investigated. A theoretical cavitation cloud model was built based on bubble dynamics. In order to solve the mathematic cavitation model, the velocity field and pressure distribution of the novel throttle valve were simulated through Computational Fluid Dynamics(CFD). Combining the simulation results, the mathematic cavitation cloud model was solved through numerical calculations. Moreover, new indexes estimating cavitation intensity were proposed scientifically to investigate cavitation phenomenon. Then, the comparison of the novel throttle valve (with an innovative valve chamber) and traditional throttle valve in anticavitation performance was conducted under different conditions. Finally, the experiment about anticavitation performance was completed on the test rig. The calculation and experiment results indicated that the approach, inducing the outlet pressure back to the orifice, was effective in suppressing cavitation.
In nanoindentation, roughness of the sample surface can be a severe source of error in the determination of properties from indentation tests. Recently, roughness was also considered as a crucial issue in understanding the indentation size effect where a significant increase in hardness was seen with the decrease of depth. A three-dimensional roughness model with the Johnson–Cook material model is employed to study the roughness effect in nanoindentation on AISI316L stainless steel by use of finite element method. The rough surface is obtained by generating a random function in Matlab and then applying fast Fourier transform. With the quantitative analysis the mechanical properties such as the hardening and variation of the reduced modulus are found. From both the experimental and simulation results, the hardness distribution shows strengthening effect with the increased surface roughness. Both the scatter of hardness and indentation modulus increases with the increased roughness. In addition, the dependence of the pile-up effect and the contact area on the roughness is studied and analyzed.
In recent years, optimization started to become popular in several engineering disciplines such as aerospace, automotive and turbomachinery. Optimization is also a powerful tool in hydraulic turbine industry to find the best performance of turbines and their sub-elements. However, direct application of the optimization techniques in design of hydraulic turbines is impractical due to the requirement of performing computationally expensive analysis of turbines many times during optimization. Metamodels (or surrogate models) that can provide fast response predictions and mimic the behavior of nonlinear simulation models provide a remedy. In this study, simulation-based design of Francis type turbine runner is performed by following a metamodel-based optimization approach that uses multiple types of metamodels. A previously developed computational fluid dynamics-based methodology is integrated to the optimization process, and the results are compared to the results obtained from on-going computational fluid dynamics studies. The results show that, compared to the conventional methods such as computational fluid dynamics-based methods, metamodel-based optimization can shorten the design process time by a factor of 9.2. In addition, with the help of optimization, turbine performance is increased while cavitation on the turbine blades, which can be harmful for the turbine and reduce its lifespan, is reduced.
The dynamical behaviors of steel ropes and containers caused by different dangerous hoisting loads are theoretically and experimentally investigated to improve the hoisting safety in coal mines. Subsequently, the identification method is studied. The modal analysis technique based on Ritz Series and the Dempster–Shafer evidence theory is respectively employed during the study on vibration and identification. The vibration characteristics are apparently different with different categories and severities of dangerous loads. The different dynamical behaviors could be used as the basis of identification. The Dempster–Shafer evidence theory efficiently reduces uncertainty during the identification process of dangerous hoisting loads. Outcomes of this study might make a significant contribution to the hoisting safety in coal mines.
Induced-charge electro-osmosis around multiple gold-coated stainless steel rods under various AC electric fields is investigated using the techniques of microparticle image velocimetry and numerical simulation. In this study, the results of interactions between induced electric double layers of two identical conductive cylinders on surrounding fluid are presented. The induced-charge electro-osmosis flow around multiple rods in touch and with one cylinder diameter gap reveals quadrupolar flow structures with four vortices. The induced-charge electro-osmotic flow structure and velocity magnitude also depend on the cylinder geometry and orientation. It is seen that four small vortices develop in the close region of cylinder surface for multiple rods with gap, while the other four large vortices are surrounding them. The distributions of vorticity patterns also strongly depend on cylinder orientation in the close region of cylinder surface.
In this paper, the effect of finite strain on the nonlinear free vibration and bending of the symmetrically micro/nanolaminated composite beam under thermal environment within the framework of the Euler–Bernoulli and modified couple stress theory is studied. The governing equation of motion and boundary conditions are obtained using Hamilton’s principle, and then they are solved by generalized differential quadrature method. The bending and free vibration of the beam are investigated for both carbon/epoxy and glass/epoxy materials based on the finite strain and von Karman assumptions subjected to different boundary conditions. Also, two different fiber orientations including unidirectional and cross-ply are considered in this research. Comparison of the bending results show that there is a significant difference between the finite strain and von Karman particularly for
The vibration signals of fault rolling bearing are high-dimensional information with complex components. In order to identify different classes of bearing fault, a new multiscale morphological manifold method based on multiscale morphology and manifold learning is proposed. The multiscale morphological manifold method consists of three main steps. Firstly, multiscale difference filter based on multiscale morphological transformation is applied to obtain multiscale observation results of each signal sample. Secondly, the nonlinear feature vectors of each signal sample are constructed according to the observation approach. Finally, manifold learning is introduced to extract the low-dimensional multiscale morphological manifold features through reducing the dimension of nonlinear features. The low-dimensional multiscale morphological manifold features can reveal the differences of signal classes, which are applicable for fault diagnosis. The performance of proposed method is tested by experimental data from bearings with different types of defects. Experimental verifications confirm that the proposed method is applicable and effective for rolling bearing fault diagnosis.
This article develops and compares health indices using different approaches namely singular value decomposition, average value of the cumulative feature and Mahalanobis distance for assessing the rolling element bearing condition. The vibration signals for four conditions of rolling element bearing are acquired from a customized bearing test rig under variable load conditions. Seventeen statistical features are extracted from wavelet coefficients of the denoised signals. Feature selection is performed using singular value decomposition and kernel Fisher discriminant analysis. These selected features are used in these three approaches to develop health indices. Finally, a comparison of the three proposed approaches is made to select the best approach which can be effectively used for fault diagnosis of rolling element bearings.
A steady state simulation procedure is proposed to capture localized flow reversal inside of a centrifugal compressor vaneless diffuser. The procedure was performed on 12 compressor stages of varying geometry for speed lines of 13,100, 19,240, and 21,870 r/min. The simulations were run for all points from choke to surge including the experimentally determined rotating stall onset point. The experimental data and geometry were provided by Solar Turbines Inc. San Diego, CA. It was found possible to capture localized flow reversal inside of a vaneless diffuser using a steady state simulation. The results showed that using a geometric parameter, comparing the diffuser width, b4, to the impeller blade pitch distance, dpitch, it could be determined whether or not a steady state simulation could capture localized flow reversal. For values of b4/dpitch beneath 0.152 flow reversal could not be captured. But, for values of b4/dpitch above 0.177 localized flow reversal was captured. For values between 0.152 and 0.177, no conclusions could be drawn. Where possible, experimental data were compared against the diffuser inlet and outlet numerical profiles and the meridional contour plot. These comparisons served to validate the approach used in this article. These validations showed that the procedure defined herein is accurate and trustworthy within a specific range of geometric and flow characteristics. There are two other conclusions. First, the b4/dpitch parameter helps to define the type of flow breakdown. For b4/dpitch below 0.152, the flow breaks down in the circumferential direction, but for values of b4/dpitch above 0.177, the flow breaks down in the span-wise direction. Second, the simulations were able to capture instances of localized flow reversal before rotating stall onset. This concludes that localized flow reversal is not the determining factor in rotating stall onset as has been suggested by other investigators.
This paper studies the shear stresses appearing in the contact zones of dowel-type joints of timber structures using expansive kits. To achieve this goal, a finite element model capable of determining the effect of using these kits on the global response of the joint has been prepared. For its development, different tools have been used to model the expansion process, the contact between the different parts of the joint, the compression pressures triggered by this contact, the resulting shear stresses caused by friction and, finally, the effect of all these circumstances on the overall performance of the joint, especially on the relationship between the applied load and the related displacement. The design of the model has been checked for correctness using experimental tests. The results obtained show that the use of expansive kits slightly improves the load-carrying capacity of the dowel through the rope effect.
The vibration signals coming from a hydropower unit have strong nonstationary characteristics when strong vortex develops in the hydraulic turbine draft tube. Related to this problem, a new vibration analysis method for a hydropower unit based on adaptive local iterative filtering is proposed. Firstly, adaptive local iterative filtering was used to decompose the complex vibration signal into several intrinsic mode functions. Then, frequency spectrum analysis of these components was performed to obtain the vortex characteristic frequency from the vibration signal. Simulated and real-world signals were used to verify the proposed method. The obtained results show that this method can overcome the problem of mode mixing in the existing empirical mode decomposition method, since it improves the efficiency and accuracy of feature extraction for nonstationary vibration signals from a hydropower unit.
A curved slotted Geneva mechanism can eliminate the adversely infinite angular jerks of the Geneva wheel and might reduce the peak angular acceleration of the Geneva wheel by using a proper indexing motion program. In the literature, the cycloidal, fifth-order polynomial and modified sine indexing motion programs are frequently used for curved slotted Geneva mechanisms. To achieve the better kinematic performance of the curved slotted Geneva wheel than that obtained using the above-mentioned indexing motion programs, a new indexing motion program based on the Hermite interpolating polynomial is proposed for an optimum design with the goals of minimizing the peak angular acceleration and eliminating the adversely infinite angular jerks. The domain of the indexing position function is divided into several segments. Each segment is termed an element, and both ends of each segment are termed nodes. The nodal values of the indexing position function and its derivatives are used as design variables. The position function for each element can be described using the Hermite interpolating polynomial and the design variables. The reason behind the use of the Hermite interpolating polynomial is that the design variables have the clear physical meanings. The four-level Hermite interpolating polynomial is used and two elements are sufficient to obtain the optimum results. In addition, the constraint regarding the radius of curvature of the profile of the inner slot is proposed to prevent sharp curvature of the profile of the inner slot. The findings show that there is a decline in the peak acceleration of the Geneva wheel with six curved slots for the optimum results obtained using the proposed indexing motion program by 33.4% and 24.3%, respectively, as compared with the cycloidal and modified sine indexing motion programs.
Disassembly sequencing is a concurrent research subject in design for life-cycle. Many past and recent researches are made to give practical methods for disassembly sequencing. The problem of assembly information’s modeling is one of the important sub-problems of disassembly simulation. The problem includes connection determination, disassembly direction identification, and part mobility state definition. In the present paper, the authors propose a new representation model of disassembly directions, starting from geometric and assembly data of computer aid design models. This model is based on a mobility matrix definition for every part. This matrix is also called disassembly direction matrix. The model gives information about the mobility state of a part during disassembly sequencing by updating its mobility matrix. Mobility state data are used in a practical computing of disassembly sequence feasibility. In this paper, theoretical explication of this modeling is given and validated by computational results. In the validation section, the model is applied to a computer aid design mechanism using a selective disassembly.
In this paper, a new type of lower limb powered exoskeleton is presented, which is based on a screw-nut actuated mechanism to help paraplegics to stand, walk and accomplish activities of daily living. The Denavit–Hartenberg method and the Kane method are adopted to establish a kinematic and dynamic model of novel lower limb powered exoskeleton to analyze the workspace and the control strategy simulation. A double-closed loop control strategy is proposed to ensure precision, and its effectiveness is validated. The results of prototype gait control and patient experiments show that the new type of lower limb powered exoskeleton can enable patients to realize stable and smooth walking.
The uncertainties of design variables, noise parameters, and metamodel are important factors in simulation-based robust design optimization. Most conventional metamodel construction methods only consider one or two uncertainties. In this paper, a new surrogate modeling method simultaneously measuring all the uncertainties is proposed for simulation-based robust design optimization of complex product. The effect of metamodel uncertainty on product performance uncertainty is quantified through uncertainty propagation analysis among design variables uncertainty, noise parameters uncertainty, metamodel uncertainty, and performance uncertainty. Then, the sampling points are selected and the metamodel is constructed based on the predictive interval of product performance and mean square error of the Kriging metamodel. The constructed metamodel is applied to robust design optimization considering multiple uncertainties. Results of two mathematical examples show that the proposed metamodel considering multiple uncertainties increases the result accuracy of robust design optimization. Finally, the proposed algorithm is applied to robust design optimization of a heat exchanger, and the total heat transfer rate is enhanced under uncertainties of fin structural parameters, operation conditions parameters and simulation metamodel.
This paper makes a focus on the design of a micro-testing machine used for evaluating the mechanical properties of solder alloys. The different parts of the testing device have been developed and assembled in a manner that will facilitate the study of miniature solder joints as used in electronic packaging. A specific procedure for fabricating miniature lap-shear joint specimens is proposed in this work. The tests carried out with the newly developed machine serve to determine the material behavior of solder joints under different controlled loading and temperature conditions. Two new solder alloys, namely SACBiNi and Innolot, are characterized in the study, showing the influence of strain rate and temperature parameters on their respective mechanical responses. In addition, the as-cast and fracture surfaces of the solder joints are observed with a scanning electron microscope to reveal the degradation mechanisms. The SACBiNi solder alloy, which contains less Ni and Sb elements, is found to have smaller shear strength than the Innolot alloy, while its elongation to rupture is significantly improved at the same strain rate level and testing temperature. The highest shear strength is 58.9 MPa and 61.1 MPa under the shear strain rate of 2.0 x 10–2 s–1 and room temperature for the SACBiNi and Innolot solder joints, respectively. In contrast, the lowest shear strength values, 26.6 MPa and 29.5 MPa for SACBiNi and Innolot, respectively, were recorded for the strain rate value of 2.0 x 10–4 s–1 and at temperature of 125℃.
Dynamic response of structures can be determined by mode superposition method which uses mode shape functions and modal coordinate functions. If the structure can be modelled with a uniform Euler–Bernoulli beam and a combination of clamped, free, pinned or sliding boundary conditions, analytical expressions for mode shape functions and modal coordinate functions are used. If analytical expressions for higher-order mode shapes or analytical expressions for the modal coordinate functions at high value of time are numerically evaluated, errors occur since the programming language cannot recognise the resulting value as a number, due to ill-conditioned analytical expressions. An analytical expression is ill-conditioned if small errors in the data may produce large errors in the solution. In this paper, we present a procedure for the exact numerical evaluation of analytical expressions for modal coordinates at high value of time while existing modified analytical expressions are used for exact calculation of higher-order mode shapes of the Euler–Bernoulli beam. The proposed procedure can be applied in the design of structure elements whose response is calculated with mode superposition method, e.g. for designing of metal frames for sawing machines in woodworking industry.
Rheological properties of magnetorheological (MR) fluids can be changed by application of external magnetic fields. These dramatic and reversible field-induced rheological changes permit the construction of many novel electromechanical devices having potential utility in the automotive, aerospace, medical and other fields. Vibration control is regarded as one of the most successful engineering applications of magnetorheological devices, most of which have exploited the variable shear, flow or squeeze characteristics of magnetorheological fluids. These fluids may have even greater potential for applications in vibration control if utilised under a mixed-mode operation. This article presents results of an experimental investigation conducted using magnetorheological fluids operated under dynamic squeeze, shear-flow and mixed modes. A special magnetorheological fluid cell comprising a cylinder, which served as a reservoir for the fluid, and a piston was designed and tested under constant input displacement using a high-strength tensile machine for various magnetic field intensities. Under vertical piston motions, the magnetorheological fluid sandwiched between the parallel circular planes of the cell was subjected to compressive and tensile stresses, whereas the fluid contained within the annular gap was subjected to shear flow stresses. The magnetic field required to energise the fluid was provided by a pair of toroidally shaped coils, located symmetrically about the centerline of the piston and cylinder. This arrangement allows individual and simultaneous control of the fluid contained in the circular and cylindrical fluid gaps; consequently, the squeeze mode, shear-flow mode or mixed-mode operation of the fluid could be activated separately. The performance of these fluids was found to depend on the strain direction. Additionally, the level of transmitted force was found to improve significantly under mixed-mode operation of the fluid.
In this paper, the configuration parameters of pre-designed composite patch repair are optimized with the aim of achieving the highest level of stability of crack growth in aluminum in the presence of some constraints such as weight, load sustainability, shear stress in the adhesive layer and maximum stress in the patch. For this purpose, the patch is modeled in full scale by ABAQUS, a commercial finite element code. The crack growth process is simulated with the extended finite element method under uniaxial tensile loading, and the Cohesive Zone Model is used to model the progressive damage in the adhesive of the composite patch repair. Also, sensitivity analysis is performed on the configuration parameters and it is shown that three parameters, i.e. width, stiffness ratio, and height of the patch are more important. Nonlinear fracture mechanics concepts have been used in calculating the stability of crack in the cracked aluminum plate. The results show that optimization based on the method proposed in this paper causes the stability of crack growth to increase by 21% while the patch weight is reduced by 52%.
In this paper, the magneto-mechanical nonlinear vibration behavior of rectangular functionally graded carbon nanotube reinforced composite (FG-CNTRC) sandwich Timoshenko beam based on modified couple stress theory (MCST) is investigated by the generalized differential quadrature method. The FG-CNTRC sandwich beam consists of two FG-CNTRC face sheets and homogenous core subjected to longitudinal magnetic field. In the FG-CNTRC face sheets, carbon nanotubes are disseminated in different patterns as uniform distribution, FG-X, FG-V, and FG-O. Based on von Kármán geometric nonlinearity, the nonlinear governing equations are derived by the Hamilton’s principle. Accuracy and convergence of this study are validated by comparing the numerical results with those found in literature. Various parameters effects are examined on the nonlinear 1st frequency of the sandwich beam. The results reveal that composition of the CNTRC face sheets and homogenous core in sandwich beam can be achieved remarkable stiffness in comparison to only CNTRC beam or only homogenous beam. For achieving the highest stiffness of FG-CNTRC sandwich beam, the value of thickness ratio is obtained about 0.34 and 0.27 in the presence and absence of Pasternak foundation, respectively. Moreover, the linear and nonlinear 1st frequencies increase with an increase in the magnetic field for all of CNT distribution types of sandwich beam and different boundary conditions whereas the frequency ratio decreases. Also the highest and lowest nonlinear 1st frequencies are corresponding to FG-A and FG-V distributions of CNT in face sheets, respectively.
This paper proposes a novel high capacity servo press system with two servo motor inputs and high ratio force amplifier mechanism for metal forming. First, the press structure was expressed. The force amplifier was made of seven-bar mechanism which possesses quick-return character and high ratio force amplifier. The symmetric structure balanced the force in horizontal direction, and dispersed the forces on two transmission routes. In theoretical study of the new structure, kinematic and dynamic analyses were obtained by examining the geometry of the structure. The performance of press was discussed by example demonstration. Finally, the kinematic experiments and metal forming experiments were carried out on the prototype machine by using grating scale system. The measured data match the theoretical calculation well, which validates the feasibility of this new press mechanism.
This paper initially deals with the design of a new customized reconfigurable mobile parallel mechanism. This mechanism is called the ‘Taar Reconfigurable ParaMobile’ (TRPM), consisting of three mobile robots as the main actuators. Then, the kinematics and path planning for this mechanism are presented. The newly proposed mechanism is expected to circumvent some shortcomings of inspection operation in unknown environments with unexpected changes in their workspace, for example, in a water pipe with a non-uniform cross-sectional area. In this paper, ‘Artificial Potential Field’ (APF) has been assumed to be the path planning algorithm and its resulting attractive and repulsive forces are only applied to the end-effector to generate the desired path. It is worth mentioning that the obstacle considered in this paper is a wedge which models an environment with non-uniform cross-sectional area along the path travelled by the end-effector. The inverse kinematics of the TRPM is then solved by resorting to the Resultant method as well as the Homotopy continuation method. The objective of utilizing these two well-known methods is to verify the correctness of the upper bound of solutions. It should be mentioned that solving the inverse kinematic problem obtained from both above-mentioned methods, leads to 12 solutions: eight real and four complex solutions. As a novel parallel mechanism, the TRPM yields a three-degrees-of-freedom kinematic redundancy. Despite the fact that the redundancy is sometimes beneficial for the control procedure, solving the inverse kinematics of the TRPM would be feasible only by adding some constraints. As a result, there will be a system of equations consisting of three kinematic equations and three auxiliary equations. Results from this study reveal that, by applying APF as the path planning algorithm to the TRPM, it is possible to track proper paths to reach the target.
This paper presents the design and development of a hybrid bearing set for complete passive levitation of a typical rotor. A hybrid bearing set consists of permanent magnet thrust bearing and radial discrete bump foil bearings. The permanent magnet thrust bearing is made up of three pairs of ring magnets arranged in rotation magnetized direction. The mathematical model to determine the force and stiffness in rotation magnetized direction configuration is presented using Coulombian model and vector approach. Bump foil bearings are designed and developed for rotor weight to provide the radial support to the rotor system. The proposed bearing set with rotor is analysed using finite element analysis for rotor dynamic characteristics. The experiments are conducted on the fabricated rotor-bearing configuration by rotating the rotor up to the speeds of 40,000 r/min. The system response is acquired using advanced rotor-dynamic data acquisition system. The experimental results show that the rotor is completely airborne and stable at the desired speed.
The dynamic modeling for the rotor with large diameter thrust bearings is one of the key issues in the design and operation of water-lubricated motorized spindle. In the machining process, the spindle not only translates along the x, y, z directions, but also tilts about the x and y axes under the cutting forces. As a result, the tilting effect of the thrust bearing on the dynamic performances of the motorized spindle should be considered. A five degree-of-freedom dynamic model for the spindle is established based on the Newton’s Laws and the principle of Angular Momentum. The translational and tilting dynamic coefficients for both the journal and thrust water-lubricated bearings were obtained by using Reynolds equation. The computed results show that the tilting effect of the thrust bearing on the dynamic performance of the motorized spindle should be considered when a large diameter thrust bearing is employed.
This work considers a disc cam mechanism with an upright installed negative radius translating roller follower. Accurate descriptions, as well as the basic concept and steps, are given for the shape, basic/overall size, and size synthesis of the new mechanism. A size coordinate system O – r0R and size domain (r0, R) are established, which are given discrete-meshing (grid) treatment. In addition, four constraints are proposed for the calculation formula. The traversal technique is used to achieve visual mapping under single/merged constraints, which gives the corresponding boundary and solution domain. Then, a combination of multiobjective planning and visual mapping reveals important principles such as the non-inferior region
A new forward kinematic analysis is proposed to describe the motion of a reptile-like four-legged walking robot using a new dimensionality-reduction method. The three standing legs (assuming one leg is swinging) contain nine driven joints. Only six of these joints, however, are independently driven joints. The remaining joints are redundant driven joints. Finding the redundant driven joint angles has been a key problem in improved forward kinematic analysis of a reptile-like forward kinematic analysis. Solving the associated high-order equation, which is derived using the analytic method, is problematic and slow. In this paper, we use a new dimensionality reduction method to solve this problem. First, we deduced the formulas for the redundant driven joint angles. Then, one of the formulas is transformed to take into account the constraint condition. We then use iteration to find solutions for the remaining equations that satisfy the constraint condition. With the help of MATLAB, a solving system for the forward kinematic analysis of this robot is introduced. Our results show two improvements over the conventional method: shorter computation time and higher precision.
A computational simulation and experimental work of the fluid flow through the pneumatic circuit used in a stretch blow moulding machine is presented in this paper. The computer code is built around a zero-dimensional thermodynamic model for the air blowing and recycling containers together with a non-linear time-variant deterministic model for the pneumatic three stations single acting valve manifold, which, in turn, is linked to a quasi-one-dimensional unsteady flow model for the interconnecting pipes. The flow through the pipes accounts for viscous friction, heat transfer, cross-sectional area variation, and entropy variation. Two different solving methods are applied: the method of characteristics and the Harten-Lax-Van Leer (HLL) Riemann first-order scheme. The numerical model allows prediction of the air blowing process and, more significantly, permits determination of the recycling rate at each operating cycle. A simplified experimental set-up of the industrial process was designed, and the pressure and temperature were adequately monitored. Predictions of the blowing process for various configurations proved to be in good agreement with the measured results. In addition, a novel design of a valve manifold intended for the polyethylene terephthalate (PET) plastic bottle manufacturing industry is also presented.
The rivet joint is an important mechanical connection for hot structures made of ceramic matrix composites. The development of chemical vapor infiltration technology provides a possible application of novel rivets for these structural components. However, connectors can still be the weakest link for structural integrity due to the severe stress concentration around the rivet joint holes. The geometry parameters of the rivet hole can be key influencing factors to the structural strength. A comparative evaluation is presented to analyze the influence of opening-hole shapes on the structural stress concentration of a composite plate. The opening-hole shapes considered include circle, ellipse, and racetrack. The finite element (FE) models of specimens with the three shapes of rivet holes were constructed. The stress distributions of the specimens under tensile loading were analyzed to compare the stress concentration factor (SCF) of different opening-hole shapes. An optimal shape, i.e. racetrack-shaped, was determined based on the SCF reduction of specimen-level comparison. Then, FE models of a composite plate containing rivet holes were built to verify the outperformance of the racetrack-shaped hole. A stress concentration reduction of the plate with racetrack-shaped holes was observed compared to the one with circular holes.
The zero-bias current controlled way is proposed to cut down the power consumption of the active magnetic bearing in a power magnetically levitated spindle system. The zero-bias current controlled way is easier to realize than the zero-bias flux controlled way, since current can be detected directly, while flux is hard to be measured in practice. Besides, the active magnetic bearing suffers from lumped uncertainty including parameter uncertainty and external load, and the displacement of rotor caused by lumped uncertainty is undesirable. In practice, the upper bound of the lumped uncertainty especially the external load is hard to obtain, making it hard to choose parameters for a traditional sliding mode control. The adaptive backstepping sliding mode control method combining both the advantages of sliding mode procedure and backstepping procedure is proposed to solve this problem. Furthermore, the upper bound of lumped uncertainty is estimated in real time by an adaptive law. In this paper, first a new zero-bias current active magnetic bearing system model with lumped uncertainty is built; then two controllers based on the sliding mode control and adaptive backstepping sliding mode control methods are designed, respectively, and the stability analyses are given for the two controllers via Lyapunov function; finally, the effectiveness of the proposed adaptive backstepping sliding mode control approach for a zero-bias current active magnetic bearing system is verified by the simulation and experiment results.
The dynamic buckling of rectangular plates with the elastically restrained edges subjected to in-plane impact loading is investigated. Budiansky–Hutchinson criterion is employed for calculation of dynamic buckling loads. The displacement function concluding the elastically restrained boundary condition is expressed as Navier’s double Fourier series. In order to solve the large deformation equations of plate, Galerkin method is applied. Also, the non-linear coupled time integration of the governing equation of plate is solved by using fourth-order Runge–Kutta method. The correctness of the method presented in the paper has been validated by comparing the results with the published literature. It is proved that the rotational restraint stiffness that is usually ignored by previous researchers plays an important role in dynamic response and dynamic buckling of the rectangular plates subjected to in-plane impact loading. Furthermore, the influence of the other parameters (initial imperfections, impact duration and geometric dimensions) on the dynamic response and dynamic buckling is studied in detail.
In this paper, linear time-invariant square systems are considered. A procedure to design infinitely many proportional–integral–derivative controllers, all of them assigning closed-loop poles (or closed-loop eigenvalues), at desired locations fixed in the open left half plane of the complex plane is presented. The formulation accommodates partial pole placement features. The state-space realization of the linear system incorporated with a proportional–integral–derivative controller boils down to the generalized eigenvalue problem. The generalized eigenvalue-eigenvector constraint is transformed into a system of underdetermined linear homogenous set of equations whose unknowns include proportional–integral–derivative parameters. Hence, the proportional–integral–derivative solution sets are infinitely many for the chosen closed-loop eigenvalues in the eigenvalue-eigenvector constraint. The solution set is also useful to reduce the tracking errors and improve the performance. Three examples are illustrated.
In the present study, a methodology for conducting a system-level analysis of a fan–motor assembly in a vacuum cleaner is presented. This system consisted of three components, a fan, motor, and the flow resistance of the motor, or of the vacuum cleaner. The combined characteristics of the fan and the motor were obtained from torque matching at a constant throttling condition, and a pressure drop was implemented under a constant flow rate to account for the flow resistance. By combining these two steps, the performance characteristics of the fan–motor assembly and the vacuum cleaner system could be predicted over the whole range of operation, based on the characteristics of each component. The predicted performance for power, flow rate, pressure, and efficiency using the present method agreed well with the experimental results obtained for an equivalent system, within 2% difference at best efficiency point. Three models of the fan–motor assembly (S1, S2, and S3) were analyzed at the component level, and the decrease in efficiency produced by flow resistance was estimated to be 1% (S1 and S3 models) or 4.7% (S2 model) using the present method. The characteristics of the fan, extracted from those of the fan–motor assembly, were used for validating the computational fluid dynamics. The computational fluid dynamics results of this study predicted higher efficiency due to simplification of the geometry, but an accurate prediction of best efficiency point location was obtained. The proposed method is also applicable for detecting system leakage and identifying system resistance without direct measurement.
This study introduces a new type of end-face structure with polytetrafluoroethylene seals that improves the reliability of the synchronal rotary multiphase pump (SRMP). End-face models, including the relative motion and friction loss between the rotor and cylinder end faces, are established for both the original and the improved end-face structures. The end-face friction losses are analytically investigated based on the theoretical calculations. Due to the low relative velocity between the rotor and cylinder end faces, the end-face friction losses for both of the end-face structures are found to be insignificant compared to the total friction loss in the SRMP. The increased end-face friction loss caused by the polytetrafluoroethylene seals in the improved end-face structure is also negligible. Assessment of the friction losses of two end-face structures in high-speed and high-pressure applications shows that the improved end-face structure exhibits better performance than the original. The parametric analysis suggests that the wider but taller cylinder is helpful in reducing the end-face friction loss of SRMP.
Parametric studies are conducted on different aspects of a planar MHD propulsion system called propulsive MHD blanket. Effects of nine different parameters on the electro-magnetic thrust, efficiency, and heat transfer of the blanket are investigated. To efficiently conduct the parametric analysis, the Taguchi test design method is used and 16 cases are defined. The Ansys-CFX commercial code is utilized as numerical solver and the obtained results are validated using the Hartman problem which indicated a negligible error of 0.16%. Electromagnetism, energy, mass, and momentum equations are considered for the fluid domain and heat transfer and electromagnetism equations are solved for the solid domain. On one hand, magnet shapes and type are found to be the highest effective parameters, followed by the electrodes voltage, length, and width. On the other hand, a prediction of the best combination of parameters for obtaining the highest electro-magnetic thrust are statistically accomplished which has produced an electro-magnetic thrust of 18.02 N per square meter for the MHD blanket which is twice the maximum electro-magnetic thrust obtained in the 16 initial test cases. It is demonstrated in the present paper that the unique applications of propulsive MHD blanket can compensate the very low efficiencies of MHD systems. It has also been shown that efficiency can be improved by enhancing the water conductivity, which is intended as a future study.
Chatter phenomenon is one of the essential problems in metal machining processes. It causes cutting tool wear and increase of production costs. Chatter vibration is an unstable self-excited vibration that the regenerative chatter is its most common type. In this paper, regenerative chatter in turning process is investigated. A three-dimensional nonlinear dynamic model of the turning process including both structural and cutting force nonlinearities and gyroscopic effects is presented. The workpiece is modeled as a rotating clamped–free beam which is excited by cutting forces. Using the method of multiple-scales, analytical approximate response of the system is obtained. To validate the model its responses are compared with the experimental results. Using this model the influences of tool longitudinal position, workpiece diameter, depth of cut, and rotational speed of workpiece on the stability results are studied. Using these results, turning velocity intervals for stable and unstable cuts are determined.
The effect of dead volume on the power output and efficiency of an alpha-Stirling engine is investigated in the form of an exploratory parameter study using the third-order simulation software Sage. This paper aims at identifying the underlying mechanisms in order to better understand the resulting design implications of this phenomenon that is in clear contradiction to what can be found in the literature. It turns out that additional ‘passive’ dead volume that does not even take part in the heat transfer processes leads to a phase shift of the pressure, resulting in increased pV-work output, especially at lower heat source temperatures. Of even greater significance, dead volume has a positive effect on the efficiency at lower heat source temperatures by reducing the temperature swing in the heat exchangers and by bringing the gas temperatures closer to the wall temperatures of the respective heat exchangers, and thus increasing the effective temperature difference. Furthermore, to a large extent the beneficial effects of dead volume can also be achieved by changing the phase angle.
The feasibility of ultrasonic vibration-assisted grinding in dental restoration has been preliminarily proved. Improving the machining quality of zirconia ceramics by controlling cutting force is the focus of the researchers. However, the existing feed direction cutting force model for ultrasonic vibration-assisted grinding does not take the ultrasonic vibration amplitude and frequency into account. This paper presents a mathematical model for feed direction cutting force in ultrasonic vibration-assisted grinding of zirconia under the consideration of amplitude and frequency, and assuming that brittle fracture is the primary mechanism of material removal in ultrasonic vibration-assisted grinding of zirconia. The effects of amplitude and frequency on the motion, effective cutting distance, and theoretical removal of an abrasive particle have been analyzed. Besides, the number of active abrasive particles is calculated with analyzing the influences of lateral cracks and ultrasonic vibration. The variation laws of cutting force and penetration depth of an abrasive particle during ultrasonic vibration-assisted grinding have also been analyzed. Therefore, the relationship between feed direction cutting force and input variables is predicted through the developed model. Finally, pilot experiments are conducted for the mathematical model verification. Experimental results show that the trends of input variables for feed direction cutting force agree well with the trends of the developed cutting force model. Hence, the mathematical model can be applied to evaluate the feed direction cutting force in ultrasonic vibration-assisted grinding of zirconia ceramics.
The use of light composites when designing fast moving parts for machine tools is emerging as a very efficient solution for improving productivity. Nevertheless, several aspects of these materials have to be carefully considered in woodworking. This paper aims to investigate the effect of interleaved nanofiber on mode I interlaminar properties and the failure modes that occur in this mode. For this purpose, woven carbon/epoxy laminates with and without Polyvinylidene difluoride nanofibers in the mid-plane were subjected to mode I interlaminar loading and the results were compared with each other. Acoustic emission technique was also utilized for better understanding of the failure modes that occurred in the virgin and nanofibers-modified specimens. Mechanical data and acoustic emission parameters associated with pattern recognition analyses were used for investigation of the interlaminar properties and the occurred failure modes. The mechanical results showed that the electrospun nanofibrous mat was able to increase the GIC by 98%. The acoustic emission results highlighted that different failure modes were the origin of different interlaminar failure behaviors. Different percentages of the failure modes in the modified specimens compared with the virgin ones were observed. Furthermore, the number of occurred interlaminar failure modes diminished in the modified composite layers.
Gearbox vibration signals with defects often show some important characteristic information. However, the feature information is difficult to extract since it is often flooded in the noise. To solve this problem, we present a novel detection approach for weak signals based on the multi-time-delayed feedback stochastic resonance model (MTFSR). Because the shape of the bistable potential well can be changed by the number of time-delayed terms, the MTFSR method can use historical information which is formed by the superposition of multiple time-delayed feedback items to enhance signal periodicity and obtain better output waveform and higher signal-to-noise ratio (SNR). Moreover, the presented method is also insensitive to the noise, and can detect the weak signals with different noise levels. Additionally, by selecting the proper calculation step, the approach has the ability to detect weak signals with different driving frequencies. With these properties, the proposed MTFSR is considered to be very suitable for gearbox fault diagnosis. Both simulation study and practical application confirm that the proposed strategy is feasible and superior in comparison with some traditional methods.
A new "whole close-chain mechanism" concept is proposed for the design of the modular legged unit of walking vehicles. Based on this concept, the walking vehicle called dual quadruped vehicle is developed and constructed. The vehicle designed as an omnidirectional carrying platform contains two identical single-driven quadruped mechanisms. The details of the design procedure are given, including the single close-chain legged mechanism, the modular legged unit, and the dual quadruped vehicle. The construction description of the single leg is presented. With the optimum design of the whole close-chain legged mechanism, the two foot-point characteristic trajectories are investigated. Based on the strategies of the legged module integration, the best phase configuration in pitching movement and the steering analysis are discussed and illustrated. Dynamic simulations and experiments are performed to verify the validity of the theoretical analysis of the new concept and the maneuverability of the vehicle prototype.
For the existing roadheader, the transmission system of the cutting unit cannot regulate speed and the cutting motor may break down because of the impact vibration. In this study, the power reflux hydraulic transmission system, which is a new continuous variable transmission system, is put forward to ameliorate these problems. The basic characteristics such as the speed ratio, efficiency and torque ratio are analysed on the basis of expounding the basic structure and operational principle of the power reflux hydraulic transmission system. The dynamic model of the transmission system of the cutting unit is established. The pulse signal is used as the simulation of the loads, when the roadheader suddenly encounters the high strength rock. Then the torsional vibration characteristics of the existing roadheader and the roadheader that is equipped with the power reflux hydraulic transmission system are analysed. The contrastive simulation results show that the motor and transmission system vibration of the roadheader which is equipped with the power reflux hydraulic transmission system is markedly attenuated relative to the existing roadheader. So the power reflux hydraulic transmission system can protect the cutting unit's motor and the transmission system.
The electrostatic sensing technique has been verified to be a viable method for tribo-contact monitoring under laboratory conditions in previous investigations. This paper reports on the evolution of electrostatic monitoring on a real oil-lubricated wind turbine gearbox, using a modified oil-line sensor. In a nominal test and a ramp-up test, features were extracted and the presence of debris can be detected. The permutation entropy was further introduced in an accelerated life test. It can accurately reflect the wear condition of the gearboxes and detect early faults earlier than conventional techniques, which also has a better sensitivity and performance degradation trend than time-domain features.
Peripheral pocket or contour milling in wood machining, using flat end milling tool, can be performed with different tool paths. Technology designers of multi axis CNC wood machining use their experience and intuition to choose some of the options offered by CAM systems that determine the final shape of tool path, thus the generated tool path largely depend on individual judgment. Minimum cutting force, maximum dynamic stability of the process and minimum tool wear are achieved, or some other technological requirements are met, by using optimal tool path. Tool path optimisation is based on analysis of possible tool paths and determination of cutting parameters which are dependable of chosen tool path and are affecting the main wood processing factors. Axial and radial depth of cut, engagement angle, feed and feed rate profile are identified as key parameters dependable of tool path, and their values and variations along the tool path influence the cutting speed, tool wear and cutting force. Knowledge of values and changes of those key machining parameters along the tool path is necessary for simulation and monitoring of the main cutting factors during the wood machining process. NC code transformation methodology and generation of tool path parameters necessary for calculating all elements needed for tool movement simulation from given NC programs are shown. Blank and tool mathematical description are used with tool movement information for simulation of wood machining process. Simulation of cutting parameters and their variation along the tool path, presented in this paper, can be used as bases for development of methodology for choosing the most adequate tool path for wood machining of given contour considering minimum cutting force and cutting force variation, minimum tool wear, maximum productivity or some other criteria.
In this paper, three-dimensional velocity field is proposed by means of stream function method with bisecting yield criterion in chamfer edge rolling of ultra-heavy plate. Parabolic dog-bone shape function is derived so as to obtain velocity field with fixed angle of chamfer edge by stream function method, dog-bone shape coefficient can be derived from volume invariant condition, and then the plastic deformation power, shear power as well as friction power are obtained respectively with the bisecting yield criterion. Summing up the power contributions, total power functional is presented, from which minimum value can be obtained by searching method, and vertical rolling force and torque are also finally obtained. The predictions of roll force and torque are compared with different angles of chamfer edge as well as different plate thicknesses. The results are shown to be in a very good agreement with the analytical and experimental results.
Coupling mechanism plays an important role in transmitting, motivating and actuating mechanical functions. However, it is difficult to obtain the transient dynamics performance of mechanism with variable degree of freedom precisely. Therefore, an interruption performance design method of variable freedom mechanism triggered by electro-magneto-thermo coupling is put forward. The Euler-Lagrange partial differential equations of variable freedom mechanism are built using generalized coordinates. Degree of freedom reduction rules are proposed to merge transformation or rotation constraints and obtain the total degrees of freedom of variable freedom mechanism at each transient status. Bivariate interpolating is employed to determine the electro-mechanical-magnetic coupled Lorentz force. Dynamics performance is simulated by iteration of linear algebraic equations using implicit predictor-corrector integration method. The design parameters such as stiffness and pre-tightening force of trigger spring, permissible dimension deviations and hole-shaft fit tolerance are determined and improved using the sensitivity analysis of simulation results. The pneumatic mechanical endurance and thermal infrared temperature rise experiments are accomplished to determine the infrared radiation energy distribution and transient working status of components. It gives an auxiliary thermo-visual approach for transient performance design of coupling mechanism.
This study has been carried out in order to measure friction coefficient of friction materials used in autos through computer program. Variants such as speed, temperature, and pressure have been discussed and the effect of these variants on friction materials of autos. Variants such as speed, temperature, and pressure resulting from various effects in autos have been discussed, the effects of these variants on friction materials have been examined and their friction coefficients have been detected. In the test device whose manufacturing has been completed, temperature value between surface of brake lining and disc used during tests a machinery has been prepared in a way that temperature values are 0–400 ℃, speed values are 0–1400 rev/min, pressure values are 0–1.05 Mpa. In consideration of these dates, it has become possible to constitute friction coefficient–temperature, friction–time and temperature–time diagrams. By benefiting from the tests to be performed through friction coefficient test device, enhancement or progress will be ensured in material selection, technology and theory. Control pf parameters such as speed, temperature, pressure, force, and friction coefficient to be measured are performed easily through test device; moreover, thanks to electronically sensitivity of electronically and mechanical materials used in test device, it is ensured that you can reach the values you want to reach correctly. Friction tests have been carried out on samples having different properties in auto regulative test device. Friction coefficient values of automotive brake linings in the new system design and manufacturing which is carried out, have been in conformity with SAE-J661 Standard and TSE 555-9076 Standard (Turkish Standards Institution). Test results obtained are in parallel with the literature.
Bolted joints are widely used in a variety of engineering applications where they are dynamically loaded with frequencies of vibration spread over a wide spectrum with the same general effects. When under dynamic loading, bolted joints can become loose due to a loss in clamping pressure in the joints. This vibrational loosening sometimes can cause serious problems, and in some cases can lead to fatal consequences if it remains undetected. Non-intrusive ultrasonic and image processing techniques were simultaneously used to investigate the relaxation of contact pressure and loosening of bolted joints subjected to cyclic shear loading. Three critical areas, the contact interface of the bolted component, the bolt length and the rotation of the bolt head, were monitored during loosening of the joints. The results show that loosening of bolted joints can be grouped into three stages: very rapid, rapid, and gradual loosening. The earliest stage of the loosening of bolted joints is characterised by cyclic strain ratcheting–loosening of the bolted joint during vibration without rotation of the bolt head. The higher the rate of relaxation at this early stage, the lower is the resistance of the bolted joint to vibration-induced loosening. Both the dynamic shear load and an additional constant shear load in another direction were observed to affect the rate of loosening, and at this early stage, a rise in the magnitude of the additional constant shear load increases the rate of loosening. Furthermore, the contact pressure distribution affects the rate of loosening at the bolted joint interface, as loosening increases away from area of high contact pressure.
The authors have established the mathematical equations for the tooth surface of non-circular gear and curve-face gear based on the external generating method with the same shaper cutter. The paper covers the derivation of contact line on both non-circular gear and curve-face gear, the derivation of contact point on curve-face gear, the transmission functions with errors of alignment, the analysis of transmission errors and the comparison between curve-face gear pair and normal face gear pair. The developed theory is verified by experiment.
Bonnet polishing is widely used in final processing of optical elements, as the bonnet tool has the characteristic of fine surface adaptability and controllable pressure. For the purpose of ensuring the stability and exact controllability of polishing process, it is necessary to make precise dressing of bonnet tool. In this paper, first a dressing scheme using cup diamond wheel is proposed for bonnet tool, and then the feasibility of the dressing scheme is verified by analyzing the trajectory and the envelope of the diamond particles on the cup wheel. After that, the influences of the dressing process parameters on the dressing efficiency and trajectory distribution are defined through theoretical analysis and MATLAB simulation, and by simulation the dressing process parameters are determined. In addition, a trimmed program with variable speed ratio is proposed to homogenize the dressing tracks. Finally, an experiment was conducted to test the simulation result. This paper provides the theoretical basis for actual dressing process of the bonnet tool.
The present work aims to analyze the influence of the in-plan distribution of asperities on the contact between periodically rough surfaces. Square pattern and hexagonal pattern rigid surfaces are considered. Their contact with an elastic half-space is analyzed by numerical simulations. Three surfaces are generated with identical asperities periodically distributed in a plan according to different patterns. It follows from numerical results that when the load and the real contact area are small, the asperities act almost independently. However, the interaction between close asperities increases with the load becomes intensified and has a significant effect on the contact area when the situation is close to full contact.
Since inchworm-like robots can exhibit excellent mobility in unstructured environments, it will be widely applied in agriculture, forestry, and high-altitude operations. Trajectory planning is an important issue for a climbing robot. This paper focuses on an inchworm-like climbing robot to plan its trajectory. The climbing process of the robot, especially the transitional gait when the robot is planned to climb over tree branches, is analyzed. Based on the gait analysis, the robot’s geometrical path is determined, and its waypoints are described by joint angles. 3-5-3 type polynomial interpolation function is adopted to fit the robot’s motion trajectory. To save the climbing time for the robot, its climbing transitional gaits for climbing over tree branches are optimized by using quantum-behaved particle swarm optimization algorithm to minimize the climbing time. Simulations are carried out to verify the developed trajectory planning, and the optimal results obtained from quantum-behaved particle swarm optimization are compared with the optimal solutions obtained by particle swarm optimization and genetic algorithm to further validate the effectiveness of the proposed method.
Based on the sliding-mode and adaptive control theories, the distributed consensus tracking problem under directed topology is investigated for multiple mechanical systems in the presence of general disturbances. We consider that only a subset of the follower mechanical systems can get the information from the dynamic leader mechanical system. First, with the upper bounds of the general disturbances and the leader’s acceleration, a distributed sliding-mode tracking scheme is proposed. Then, when considering the high conservation of sliding-mode control, an improved algorithm with adaptation laws for the upper bounds is developed. Both the proposed algorithms can make tracking errors for each follower mechanical system asymptotically stable. Numerical examples and comparisons are provided to show the effectiveness and the performance of the proposed control strategies.
Milling is a typical intermittent cutting process. As a result, tool wear is generated cyclically due to periodic process variables. However, the traditional tool wear prediction strategy based on continuous cutting model is no longer applicable. In this paper, a novel geometric approach through mesh node rigid moving for the milling cutter tool wear prediction has been developed. Firstly, a unified tool wear predictive model is established through bridging the two wear configurations before and after worn. A coupled abrasive–diffusive model is employed to calculate the tool wear volume of each point on tool face. Further, a novel iterative algorithm for tool wear prediction through mesh node rigid moving layer-by-layer and process variables redistribution is designed in discrete-time domain, which is generally decomposed into two phases according to cutting heat equilibrium state, FEM simulation and offline calculation. Last, a series of numerical and saw-milling experiments for flank wear prediction were implemented to verify the developed approach. The AISI304 and the high vanadium high-speed steel tool without coating were adopted. By comparison, the predicted results were consistent with the experimental overall. It has been proved that the proposed approach is more effective than pure FEM simulation and is suitable for long-term milling tool wear prediction.
Modern product design can be considered as a process, which involves intensive iteration, complex reasoning, and mutual cooperation among the design groups in different disciplinary areas. In order to meet the requirements of modern products on multidisciplinary collaboration, the traditional method, where the product conceptual design is usually solved only within a single discipline, should be improved. Based on the classic function–behavior–structure model of product conceptual design, this paper studied the collaborative mechanism of functions, behaviors and structures, and proposed a new method/system of implementing formalized multidisciplinary collaboration in the product conceptual design process. In this method, the model/system of conceptual design process with multidisciplinary collaboration was established first, and three collaboration mechanisms were developed. After the coupling relationship among the design sub-states and the disciplinary classification characteristics of the design sub-states were expressed by the mathematical ways, the particle swarm algorithm was applied for the discipline planning, next the solving process for multidisciplinary collaboration were proposed. Finally, the conceptual design process of a stylus printer was used to illustrate the application of the proposed method.
We present the numerical results for the viscoelastic and adhesive contribution to rubber friction for a tread rubber sliding on a hard solid with a randomly rough surface. In particular, the effect of the high- and low-frequency roughness power spectrum cut-off is investigated. The numerical results are then compared to the predictions of an analytical theory of rubber friction. We show that the friction coefficient for large load is given exactly by the theory while some difference between theory and simulations occur for small loads, due to a finite sample-size effects, whereas the contact area is almost unaffected by the low frequency cut-off. Finally, the role of a finite rubber thickness on viscoelastic friction and contact area is introduced and critically discussed. Interestingly, we show that classical rough contact mechanics scaling rules do not apply for this case.
The effect of angular misalignment between inner and outer raceways on the stiffness characteristics of tapered roller bearings (TRBs) is investigated. A computational procedure is introduced to solve the equations of TRB in the presence of angular misalignment. A dynamic analysis of a spindle supported by TRBs is also performed to investigate the natural frequency behavior by the stiffness variation due to angular misalignment. An extensive simulation demonstrates the effect of angular misalignment on the TRB characteristics such as roller–raceway contact loads, radial and axial displacements, and induced moment load. Computational results show that angular misalignment alters TRB stiffness characteristics and results in the splitting of the spindle natural frequencies by inducing anisotropic behavior of the TRBs. The proposed model and computational procedure are effective in estimating TRB characteristics and thus would aid in selecting TRBs or determining TRB loading conditions in practical applications.
This paper presents the design and multi-physics optimization of a novel multi-coil magnetorheological (MR) damper with a variable resistance gap (VRG-MMD). Enabling four electromagnetic coils (EMs) with individual exciting currents, a simplified magnetic equivalent circuit was presented and the magnetic flux generated by each voltage source passing through each active gap was calculated as vector operations. To design the optimal geometry of the VRG-MMD, the multi-physics optimization problem including electromagnetics and fluid dynamics has been formulated as a multi-objective function with weighting ratios among total damping force, dynamic range, and inductive time constant. Based on the selected design variables (DVs), six cases with different weighting ratios were optimized using Bound Optimization BY Quadratic Approximation (BOBYQA) technique. Finally, the vibration performance of the optimal VRG-MMD subjected to sinusoidal and triangle displacement excitations was compared to that of the typical multi-coil MR damper.
Problems of pressure impact and improper neutral angle of a neutral valve for hydrostatic transmissions were solved using Taguchi method for robust optimal design with aids of Grey relational analysis and computer simulation. An ITI-Simulation X-based model of a hydrostatic transmission with the neutral valve was developed and used to simulate the pressure impact and extended neutral angle during the pressure modulation when the swash plate angled from neutral to forth or back. The simulation results were converted to the Grey relational coefficients for 108 combinations of 27 design and four operational conditions. The Grey relational grades were also calculated for seven design parameters and each of the design conditions as the performance index. Through three times repeated robust optimal design process, the design parameters reached to the optimal which satisfied the performance goals of the neutral valve set to smaller the better for the pressure impact and nominal the best for the extended neutral valve.
Because the relation between the arc length s and curve parameter u cannot be represented by explicit function for most of the curves, it is difficult to consider the accuracy, robustness, and computational efficiency for most of the parametric interpolation, especially when the curves are complex or extremes. Therefore, an off-line fitting interpolation method by using nonuniform rational basis spline is presented in this paper. As nonuniform rational basis spline has many geometry implementation tools and numerous good properties as compared to the polynomial, the required fitting accuracy can be obtained more easily than with polynomial. After the de Boor method is applied, the computational load of nonuniform rational basis spline is decreased as compared to the Taylor approximation and the higher order polynomial fitting method. In order to obtain the proper s-u fitting nonuniform rational basis spline and reduce the computational load of the fitting process, the sampled s-u data points are divided according to the properties of nonuniform rational basis spline, and in each segment, the knot vectors, control points, and weights are calculated by the iterative-optimization method. Then the s-u nonuniform rational basis spline can be applied in real-time interpolation, and the accuracy, robustness, and computational efficiency are demonstrated by simulations and experiments.
This paper presents a new measurement method to investigate the operational mode dependent dynamic behavior of magnetorheological fluid. The proposed measurement system is designed using an electromagnetically actuating cylindrical rod coupled with the magnetorheological fluid squeezing setup. The cylindrical rod is clamped to base at one end and the other end is free to move in the z- and y-axis. A disc-type permanent magnet is attached to the free end of the cantilever rod and an electromagnetic actuator is placed nearer to the permanent magnet. The magnetorheological fluid squeezing setup is mounted nearer to the fixed end. The magnetorheological squeezing setup is designed using two electromagnetic coils placed face to face in z-axis with the gap of "d". The magnetorheological fluid is placed between the gap "d" to form the squeezing effect. The direction of vibration of the cantilever rod to bottom surface is determined by the angular position of electromagnetic actuator. The actuator position is fixed to the desired angle with the help of stepper motor setup. The horizontal direction of vibration of cantilever rod produces the shear mode operation of the magnetorheological fluid in the magnetorheological fluid squeezing setup. Similarly, the vertical and intermediate direction of vibration of rod produces the squeeze and coupled mode operation of the magnetorheological fluid, respectively. The analytical and experiment analyses to determine the dynamic damping behavior of the magnetorheological particles for various directions of actuation angle is undertaken using the proposed measurement system. The analytical model of the proposed measurement system is firstly derived and the experimental setup is then developed in real-time laboratory environment. The analytical and experimental results show that the dynamic damping behavior of squeeze mode operation of the magnetorheological fluid is superior to the shear and coupled mode operation of the magnetorheological fluid. The effectiveness and novelty of the proposed measurement system is demonstrated by presenting dynamic force variation and vibration amplitude reduction at different modes like squeeze, shear, and intermediate mode operation of the magnetorheological fluid.
A three-dimensional finite element model has been used here to study the vibrational behavior of silicon carbide nanosheets and nanotubes. The bonds of hexagonal lattices of SiC nanosheets have been modeled by structural beam elements, and at the corners, mass elements are placed instead of Si and C atoms. Moreover, molecular dynamics simulations are performed to verify the finite element model. Comparing the results of finite element model and molecular dynamics simulations, it is concluded that the utilized approach can predict the results of molecular dynamics simulations with a reasonable accuracy. It is observed that the atomic structure does not significantly affect the vibrational behavior of nanosheets. Besides, increasing the size of nanosheet results in decreasing the effect of geometry variation. As the aspect ratio of nanotubes increases, the effects of boundary conditions and length diminish so that the frequency envelopes tend to converge.
Geometric accuracy is a crucially important performance factor for machine tools. Theoretically, the effects of source errors on pose accuracy (positional and angular accuracy) of 3-, 4- or 5-axis machine tools cannot fully be compensated by software, and only those pose errors associated with the permission motions are compensatable by means of error compensation. Therefore, the uncompensatable pose errors should be strictly guaranteed in the processes of design and manufacture. In this paper, after the geometric error model is established, the source errors affecting the uncompensatable pose accuracy are identified out of all the source errors. In order to enhance the understanding of which source errors have more influences on the pose accuracy, a probabilistic sensitivity analysis method is proposed, and the global sensitivity index is defined to evaluate the influence in the overall workspace. According to the sensitivity analysis results, the uncompensatable pose accuracy index is allocated to each source error. And then, assembly accuracy acceptance criteria are proposed as a guideline for machine assemblers. As an application example, the presented approaches are applied to the accuracy design and manufacture of a 4-axis machine tool, and double ball bar measurement and machining test are carried out to check the accuracy of the designed machine tool.
The temperature of a minute object is typically measured by an infrared thermograph, a precise and expensive device. This study presents an image–temperature model constructed by particle swarm optimization algorithm to estimate the temperature according to the color image data on object’s surface. The demonstrated case was a palladium alloy microprobe used in wafer testing. Two series of conduction experiments were implemented to imitate the probing condition of the microprobe in wafer testing. Collecting the images captured from a digital video camera and the temperatures measured by the infrared thermograph, the correlations between the color image data and their corresponding temperatures were investigated. An image–temperature model is further constructed by the particle swarm optimization algorithm based on the image components of the RGB and HSV models of the examined pixel. The model developed provides valuable references for making out the electrothermal effect of the palladium alloy microprobe used in wafer testing.
Partial surge is a new type of instability inception in transonic axial flow compressors and occurs in the form of axisymmetric low-frequency disturbances localized in the hub region. The frequency of partial surge is about 12.5 Hz at 88% of the design rotor speed, while the frequency of developed rotating stall cells in the final phase of the evolution is around 190 Hz. As there are two different frequencies in the instability evolution of partial surge, it is difficult to well denoise the experimental data by general data processing methods that are focused on one single frequency. Considering the unique feature of the partial surge initiated instability, an adaptive logarithmic threshold framelet method has been built. By this method, the well-denoised results can be obtained. Based on the results, the instability evolution of partial surge is clearly shown. At the same time, several new findings about partial surge have been presented: (1) the propagating procedure of one partial surge disturbance: the amplitude of disturbance is increasing until one partial surge disturbance is developed; (2) the occurrence of rotating stall cells is related to the partial surge disturbance; (3) the propagating procedure of one rotating stall cell is presented; (4) the partial surge disturbance is well proved to be axisymmetric. Finally, the capability of this denoise method is also discussed.
Ultra-precision diamond machining (UPDM) is widely used to manufacture high quality surface within sub-micrometric form error and nanometric surface roughness due to its high efficiency and low cost. However, in a complex UPDM process, many factors affect such sub-micrometric form error. Especially, spindle vibration produces a significant impact upon surface generation, not only influencing nanometric surface roughness, but also affecting sub-micrometric form error. In this study, a five-DOF dynamic model is established for spindle vibration in UPDM. The form error under spindle vibration is discussed with a surface generation model. The results show that (i) axial, radial, and coupled-tilting spindle vibration makes a great contribution to form error; (ii) the coupled-tilting frequencies are influenced by spindle speed; and (iii) the spindle vibration is reproduced at a machined surface to generate regular patterns consequently to cause form error, which is well identified with a focus on axial spindle vibration by face turning in UPDM. Its wavelength is linearly proportional to spindle speed and cutting radius distance, i.e. cutting speed. Significantly, the proposed models provide a possibility to predict surface roughness and form error under spindle vibration.
This paper describes the early stages of the design process of a 2-DOF parallel mechanism, based on the use of four-bar linkages and intended to move photovoltaic panels in order to perform sun tracking. Primary importance is given to the search for a way to compensate sun–earth’s relative motions with two decoupled rotations of the panel. This leads to devise a kinematic structure characterized by a particular arrangement of the revolute axes. At the same time, the structure itself is designed in order to be slender. Subsequently, the fact that during a day the earth’s revolution around the sun has negligible effects on the apparent trajectory of the sun, if compared to the rotation around the polar axis, leads to choose a control strategy which, also thanks to the said arrangement of axes, employs only 1-DOF for most of the daytime. The tracker which employs this strategy has, theoretically, an energy consumption similar to that of 1-DOF solar trackers but a precision similar to that of 2-DOF ones.
Numerical control boring and routing machines use curtains made from resistant, but flexible materials to protect end-users from the projection of wood chips and tool pieces. These curtains allow the work piece to gently pass through, but firmly stop every small sharp piece or fragment ejected at the highest speed by fast drilling tools. Nowadays, curtains are commonly made in flexible thermoplastic materials as polyamide, polyurethane, polyvinyl chloride or similar materials. Safety issues to be addressed related to the risk of projection of parts during processing are defined by EN 847-1 and EN 847-2 standards, both collecting practical experiences from manufacturers and users. The effectiveness of these curtains was investigated by technical observations, experiments and even numerical simulations, but conclusive results are not available at the moment. This independent research, where ballistic impacts on flexible curtains were simulated using finite element (FE) methods, aims at verifying the effectiveness of specific protective barriers when realized and used in accordance with the UNI EN 848-3 standard. Numerical simulations were permitted to verify the congruity of the main barrier’s characteristics (materials, shape, depth, mass, cost, etc.) in relation to the projectile parameters (shape, mass, speed, direction, etc.) identifying their mutual influence. Outcomes from this research provide useful information toward the definition of a new way for the design of efficient curtains. A comparison between numerical simulations and experimental results coming from ballistic tests was also realized, permitting to validate this predictive methodology.
Currently, operations of reversible pump turbines in pumped hydro energy storage plant suffer great instability problems in the well-known S-shaped characteristic regions, leading to the failure of start, significant pressure fluctuations, and severe vibrations of the whole system. One of the physical origins of the above instability of reversible pump turbines is the rotating stall phenomenon generated at off-design conditions in generating mode. In this review, recent studies on the rotating stall of reversible pump turbines are critically reviewed with a focus on the generating mode. In reversible pump turbine, the rotating stall initiates at runaway and is fully developed at low discharge condition with characteristic rotating frequency being 50–70% of the impeller rotational frequency. Notorious effects induced by rotating stall include generation of large pressure fluctuation, channel blockage, and strong backflow, all of which contribute significantly to the instability of reversible pump turbine. Methods for identification of rotating stall are also introduced with plenty of examples. Finally, several suggestions on the future work are given and discussed.
This paper presents, discusses, and compares different techniques to model fracture initiation and static crack growth in double cantilever beam specimen under displacement-controlled loading. Energy release rate, critical displacement for the onset of crack growth, and critical load were determined by analytical solution, standard, and extended finite element method. The crack growth was also examined, and the advantages of each method were described as well. In addition, the compliance technique was used in the analytical method. In this regard, the crack growth relations were formulated based on four models including simple Euler–Bernoulli model, Euler–Bernoulli on the elastic foundation, simple Timoshenko beam, and the beam on the elastic foundation considering shear effects. Closed-form relations were extracted for the fracture parameters. Afterward, the Abaqus software was utilized to simulate the crack growth by the standard finite element method. Since the extended finite element has the ability to model the discontinuities inside the elements, the problem was also simulated by this method. Cohesive fracture of double cantilever beam specimen was performed using a closed-form solution and using a finite element model. Results of different modeling techniques were determined and compared.
For the two failure modes of a three-row roller slewing bearing, ring fracture and raceway spalling, a method for checking the strength of a slewing bearing through finite element analysis is proposed. This method calculates the internal stress distribution of the bearing rings by using the mixed finite element model with both solid elements and spring elements of the slewing bearing assembly and checks the bearing structural strength by using the maximum internal stress of the bearing rings. The method also calculates the contact stress between the roller and raceways by using the entity contact model between the roller and the raceways; the obtained maximum contact stress is used to check the contact strength of the slewing bearing. The proposed mixed finite element model considers the structural deformation of the bearing rings, and the calculated results can reflect the real situation more accurately than the traditional analytical model with the hypothesis of rigid ring. The proposed method also avoids the solution problem, which has large-scale calculation and difficulty of convergence of the entity finite element model of a slewing bearing, and the calculation efficiency is improved effectively. The calculated results by mixed finite element model are consistent with the failure mode of this type of slewing bearing in engineering practice.
The paper discusses the potential ingress and combined effect of moisture and temperature on pre-fatigued glass fibre-reinforced polymers standard test specimens. An experimental investigation was conducted to analyse the behaviour of glass fibre-reinforced polymers’ in environmental conditions similar to that of tropical environments. The standard pre-fatigued glass fibre-reinforced polymers specimens were subjected to varying hygrothermal conditions: three different temperatures, i.e. natural bath, 45 ℃ and 55 ℃ to study the degradation in strength and related properties. Several macro-structural and micro-structural tests were conducted to determine the damage. The effect of these conditions on characteristics such as diffusivity, weight gain, resin volume fraction, conductivity and deterioration of ultimate tensile strength was determined. The maximum reduction in strength is found to be approximately 39% for the specimen exposed to 55 ℃ water bath for 60 days. This study shall be helpful in estimating the characteristics of glass fibre-reinforced polymers composites subjected to cyclic fatigue loads in the tropical conditions.
Drag reduction in wall-bounded flows can be achieved by the passive flow control technique through the application of bio-inspired ribleted surfaces. In this paper, innovative design and manufacturing of serrate-semi-circular ribleted surfaces are presented with application to friction and drag reduction on engineering surfaces. Firstly, the design of the ribleted surfaces is described particularly focusing on the serrate-semi-circular shaped structures. Secondly, machining of ribleted surfaces by fly-cutting is investigated, covering the utilization of bespoke CVD diamond tools on a micro-milling machine and the corresponding micro fly-cutting processes. Metrology measurement results show good agreement achieved between the designed and machined surface features. Experiment conducted in wind tunnel shows the machined surface can produce 7% in drag reduction. Compared with conventional micro milling, the micro fly-cutting technique resulted from this research illustrates the unique advantage and industrial significance, particularly for manufacturing micro-structured surfaces in an industrial scale.
The oil lubrication system is a critical part of the helicopter main gearbox (MGB) and this is evident in the many accidents and incidents over the last 30 years. On a category A rotorcraft, a regulatory requirement mandates the MGB to sustain operation for at least 30 minutes following the loss of the primary oil lubrication pressure. The aim of this study was to undertake a comparative investigation into the performance of mist lubrication, using commercially available thioether (MCS-293™), on a category A helicopter MGB under loss of oil conditions. Experimental observations highlighted that the high-speed input module of the MGB attained the highest temperature and was a limiting factor to continued gearbox operation under loss of oil conditions. Results showed that by routing thioether mist through existing galleries within the MGB a lower rate of temperature increase was achieved, in comparison with a dry-run condition.
In order to study the dynamic characteristics of gear transmission system of wind turbine with random wind and the effect of random backlash on system stability, a stochastic volatility model is established to obtain the external excitation of gear transmission system of wind turbine. A dynamic model of system is set up with the consideration of gear time-varying mesh stiffness, transmission error and backlash. The dynamic behavior of system with random wind and the effect of random backlash on system stability are obtained using numerical method. The results show that: (1) The vibration displacement of system components has the similar trends with external excitation, and the higher the speed, the greater the vibration displacement. (2) Random backlash has a significantly influence on system stability. The instability of system decreases at first and then increases with the increase of mean backlash, and the stability of system decrease with the increase of standard deviation of backlash. The operation stability of a wind turbine will improve if select an appropriate gear backlash.
Chatter affects the surface topography and functional performance of work pieces significantly. The surface topography of work pieces is multi-scale, and the characteristics of different levels of the surface topography are closely connected to the different functional performance of the work piece. The relationship between chatter vibration and surface micro-topography is complicated and not specified. By investigating and understanding this relationship clearly, the manufacturing process can be directed to be controlled more actively and accurately, which helps complete the product with expected surface topography and functional performance. This paper aims to reveal the effect of chatter on the surface micro-topography of gears in grinding. Grinding processes considering different machining states and surface topographies of gears under each process were analyzed comprehensively. The following findings were observed. First, chatter causes significant increase of the tooth flank surface roughness in low frequency and increase of the profile roughness, whereas in a different manner in the different gear flank directions. Second, the influence of chatter mainly concentrates on certain frequency bands of the surface topography, and the effect of chatter on the 3D surface topography is within a frequency range. Third, chatter vibration with its multi-frequency-band characteristics shows a multi-scale influence on the work piece surface topography. The possible mechanisms for the formation of these effects were also discussed.
The cooling air in a rotating machine is subject to windage as it passes over the rotor surface, particularly for cases where nonaxisymmetric features such as boltheads are encountered. The ability to accurately predict windage can help reduce the quantity of cooling air required, resulting in increased efficiency. Previous work has shown that the steady computational fluid dynamics solutions can give reasonable predictions for the effects of bolts on disc moment for a rotor–stator cavity with throughflow but flow velocities and disc temperature are not well predicted. Large fluctuations in velocities have been observed experimentally in some cases. Time-dependent computational fluid dynamics simulations reported here bring to light the unsteady nature of the flow. Unsteady Reynolds-averaged Navier–Stokes calculations for 120° and 360° models of the rotor–stator cavity with 9 and 18 bolts were performed in order to better understand the flow physics. Although the rotor–stator cavity with bolts is geometrically steady in the rotating frame of reference, it was found that the bolts generate unsteadiness which creates time-dependent rotating flow features within the cavity. At low throughflow conditions, the unsteady flow significantly increases the average disc temperature.
While comprehensive researches have been conducted on modeling the electromechanical stability of wide-enough beam-plate nano-switches, few researchers have focused on modeling the electromechanical instability of narrow-width nano-switches. For such systems, considering the coupled effects of surface stresses and size dependency of material characteristics is crucial as well as applying appropriate force models. In this paper, Gurtin–Murdoch surface theory incorporating with strain gradient elasticity is employed to study the pull-in instability of narrow-width beam-type nano-switch with small width to height ratio. The model accounts for the force corrections, i.e. the impact of finite dimensions on the fringing field, Casimir attraction and van der Waals force. Furthermore, a modified gas damping model has been incorporated in the governing equation. The nonlinear governing equation was solved using analytical Rayleigh–Ritz method. The influences of the above-mentioned corrections on the static and dynamic pull-in parameters, phase planes and stability threshold of the switch are demonstrated. The modified model is compared with conventional parallel beam-plate models in the literature.
Thermoelastic wave equations are numerically solved by using finite element method to study effect of spatial distribution of microscale heat source, created inside transparent material, on physical parameters of heat affected zone. It is observed that temperature distribution has significant effect on spatial and temporal behavior of the displacement, strain, stress and, consequently, on refractive index changes of the material. Therefore, temperature distribution, which can be caused by laser pulse, can be employed as an important parameter to control refractive index profile inside transparent materials.
The fractional model considering geometric factor of viscoelastic damping systems is proposed by adopting fractional viscoelastic oscillator. To obtain dynamic responses of the fractional model, a numerical method is derived based on matrix function theory and Grumwald–Letnikov discrete form of fractional derivative. As a special engineering application example, the vibration response of the viscoelastic suspension installed in heavy crawler-type vehicles is studied through the proposed model. Furthermore, the parameter influence on the vibration control capability of the viscoelastic suspension is researched. The results indicate that the fractional viscoelastic oscillator is a favorable choice to characterize the dynamic behavior of viscoelastic damping structures. Additionally, the parameters in fractional viscoelastic oscillator namely geometric factor and fractional order exert considerable impact on the dynamic response of viscoelastic damping structures.
With basic ideas of mixed Lagrangian formulation and sequential assigning process for initial conditions, the extended framework of Hamilton’s principle (EHP) was recently developed for continuum dynamics. Unlike the original Hamilton’s principle, this new variational framework can fully take initial conditions into account for both linear and nonlinear dynamics, so that it provides a sound base to apply a finite element scheme over the temporal domain without any ambiguity. This paper describes temporal finite element approach stemming from the extended Hamilton’s principle, which focuses initially on classical single-degree-of-freedom oscillators such as Kelvin–Voigt damped oscillator and an elasto-viscoplastic model. In each case, an appropriate weak form is provided and a corresponding formulation is discretized in the temporal domain with the adoption of Galerkin’s method. Basic numerical properties are investigated for the developed numerical algorithms with several computational examples for the elasto-viscoplastic model. For the underlying conservative system, the present method is symplectic and unconditionally stable with respect to the time step. On the other hand, the method provides unconditionally stable and noniterative algorithm for the elasto-viscoplastic model.
Hydrogen embrittlement threshold curves were derived for two quenched and tempered steel grades, AISI 4135 and AISI 4340, at varying hardness ranging from 33 to 54 HRC. For each material, hydrogen was introduced (i) by zinc electroplating as a worst case condition for internal hydrogen embrittlement and (ii) by imposing cathodic potential of –1.2 V as a worst case condition for environmental hydrogen embrittlement. Overall, AISI 4135 exhibited lower thresholds than AISI 4340, making it the more susceptible of the two alloys. The findings demonstrate although hardness and/or strength have a first-order effect on hydrogen embrittlement susceptibility, difference in chemistry leading to differences microstructural characteristics must also be considered. Below hardness of 39 HRC, both alloys were not susceptible to internal hydrogen embrittlement, a finding that is consistent with common industry practice and fastener electroplating standards that do not mandate baking of electroplated fasteners with specified hardness below 39 HRC.
This paper presents a comparative study of the kinematics and torque distribution performance of a nonredundant 3-RUU and a redundantly actuated 4-RUU (R: revolute joint, U: universal joint) translational parallel manipulators. First, the reason for unexpected rotations is analyzed based on screw theory and a redundantly actuated 4-RUU translational parallel manipulator is presented to eliminate the unexpected rotations. Then, the degrees of freedom, inverse kinematics, Jacobian matrices, and workspace of 3-RUU and 4-RUU parallel manipulators are analyzed. Finally, a comparative study of torque distribution is performed. The results show that the redundantly actuated 4-RUU parallel manipulator can overcome the unexpected rotations and possesses an improved torque distribution, compared with the nonredundant 3-RUU parallel manipulator.
In this article, a simple self-adaptive neuron based on a position state observer has been proposed to inhibit the influence of load disturbances and accomplish a self-adaptive correction of the moment of inertia. In the process of inertial correction, the error of the position state observer is gradually reduced that facilitates the simultaneous optimisation of the position observer and moment of inertia. Furthermore, it allows accurate prediction of the position value by the position state observer in the subsequent control cycle. Simulations and experiments indicate that the designed controller performs with better adaptive response and robustness compared to the controller that does not implement the proposed method, and that the position state observer estimates the position accurately, a response associated with numerous advantages for practical applications.
For improving the drilling efficiency of polycrystalline diamond compact drill bit, a novel polycrystalline diamond compact drill bit is presented with a new rock-breaking method named as cross-scraping. In the novel polycrystalline diamond compact drill bit which is referred to as a composite drill bit, polycrystalline diamond compact cutters are mounted on rotary wheels as major cutting elements, and as a result, mesh-like scraping tracks are formed in the outer radial area of the bottom-hole. Rock-breaking method of the composite drill bit causes both shearing and fracture failure of the bottom-hole rock, which will greatly increase the rock-breaking efficiency and will prolong the bit service life. By analyzing the complex motion of cutters on the composite drill bit, velocity and acceleration models of the cutters, as well as wheel/bit speed ratio model of the bit are established in accordance with the geometric relationship between cutters and bit body in a compound coordinate system. In simulation examples, motion tracks, velocity and acceleration features of the cutter and especially the bottom-hole pattern are analyzed. Further, indoor experiments are conducted to test the mesh-like bottom-hole pattern and rock-breaking features, which have proved the accuracy of the analysis model of the composite drill bit.
One of the major issues that existing crack identification methods utilizing dynamic responses are facing is the limitation of engineering feasibility. How to suppress the effect of measurement noise and improve the identification accuracy is still challenging. In this work, an effective method is proposed to identify the size of an arbitrary internal crack in plate structure based on a Kriging surrogate model, and a series of laboratory tests are designed to verify the practicability of this strategy. The initial Kriging surrogate model is constructed by samples of crack parameters (tip locations) and corresponding root mean square (RMS) of random responses as the inputs and outputs, respectively. To further improve the surrogate accuracy and reduce computational cost during the inverse problem, an optimal point-adding process for Kriging model updating is then carried out. Experimental results of crack identification in a cantilever plate indicate that the proposed method can be an alternative to conventional crack detection methods even in the presence of measurement noise and modeling errors.
Most prosthetic foot products are adjusted by skilled prosthetists using a variety of gait analysis and information given to them by patients in terms of feel and experience. The design of prosthetic foot has traditionally focused on optimising stiffness to support the body weight and storage/release mechanisms of strain energy from heel contact to push off. As a result of this, the optimisation process of a prosthetic foot is simple and sometimes insufficient. It is proposed that the stiffness and energy release mechanisms of prosthetic feet be designed to satisfy amputee’s natural gait characteristics that are defined by an effective roll-over shape and corresponding ground reaction force combinations. Each point on the roll-over shape is mapped with a ground reaction force corresponding to its time stamp. The resulting discrete set of ground reaction force components are applied to the prosthetic foot sole and its stiffness profile is optimised to produce a desired deflection as given by the corresponding point on the roll-over shape. The robustness of this novel computational method is tested on three prosthetic designs. The mesh sensitivity results and the discretisation error resulting from applying finite number of ground reaction forces are discussed. It is shown that the proposed methodology is able to provide valuable insights in the guidelines for selection of materials for a multi-material prosthetic foot.
This paper presents the design and development of a new flexure-based compliant XY micropositioning stage with large stroke. The parallel-kinematic XY compliant stage is designed based on the Roberts mechanisms. Pseudo-rigid-body model is developed to establish the quantitative models of the whole compliant mechanism. Finite element analysis is carried out to validate the performance of the XY stage. A prototype of the XY stage is developed for experimental investigations. Experimental results show that the stage can deliver a working range larger than 12 mm in each of the two working axes. Moreover, a feedback control using the proportional–integral–derivative control algorithm is implemented to demonstrate the positioning performance of the developed XY stage. The reported ideas can also be extended to the design and control of other micro-/nanopositioning systems.
Impact dampers are efficient in many industrial applications with a wide range of frequencies. An experimental analysis of the impact damping of spherical balls is investigated to simplify the particle impact damping design and improve the vibration suppression. The objective of the study is to analyze some of the design parameters of impact damper using spherical balls. The experimental investigation consists to test the effect of the ball size for each mass level, the number of balls for each size level and different exciting force levels on vibrations of the main structure. The parametric study provided useful information to understand and optimize Particle Impact Damping design.
Determining the motions and constraints of serial kinematic chains in a concise and visual way is an inevitable step in the analysis and design of both serial and parallel mechanisms. The now most used method is the numerical approach which resorts to solving linear equations. By introducing Clifford algebra, this paper intends to propose an analytical approach to determine the unknown 6-n (n < 6) constraints (motions) from the known n motions (constraints) of serial kinematic chains in different configurations only by drawing some auxiliary points, lines, and planes. The axes and action lines of motions and constraints are characterized by the lines that would be described by Clifford algebra. These lines can be determined analytically according to the relations among points, lines, and planes, which have been expressed by using the operation rules of Clifford algebra Cl(0, 3, 1) such as inner, outer, dual, and shuffle products. Based upon the mechanics principle that the constraint does not work on the motion, the unknown 6-n constraints (motions) of serial kinematic chains from known n motions (constraints) are determined both in an analytical algebraic form and in a visual manner. Finally, four examples are given to demonstrate how to use this approach and test its validity. The merit of this approach is beneficial to the digital analysis and design of both the serial and parallel mechanisms by means of computer and programming languages.
Focusing on tufting machine type DHUN801D-400, the complex dynamic model of coupling shaft system is built by using Riccati whole transfer matrix method, and the natural frequencies and mode shapes are analyzed. First, the components of coupling shafts system in tufting machine are introduced. Second, the structures of coupling shafts system are discretized and simplified. Third, the transfer matrix is constructed, the model is solved by using Riccati whole transfer matrix method, and then natural frequencies and mode shapes are obtained. Finally, the experimental results are quoted to demonstrate the applicability of the model. The results indicate that the Riccati whole transfer matrix method is well applicable for modeling the dynamics of complex multi-rotor systems.
In this paper, the dynamic behaviors of a multi-span viscoelastic functionally graded material pipe conveying fluid are investigated by dynamic stiffness method. The material properties of the functionally graded material pipe are considered as graded distribution along the thickness direction according to a power-law. Several numerical examples are performed to study the effects of volume fraction exponent, fluid velocity, internal pressure, and internal damping on the stability and frequency response of the fluid-conveying functionally graded material pipe. It’s found that the viscoelastic functionally graded material pipe exhibits some special dynamic behaviors and it could increase the stability significantly when compared with the aluminum and steel pipes. The numerical results also demonstrate that by the introduction of the functionally graded material, the stiffness of the piping system could be modulated easily by designing the volume fraction function. Therefore, if the dominant frequency contents of the external loads are known, a preferable design of the functionally graded material pipe to reduce the vibration is possible.
The aim of this paper is to present an experimental investigation of the cutting forces, surface quality, tool wear and chip shape in ultrasonic vibration assisted turning (UAT) of 304 austenitic stainless steel (ASS 304) in comparison to conventional turning (CT). This study focuses on the solution of the machining difficulties of ASS 304 and high demands for the processing quality and efficiency. The machining system of UAT is schemed out to assure the desired machining effect by utilizing ultrasonic vibration method. Meanwhile, a series of systematic experiments are performed with and without ultrasonic vibration using the designed machining system of UAT with cemented carbide coated cutting tool. The results obtained from the UAT and CT experiments demonstrate that the cutting effect of UAT is much better than that of CT. Furthermore, the results of this research indicate that the ultrasonic amplitude, cutting speed, feed rate and depth of cut in UAT of ASS 304 have visible influence on the cutting forces, surface quality and tool wear. And reasonable selection of various technological variables in UAT can obtain lower cutting forces, more superior surface roughness, advantageous surface topography, slow and less tool wear, thin and smooth chips.
The linear static elastic-plastic behavior of sandwich cylindrical shell panels under a generally distributed loading with thick flexible core is studied. The core modeling is based on high-order theory of sandwich structures in which the in-plane stresses of the core are neglected. The faces are modeled based on Kirchhoff–Love shell theory. The materials of the faces and the core are assumed to be isotropic with linear work hardening behavior. The incremental Prandtl–Reuss plastic flow theory is used in this analysis. Using the principle of virtual displacements, the governing equations are derived and solved for any sort of boundary conditions based on elastic-plastic harmonic differential quadrature method. To validate the results of present study, various responses in different sandwich shell panel configurations are compared with the results from finite element software Ansys. The effect of core flexibility and its plastic properties as well as the initiation of yield in faces and the core are studied in detail.
Automatic operation system with industrial robots has become more and more popular, especially with the urgent requirement from 3C (Communication, computer and consumer electronics) manufactory. A robot cell, which often involves one or more robots and accessory equipment, can be regarded as part of the larger theme of cellular manufacturing. The objective that most interests manufacturers is the investment return rate. It is largely determined by the productivity of robotic cell, and the leading time of robotic production system. Therefore, a fast and efficient method to design a robotic cell layout with the maximum throughput for a given task is undeniably a worthy research topic. This paper attempts to discuss the challenges and key technologies in the robotic cell layout optimal design. The proper selection of configuration for task, manual operation skill learning and translation, collaborative design tool-chain, optimization in cell layout and operation scheduling, optimal end-of-arm tooling design, and human–robot collaboration are included in this discussion with existing or on-going problem-solving key technologies.
For the unsteady characteristics of a fault vibration signal from a wind turbine rolling bearing, a bearing fault diagnosis method based on adaptive local iterative filtering and approximate entropy is proposed. The adaptive local iterative filtering method is used to decompose original vibration signals into a finite number of stationary components. The components which comprise major fault information are selected for further analysis. The approximate entropy of the selected components is calculated as a fault feature value and input to a fault classifier. The classifier is based on the nearest neighbor algorithm. The vibration signals from a spherical roller bearing on a wind turbine in its normal state, with an outer race fault, an inner race fault and a roller fault are analyzed. The results show that the proposed method can accurately and efficiently identify the fault modes present in the rolling bearings of a wind turbine.
This research presents a theoretical model to analyze the mechanical performance of spherical roller bearings, taking account of the angular and centroidal misalignments between the inner and outer rings. The angular misalignment can be improved by spherical roller bearings self-aligning feature to a certain degree. The interpolation method is used to determine the self-aligning contact angles of the different rollers. The centroidal misalignment is described by the angular and distance deviations. Non-Hertzian contact theory is applied to model and calculate the rollers load-distribution and total contact angles as well as the displacement of the inner ring. The loads of the rollers with the misalignments features and the external loads are included in the equilibrium equations, which is solved by Newton-Raphson method. This research shows spherical roller bearings self-aligning ability can balance the additional bending moment caused by the angular misalignment, which is at the cost of reducing its carrying capacity. But this carrying capacity will be improved to a certain degree by a proper axial load. It also illustrates that any kinds of centroidal misalignments are harmful for the service life of bearings. But the location of the misalignments can be roughly inferred by the external loads and the displacement of the inner ring, which is helpful for spherical roller bearings fault diagnose and elimination.
Numerous research results indicate that the finishing processing of metal materials using ball burnishing has positive effects from the aspect of surface roughness decrease to the hardness increase in the surface layers of the processed materials. Little research has been devoted to this type of processing for nonmetal materials. This paper presents research results related to the influence of ball burnishing processing on the hardness increase of a wooden element. It was determined that the hardness can be increased up to three times for processing of wood using this technology, which is not the case for processing of metal materials.
A novel five degrees of freedom deformable mobile robot composed of two spatial reconfigurable platforms and three revolute–prismatic–spherical kinematic chains acting in parallel to link the two platforms is proposed to realize large deformation capabilities and multiple locomotion modes. Each platform is an improved deployable single degrees of freedom three-plane-symmetric Bricard linkage. By taking advantage of locomotion collaborating among platforms and kinematic chains, the mobile robot can fold into stick-like shape and possess omnidirectional rolling and worm-like motions. The mechanism design, kinematics, and locomotion feasibility are the main focus. Through kinematics and gait planning, the robot is analyzed to have the capabilities of rolling and turning. Based on its deformation, the worm-like motion performs the ability to overcome narrow passages (such as pipes, holes, gaps, etc.) with large range of variable size. Dynamic simulations with detailed three-dimensional model are carried out to verify the gait planning and provide the variations of essential motion and dynamic parameters in each mode. An experimental robotic system with servo and pneumatic actuation systems is built, experiments are carried out to verify the validity of the theoretical analysis and the feasibility of the different locomotion functions, and its motion performances are compared and analyzed with collected data.
Time–frequency analysis is widely used in the field of machinery condition monitoring and fault diagnosis under nonstationary conditions. Among the time–frequency methods synchrosqueezing transform outperforms others in providing fine-resolution time–frequency representation. However, it suffers from time–frequency smear when analysing nonstationary signals. To address this issue, this paper proposes a new synchrosqueezing-transform-based method which works by (1) mapping the raw nonstationary vibration signal into a corresponding stationary angle domain signal to meet the stationarity requirement of the synchrosqueezing transform, (2) performing the synchrosqueezing transform of the corresponding signal and (3) restoring the time–frequency representation of the raw signal from the synchrosqueezing transform result of the corresponding signal. As the synchrosqueezing transform is applied to the stationary corresponding signal, the time–frequency smear is eliminated in the synchrosqueezing transform result of the corresponding signal and the final signal time–frequency representation. As such the proposed method can generate a smear-free time–frequency representation with fine time–frequency resolution and thus provide more reliable diagnosis decisions. A fast implementation algorithm is also developed to simplify the implementation of the proposed method. The effectiveness of the proposed method is validated using both simulated and experimental vibration signals of planetary gearboxes.
The paper presents a thermomechanical analysis of a circular saw with the emphasis on the influence of thermal stresses on eigenmodes. Significance of the slot’s length was also investigated. The transient thermal analysis was carried out, and based on the obtained temperature field, the modal analysis was performed accounting for both thermal and centrifugal stresses. It was found that thermal stresses have a profound influence on eigenvalues. The results clearly indicate a necessity of performing analyses of this kind in order to obtain an efficient design of the circular saw. At the end, main findings are emphasized once more.
We propose a finite element methodology to consider local material properties for large cast iron components in shape optimization. We found that considering local strength instead of uniform strength within shape optimization brings to different results in terms of safety-cost balance for the same component. It is well known that local mechanical properties of large cast iron components are defined by their microstructure and defects, which locally affect the strength of the components. Considering or not local mechanical properties can dramatically change a component reliability evaluation during its design. Since a typical industrial aim for shape optimization is trying to get the optimal solution in terms of component quality and cost, considering local material properties is even more important than in traditional design process where no optimization techniques are used. We compute solidification process parameters via finite element solidification analysis, and then we exploit experimental correlation between these parameters and ultimate tensile strength to evaluate the local reliability of the finished component under its static loading conditions. We believe that this methodology represents an opportunity to better design casting components when mechanical properties are deeply affected by their production process as described in the provided examples. In these examples, we wanted to minimize casting cost constrained by a target reliability and we get component cost reduction by considering local material properties. Future research will address the problem of using dedicated casting simulation software instead of general purpose finite element analysis software to compute solidification analysis and then introducing fatigue analysis and correlation between fatigue material properties and casting process output variables.
Wrinkling frequently occurs in tube hydroforming, resulting in an undesirable loss of quality and precision of the formed workpiece, and is generally regarded as a defect. However, wrinkling can also be utilised to improve the formability of tubular materials if it can be gradually reduced or even flattened in the follow-up tube hydroforming. For this reason, wrinkling is classified into two types—harmful wrinkle and useful wrinkle. In this paper, two prediction methods, geometry-based prediction method and mechanics-based prediction method, are proposed to predict the wrinkle type occurring in tube hydroforming under pulsating hydraulic pressure with axial feeding. Then, the corresponding tube hydroforming experiments are presented, which were carried out to validate the two proposed prediction methods by comparing the deformation and wrinkling behaviours. Finally, the characteristics of the two approaches are compared and discussed. The results indicate that the wrinkle type occurring in the present tube hydroforming experiments under pulsating hydraulic pressure with axial feeding could be predicted by both prediction methods, with the geometry-based prediction method providing more accuracy than the mechanics-based prediction method.
Residual stress of engineering ceramics is one of surface integrity evaluation indexes affecting the parts’ strength properties. Rotary ultrasonic grinding machining is the most powerful machining method for engineering ceramics with better surface integrity. The residual stress field distribution is changed due to micro cracks which are inevitable in the process. A residual stress distribution model of machined surface micro crack tip has been established in the paper. And the experimental results enable us to obtain surface residual stress distribution of engineering ceramics in rotary ultrasonic grinding machining. Then, we propose an evaluation parameter called confidence stress tolerance to evaluate surface residual stress characteristic. Preliminary results indicate that surface residual stress distribution is in line with the normal distribution. Confidence stress tolerance is an effective parameter to improve the evaluation reliability. Furthermore, precision and affecting factors of confidence stress tolerance evaluation have also been investigated.
A new type of mineral car arrester, designed for transportation in the inclined shaft rail undermine, includes three degrees of freedom and seven links, to achieve the functions, like a one-way retarder, automatic resetting. The arrester achieves opening and closing functions by air cylinder driving and gravity resetting, and it arrests the car by the way of directly stopping the slipping car. Meanwhile, a buffering system installed under the track, including three buffering springs, as flexible energy absorption equipment absorbs the striking energy. This paper introduces the dynamics analysis of the impact behavior for the car arrester in detail, so that the impact dynamics for the ideal function of car arrester can be obtained by conclusion. The oscillatory differential equations freedom kinematics equations of the impact system are developed. The mineral car and arrester, under position-type nonlinear forces, are simplified to single mass bodies. The data such as the maximum spring force, maximum amplitude, the time and the numbers of impact are achieved by Mathcad, to solve the dynamic equations and analyze the motion law of the mine car after the impact. Then, the conclusion can be obtained that there are some reliability redundancies in the car arrester. Meanwhile, the three key components of the car arrester are analyzed in ANSYS finite-element analysis software. According to the analysis, it is confirmed that design of the structure and size parameters of the car arrester meets the security and functional requirements.
Aerostatic bearings are the critical parts of ultra-high speed spindles applied to precision milling, grinding, and other precision engineering applications. In this paper, the computational design and analysis of aerostatic journal bearings at ultra-high speed spindles are investigated particularly in light of the nonlinear compressible Reynolds equation and the associated computational analysis and algorithms using the finite element method-based Galerkin weighted residual method. The steady-state static and dynamic behaviors of aerostatic journal bearings are systematically studied, including pressure distributions, load capacity, stiffness, attitude angle, and volume flow rate under conditions of various operating speeds and eccentricity ratios. The coupling of the aerostatic and aerodynamic effects within ultra-high speed aerostatic journal bearings is further explored. The obtained results are formulated as design guidelines for aerostatic journal bearings applied to air-bearing spindles operating in high precision and ultra-high rotational speeds.
An invariable compression ratio in certain conditions must be achieved to ensure a steady and efficient performance of the single-piston hydraulic free piston engine. The compression ratio is determined by the characteristics of the compression stroke. The mathematical models of the key components during the compression process are established. The kinematic characteristics of the free piston assembly are analyzed under two conditions. One condition is that free piston assembly is driven by the compression accumulator only and the other one is that free piston assembly is driven by the compression accumulator and the pump station. Pressures in compression accumulator and compression chamber are analyzed and compared in both conditions. According to the experimental results, pressures in the compression chamber and compression accumulator are not constant in both conditions during the compression process. The compression stroke and compression time vary with the changing of the pressure in the compression accumulator, which adds the complexity and changeability to the compression ratio control. An improved configuration is put forward to solve the pressure variation. The results show that the improved configuration can make the pressure invariable at the inlet of the compression chamber and the compression process keeps almost the same regardless of the pressure changing in the compression accumulator. With this new structure, there is about 2.5% energy loss, which is acceptable considering the stable compression stroke.
In order to increase the efficiency of additive manufacturing, this paper proposes a novel adaptive slicing approach of sliced data with minimum thickness based on Boolean operations of polygons. It can greatly handle the balance between the build time and the surface precision of additive manufacturing. The proposed adaptive slicing is available for the single solid model, the support of additive manufacturing, and simultaneously manufactured multiple models. At first, the Boolean operations of polygons are used to gain the relationship of the adjacent layers to serve as the topological information. Second, two parameters are proposed to evaluate the precision of sliced surface: the ameliorative area ratio and variation of the cusp height. Ameliorative area ratio overcomes the drawbacks of original area deviation ration criteria and can work on the large and complex models. Variation of the cusp height makes the calculation of cusp height suitable for sliced data of model, and it is independent of the normal vector of surfaces. Third, the adaptive slicing is realized by removing unnecessary layers based on two parameters and the maximum allowable thickness. The thicknesses are times of the minimum thickness. Moreover, the adaptive slicing for support of additive manufacturing is developed through dividing the support into two parts according to its height and location. Slicing of multiple models is also proposed by choosing the maximum ameliorative area ratio and variation of the cusp height among all models in the same z level as the two parameters. Finally, the adaptive slicing for the three types is tested with some special models, and corresponding models are printed with FDM technology based on slicing results of the proposed approach. Results show that the proposed adaptive slicing approach is effective.
This paper analyzes the possibility to substitute the gray iron, traditionally used for the production of relevant parts in woodworking machines, with ductile iron or vermicular iron. A large experimental campaign to determine the mechanical beavior of ductile and vermicular irons respect to tensile, fatigue, and fracture loads was conducted and the microstructures were also analyzed. Results show that ductile or vermicular cast iron in parts and components of machine tools could provide additional stiffness and resistance for the high precision woodworking respect to Gray Iron. A balanced utilization of these alternative irons would permit to take a full advantage by each specific property (as strength, hardness, weight, etc.).
A precision testing method based on a seven-sensor configuration is presented in this paper to quantify thermal errors (drifting, elongation, tilting) of the mandrel cross-section, for an example horizontal machining center with linear optical grating scale. Three tri-axial displacement sensors with 120° spread angles and 36 thermal couples are mounted on judiciously chosen locations to record the temperatures and thermal expansions for various operating conditions. Based on the measurements covering a wide range of spindle locations, environment temperatures, coolant temperature, and spindle rotational speeds, we found that (i) the maximum thermal drifts of the mandrel are 11.3 µm in the x direction with a compensation rate of 62%, and 165.3 µm in the y direction with a compensation rate of 93%, (ii) the maximum thermal tilt of the mandrel is 0.005°, and (iii) the thermal elongation of the mandrel in the z direction, which could not be compensated by the linear optical grating scale, is 51.9 µm. From a correlation study, the thermal elongation of the mandrel is most closely correlated to the temperatures recorded for the thermal couple mounted at the front surface of the spindle bearing with a correlation coefficient of 0.83.
In the past, milling operations have been mainly considered from the economic and technological perspectives, while the environmental consideration has been becoming highly imperative nowadays. In this study, a systemic optimization approach is presented to identify the Pareto-optimal values of some key process parameters for low-carbon milling operation. The approach consists of the following stages. Firstly, regression models are established to characterize the relationship between milling parameters and several important performance indicators, i.e. material removal rate, carbon emission, and surface roughness. Then, a multi-objective optimization model is further constructed for identifying the optimal process parameters, and a hybrid Non-dominated Sorting Genetic Algorithm-II algorithm is proposed to obtain the Pareto frontier of the non-dominated solutions. Based on the Taguchi design method, dry milling experiments on aluminum are performed to verify the proposed regression and optimization models. The experimental results show that a higher spindle speed and feed rate are more advantageous for achieving the performance indicators, and the depth of cut is the most critical process parameter because the increase of the depth of cut results in the decrease of the specific carbon emission but the increase of the material removal rate and surface roughness. Finally, based on the regression models and the optimization approach, an online platform is developed to obtain in-process information of energy consumption and carbon emission for real-time decision making, and a simulation case is conducted in three different scenarios to verify the proposed approach.
Unsteady numerical simulations are conducted to investigate the unsteady effects of axial spacing on the performance of a contra-rotating axial compressor. The results show that the stage efficiency is dominant by unsteady effects between two rotors at lower axial gap ranges. As the axial spacing is increased, the variation of aerodynamic force is different for the two rotors. As a whole, the oscillation on the pressure surface is much stronger than that on the suction side in rotor1. For rotor2, however, the local maximum amplitude is just located at the blade leading edge, especially near the tip region. Additionally, the maximum amplitude of the pressure fluctuations generally decreases with an increase of axial spacing. The dominating frequency is different for monitors located at different positions and varies with the increasing of axial gaps. As the axial gap is increased, the potential effects decay in the process of propagating. Meanwhile, the incoming wakes are mixed out more sufficiently which would reduce the fluctuations at leading edge of rotor2. Therefore, a proper axial spacing should be chosen in the design process of a contra-rotating axial compressor considering both the performance and structure.
To make water in urban rivers flowing and improve water quality, an eco-gate pump unit which uses plate gate as a carrier was designed and developed based on computational fluid dynamics method and the model test in this paper. Firstly, the bidirectional operation energy performance of eco-gate pump was verified by the model test. The results showed that the numerical simulation results were consistent with the model test results with an error of ±2% at the optimum operating condition both in the pumping mode and the powering mode, which verified the reliability and accuracy of numerical stimulation. The major sources of error associated with the power losses were due to the fact that the blade tip leakage and the blade deflection were not considered in computational fluid dynamics simulation. The thickened blade edges also contributed to the differences. On this basis, different schemes of runner blade’s setting angles, blade number, blade lean angle, bulb body’s length, and shoulder profile line were designed, and their influences on eco-gate pump’s performance were analyzed to choose the best runner type and bulb body’s profile line through the computational fluid dynamics numerical simulations. The numerical results showed that the eco-gate pump had the best hydraulic performance when the blade’s setting angle was = 23°, blade number z = 5, blade’s lean angle a = 0° and bulb body’s shoulder profile line was convex type with length L = 100 mm. The developed pump showed the highest efficiency of 70.95% under the condition of design discharge of 500 L/s and design lift of 1.0 m. Furthermore, the whole flow pattern of the optimized pump was analyzed. Overall, the eco-gate pump presented in this paper can make use of its low-lift pumping function to replenish the target water body more efficient than other similar products. At the same time, it also can utilize the micro-head water energy fully to generate power.
Measuring and controlling the flow rate is a widely concerned problem in engineering fields. The direct flow rate measurement employing conventional flow meters and the indirect flow rate measurement using speed/position transducers or other particular techniques would result in inevitable pressure drop in hydraulic circuits, more energy consumption for pumping fluid, and higher cost of hydraulic systems. This paper presents a novel flow rate inferential measurement method and its application in hydraulic elevators. Mathematical modeling of the proposed method is deduced. The key component of the hydraulic elevator circuit, a two-stage proportional flow rate valve, is verified by experiments as one of the contributions of this paper. Based on the mathematical modeling and the valve validation test, the feasibility and validity of the proposed method are verified by the experiments performed on a test rig which is designed to imitate work situations of a hydraulic elevator. Moreover, sensitivity analyses of the proposed flow rate inferential measurement method are carried out to find the ways how to improve the accuracy of the proposed method. It is believed that this method can be applied in various engineering devices.
In this paper, a dynamic model for the offshore wind turbine installation is proposed. And this model is coupled by the wind turbine and the floating crane considering 6-DOF floating crane, 5-DOF wind turbine and elastic stretch of the hoisting cable. And when the wind turbine lands on the supporting structure, the displacement constraint is applied at the wind turbine. During the process, the relaxation of the hoisting cable is considered. In addition, the nonlinear hydrostatic force, environmental force, hoisting cable force and mooring force are considered as the external force. The motions of wind turbine and the floating crane are studied. From the numerical analysis, it is found that the release velocity, the release height and wave condition have a great effect on the motion of wind turbine.
Development of reliable computational models to predict the high temperature deformation behavior of nickel-based superalloys is in the forefront of materials research. These alloys find wide applications in manufacturing of turbine blades and discs of aircraft engines. The microstructure of these alloys consists of the primary '-phase, and the secondary and tertiary precipitates (of Ni3Al type) are dispersed as '-phases in the gamma matrix. It is computationally expensive to incorporate the explicit finite element model of the -' microstructure in a crystal plasticity-based constitutive framework to simulate the response of the polycrystalline microstructure. Existing models in literature do not account for these underlying micro-structural features which are important for simulation of polycrystalline response. The aim of this work is to develop a physically motivated multi-scale approach for simulation of high temperature response of nickel-based superalloys. At the lower length scale, a dislocation density-based crystal plasticity model is developed which simulates the response of various types of microstructures. The microstructures are designed with various shapes and volume fractions of '-precipitates. A new model for simulation of the mechanism of anti-phase boundary shearing of the '-precipitates, by the matrix dislocations, is developed in this work. The lower scale model is homogenized as a function of various micro-structural parameters, and the homogenized model is used in the next scale of multi-scale simulation. In addition, a new criterion for initiation of micro-twin and a constitutive model for twin strain accumulation are developed. This new micro-twin model along with the homogenized crystal plasticity model has been used to simulate the creep response of a single crystal nickel-based superalloy, and the results have been compared with those of experiment from literature. It was observed that the new model has been able to model the tension–compression asymmetry as observed in single crystal experiments.
A theoretical magnetic field intensity model within giant magnetostrictive material was presented. This model was established just like the reluctance model, while could describe the non-uniform distribution flexibly for its integral form. This model employed magnetic circuit theorem calculating the mean of the magnetic field, while used a normalized function describing the distributing character. The distributing function was determined by Biot–Savart law and relative permeability of the material. The model was validated with the help of the experimental device. At last, the fitting degree of the model with the tested results in predicting the performance of the actuator is researched.
The extraction of single train signal is necessary in wayside fault diagnosis because the acoustic signal acquired by a microphone is composed of multiple train bearing signals and noises. However, the Doppler distortion in the signal acquired by a microphone effectively hinders the signal separation and fault diagnosis. To address this issue, we propose a novel method based on the generalized S-transform, morphological filtering, and time–frequency amplitude matching-based resampling time series for multiple-Doppler-acoustic-source signal separation and correction. First, the original time–frequency distribution is constructed by applying generalized S-transform to the raw signal acquired by a microphone. Based on a morphological filter, several time–frequency distributions corresponding to different single source Doppler fault signals are extracted from the original time–frequency distribution. Subsequently, the time–frequency distributions are reverted to time signals by inverse generalized S-transform. Then, a resampling time series is built by time–frequency amplitude matching to obtain the correct signals without Doppler distortion. Finally, the bearing fault is diagnosed by the envelope spectrum of the correction signal. The effectiveness of this method is verified by simulated and practical signals.
This paper deals with the output tracking control of gear transmission servo (GTS) systems in the presence of deadzone nonlinearity with nonsymmetric beak points and unknown parameters. A novel differentiable deadzone model with nonsymmetric break points is put forward, which greatly facilitates the control design for a class of mechanical systems in the presence of deadzone nonlinearity. A new smooth backstepping controller, based on the newly-developed model, is proposed for the nominal system. Then, guaranteed robust steady-state performance of the closed-loop system with parametric uncertainties is derived by using Lyapunov analysis for the perturbed nonlinear systems. Simulations are carried out to validate the proposed algorithm and analysis in this paper.
Optimization design of centrifugal pumps involving multiple parameters and objectives is a complicated research topic. The orthogonal method is introduced in the present study to find a high efficiency and low cost way in the optimization process of a centrifugal pump. A orthogonal table designation L16(45) is established, in which 16 individuals of impellers are generated with five design parameters: blade wrap angle, blade angles at impeller inlet and outlet, blade leading edge position, and blade trailing edge lean varying at four levels for each parameter. To realize the multiobjective optimization of both pump efficiency and cavitation performance, an integrated factor considering the weight of two objectives is introduced. On the basis of validated computational fluid dynamics (CFD) technique, the range analysis gives the influence order of five parameters and also determines the value of each parameter. Finally, the optimal centrifugal pump is obtained with remarkable superiority on the efficiency of 3.09% rise and cavitation performance of 1.45 m promotion in comparison with the original pump.
A novel methodology for simultaneous parametric fault isolation and mode switching identification in the spool motion of a Directional Control Valve (DCV), under multi fault assumption, has been reported in this paper. The shape of the profile traversed by the DCV spool was assumed to be trapezoidal in both healthy and faulty condition, but the slope of trapezoidal may change due to fault. Under this assumption, the real valued fault parameter and binary mode switching were identified by real valued Particle Swarm Optimization (PSO) alone instead of a combined real and binary valued PSO (Hybrid PSO). A novel PSO algorithm by combining the concepts of varying inertia weight (both increasing and decreasing trend) and constriction factor has been proposed in the article to achieve more accurate identification. Its validity was examined using an existing heuristic formula and by conducting several tests on a benchmark function used for fault identification. Superior improvement was observed in the identification with increasing inertia weight than that of widely used decreasing inertia weight, when combined with the constriction coefficient. A high pressure hydraulic circuit used in dumper and several other lifting machines was used as a simulation example.
The trend of large-scale development of design industry requires efficient and full use of the rich design resources in the distributed multi-disciplinary resource environment. However, the designers are susceptible to many subjective and objective impacts, like knowledge structure, computing capability, geographic position, and administrative division. These impacts make the usage of design resources unstable and inefficient. Therefore, this paper proposed a computer-assisted automatic conceptual design system (CACDS). This system assumes that the design resources in the distributed multi-disciplinary resource environment exist in the form of functional elements with the same format, so that, the geographic, administrative, and disciplinary barriers in the design process can be broken, and the design resources can be fully used. CACDS is based on a group of basic concepts and their representations, its core is a functional solution generating algorithm, which is used to automatically generate functional solutions. As the result of the conceptual design, these functional solutions are also the starting point of the following detail design phase. Finally, a lighting system for underground greenhouse is designed as an illustrative case to validate the feasibility of the proposed CACDS.
This paper proposes an intelligent diagnosis method for gearbox using local mean decomposition and discrete hidden Markov models, including local mean decomposition, the energy difference spectrum of singular value, multiscale sample entropy, and the discrete hidden Markov model. How to extract feature information effectively and identify the fault type is key to making a diagnosis in the presence of strong noise. Combined with the Kurtosis criterion and correlation coefficient, the product function that contains the main characteristic frequency is filtered out by local mean decomposition. Next, the filtered local mean decompositions are used to construct the Hankel matrix and complete singular value decomposition. The denoised and reconstructed signals are achieved by an energy difference spectrum of singular value. Furthermore, the feature information after denoising is extracted by multiscale sample entropy. After combining the discrete hidden Markov models, the mechanical condition is identified. Practical examples of diagnoses for four gear types used in the gearbox can accurately identify the gear types, and the recognition rates of the various types are above 92%. The experiments shown here verify the effectiveness of the method proposed in this paper.
A one-phase synthesis method using heuristic optimization algorithms can solve the dimensional synthesis problems of path-generating four-bar mechanisms. However, due to the difficulty of the problem itself, there is still room for improvement in solution accuracy and reliability. Therefore, in this study, a new differential evolution (DE) algorithm with a combined mutation strategy, termed the combined-mutation differential evolution (CMDE) algorithm, is proposed to improve the solution quality. In the combined mutation strategy, the DE/best/1 operator and the DE/current-to-best/1 operator are respectively executed on some superior parents and some mediocre parents, and the DE/rand/1 operator is executed on the other inferior parents. Furthermore, the individuals participating in the three mutation operators are randomly selected from the entire set of parents. The proposed CMDE algorithm with the three different search modes possesses better population diversity as well as search ability than the DE algorithm. The effectiveness of the proposed CMDE algorithm is demonstrated using five representative problems. Findings show a marked improvement in solution accuracy and reliability. The most accurate results are obtained with an approximate combination ratio for the three mutation operators.
This work seeks to study the potential effectiveness of the Blind Signal Extraction (BSE) as a pre-processing tool for the detection of distributed faults in rolling bearings. In the literature, most of the authors focus their attention on the detection of incipient localized defects. In that case, classical techniques (i.e. envelope analysis) are robust in recognizing the presence of the fault and its characteristic frequency. However, when the fault grows, the classical approach fails, due to the change of the fault signature. De facto, in this case the signal does not contain impulses at the fault characteristic frequency, but more complex components with strong non-stationary contents. Moreover, signals acquired from complex machines often contain contributions from several different components as well as noise; thus the fault signature can be hidden in the complex system vibration. Therefore, pre-processing tools are needed in order to extract the bearing signature, from the raw system vibration. In this paper the authors focalize their attention on the application of the BSE in order to extract the bearing signature from the raw vibration of mechanical systems. The effectiveness and sensitivity of BSE is here exploited on the basis of both simulated and real signals. Among different procedures for the BSE computation, the Reduced-Rank Cyclic Regression algorithm (RRCR) is used. Firstly a simulated signal including the effect of gear meshing as well as a localized fault in bearings is introduced in order to tune the parameters of the RRCR. Next, two different real cases are considered, a bearing test-rig as an example of simple machine and a gearbox test-rig as an example of complex machine. In both examples, the bearings were degreased in order to accelerate the wear process. The BSE is compared with the usual pre-processing technique for the analysis of cyclostationary signals, i.e. the extraction of the residual signal. The fault detection is carried out by the computation of the Integrated Cyclic Modulation Spectrum on the extracted signals. The results indicate that the extracted signals via BSE clearly highlight the distributed fault signature, in particular both the appearance of the faults as well as their development are detected, whilst noise still hides fault grow in the residual signals.
Rotating machinery response is often characterized by the presence of periodic impulses modulated by high-frequency components. The fault information is often hidden in its envelope signal which is unilateral when demodulated. Conventional stochastic resonance with a symmetric potential cannot always contain the signal’s original features especially the asymmetry. In this article, a step-varying asymmetric stochastic resonance system for impulsive signal denoising and recovery as well as the rotating machine fault diagnosis is proposed to further improve the impulsive signal-to-noise ratio. In the method, the asymmetry of step-varying asymmetric stochastic resonance can match the unilateral impulsive signal well to generate an optimal dynamic system by selecting proper system parameters and degree of asymmetry. Systems with different simulated or experimental signals are also studied to verify its effectiveness and availability. Results indicate that the step-varying asymmetric stochastic resonance performs much better in detection of impulsive signal than the conventional stochastic resonance with merits of good frequency response, anti-noise capability, adaptability to asymmetric signal and original waveform preserving.
The full understanding of the viscoelastic contact mechanics between rough surfaces is a crucial issue in modern engineering research. This paper investigates the role that the number of rough scales, i.e. the cut-off of the power spectrum of the surface roughness, has on quantities like contact area, mean separation, and friction. Furthermore, an effective, though approximate, definition of an equivalent modulus is provided in order to reduce the viscoelastic contact domain to an elastic equivalent one.
According to the non-stationary characteristic of rotating machinery vibration signals of a rotor system with a loose pedestal fault, variational mode decomposition was applied in the pedestal looseness fault diagnosis for such a rotor system. Variational mode decomposition is used to decompose the rotor vibration signal into several stable components. This can achieve the separation of the pedestal looseness fault signal from the background signals, and extract the fault characteristic of a vibration signal from a rotor system with pedestal looseness. Experimental data from a rotor system with pedestal looseness were used to verify the proposed method. The results showed that the stable components of the rotor vibration signal obtained by variational mode decomposition have obvious amplitude modulation characteristics. The components which contain fault information were analyzed by envelope demodulation, which can extract the pedestal looseness fault features of a rotor vibration signal. Therefore, the variational mode decomposition method can be effectively applied to the pedestal looseness fault diagnosis of such a rotor system.
New
A novel gravity-based power-free solar tracking mechanism has been developed to track a linear solar concentrating collector. Multireflector compound parabolic collectors having three parabolic segments and two flat surfaces is chosen due to its high intercept factor and suitability to the current tracking. The working of tracking mechanism is studied to find the tracking loads in the east and the west sides of collector. A generalized mathematical model is derived to simulate the tracking motion from the sunrise to sunset. The identified design variants are sprocket wheel diameter, spring stiffness, solar collector’s weight, counter balance, and tracking wheel radius. The spring length is derived from the constraints. To make a compact product, the tracking load has been minimized at large sprocket wheel, low stiff spring, lighter collector weight, and small radius of tracking. For a typical collector load of 50 kg, the designed tracking load is 50 kg with 620 mm spring length, 250 mm of sprocket wheel diameter and 60 mm tracking radius.
Ceramic-on-ceramic bearings in total hip replacements have shown superior wear performance compared to other material couples. However, 1–10% of patients have reported squeaking with the use of ceramic-on-ceramic bearings. A ceramic-on-ceramic bearing was retrieved from a patient after 4.5 years in service secondary to squeaking. The explant was analyzed to investigate the possible factors attributing to the hip squeak utilizing acoustic analysis, visual inspection, modal analysis, random vibration analysis, and mathematical modeling. Random vibration analysis of the parts of the implant showed that boundary conditions along the metallic shell play an important role in squeal occurrence. The implant also showed the evidence of material transfer. Using the results of modal analysis, a 2-degree of freedom friction model demonstrated the influence of third body material transfer on the stability of the system to be an important factor in squeaking. The mathematical parametric analysis showed that a larger mass creates more instability, and hence more noise and vibration. Increased stiffness of the shell proved to stabilize the system for most loading conditions. Limit-cycle plots showed a definite change in the system behavior but stability was maintained through a significant increase in contact stiffness.
Craniotomy is an essential neurosurgical procedure to remove a section of patient’s skull. In order to do this, the surgical tools need to execute a one-degree-of-freedom skull drilling followed by a two-degrees-of-freedom skull cutting. Particularly, this two-degrees-of-freedom skull cutting motion can be treated as a pivot rotation ideally. Therefore, the craniotomy tool motion is equivalent to a remote center-of-motion (RCM), which is renowned in surgical robotics. In this paper, we proposed a novel hybrid RCM mechanism for robotic craniotomy. The mechanism is made of two orthogonal parallelogram-based linkages, which make the two rotational degrees-of-freedom decoupled. We also studied the position and differential kinematics of this new architecture and analyzed its potential singular configurations. We then set the local and global kinematic performance indices for obtaining the optimal mechanism dimensions. Finally, according to the optimization result, we created a mechanical prototype to verify the motion of the designed mechanism.
In this study, the influence of spanwise positions of vortex generators on the fin performance is determined numerically by considering global and local flow and heat transfer fields. The vortex generators are located on the inclined surfaces of equilateral triangular fins and the spanwise distances between them are altered as much as possible depending on the extents of the triangular duct. "RNG k-" turbulence model with "Enhanced wall treatment" option is determined as the best turbulence model to predict the flow fields inside the triangular fins with built-in vortex generators, for Reynolds number of 5000. It is found that the best performance is achieved when the spanwise distance between the common flow up and common flow down type vortex generator pairs and the triangular duct base are equal to 0.23 and 1.11 times the vortex generator length, respectively. The optimum spanwise distance between the vortex generators is determined as 0.88 times the vortex generator length. The determined values reinforced the secondary flow interactions including mixing of hot and cold fluids, generation of turbulence, swirling motion of vortices, and interaction of vortices with the main flow. The obtained results are useful in designing triangular heat exchangers with built-in delta-winglet type vortex generators.
Lipid nanotubes with well-designed cylindrical structures, tunable dimensions and biocompatible membrane surfaces have found potential applications such as templates to create diverse one-dimensional nanostructures and nanocarriers for drug or gene delivery. In this regard, knowing the encapsulation process is of crucial importance for such developments. The aim of this paper is to study the suction and acceptance phenomena of metallic nanoparticles, and in particular silver and gold, inside lipid nanotubes using the continuum approximation and the 6–12 Lennard-Jones potential function. The nanoparticle is modelled as a perfect sphere and the lipid nanotube is assumed to comprise six layers, namely two head groups, two intermediate layers and two tail groups. Analytical expressions are derived through undertaking surface and volume integrals to evaluate van der Waals potential energy and interaction force of a nanoparticle entering a semi-infinite lipid nanotube. These expressions are then employed to determine the suction and acceptance energies of system. To ascertain the accuracy of the proposed analytical expressions, the multiple integrals of van der Waals interactions are evaluated numerically based on the differential quadrature method. A comprehensive study is conducted to get an insight into the effects of different geometrical parameters including radius of nanoparticles, innermost radius of lipid nanotube, head group and tail group thicknesses on the nature of suction and acceptance energies and van der Waals interactions. Numerical results show that maximum suction energy increases by enlarging the nanoparticle size, while it decreases by increasing the head group thickness or the tail group thickness. It is further found that gold nanoparticle experiences higher maximum suction energies inside lipid nanotubes compared to silver nanoparticle.
Pulsed laser butt welding of miscible dissimilar couple has been studied numerically based on a three-dimensional heat and mass transfer model. Driving forces of molten metal flow in the case of stainless steel and nickel are compared using dimensional analysis. Thermo-capillary convection due to surface temperature gradient is recognized as the dominating fluid flow. Temperature coefficients of surface tensions are varied to investigate the influences of the convection on heat and mass transfer phenomena in weld pool. The temperature fields at stainless steel and nickel sides are found to be asymmetric and are greatly affected by different Marangoni convections. Concentration of Ni increases as the temperature coefficient of surface tensions changes from negative to positive. The temperature coefficient of surface tension of stainless steel has greater impact on the weld pool configuration and element concentration than that of nickel. The obtained weld pool configurations are found to be dependent on Prandtl number and convection patterns.
This paper proposes a time-varying sliding surface for a second-order sliding mode controller to improve the control performance and energy efficiency of a quad-rotor helicopter. The time-varying sliding surface is designed with a nonlinear function to provide varying properties of the closed-loop dynamics in order to reduce energy consumption. It is shown that the second-order sliding mode technique, known as a generalized super twisting algorithm, providing a robust controller and a nonlinear sliding surface is effective in reducing the energy consumption. A Lyapunov stability analysis is described to prove the stability of the proposed method. The effectiveness and reliability of the proposed method are evaluated by performing experiments several times using a quad-rotor helicopter experimental testbed under wind disturbance.
The purpose of this work is to identify simultaneously two irregular interfacial boundaries configurations between the components of three connected domains using a discrete number of displacement measurements obtained by a simple tension test. A unique combination of a global optimization method, i.e., the imperialist competitive algorithm and two local optimization methods, i.e., the conjugate gradient method and Simplex method along with the inverse application of the boundary elements method are employed in an inverse software package. A fitness function, which is the summation of squared differences between calculated displacements and measured displacements at identical locations on the outer boundary, is minimized. Due to the complexity and the ill-posed nature of this identification problem, imperialist competitive algorithm is used to find the best initial guesses of the unknown interface boundaries in order to be used by the local optimization techniques, i.e., conjugate gradient method and then Simplex method to accurately converge to the optimal shape of two irregular interfacial boundaries between the components of an inhomogeneous body. Several examples are selected, and the accuracy of the obtained results is discussed. The effect of experimental measurement errors and the influence of material properties of the sub regions on the identification process are also investigated.
Correct determination of ratcheting strain is very important in cyclic loading. A new simple yield surface distortion model is presented and its effect on cyclic loading and ratcheting prediction is investigated in this research. Model of Baltov and Sawczuk was modified in order to be able to consider directional distortion of the yield surface. Movement of the yield surface center is modeled by Chaboche's nonlinear kinematic hardening model. Isotropic hardening was also considered. A triangular function is used and necessary cyclic plasticity relations are developed. Convexity of the proposed model is discussed and verified. Performance of the proposed model in ratcheting strain prediction is investigated in multiaxial non proportional loadings under different paths. Experimental results with stress, strain and combined stress-strain control paths are compared with the proposed model results. Incorporation of the yield surface distortion of this new model, predicts better ratcheting strain for different stress, strain and stress-strain paths.
In the pump mode (storage mode) of a pump-turbine, unstable head variations occur as the flow rate decreases, leading to unstable, unsafe operation. Thus, the hydrodynamics of pump-turbines in the unstable operating range should be investigated to improve their designs. This study presents experimental and numerical studies of the hydrodynamics. The experiments investigated the external characteristics with the head instabilities captured by both the model tests and the computational fluid dynamics simulations. The computational fluid dynamics model used detached eddy simulations to study the flow details which showed that hydraulic losses were the reason for the unstable head variations and the poor flow regime was the source of the losses. In the unstable, low flow rate range, the flow direction is no longer consistent with the guide vane direction, so undesirable flow structures develop in the passages. Therefore, appropriate guide vane opening angles are needed to improve the flow regime and reduce the hydraulic losses. These will enhance the operating stability and safety in engineering applications.
Industrial applications of glass and ceramic materials have increased manifold due to their relatively low friction, high compression strength, high temperature and wear resistance, and excellent chemical inertness, etc. In microelectromechanical systems the use of glass, along with silicon and polymer, has become very popular. However, microfabrication of glass is a difficult process. The electrochemical discharge machining is now often used as one of the chipless machining solutions for these materials. The electrochemical discharge machining, however, is a complex process with multiple controllable parameters and exhibits stochastic nature. The mechanism of material removal in the process is yet to be understood well in spite of many theories. In this paper, an attempt has been made to develop a three-dimensional finite element model for simulation of material removal in electrochemical discharge machining drilling in order to explore the mechanism further and correlated the findings with the experimentally obtained values. The model outputs were compared with experimental results available in literature. The computed results from the model show good agreement with the trial results.
Rapid prototyping uses layered manufacturing technology to produce functional parts directly from 3D computer-aided design model without involving any tools and human intervention. Due to layer by layer deposition, volumetric error remains in the part which is basically the volumetric difference between computer-aided design model and the fabricated part. This volumetric error causes poor dimensional accuracy and surface finish, which has limited the widespread applications of rapid prototyping. Although rapid prototyping is able to produce functional parts in less build time with less material wastage, today many industries are looking for better surface quality associated with these parts. Literature discloses that the part quality can be improved by selecting proper build orientation that corresponds to minimum volumetric error. In support of this, current study presents a computer-aided design-based novel methodology to precisely measure the volumetric error in layered manufacturing process, in particular fused deposition modeling process. The proposed method accepts computer-aided design model of the part in .CAT format and automatically calculates volumetric error for different build orientations. An Excel function is integrated with it to determine optimum build orientation based on minimum volumetric error. Several simple and complex examples verified the robustness of our proposed methodology. We anticipate that the current invention will help future rapid prototyping users in producing high-quality products through an intelligent process planning.
Electromechanical actuators (EMAs) are of interest for applications which require easy control and high dynamics. This paper addresses the experimental identification, structured and unstructured uncertainties modeling, and robust control design for an EMA system with harmonic drive. Two robust controllers are designed by two proposed approaches: The first is based on Kharitonov theorem, which not only robustly stabilizes the uncertain EMA system but also maintains the pre-specified margins and bandwidth constraints. The second is feedback compensation design procedure based on H control theory, verifying good tradeoff between the powerful H controller and the unique features of feedback compensation, such as simplicity, effectiveness, low sensitivity to parameters variations, low cost, and easy implementation. Simulation and experiments prove the robustness and high tracking performance of the robust EMA systems which reveals the affectivity of the proposed robust control design methods.
In marble industry, it is of vital importance to determine the damaged discs on time to prevent possible industrial injuries. Therefore, in this study, it is proposed to classify the status of the cutting discs that are used while cutting the natural stones. To classify the deflections of the discs, 673 different experiments are performed. Cutting discs corresponding to four different damage classes (undamaged disc, less damaged disc, much damaged disc, and broken disc) are employed in the tests. Eight different parameters (cutting forces (Fx, Fy, Fz), noise, peripheral speed of the disc, current, voltage, power consumption) are measured and recorded in the experiments. For each experiment, mean values of different measured data are studied. Artificial neural networks are employed as classifiers. In the first stage, all of these mean values corresponding to eight parameters are selected as the input vectors of the artificial neural networks, whereas in the second stage, the dimension of input vector is decreased by leaving out the parameters one by one. In this stage, it is aimed to determine the most important parameter that caries much more information about the cutting process.
Functional adaptability makes a product not only multifunctional but also compact in structure and flexible in application. An adaptable-function mechanical product generally demonstrates various degrees of similarity in its behavioral processes for different adaptable functions. Evaluation of this similarity is an important aspect of research for the design of such products, especially for redesigning existing products towards functional adaptability. Until present there lacks research on the design and development of this specific kind of products, including the work on the similarity evaluation of their behavioral processes. To address this problem, this paper investigates the functional and structural characteristics of adaptable-function products first. Based on this, by applying the function-behavior-structure design rationale, a redesign framework of mechanical product for functional adaptability was proposed, and the similarity characteristic of behavioral process was investigated, both on that of the behavior structure and that of behavior characteristics. Furthermore, the paper applied a fuzzy mathematics method for the evaluation of behavioral process similarity, for which a fuzzy comprehensive evaluation model was constructed and the corresponding evaluation method was proposed. Finally, a mini-combined machine tool with adaptable-functions was taken as an example to analyze the behavioral processes and to illustrate the proposed similarity evaluation procedure. The results demonstrated the feasibility and effectiveness of the proposed methodologies.
A new design method for selecting the physical parameters of a free piston Stirling engine (FPSE) is presented. The dynamics of FPSE are described in the form of a transfer function including the inherent feedback mechanism. The simplified Nyquist stability criterion is used to derive the operation condition, where the indices of the magnitude amplification factor (MAF) and the operation limit factor (OLF) are introduced in terms of the physical parameters. Further, a measure for the efficiency of the engine is defined as the damping ratio of the power piston system (DRP). Parametric studies of these quantities are carried out as well as benchmarking against the design values of the standard RE-1000 engine. A design method is presented that defines the physical parameters of an FPSE which is working at a given operation frequency.
A spectral collocation approach based on integrated polynomials is presented to investigate the statics and free vibrations of Euler–Bernoulli beams with axially variable cross section, modulus of elasticity, and mass density. The basic concept of the approach is the expansion of the highest derivatives appearing in the governing equations instead of the solution function itself by the truncated basis function. Then lower order derivatives and the function itself are obtained by integration. The constants appearing from the integrating process are determined by given classical or elastic restrained boundary conditions. Also, by incorporating the decomposition technique into the present approach, higher order vibration modes can be achieved even for stepped beams. Numerical examples including the statics and free vibrations of the beams with variance in geometry or material have been successfully solved, and the results are compared with those analytical or numerical solutions in the existing literature. The convergence and comparison studies show that convergent speed is rather rapid and the present approach can yield high accurate results with low computational efforts. Furthermore, the accuracy is not particularly affected by the adopted polynomials.
The Gough-Stewart platform has been successfully used in a wide variety of fields ranging from medical to automotive applications. This paper proposes a 6-RRRPRR parallel manipulator with orthogonal non-intersecting RR-joint configurations and ball screw actuators without guide mechanisms. A novel methodology is developed to define the dependent RR-joint variables and a numerical algorithm is employed to calculate the joint variables. The parasitic motion caused by the helical motion of the ball screw can be expressed and solved with vector method. The inverse kinematics of this manipulator can be solved. To verify the effectiveness of the proposed approach, simulations are performed with software package ADAMS. A prototype of this manipulator is manufactured. Its resolution, accuracy, and repeatability are measured. It is shown that the presented method is effective for this parallel manipulator.
There exist some problems when the fractal feature method is applied to identify thruster faults for autonomous underwater vehicles (AUVs). Sometimes it could not identify the thruster fault, or the identification error is large, even the identification results are not consistent for the repeated experiments. The paper analyzes the reasons resulting in these above problems according to the experiments on AUV prototype with thruster faults. On the basis of these analyses, in order to overcome the above deficiency, an improved fractal feature integrated with wavelet decomposition identification method is proposed for AUV with thruster fault. Different from the fractal feature method where the signal extraction and fault identification are completed in the time domain, the paper makes use of the time-domain and frequent-domain information to identify thruster faults. In the paper, the thruster fault could be mapped multisource and described redundantly by the fault feature matrix constructed based on the time-domain and frequent-domain information. In the process of identification, different from the fractal feature method where the fault is identified based on fault identification model, the fault sample bank is built at first in the paper, and then pattern recognition is achieved by calculating the relative coefficients between the constructed fault feature matrix and the elements in the fault sample bank. Finally, the online pool experiments are performed on an AUV prototype, and the effectiveness of the proposed method is demonstrated in comparison with the fractal feature method.
In 2008, the Journal of Mechanical Engineering Science was approaching its 50th anniversary and the editorial board arranged some personal contributions from those who had been material in the journal’s success. In response to this initiative, the authors spoke informally to Ken Johnson about his life and work. However, typically modest in his approach, Ken was reluctant to see the article published during his lifetime, and so it has remained in the ‘bottom drawer of the desk’ ever since. But now, following Prof. Johnson’s passing in September 2015 we thought it appropriate to publish our brief article with minor modifications, and hope that it will serve as a memorial to the enormous contribution he made to his chosen field of study.
Lack of objective design change analysis model is a major problem for the accurate change impact prediction. To solve this problem, this paper proposes an ontology-based model named design change analysis model to organize the unstructured design properties as a basis for design change management. Design change analysis model is constructed by formalizing the mechanical design specifications in the form of design property network. Benefiting from the fine-grained organization, design change analysis model ensures the objectivity and accuracy of design change impact assessment. Since design change analysis model satisfies the attributions of small-world network, the change impact assessment should focus on more meaningful aspects including the linkage weight, node degree, and long-chain linkages of design change analysis model. With design change analysis model, the changeability of each design property which provides a quantified change propagation measurement could be evaluated. Additionally, different components could be distinguished in design change analysis model by using clustering algorithms without specializing them in advance. Design change analysis model modeled in web ontology language is a semantic enrichment model. It supports the semantic design change management due to the mathematic logic-based semantics of web ontology language and semantic web rule language. These lays a basis for updating changes among heterogeneous product development systems, and acquiring feasible change impacted properties.
This paper proposes a new diagnostic framework, namely, probabilistic committee machine, to diagnose simultaneous-fault in the rotating machinery. The new framework combines a feature extraction method with ensemble empirical mode decomposition and singular value decomposition, multiple pairwise-coupled sparse Bayesian extreme learning machines (PCSBELM), and a parameter optimization algorithm to create an intelligent diagnostic framework. The feature extraction method is employed to find the features of single faults in a simultaneous-fault pattern. Multiple PCSBELM networks are built as different signal committee members, and each member is trained using vibration or sound signals respectively. The individual diagnostic result from each fault detection member is then combined by a new probabilistic ensemble method, which can improve the overall diagnostic accuracy and increase the number of detectable fault as compared to individual classifier acting alone. The effectiveness of the proposed framework is verified by a case study on a gearbox fault detection. Experimental results show the proposed framework is superior to the existing single probabilistic classifier. Moreover, the proposed system can diagnose both single- and simultaneous-faults for the rotating machinery while the framework is trained by single-fault patterns only.
In this study, numerical methods are used to investigate the flow and temperature fields of the air-cooled motorized spindle. The wind speed effects on the motorized spindle temperature and the relationships between the rotating speed, vibration and noise are studied experimentally. The purpose of this work is to provide the basis for optimization design of the air-cooled motorized spindle. First, the boundary conditions are defined and the wind speed in the heat sink groove, fluid field of the fan area and temperature distribution of the spindle in the thermal steady state are predicted by the finite element method. Second, the temperature, wind speed, vibration of the key points on the motorized spindle and the noise are measured experimentally. The results show that the wind speed of the fan area is high in the center and low near the wall. The spindle temperature is higher in the area of contact with the rotor and the front bearings, while changes in the heat sink section have little effect on the wind speed. It is found experimentally that the vibration, noise and temperature increase with rotating speed. The numerical and experimental results are consistent. It is suggested to improve the design of the motorized spindle through optimizing the blade structure to decrease the temperature, vibration and noise.
Magnetically suspended sensitive gyroscopes (MSSGs) provide an interesting alternative for achieving precious attitude angular measurement. But the high accuracy is sensitive to various disturbing torques acting on the rotor. In order to compensate for the drift errors produced by disturbing torques, this paper proposes a compensation system of Lorentz force magnetic bearings. Based on the geometric construction and running regularity of the compensation system, the analytical expression of the compensation torque has been deduced, and the generation mechanism of the compensation torque is revealed, which laid the foundation for the design of high-precision MSSGs. The common issues caused by disturbing torques can be effectively resolved by the proposed method in gyroscopes with a levitating rotor. To verify the feasibility and superiority of this compensation method, comparative simulations are carried out before and after the disturbing torques were compensated.
In order to improve the machining accuracy and production efficiency of face-gear, a method of face-gear generating hobbing by worm is provided in this paper. The principle of face-gear hobbing worm is analyzed, and the mathematical model of the worm is presented based on the principle and the theory of meshing. Taking the hobbing needs into account, the special machine tool is provided, and the movement control method of face-gear hobbing by the worm on the machine tool is proposed. The equation of face-gear tooth surface is calculated, and the 3-D model of face-gear is established based on CATIA software. To reduce the face-gear tooth profile errors induced by ratio errors, an error analysis model of face-gear hobbing is established. The experiment is carried out, and the completed specimen is detected by Coordinate Measuring Machining (CMM). The processing parameter is amended according to the tooth flank detection results, and the maximum normal deviation of the whole tooth surface of the face-gear specimen is improved from 243.2 µm to 61.0 µm. Experiment results demonstrate that the method of face-gear hobbing by worm is an effective approach to achieve the precision face-gear with high dimensional accuracy.
A novel parallel compliant mechanism with one translation and two rotations is proposed. Its stiffness matrix and force/torque performance indices are derived. The influence of temperature on the output displacement of the compliant mechanism is deduced. Structure parameters of the compliant are optimized with the force and torque performance indices as objective and the equivalent nodal thermal load as constraint condition. The statics and dynamics experiments are conducted to verify the compliant mechanism rationality.
Compared with unbalance forces and moments of four- and six-cylinder engines, forces and moments applied to the engine block from a three-cylinder engine are large and the mechanism for balancing the unbalance forces are complex. So design of a mounting system for the powertrain with a three-cylinder engine is more challenging. This paper presents the analytical methods for obtaining the unbalance forces and moments applied to the engine block for a three-cylinder engine with or without balance measures, and develops a design methodology for the Powertrain Mounting System with a three-cylinder engine. The unbalance forces and moments generated by cylinders, crank and connecting rod mechanisms and applied to the engine block are analyzed firstly. Then, three balance methods for reducing the forces and moments applied to the engine block are proposed and discussed. Three balance measures are described and analyzed. The methods for estimating forces and moments applied to the engine block under the three balance measures are developed and compared. Thirdly, an optimization method is proposed to estimate mount stiffness based on minimization of mount forces transmitted to the car body or sub-frame, along with meeting requirements for placing natural frequencies of the powertrain in prescribed ranges and those for maximizing modal energy distributions of the powertrain in six directions. An example is given to validate the calculation methods and design philosophy for the mounting system of a powertrain with a three-cylinder engine.
Emphasis is placed on the performance of a two-stage pump equipped with an eroded impeller. Non-contact reverse engineering technique is utilized to acquire the point data constituting the three-dimensional geometrical model of the eroded impeller. With computational fluid dynamics, both the operation performance of the pump and flow patterns adjacent to the eroded blade surface are obtained. For comparison, the corresponding undamaged impeller is investigated as well. Preferable fidelity of the approach of constructing geometrical model of the damaged impeller is substantiated. The mechanism underlying performance degradation of the pump with the eroded impeller is evidenced. Local flow patterns near the eroded area are featured by explicit irregularity. Furthermore, between the defective and the undamaged pumps, disparity in positions where cavitation occurs is negligible.
Electro-hydraulic hybrid testing, which imposes the desired acceleration and force on the specimen in parallel, is a novel structural testing method for structures or facilities and is extensively applied in civil and seismic engineering. To efficiently suppress the surplus force resulted from the acceleration motion of the specimen during the force control process, a compound force tracking control strategy comprised of a force and voltage feedforward controller (FVFC) and feedforward inverse with disturbance observer (FIDOB) controller is presented in this research. The FVFC controller as an inner loop feedforward component is first constituted by the generated force feedback signal and the real-time control voltage signal of the acceleration actuator so as to compensate for the acceleration motion of the specimen for a better disturbance rejection performance, and the FVFC controller requires little information of the system dynamic structure or parameters. The FIDOB controller composed by a feedforward inverse controller and an inverse model-based disturbance observer is then combined with the FVFC controller as an outer loop to further deal with the remaining disturbances for the FVFC-controlled electro-hydraulic hybrid testing system. The inverse model applied in the FIDOB controller is obtained with the frequency domain complex curve fitting and zero magnitude error tracking technology with respect to the proportional–integral controlled static loading system. Hence, the proposed controller integrates the advantages of the FVFC controller and FIDOB controller in terms of easy implementation and high tracking performance. Finally, comparative experiments are carried out on an uniaxial electro-hydraulic hybrid testing test rig with the xPC rapid prototyping technology and experimental results demonstrate the effectiveness of the proposed control strategy.
In this study, three-dimensional computational fluid dynamics simulation was adopted to evaluate the valve-induced water hammer phenomena in a typical tank-pipeline-valve-tank system. Meanwhile, one-dimensional analysis based on method of characteristics was also used for comparison and reference. As for the computational fluid dynamics model, the water hammer event was successfully simulated by using the sliding mesh technology and considering water compressibility. The key factors affecting simulation results were investigated in detail. It is found that the size of time step has an obvious effect on the attenuation of the wave and there exists a best time step. The obtained simulation results have a good agreement with the experimental data, which shows an unquestionable advantage over the method of characteristics calculation in predicting valve-induced water hammer. In addition, the computational fluid dynamics simulation can also provide a visualization of the pressure and flow evolutions during the transient process.
Clearances existing in artillery mechanism cause the muzzle disturbance and reduce the artillery firing accuracy. If the parameters of the clearance nonlinearity can be identified by taking advantage of the dynamic information, the quantitative relation between the clearance and muzzle disturbance can be established, and then the clearances of such nonlinear system can be controlled in a reasonable range to improve the artillery firing accuracy. This paper proposed a nonlinear identification method for the cantilever beam with clearances reduced from barrel-cradle structure. A modified restoring force surface method is proposed to identify the clearance value of the cantilever beam in time domain, and then a modified nonlinear identification through feedback of outputs method, i.e., reduced-order nonlinear identification through feedback of the output method, is proposed to recognize the related contact stiffness in frequency domain. The feasibility of the combined identification process is verified by a cantilever beam with two clearances in simulation, and a test-bed with adjusted clearance and contact stiffness which is regardless of other nonlinear factors by adjusting the position of the clearance and excitation method was designed to verify the effectiveness of this method. In the end, some influence factors of this identification process are discussed in detail. The results show that the proposed methods can identify clearance-nonlinearity parameters with high precision.
The rectilinear rear-independent suspension investigated in this paper could remain the wheel alignment parameters invariable in theory. However, its dynamics is much more complex than that of the existing suspensions because of its redundant constraints in structure. Considering the elasticity of the rectilinear rear-independent suspension, a rigid-flexible half-car dynamic model is established for the first time based on the discrete time transfer matrix method. At the same time, a rigid half-car dynamic model is established as a comparison. The natural frequency characteristics and dynamic response of the rectilinear rear-independent suspension under random road excitations are analyzed and compared with those of rigid half-car dynamic model. The results reveal that the suspension system has apparent influence to the dynamics of vehicle. The wheel alignment parameters will fluctuate within a narrow range which is mainly determined by the rolling vibration of vehicle. And the suspension system could reduce and filter the road excitations with high frequency and small amplitude. This provides a good effect on the ride comfort of vehicle. Dynamics analysis of the rectilinear rear independent suspension reveals that the proposed modeling approach could deal with the dynamics of rigid-flexible multibody systems with redundant constraints effectively.
The flat-walled diffuser/nozzles are classified into two types, i.e. Tube I and Tube II, based on their different flow resistance characteristics. Tube I has less pressure loss coefficients in the diffuser direction than the nozzle direction, and Tube II has larger pressure loss coefficients in the diffuser direction than the nozzle direction. This work focuses on the characterization of the diffuser efficiency, and flow rectification of these two types of diffuser/nozzles. The characterization is performed with diverging angles in the range of 5°–60° and length–width ratios in the range of 1–20, and the pressure drop ranging from 1 to 10 kPa. The results show that with the increase in pressure drop and the decrease in length–width ratio, Tube I type of diffuser/nozzles can change to Tube II. For Tube I type of diffuser/nozzles, the smaller the diverging angle and the longer the length, the better the performance. For Tube II type of diffuser/nozzles, the larger the diverging angle and shorter the length, the better the flow rectification performance. Simulation results match well with the experiment data. Of particular interest, simulation of the diffuser flow fields suggests that the flow separation has a significant impact on pressure loss coefficients in the diffuser direction.
Consideration is given to dynamic behavior of cylindrical pressure pipe with elastic boundary conditions. Based on Sanders’ shell theory and Hamilton principle, the system equations are established for integrating the uniform distributed pressure into the elastic boundary condition. In the analytical formulation, the Rayleigh–Ritz method with a set of displacement shape functions is used to deduce mass, damping, and stiffness matrices of the pipe system. The displacements in three directions are represented by the characteristic orthogonal polynomial series and trigonometric functions which are satisfied with the elastic boundary conditions, which are represented as four sets of independent springs placed at the ends including three sets of linear springs and one set of rotational spring. The pressure pipe always suffers a uniform distributed pressure in radial direction. To verify the accuracy and reliability of the present method, several numerical examples with classical boundary condition, including free and simply supported supports are listed and comparisons are made with open literature. Then the influences of boundary restraint stiffness and the distributed pressure on natural frequency and the forced vibration response are studied: The natural frequencies increase significantly as the restraint stiffness or the distributed pressure increases. Compared to the rotational spring stiffness, the stiffnesses of axial, radial, and circumferential springs have more significant effect on natural frequency. And the lower modes are more sensitive on restraint stiffness than higher modes. But the variation of natural frequency with respect to the spring stiffness decreases monotonically with the increasing distributed pressure. The forced vibration response is also affected by the restraint stiffness.
Taking into account different drag torque, this paper investigates the influence of the lubricant films located in the backlash between meshing gear teeth pair on the gear dynamical behaviors. Numerical simulations show that the influence of the lubricant film on the coast side is significant under low loading, but under increased drag torques the influence is diminished. The shape of the hysteresis loop of double-sided films suggests that this model can make more sense. The sensitive of the drag torque is studied to illustrate the inverse relationship between drag torque and gear rattle: increased drag torque loading will increase to possibility of metal–metal contact which could generate noise, while decreased drag torque loading can promote noise due to rattle.
The machine tools are consisted of many parts and most of them are connected by the bolts. Accurate modeling of contact stiffness and damping for bolted joint is crucial in predicting the dynamic performance of machine tools. This paper presents a modified three-dimensional fractal contact model to obtain the stiffness and damping of bolted joint. Topography of the contact surface of bolted joint is fractal featured and determined by fractal parameters. Asperities in microscale are considered as elastic, elastic–plastic, and full plastic deformation. The expand coefficient is introduced to the size-distribution function of asperities. The real contact area, contact stiffness, and damping of the contact surface can be calculated by integrating the microasperities. The relationship of contact stiffness, damping, fractal dimension D, and fractal roughness parameter G can be obtained. Experiments are conducted to verify the efficiency of the proposed model. The results show that the theoretical mode shapes are in good agreement with the experimental mode shapes. The relative errors between the theoretical and experimental natural frequencies are less than 3.33%, which is less than those of the W-K model and L-L model. The presented model can be used to accurately predict the dynamic characteristic of bolted assembly in the machine tools.
Molecular dynamics simulations are used to investigate the mechanical properties of graphynes. To study the effect of atomic structure and graphyne size on Young’s and bulk modulus, armchair and zigzag nanosheets with different side lengths and aspect ratios are considered. It is observed that at a constant aspect ratio (the ratio of height to side length), variation of side length has no significant effect on Young’s modulus of graphynes. Besides, using the obtained results by molecular dynamics simulations, a finite element model is proposed to study the vibrational and buckling behaviors of graphynes. The effects of different parameters such as nanosheet geometry and boundary conditions on the fundamental natural frequency and critical buckling force of graphynes are explored. It is shown that increasing side length has an inverse effect on the frequency and buckling force. Increasing aspect ratio results in decreasing the frequency. However, this effect reduces for longer sheets. Increasing aspect ratio results in converging the vibration curves associated with graphynes under different boundary conditions. Moreover, by increasing aspect ratio, the sensitivity of buckling force to aspect ratio variation decreases.
High-speed spindles often suffer from degeneration in its machining accuracy caused by the uneven distribution of temperature field. In order to improve the machining accuracy of high-speed spindles, a three-dimensional (3D) finite element analysis (FEA) model, which considered the combined effect of thermal contact resistance (TCR) and the change in heat power and stiffness caused by thermal displacements of bearing components on the accuracy of simulation results, was proposed to conduct transient thermal-structure analysis of high-speed spindles. The predictive model for TCR was proposed based on the fractal theory to characterize the rough surface morphology with disorder, self-affinity and non-stationary random features. And a contact mechanics model was developed to consider the influence of asperities’ deformation on TCR. The thermal-structure model of bearing was proposed to calculate the heat power and stiffness based on the quasi-static mechanics analysis. The FEA model proposed in this paper was used to simulate the temperature field distribution and thermal deformations of the high-speed spindle system. Then thermal characteristic experiments were conducted to validate the effectiveness of this model. The results showed that the FEA model was much more accurate than the traditional model which ignored the above two important factors. The temperature field and thermal errors of the spindle system were analyzed.
An approach for designing compliant mechanisms with glass fiber-reinforced epoxy materials is presented to obtain the optimum fiber orientation and topology structure simultaneously in this paper. Four-node hybrid stress elements and nodal design variables are adopted to suppress the islands and checkerboard phenomenon without additive filter technology and constraint. Taking fiber orientation and relative density as design variables, minimizing the weighted linear combination of the mutual strain energy and the strain energy is considered as objective function to achieve the desired deformation and enough load-carrying capacity of compliant mechanisms with the volume constraint. The displacement field of structure is obtained by the finite element analysis, and the non-linear optimization problem is solved via the well-known method of moving asymptotes. The numerical examples of designing compliant inverters and grippers with different weighted factors are investigated to demonstrate the effectiveness of the proposed method.
This paper studies the flow characteristics and flow ripple reduction techniques of a spool valves distributed radial piston pump. The mathematical models of the pump are established, and simulations based on the mathematics are performed in AMESim environment. The results indicate that the spool valves distributed radial piston pump has fewer flow fluctuations than the pump distributed by check valves, due to the rigid motion of its distribution component—the spool valves. Then, in order to reduce the flow ripple of the spool valves distributed radial piston pump, three techniques, namely, time delay, relief chamfer and transition compression filter volume, are proposed and their working principles are illustrated. Particularly, the design method of time delay is elaborated and its effectiveness is evaluated. The simulation results suggest that with the usage of the time delay method, the fluctuation range of the spool valves distributed radial piston pump is expected to be reduced by 21.7%.
A major challenge of metamodeling in simulation-based engineering design optimization is to handle the "curse of dimensionality," i.e. the exponential growth of computational cost with increase of problem dimensionality. Encouragingly, it has been reported recently that a high-dimensional model representation assisted by a radial basis function is capable of deriving high-dimensional input–output relationships at dramatically reduced computational cost. In this article, support vector regression is employed as an alternative to be coupled with high-dimensional model representation for the metamodeling of high-dimensional problems. In particular, the bisection sampling method is proposed to be used in the metamodeling process to generate high-quality training samples. Testing and comparison results show that the developed bisection-sampling-based support vector regression–high-dimensional model representation metamodeling technique can achieve high modeling accuracy with a smaller number of training sample evaluations. For the problem examined in this study, the bisection-sampling-based support vector regression–high-dimensional model representation enables high modeling accuracy and linear computational complexity as the problem dimensionality increases. Analysis of this performance advantage shows that the use of bisection method enables the developed metamodeling technique to be more effective in dealing with high-dimensional problems.
This paper presents a new approach based on Extended Kantorovich Method to simulate the static response of micro-plates to electrostatic actuation. The presented model accounts for the electric force nonlinearity of the excitation as well as the applied in-plane loads. Using a one term Galerkin approximation and following the extended Kantorovich procedure, the nonlinear partial differential equation governing the micro-plate deflection reduces to two un-coupled nonlinear ordinary differential equations with constant coefficients which can be solved iteratively with rapid convergence to yield the desired solution. A parametric study has also been performed to characterize the effect of various design parameters such as applied in-plane loads and micro-plate aspect ratio to pull-in limits of micro-plates. Results in some specific cases have been validated, comparing them with other theoretical and experimental findings reported in the literature as well as the results of the finite element simulation of the problem. It is shown that rapid convergence, high precision and independency of initial guess function make extended Kantorovich method an effective and accurate design tool for design optimization of micro-plates under electrostatic actuation.
Bolted joint railroad is the subject matter of this paper. Rail joint elements are subjected to cyclic and impact loads as a result of the passage of trains, which causes the origination and growth of fatigue cracks occurring, in most cases, around the bolt holes. Fatigue failure around rail-end-bolt holes is particularly dangerous because it leads to derailment of trains and, consequently, to inevitable accidents. Moreover, the cracking at rail-ends, which starts from bolt hole surface, causes premature rails replacement. The presence of residual compressive hoop stresses around the bolted holes, which is achieved by prestressing of these holes, extends the fatigue life of bolted joint railroads. This article presents an innovative technology for pre-stressing of rail-end-bolt holes, implemented on a vertical machining centre of Revolver vertical (RV) type. Two consecutive operations are involved in the manufacturing technology process: formation of the hole by drilling, reaming and making of a chamfer through a new combined cutting tool; cold hole working by spherical motion cold working through a new tool equipment, which minimizes the axial force on the reverse stroke. The new technology introduces beneficial residual compressive stresses around the bolted holes thereby preventing the fatigue cracks growth and increasing the fatigue life of these openings.
The surface/subsurface integrity and grinding force formed during grinding processes of have been researched on BK7 glass using a surface grinder with diamond grinding wheel. The values of surface roughness, subsurface damage and grinding force were measured and the morphology of surface roughness, and subsurface damage were observed with different grinding parameters. The experimental results show that the values of surface roughness, subsurface damage and grinding force increase with the increasing of feed rate and grinding depth and decreasing of wheel speed. The effects trend of grinding parameters on surface roughness, subsurface damage and grinding force are almost the same and the normal grinding force have great influence on surface roughness and subsurface damage, which agree well with theoretical analysis. These relationships can serve as a useful method for non-destructively predicting subsurface damage depth and a theoretical basis for proposing the appropriate grinding parameters to obtain better surface/subsurface integrity and high efficiency.
Central pose errors involving central position error and central orientation error are critical indexes for 6-degrees of freedom docking mechanism assembly quality. The performance of assembly could be evaluated during virtual assembly stage in terms of these indexes. However, the evaluation process for assembly has to employ Monte Carlo simulation, which leads to huge computation cost and usually makes the process impossible. This paper gives an insight of the relation between central pose errors and structural errors and finds that the central position error and central orientation error of docking mechanism conform to Rayleigh distribution model at symmetric pose configuration. In comparison, the maximum difference between results with Rayleigh model-based assembly performance and Monte Carlo simulation-based one is no more than 1.22%. With this model, the evaluation process for assembly performance could be facilitated significantly.
As one of major failure modes of mechanical structures subjected to periodic loads, edge cracks due to fatigue can cause catastrophic failures in such structures. Understanding vibration characteristics of a structure with an edge crack is useful for early crack detection and diagnosis. In this work, a new cracked cantilever beam model is presented to study the vibration of a cantilever beam with a slant edge crack, which cannot be modeled by previous methods considering a uniform edge crack along the width of the beam in the literature. An equivalent stiffness model is proposed by dividing the beam into numerous uniform independent thin pieces along its width. The beam is assumed to be an Euler–Bernoulli beam. The crack is assumed to be distributed along the width of the beam as a straight line and a parabola. The methodology proposed in this work can also be extended to model a crack with an arbitrary curve. Effects of crack depths on the nondimensional equivalent stiffness at the crack section of the cracked cantilever beam are studied. The first three nature frequencies and mode shapes of the cracked cantilever beam are obtained using compatibility conditions at crack tips and the transfer matrix method. Effects of depths and the location of the crack on the first three natural frequencies and mode shapes of the cracked cantilever beam are studied using the proposed cracked cantilever beam model. Numerical results from the proposed model are compared with those from the finite element method and an experimental investigation in the literature, which can validate the proposed model.
In this paper, the empirical mode decomposition as a signal processing method has been studied to overcome one of its shortcomings. In the previous studies, some improvements have been made on the empirical mode decomposition and it has been applied for condition monitoring of mechanical systems. These improvements include elimination of mode mixing and restraining of end effect in empirical mode decomposition method. In this research, to increase the accuracy of empirical mode decomposition, a new local mean has been proposed in the sifting process. Through the proposed local mean, the overshoot and undershoot problems in defining the local mean of common algorithm are alleviated. Meanwhile, it is capable to separate the components with close frequencies. Through the analysis of simulated signals via the new algorithm, it is shown that the accuracy is improved. Finally, empirical mode decomposition-based fault diagnosis approach has been applied to a vibration signal obtained from a faulty gearbox. The results show that the proposed method can resolve the effects of damage in vibration signals better than the common empirical mode decomposition method and helps for the isolation and localization of the fault.
The stators of hollow-type traveling wave ultrasonic motors have certain problems stemming from their complex and hollow structures, significant differences between the two orthogonal modal frequencies, incomplete separation of the design model and interferential model, low-vibration amplitude, and significant localized inner stress during vibration, etc. In this paper, a dimensional parameterized finite elemental model for the motor was established by utilizing the finite elemental method. Afterwards, modal assurance criteria were used to identify the vibration models with various objectives for optimization established from this and integrating multiple objectives for optimization into a single optimization objective. Then a response surface model was established in the design space the Latin-hypercube random sampling method. Finally, a globally optimal solution was obtained according to the self-adaptive genetic algorithm and the response surface model. In order to prove the reasonableness of the optimized result, the stators are processed according to the sizes determined before and after the optimization. This paper describes the vibration of stators tested by a Doppler vibration tester. The Z-direction amplitude of the optimized stator changed from 1.0 µm to 2.5 µm. According to the testing results, the structural optimization plan used in this paper is reasonable and obviously helpful for vibration optimization of the stator.
In a bearing chamber, oil droplets shed from the bearing impinge on the outer chamber housing with different angles. The outcome of oblique collision between an oil droplet and the outer chamber housing determines the flow characteristic of wall oil film which has an important meaning to realize the rigorous lubrication design in the bearing chamber. However, the study of predicting the outcome of oblique collision between an oil droplet and solid surface is relatively rare. In this paper, an experimental setup about oil droplet–solid surface oblique collision and a numeric calculation model using Volume of Fluid (VOF) method have been built. And a lot of experimental work and numerical calculations have been done in a wide range of conditions. Based on that, a determination criterion is ultimately established for predicting the outcome of oblique collision between an oil droplet and solid surface. With the experimental data from literatures and this paper, the determination criterion is verified. The research work in this paper is not only a foundation work for better understanding the conditions of lubrication in bearing chamber but also an important reference for the study of droplet–solid surface collision.
The objective of this paper is to develop a multiple objective optimization procedure for crashworthiness optimization of circular tubes having functionally graded thickness. The proposed optimization approach is based on finite element analyses for construction of sample design space and verification; artificial neural networks for predicting objective functions values (peak crash force and specific energy absorption) for design parameters; and genetic algorithms for generating design parameters alternatives and determining optimal combination of them. The proposed approach seaminglesly integrates artificial neural networks and genetic algorithms. Artificial neural network acts as an objective function evaluator within the multiple objective genetic algorithms. We have shown that the proposed approach is able to generate Pareto optimal designs which are in a very good agreement with the finite element results.
Large spot welder is an important equipment in rail transit equipment manufacturing industry, but having the problem of low utilization rate and low effectlvely machining rate. State monitoring can master its operating states real time and comprehensively, and providing data support for state recognition. Hidden Markov model is a state classification method, but it is sensitive to the initial model parameters and easy to trap into a local optima. Genetic algorithm is a global searching method; however, it is quite poor at hill climbing and also has the problem of premature convergence. In this paper, proposing the improved genetic algorithm, and combining improved genetic algorithm and hidden Markov model, a new method of state recognition method named improved genetic algorithm–hidden Markov model is proposed. In the proposed method, improved genetic algorithm is used for optimizing the initial parameters, and hidden Markov model as a classifier to recognize the operating states for machining process. This method is also compared with the other two recognition methods named adaptive genetic algorithm–hidden Markov model and hidden Markov model, in which adaptive genetic algorithm is similarly used for optimizing the initial parameters, however hidden Markov model (in both methods) as a classifier. Experimental results show that the proposed method is very effective, and the improved genetic algorithm–hidden Markov model recognition method is superior to the adaptive genetic algorithm–hidden Markov model and hidden Markov model recognition method.
This paper presents a planar five-bar metamorphic linkage which has five phases resulting from locking of motors. Reconfigurable limbs are constructed by integrating the five-bar metamorphic linage as sub-chains. The branch transition of metamorphic linkage is analyzed. By adding appropriate joints to the planer five-bar metamorphic linkage, reconfigurable limbs whose constraint can switch among no constraint, a constrained force and a constrained couple are obtained. Serial limb structures that can provide a constraint force and a constraint couple are synthesized based on screw theory. Reconfigurable limbs that have five configurations associated with the five phases of the five-bar metamorphic linkage are assembled with 4-DOF (degrees-of-freedom) serial chains. A class of reconfigurable parallel mechanisms is derived by connecting the moving platform to the base with three identical kinematic limbs. These parallel mechanisms can perform various output motion modes such as 3T, 3R, 2T1R, 1T2R, 3T1R, 2T2R, 1T3R, 2T3R, 3T2R and 3T3R. Finally, the potential application of the proposed mechanisms is analyzed and conclusions are drawn.
A major challenge in studying impact problems analytically is solving the governing equations of impact events, which are mostly in the form of nonlinear ODEs. This paper focuses on the solution of nonlinear models for impact problems in asymptotic cases, where local indentation is significant. The asymptotic cases consist of both half-space and infinite plate impacts, which cover a wide range of practical impact events. A so-called force–indentation linearisation method (FILM), first described in a previous study, is reformulated here in a more general form in order to broaden its scope of application. The generalisation of the FILM facilitates stable and convergent solutions even when complex nonlinear contact models are used to estimate the impact force. Simulations based on the FILM approach are validated using numerical solutions.
This paper proposes the design of a wholly mechanical constant-force gripper that can accommodate the imprecise manipulation of brittle/delicate objects by the actuation. This was achieved by designing a constant-force mechanism as the jaw that allowed a constant force to be applied to the grasping objects regardless of the displacement of the mechanism. The constant-force mechanism is attached to the end effector of the gripper via a parallelogram mechanism which ensures that the jaws remain in parallel. The constant-force mechanism combines the negative stiffness of a bistable mechanism and the positive stiffness of a linear spring to generate a constant force output. By preloading the positive stiffness mechanism, the magnitude of the constant force can be adjusted to be as low as zero. The constant-force mechanism has been fully modelled and simulated using finite element analysis. A normalised force-displacement curve has been developed that allows to obtain the simplified analytical negative stiffness of the bistable mechanism. The design formulation to find the optimal configuration that produces the most constant force has been developed. Illustrated experiments prove the concept of the design although the discrepancies between finite element analysis results and testing results exist due to bistable beam manufacturing error.
In the present study, the effect of cryogenic treatment on the machining performance of Ti–5Al–2.5Sn alpha titanium alloy was investigated during electric discharge machining. Untreated, shallow cryogenically treated (–110 ℃), and deep cryogenically treated (–184 ℃) titanium alloys were machined by varying current and pulse-on-time. The machining performance was measured in terms of higher material removal rate and microhardness and low tool wear rate and surface roughness. The results showed a significant improvement in the machining performance with deep cryogenically treated alloy when compared with shallow and untreated alloy. Current and pulse-on-time also affected the machinability of titanium alloy. Higher material removal rate and microhardness were observed when titanium alloy was machined at high current and pulse-on-time. During machining, carbon was deposited on the machined surface due to the breakdown of hydrocarbon dielectric at high temperature thereby, affecting its properties.
The propagation characteristic of guided waves is important to acoustic emission nondestructive detection for the structural integrity of engineering components. The finite element method is introduced to study the propagation of guided waves in plate structure with different materials, cracks and coating metal. The displacement contours and wave curve at different receiving positions are examined first for the propagation characteristics of guided waves in plate structure with different homogeneous material of steel 45 and GCr15. Next, the interface reflection, refraction and diffraction characteristics of guided waves in plate structure with cracks and steel 45 with coating metal of aluminium 2024 are investigated. Finally, these FE results are compared with the mechanical pencil lead fracture experiment results. The results of this study clearly illustrate the accuracy and reasonableness of the finite element method to predict propagation characteristic of guided wave.
Backlash is a key internal excitation on the dynamic response of planetary gear transmission. After the gear transmission running for a long time under load torque, due to tooth wear accumulation, the backlash between the tooth surface of two mating gears increases, which results in a larger and irregular backlash. However, the increasing backlash generated by tooth accumulated wear is generally neglected in lots of dynamics analysis for epicyclic gear trains. In order to investigate the impact of backlash generated by tooth accumulated wear on dynamic behavior of compound planetary gear set, in this work, first a static tooth surface wear prediction model is incorporated with a dynamic iteration methodology to get the increasing backlash generated by tooth accumulated wear for one pair of mating teeth under the condition that contact ratio equals to one. Then in order to introduce the tooth accumulated wear into dynamic model of compound planetary gear set, the backlash excitation generated by tooth accumulated wear for each meshing pair in compound planetary gear set is given under the condition that contact ratio equals to one and does not equal to one. Last, in order to investigate the impact of the increasing backlash generated by tooth accumulated wear on dynamic response of compound planetary gear set, a nonlinear lumped-parameter dynamic model of compound planetary gear set is employed to describe the dynamic relationships of gear transmission under the internal excitations generated by worn profile, meshing stiffness, transmission error, and backlash. The results indicate that the introduction of the increasing backlash generated by tooth accumulated wear makes a significant influence on the bifurcation and chaotic characteristics, dynamic response in time domain, and load sharing behavior of compound planetary gear set.
This article studies the nonlinear vibration of a -shaped mass attached to a clamped–clamped microbeam under electrostatic actuation considering the effect of stretching. The DC and AC electrostatic force is applied to the horizontal part of -shaped mass. The dynamic solution is studied using two methods of modeling. In the first model, the -shaped mass is considered as a rigid body between two flexible microbeams. Then, the discretized equation of motion is derived using Lagrange’s equation combined with assumed mode method. The vibration mode shape of linear system is used as the comparison functions. In the second model, the dynamical effect of -shaped mass is modeled as a concentrated force and moment, and it is introduced in the equation of motion by the Dirac function. Afterwards, the equation of motion is discretized using Galerkin method. In both methods of modeling, the equations of motion are solved using two methods. The first method is approximate analytical perturbation and the other one is Runge–Kutta numerical method. The effect of geometrical dimension of -shaped mass on the nonlinear shift of resonance frequency and dynamic pull-in voltage is studied. The efficiency and accuracy of the presented formulations is verified by comparing the obtained results by two methods of modeling and two methods of solution.
The original formulation of the quasi-3D sinusoidal shear deformation plate theory (SSDPT) is here extended to the wave propagation analysis of viscoelastic sandwich nanoplates considering surface effects. The sandwich structure contains a single layered graphene sheet as core integrated with zinc oxide layers as sensors and actuators. The single layered graphene sheet and zinc oxide layers are subjected, respectively, to 2D magnetic and 3D electric fields. Structural damping and surface effects are assumed using Kelvin–Voigt and Gurtin–Murdoch theories, respectively. The system is rested on an elastic medium which is simulated with a novel model namely as orthotropic visco-Pasternak foundation. An exact solution is applied in order to obtain the frequency, cut-off and escape frequencies. A displacement and velocity feedback control algorithm is applied for the active control of the frequency through a closed-loop control with bonded distributed zinc oxide sensors and actuators. The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, magnetic field, viscoelastic foundation, surface stress, applied voltage, velocity feedback control gain and structural damping on the wave propagation behavior of nanostructure. Results depict that with increasing the structural damping coefficient, frequency significantly decreases.
This article develops an alternative approach in modeling a hysteresis using Preisach model. A Preisach model is demonstrated geometrically by an inverted triangle, namely Preisach triangle, which contains an amount of fundamental operators. In a conventional Preisach model, these fundamental operators are ideal relays. Consequently, there exists an inherently discontinuous jump between two consecutive relays. To resolve this problem, in this work, a generalized linear operator is used as the fundamental elements. Correspondingly, its representative Preisach triangle consists of numerous discrete elements whose weight concentrates just along their diagonal. With such approach, it is possible to predict the response of the model according to any input without the aid of numerical interpolation tools. In addition, in this work, to determine the elements’ weights of the model, two accurate identification methods corresponding to two schemes of experimentally biased and unbiased dataset are developed. At last, several simulations and experiments are conducted to assess the effectiveness of the proposed approach showing comparative results with conventional Preisach model.
The large face-shovel hydraulic excavator is one of the significant tools in mining, and widening its range of excavating and increasing its excavating force have been an important research trend. To realize that, this paper proposes a new type face-shovel hydraulic excavator which uses stick rockers and boom linkages to effectively increase the thrust and piston travel of stick hydraulic cylinders, with analyses of its kinematic and dynamic characteristics. The structure and constructional dimensions of the excavator are presented in detail. Based on the graphical modularization and the loop algebra theory, the forward and inverse kinematics as well as the workspace is examined, after which velocities and accelerations are analyzed. The dynamic mathematical model of the excavator is developed using Kane’s equations and the equivalence principle, and it is tested through the MATLAB simulations, with a comparison with those by ADAMS. It is concluded that with the new-type face-shovel hydraulic excavator, the excavating range can be broadened and the excavating force can be raised.
This study proposes a large-scale modular deployable mechanical network constructed by networking Altmann linkages, which are spatial single-loop mechanisms with six revolute joints and four bars, and develops a theoretical approach to verify the feasibility of the networking method. First, the screw motion equation of the linkage is derived, and the deployability of the linkage is demonstrated through a motion simulation. Second, using the overlapping-unit method, a deployable mechanical network is constructed. The constraint graph of the mechanical network is deduced subsequently. The mobility of the mechanical network is proved by screw theory, which demonstrates the feasibility of the networking method. Then, the motion of the mechanical network is simulated and it is found to have excellent deployability. Finally, a prototype of the mechanical network is fabricated. Results show that spatial single-loop linkages can construct modular deployable mechanical networks with the overlapping-unit method under appropriate connections. This networking method can be verified with the theoretical approach proposed in this work.
Non-resonant vibration-assisted machining involves the superposition of controlled vibrations onto traditional machining processes such as turning or milling. In this study, a novel variant of this technique has been investigated using an off-the-shelf piezoelectric actuator to create bespoke surface textures in a conventional milling machine. The purpose of these surfaces is to provide enhanced tribological performance by reserving lubricant, trapping and discharging debris and wear particles, and delaying the collapse of the full hydrodynamic lubricant film. Surface textures consisting of a repeating radial striation pattern of sine waves were reproducibly generated on the face of the disc work piece (an aluminium alloy AlSi1MgMn and a low-alloyed steel 16MnCr5) when the frequency of the superposed vibration was in phase with the rotational speed of the work piece. The texture parameters were controllable from approximately 1 mm to 8 mm in the wavelength and from a few microns to 25 µm in the peak to peak amplitudes which would reasonably cover the range of hydrodynamic lubrication film thickness.
It has been observed during the operation of the diesel engine fuel injection pump that the fuel and the lubrication oil leak through the working clearance between the piston and the cylinder bore and mix with each other. The leakage of lubrication oil to fuel (OtF) leads to injector nozzle coking and emission, which necessitates the automotive industry to design a robust fuel injection pump to meet stringent emission norms. Similarly, the leakage of fuel to lubrication oil leads to depreciation of lubrication property of the oil, thereby reducing the life of engine oil lubricated components. In this research, the leakage flow through this clearance gap was studied using the numerical simulation tool, Ansys CFX, to estimate the volume flow rate of lubrication oil to fuel and fuel to lubrication oil. Pressure and drag effects are two important mechanisms that drive the leakage process. The simulation was carried out for various design parameters such as clearance, clearance taper and speed, and experiments were performed to determine the lubrication oil to fuel and fuel to lubrication oil flow rates. The diluted samples collected from fuel and lubrication oil tanks were analyzed using ICP-AES (inductively coupled plasma – atomic emission spectrometry) for calcium and barium element tracing. Calibration was performed on the ICP bench to study the accuracy and repeatability of the test sample analysis method. The results of numerical simulations and experiments were compared for various design parameters. The proposed analysis could serve as a valuable aid in the fuel injection pump development process.
This article presents the linear stability analysis of an electrified liquid sheet injected into a compressible ambient gas in the presence of a transverse electric field. The disturbance wave growth rates of sinuous and varicose modes were determined by solving the dispersion relation of the electrified liquid sheet. It was determined that by increasing the Mach number of the ambient gas from subsonic to transonic, the maximum growth rate and the dominant wave number of the disturbances were increased, and the increase was greater in the presence of the electric field. The electrified liquid sheet was more unstable than the non-electrified sheet. The increase of both the gas-to-liquid density ratio and the electrical Euler number accelerated the breakup of the liquid sheet for both modes; while the ratio of distance between the horizontal electrode and the liquid-sheet-to-sheet thickness had the opposite effect. High Reynolds and Weber numbers accelerated the breakup of the electrified liquid sheet.
A kinematic optimization of a redundantly actuated parallel mechanism is developed via the Taguchi method to maximize the sum of energy efficiency and workspace. In the optimization process, the energy consumption in a representative pathway of a predefined workspace is used as the performance index of the energy efficiency. The horizontal reach and stroke, and the vertical reach of mechanism, are used for the performance index of the workspace. The kinematic parameters of a chain that was added to the proposed non-redundantly actuated parallel mechanism as an extension to achieve redundant actuation are selected as the controllable factors. The velocity of the end-effector is considered to be a noise factor. Because the Taguchi method was originally used for robust optimization, we can improve the energy efficiency and workspace under various velocities for the end-effector. In the first stage of optimization, the number of controllable factors is reduced, and their correlations are eliminated using a response analysis. Quasi-optimized results are derived after the second stage of optimization. The optimized redundantly actuated parallel mechanism result is validated by comparing the energy efficiencies and workspaces of the original and optimal redundantly actuated parallel mechanisms.
Next-generation exoskeleton and humanoid robots are expected to behave similar to the human neuro-muscular system to perform stable, flexible, and biomimetic movements. To achieve this goal, the variable stiffness actuators have been widely used in various robots. Using variable damping actuators along with variable stiffness actuators will be extremely beneficial for wide range of stable movements. Magnetorheological (MR) brakes are one of the most promising electromagnetic structures that can provide such variable damping in a relatively small actuator volume. In this paper, we focused on the design, characterization, selection and implementation of T-shaped, inner coil and outer coil multi-pole MR brakes to the ankle of an exoskeleton robot. Analytical models are developed using the magnetic circuit analysis to determine the braking torque. Then, magnetic finite element models are developed and coupled with an optimization algorithm to determine the optimal set of parameters of each MR brake design. Prototypes are manufactured in same size and tested experimentally to characterize the actuators’ torque-to-volume ratio, transient response, hysteresis, torque tracking, energy consumption, and damping performances. The performance comparison of the brakes showed T-shaped multi-pole MR brake design has superior characteristics compared to two other designs. Therefore, T-shaped multi-pole MR brake design is coupled with a variable stiffness actuator and implemented in an ankle joint of an exoskeleton robot and experimentally tested. The results show that the developed new hybrid robot joint is capable of stable movement with a simple control algorithm by changing its stiffness and damping independently.
In recent years, cellular lattice structures are of interest due to their high strength in combination with low weight. They may be used in various areas such as aerospace and automotive industries. Accordingly, assessment of their manufacturability, repeatability and mechanical properties is very important. In this paper, these issues are investigated for Polylactic Acid cellular lattice structures fabricated by fused deposition modeling. To do so, some benchmarks are designed and fabricated to find suitable processing parameters as well as the structural dimensions. In addition, to evaluate the mechanical properties of the lattice’s material, a number of tension and compression specimens are fabricated and tested. The material’s stress–strain curves reveal non-linear behaviors. These curves are not coincided in tension and compression which shows an asymmetric material behavior. To characterize the fabricated cellular lattices, they are tested in compression, and the deformation mechanisms of the structures are analyzed. To investigate the correlation between the bulk material and the material of the ligaments, a solid finite element model is developed to predict the stress–strain response of the lattice. The obtained result shows a reasonably good correlation between the model and experiments.
Two types of clapboard-type lead dampers were designed based on plastic energy absorption of lead metal. The hysteretic curves and energy dissipation properties were studied through low cyclic loading test. Also, the typical restoring load model was extracted. The finite-element numerical model of type-A damper was build according to the characteristics and principle of clapboard-type lead dampers. And the damping effect of high-structural Benchmark model installed with type-A damper was analyzed. The results show that the structure of clapboard-type lead dampers is simple, hysteretic curves are plump, hysteretic properties are steady and yield displacement is small, and thus its energy dissipation ability is excellent. The models of finite element and restoring load of dampers are in good agreement with the results of tests, so they have good applicability. The seismic system installed with type-A dampers has an excellent vibration reduction effect. The top-floor acceleration and displacement control effects are 26.7% and 37.4%, respectively.
We study the contact between a rigid flat punch and an elastic half-space using Coulomb friction for a normal load followed by a tangential load applied at a certain height above the interface line. The study is inspired by recent experiments by the group of Jay Fineberg in Israel. Three regimes are found in the evolution of slip at the interface depending on a dimensionless parameter
A novel serial–parallel kinematic machine based on a serial–parallel manipulator is proposed and its kinematics and statics are studied systematically. First, the concept of serial–parallel kinematic machine formed by the 3-PRS parallel manipulator and the 2-UPR + SPR PM is proposed. Second, the displacement is derived in close form based on the geometrical and dimensional constraints existed in the serial–parallel kinematic machine. Third, the Jacobian, velocity and statics of the serial–parallel kinematic machine are derived in the explicit and compact form. Finally, the formulas for solving the acceleration of this serial–parallel kinematic machine are derived. This research will lay a good foundation for the development of the serial–parallel kinematic machine.
A novel gear transmission with double circular arc-involute tooth profile is studied in this paper. The generation principle and mathematical models of this proposed gear drive are provided based on gear geometry. The meshing characteristics of tooth surfaces are evaluated according to the analyses of motion simulation, mechanics property and sliding coefficient. The transmission efficiency experiment is based on the developed gear prototype, and a comparison with an involute gear drive is presented. The further study on dynamics analysis and key manufacturing technology will be conducted, and this new type of gear drive is expected to have excellent transmission performance.
This article proceeds with investigations on a 5 MW direct-drive floating wind turbine system (FWTDD) that was developed in a previous study. A fully integrated land-based direct-drive wind turbine system (WTDD) was created using SIMPACK, a multi-body simulation tool, to model the necessary response variables. The comparison of blade pitch control action and torque behaviour with a similar land-based direct-drive model in HAWC2 (an aero-elastic simulation tool) confirmed that the dynamic feedback effects can be ignored. The main shaft displacements, air-gap eccentricity, forces due to unbalanced magnetic pull (UMP) and the main bearing loads were identified as the main response variables. The investigations then proceed with a two-step de-coupled approach for the detailed drive-train analysis in WTDD and FWTDD systems. The global motion responses and drive-train loads were extracted from HAWC2 and fed to stand-alone direct-drive generator models in SIMPACK. The main response variables of WTDD and FWTDD system were compared. The FWTDD drive-train was observed to endure additional excitations at wave and platform pitch frequencies, thereby increasing the axial components of loads and displacements. If secondary deflections are not considered, the FWTDD system did not result in any exceptional increases to eccentricity and UMP with the generator design tolerances being fairly preserved. The bearing loading behaviour was comparable between both the systems, with the exception of axial loads and tilting moments attributed to additional excitations in the FWTDD system.
Few interface systems designed to control continuum robots have been developed. This work presents a master device for multi-unit continuum robots. The master mechanism has the same kinematic structure as the slave device. The kinematic structure, which uses a spring as a backbone, allows for a unique forward kinematic solution. This design is slim-sized, light-weight, and easy to implement. As an example mechanism, a continuum unit with two degrees of freedom was developed. Two-unit modules were assembled to generate four degrees of freedom. The performance of the master device is verified through a master-slave control experiment.
Performance degradation feature extraction is the basis of degradation condition recognition and remaining service life prediction. In this paper, morphological corrosion operator is introduced into mathematical morphological particle analysis (abbreviated as MMP), proposing a new analytical method named generalized mathematical morphological particle analysis (abbreviated as GMMP). On this basis, a new approach for degradation feature extraction based on generalized pattern spectrum entropy (abbreviated as GPSE) is proposed taking GMMP and information entropy as the theoretical foundation. In this approach, GPSE is calculated as degradation feature parameter in describing performance degradation degree of machinery equipment. Simulation analysis is processed, and the result shows that the value of GPSE will increase correspondingly along with the deepening of the degradation degree and the relevance between GPSE and degradation degree is stable. The effectiveness and practicality of the approach is tested through rolling bearing whole lifetime vibrating data. Rolling bearing fatigue life enhancement testing was carried out in Hangzhou Bearing Test & Research Center, getting the whole lifetime data which is able to cover each degradation condition from normal to invalidation. The approach is applied into analysis of rolling bearing data and the results verify its validity and feasibility.
The effect of a seal device on the performance of aeroengines is obvious. As well as the complicated operating state of aeroengines also has important influence on seal device performance. Finger seal is a new seal device, which has been extensively studied recently. However, so far there is little work about finger seal’s dynamic performance considering work status. For this reason, finger seal’s dynamic performance considering work status is proposed using equivalent dynamic model with distributed mass in this paper. The effects of the precession and nutation incline of rotor on the finger seal’s performance are investigated. Meanwhile, density and preparation direction of fiber bundle have influence on its dynamic performance and that is studied under the rotor precession incline. Based on this, it is shown that the effect of rotor precession incline on the finger seal dynamic performance is obvious, thus it is necessary to consider the effect of the factor on finger seal dynamic performance. The present work is conducive to promote dynamic analysis technology of finger seal to engineering application, and also improve the theoretical research system and methodology of finger seal.
Product service system is one new production paradigm for manufacturing enterprises to cope with fierce market competition in service economy environment. Product modularization is an important part of product service system development. In this paper, the design process model of product service system is built on the basis of current product service system modeling methods. Guided by lifecycle-oriented modular design idea, the product function is decomposed and the function units are obtained, which correspond to specific parts in the product. Using fuzzy C-means clustering algorithm based on simulated annealing and genetic algorithm for clustering analysis, the division scheme of product modules is got. Lifecycle-oriented product modular design method pays more attention to environmental attributes of the product, and considers the consciousness of environmental protection and sustainability in product design well. Using CNC machine tools as an example, this paper verifies the reliability, rationality and superiority of presented product module division method oriented on CNC machine tools.
The article deals with the design, modeling, and simulation of an innovative four-wheel steering system for motor vehicles. The study is focused on the steering box of the rear wheels, which is a cam-based mechanism, while the front steering system uses a classical pinion—rack gearbox. In the proposed concept, the four-wheel steering aims to improve the vehicle stability and handling performances by considering the integral steering law, which is formulated in terms of correlation between the steering angles of the front and rear wheels. In this regard, a double-profiled cam is designed, in correlation with the input motion law applied to the steering wheel. The cam profile dictates (prescribes) the translational movement of the rear follower, which is connected to the left and right steering tierods, turning—as appropriate—the rear wheels in the same direction (for stability) or in opposite (for handling) to the front wheels. The cam-based mechanism is able to carry out complex motion laws, providing accurate integral steering law. The dynamic modeling and simulation of the four-wheel steering vehicle was performed by using the Multi-Body Systems package Automatic Dynamic Analysis of Mechanical Systems of MSC.Software, the full-vehicle model containing also the front and rear wheels suspension systems, as well the vehicle chassis (car body). The dynamic simulations in virtual environment have resulted in important results that demonstrate the handling and stability performances of the proposed four-wheel steering system by reference to a classical two-wheel steering vehicle.
The bearing fault diagnosis is of vital significance in maintaining the safety of rotation machine. Among various fault detection techniques, the diagnosis based on vibration signal is widely applied in monitoring the condition of rotation machine. Variational mode decomposition (VMD) is a novel signal analysis method, which can decompose a multi-component signal into a certain number of band-limited intrinsic mode functions (BLIMFs) nonrecursively. VMD could overcome some problems such as mode mixing, the inference of noise, the determination of wavelet base, which exist in empirical mode decomposition, ensemble empirical mode decomposition, wavelet transform, respectively. However, the empirical selection of the parameters for VMD would affect the result of the decomposition. This paper presents an adaptive VMD method with parameter optimization for detecting the localized faults of rolling bearing. Kurtosis, sensitive to transient impulsive components, is employed as optimization index to evaluate the performance of the VMD. Two parameters in the VMD, namely the number of decomposition modes and data-fidelity constraint, are optimized synchronously based on the kurtosis index through artificial fish swarm algorithm. Executing VMD with the acquired parameters, the optimal BLIMF is obtained. The spectrum analysis of the optimal BLIMF could identify the characteristic frequency caused by the localized crack effectually. The validity of the proposed method is proved by means of a cyclic transient impulse response signal and two experiments with practical vibration signals of rolling bearings. Compared to several existing methods, the proposed method demonstrates reinforced results.
In this paper, modeling and vibration control of a strain-gradient clamped-free Euler–Bernoulli micro-beam exposed to varying disturbance is studied. A strain-gradient model of the Euler–Bernoulli micro-beam is represented in this paper and consisted of one partial differential equation and six ordinary equations as governing motion equation and boundary conditions, respectively. A boundary controller is proposed to suppress the system’s vibration. The controller is derived based on the direct Lyapunov method. An adaptation law is devised to assure system’s stability under parametric uncertainties. With the proposed adaptive robust boundary control, uniform boundedness under environmental and input disturbances could be achieved. The state of the system is proven to converge to a small neighborhood of zero by appropriately choosing design parameters. Simulations are provided to illustrate the applicability and effectiveness of the proposed controller.
Metamodel-based crashworthiness optimization is an expensive and highly nonlinear design problem. Due to the lack of finite element simulations, the responses fitted by different metamodeling methods are not fully equivalent to the real responses. The metamodel error may induce to find a local or an infeasible design solution. Compared to the traditional one-step sampling DOE method, the objective-oriented sequential sampling strategies have been demonstrated as a higher efficient way to find the true optimum design. However, existing infilling criteria of the sequential sampling methods are restricted to specify the number of the sequential samples obtained in each iteration. It is not practical for the real engineering optimization applications. In this paper, a new adaptive multi-point sequential sampling method is developed. The sequential samples obtained in each iteration are determined by the prediction states of the fitting metamodels. To demonstrate the benefits, the new proposed method is applied to a high-dimensional and highly nonlinear frontal crashworthiness optimization problem. Results show that the proposed method can mitigate the effect of the metamodel prediction error and more efficiently find the global design solution compared to the conventional approach.
Dynamic properties of the whole broaching machine structure greatly contribute to the broaching quality and efficiency. However, it is hard to measure the dynamic parameters because they will change during operation compared with the static results from classic experimental modal analysis. This study is to examine the dynamic parameters of broaching machine LG7120KT using both the numerical finite element (FE) method and the experimental operational modal analysis (OMA). Firstly, FE analysis model of the broaching machine with the real dimension is constructed and calculated. Second, experimental results are obtained from OMA in practical broaching process, which can be used to identify steady-state modes. Modal parameters including mode shapes, damping ratio, and natural frequencies are examined, using both LMS SCADAS III-305 system and PolyMAX method in OMA. The numerical and experimental results show high agreement in their calculated natural frequencies. From the modal analysis results, it is also found the vibration normal to cutting direction can be greatly reduced by adjusting broaching speed. From the topology optimization result based on the already correlated FE model, we redesigned a lightweight machine structure with a better dynamic performance, due to its lower displacement of broaching machine at force point and its higher first-order natural frequency. The experimental and numerical results in this paper help to design the structural parameters of broaching machine and propose a better broaching process.
This paper introduces a new signal processing algorithm for vibration-based fault detection and diagnosis of roller bearings. The methodology proposed in this paper is based on the combination of two data-adaptive techniques which are further enhanced through the use of an automatic feature identification mechanism. The new technique, introduced as empirical mode envelope with minimum entropy, combines elements from the empirical mode decomposition (EMD) and minimum entropy deconvolution (MED) approaches with an energy moment technique to improve the feature selection stage of the EMD algorithm. This improvement allows the processing chain to identify early stage roller bearing faults in noisier signals. The energy moment technique is used to automatically identify the most appropriate intrinsic mode function from the EMD process prior to the MED algorithm being applied. This is in contrast to conventional approaches which tend to use the first mode or make selections based on traditional energy techniques. The combination of the adaptive techniques of EMD and MED allows the development of an improved technique for fault detection and diagnosis of signals. Combining these techniques with the energy moment approach allows further improved fault detection in complex non-stationary conditions. The processing chain has been tested using data obtained during laboratory testing. From the experimental results, it is shown that the new technique is capable of the detection of early stage (minor) roller and outer race defects found in tapered-roller-bearings rotating at a variety of speeds and noise scenarios.
Ensemble empirical mode decomposition (EEMD) represents a valuable aid in empirical mode decomposition (EMD) and has been widely used in fault diagnosis of rolling element bearings. However, the intrinsic mode functions (IMFs) generated by EEMD often contain residual noise. In addition, adding different white Gaussian noise to the signal to be analyzed probably produces a different number of IMFs, and different number of IMFs makes difficult the averaging. To alleviate these two drawbacks, complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) was previously presented. Utilizing the advantages of CEEMDAN in extracting weak characteristics from noisy signals, a new fault diagnosis method of rolling element bearings based on CEEMDAN is proposed. With this method, a particular noise is added at each stage and after each IMF extraction, a unique residue is computed. In this way, this method solves the problem of the final averaging and obtains IMFs with less noise. A simulated signal is used to illustrate the effectiveness of the proposed method, and the decomposition results show that the method obtains more accurate IMFs than the EEMD. To further demonstrate the proposed method, it is applied to fault diagnosis of locomotive rolling element bearings. The diagnosis results prove that the method based on CEEMDAN may reveal the fault characteristic information of rolling element bearings better.
This paper applies a numerical approach to improve the understanding of reaction to various inflow conditions for the compressor system and the mechanism of stall inception under rotating inflow distortions. Full annulus, unsteady, three-dimensional computational fluid dynamics has been used to simulate an axial low-speed compressor operating under rotating distorted inflow conditions. The development of the flow through the rotor is then explained in terms of the redistribution of the flow field and the process of stall inception. The results suggest that the increased flow incidence close to the tip region under co-rotating inflow distortion plays an important role on the stall inception process. The presence of a strong modal wave is observed under co-rotating inflow distortions. This leads to a significant impact on the loss of stall margin, as compared with other distorted inflow conditions. There is a significant peak in the flow coefficient at stall for co-rotating inlet distortion. It can be interpreted as a resonant behavior of the compressor under a strong interaction between the flow field and inlet distortion. It indicates that the stall inception is triggered by the perturbation of the rotating distorted inflow through the long length scale disturbances.
The formation mechanism of linear macro-segregation in Al–Cu–Mn–Ti alloy cylindrical shell casting was studied by characterizing samples by X-ray detection, microscopic examinations, composition analysis, and simulation of the heat transfer of Al–Cu–Mn–Ti alloy cylindrical shell casting in the solidification process. Numerical and experimental results indicated that linear macro-segregation always occurred in the portion of casting connected with the slit gating system, because of the great hot tearing tendency, the hot cracks formed could be fed by the melt through the slit gating system with an excellent temperature gradient and feeding angle. According to significant effect of floatation of lower density α-Al grains, the solute gradient was formed along the vertical direction of the slit gating system. The hot cracks near the bottom of casting were fed by melt with high concentration of Cu and so, they were cicatrized by the eutectic structure/α-Al + Al2Cu at a temperature of 548℃.
In shipyard, triangle heating technology with irregular multi-heating paths and highly concentrated heat input is used to form a curved plate, especially a concave type plate. Compared with line heating process with simple line segment path, its main purpose is to get a bigger contraction deformation at the plate edge. Hence, triangle heating technology is important for most shipyards to increase hull-forming productivity and study the automation. This paper focuses on the moveable triangle induction heating technology. An electromagnetic coupling finite element model is built to simulate the moveable triangle induction heating process and reveal the temperature characteristics and deformation behavior. The results of the simulation are compared with those obtained from experiments and show good agreement. It demonstrates that the numerical model used in this study is effective for simulating triangle heating for the steel plate forming process in shipbuilding. With the numerical model, the paper further investigates the effect of heating parameters on temperature and shrinkage deformation. These are traced here with a modified mechanical model whose results are in accord with the numerical results. This modified model can be applied to predict the edge shrinkage and explain the effect of heating parameters on transverse shrinkage.
In this paper, a new volumetric heat source model is developed for predicting the weld bead geometry during plasma arc welding of thin sheets of titanium alloy. Numerical simulations are carried out with the proposed parabolic Gaussian heat source (PGHS) model and already prevailing familiar heat source models namely, conical heat source and modified conical heat source, using finite element package COMSOL. The temperature-dependent material properties for Ti–6Al–4V alloy are considered for performing numerical calculations, which tend to influence the temperature fields while computing. Besides, the effect of trailing gas shielding, latent heat, and radiative and convective heat transfer are taken into account while performing the transient thermal analysis which significantly alters the sensitivity and accuracy of the model. Experimental trials on thin titanium alloy sheets are carried out to enable the validation of the proposed PGHS model. Subsequently, the outcome reveals that the PGHS model is capable and proved its high degree of efficiency in predicting the weld bead geometry more accurately than the existing heat source models. The distribution of heat intensity along the thickness of thin sheet is observed to be parabolic as predicted by the proposed model. The prediction appears to have a good correlation with the experimental result and it is clearly perceptible that the parabolic shape is more reliable and yields greater accuracy of the proposed heat source model.
This paper aims at obtaining the mathematical model of the general spiral bevel gears of local bearing contact from spatial conjugate curve theory. Differential geometry and gearing kinematics are introduced to derive this model. Meshing-correctly conditions are set in the theoretical derivation process. The final model is represented in the form of equations and inequalities. According to the arguments in this paper, a process of designing the tooth surface of spiral bevel gears of local bearing is proposed. Based on this process, the numerical example of a pair of these gears with specific profiles is represented by applying the finite element analysis. Results show that the magnitudes of the deviations between theoretical contact points and real contact points are small. Therefore, the results agree with the mathematical model of the spiral bevel gears of local bearing contact in this paper.
Selection of optimized assembly sequence is significantly essential to achieve cost-effective manufacturing process. This paper presents a novel efficient methodology to generate cost-effective feasible robotic assembly sequences though concatenation of parts. Part concatenation process will be followed with liaison predicate test and feasibility predicate test. A unique method called bounding box method is described to test the feasibility predicate efficiently in the computer-aided design environment. Assembly indexing technique is proposed to filter the redundant assembly subsets with high energy in order to minimize the computational time. The cost of collision free assembling operation is considered by the weight and distance traveled by the part in the assembly environment to join with the mating part. The method is successful in finding feasible optimal assembly sequence without ignoring any possible assembly sequence and found to be efficient in solving computer-aided assembly sequence generation. The correctness of the methodology is illustrated with an example.
The isotropic property at home configuration for a semi-regular Stewart platform manipulator with equal leg lengths has been found to be nonachievable by kinematic design optimization study. In this context, a new approach of design optimization has been formulated here for achieving semi-isotropicity through variable transformation that has rendered the constrained optimization over a finite workspace to infinite workspace in the transformed domain. The proposed minimization methodology of a positive definite function for all the angular and translational motion has exhibited strong convergence to zero for values of the design parameters that can be worked out as a closed-form solution only for the cases of linear translation. Finally, the variations of the condition number over the permissible range of all single-degree-of-freedom motions have been carried out. The absence of any other minima in the entire workspace has clearly established the home position as globally optimized.
This paper proposed a novel double-row radial piston pump. In this pump, the transformation from the rotation of the shaft to the reciprocation of the piston is realized by a pentagon mechanism, and the oil is distributed by check valves, which are integrally designed on the pump body. Theoretical calculation demonstrated that this improved design can substantially reduce the force on the main shaft of pump. The formulas of instantaneous flow rate and fluctuation coefficient of the pump are deduced. For studying the working characteristics of the pump further, a prototype was manufactured and tested. Results show that when the rotation speed is over 125 r/min, the performances of pump prototype are qualified, the fluctuation rate is limited to 20% and the volumetric efficiency can reach 90%. Moreover, the pump was disassembled after 100 h of service and the wear condition was checked. Except for the pentagon which has indentation on the surface, the components of the pump are all kept intact.
Gas–solid beds are ubiquitous in industrial and energy production applications. Examples include fluidized beds, which are used in many systems such as in integrated gasification combined cycle power plants or in chemical looping systems. These examples and others involve complicated interactions between each phase of reactants in the system. The motivation of this work stems from the need for a better understanding of bed hydrodynamics in existing energy systems; results from this work can be used directly in software such as Fluent to more accurately predict flow behaviors of gas and solid phases. The experimental data are collected from two setups including an optically accessible drag measurement facility that was used to obtain the drag coefficient at various particle Reynolds numbers and a lab-scale gas–solid packed bed which was used to validate the computational correlation through pressure drop measurements across the packed bed. Results showed that the new correlation predicted drag coefficients as accurate as 10% and deviated by up to 15% for particles with sphericities less than 0.9. This is a significant improvement compared to existing correlations, which can deviate as much as 50% for the same range of tested values. Similar findings are observed when the drag correlation is implemented into Fluent. It was found that the model predicted pressure drop in a particle bed with nonspherical particles with an error as low as 5% and as high as 28% near the fluidization velocity.
Two-level contact problem is proposed to study the effect of roughness of elastic coatings. The solution is based on using a function of additional displacements in a macrolevel contact problem formulation. The dependence of additional displacements on nominal pressure is obtained from consideration of a periodic model of roughness. Analytical–numerical method, which is based on Hankel integral transforms, boundary elements, and iteration procedure, is used to find macrocontact characteristics. The influence of the parameters of microgeometry on contact characteristics at macroscale is analyzed.
A new harmonic drive model considering the geometry, internal interactions and assembly error of key parts is proposed in this paper. In this model, a single tooth pair is used to represent the transmission mechanism of harmonic drive. The meshing stiffness between the flexspline and the circular spline, the torsional stiffness of the flexspline cylinder, and the radial stiffness of the thin-walled ball bearing are included and formulated. The kinematic error is fitted using a low-velocity test, and its generating mechanism is analysed. The friction of the harmonic drive is formulated at the tooth meshing section and at the ball bearing, where its parameters are identified based on experimental results. Based on the new model, velocity step simulations are conducted. For comparison, velocity step experiments at eight different velocities from 60 to 3000 r/min are performed, and the simulation results are in good agreement with the experimental results. The new model reveals the dynamic behaviour of the harmonic drive system; therefore, it will be useful for the dynamic design and precision control of harmonic drive systems.
An optimum design of variable input speed for the Geneva mechanism is aimed at improving the kinematic performance of the traditional Geneva mechanism by eliminating infinite angular jerks and reducing the peak angular acceleration of the Geneva wheel during the indexing motion. The normalized angular velocity and acceleration of the Geneva wheel corresponding to the normalized time are introduced. A polynomial function of the normalized time is used to describe the normalized angular position of the crank, and therefore, the corresponding polynomial coefficients are considered as the design variables. The optimum design task is very specialized and difficult to solve with some evolutionary and swarm optimization methods because of the extremely large range for the value of the design variable, arising from the utilization of a higher order polynomial for the normalized time parameter with a value between 0 and 1. A new evolutionary algorithm termed teaching-learning-based optimization comprises a teacher phase and a learner phase. In the teacher phase, the entire population can be gradually shifted to a more promising region, which may be very far from the relatively small initial region. The obtained optimal results are compared with those obtained using the length-adjustable deriving link method discussed in the literature. The findings show that the difference in the effectiveness of the variable input speed method and the length-adjustable driving link method for the reduction of the peak angular acceleration of the Geneva wheel is small.
Utilization of full potential of electrochemical machining (ECM) is not yet achieved because of its lack of accuracy, difficulty in proper tool design and control of parameters. The enhancement of performance of ECM is still a subject of concern in this modern manufacturing world. In this work, low frequency vibrating tool assisted by a magnetic flux was used as an efficient hybrid technique in ECM for improving material removal rate (MRR) and surface roughness (Ra). This paper presents a development of mathematical model correlating MRR and Ra with machining conditions such as voltage, electrolyte concentration, and inter-electrode gap. The significance of ECM process parameters has been investigated using contour plots. The inter-electrode gap (IEG) is considered slightly higher than the maximum tool amplitude that otherwise leads to tool damage. Results indicate that magnetic flux-assisted vibrating tool increases the MRR from 10% to 96%. A magnetic flux-assisted vibrating tool in ECM facilitates and drives out the sludge in the IEG to improve the machining performance. MRR is enhanced due to the movement of ions triggered by magnetic flux, which assures an increase in anodic current. A slight increase in Ra was also noted in comparison to machining with aqueous NaCl electrolyte alone.
The objective of this paper is to investigate the operation of a mono-tube damper through the application of Computational Fluid Dynamics analysis to the piston and flows through a series of flexible shims which cover exits of the piston orifices. The shims and orifices combine to form a system of variable area flow paths of the damper in parallel with the permanent bleed orifices. Shim stack stiffness characteristics were obtained using experimental and Finite Element techniques. The deflection characteristics were non-linear and were highly dependent upon small gaps present between shims and the restraining bodies. With the nature of the shim deflection being highly complex the computational fluid dynamics models investigated the shim deflection using a global uniform displacement method and also a more representative displacement based upon the finite element shim modelling. It was observed that the global displacement models allowed radially inward flow to establish and also overpredicted pressure drops. Finite element analysis of the shims allowed accurate representation of flow paths to be simulated which closely matched experimental and mathematical predictions. The computational fluid dynamics analyses showed that the discharge velocity for the global shim offset is greater than that from a variable shim deflection calculation. The damper pressure drop is highly dependent upon the shape of the flow path formed by the shim deflection. The presence of sharp direction changes through the piston and valve assembly leads to increased damping rates and piston pressure drops.
Experimental and numerical investigations on the effect of deflecting rings featuring different axial lengths on aerodynamic performance of the small axial flow fan were conducted under the condition of maximum flow rate. Two deflecting rings, the semi-open type and closed type, were investigated. Aerodynamic and aeroacoustic performances have been measured in experiment, and key analysis of flow was based on computational fluid dynamics results. The numerical and experimental results show that the deflecting ring has great influence on the performance of an axial flow fan. For the semi-open-type deflecting ring, the fan has better P-Q performance and higher efficiency; pressure, vorticity, and vorticity gradient distributions on the blade surface are more uniform; and noise level of the fan is lower at wider frequency bands. For the closed-type deflecting ring, the performance curve has a convex feature; blade pressure difference between the pressure surface and the suction surface is much bigger. The result shows that better aerodynamic and aeroacoustic performances of the axial flow fan can be acquired when the semi-open-type deflecting ring is adopted.
The thickness of the plate in temperature gradient rolling is first divided into 2 m elements, and m is an undetermined parameter which can be limited. Based on these thickness elements with different temperatures, the rolling force of this advanced process is first analyzed with slab method. Also the predictions of thickness ratio with different temperatures and reductions of each thickness elements are proposed in this paper. The results measured after rolling experiments are used to compare with these calculated by this model in order to verify its accuracy. In the experiment, a multi-metals riveting plate in the same temperature is designed to simulate a single metal one in gradient temperatures based on the thickness elements. Since the model is based on an analytical method which is strongly supported by the rolling theories, it can be applied in real gradient temperature rolling for ultra-heavy plate.
Structural elements like bars, trusses, beams, frames, plates, and shells have long been used in structures and machines because of their large stiffness-to-weight ratios. The Euler–Bernoulli theory for beam elements is currently used in a wide range of engineering fields. Frames may essentially be considered to be a type of general beam with axial loads. In the analysis of a right-angle frame, the stiffness of a corner has been assumed to be infinite, which is allowable only when the frame is sufficiently slender. However, a comparison of the results of a finite element analysis showed that the assumption of rigid corner stiffness is unacceptable for most cases because of the considerable errors that result. To resolve this problem, we assumed that the stiffness of a corner in a right-angle frame was finite, which is mostly the case, and solved the problem of a right-angle frame with round corners under internal pressure. Using the derived formula based on the assumption of finite corner stiffness and the formula for the round corner stiffness, we analyzed the entire right-angle frame structure and compared the results to finite element analysis results. As a final attempt, the quasi-optimal dimension of the corner was found to exhibit the lowest von Mises equivalent stress. This proposed approach could be applied to many problems involving frames with various boundary conditions to improve the accuracy.
Pressure pulsation of an aircraft piston pump and accompanying vibrations are often sources of unreliability and fatigue of an aircraft hydraulic energy system. To reduce discharge pressure pulsation, a buffer bottle is usually installed inside the pump for space consideration that generally restricts its chamber volume resulting in a high working frequency range usually well exceeding the pressure pulsation frequencies corresponding to the normal operating speed range of the pump and hard to be adjusted once installed. To meet this challenge, this paper presents a method for designing a multi-element buffer bottle as an integrated fluid filter network formed by sub-elemental circuits (consisting of orifice, pipe and T-off) that can be assembled in an aircraft piston-pump. This design method of a compact fluid filter network is illustrated with a practical example based on a multi-element buffer bottle. Based on impedance models, results of an in-depth numerical investigation analyzing the effects of different buffer-bottle designs, geometrical parameters and adjustable orifice dimensions on pressure pulsation attenuation are discussed. The method for tuning the operating resonant frequency of a multi-element buffer bottle for pressure attenuation using a changeable orifice diameter is demonstrated experimentally confirming the buffer bottle as an attractive alternative to the conventional methods based on large-volume chambers.
In this paper, a new objective function named circular proximity function (CPF) is proposed for the synthesis of four-bar motion generator linkages. This function is designed to measure the similarity of a group of points in Cartesian space to a circular curve. This function lowers the number of optimization variables to only two variables reducing the computational cost significantly. The optimization process has been carried out by the method of Differential Evolution (DE). Four case studies have been investigated in this study to demonstrate the advantages and disadvantages of the proposed method.
Data-driven approaches have been proved effective for remaining useful life estimation of key components (bearings for example) in rotating machinery. In such approaches, it is important to determine an appropriate degradation indicator from the collected run-to-failure life cycle data. In this paper, a new degradation indicator is introduced based on the joint approximate diagonalization of eigen matrices algorithm. First, a matrix consisting of time domain, frequency domain, and time–frequency domain features extracted from the collected data instances is created. Then a two-layer joint approximate diagonalization of eigen matrices is introduced to transform the matrix to the advanced features (a vector) that represents the behavior of the bearing’s degradation. As an independent component analysis method, the designed two-layer joint approximate diagonalization of eigen matrices is able to eliminate the redundancy of the directly extracted features. Further, the obtained vector is input into an extreme learning machine to train a remaining useful life prediction model. Finally, a set of experimental cases are utilized to verify the presented method. Results show that the two-layer joint approximate diagonalization of eigen matrices is capable of exploring features that reflects the trend of bearing’s degradation state much better. And due to the easy parameter configuration and fast learning speed, the extreme learning machine is capable of training a model that can effectively predict the remaining useful life of the bearings.
During the composite winding process, pressure fluctuation will affect the density and homogeneity of the products and will make the interfacial strength disaccord with the fiber volume fraction. In order to improve the guiding precision and stability of the winding pressure, the bearing guide is replaced by the rolling guide in designing the pressure guiding mechanism, and parametric model of the guiding mechanism is established based on dynamics experiment of the joint surfaces. By analyzing the modal and harmonic response, the corresponding measures for improvement are proposed. Experimental results show that the designed guiding mechanism based on the rolling guide has high precision and perfect stability. Additionally, roundness error and installation error of the mandrel can cause the winding pressure to fluctuate and the gas compressibility, nonlinear flow, dead zone, cylinder friction, measurement noise and other nonlinear disturbances have significant impact on the pneumatic pressure control system. Considering the above circumstance, an adaptive fuzzy proportional–integral–derivative (PID) controller based on the grey prediction is proposed. By predicting the output pressure, trend of the pressure signal can be reflected accurately, which provides a reliable basis for the decision-making of the fuzzy PID controller. Simultaneously, two separate fuzzy inference systems are employed to adjust the step length of the predictive control and the scale factor of the step self-tuning algorithm. Simulation and experimental results show that the fuzzy PID controller based on grey prediction has shorter settling time, smaller overshoot and error, stronger robustness and interference immunity. The designed guiding mechanism and control algorithm have effectively improved the precision and stability of the pressure control system for the composite materials winding formation.
Numerical analysis of combined heat and power plant consisting of a solid oxide fuel cell and autothermal gasification system has been made for several cases of different composition of fuel relevant to air and steam blown biomass gasification process. Wet wood is fed to the fixed-bed downdraft gasifier and gaseous fuel is produced then after gas cleaning and conditioning can be used in solid oxide fuel cells. The integrated plant is investigated by thermodynamic modeling combining a one-dimensional model of direct internal intermediate planar type solid oxide fuel cell which allows monitoring the temperature gradients along the cell length in different operating conditions and a zero-dimensional autothermal gasifier. The solid oxide fuel cell mathematical model is developed based on gas species mass balances, energy balance, and an electrochemical model beside the kinetics describing internal reforming and water-gas shift reactions. Such a model can be integrated with adiabatic gasification modeling which includes atom balance conservation for assumed gas species and a modified thermodynamic equilibrium analysis. Both gasifier and solid oxide fuel cell models are verified against experimental and previous numerical data available in the literature. Two main parameters, namely modified equivalence ratio and air-to-steam ratio are investigated and the most important cycle parameters such as power, electric and combined heat and power efficiencies, temperature gradients along the cell length, and mole fractions of gaseous species of the produced fuel are analyzed. It has been revealed that any increase in air-to-steam ratio at fixed modified equivalence ratio leads to penalty on cold gas efficiency of the gasifier and both solid oxide fuel cell and combined heat and power plant electric efficiencies. Increased air-to-steam ratio at constant modified equivalence ratio produces a mixture with lower low heating value, higher steam-to-carbon ratio, rich in CO and lower in CH4 content. Under this condition the operating temperature of the cycle and solid oxide fuel cell increases and consequently improves the operating voltage of the cell and combined heat and power efficiency of the plant. On the other hand, results show that gasification with increased modified equivalence ratio at constant air-to-steam ratio produces mixtures richer in CH4 and CO, poorer in H2 with higher low heating value and cold gas efficiency, and lower steam-to-carbon ratio. Such condition improves the electric efficiency of the solid oxide fuel cell and the integrated plant, but the combined heat and power efficiency of the cycle decreases due to decreased operating temperature of the solid oxide fuel cell and the cycle.
The rotational self-loosening of bolted joints under cyclic loading is a process, which means a screw rotation against the assembly direction by periodic load cycles. Thus, the preload balance is released and the clamping function is no longer maintained. The effect is well known, but prevention is usually performed experimentally only after occurrence of self-loosening events. The paper gives a systematic presentation of the dimensioning and the possibility to consider self-loosening in the development process. The procedure for self-loosening dimensioning and the influences are demonstrated with safety-relevant multi-bolted connections from the automotive industry. The aim of this paper is to provide a numerical design method with finite element analysis for detecting and understanding of the self-loosening process at bolted joints. Another focus of the work is to investigate the self-loosening behaviour under combined loading with a superposition of translation and rotation. Combined loading can lead to self-loosening even before reaching the limit of self-loosening for transverse loading. The computational results of the numerical simulation (FEA) are compared with experimental investigations.
Clamp force and its accuracy are investigated using torque, angle, gradient, and clamp force/elongation control. Phosphated, lightly oiled M14 and M10 bolts are tightened. A PowerMACS 4000 system with a QST62-350CT nutrunner is used in the experimental setup. An ultrasonic signal processing unit using a piezoelectric sensor fitted to the socket is used for signal generation and processing when evaluating clamp force. The ultrasonic clamp force control is based on a novel method for assuring correct echo and high repeatability measurements in the tightening system. Torque and angle are extracted from the tool control system. During the experiments a load cell is used to measure the clamp force in the joint. Combined head and thread friction is calculated at final torque and clamp force. The results show that the lowest scatter (3 s) in clamp force, approximately 2.9% can be obtained using ultrasonic clamp force control and the highest, approximately 18% when using torque control. The results are also compared to tightening factors described in VDI2230.
Mechanical properties are critical to the working performance of magnetorheological fluids (MRFs), especially in high temperature situations. This paper presents an experimental investigation to analyze the effects of temperature on mechanical properties of MRFs. First, a parallel disk method was implemented for the shear stress measurement of MRFs and the measurement principle was theoretically illustrated. Then, a detailed introduction to the MRF sample preparation and the testing device development was performed as well. In the study, five kinds of MRF samples with different material parameters were prepared and a shear stress testing device which possesses the temperature control function was developed and evaluated. After these, a series of measurements were conducted on the viscosity–temperature characteristic, shear stress–temperature characteristic and thermal stability of MRF samples. Measuring results indicated that the mechanical properties of MRFs were obviously dependent on temperature. The phenomenon mainly embodied in the reduction of off-field viscosity and shear stress with increasing temperature, as well as the performance degradation after undergoing a low–high–low temperature cycle or a high temperature treatment of more than 150 ℃.
The kinematical behavior of 5-axis machine tool introduced by toolpath calculation has a close relation with processing efficiency and quality of parts. For the category of sculptured surface parts with abrupt curvature, such as turbine blade and fixed guide vane, the most commonly utilized spiral contouring toolpath modes usually encounter some trouble during actual machining, the reason lies in the difficult tool orientation control near the edge of such parts. However, the global optimization for the spiral toolpath means increased computation burden, and so it is time consuming. In this paper, an efficient 5-axis toolpath optimization algorithm is presented, and the objective is to smooth the rotary axes’ motion caused by drastically changed tool orientation on spiral toolpath for abrupt curvature parts machining. To reduce the computation burden, only path segments on the spiral trajectory-owned weak kinematic performance are selected for further optimizing. To obtain smoother motion for rotary axes, the specific optimization computation for the selected path segments is conducted in the Machine Coordinate System (MCS) instead of the Part Coordinate System (PCS). The optimization model is constructed and a related solution method is presented to ensure the high-performance optimization. The complete optimization algorithm is demonstrated on a spiral 5-axis toolpath for the turbine blade finish machining, and the result shows that only 25.9% optimization computation is needed compared with global optimization algorithm. And then, the actual machining experiments are carried out by using paraffin as cut material, and the machining time with optimized toolpath is decreased by 19.7% compared with initial toolpath. In addition, the surface quality of parts is significantly improved after conducting the optimization. This study proves that the proposed algorithm can significantly improve the processing efficiency and surface quality of parts with abrupt curvature and provides an efficient method to optimize the spiral 5-axis toolpath used for finish machining parts with abrupt curvature.
Industry 4.0 describes future workpieces would be smart. They can control the individual stages of their production semiautonomously through negotiation with production resources. To this end, RFID is introduced into machining processes. The current applications of radio frequency identification mainly include two approaches: one is data-on-network approach which centrally stores workpiece-related data on network; another is data-on-tag approach, which stores the data on RFID tag. Data-on-network approach cannot adapt to flexible automated production lines, which require decentralized control system for flexible process and rapid response, and data-on-tag approach makes RFID tag store large amounts of data, which would result in slow data reading and writing problems. For solving this problem, a hybrid-data-on-tag approach is proposed. The on-tag data contains the basic machining information and the index of further machining information which is stored in the backend database. Based on the hybrid-data-on-tag approach, the control node model of decentralized control system and the corresponding cyber-physical systems architecture of flexible manufacturing shop floors are presented. Furthermore, a multi-agent-based decentralized control system is used to describe the communication of smart workpieces with production resources during their production procedures. Finally, a small-scale flexible automated production line is taken as an example to illustrate the utility of hybrid-data-on-tag approach.
This paper proposes a new approach to modeling and compensating for a rate-independent hysteresis of a piezoactuator. The model—namely, congruency-based hysteresis—is developed based on two very important characteristics of the hysteresis. These are congruency and wipe-out. The proposed approach consists of two branches for cases of monotonic increase and monotonic decrease of input excitation. In order to realize this model, datasets of first-order minor-loop values should be determined in advance. This can be done using the adaptive neuron fuzzy system (ANFIS) technique and experimental data. With this technique, an input-output relationship of first-order minor-loop values is estimated effectively. In addition, the ANFIS technique is also used in constructing datasets of inverse first-order minor-loop values, which are essential parts of a congruency-based hysteresis compensator. Several experiments in modeling and open-loop control are conducted to show the effectiveness of the proposed approach. In addition, a comparative work between the proposed approach and one of previous works is undertaken to demonstrate the benefit of the proposed method.
The sliding velocity plays an important role on the energetic efficiency and longer life of cam mechanisms with flat-faced translating followers. In this work, an optimization procedure published recently and based in the Bézier curves, is adapted to minimize the sliding velocities in this kind of cam mechanisms. Specifically, when the maximum lift of the follower, h, the total rise angle, β, and the angular velocity of the cam,
In this paper, we present a novel method for fault identification in the case of an incipient wheel fault in mobile robots. First, a three-layer neural networks is established to estimate the deviation of the robot dynamics due to the process fault. The estimate of the faulty dynamic model is based on a combination of the nominal dynamic model and the neural network output. Then, by replacing the faulty dynamic model with its estimate value, the primary estimates of the wheel radius appear as the solutions of two quadratic equations. Next, a simple and efficient way to perform these primary estimate selections is proposed in order to eliminate undesired primary estimates. A recursive nonlinear least squares is applied in order to obtain a smooth estimate of the wheel radius. Two computer simulation examples using Matlab/Simulink show that the proposed method is very effective for incipient fault identification in the setting of both left and right wheel faults.
There are two drive modes for an active magnetic bearing (AMB), namely the current and voltage drive modes. The analytical model of an AMB is second-order under current drive and third-order under voltage drive. The current drive is widely used due to its simple model. However, it is not the case in a solid-core AMB since it is subject to strong eddy currents. System identification is adopted in this paper to obtain the accurate model of a solid-core AMB, which shows that a third-order model is required to describe the real system in both current and voltage drive modes. Under the influence of eddy currents, the order of the model is increased in the current drive mode, whereas is not in the voltage drive mode, indicating that the model in the voltage drive mode describes the system dynamics better. All the details of the solid-core AMB, identification method and experimental results are given in this paper. In addition, a new numerical algorithm is proposed to simplify the existing least square method, which needs no iteration, achieves similar accuracy and is not restricted to our application.
Machining science is aimed at defining both cutting tools and machining conditions based on economic performance and to maintain workpiece surface integrity. Currently, machinists face a wide offer of turning, milling, drilling, and threading tools. Tools present a lot of similarities and light differences between them, being the latter the concealed reasons for a better or worse performance on difficult-to-cut alloys machining. However machinists had not useful methods for detecting which key tool aspects implies the best performance. The classic and expensive `test-trial' method results non-viable due to the market exponential increase, both in size and specialization. This paper brings up an indirect method for seeking common features in the group of those tools with the best performance on machining Inconel 718. The method is divided into five stages, namely: (a) raw testing of a basic operation with a lot of commercial solutions for the same operation; (b) filtering of results to reduce the feasible solutions to a few ones, studying the common features of successful cases; (c) testing of these feasible solutions aimed at choosing the best insert or tool (d); and finally (e) full testing concerning all workpiece surface integrity issues. The proposed method provides knowledge based on the distilling of results, identifying carbide grades, chipbreakers shapes, and other features for having the best tool performance. All surface integrity effects are checked for the best solution. This new point of view is the only way for improving the difficult-to-cut alloys machining, reaching technical conclusions with industrial interest. This paper shows the method applied on Inconel 718 turning, resulting in a carbide grade with 10% cobalt, submicron grain size (0.5–0.8 µm) and hardness around 1760 HV, coating TiAlN monolayer with 3.5 µm thickness, chipbreaker giving 19° of rake angle that becomes 13° real one after insert is clamped on toolholder. Cutting edge radius after coating was 48 µm approximately. Cutting speed was 70 m/min higher in comparison with that recommended in handbooks.
In the present research, vibration and instability analysis of a viscoelastic Y-shaped single-walled carbon nanotube conveying fluid is carried out. The surrounding viscoelastic medium is simulated by various models such as Kelvin–Voigt, Maxwell, standard linear solid Reissner, and nonlocal models. The size effects are considered based on modified couple stress theory. In order to achieve more accurate results, fourth-order beam theory is utilized. Surface stress effects are considered based on Gurtin–Murdoch theory. In addition, effects of the asymmetry of Y-shaped single-walled carbon nanotube are also taken into account. Regarding fluid–structure interaction, the equations of motion as well as boundary conditions are derived using Hamilton’s principle and solved by means of hybrid analytical–numerical method. Regarding the temperature changes on visco-Pasternak foundation, the effects of different surrounding medium models are discussed in detail. The overall results indicated that the stability and vibration characteristics of Y-shaped single-walled carbon nanotube conveying fluid are strongly dependent on damping coefficient. The results of this work are hoped to be useful in design and manufacturing of nanodevices where Y-shaped nanotubes act as a basic element.
Dynamic analysis of a mechanism with clearance joints and flexible links is a research focus in the field of multibody dynamics. In this study, a general modular dynamic modeling approach based on Lagrange multiplier method for planar closed-loop mechanisms is proposed in order to improve the modeling efficiency and reusability of a structure having same topology. With this approach, dynamic analysis considering clearance joints and flexible links can be performed conveniently. A novel mathematical model to determine the relative motion modes between the two components of a clearance joint is developed based on the previous contact detection method. A complete dynamic effect evaluation system, which measures the influence of clearance joints and flexible links on the dynamic performances more conveniently and intuitively, is established. A planar 3-RRR parallel mechanism that is a closed-loop system including imperfect joints and flexible links is studied as an example. The dynamic model of this mechanism is established and its dynamic characteristics are investigated. The couple effects of clearance joints and flexible links for a parallel mechanism are investigated first. The contact forces existing in the clearance joints can cause system vibration and thus reduces the dynamic stability of the whole mechanical system. Meanwhile, the simulation results indicate that the flexible links can damp the vibration of the moving platform caused by clearance joints is certain.
We consider fretting wear due to superimposed normal and tangential oscillations of two contacting bodies, one of which is an elastomer with a linear rheology. Similarly to the contact of elastic bodies, at small oscillation amplitudes, the wear occurs only in a circular slip zone at the border of the contact area and the wear profile tends to a limiting form, in which no further wear occurs. It is shown that under assumption of a constant coefficient of friction at the contact interface, the limiting form of the wear profile does depend neither on the particular wear criterion nor on the rheology of the elastomer and can be calculated analytically in a general form. The general calculation procedure and explicit analytic solutions for two initial forms, parabolic and conical, are presented for various combinations of frequencies and phases of normal and tangential oscillations as well as for various linear rheologies of the elastomer.
This paper investigates vibration of a moving flexible robot through modal analysis and by constructing vibration spectra of operational signals. A vector autoregressive model combined with a sliding window technique is used for signal processing in order to take into account system nonstationarity. Modal decomposition is conducted on the state matrix constructed from the appropriate vector autoregressive model parameters. A complete modal decomposition and spectrum construction algorithm able of highlighting the structural modes and harmonic excitations is presented. Through accurate identification from the vector autoregressive model, the method presented is able to discriminate, display and monitor the harmonics and structural modes during the processes investigated. This method is validated first by numerical simulation and then experimentally with a flexible robot performing three processes: moving a manipulator through the workspace, steady rotation of a grinder on the end effector and moving the manipulator combined with rotating the grinder. It is found on the operating robot that participation of the first structural mode is negligible when rotating the grinder but must be taken into account when moving the manipulator. The analysis presented and results obtained provide a sound basis for further investigation of vibroimpact behaviour in a robotic grinding process.
Fully-developed, turbulent rotating pipe flow and swirling jet flow, emitted from the pipe, into open quiescent ambient are investigated numerically using large eddy simulation. Simulations are performed at various rotation rates and Reynolds numbers. Time-averaged large eddy simulation results are compared to experimental and simulation data from previous studies. Pipe flow results show deformation of the turbulent mean axial velocity profile towards the laminar-type Poiseuille profile, with increased rotation. The Reynolds stress anisotropy tensor experiences a component-level redistribution due to pipe rotation. Turbulent energy is transferred from the axial component to the tangential component as rotation is increased. The Reynolds stress anisotropy invariant map also shows a movement away from the one-component limit in the buffer layer, with increased rotation. Exit conditions for the pipe flow simulation are utilized as inlet conditions for the jet flow simulation. Jet flow without swirl and at a swirl rate of S = 0.5 are investigated. Swirl is observed to change the characteristics of the jet flow field, leading to increased jet spread and velocity decay, and a corresponding decrease in the length of the jet potential core. The Reynolds stress anisotropy invariant map shows that the turbulent stress field, with or without rotation straddles the axi-symmetric limit.
Based on the deficiency of fixed-kernel in the traditional time–frequency distribution, which is lack of adaptability, a new adaptive kernel function, which is named as the adaptive radial sinc kernel, is proposed according to design criteria of adaptive optimal kernel. The definition and algorithm of radial sinc kernel are given, and the proposed method is compared with the tradition time–frequency distribution. The simulation results show that the proposed method is superior to the traditional fixed-kernel functions, such as Wigner–Ville distribution, Choi–Williams distribution, cone-kernel distribution and continuous wavelet transform. The adaptive radial sinc kernel can overcome the deficiency of fixed-kernel function in traditional time–frequency distribution, adopt the optimizing method to filter the cross-terms adaptively according to the signal distribution, obtain good time–frequency resolution and has extensive adaptability for an arbitrary signal. Finally, the proposed method has been applied to the fault diagnosis of rolling bearing, and the experiment result shows that the proposed method is very effective.
The mobility(or degree of freedom) analysis of planar mechanisms is traditionally calculated using the Grübler–Kutzbach formula. However, this method often fails in practice due to overconstraint, which is a core problem in all mobility analysis. Analyzing the cause of overconstraint, it is presented that overconstraint in closed-loop mechanisms can be recognized by analyzing the relative movements of the two elements in a rigidity re-closure. A solution to determine the overconstraint in multiloop mechanisms is also proposed. In this method, each loop is opened and the overconstraint can be calculated when the loop is reclosed. A mobility analysis must begin by determining the overconstraint. However, given that most planar mechanisms do not have any overconstraint, it is important to identify rapidly whether overconstraint exists in a mechanism. This paper proposes a concise technique to determine the existence of overconstraint based on the concept of "Assur groups". To simplify the process of mobility analysis, three new concepts and four relevant theories are introduced. In this paper, the proposed methodology is applied to several types of planar mechanisms, producing results in accordance with the prototype. This shows that the proposed methodology makes performing the mobility analysis of planar mechanisms, including complicated planar mechanisms, accurate, convenient, and fast.
This work addresses the problem of bubble evolution arising from gas cavitation in hydraulic oils. Two significant aspects, including the interphase mass transfer represented by air release and absorption phenomena and different thermodynamic considerations, are currently taken into account using a simplified method. In particular, three new models in progressive relationship are proposed on the basis of Rayleigh–Plesset equation which describes bubble dynamics. They are Model A in which air content is assumed to be constant, Model B in which the interphase mass transfer is introduced with the air undergoing an isothermal transformation, and Model C assuming an adiabatic process for the bubble evolution. With the goal of investigating the effects of these aspects, comparisons of the three models for two typical cases are presented with regard to the practical circumstances in which the oil pressure is set to increase linearly or oscillate sinusoidally. Results show a consistent trend for both cases concerning Model B and Model C compared to Model A. Although its speed relates to many factors, air release and absorption has a relevant impact on gas bubble radius. By the reason of adiabatic assumption, Model C provides a slower response regarding the oil pressure change. However, Model B and Model C may be both inaccurate if considering the actual interfacial heat transfer. In this viewpoint, the oil temperature in fluid power system could be affected.
Identification of the critical angle between fiber and crack direction in orthotropic materials for avoiding catastrophic failure is necessary. Recognition of the optimum regions for creating notches in orthotropic materials for creation of maximum load-bearing capability is an important parameter in structural design. In this paper, the critical angles between crack and fiber direction are predicted, extracting crack tip parameters in orthotropic materials using stress series expansion and numerical method. The variations of crack tip parameters with respect to the angle between crack and fiber for modes I and II are presented. The presented functions for these variations can be used in the optimum design procedure of orthotropic structures. The obtained results are validated using experimental study.
In nanopositioning system, the compliant tripod stages have proved to have enormous advantages for out-of-plane (z/tip/tilt) positioning in turns of compactness, simplicity in structure, and economic cost. However, most of the present-day compliant tripod stage undergo manufacturing problems due to a complicate structure, and little study has been carried out to formulate the tri-inputs and tri-outputs relationship, which is essential for precise positioning. Accordingly, this paper presents the quasi-static analysis of a novel compliant tripod stage with an equivalent plane model to achieve precise position analysis for nanopositioning. Three-plane compliant lever mechanisms and cylindrical flexure hinges with high length–diameter ratio are employed, which mitigate couple influence and enable easy fabrication via planar manufacturing processes. The spatial output motions of the compliant tripod stage are first split among inputs of the three-plane compliant lever mechanisms, where the lateral translations of the compliant tripod stage are included. Then the displacement equations of the plane compliant lever mechanism are formulated through Castigliano’s second theorem. The model is further verified by finite element analysis. Finally, an experimental test system is set up and the test results validate the proposed approach.
This paper presents an investigation on the performance characterization of viscous fan clutch with double grooves including thermal behaviors. A detailed mathematical model of the fan clutch is established by taking into account the viscosity variation of the viscous fluid with shear radius and temperature, and an iterative algorithm is proposed to calculate the performances of the fan clutch. Laboratory experiments are then carried out on a performance measurement setup for viscous clutch, for validating the proposed mathematical model and calculation method. Based on the verified model and calculation algorithm and the experimental setup, the performances of six alternative viscous fan clutch designs are studied. The combined analytical/experimental results suggest that the clutch performances degrade with the increase of the input speed, and the proposed model and calculate method are valid and can be successfully employed to facilitate the design of new viscous fan clutches as well as control system development, for saving cost and shortening development period.
The purpose of this paper is to investigate the dynamic performances of a motorized spindle supported on water-lubricated bearings. A modified transfer matrix method considering both of the translational and tilting dynamic coefficients of the bearings is established. The turbulent Reynolds equation is adopted and numerically solved by the perturbation method and the finite difference method, and the dynamic characteristics of the water-lubricated journal bearings are obtained; the effects of the eccentricity ratio, tilting angle, and the rotational speed on the dynamic coefficients of the water-lubricated journal bearings are analyzed. The critical speed, the dynamic stiffness of spindle nose, and unbalance response of the motorized spindle are investigated. Finally, a comparative study of rotor dynamic behaviors between the 32- and the eight-coefficient bearing models is conducted. The numerical predictions obtained by the 32-coefficient bearing models correlate well with the experimental values available in the literature.
In this paper, the problem of a rectangular plate with functionally graded soft core and composite face sheets is considered using high order sandwich plate theory. This theory applies no assumptions on the displacement and stress fields in the core. Face sheets were treated using classical theory and core was exposed to the theory of elasticity. Governing equations and boundary conditions are derived using principle of virtual displacement and the governing equations are based on eight primary variables including six displacements and two shear stresses. This solution is able to present localized displacements and stresses in places where concentrated loads are exerted to the structure since the displacements in the core can take a nonlinear form which could not be seen in the previous theories such as classical and higher order shear theories. This theory is suitable for rectangular plates under all types of loadings distributed or concentrated which can be different on upper and lower face sheets at the same point. The results were compared with the published literature using theory of elasticity and showed good agreement confirming the accuracy of the present theory. Subsequently, the solution for the core with functionally graded material is presented and effectively indicates positive role of functionally graded core.
Legged robots have superior advantages rather than wheeled robots for moving over uneven terrains in the presence of various obstacles. The design of an appropriate path for the main body and legs is an important issue for such robots especially on the uneven terrains. In this paper, the focus is to develop a stable gait for a quadruped robot to trot on uneven terrains. First, a stability condition is developed for a whole-body quadruped robot over uneven terrains based on avoiding the tumbling. By using a simple model, a point with zero moments is calculated in the three-dimensional space. Then, the reference path of this point is determined so that the tumbling moments become zero. The path of the main body will be calculated by using an optimal controller. The main feature of the proposed gait generation framework is that the height of robot can change continuously and stably on uneven terrains. To evaluate the robot stability, the tumbling moments around diagonal lines are calculated and some methods are proposed to reduce these moments to improve the robot stability. The tip of swing foot is also planned to avoid any collision with the environment. The proposed method will be demonstrated using an 18-Degrees of freedom (DOF) quadruped robot in simulation and experimental studies. The experimental setup is a small-size quadruped robot, which is composed of a rectangular plate as its main body with four legs that each one has three active joints with DC servo motors. Obtained results reveal that the robot can trot on uneven terrains stably. Besides, the comparison with the previous methods approves the merits of proposed algorithm on uneven terrains.
An analytical model, in which unequal radii are replaced with an equivalent radius, is creatively proposed to predict the rolling force and roll torque in general case of snake rolling. With the model, the effects of roll radius ratio, roll speed ratio, offset distance between rolls, reduction and friction coefficient on rolling forces in hot snake rolling of aluminum alloy are obtained. Also, the thicknesses of slab are investigated in different zones, which firstly propose the changes of thickness during snake rolling. Owing to the good agreement with the results measured in experiments and calculated by finite element method and other traditional models, those calculated by the proposed model are verified. The proposed model can be used to predict more accurate theoretical results for snake rolling force and torque.
Accurately and rapidly evaluated error sensitivity of actual tooth surfaces of hypoid gears can be a significant foundation for a variety of dynamic preference analysis and machine tool setting readjustments. Due to the complexity of local geometric features as well as the limitations of the data measurement on tooth surfaces of hypoid gears, automated error-sensitivity analysis for actual tooth surfaces still presents many substantial challenges. This paper presents a novel methodology for the error-sensitivity analysis of real tooth surfaces of hypoid gears. The methodology combines an error-sensitivity analysis model with a numerical analytical real tooth contact analysis (RTCA) model. The real tooth surfaces, describing local micro-geometry features on actual tooth surfaces, have been produced by 3D discrete data points reconstruction. In this method, the discrete data points on actual tooth surfaces are measured by using a coordinate measure machine (CMM). The location, size, and shape of contact patterns are determined from the predicted interference areas distribution by numerical analysis. In addition, the error-sensitivity analysis model is established for evaluation of the sensitivity of hypoid gears with real tooth surfaces that corresponds to misalignments. The results of experiment show that the proposed method can obtain actual contact properties that significantly improve the basic design performances significantly.
The optimization of the hull–propeller system of a ship has always been one of the most important aspects of design in order to reduce the costs, mechanical losses and increase the life of system components. The proposed design methodology represents a comprehensive approach to optimize the hull–propeller system simultaneously. In this study, two objective functions are considered, i.e. lifetime fuel consumption (LFC) and lifetime cost function (Cost). The mission profile of the vessel is adopted to minimize the LFC and Cost over their operational life. The well-known evolutionary algorithm based on NSGA-II is employed to handle the multi-objective problems, where the main propeller and hull coefficients are the unknown and are considered as design variables. The results are presented for a commercial container ship driven by B-series propeller. Three different engines with the same mission profile were taken and the results revealed that the proposed method is an appropriate and effective approach for finding Pareto optimal solutions distributed uniformly and is able to improve both of the objective functions significantly and other performances of the system.
An innovative design of magnetic coupler for shaft speed amplification is proposed and verified by experiments. The structure of proposed magnetic coupler is similar to an infinite-stage gearbox. In addition, the mathematical model of flux density is derived to look into the equation of adjustable gear ratio and effect of speed amplification. Moreover, two sets of experiments, namely verification of gear ratio and observation of stall phenomenon, are built up to examine the capability and drawback of the proposed variable-gear-ratio magnetic coupler. Three types of gear ratio are presented by theoretically analysis at first and then examined by experiments. The gear ratios for these three specific types between the input and output rotors are 4.75, 5.75, and 10.5, respectively. That is, the rotational speed of the output rotor can be precisely and realistically amplified. Besides, in order to reduce the torque inertia of outer rotor, a ferrite bush is inserted to the inner side of the core rotor to decrease the flux density at air gap. On the other hand, the overlapped area of permanent magnets, which are attached onto the inner rotor and outer rotor, has to be appropriately chosen. The smaller the overlapped area, the weaker is the magnetic attractive force at air gap. As long as these two modifications (an inserted ferrite bush and the aforesaid overlapped area) are validated, the torque inertia of outer rotor can be significantly reduced. Accordingly, the required power to rotate the outer rotor can be greatly reduced if the overlapped depth is shortened. However, insufficient overlapped depth between the high-speed rotor and low-speed rotor will bring about stall phenomenon caused by the magnetic attractive force between the high-speed rotor and the low-speed rotor being weaker than the start-up torque inertia. In other words, the reduced overlapped depth can also reduce the start-up torque inertia but stall phenomenon may easily occur relatively.
An adaptive robust control that does not need sophisticated plant modeling work is proposed for precise output positioning of a servo system in the presence of both friction and deadzone nonlinearities. It is difficult to achieve effective motion control by traditional linear control methodology for these types of nonlinearities, without the aid of a proper compensation scheme for nonlinearity. In this study, dynamic friction is modeled by a Tustin friction model, and inverse deadzone method is adopted to compensate deadzone effect. The adaptive laws of the unknown system dynamic parameters, friction and deadzone, are derived. Furthermore, a robust control method with funnel control is proposed to compensate for unmodeled and estimation errors. The boundedness and convergence of the closed-loop system are ensured by a Lyapunov stability analysis. The performance of the proposed control scheme is verified through experiments on the XY table servo system and the robotic manipulator.
This paper proposes an efficient approach for dynamic analysis of a rotating beam using the discrete singular convolution (DSC). By spatially discretizing the nonlinear equations of motion of the rotating beam using the DSC method, natural frequencies of the rotating beam are obtained. Numerical results show that the DSC method accurately captures not only the low-order but also the high-order frequencies of the beam rotating at a high angular velocity in very short time, compared with the classical finite element method. Moreover, by combining the DSC method and the differential quadrature method, the dynamic equations are reduced to a set of algebraic equations. Thus the dynamic response of the rotating beam is resolved accurately and efficiently with much less computational effort, and is able to be numerically stable for long-time integration.
The random fibre oscillatory behaviour induced by turbulence in the diffuser of an industrial spunbonding rig is measured experimentally. The turbulent air flow is firstly characterised by constant temperature hot-wire anemometry: averaged flow quantities, such as the mean velocity and the turbulent kinetic energy, as well as time dependent quantities, such as the integral time and the energy spectrum, are measured. The influence of the turbulent flow on the dynamics of a nylon fibre of diameter 200 µm and a spunbonding fibre of diameter 18 µm in the diffuser is then investigated by extracting the transverse displacement from images acquired by a digital camera.
The current study focuses on performance analysis and structural optimization of the 2.5 D C/C composite finger seal. A micro/macrostructural integrated optimization method of 2.5D C/C composite finger seal is presented. Based on uniform strain assumption the stiffness average method is used to predict the elastic properties of 2.5D C/C composite material. In order to achieve the advantage of the designability of composite material, the microstructure parameters are also as design variables together with the macro structure of finger seal. Considering the two optimization objectives, leakage and contact pressure, are both implicit functions of the structure parameters of finger seal which obtained by finite element method, a Krige model is established to replace the finite element method analysis in each optimization iteration, which could improve the optimization calculating efficiency obviously. By using the multi objective genetic algorithm NSGA-II the 2.5D C/C composite finger seal optimization is implemented availably. An example is given which indicates the leakage and contact pressure of finger seal decrease significantly through the integration optimization of 2.5D C/C composite finger seal which develop a new approach to design finger seal with high performances.
In the present paper, mixed convection of TiO2-water and CuO-water nanofluids in a laminar flow within a vertical rectangular duct is investigated numerically. The two-phase Euler-Lagrange approach is applied to simulate nanoparticles dispersion in the base fluid. Effects of nanoparticles concentration, aspect ratio, buoyancy and Brownian and Thermophoretic forces in a wide range of Richardson number (
This paper proposes an obstacle avoidance trajectory generation method that provides a smooth trajectory in real time. The trajectory is generated from an environmental top-view image, where a fisheye lens is used to capture a wide area at low height. Corners of the obstacles are detected and corrected using the log-polar transform and are used to generate a simple configuration space that reduces the computation time. An optimal path is computed by using the A
Product–service system is a new globally optimized production system with high-degree integration of product and service, which is formed under the product lifecycle management thinking of manufacturing enterprises. This paper applies the modular design method in the development of CNC product–service system and studies the module division and configuration modeling method oriented to configuration design process. First, a service module division method based on design structure matrix is proposed, and the relationship of service activities is established through directed graph and the module division of service activities is determined by calculating reachable matrix. Next, the product–service integration strategy is analyzed, the product–service integration model is built, and the organic integration of product and services is achieved. Then, the meaning of configuration model of product–service system is introduced and the configuration model is established. At last, the economical turning center is selected as an example of CNC to implement the module division and configuration modeling of CNC product–service system and to verify the feasibility of proposed methods.
This paper studies the load balancing problems caused by manufacturing and assembly errors of 2K-H planetary gear train. Based on the geometric equivalent relationship and spring mechanical model of load transfer, the relations between the load balancing of planetary gears and the mesh clearance and meshing stiffness are derived. Besides, the vector method is also derived to calculate the meshing clearance which is a result of the deviation of the component center caused by manufacturing errors and assembly errors. On the basis of the meshing clearance calculation formulas, the balanced load structure based on floating members is analyzed, and the results show: 1) when the number of planet gears is
In this study, we propose a cantilever-type ferro-actuator using porous polyvinylidene fluoride (PVDF) membrane. Generally, a ferro-actuator is fabricated by the absorption of ferro-fluid on a backbone membrane containing strongly magnetized nanoscale Fe particles that are responsive to an external magnetic field. We suggest a porous PVDF membrane fabricated using a zinc oxide (ZnO) particulate leaching method as a backbone membrane of the ferro-actuator to increase the absorption of ferro-fluid. Ferro-fluid is absorbed on the porous PVDF membrane using a dip-coating method. First, we observe from scanning electron microscopic images the surfaces and cross sections of a pure PVDF membrane and the porous PVDF membrane using a ZnO particulate leaching method. Second, an energy-dispersive X-ray spectroscope is used to confirm the configuration of the elements and the absorption of Fe particles in the ferro-actuator. Third, we execute thermogravimetric analysis and X-ray diffraction analysis of the pure PVDF membrane, the PVDF membrane before/after particulate leaching, and of the ferro-actuator using the porous PVDF membrane. Through these analyses, we can confirm that ZnO particles in the PVDF membrane were clearly removed by the particulate leaching method and Fe particles were included in the fabricated ferro-actuator. Finally, we fabricate cantilever-type ferro-actuators using pure PVDF membrane and the porous PVDF membrane and execute blocking force and displacement tests. Compared with the ferro-actuator using the pure PVDF membrane, the ferro-actuator using the porous PVDF membrane had an increased displacements—about a 3-fold increase at the DC input and at the AC input, along with increased blocking force (about a 6-fold increase) at the DC input. Consequently, the concept that a ferro-actuator using the porous PVDF membrane exhibits enhanced actuating performance is validated.
With the rapid development of the machinery and the increasing complexity of the steam turbine generator set, it is a great challenge for the safe and reliable operation of the steam turbine generator set. The uncertainties of fault classification and complicated working conditions become important research fields of steam turbine generator. A probability method on the uncertainty reasoning of fault classification for steam turbine generator is proposed in this paper based on the 2D-holospectrum and Bayesian decision theory. Firstly, Bayesian decision theory is adopted for the preliminary fault estimation on actual risk loss by calculating the loss expectation of each decision. Then, the area ratio of overlap region in 2D-holospectrum and the evidence theory can give the probability of the fault. Framework and model of the uncertainty reasoning are also described in this paper. Finally, the model is verified by the experiment of the rotor vibration on test rig. The results show that the method proposed is feasible for reasoning under imperfect information condition.
In order to investigate the impact factors and their affection on high-speed precision multilink punch press (MPP), the dynamic model with different joint clearance was established, and the influence of different clearance and speed on the dynamic positional repeatability of bottom dead center (BDC) was analyzed. The elastic dynamic model of high-speed MPP was established, the affection of the elastic deformation and elastic wave on the positional repeatability of the BDC were presented by using modal superposition method to solve dynamic equation. Meanwhile, experiments on the dynamic repeatability of the BDC of the punch during working were completed. At last, the comparison of the experimental results with the analyzed results was given, and based on which, it can be concluded that the clearance, elastic wave and deformation are the key factors of the dynamic repeatability precision of the BDC.
The locomotive bearings support the whole weight of the train under the high speed and its continuous running is a key factor of the train safety. The collected Doppler distorted signal greatly increases the difficulties in detecting the whelmed fault information. To overcome this disadvantage, a novel Doppler distorted correlation matching model using the single side Laplace wavelet and acoustic theories is constructed to recognize the bearing fault-related impulse intervals. The parameterized Doppler distorted model is assessed by the correlation coefficient with the bearing fault signal in waveform. The optimal Doppler distorted model, that is the Doppler distorted correlation matching model which matches the fault component in the acoustic signal could be used for identifying the fault impulse interval. Then, the bearing fault can be successfully detected from the parameters of the Doppler distorted correlation matching model due to its maximum similarity to the real signal. Except for the simulation study, the proposed model is also employed to match the fault components in some real acoustic bearing fault signals. The recognized fault impulse period in the Doppler distorted correlation matching model’s initial model keep in good accordance with the correct fault impacts, which represent the locomotive bearing fault characteristics.
Bistable mechanisms have two stable positions and their characteristic analysis is much harder than the traditional spring system due to their postbuckling behaviour. As the strong nonlinearity induced by the postbuckling, it is difficult to establish a correct model to reveal the comprehensive nonlinear characteristics. This paper deals with the in-plane comprehensive static analysis of a translational bistable mechanism using nonlinear finite element analysis. The bistable mechanism consists of a pair of fixed-clamped inclined beams in symmetrical arrangement, which is a monolithic design and works within the elastic deformation domain. The displacement-controlled finite element analysis method using Strand7 is first discussed. Then the force–displacement relation of the bistable mechanism along the primary motion direction is described followed by the detailed primary translational analysis for different parameters. A simple analytical (empirical) equation for estimating the negative stiffness is obtained, and experimental testing is performed for a case study. It is concluded that (a) the negative stiffness magnitude has no influence from the inclined angle, but is proportional to the product of the Young’s modulus, beam depth, and cubic ratio for in-plane thickness to the beam length; (b) the unstable position is proportional to the product of the beam length and the Sine function of the inclined angle, and is not affected by the in-plane thickness and the material (or the out-of-plane thickness). The in-plane off-axis (translational and rotational) stiffness is further analysed to show the stiffness changes over the primary motion and the off-axis motion, and a negative rotational stiffness domain has been obtained.
A mode shape based damage detection method for a cantilever beam is proposed in this paper. The idea involves use of spatial Fourier series expansion of mode shapes. Mode shapes of a cantilever beam are not periodic in nature. However, by taking their mirror image about the fixed end, an augmented periodic mode can be created which permits spatial Fourier analysis. It is observed using finite element simulations that damage has a considerable impact on the spatial Fourier coefficients of the mode shapes of a damaged beam. It is also found that the Fourier coefficients are sensitive to intensity of damage and its location on the beam. Sensitivity of the Fourier coefficients in presence of noise is also analyzed and they are found to be effective in indicating the damage.
This paper experimentally investigates the effects of a cross-flow perforated tube on the pressure pulsation attenuation and pressure loss in a reciprocating compressor piping network, with particular focus on the structure parameters and installation positions. The results demonstrate that significant pressure fluctuation attenuation and less pressure loss in the whole piping system can be achieved when a well-designed cross-flow perforated tube is installed downstream of the pulsating bottle. The pressure pulsation is reduced as the perforated rate decreases and as the perforated tube length increases, while the hole diameter has little effect upon the pulsation attenuation. In the aspect of reducing pressure loss, the perforated rate should be larger than 0.05 and the hole diameter should be larger than 8 mm. In addition, a pressure pulsation computation model based on the linear acoustic wave theory and transfer matrix method is developed to predict the pulsating pressure in compressor piping systems with an installed cross-flow perforated tube. With favorable agreement between the model prediction and the present experimental results (maximum deviation within 6.8%), the predicted pulsating pressure can be attenuated for the reciprocating compressor piping system with various compressor speeds when a cross-flow perforated tube is reasonably designed and installed.
The behaviour of a fibre subject to the turbulent air flow in the diffuser in the spunbonding process is studied using a three-dimensional dynamics model in which the fibre is discretised as a chain of beads connected by linear and rotational springs. The turbulent air drag acting on the fibre is modelled as a random force, as a function of the mean air velocity, the turbulence intensity, and the spectrum of turbulence. The effect of the air flow parameters and the fibre diameter on the amplitude and the frequency of the fibre oscillations is analysed to understand how the fibre position at the exit of the diffuser is controlled by the turbulent air flow in spunbonding. This in turn will affect fibre laydown and the associated web formation.
Robot-assisted therapy has become an important technology applied in rehabilitation engineering, allowing patients with motion impairment problems to perform training programs without continuous supervision from physiotherapists. The goal of this paper is to develop a gravity balanced exoskeleton for active rehabilitation training of upper limb. The mechanical structure and kinematics of the exoskeleton are described and optimized to enable natural interaction with user and avoid singular configurations within the desired workspace. The gravity balancing of the human arm and mechanism is achieved through a hybrid strategy making use of auxiliary links and zero-free-length springs to balance the effect of gravity over the range of motion. The balance errors resulting from the variation of anthropometric parameters are analyzed and discussed. Further experiments involving trajectories tracking tasks with and without gravity balancing are conducted to evaluate the improvement of the control performance and energetic efficiency made by the developed balanced mechanism. The experimental results indicate that the proposed balance strategy can achieve a reduction of 34.56% in overall power consumption compared with the cost in unbalanced condition.
The enhancement between cost and reliability is the developmental direction of modern manufacturing enterprises. On the basis of fuzzy theory, the relationship among the cost of product quality loss, the reliability of the assembly dimension chain and assembly tolerance is studied together in this article. Processing cost can be considerably reduced and the target of quality engineering is realized by optimization design. As an example, a tolerance design model is determined for gear and shaft assembly. Moreover, the mathematical model of the relationship between the cost of fuzzy quality loss and the fuzzy reliability of the assembly dimension chain is determined in combination with a processing cost function. The optimistic results of key dimensions of gear and shaft assembly are identified through through orthogonal experiments. This method can facilitate product quality control by enterprises and the realization of economic targets. The study findings can also serve as references for other similar studies.
In industries, the use of appropriate junctions between components is of paramount interest. Coupling loss factor is one of the important parameters in statistical energy analysis for vibroacoustic analysis of complicated structures in drawing board stage. The values of coupling loss factor were calculated and compared for different junctions. The screwed and bolted junctions were examined for thin rectangular plates of same size. The energy level difference method was used to find coupling loss factors because of its simplicity. These experimentally found coupling loss factors were later compared with analytical solutions. It is noticed that the analytical results are in good agreement with experimental results. It is also observed that coupling loss factor for bolted junction are relatively high than that for screwed junction.
The microcantilever used in micro–nanomanipulator is a spatially distributed and flexible mechanical system. An accurate model of the microcantilever is essential for the accurate tip positioning and force sensing. Traditional lumped parameter model will lose the spatial dynamics. Though the nominal Euler–Bernoulli model is a distributed parameter model, in practice there are still some unknown nonlinear dynamics. In this study, a neural network-based distributed parameter model identification approach is proposed for modelling the microcantilever. First, a nominal Euler–Bernoulli beam model is derived. To compensate unknown nonlinear dynamics, a nonlinear term that needs to be estimated is added in the nominal model. For finite-dimensional implementation, the infinite-dimensional partial differential equation model is reduced into a finite-dimensional ordinary differential equation model using the Galerkin method. Next, a neural network-based intelligent learning approach is developed to learn the unknown nonlinearities from the input–output data. A radial basis function recurrent neural network observer is designed to estimate the finite-dimensional states from a few sensors of measurements. After that, a general regression neural network model is identified to establish the nonlinear spatiotemporal dynamic model between the inputs and outputs. The effectiveness of the proposed neural network-based distributed parameter modelling approach is verified by the simulations on a typical microcantilever.
Multi-bolt joint distributed around the connecting members are generally adopted to meet the high-performance assembly requirements in aerospace, energy and power industries. However, the initial preload could be low due to non-optimized preload sequence and bolt stress relaxation, especially at elevated temperature. Thus, it is necessary to take elastic interaction and bolt stress relaxation into account before jointing. In this article, a general multi-bolt elastic interaction with bolt stress relaxation is modelled analytically. First, the multi-bolt joint is characterized by ‘spring-node’ model and elastic interaction stiffness. Second, the bolt residual preload can be estimated according to linear superposition of elastic interaction and bolt stress relaxation under the condition of node displacement equilibrium. Further, the influence of preloading sequence and bolt stress relaxation on residual preload distribution was numerically analyzed using a typical circular ring with 8-bolt joint. Two bolts’ preloading sequences were planned, star sequence and counterclockwise sequence, respectively. The bolt creep simulation time was set as 10 h using the power-model at intermediate temperature. From comparison, the predicted results using the developed model were consistent with the FE simulations both with and without bolt stress relaxation.
In this study, the influence of material damage and the Bauschinger effect on the autofrettage of thick-walled pressure vessels is investigated. Constitutive equations for the elasto-plastic deformation and damage processes are presented. Boundary value problems for a thick-walled cylinder and for a thick-walled sphere of constant thickness are formulated. Computations are preformed to find the optimum autofrettage pressure, for which the equivalent stresses in the vessel take the minimum value under process conditions. Furthermore, residual stress fields after the autofrettage are analyzed. The results show that the Bauschinger effect and damage lead to essential reduction of favorable residual stresses.
The development of fully personalised product design solutions for customers is hindered by lack of a satisfactory means of interaction. Mass production techniques used by manufacturing firms cannot be applied for user-centred design. A stronger interaction between customer and product can only be achieved when the customer guides the product generation via individual preferences and emotional needs. The aim of this article is to introduce a Kansei engineering (KE)-based methodology that involves customers in the product generation process by taking their preferences and emotional needs into account. The methodology is integrated by a CAD environment to provide a 3D dynamic product representation which is generated by individual customer preferences via fuzzy logic (FL) reasoning. For validation, the methodology was demonstrated by using the case study of an ironing board. Both functional and emotional needs were handled by KE implementation. By combining KE and FL, the methodology enabled the multiple quantitative demands of the customer to be addressed in order to generate a more personalised product in a responsive manner. Located in shopping venues, fixed and mobile stations for the customer decision-making process could facilitate increased customer satisfaction without need of a customer assistance desk.
When sinusoidal vibration waveform is required, the frequency bandwidth of conventional electro-hydraulic vibration exciter controlled by servo valve is always limited to a rather narrow range due to the limits of slide valve structure and response speed, and no parameter is available for defining and evaluating the waveform quality. In this paper, a novel electro-hydraulic vibration exciter controlled by electromotor driven rotary valve is proposed to significantly extend the frequency range compared to the conventional servo valve controlled counterpart. Total harmonic distortion (THD) theory which is usually used to cope with voltage and current in electric system is borrowed to evaluate the quality of theoretical and experimental vibration waveforms at different supply pressures and vibration frequencies, quantitatively and qualitatively. The results show that the waveform quality is mainly influenced by the 3rd harmonic resonance. The proposed vibration exciter can output sinusoidal waveform with THD less than 5% at the vibration frequency higher than 70 Hz. In this frequency domain, the supply pressure has an extremely low impact on the THD of the waveform. The amplitude of the waveform can be adjusted by changing the supply pressure with almost no effect to the waveform quality at a certain vibration frequency.
This paper proposes a tool following function-based identification approach (TFFIA) for geometric errors of two rotary axes for one five-axis machine tool. It is comprehensive to identify all geometric errors of rotary errors. Firstly, synthetic error formulas of ballbar originate from the geometric error model of machine tools in order to consider the influences of 21 errors of three translational axes. It makes the approach more reasonable and precise. Secondly, the structures of three measurement patterns of TFFIA are described. Thirdly, in each pattern, errors of rotary axes affecting the accuracy of the sensitive direction are identified. As the result, the identification equations of all 20 errors coincide with the geometric properties of errors. Moreover, the impacts of setup errors of ballbar are eliminated with least square method to improve the precise of TFFIA. According to the structures of three patterns, only three installation of workpiece ball of ballbar are needed in the whole identification of two rotary axes to obtain the required ballbar readings. It greatly shortens the measurement time. Twenty geometric errors of two rotary axes are calculated with identification equations and ballbar readings. Finally, TFFIA is applied to a SmartCNC500 five-axis vertical machining center. The corresponding comparisons are proposed to verify the effectiveness and accuracy of TFFIA.
This paper describes the experimental setup of combustion chamber, and the shock loads resultant of gases mixture detonation. The results of experiments performed with fully clamped circular steel plates subjected to detonation of acetylene (C2H2)–oxygen (O2) in various volume ratio and different initial pressure. The energy of deformation of plates is determined by measuring pressure of explosion chamber after detonation and the results presented in terms of central deflection of the plates. Also, in this paper, theoretical modelling is presented to predict the midpoint deflection versus impulsive loading by assuming a zero Bessel function shape of the deformed circular plate. This approach is developed based on energy method for plastic material behaviour, and since the shock wave energy is equal to the deformation energy. The strain energy of the plate can be calculated by using the initial shock load energy imparted to the circular plate. The results of this model have good agreement with the experimental values. Moreover, it has been shown that the obtained model has much less error compared with those previously proposed in the literature.
Quaternions, particularly the double and dual forms, are important for the representation rotations and more general rigid-body motions. The Cayley factorization allows a real orthogonal 4 x 4 matrix to be expressed as the product of two isoclinic matrices and this is a key part of the underlying theory and a useful tool in applications. An isoclinic matrix is defined in terms of its representation of a rotation in four-dimensional space. This paper looks at characterizing such a matrix as the sum of a skew symmetric matrix and a scalar multiple of the identity whose product with its own transpose is diagonal. This removes the need to deal with its geometric properties and provides a means for showing the existence of the Cayley factorization.
The conventional modal testing (referred to as displacement modal testing (DMT)) is based on measurement of displacement, velocity or acceleration as well as excitation force. Though there exits an enormous literature with regard to DMT, on the contrary, a few papers address modal testing based on strain gauges or strain sensor (referred to as strain modal testing (SMT)). The main reason for this scenario is due to practical problems in the use of strain gauges as calibration procedure, ground loop sensitivity are not adequate at high frequency, bonding quality. In this work, a novel piezoelectric strain sensor is used for SMT. In this study it is demonstrated that this sensor overcomes the practical drawbacks related to the use of strain gauges. Thus, SMT based on piezoelectric strain sensors can be a valid alternative to DMT which is usually based on accelerometers. Comparisons between the modal testing results concerning brackets with different constraint conditions using both accelerometers and strain sensors are given in terms of modal parameters, highlighting their pros and cons.
A novel method for the design of discretionary N-lobed pitch curve and intermittent N-lobed pitch curve is presented. And a general formulation for classification identification model of the pitch curve with nondifferentiable points for N-lobed noncircular gear (N-LNG) is proposed. The formulation is based on the differentiable principle. In particular, the steepest rotation modification model and method of the pitch curve with discontinuous points for any type of N-LNG are established by resorting to fundamentals of the calculus of variations. The modification model can be calculated via the Euler–Lagrange equation, and its conjugate pitch curves which contain outer contact and inner contact can be obtained in general by using the principle of noncircular gear meshing. This identification and modification model and method are implemented in several numerical examples, and simulation results demonstrate that the pitch curve with nondifferentiable points for N-LNG can be effectively identified and modified.
The Mach number and pressure at the outlet plane of a straight micro-tube were investigated numerically for both laminar and turbulent flow cases. The numerical methodology is based on the arbitrary Lagrangian-Eulerian method. The LB1 turbulence model was used for the turbulent flow case. The compressible momentum and energy equations with the assumption of the ideal gas were solved. The computational domain is extended to the downstream region from the micro-tube outlet. The back pressure was given to the outside of the downstream region. The computations were performed for a tube whose diameter ranges from 50 to 500 μm. The average Mach number at the outlet plane of the choked flow depends on the tube diameter and ranges from 1.16 to 1.25. The flow characteristics of the under-expanded gas flow in a straight micro-tube were revealed.
The first three mode shapes of a cantilevered NACA0009 hydrofoil were experimentally investigated in air and under different flow conditions in a cavitation tunnel. First and second bending modes and first torsion mode were determined in resonance conditions with the hydrofoil vibrating in air, in still water, in flowing water, or with leading edge sheet cavitation. The hydrofoil was excited with embedded piezoelectric ceramic patches, and the response was measured along the surface at selected positions by means of a laser Doppler vibrometer. The modes of vibration obtained from a cross correlation analysis of the signals were compared for the different conditions, and the most significant differences were identified. In particular, it was found that the mode shape deformation and the location of the nodal lines are dependent on the fluid conditions.
In this study, an experimental methodology based on micromechanical testing inside a scanning electron microscope is proposed to characterise bonding of paper layers connected by wet pressing. The peeling force–displacement evolution law that characterises the delamination of micromechanical double cantilever beam specimens of paper tissue have been extracted from such peeling tests. It is observed that the force–displacement evolution curve achieves a steady-state value related to the effective adhesive energy of the interface. This behaviour is explained by examining the complex load transfer mechanism between the layers exerted by cellulose fibrils. A statistical approach is used for the computation of the effective adhesive energy. It is argued that the observed force–displacement evolution law may be satisfactory described by a stochastic model that depends on the distribution function of the fibrils strength, and on two geometrical distribution functions related to the in-plane and out-of-plane fibrils angles with respect to the undeformed interface configuration. Some applications of the proposed model are demonstrated on examples.
A giant magnetostrictive actuator is designed with strong bias magnetic field. The influence of the strong bias field is introduced, and the corresponding exciting input signal is selected. Magnetic reluctance estimation, approximate linearity between the strain and magnetic field, and a mass–spring–damper system assumption are employed to analyze the actuator’s displacement with low-frequency signal input. An experimental system is designed, and properties of the proposed actuator are tested. With the help of square wave test, appropriate direction of exciting signal for the magnetostrictive actuator is determined. With the help of sinusoidal wave test, the established model is validated and the relationship between the maximum value of the displacement and of the current is analyzed. With exciting frequency lower than 200 Hz, the errors between the calculating and testing results are within 1.0 m, which validates the model.
A three-dimensional micromechanics-based analytical model is developed to investigate the influence of interphase on the thermo-mechanical properties of three-phase composites. The representative volume element (RVE) of composites is extended to c x r x h cells in three dimensions and the RVE consists of three phases including filler, matrix and interphase. The arrangement state of filler within the matrix materials is assumed to be random with uniform distribution. Fillers are surrounded by the interphase in the whole composite. The effects of interphase such as its thickness and stiffness on the thermo-mechanical properties of composite with various aspect ratios of filler are studied. The results illustrate that while the effects of interphase is significant for composites with randomly distributed spherical particles, it turns to be less effective as the aspect ratio of filler of composite increases. Moreover, the results demonstrate that the effect of interphase on the thermo-mechanical properties of fibrous composites in the transverse direction is more significant than that of fiber composites in the longitudinal direction.
In this study, heat transfer characteristics of slip flow over an isolated impermeable solid sphere are investigated numerically. An isothermal solid sphere is considered at intermediate Reynolds numbers (0 ≤ Re ≤ 50) for Prandtl numbers in the range of 0.7–7.0. The Navier–Stokes and energy equations are solved by a control volume technique in conjunction with the velocity slip and temperature jump boundary conditions. It was found that the size of the thermal wake region according to the Knudsen number depends on the Prandtl number. At lower Prandtl numbers (0.7 ≤ Pr ≤ 2.0), the thermal wake region shrinks as the Knudsen number increases, while at higher Prandtl numbers, it grows as the Knudsen number increases. The maximum temperature jump occurs at the front stagnation point where the local Nusselt is itself maximum, owing to the maximum temperature gradient at this point. The results show that due to the opposing effects of the velocity slip and temperature jump, the average Nusselt number variation with the Knudsen number depends nonlinearly on both the Prandtl and Reynolds numbers. Furthermore, for the limiting case of Re -> 0, an analytical solution for the problem is presented which has also served as a validation case.
Fretting tests are usually performed on flat specimens with lateral contacting pads. The shrink-fitted connection, which experiences fretting at the edge of the contact, prompted the alternative use of a round-shaped specimen. This simplified the equipment and provided an accurate alignment between the fretting specimen and the external hub which plays the role of the pad. The deep rolling treatment can also be efficiently applied to a round shape, which would otherwise be difficult on the flat specimen geometry. After introducing this solution for fretting testing, the paper shows an experimental campaign on three shrink-fitted connections with different sizes and material combinations. There was a significant improvement in fretting fatigue strength, induced by the deep rolling, for all three specimen types. Finally, scanning electron microscopic analyses provided insights into the fretting fatigue nucleation mechanisms both for untreated and deep-rolled specimens.
Optimum tolerance allocation plays a vital role in minimization of the direct manufacturing cost, and it is sensitive to tolerances related to variations in manufacturing processes. However, optimal adjustment of both nominal dimensions and selection of tolerances may further reduce assembly manufacturing cost and wastage of materials during processing. Most studies in existing literature focus on optimum tolerance allocation for the assemblies without considering nominal dimension selection. The method proposed in this work uses genetic algorithm techniques to allocate tolerances to assembly components, thereby minimizing costs. The component alternate nominal dimensions are predicted based on critical dimensions and its tolerances. The effectiveness of the developed algorithms demonstrated using randomly generated problems as well as sample problems taken from the literature. Test results are compared with those obtained using the Lagrange multiplier method. It is shown that by adjusting the nominal dimensions, the proposed method yields considerable savings in manufacturing costs.
Gear geometry is critical to the transmission performance. It not only affects the relative motion characteristics, lubrication, efficiency, and loading capacity but also affects the noise and vibration, as well as working reliability of system. The generating principles of one kind of torus involute (TI) gears is presented in this paper. The mathematical model and profiles equation of torus involute gears are derived and the profiles equation and its parameters are proposed. The correct meshing condition and tooth contact analysis (TCA) are analyzed. The loading capacity including contact stress and bending stress, etc., are proposed after compared with cylindrical spur gears. One pair of TI gears is machined according to the generating principles. The analysis results show that the TI gears can reduce the contact stress efficiently and it can effectively improve the bending strength of convex involute gear while the bending strength of concave TI gears is not significantly affected.
Torsional stiffness of a rotary table plays an important role in the static and dynamic characteristics of a rotary feed drive system. This paper proposes an effective approach to estimate the torsional stiffness of a worm geared transmission usually employed in rotary table. First, the stiffness models of each component used in the transmission are extracted. Then, an expression for the coefficient relating angular displacements is derived and a general torsional stiffness model for the rotary feed drive is developed, taking the time-varying mesh stiffness into account. Finally, a stiffness test scheme is presented and conducted to verify the proposed stiffness model. Furthermore, the influences of the gear’s parameters on the resultant torsional stiffness are investigated based on the developed model. Results indicate the necessity to incorporate a time-varying mesh stiffness when the torsional stiffness of the rotary table is under estimation. Also, a high-frequency variation in profile of torsional stiffness is induced by the mesh stiffness of gear pairs at the high-speed stage. Parametric studies show that tooth width and number of teeth of the driven gear at low-speed stage are more sensitive to stiffness than those at high-speed stage. However, the number of teeth of the driving gears introduces different effects onto the torsional stiffness. The presented model can be used to estimate the torsional stiffness of a rotary feed system efficiently, especially during the preliminary design stage.
The quantitative calculation of the source contribution is very important and critical for the identification of the main vibration sources and the reduction of vibration and noise in submarine. It is difficult to calculate the source contribution because of the submarine’s complex structure and the large amount of vibration sources. As a typical blind source separation method, independent component analysis (ICA) has recently been proved to be an effective method to solve the source identification problem in which the source signals and mixing models are unknown. However, the outcomes of the ICA algorithm are affected by random sampling and random initialization of variables. In our study, the prior knowledge of the vibration sources can be obtained through the vibration measurement of submarine. Obviously, information in addition to mixed signals from sensors can lead to a more accurate separation. Therefore the contrast function of ICA can be enhanced by the reference signals obtained by the prior knowledge. In this paper, a closeness measurement between the independent components and the reference signals obtained by the prior knowledge is introduced, and the closeness measurement is constructed to have the same optimization direction with the traditional contrast function: negentropy. The closeness measurement is used to enhance the contrast function and then the enhanced contrast function is optimized by means of the Newton iteration and the deflation approach. Thus the simplified independent component analysis with reference (ICA-R) algorithm is obtained. After that a method to quantitatively calculate the source contribution is proposed based on the outcomes of the simplified ICA-R. Finally, the effectiveness of the proposed method is verified by the numerical simulation studies. The performance offered by the proposed method is also investigated by the experiment: it appear as a very appealing tool for the quantitative calculation of the source contribution.
A two-stage optimization method for optimal dynamic design of planar mechanisms is presented in this paper. For dynamic balancing, minimization of the shaking force and the shaking moment is achieved by finding optimum mass distribution of mechanism links using the equimomental system of point-masses in the first stage of the optimization. In the second stage, their shapes are synthesized systematically by closed parametric curve, i.e. cubic B-spline curve corresponding to the optimum inertial parameters found in the first stage. The multi-objective optimization problem to minimize both the shaking force and the shaking moment is solved using evolutionary optimization algorithm – "Teaching-learning-based optimization (TLBO) algorithm". The computational performance of TLBO algorithm is compared with another evolutionary optimization algorithm, i.e. genetic algorithm.
Conceptual design is the most creative and important stage in product design process. A computer-aided creative design (CACD) system is indispensable to provide effective support for human-oriented creative behavior and iterative decision-making during the conceptual design process. Based on cognition and iteration, this study proposes a triplhelix innovative solving model to guide the construction of CACD system. In this model, three types of space are established, including design flow space as reference for mapping direction, knowledge inspiration space as source of stimulus information, and solution operating space as carrier. The cooperation among the triple space is organized based on memory information processing theory, so as to inspire designers’ cognitive thinking to generate product solutions. In addition, the iterative operations of design elements among function, behavior, and structure utilizing the proposed triple space are discussed. With this model, the designers can develop multiple innovative solutions according to expected design types (variant, adaptive, original), and different cognitive stimulation (extension, analogy, mutation) of design knowledge can also be obtained. Then, a prototype system of computer-aided creative design platform is developed to implement this innovative solving model. Finally, a design case of espresso machine is presented to demonstrate the practicability and validity of the prototype system.
This paper presents a novel multi-diamond kinematotropic chain that has various motion branches. The motion allowed by the chain in different branches is identified based on Lie group theory. A planar reconfigurable limb is obtained by adding a prismatic joint to the output link of the multi-diamond kinematotropic chain, leading to the construction of a class of planar reconfigurable parallel mechanisms. With the multi-diamond kinematotropic chain evolving into different motion branches, the planar reconfigurable mechanisms have three distinct configurations in which different operation modes including the 2T1R mode, 2T mode and 1T1R mode can be carried out. The multi-diamond kinematotropic chain is also integrated in the design of spatial reconfigurable limbs, resulting in the construction of a class of spatial reconfigurable parallel mechanisms with ten mobility configurations.
The bolted joints fatigue behavior was analyzed by using torque as tightening method and steel and aluminum as members’ material. The bolt used in the current study was the M6 class 8.8. The bolt preload value was calculated based on the bolts’ elongation in each applied torque. The fatigue limit increases as the torque increases up to the torque limit to fracture the bolt. This behavior was seen in both members’ material. Steel members support higher torque before bolt fracture. An analytical study also evaluated the relationship between the cyclic stress amplitude and the mean stress experienced by fatigue-tested bolts based on the available models for joint stiffness. The results were compared to the bolt fatigue diagram by Burguete and Patterson. The herein studied linear elastic theoretical models showed wide range in the correlation between stress amplitude and mean stress.
This study examined the effect of changes in center distance on a circular-arc gear pump that operates at high pressure and high speed. In principal these types of gear pumps have no trapped-oil and flow ripples. The effect of changes in center distance caused by assembly, machining, radial force and oil film force on the performance of circular-arc gear pumps was studied. The results show that the flow rate, axial force and torque increased linearly with an increase in variables
Aiming at the non-parametric and time-varying parametric uncertainty problems such as the external disturbances, smooth parameter variations and jump parameter changes existing in the robot satellite system with floating base, an adaptive variable structure trajectory tracking control method in Cartesian space is proposed. The dynamics equation in joint space of the robot satellite system with floating base is established based on the extended manipulator model, and the dynamics model of the system in Cartesian space is derived considering external disturbances to the manipulator and the base simultaneously. An adaptive variable structure controller is designed by adopting the composite adaptive control combined with variable structure control under the condition that the bounds of external disturbances and parameter variations are unknown, and the robustness analysis of the controller is performed. The simulation of a two-link planar robot satellite system with floating base adopting the control method presented is implemented. The simulation result shows that the end-effector of the robot satellite with floating base has a good capability of trajectory tracking in Cartesian space.
The concept of structural similitude provides a powerful tool for engineers and scientists to predict the behaviour of a structure using an appropriate scaled model. Even tough theoretical and numerical investigations of similarity conditions or scaling laws have shown to be feasible, their accuracy is not necessarily guaranteed when these laws are applied to real (experimental) structures. Herein, structural scaling laws are investigated for the analysis of the dynamic response of simple flexural plates. Specifically, the possibility to define exact and distorted similitudes is discussed through numerical and experimental data. This paper focuses on exact and distorted similitudes in the analysis of the dynamic response of flexural plates. The similitude laws are defined by invoking the classical modal approach and looking for (in)equalities in the structural dynamic response. A total of seven aluminium rectangular plates with one clamped edge are modelled in finite elements and tested experimentally to study the effect of distorted similitudes and experimental variations in the performance of the predicted dynamic response.
Heat transfer is very essential process and, therefore, it is necessary to develop the optimization model. In this paper, an attempt has been made to develop an optimization model for complex heat transfer process using the Taguchi method. This paper presents the findings of an experimental investigation on the effects of input parameters such as Reynolds number, heat input, and Lx/Ly ratio in a channel mounted with square blocks in staggered manner. The Nusselt number is considered as the output quality characteristics. Taguchi-based L27 orthogonal array has been used to accomplish the objective of the experimental study. An orthogonal array, signal-to-noise (S/N) ratio and analysis of variance (ANOVA) are employed to analyze the effect of input parameters on heat transfer enhancement. Based on the S/N ratio value the optimal level of the input is identified and significant contribution of these parameters is determined by ANOVA. Confirmation test is also conducted to validate the optimal results. It is clearly shown that the output characteristic is improved by this approach. Taguchi method revealed that optimal combination of the heat transfer parameters for the enhancement of heat transfer rate is set as: Lx/Ly at 2.5, heat input to be 250 W, and Reynolds number to be 300.
A model of load distribution over threads of planetary roller screw mechanism (PRSM) is developed according to the relationships of deformation compatibility and force equilibrium. In order to make the applied load of PRSM uniformly distributed over threads, an improvement approach is proposed, in which the parameters of thread form of roller and nut are redesigned, and the contact conditions of roller with screw and nut are changed to compensate the axial accumulative deformation of shaft sections of screw and nut. A typical planetary roller screw mechanism is taken as example to analyze the load distribution, and the effects of installation configurations, load conditions and thread form parameters on load distribution are studied. Furthermore, the improvement approach is applied to the PRSM, and it is proved to be beneficial to reach uniform load distribution over threads.
The spatial correlation function (SCF) is an important part of the Kriging surrogate model that describes the sample data structure, and the SCF affects the fitting accuracy of the Kriging surrogate model directly. In a Kriging surrogate model, a single SCF is typically selected to describe the sample data structure, which may cause sample information loss and fitting error. A new Kriging surrogate model for combination forecasting (CF-Kriging) was constructed by integrating of linear weighted approach based on the combination forecasting method, in which the differences in the sample information described by the diverse SCFs for the same sample data structure were considered. The integrity of the sample information of the CF-Kriging model was improved using single-SCF Kriging surrogate models as sub-models and considering the minimum mean absolute percentage error as the improved target for the fitting accuracy. The effectiveness of the CF-Kriging surrogate model was demonstrated using four test functions and two engineering problems, which indicated that the CF-Kriging surrogate model could effectively improve the fitting accuracy and the fitting stability of an ordinary Kriging surrogate model.
In data-driven prognosis approach, indicator information plays an important role for reliable prediction. Although lots of researches have been carried out on prognosis algorithms, only few have paid attention on developing an effective method to select ‘good’ degradation indicators. This paper presents a novel strategy to address the problem, which mainly proposes methods of monotonic feature selection using rank mutual information, and similarity-based modeling for remaining life estimation. The proposed system is demonstrated based on open source data of bearing life cycle. The experiment results show that satisfactory prognostic performance can be obtained with advantages of simplicity, accuracy and generality.
The work deals with consideration of the technology of forming many-sided outer surfaces with the variable profile of planetary turning. The peculiarities of this technology were detected and the actuality of the research problem was specified. The essence of study lies in the determination of the cutting force’s effect on the blank rigidity. The calculation scheme and mathematical model, which allow studying the cutting forces effect on the rigidity of technological system during processing, were stated. The dependence of blank rigidity on the form of cross section processing with multiple-blade instrument with planetary movement was determined. The mathematical expression of the allowable twist angle under effect of cutting forces on the blank was offered. This study can be applied as the test calculation at projecting of technological rigging and setting modes of cutting at forming of many-sided outer surfaces with variable profile of planetary turning.
In this paper, a method of measuring the relative torsional angles of the flexible coupling under working condition was developed. A double-encoder measurement system was proposed to get the torsional angles. The torsional angles were divided into "constant torsional angle" and "alternating torsional angle". The measured results were analyzed further, which were applied to a series of flexible couplings. Firstly, the torsional stiffness of D-type flexible coupling was obtained according to the relationship between torques and torsional angles. The proposed method overcomes the difficulty that the angular displacements of flexible coupling cannot be measured online under operating condition. The feasibility and accuracy of the method developed in this study was verified by comparing stiffness curve with unloading curve obtained from static torsional experiment and values from factory inspection report. Furthermore, in view of the tear fault of A-type flexible coupling in a diesel generator set, the maximum alternating torsional angles of A-type, B-type, and C-type flexible couplings were measured under working condition, then safety margins were obtained for the diesel generator set. According to the safety margins of the three kinds of couplings, C-type flexible coupling is chosen to replace A-type, which provided the basis for type selection of flexible coupling. Finally, the method developed in this study would also be applied to the operation monitoring and fault diagnosis of flexible coupling online.
In this paper, a new gravity-balanced 3T1R parallel mechanism is addressed. Firstly, structure description, inverse and forward kinematic modeling are performed in detail. Secondly, Jacobian derivation based on screw theory and singularity analysis using Grassmann Line Geometry is performed, and then optimal kinematic design with respect to workspace size, kinematic isotropy and maximum force transmission ratio are conducted. Thirdly, the gravity balancing design using both counterweights and springs is proposed and a prototype of this mechanism is also presented. Results of analysis show that the proposed mechanism has quite a few potential applications.
The paper presents direct measurement of in-cylinder friction from a single cylinder motocross race engine under motored conditions and compares the same with a new analytical predictive method. These conditions are encountered in piston–cylinder system with the application of cylinder deactivation (CDA) technology, which is a growing trend. The analytical method takes into account the various regions within instantaneous contact of compression ring–cylinder liner, including lubricant film rupture, cavitation zone and the subsequent lubricant film reformation. The analysis also includes the effect of boundary friction and lubricant rheology. The predictions and direct measurements of cyclic friction show good agreement and indicate dominance of viscous friction under the investigated engine running conditions. In particular, it is shown that the compression ring contribution to in-cycle friction is most pronounced in the region of high cylinder pressures because of combined Poiseuille friction and some boundary solid interactions. The combined experimental-analytical approach has not hitherto been reported in literature.
To achieve lightweight vehicle door, this paper presents a novel design with a hybrid material tailor-welded structure (HMTWS). A multiobjective optimization procedure is adopted to generate a set of solutions, in which the door stiffness and mass are taken as objective functions, and the material types and plate thicknesses are regarded as the discrete and continuous design variables, respectively. To improve the optimization efficiency, Kriging algorithm is used for generating surrogate model through a sequential sampling strategy. The non-dominated sorting genetic algorithm II (NSGA-II) is employed to perform the multiobjective optimization. It is found that for the same computational cost, the sequential sampling strategy can yield more accurate optimization results than the conventional one-step sampling strategy. Most importantly, HMTWS is found more competent than the traditional thin-walled configurations made of steel or other lighter mono-materials for maximizing the usage of materials and stiffness of the vehicular door structures.
In this paper, the design process of a new model predictive control (MPC) for force-balancing operation mode of a vibratory Micro-Electro-Mechanical-System (MEMS) gyroscope is investigated. Based on the internal model principle, a robust repetitive MPC is proposed to regulate the gyroscope’s drive mode output to a pre-specified periodic reference signal and to set the sense mode vibration to zero. Owing to the fast dynamics of the MEMS gyroscope, large prediction horizons are required to attain the closed-loop stability as well as tracking objectives. In order to alleviate the computational burden of online optimization within large prediction horizons, a set of orthonormal functions, named Laguerre functions are used to parameterize the system trajectories. Distinguishing features of the proposed control method, for MEMS gyroscope applications, are robustness to large parametric uncertainty, exogenous disturbances/noises and the capability to handle the hard input constraints within an optimal setting. Using a recursive least squares algorithm, on-line estimation of the unknown angular rate and the quadrature error of the force-balanced gyroscope is performed. Through computer simulations, the tracking accuracy of the proposed control method together with the convergence of the parameter estimation algorithm is assessed.
To establish accurate finite element (FE) model of bolted joint structures of aeroengine stator system (casings), this work implements the parametric FE modeling and updating of bolted joints of aeroengine stator system with multi-characteristic responses (multi-object). Firstly, the parametric FE modeling approach of bolted joint structure was developed based on the thin layer element method. And then the FE model updating thought of aeroengine stator system was developed based on the probabilistic analysis method. Finally, the parametric modeling and updating of the bolted joints of aeroengine stator system with multi-characteristic responses was completed by the optimization iteration calculation of objective function based on the proposed methods and the static stiffness testing data. Through the parametric modeling of bolted joint structures based on the thin layer method, the complexity of FE model of aeroengine casings with many bolted joint structures is reduced. As shown in the FE model updating of casings with multi-characteristic responses analysis, the static stiffness from the updated model are very close to the test data, in which the maximum relative error decreases to 3.9% from 30.52% and the others are less than 3%, so that the design precision of aeroengine stator system with the many and wide variety of bolted joints gets a great improvement. Moreover, the proposed methods of parametric modeling and model updating for multi-characteristic responses are validated to be effective in the simulation and equivalent of the mechanical characteristics of bolted joints in complex systems like aeroengine stator system.
Vibration analysis has been extensively used as an effective tool for bearing condition monitoring. The vibration signal collected from a defective bearing is, however, a mixture of several signal components including the fault feature (i.e. fault-induced impulses), periodic interferences from other mechanical/electrical components, and background noise. The incipient impulses which excite as well as modulate the resonance frequency of the system are easily masked by compounded effects of periodic interferences and noise, making it challenging to do a reliable fault diagnosis. As such, this paper proposes an envelope demodulation method termed short time fractal dimension (STFD) transform for fault feature extraction from such vibration signal mixture. STFD transform calculation related issues are first addressed. Then, by STFD, the original signal can be quickly transformed into a STFD representation, where the envelope of fault-induced impulses becomes more pronounced whereas interferences are partly weakened due to their morphological appearance differences. It has been found that the lower the interference frequency, the less effect the interference has on STFD representations. When interference frequency keeps increasing, more effects on STFD representations will be resulted. Such effects can be reduced by the proposed kurtosis-based peak search algorithm (KPSA). Therefore, bearing fault signature is kept and interferences are further weakened in the STFD-KPSA representation. The proposed method has been favourably compared with two widely used enveloping methods, i.e. multi-morphological analysis and energy operator, in terms of extracting impulse envelopes from vibration signals obscured by multiple interferences. Its performance has also been examined using both simulated and experimental data.
In the present paper, the problem of transverse free vibration of two parallel beams partially connected to each other by a Winkler-type elastic layer is investigated. Euler–Bernoulli beam hypothesis has been applied, and translational and rotational elastic springs in each end considered as support. The motion of the system is described by coupled, piece-wise differential equations. The differential transform method (DTM) is employed to derive natural frequencies and mode shapes. DTM is a semi-analytical approach based on Taylor expansion series which does not require any admissible functions and yields rapid convergence and computational stability. After validation of the DTM results with results reported by well-known references and finite elements solution, the influences of the inner layer connection length, boundary conditions, the coefficient of elastic inner layer and ratio of beam’s flexural rigidity on natural frequencies as well as influences of the inner layer connection length on mode shapes are discussed. This problem is treated for the first time, and results are completely new which candidate them to being considered for practical engineering applications.
This paper aims at investigating precisely the dynamic performance of deployable structure constituted by scissor unit mechanisms with clearance joint. Based on the motion law in real joints, the contact model is established using an improved Gonthier nonlinear continuous contact force model, and the friction effect is considered using LuGre model. Moreover, the resulting contact force is suitable to be included into the generalized force of the equations of motion of a multibody system and contributes to replace motion constraints. In the sequel of this process, the effect of joint clearance is successfully introduced into the dynamical model of scissor deployable structure and the dynamic characteristics of deployable structure with joint clearance are obtained using a direct default correction method, which can directly modify the coordinates and speed of the system to avoid the numerical results divergence. Also, the new hybrid contact force model of revolute joint clearance is verified through comparing with the original model. The numerical simulation results show that the improved contact model proposed here has the great merit that predicts the dynamic behavior of scissor deployable structure with joint clearance.
A new method was presented by utilizing the structural circumferential periodicity of the inertia excitation due to the concentrated masses to compute the transverse vibration for thin circular plate carrying concentrated masses. Comparison between the calculated fundamental frequency coefficients and those from other approaches validates the method. And then, the point mobility matrices and the power flows were solved on the basis of modal function solutions and the analytical results of simply supported case were presented. Finally, the parametric effect of the single concentrate mass on the power flows was investigated.
This paper presents a novel design of an inclined feeder with a chute that vibrates like a simple pendulum. It is designed with a horizontal vibration and an inclined chute for feeding steel scraps in electric furnace steelmaking. The simplified model of the feeder and the governing equations of kinematics analysis are introduced. Numerical integration programs were developed to investigate the kinematics characteristics of the feeder. The inclination angle of the chute and the vibration frequency, two vital impact factors affecting the motion of the fed block, were analyzed. Compared with the traditional horizontal chute feeder, this novel feeder has proved to be more efficient and speed-controllable. An experimental prototype was fabricated and feeding tests were performed. Results indicate that good agreement between calculation and experiment was achieved on the motion of the fed block. A stepped chute was proposed to solve the problem of block intertwining and uneven dropping during the feeding. The simulation of the multi-block feeding showed that the feeding with the stepped chute was steadier than that with the smooth chute. This research indicates that the mathematical model is able to predict the motions of the system and the new feeder will be capable and effective in performing the steel scrap feeding task.
In this work, the controlled synchronization of two nonidentical homodromy coupling exciters driven by inductor motors in a vibratory system is investigated. According to the previous works, using small parameter perturbation method deduces the conditions of implementing self-synchronous motion of two exciters. The shortage of self-synchronization method in design of vibratory system is found. The controlled synchronization method is proposed by employing sliding mode control and proportional–integral method on two inductor motors based on the master-slave control strategy to replace the self-synchronization. The stability of the controllers is proved by Lyapunov theorem. The performances of the control system are demonstrated by numerical simulation, which shows the controlled synchronization method is feasible. Additionally, the effects of various uncertainties including internal parameter perturbations and external disturbances on the control system are discussed, which indicate the proposed controllers have a good robustness.
The profile designs of screw elements are very crucial to improving the mixing performance for the intermeshing counter-rotating twin-screw kneader. In order to find the inherent law among different profiles of screw elements and to derive a mathematical model which evolves different types of end cross-section profiles of screw elements, a universal mathematical model of end cross-section profiles of screw elements is presented in this work. Different types of profiles of screw elements, including those traditionally used can be obtained by evolutionary design method after changing the tooth number of female and male elements and other design parameters. Several typical screw elements with different types of end cross-section profiles are selected to analyze the mixing performance. Spatial flow patterns in flow channel of the screw elements are presented with particle tracking analysis by using mesh superposition technology. The mixing performance of different screw elements including distributive and dispersive mixing, contrastive analysis for some parameters, such as residence time distribution density function, segregation scale, rate of stretching, rate of shear, etc. are proposed. The results in this paper provide a data basis for the profiles selection of screw element for intermeshing counter-rotating twin-screw kneader.
This article provides a mathematical framework based on the basic law of gear kinematics for calculating the tooth geometry of arbitrary gear types. The described algorithms are illustrated by means of practical applications, especially nonstandard gearings. The computed geometry is exported as a point cloud with integrated STEP-modeling. Thus, further analysis of the generated gear types are possible, e.g. by computer-aided design or finite-element software tools as well as manufacturing on 5-axis-CNC or forging machines.
Ring periodic structures are widely spread in engineering applications, where natural frequencies can split due to the deviation from axisymmetry. This work aims at the elimination of the dual-mode natural frequency splitting by using feature shifting. A concept of equivalent feature is introduced based on the grouping idea and an analytical model with discrete features is established. The relationships between the group number, feature number, shifting angle and excited circumferential wavenumber are identified as closed-form expressions. The splitting for structures with unshifted standard features depends on the feature number and wavenumber regardless of the grouping patterns. The equivalence between various groupings is verified. Simple rules governing the dual-mode splitting are elaborated, where one splitting is removed by a combination of equivalent feature number and wavenumber, and the other is eliminated by feature shifting. The rules allow immediate estimation and elimination of the dual-mode splitting where the modified structures still hold symmetry. The results can find application in vibratory structures where the frequency splitting is the key concern. The main results are verified by the Finite Element method.
Attempts are being made to improve mechanical design by using nonlinearity rather than eliminating it, especially in the area of vibration control and in energy harvesting. In such systems, there is a need to both predict the dynamic behavior and to estimate the system properties from measurements. This paper concerns an experimental investigation of a simple identification method, which is specific to systems in which the behavior is known to be similar to that of a Duffing-type system. It involves the measurement of jump-down frequencies and the amplitudes of displacement at these frequencies. The theoretical basis for the method is briefly described as, is an experimental investigation on a beam-shaker system. The results are comparable with those determined by the restoring force surface method. The method described in this article has the advantage that the data can be collected and processed more easily than the restoring force surface method and can be potentially more suitable for the engineering community than existing identification measures.
Planetary gearboxes generally consist of a ring gear, or gear body, connected with the input and output flanges by means of several screws, equally spaced along the diameter. The ring gear is manufactured with steel, whereas the flanges are usually made of cast iron. These screws must provide axial preload between the parts, allowing the assembly withstanding the breakaway torque given by the difference between the output and input torque applied to the gearbox. For a given screw geometry, the axial preload can be calculated, provided that the friction coefficients in the thread and in the underhead are known. Most often, the tightening torque is the only parameter being controlled during assembly and service operations. Hence, it is mandatory to know the friction coefficients of the joint. These depend, among others, on the hardness, roughness and texture of the mating surfaces, as well as on the lubrication state of the joint. In fact, the addition of a lubricant modifies the tribological behavior of the joint, thus the wearing evolution of the surfaces across repeated tightening operations. The present work tackles the following two aspects: (i) the characterization of the preloading force–tightening torque relationship on the actual component by means of a dedicated specimen, (ii) the evaluation of the influence of lubrication on the evolution of the frictional characteristics of the joint across several re-tightening operations. The present work has been carried out by means of both numerical finite element analyses and experimental stress analysis techniques.
To reveal the mechanism and evolution laws of the braking performance declining from heat load in the repeated braking applied for wet multidisc brake, a finite element analysis was carried out by using the bidirectional thermal-structure coupling method. Based on the fundamental principles of the energy conservation and virtual work principle, the elemental equations between temperature and heat load, and deformation displacement and load with heat transferring boundary conditions and heat–structure interaction were derived. Taking a steel disk in the brake for example, the deformation state of its elements, and the starting time, the location, the severity, and evolution laws of the plastic deformation were analyzed and demonstrated by using dimensionless stress distribution contours. The area in contact along the interface and the ratio of the element numbers to produce plastic deformation to the total element numbers on the steel disk were described by contact ratio and plasticity ratio, respectively. Moreover, the results under the repeated braking case were compared with that under the lasting braking case, which indicates that the influence of the temperature load on the performance declining of the repeated braking case is much lower than one of the lasting braking case, and the temperature is lower than 40 K and the plasticity ratio is smaller than 0.35 after the braking time is longer than 350 s. The conducted finite element analyses provided the theoretical fundamentals for the design and the application of the brake in the heavy type of trucks.
An approach for designing compliant mechanisms with curvilinear fiber path laminated composites is presented to obtain the optimum topology structure in this paper. A laminated plate with curvilinear fiber path is built by using the shifted fiber path method. Meanwhile, an equivalent constitutive relationship of the laminated plate has been obtained based on the laminated plate theory. Taking the element relative density as design variable, minimizing the weighted linear combination of the mutual strain energy and the strain energy is considered as an objective function to achieve the desired deformation and enough load-carrying capacity of compliant mechanisms with the volume constraint. The topology optimization problem is solved via the optimality criteria and the sensitivity filtering technology. The numerical examples of designing compliant inverters are investigated to demonstrate the effectiveness of the proposed method. And furthermore, the displacements and the stress levels are also discussed for the compliant inverters with different curvilinear fiber laminated sequences.
This paper presents an activity concerning the modeling and the control of an innovative power-assisted electric bicycle. The proposed control method is based on a torque control designed via an optimal approach to achieve multi-objective performances regarding the external disturbance input, control signal magnitude, and velocity tracking error. The performance of the methodology has been evaluated applying the proposed control to a new pedelec (pedal electric cycle) model characterized by the measurement of the total torque (rider torque and electric motor one) employed as a feedback for the control. To this aim, a mathematical model of the bicycle, equipped with the electric motor, has been developed. Simulations have been performed in order to evaluate the tracking capability and the disturbance rejection. The performances have been compared with the ones referred to a traditional assistance approach, and the results demonstrate that the proposed approach provides improvements in terms of riding comfort and energy employment.
As a result of the manufacturing errors in the main parts of spindle, and the errors in assembly process of spindle, as well as the non-uniform heat distribution during spindle operation, the non-uniformly distributed preload in rolling bearing is inevitable. The non-uniform preload has not only axial force on the rolling bearing, but also the bending moment around the rolling bearing center. The effect of preload in bearing being non-uniform on the spindle performance is still unclear. In order to analyze the spindle performance with rolling bearing under non-uniform preload, a spindle test system with adjustable non-uniform distribution preload is built. By changing the magnitude of preload force on each action point, it can make the preload force distribute non-uniformly. In the static state of spindle, upon the change of non-uniformly distributed preload, the radial displacement of spindle shaft end is also changed, while in the dynamic state of spindle, it will lead to the change of the rotation center of spindle as a result of bending moment accompanying the non-uniform preload. Furthermore, the dynamic and static results show that when the preload is under non-uniform distribution, the spindle performance is significantly different from that under uniform preload. So this study would have certain reference value to check the spindle performance and explore novel preload method for rolling bearing.
The in-plane compressive collapse and fracture toughness of a hierarchical hexagonal honeycomb with sandwich walls consisting of corrugated cores are studied by using finite element method. Its near-optimal configuration is identified by maximizing its elastic limit, which is determined by three competing failure modes including plastic yielding of the larger struts, or elastic wrinkling of the face sheets of the larger struts, or elastic buckling of the smaller struts. The overall mechanical properties of the optimal hierarchical honeycomb, including the Young’s modulus, elastic limit, peak strength, and fracture toughness are obtained from finite element method simulation and compared with analytical predictions, and the discrepancy between the two is explained. The optimal hierarchical honeycomb is found to be superior to its equivalent mass first-order honeycomb in all the mechanical properties listed above when the relative density is low (about 10%). Moreover, the Young’s modulus, elastic limit and peak strength under plastic failure mode, and the fracture toughness of this optimal hierarchical honeycomb are shown to depend linearly upon its relative density. This paper provides additional insights into hierarchical cellular materials.
This paper provides a comprehensive assessment on some commonly used thermo-viscoplastic constitutive models of metallic materials during severe plastic deformation at high-strain rates. An hcp model previously established by us was improved in this paper to enhance its predictability by incorporating the key saturation characteristic of strain hardening. A compensation-based stress-updating algorithm was also developed to introduce the new hcp model into a finite element program. The improved model with the developed algorithm was then applied in finite element simulation to investigate the high-speed machining of Ti6Al4V. It was found that by using different material models, the simulated results of cutting forces, serrated chip morphologies, and residual stresses can be different too and that the improved model proposed in this paper can be applied to simulate the titanium alloy machining process more reliably due to its physical basis when compared with some other empirical Johnson–Cook models.
The static and dynamic properties of the frame and the front fork of a single track vehicle play a critical role from the point of view of vehicle stability. A turning point in the study of motorcycle stability was established by the introduction of lumped stiffness elements to characterize the critical compliances of the motorcycle elements, this approach being still in use with advanced multibody codes. Nonetheless, up to now very few scientific studies have been carried out to identify the parameters that account for the stiffness and damping properties of motorcycle front forks and frames. This work addresses the problem of identifying the parameters needed for developing lumped element models of motorcycles from experimental results. Two motorcycle frames are studied performing static, dynamic, and modal tests by means of a specific testing equipment. The frames have been tested in two different conditions: fixing them at the steering head or at the swing-arm pivot.
In the first section of the paper a general definition of the twist axis, based on the concept of "Mozzi" or instantaneous screw axis, is presented. The twist axis is used for characterizing the deformation patterns of the tested frames. The static twist axis is identified loading the frames at low rate by means of a servo-hydraulic actuator and measuring the deformation of a reference plate by means of three laser sensors; the dynamic twist axis is identified exerting an impulsive excitation and measuring the vibration of a reference plate by means of three accelerometers. In the last section of the paper, experimental results obtained on motorcycle frames are shown. A method to identify the stiffness properties of the frames from the measured twist axes is presented. Results obtained with the proposed method are in good agreement with the ones presented in literature.
Large components such as wing sections should be aligned and positioned in a desired position prior to the final manufacturing or assembly, so a digital alignment and position device based on six degree of freedom parallel manipulator with several prismatic-prismatic-prismatic-spherical branches was designed and fabricated to meet the needs. The digital alignment and position device is an alignment device based on the parallel manipulator, and it is also a positioning and holding fixture for large components manufacturing or assembly. In order to effectively and efficiently select the supporting points of large component where the digital alignment and position device branch is connected with, the performance of the parallel manipulator and the fixture should be comprehensively analyzed at the same time. The global performance indices such as the dexterity index, the bearing capacity index, and the stiffness index are calculated based on the mechanism Jacobean matrix of the parallel manipulator, and the positioning stability index is calculated based on the position Jacobean matrix of the fixture. The results show that the global performance indices are not related to the pose, but the positioning stability index is; in addition, all indices rely on the originally selected supporting points and provide the basis for the effective selection of the supporting points for large component aligned and positioned by the digital alignment and position device, which is based on parallel manipulator with prismatic- prismatic-prismatic-spherical pairs.
Wrapping machines usually consist of a two- or a four-column frame, supporting a huge rotating ring, connected to a pre-stretch unit with film coil carrier. Stiffness is a key point of packaging machines, since it is strictly related to the accuracy of the wrapping task. It depends on the stiffness of the frame, which can be achieved by the four-column architecture, and on the ring constraint system. As a consequence, the ring structures are usually highly statically indeterminate. Nowadays, there is an increasing demand for higher rotational speeds and more reduced operation times. Therefore, an accurate structural analysis of the ring, considering its actual loading and constraints is more and more important. The structural analysis of the rotating ring is treated by many references; however, such a statically indeterminate constraining makes this problem highly complicated. The goal of this paper consists in the development of a general and original computational algorithm for the structural analysis of rotating rings. The results are collected in a user-friendly way in terms of normalized internal loads, so that they can be of a great help even for not expert users. This model has been experimentally validated and easily applied to case studies and optimization tasks.
A hybrid vibration isolator (HVI) is presented with its structure, dynamic model, control strategy and preliminary experiments. The HVI is composed of the active piezostack actuator and the passive rubber isolator, which has compact structure and high reliability. Based on the dynamic model and the formula derivation of the transmissibility, the control algorithm is established using the linear quadratic regulator method. The simulations indicate that the vibrations acting on the load platform are vastly reduced, where the active piezostack-based actuator can eliminate the resonance peak significantly. Moreover, the passive rubber-based isolator is effective to isolate a part of vibration once active control fails. Finally, an experimental system is built up to implement integrated passive and active vibration control using the HVI prototype. The experimental results verify the theoretical analysis work.
The ability of selected dexterity and cutaneous sensibility tests to measure the effect of medical glove properties (material, fit, and number of layers) on manual performance was analyzed. Manual performance testing of gloves to-date has focused on thicker gloves where the effects are more obvious. However, clinicians have reported dissatisfaction with some medical gloves and a perceived detriment to performance of new materials compared to latex. Three tests (Purdue Pegboard Test, Crawford Small Parts Dexterity Test, and Semmes-Weinstein Monofilaments) were performed by 18 subjects in five hand conditions (ungloved; best-fitting, loose-fitting and a double layer of latex examination gloves; best-fitting vinyl gloves). Tests were performed in the ungloved condition first, and the order of the gloved tests was randomized. Learning behavior was also measured. The Purdue test showed a significant effect of hand condition, but no differences between latex and vinyl. No significant effect of hand condition was found in the Crawford "Pins and Collars" test, but the "Screws" test showed promising discrimination between glove types. The Monofilaments test showed a significant effect of hand condition on cutaneous sensibility, particularly a reduction when "double-gloving," but no significant differences between glove types. Existing tests show some ability to measure the effect of gloves and their properties on manual performance but are not comprehensive and require further validation. In order to fully describe the effects of medical gloves on manual performance, further tests should be designed with greater resolution and that better replicate clinical manual tasks.
Spline couplings are mechanical elements used to transmit power by joining two coaxial rotating shafts. The main damaging phenomenon on these elements is fretting wear, which can occur on teeth surfaces when there is a relative movement. Therefore, specific design criteria to evaluate teeth damage of spline couplings subjected to fretting wear are needed. In this work, the criterion proposed by Ruiz is considered and criticalities of the first Ruiz parameter are analysed by performing an uncertainty evaluation. The specific working misaligned conditions of a dedicated test rig were considered in this analysis. An uncertainty table allows the comparison of main geometrical and mechanical factors, evidencing their relevant effects. It shows the need of a deeper analysis on the coefficient of friction between the contact surfaces of spline couplings working in misaligned conditions.
In view of the limited quantity of modified segments for high-order and two-stage modified elliptical helical gears, and poor adjustment capacity for transmission ratio, the formation mechanism of a high-order multistage modified ellipse was studied, and a unified mathematical expression of the family of ellipses was derived. Thus, a design procedure for the helical gear pairs of the high-order multistage modified ellipse was suggested, and then their transmission characteristics were discussed exhaustively. Moreover, some checking methods such as curvature radius of pitch curve, convexity, pressure angle, undercutting, and contact ratio were offered. Finally, two design cases, including two-order and three-stage modified elliptical helical gear pair and two-order and four-stage one, were implemented. The cases indicate that a high-order multistage modified elliptical helical gear can be utilized in practice.
Owing to their locally resonant mechanism, internal resonators are usually used to provide band gaps in low-frequency region for many types of periodic structures. In this study, internal resonators are used to improve the vibration attenuation ability of finite periodic tetra-chiral coating, enabling high reduction of the radiated sound power by a vibrating stiffened plate. Based on the Bloch theorem and finite element method, the band gap characteristics of tetra-chiral unit cells filled with and without internal resonators are analysed and compared to reveal the relationship between band gaps and vibration modes of such tetra-chiral unit cells. The rotational vibration of internal resonators can effectively strengthen the vibration attenuation ability of tetra-chiral lattice and extend the effective frequency range of vibration attenuation. Two tetra-chiral lattices with and without internal resonators are respectively designed and their vibration transmissibilities are measured using the hammering method. The experimental results confirm the vibration isolation effect of the internal resonators on the finite periodic tetra-chiral lattice. The tetra-chiral lattice as an acoustic coating is applied to a stiffened plate, and analysis results indicate that the internal resonators can obviously enhance the vibration attenuation ability of tetra-chiral lattice coating in the frequency range of the band gap corresponding to the rotating vibration mode of internal resonators. When the soft rubber with the internal resonators in tetra-chiral layers has gradient elastic modulus, the vibration attenuation ability and noise reduction of the tetra-chiral lattice coating are basically enhanced in the frequency range of the corresponding band gaps of tetra-chiral unit cells.
Assembly of critical threaded connections such as safety belt and steering wheel screw joints must be quality assured to 100%. Not only the screw needs to be in position but the strength of the joint must also be guaranteed. To accomplish this, classical process surveillance is combined with angle monitoring and screws with special features. A plant system that keeps track on cars of various variants sends information to a screw joint controller that in turn sends a unique parameter set to the screw joint equipment. Together with so-called socket trays and balancing rules, the process arrangement can be made in such a way that the wrong screw can never be assembled without detection. To provide sufficient strength of joints, different kinds of angle monitoring are used. For example, entering/down running angle monitoring that are used to secure sufficient thread engagement with static high strength joints. Angle monitoring is also used to control that all parts are in position before the joint is tightened. For clamp load critical joints, final angle monitoring is used. Together with standard torques and standard assembly friction given by standard fasteners, sufficient clamping force can be guaranteed. With clamp load critical chassis joints, gradient-controlled yield point tightening has shown to be a successful assembly technique with the all new Volvo XC90. Furthermore, screws with special thread geometries are used to avoid cross threading, and in many cases hand entering can be taken away. Altogether, it can be concluded that the Volvo Cars assembly technology not only is very safe but also at a relatively low cost.
The design of space systems is a complex and multidisciplinary process. In this study, two deterministic and nondeterministic approaches are applied to the system design optimization of a spacecraft which is actually a small satellite in low Earth orbit with remote sensing mission. These approaches were then evaluated and compared. Different disciplines such as mission analysis, payload, electrical power supply, mass model, and launch manifest were properly combined for further use. Furthermore, genetic algorithm and sequential quadratic programming were employed as the system-level and local-level optimizers. The main optimization objective of this study is to minimize the resolution of the satellite imaging payload while there are several constraints. A probabilistic analysis was performed to compare the results of the deterministic and nondeterministic approaches. Analysis of the results showed that the deterministic approaches may lead to an unreliable design (because of leaving little or no room for uncertainties), while using the reliability-based multidisciplinary design optimization architecture, all probabilistic constraints were satisfied.
Dielectric elastomers are composite thin film structures composed of a dielectric polymer between compliant electrodes. Previous hyperelastic models have not modeled the constraint effects of compliant electrodes on the lateral contraction of the dielectric material as it stretches, and are therefore unable to fully describe the electromechanical behavior of the dielectric elastomer or provide a means to understand the constraint effects. An empirical boundary coefficient is introduced to model these constraint effects on the lateral boundaries of the material under uniaxial tension. Employing an averaged stretch ratio concept, it is shown that this coefficient can be obtained from experimentally measurable geometric variables. Values for the boundary coefficients of sample dielectric elastomer films were obtained from experiments performed on a uniaxial test stand. Incorporating the boundary coefficient into the model formulation, a specific hyperelastic stress–strain relation is derived to describe the electromechanical behavior of dielectric elastomers under combined uniaxial tension and electrical loading. Comparison of the experimental and predicted values of the induced force in the axial direction due to the Maxwell stress based on the uniaxial model shows favorable agreement.
Within a research project, experimental investigations of large-sized worm gears (pairing steel worm with bronze worm wheel) with centre distance a = 315 mm are carried out. The primary aim is to gain verified knowledge regarding load-carrying capacity and efficiency for this worm gear size. The paper describes the conducted tests in detail and shows basic examples of experimental test results. In the course of these investigations, an overall worm gearbox efficiency of up to = 96% is measured.
This paper introduces an application of non-linear partial least squares for vibro-acoustic regression modeling and for an industrial sewing machine. In the vibro-acoustic regression model, the vibration accelerations of reference points are defined as explanatory variables, while the noise sound pressure of target points is defined as response variables, and the number of explanatory variables is determined initially by a correlation analysis in the time domain. To improve predictive accuracy while a non-linear relationship exists between the explanatory and response variables, the explanatory variables are preprocessed by kernel function transformation. The comparison of regressive noise sound pressure to experimental data indicates that the non-linear partial least squares regression model has high predictive accuracy. Furthermore, the contributions of vibration accelerations to noise sound pressure are analyzed, by which the structure optimizations are guided and practiced. The comparison of noise test results before and after optimization testifies to the effectiveness of the contribution analysis.
Hydraulic piston pumps are commonly used in aircrafts and various other equipment, and efficient fault diagnosis of them is playing an important role in improving the reliability and performance of hydraulic systems. Given that the discharge pressure signal of piston pump is a quasi-periodic signal and contains variety of state information, this article proposes a fault diagnosis method combining a two-step empirical mode decomposition (EMD) method based on waveform matching and extrema mirror extension with fuzzy C-means clustering. Based upon discharge pressure signals of piston pumps, the two-step EMD method which can restrain the end effects of traditional EMD is adopted to decompose the original signal. Characteristic vectors are then constructed by computing the normalized characteristic energy of selected Intrinsic Mode Function (IMF) components on the basis of local Hilbert marginal energy spectrum. Finally, fuzzy C-means clustering algorithm is used to identify the faults of pumps. Experimental results indicate that the proposed method can identify the faults of pumps effectively.
Based on the Sanders thin shell theory, this paper presents an exact solution for the vibration of circular cylindrical shell made of two different materials. The shell is sub-divided into two segments and the state-space technique is employed to derive the homogenous differential equations. Then continuity conditions are applied where the material of the cylindrical shell changes. Shells with various combinations of end boundary conditions are analyzed by the proposed method. Finally, solving different examples, the effect of geometric parameters as well as BCs on the vibration of the bi-material shell is studied.
The Method of Dimensionality Reduction (MDR) can be regarded as a formalism for analytical solution of some commonly encountered classes of contact problems using a "mechanical intuition" based on the Winkler foundation model. Such an approach makes it much easier to account for a wide range of physical effects associated with contact interaction (e.g. friction, adhesion, and damping). However, there is still a controversy about the method and its applications (see, e.g., the comment on validity of the MDR-based model of rough contact) – which we believe comes from a misunderstanding of the method itself, and which, in turn, can be reconsidered in view of the recently published book on the MDR. The MDR was originally introduced for Hertz’s problem of axisymmetric frictionless local contact and was generalized subsequently for arbitrary axisymmetric geometry of linearly elastic bodies in unilateral local contact. The latter problem, for which the MDR yields the exact analytical solution, can be viewed as a base case that is used to extend, in a unified manner, the model of local contact by taking into account adhesion, friction, and viscous damping. In what follows, we overview the main concepts of the method starting with the base-case contact problem in which the MDR is rooted, and discuss limitations of the MDR as well. For the sake of their completeness, some criticisms that apply equally to conventional contact mechanics solutions are also considered. It is emphasized that the axisymmetric Hertz-type contact problems with a circular contact area constitute the proven range of validity of the MDR, while the extension of the method to other types of contact (e.g. axisymmetric with a multiply-connected contact area, non-axisymmetric) is a field ripe for research.
Efforts have been targeted at providing a comprehensive simulation of a centrifugal compressor undergoing surge. In the simulation process, an artificial neural network was utilized to produce an all-inclusive performance map encompassing those speeds not available in the provided curves. Two positive scenarios for the shaft speed, constant, and variable, were undertaken, and effects of load line on the dynamic response of the compressor have been studied. In order to achieve high-fidelity simulation in the variable speed case, an artificial neural network was utilized to produce an all-inclusive performance map encompassing those speeds not available in the provided curves. Moreover, effects of dynamic characteristics of throttle valve were also investigated. A novel controlling scheme, based on neuro-fuzzy control philosophy, was implemented to stabilize the compressor performance in the unstable region. Results indicate that if applied, this scheme could produce practical and satisfactory outcomes, possessing certain virtues compared to available techniques.
In order to accurately and conveniently identify the shearer running status, a novel approach based on the integration of rough sets (RS) and improved wavelet neural network (WNN) was proposed. The decision table of RS was discretized through genetic algorithm and the attribution reduction was realized by MIBARK algorithm to simply the samples of WNN. Furthermore, an improved particle swarm optimization algorithm was proposed to optimize the parameters of WNN and the flowchart of proposed approach was designed. Then, a simulation example was provided and some comparisons with other methods were carried out. The simulation results indicated that the proposed approach was feasible and outperforming others. Finally, an industrial application example of mining automation production was demonstrated to verify the effect of proposed system.
In this paper, the problem of velocity control of a micro-robot’s locomotion with nanometric resolution has been investigated. A sliding, A-shaped micro-robot, used in precision positioning applications is analyzed. This micro-robot is actuated by means of a piezoelectric stack actuator in order to produce translational and periodic motion. A dynamic model of the robot is proposed assuming linear behavior for the piezoelectric stack and Coulomb friction model. Then, in order to control the velocity of micro-robot, first a robust sliding mode control is used so that the relative angle between the legs in the micro-robot tracks a periodic reference signal. The velocity tracking for the micro-robot is achieved using an amplitude modulation strategy by adapting the amplitude of this reference signal. Velocity control of locomotion is assumed to be in the presence of a non-separation constraint (between the legs and the substrate) and friction uncertainties. Also, a state observer is designed to estimate the rate of change of the relative angle between the legs of the micro-robot, which is needed in the velocity control algorithm. Finally, simulation results are presented which illustrate the effectiveness of the proposed control strategy.
An approximate and simple expression is presented to calculate the crack face displacements of collinear cracks and center cracks by use of only one reference stress intensity factor. The crack face displacement and its partial derivative determined by the present method are in good agreement with their exact solutions. Calculations of weight functions for the center crack are reduced to the simple quadrature of the correction function and of the partial derivative of the crack face displacement. Based on the weight function method, the relationships between the stress intensity factor of the rotating blade with a center crack to the crack length, crack location, rotating speed and angular acceleration are studied. The critical rotating speed of the blade is evaluated based on the fracture law.
Thin-walled parts are often used in various industrial applications and due to their functional requirements, higher accuracies are generally desired. But due to their low stiffness characteristics, deformation and chatter problems are frequently encountered in their machining, thus resulting in poor accuracy. Moreover, due to 5-axes milling, which is usually required for finish machining of such parts, further complexities in the process are added and, consequently, achieving higher accuracy becomes more challenging. Therefore, in this study, the influence of tool inclination angle and feeding direction has been investigated on the resultant surface accuracy of thin cantilever shaped parts in finish milling conditions through experiments, finite element method simulations and theoretical discussions. Moreover, since work material’s microstructure and hardness also have key influence on its machinability, therefore, the effect of heat treatment state on resulting surface accuracy also has been explored. Three different titanium alloy, Ti–6Al–4 V specimens have been used. Two of the specimens were given solution treatment at 1050 ℃/1 h followed by aging at 550 ℃/4 h. One of the specimens after being solution treated was allowed to cool in air while the other was cooled in water to obtain different microstructure and hardness whereas the third specimen was used in as-received condition (casted). The three Ti–6Al–4 V specimens were machined at five different tool inclination angles (60°, 70°, 75°, 80°, and 85°) with two feeding directions (horizontal inwards and vertical inwards). Results have shown that the angle near the perpendicular to the surface i.e. 85° (5° away from the perpendicular) has lowest deformation value and also has better surface quality, which shows that the lowest effective cutting speed at this angle has helped in achieving higher accuracy. Moreover, among the cutting directions studied, vertical inward direction produces smoother surface due to its less pushing effect on the surface being cut as compared to horizontal inwards direction. And in terms of heat treatment state, the specimen which was cooled in air after being solution treated has produced better results for all cutting conditions studied, mainly attributed to fine homogenous lamellar α + β Ti–6Al–4 V structure achieved due to slow cooling rate of air. Analysis of variance using response surface methodology has been carried out to develop predictive model and to study the influence of each variable on the accuracy. The developed model has shown good accuracy when validated through additional experiments.
This is an overview of current research in origami applied to mechanical engineering. Fundamental concepts and definitions commonly used in origami are introduced, including a background on key mathematical origami findings. An outline of applications in mechanical engineering is presented. The foundation of an origami-based design procedure and software that is currently available to aid in design are also described. The goal of this review is to introduce the subject to mechanical engineers who may not be familiar with it, and encourage future origami-based design and applications.
With increasing demands of machining accuracy, designing of machine tools for satisfactory performance using cost-effective geometric accuracy configurations is becoming a complex problem to the machine tool manufacturers. In this paper, a novel robust accuracy allocation method is proposed for multi-axis machine tools based on multi-objective quality and cost trade-offs. To model the volumetric accuracy of machine tool based on geometric errors, the multi-body system theory was introduced. A manufacturing cost model for the machine tool components with a significant effect on geometric errors was established based on the machining features. The quality loss of the machine tool was also integrated into a single optimization objective. After identifying the relationship between the accuracy grade parameters of the feeding components and the geometric errors, the maximum in the Euclidean norm of all the accuracy parameters was defined as another optimization objective. The robust accuracy allocation was performed using Isight software and the Non-Dominated Sorting Genetic Algorithm-II built in the MATLAB. The optimization results for a four-axis horizontal machining center showed that the proposed method can realize the optimization of geometric accuracy and can determine the optimal accuracy grade of the feeding components satisfying the machining accuracy requirements.
Polishing process is the final step for the fabrication of optical surfaces. This paper presents a theoretical and experimental investigation on the removal of material from a surface during the polishing process. The model in this paper assumes that the material removal rate follows Preston equation and the pressure distribution at the contact area is Hertzian. Particularly, the effect of the tool posture, which is described by the inclination angle and declination angle, upon the local material removal profile is modeled and analyzed. On the basis of the analysis, a novel method is proposed to optimize the tool angles. A series of polishing experiments were conducted to verify the effectiveness of the proposed model. The theoretical and experimental results indicate that (1) the inclination angle has large effect on the local removal depth, and (2) the location of the maximum removal depth bias away from the center of the profile and the direction of this bias is determined by the declination angle. The model in this paper is potentially useful for the planning of the polishing posture and the tool path during the polishing process.
The dimensionless velocity of steady streaming flow with small oscillation amplitude and low viscous layer thickness was assumed to be a function of one dimensionless parameter (viscous layer thickness). This functional relationship was validated by measuring the streaming velocities for bubbles on the size scale of hundreds of micrometers. The streaming velocities were computed for smaller bubbles to extend the range of viscous layer thickness applicable in the functional relationship. The dimensionless velocities were fitted well to the negative three-fourth power of the dimensionless viscous layer thickness, and a scaling law between the streaming velocity and bubble radius was proposed.
In comminution, mill power plays a major role from the economics standpoint and is a critical design criterion. It is influenced by a range of parameters such as media charge level (ball filling), slurry filling, slurry concentration and mill speed. In this work, the effects of these operating parameters were investigated using a pilot mill (1000 x 500 mm). To this end, a copper ore (–1000 µm) was used to prepare the slurry. The tests covered a range of slurry filling (U) from 0 to 1.7 with media charge between 12% and 36% of the mill volume and six different speeds between 60% and 85% of critical speed. A power analyser was utilized to measure mill power. Increase in mill speed and ball filling leads to a remarkable increase in the amount of the power. Preliminary results show that there is a definite trend between the power and the slurry filling U. Mill power draw is maximum at slurry concentration 60–70% and slurry filling 0.84. An empirical equation was given that fits the data reasonably well.
The dynamic characteristic parameters of mechanical joints are difficult to determine in theoretical modeling, dynamic simulation, and servo controller design for the ball screw feed drive system. Therefore, this study proposes a novel method for identifying the axial stiffness and damping parameters of the rolling joints in an assembled ball screw feed drive system. First, the proposed method deduces the axial vibration equations of the feed drive system with a harmonic excitation force exerted on its worktable. Second, the identification model of the axial stiffness and damping parameters of the rolling joints is established on the basis of the equations. Third, the identification equations are built by measuring the distance between the screw supporting points, the frequency, and the amplitude of the harmonic excitation force, as well as the amplitude of the axial vibration velocity of the screw end section. The axial stiffness and damping parameters of the rolling joints are finally determined by solving the identification equations using the genetic algorithm. With a ball screw feed drive system as the research object, the proposed method is used to identify the rolling joints’ axial stiffness and damping parameters of the ball screw assembly, as well as the left and the right bearing groups. The experiments show that the proposed method is correct, effective, and achieves high identification accuracy.
This paper presents an improved zero vibration method for the swing control of bridge-type grab ship unloader. With the method, the concepts of equivalent frequency and the equivalent damping ratio are proposed to cope with the changeable length of rope, and the optimal path planning is considered to avoid collision and improve efficiency. Numerical simulation results of a case study indicate that the maximum residual swing angle of the grab can be limited to a small range to ensure safety using the improved zero vibration method, whereas the traditional zero vibration method with average frequency and zero damping ratio gets poor results of swing control. After that, the sensitivities of the max residual swing angle to the changes of some main design parameters (damping coefficient, deviation of the center of gravity of the grab in rope direction, and time delay of the system) and operating parameters (position deviation of the trolley, initial length deviation of the rope, and initial swing angle) are analyzed. The results obtained display that the residual swing angle is sensitive to the deviation of grab’s center of gravity, the deviation of trolley’s position, and the initial swing angle under the same control parameters, but insensitive to the damping coefficient, the time delay of the system, and the initial length deviation of the rope. This can help to select the appropriate parameter values or adaptive range in an actual unloader.
Convective heat transfer in a microchannel rarefied gas flow with a constant wall temperature boundary condition is investigated numerically. The boundary shear work, viscous dissipation and axial conduction are all included in the study. An analytical solution is also derived for the fully developed flow condition including the boundary shear work. The proper thermal boundary condition considering the sliding friction at the wall is implemented. A comparative study is performed to quantify the effect of the shear work on heat transfer in the entrance – and the fully developed – regions of the microchannel for both gas cooling and heating. The results demonstrate that the effect of shear work on heat transfer is significant and it increases with increasing both the Knudsen number and Brinkman number. Neglecting the shear work in a microchannel slip flow leads to over- or under estimation of the Nusselt number considerably. For a fully developed flow in a microchannel with constant wall temperature boundary condition, the contribution of the shear work to heat transfer can be around 55% in the vicinity of the upper limit of the slip flow regime, regardless of how small the non-zero Brinkman number can be. Including the shear work is therefore crucial in the analysis of microchannel heat transfer and should not be neglected.
The present study investigates a film actuator made with dielectric cellulose acetate films separated by narrow spacers as a means of electrostatic actuation for potential haptic application. Fabrication process for the actuator is explained along with experiments conducted over a wide frequency range of actuation frequency. A valid finite element simulation of the actuator is made on the quarter section of the actuator by using full 3D finite elements. Vibration characteristics such as fundamental natural frequency, mode shape and output velocity in the frequency range for haptic feeling generation are obtained from the finite element analysis and compared with the experimental results. Experimental results demonstrate that the finite element model is practical and effective enough in predicting the vibration characteristics of the actuator for haptic application. The film actuator shows many promising properties like high transparency, wide range of actuation frequency and high vibration velocity for instance.
This paper presents the simulation study of internal flow of open-end swirl injectors under steady and oscillating ambient pressures. A two-dimensional swirl axisymmetric model based on the volume of fluid method was developed to study the effect of ambient pressure on the internal flow of open-end swirl injectors. The response of injector flow to the ambient pressure oscillation was investigated by superimposing periodical oscillation of ambient pressure at the spout outlet. The results show that the variation of ambient pressure affects the liquid phase volumetric fraction within the gas–liquid shear layer. The spray angle near the wall remains constant independent of the ambient pressure. The velocity distribution on different axial sections rarely varies with ambient pressure. When the ambient pressure oscillated, the ambient pressure oscillation would cause the flow rate oscillation at the spout. The phase delay between the flow rate oscillation at spout and the ambient pressure oscillation is proportional to the oscillation frequency.
The dynamic responses of the cutterhead driving system (CDS) of the tunneling boring machine with impact loads are investigated according to its typical structure in this paper. First, finite element model of CDS is proposed based on linear mesh stiffness hypothesis, in which the rotating components are introduced as beam elements with the same mass and stiffness characteristics, and the effects of cutterhead-rock stiffness and carrier stiffness of CDS are also taken into account. Then, the natural characteristics of the CDS and the corresponding energy distribution for the components are investigated using this model. Finally, numerical simulations are carried out to determine the dynamic responses under two different typical impacts, by means of transient trajectories in time-domain and amplitude-frequency spectra in frequency domain, respectively. With the dynamic behaviors analysis, the response frequency of the CDS and the corresponding components with the maximum load is shown at the end. This modeling approach should provide a new idea for the CDS dynamic designing.
Time synchronous averaging has been widely used for machinery fault diagnosis. However, it cannot reveal signal characteristics accurately in conditions of speed fluctuation and no tachometer due to the phase accumulation error. In this paper, an improved dynamic-time synchronous averaging method is proposed to extract the periodic feature signal from the fluctuated vibration signal for fault detection when no tachometer signal is available. In this method, empirical mode decomposition, dynamic time warping, and time synchronous averaging are performed on gear vibration signals to detect fault characteristic information. First, empirical mode decomposition is performed on the vibration signal and a series of intrinsic mode functions are produced. The sensitive intrinsic mode functions providing fault-related information are selected and reconstructed and the corresponding envelop signals are equal-space intercepted. Then, the phase accumulation error among the envelop signal segments is estimated by the dynamic time warping, which is further used to compensate the phase accumulation error between the intrinsic mode function segments of the reconstructed signal. Finally, the compensated intrinsic mode function segments are averaged to obtain the feature signal. Simulation analysis shows the advantages of the proposed method in extracting faulty feature signal from speed fluctuation signal without tachometer and identifying gear fault. Experiments with both normal and faulty gear were conducted and the vibration signals were captured. The proposed method is applied to identify the gear damage and the diagnosis results demonstrate its superiority than other methods.
Two-dimensional stick-slip motion of an oscillator subjected to dry friction is investigated in this paper. The equations of motion of the non-smooth system are discretized in the time domain by means of the implicit Bozzak-Newmark scheme. The system state equations in a time step are written in the incremental displacements to model the frictional constraints in accordance with Coulomb’s law. With the help of a coordinate transformation and introduction of paired non-negative and complementary variables, the non-smooth vibration problem is reduced to a mathematical programming problem for which a numerical solution can be obtained. Numerical results for a single body oscillator under a harmonic excitation are obtained using the proposed method and compared with those in the literature; excellent agreement is achieved. The proposed method is then applied to a general two-dimensional oscillator with stiffness and viscous coupling in addition to the frictional coupling. Experiments are conducted for free vibration of a single body vibration system subjected to two-dimensional dry friction. Good agreement between the measurements and numerical results obtained using the proposed scheme is observed.
In order to evaluate the stability of a camera robot, a new stability performance index with combination of force and position based on the determinations of the cable tensions is proposed in this paper. First, two position factors based on the kinematic model of the camera robot are presented to show how far the specified position is away from the center of the horizontal plane at which the specified position locates within the workspace and how far the specified position is away from the top of the workspace, respectively. Then, two force factors are also developed to show the distributions of the minimum cable tensions in the specified region of the workspace. Furthermore, the stability performance index is described using the weighted method. And subsequently, the stability workspace is designed with the stability performance index. Finally, a robustness workspace with the external wrench is selected to demonstrate the effectiveness of the stability performance index above for the camera robot. Simulation results show that it is suitable to employ stability performance index to evaluate the stability of the camera robot.
This paper presents a study analyzing the aerodynamic effect and loss mechanism of hub and shroud leakage flow for an axial turbine stage. A series of computational fluid dynamics computations were performed to investigate the effect of various complexity of leakage configurations on the flow field. It is found that a non-linear relationship between different flow systems emerges in the vicinity of both the shroud and hub leakage flow exhibiting a deviation of flow direction and a radial shift of flow pattern, while the efficiency drop caused by the shroud and hub leakage configurations can be added linearly. By analyzing the expansion process in the cooled turbine and the spatial distribution of viscous dissipation term, the loss sources which can be directly traced back to the flow phenomena were indentified. Based on the aerodynamic feature of the turbine, an analytical approach to separate and quantify loss sources was proposed and applied to analyze the turbine. Four kinds of loss mechanisms, referred to as cavity losses, mixing losses, extra losses, and the leakage work reduction, were observed and their contributions were eventually represented by efficiency penalty.
This paper investigates the static bending and free vibration analysis of functionally graded piezoelectric material beam under electromechanical loading. The effective material properties of functionally graded piezoelectric material beam are assumed to vary continuously through the thickness direction and are graded according to sigmoid law distribution. Both multi-layered and monomorph models have been considered in the present work. A two-dimensional finite element analysis has been performed using COMSOL Multiphysics® (version 4.2) software. The accuracy of the method was validated by comparing the results with the previous published work. The results presented in the paper shall be useful in the design of functionally graded piezoelectric material beam.
A novel piezoelectric pump called single-bimorph double-acting check-valve piezoelectric pump was proposed in this paper in order to improve the output performance of the single-bimorph single-chamber piezoelectric membrane pump. The constituent parts of the newly designed piezoelectric pump have no difference with the single-bimorph single-chamber check-valve piezoelectric membrane pump except the structural difference of the pump body. There are two serial-connection pump chambers which are formed by the two sides of the piezoelectric bimorph and the pump body of the newly designed piezoelectric pump. The new piezoelectric pump was fabricated, and output performance was experimentally investigated. The maximum flow rate against zero back pressure of the new pump was 318 ml/min and the pumping pressure reached 40.5 kPa at the operating voltage of 90 V. The output power was roughly twice that of the single-bimorph single-chamber check-valve piezoelectric membrane pump. The testing results proved that the new piezoelectric pump could enhance the output performance and the energy conversion efficiency of the piezoelectric bimorph comparing with the single-bimorph single-chamber check-valve piezoelectric membrane pump.
A novel soft contacting technology is proposed to reduce the risks of contacts that space manipulator is on-orbit service. The magnetorheological (MR) rotational damper is considered and utilized for cushioning and vibration reduction in the space manipulator. Based on the extended manipulator model, a linear dynamic formulation of free-floating space manipulator is built. Subsequently, the mechanical property of magnetorheological rotational damper is analyzed by using Bingham model. Then, the optimal control force can be obtained by using the linear quadratic optimal control theory. Finally, the optimal control force is served as the parameters to achieve the semi-active control of soft contacting by employing the clipped optimal control theory. The hard contacting and passive control technology are introduced to make comparison with the results of soft contacting. Some numerical simulations are made to demonstrate the validity and capability of the proposed soft contacting technology.
This paper describes the dynamics of a laminar separation bubble formed on the semi-circular leading edge of constant thickness aerofoil model. Detailed experimental studies are carried out in a low-speed wind tunnel, where surface pressure and time-averaged velocity in the separated region and as well as in the downstream are presented along with flow field visualisations through PIV for various Reynolds numbers ranging from 25,000 to 75,000 (based on the leading edge diameter). The results illustrate that the separated shear layer is laminar up to 20% of separation length and then the perturbations are amplified in the second half attributing to breakdown and reattachment. The bubble length is highly susceptible to change in Reynolds number and plays an important role in outer layer activities. Further, the transition of a separated shear layer is studied through variation of intermittency factor and comparing with existing correlations available in the literature for attached flow and as well as separated flow. Transition of the separated shear layer occurs through formation of K-H rolls, where the intermittency following spot propagation theory appears valid. The predominant shedding frequency when normalised with respect to the momentum thickness at separation remains almost constant with change in Reynolds number. The relaxation is slow after reattachment and the flow takes about five bubble lengths to approach a canonical layer.
In this study, heat and mass transfer characteristics of the magnetohydrodynamic nanofluid flow over a radiating nonlinear permeable stretching surface are studied. The flow considered here is under both the hydrodynamic and thermal slip conditions in presence of first-order chemical reaction. The resulting governing equations are transformed into a system of nonlinear ordinary differential equations by applying a suitable similarity transformation and then solved numerically. A parametric study, of the physical parameters, is conducted and a representative set of numerical results for the skin friction coefficient, the Nusselt number and the local Sherwood number are tabulated. Graphical results for dimensionless temperature, velocity and concentration are presented and discussed in details from the physical point of view.
The current article deals with finite element (FE)- and genetic algorithm (GA)-based vibration energy harvesting from a tapered piezolaminated cantilever beam. Euler–Bernoulli beam theory is used for modeling the various cross sections of the beam. The governing equation of motion is derived by using the Hamilton's principle. Two noded beam elements with two degrees of freedom at each node have been considered in order to solve the governing equation. The effect of structural damping has also been incorporated in the FE model. An electric interface is assumed to be connected to measure the voltage and output power in piezoelectric patch due to charge accumulation caused by vibration. The effects of taper (both in the width and height directions) on output power for three cases of shape variation (such as linear, parabolic and cubic) along with frequency and voltage are analyzed. A real-coded genetic algorithm-based constrained (such as ultimate stress and breakdown voltage) optimization technique has been formulated to determine the best possible design variables for optimal harvesting power. A comparative study is also carried out for output power by varying the cross section of the beam, and genetic algorithm-based optimization scheme shows the better results than that of available conventional trial and error methods.
In this paper, a mapping model for product surface morphology design based on ergonomics is proposed. The method advances the traditional approaches based on anthropometric measurements to a new one based on digitised product surfaces; thus, it simplifies the complexity of non-uniform rational B-spline surface representation during product design. The method was constructed by converting the experimental data to the surface shapes based on the pressure distribution map. An adjustment algorithm is presented to eliminate the errors in mapping non-planar base shapes. The experimental mapping data are pretreated, so that the mapping process reflects the statistical characteristics of the tested groups as far as possible. Based on the mapping model, a prototype implementation system for ergonomic product design is developed. As an example, a car seat design is presented to show the performance and availability of the method.
This paper focuses on investigating friction behaviors in pre-sliding state and developing a new mathematical model of friction for pneumatic cylinders. Using pneumatic cylinders with different sizes, an experimental setup is made to measure friction force–displacement characteristics in pre-sliding state under various conditions of applied force and pressures in the cylinder chambers. A new mathematical model of friction is proposed by incorporating a hysteresis function into the new modified LuGre model. The friction behaviors of the pneumatic cylinders in pre-sliding state are clarified and the usefulness of the proposed mathematical model is verified through various experimental results.
The dimensionless fundamental frequencies and critical axial loads of sandwich cylindrical thin shell with a functionally graded (FG) core are studied by taking into account the combined and separately influences of the shear stresses and rotary inertia. The governing equations of sandwich cylindrical shell with an FG core are derived based on Donnell’s shell theory using the shear deformation theory. The governing equations are reduced the sixth-order algebraic equation using the Galerkin’s method. Numerically solving this algebraic equation gives the magnitudes of the dimensionless fundamental frequency. In addition, the expressions for the dimensionless fundamental frequencies and critical axial loads of the sandwich cylindrical shell containing an FG core with and without the shear stresses are obtained in a special case. To validate the present method, the numerical example is presented and compared with the available existing results. Finally, the influences of variations of the FG core, shear stresses, rotary inertia and sandwich shell geometry parameters on the dimensionless fundamental frequencies and critical axial loads are analyzed numerically.
Reasonable selection of cutting tool materials has an important effect on machining efficiency, machining quality, cutting tools life, and production cost. There always exists a problem of correct matching between cutting tool materials and workpiece materials. The multi-criteria decision-making is currently the predominant method for cutting tool material selection, and its accuracy can be further improved based on full consideration of the workpiece materials and cutting parameters. For this reason, a granulation analysis method based on granular computing is presented. Firstly, according to the similarity of various cutting tool materials across different attributes represented in interval values including physical properties, mechanical properties, and cost, a fuzzy similarity matrix of all the cutting tool materials to be analyzed is established; and a series of material information granular layers with different granularity is constructed by using quotient space theory based on fuzzy tolerance relation. Afterwards, information entropy is applied to measure their granularity, and an optimal granular layer is determined based on a quantitative and objective standard. Finally, in the optimal granular layer, through determining the averages and ranks of all the material information granules under different attributes, the corresponding common characteristics of similar cutting tool materials in each material information granule are analyzed, and their matching workpiece materials and cutting parameters are summarized. The analysis and summary will provide effective guidance for subsequent multi-criteria decision-making of cutting tool materials. An application example proves the feasibility and validity of the proposed method.
This paper presents a method of friction compensation for a linear electric motor in a model in the loop suspension test rig. The suspension consists of a numerically modeled spring and damper, with inputs of suspension motion. The linear motor is force controlled using a force sensor to track the output of the numerical model. The method uses a Coulomb friction model and applies a feedforward step signal when velocity zero crossing occurs. Velocity zero crossing estimation is achieved using an algorithm based on measured feedback velocity and force. Experimental results indicate reduction of force tracking error caused by Coulomb friction leading to improved test rig accuracy.
Aiming at the non-linear characteristics of bearing vibration signals as well as the complexity of condition-indicating information distribution in the signals, a new rolling element bearing fault diagnosis method based on hierarchical fuzzy entropy and support vector machine is proposed in this paper. By incorporating the advantages of both the concept of fuzzy sets and the hierarchical decomposition of hierarchical entropy, hierarchical fuzzy entropy is developed to extract the fault features from the bearing vibration signals, which can provide more useful information reflecting bearing working conditions than hierarchical entropy. After feature extraction with hierarchical fuzzy entropy, a multi-class support vector machine is trained and then employed to fulfill an automated bearing fault diagnosis. The experimental results demonstrate that the proposed approach can identify different bearing fault types as well as severities precisely.
In order to capture nonlinear and dynamic behaviors of the V-belt continuously variable transmission system with lots of unknown nonlinear and time-varying characteristics, an intelligent dynamic control system using modified particle swarm optimization is proposed for controlling a permanent magnet synchronous motor servo-drive V-belt continuously variable transmission system to raise robustness. The intelligent dynamic control system comprised an inspector control system, a recurrent Laguerre-orthogonal-polynomials neural network controller with adaptive law and a recouped controller with estimation law. The adaptive law of parameters in the recurrent Laguerre-orthogonal-polynomials neural network is derived according to Lyapunov stability theorem. To achieve better learning performance and faster convergence, the modified particle swarm optimization is employed to regulate two varied learning rates of the parameters in the recurrent Laguerre-orthogonal-polynomials neural network. At last, comparative studies shown by experimental results are illustrated to demonstrate the control performance of the proposed control scheme.
Inner wall profile of the cylinder in a rotary vane compressor (RVC), which influences the motion characteristics of vanes, suction volume, friction characteristic, etc., plays an important role in the performance of the compressor. This work mainly aims at the profile design of a new cylinder for a double-acting RVC with harmonic profile cylinder on the basis of not changing integrate size. According to the relation between cylinder profile and vane motion characteristics, a method for the cylinder profile design is proposed in this paper. With an assumed vane motion, equations of the cylinder profile, cell volume of the compressor as well as pressure angles between vanes and cylinder inner wall are constructed preliminarily. And then through adjusting parameters and optimization with an independently developed procedure, a new cylinder with the so-called combined profile is obtained. Theoretical analysis of the cell volume variations and the pressure angles between vanes and cylinder are conducted. The results show that there is neither rigid impulse nor soft impulse between vanes and cylinder due to the vane continuous motion including displacement, velocity and acceleration. And the pressure angles between vane and cylinder and working volume of the compressor with the new profile cylinder are superior to harmonic profile cylinder, which is useful for the reduction of friction power in the operation of compressor. Experiments show that the cooling capacity and COP of the test refrigeration cycle with the proposed combined profile cylinder is higher than the compressor with harmonic profile cylinder. And the volumetric efficiency and isentropic efficiency of the compressor with combined profile cylinder have better performance. This method can be applied to the design of the cylinder for multiple-acting rotary vane compressors, rotary vane expanders and vane pumps.
In this paper, an analytical approach was used to formulate for gathering energy from ambient sources of vibrations. The apparatus consists of a cantilevered beam harvester with a piezoelectric patch. A coupled electromechanical modal model based on Euler–Bernoulli theory is used. The governing equations were extracted using Hamilton’s principle and then were discretized by using the Rayleigh–Ritz approach. The expected value of the electrical power output was obtained for a weakly stationary, Gaussian bandpass with zero mean base excitation. Next, a numerical solution for the beam under band-limited ambient random acceleration as the input was calculated and validated by experiment. The numerical results closely correlated to the experimental data with a deviation of about 10%.
Fixtures are the work-holding devices, widely used in manufacturing, to completely immobilize the workpiece during machining. The position of fixture elements around the workpiece strongly influences the workpiece deformation which in-turn affects the machining accuracy. The workpiece deformation can be minimized by finding the appropriate position for the locators and clamps. Thus, it is necessary to model the complex behavioral relationship that exists in the fixture–workpiece system. In this research paper, response surface methodology is used to model the relationship between position of locators and clamps and maximum deformation of the workpiece during end-milling, and then the developed model has been optimized by genetic algorithm and particle swarm optimization. As the predictive model is being developed by response surface methodology, a huge reduction in computational complexity and time is achieved during the optimization of machining fixture layout. Also, it is evident that the approach which integrates response surface methodology and particle swam optimization produces better results.
The failure of suction/discharge valves is the most common cause of unscheduled compressor shutdowns; therefore, the in-time fault diagnosis of valves is crucial to the reliable operation of reciprocating compressors. Major valve faults include leakage, valve flutter, delayed closing, and improper lift. To determine the features for diagnosing these typical valve faults, this paper presents an experimental study of the fault diagnosis of reciprocating compressor valves with acoustic emission technology and simulated valve motion. The measured AE signals and simulated valve motions of normal and failed valves are studied. The results of the fault diagnosis indicate that an earlier occurrence of the suction process can diagnose suction valve leakage and that an earlier occurrence of the discharge process can be used for detecting discharge valve leakage. The leakage also causes an increase in the amplitude of the continuous acoustic emission signal. Valve faults resulting from improper valve lift can be diagnosed by the amplitude of the burst acoustic emission signal. The number of burst acoustic emission signals and the shape of the simulated valve motion can be used to monitor the valve flutter conditions. The location where the valve closes can diagnose a valve-delayed closing fault.
Tooth flank reconstruction and optimization methodologies after simulation process modeling are presented, in order to provide accurate model and tooth data for digitized design and manufacture of the spiral bevel gear. Firstly, a simulation process modeling utilizing universal machine settings is developed for an initial solid model. Then, due to its poor accuracy, tooth flank reconstruction exploiting the Non-Uniform B-Spline fitting method is carried out. Finally, some tooth flank optimizations are introduced for higher tooth flank precision and accurate tooth data: (1) Overall tooth flank interpolations based on the Energy method; (2) Tooth flank approximation based on the least square (LSQ); (3) Tooth flank parameterization based on the Newton Iteration method. Results obtained from some numerical examples indicate that validation of the proposed approaches and tooth flank form error is significantly reduced.
This paper presents an optimum design of a 4-PSS-PU redundant parallel manipulator by taking the workspace, conditioning performance, and acceleration into account. On the basis of rank of the Jacobian matrix, a method to directly find out the workspace is presented, rather than the search method. Based on the dynamic model, a maximum acceleration index is defined. The corresponding atlases of these performance indices are represented graphically in the established design space. Based on these atlases, the optimum design is performed and the optimum region is determined. It is expected to realize the high acceleration of parallel manipulators by using the optimum method.
For the design problem of dynamic similitude models of an aero engine’s turbine discs, distorted scaling laws and structural size intervals of thin walled annular plates are established in the research. According to the governing equation, the geometrically complete scaling law of thin walled annular plates is firstly established. In order to determine accurate distorted scaling laws of thin walled annular plates, three significant principles are proposed and theoretically proved combining the governing equation and the sensitivity analysis. According to results of the sensitivity analysis, accurate distorted scaling laws of thin walled annular plates are obtained based on significant principles. In addition, structural size intervals of distorted scaling laws of thin walled annular plates are calculated by the numerical method. Finally, the previous six orders’ natural frequencies of thin walled annular plates are discussed as examples to verify the theory presented in this research, and distorted scaling laws of each order’s natural frequency are obtained and the corresponding structural size intervals are analyzed.
Rolling element bearings are vital components in most rotating machines. Bearings often operate in harsh environments where manufacturing imperfections, misalignments, and fatigue can result in reduced component lifespan. These failures are often preceded by changes in the normal vibration of the system. Modeling and detecting these vibrational anomalies is common practice in predicting machine failure. This paper develops and implements a novel approach to detecting bearing vibration anomalies in the time–frequency domain. The performance of the new approach is quantified using both simulated and experimental bearing vibration data. In these ground-truth experiments, the proposed time–frequency method successfully detects anomalies (>98% true positive) using short time spans (<0.1 s) with low false alarm rates (<1% false positive). Using experimental data, this time–frequency approach is shown to outperform one-dimensional time series analysis techniques.
The three high-performance indicators (low retrace tolerance, long life and low vibration) of N–N type planetary gear apparatus with small tooth number difference (abbrev "N–N–PGA") are hardly achieved simultaneously until recently. At present, the root cause analysis (RCA) and TRIZ are considered to be comprehensive and systematic new theories for technological innovation, which provides a new way to figure out the conundrum existed in the N–N–PGA. In the present study, the "root cause" of the problem is proposed with the RCA approach and two contradictions existed in the N–N–PGA have been revealed: Harmful side effect and stability of composition; harmful side effect and durability of a moving object. Besides, two reasonable principles ("Dynamicity" and "Composite materials") for the N–N–PGA design recommended by the TRIZ method are used to eliminate these contradictions. In addition, a prototype of the obtained new type N–N–PGA design is developed for experimental testing. The obtained result demonstrates the capability of the above method for obtaining low retrace tolerance, long life, and low vibration.
Based on the meshing principle of silent chain and the structure of an automobile engine, timing silent chain system including involute tooth sprocket, guide plate, tension plate, and silent chain is designed in this paper. Dynamics analysis model is built, and vibration of the chain system is studied. The link tensile force and the contact force between link and other components, and the transmission error of crankshaft sprocket and exhaust camshaft sprocket are analyzed. The design and analysis method of the timing silent chain system is proposed. The wear elongation of the timing silent chain system is studied through the road test. The wear morphology of the link plate and pin working surface are observed. Analysis results show that the design method of the timing silent chain system is feasible. The major wear mechanism of the pin is fatigue wear, and the major wear mechanism of the link plate is fatigue wear and abrasive wear. The results of the dynamic simulation and the experimental research show that the design and analysis method of timing silent chain system is scientific and feasible, and wear resistant of the timing silent chain system is high.
An accurate and reliable wear analysis requires detailed knowledge of the tribological conditions of the studied system. In this work, a numerical model which can quantify wear and is applicable to hydraulic motors is developed. Detailed tribological knowledge can be acquired through strategic experimental testing and numerical simulations. The model is constructed to include the effect on wear from varying lubricant film thickness. The development of the wear model includes consideration of wear observed in the Scanning Electron Microscopy (SEM) analysis of tested motors. The model is of the Archard type, in which the k-value is estimated from experiments, after considering the effect of lubrication. The contact pressure is the solution to a lubrication model that governs both the hydrodynamics of the lubricant film and the direct contact between the rough surfaces. To validate the model, a hydraulic motor is run at different operating conditions and the apparent wear depth is analysed after the tests. Numerical simulations mimicking the same configuration are performed and the predicted wear depths are compared to the experimental results. Similarities and differences are discussed and it is evident that a clear correlation exists between the wear predicted with the model and the measurement data of the apparent wear in the hydraulic motor. There are also discrepancies because of the model simplicity and the uncertainty in the specifications of the tested system. The results imply that wear analysis using numerical simulations aid the understanding of wear in machinery. The combined knowledge of physical conditions on different important scales enables in-depth analysis with numerical tools which cannot be achieved through experimental investigations alone. Furthermore, the numerical model can be refined leading to better wear predictions.
Dynamic behaviour of gearbox transmitting power to milling tool in a milling process application is considered in this paper. The gearbox is subjected to variable cutting torque induced by the milling operation. This variability will lead to fluctuating speed. The dynamic behaviour of the system should be investigated according to this non-stationary operating condition. To achieve this objective, a simple model of motor-gearbox-milling tool system is developed. The influence of variable cutting torque on driving motor speed is taken into account. The gearmesh function which describes the meshing phenomena is modified according to this specific operating condition. Simulations of the dynamic behaviour of the gearbox show a simultaneous frequency and amplitude modulation. These modulations are highlighted using time frequency representation which is necessary to implement so that it is possible to achieve a correct diagnosis of the transmission. Simulations in presence of tooth crack defect confirmed the necessity to implement time frequency techniques to characterize time varying systems.
An active actuator of electro-active polymer (EAP), i.e. ionic polymer metal composite (IPMC), is subjected to alternating electric potential to investigate and study the time-delayed vibration characteristics. A generalized mathematical model of the actuator is obtained assuming multi-mode excitation and applying the Hamilton’s principle. Lambert W-function is then applied and a closed form solution of the transcendental characteristic equation of delay differential equation (DDE) is obtained. Delay differential equations (DDEs) are then solved taking into account the experimental data and physical properties of IPMC, and the results are discussed and validated.
Application of Impact damper for reduction of vibration amplitude through momentum transfer is now well established. However, no literature is available for the effect of an impact damper on axial vibration of a rod as a continuous system. The equation for axial vibratory displacement of the rod, fixed at one end and a lumped mass at the other end, is derived by considering steady state vibrations having a period equal to that of the forcing function at the free end. Structural damping is assumed to be modal with a damping ratio of 0.005. Taking this periodicity into account, the repetitive impact force is resolved in the sinusoidal functions through Fourier series analysis. The forcing function thus will have components with the frequency of the external force and the multiple harmonic forces resulting from impacts. Since an infinite series is involved, the solution is obtained for a truncated series using MATLAB. It is observed that the damper is most effective when the Impact distribution parameter is equal to 0.5. The results of the numerical analysis are supported by experiments and are found to be in good agreement with the theoretical results. The reduction of vibration amplitude is observed to be dependent on the clearance (travel of impacting mass), mass ratio of the impacting mass to the main system, frequency of excitation, and the location of the stop in addition to the impact distribution.
The non-linearity of a hardening-type oscillator provides a wider bandwidth and a higher energy harvesting capability under harmonic excitations. Also, both low- and high-energy responses can coexist for the same parameter combinations at relatively high excitation levels. However, if the oscillator’s response happens to coincide with the low-energy orbit then the improved performance achieved by the non-linear oscillator over that of its linear counterpart, could be impaired. This is therefore the main motivation for stabilisation of the high-energy orbit. In the present work, a schematic harvester design is considered consisting of a mass supported by two linear springs connected in series, each with a parallel damper, and a third-order non-linear spring. The equivalent linear stiffness and damping coefficients of the oscillator are derived through variation of the damper element. From this adjustment the variation of the equivalent stiffness generates a corresponding shift in the frequency–amplitude response curve, and this triggers a jump from the low-energy orbit to stabilise the high-energy orbit. This approach has been seen to require little additional energy supply for the adjustment and stabilisation, compared with that needed for direct stiffness tuning by mechanical means. Overall energy saving is of particular importance for energy harvesting applications. Subsequent results from simulation and experimentation confirm that the proposed method can be used to trigger a jump to the desirable state, thereby introducing a beneficial addition to the performance of the non-linear hardening-type energy harvester that improves overall efficiency and broadens the bandwidth.
A novel deformable rolling mechanism is proposed in this paper. The mechanism can switch between two modes: a planar linkage mode and a spherical linkage mode. In the planar linkage mode, the mechanism rolls like a planar four-bar mechanism and moves along a straight line. In the spherical linkage mode, the mechanism rolls as a spherical four-bar mechanism and moves along a polygon. A standing posture, which likes an upright pyramid, of the rolling mechanism is also identified. After the description of the novel mechanism, the kinematic analysis of the mechanism is presented, and appropriate control strategies are proposed. Then, the rolling conditions of the mechanism are investigated based on the zero-moment-point theory. Finally, the various modes of the mechanism are verified by both simulations and prototype experiments.
The traditional filling control strategy mainly relies on a large number of calibrations and is an open loop control. In order to avoid cumbersome calibrations and improve the control precision, a systematic approach of the filling control for wet dual clutch transmission is established in this paper. First, a model of the electro-hydraulic actuator for the wet dual clutch transmissions is presented and validated by the experiments. Then, an analytic solution method is developed for the filling control. To obtain the analytic solution of the filling pressure trajectory in the filling phase, the nonlinear mathematic model for wet clutches is transformed into a model in linear space by the feedback linearization, and then the optimal filling pressure trajectory is obtained based on Pontryagin’s Minimum Principle. Furthermore, to improve the control accuracy of a variable force solenoid, a closed loop control based on adaptive generalized predictive control algorithm is applied to the developed model of the electro-hydraulic actuator to track the optimal filling pressure trajectory. The simulation results indicate that the control strategy is effective for solving the filling control problem.
This paper presents a new algorithm for smooth trajectory planning optimization of isotropic translational parallel manipulators (ITPM) that their Jacobian matrices are constant and diagonal over the whole robot workspace. The basic motivation of this work is to formulate the robot kinematic and geometric constraints in terms of optimization variables to reduce the mathematical complexity and running time of the resulting algorithm which are important issues in trajectory planning optimization. To achieve this aim, the end-effector trajectory of ITPMs in Cartesian space is defined using fifth-order B-Splines, and as a main contribution, all of the actuators limitations and robot constraints are formulated in terms of B-Spline parameters with no need of any information about the workspace geometry. Then the total required energy, total time of motion, and maximum absolute value of actuators’ jerk are defined as objective functions and non-dominated sorting genetic algorithm-II (NSGA-II) is used to solve the resulting nonlinear constrained multi-objective optimization problem. Finally, the proposed algorithm is implemented in MATLAB software for Cartesian parallel manipulator (CPM) as a case study, and the results are demonstrated and discussed. The obtained results show the significant performance of the proposed algorithm with no need to evaluate the robot’s constraints and boundaries of its workspace in each point of the end-effector trajectory.
Conceptual design plays a pivotal role in generating creative design solutions and, in most cases, reuse of existing design knowledge is necessary. However, lack of a consistent design knowledge representation model and neglect of an integrated approach to support various formats of design knowledge reuse constrain conceptual design from transforming design requirements into practical promising design solutions. In order to solve these problems, this paper presents a constrained function-behavior-structure knowledge cell (CFBS) model to provide conceptual design process with a consistent knowledge representation model. CFBS-based integrated approach for design knowledge reuse is proposed, which includes three-level CFBS retrieval process to obtain most relevant CFBS expressed in various types, three-stage design synthesis process to produce suggested design solutions, and evaluation process to select the most feasible design solutions. The effectiveness of the proposed design process was illustrated with conceptual design of the micro-feed drive module of insulin pump based on the CFBS library.
Aiming to the lightweight design of the long glass fiber reinforced thermoplastic (LGFT) composite wheel, this paper constructs the design process and the strength analysis method of long glass fiber reinforced thermoplastic wheel. First, the multi-objective topology optimization under multiple design spaces and multiple loading cases is conducted to obtain the robust structure, where the complicated ribs generated in design spaces are quite distinct from conventional steel or aluminum alloy wheel. The effects of weighting factors of two objectives and three loading cases on the topological results are discussed. And the long glass fiber reinforced thermoplastic wheel including the aluminum alloy insert is also designed in detail based on the concept structure and molding process. The novel metallic insert molded-in is another typical feature of long glass fiber reinforced thermoplastic wheel. Capturing the material anisotropy, the strength performances of long glass fiber reinforced thermoplastic wheel are simulated by using the finite element analysis method. The results show that there is a larger safety margin than the baseline wheel based on the maximum stress failure criterion. The long glass fiber reinforced thermoplastic wheel of 5.59 kg saves 22.3% weight compared to the aluminum alloy baseline. For the increasing requirement of automotive components lightweight design, the method and consideration in this paper may also provide some ways for the design and strength analysis of other carrying structures made of thermoplastic composite.
The fast kurtogram, a faint signal extraction method, has been regarded as an effective approach to detect and characterize faint transient features in vibration signals. However, the fast kurtogram, a band-pass filtering method, which extracts transient signals by optimal frequency band selection and leaves the noise in the selected frequency band unprocessed. Therefore, to overcome the shortcoming of the fast kurtogram method, a method which can wipe off the noise in the whole frequency band is necessary. This paper proposes a novel faint signal extraction method by time–frequency distribution image dimensionality reduction. Since time–frequency distribution image can reveal intrinsic feature of nonstationary signals and can make the weak impulses feature prominent, and besides, the transient impulse feature and the noise component lie in different dimensions, so using the dimensionality reduction method based on singular value decomposition to suppress the background noise in the raw time–frequency distribution image is motivated. A bearing outer race fault signal obtained from a test-to-failure experiment and a bearing inner race fault signal obtained from an experimental motor are employed to demonstrate the enhanced performance of the proposed method in faint signal extraction. The results indicate that the proposed method outperforms the fast kurtogram method and is effective in faint signal extraction.
The theoretical and experimental investigations on gear drive with tubular meshing surfaces are studied in this paper. Based on the theory of conjugate curves, parametric design for tubular tooth profiles is provided, and solid models are established. The performance evaluation of tubular meshing surfaces is carried out according to geometric and meshing characteristics analysis. The meshing essence of tubular tooth surfaces is revealed. Mechanics property of tooth surfaces is analyzed by finite element model. The contact stress, meshing law and deformation of tooth surfaces are introduced, respectively. Transmission efficiency experiment is made based on the developed gear prototype, and a comparison with involute gear drive is also shown. The further study on the dynamics analysis and key manufacturing technology will be carried out, and it is expected to have excellent transmission performance.
To design a controller for the purpose of control of hand exoskeleton force, the critical question is to model the human finger impedance properly. The difficulty is that the parameters of the impedance model are perturbative in different postures. In this paper, multiplicative uncertain models of human finger impedance are presented. We describe the impedance as a mass-spring-damping system. The experiments are set in extension, half-flexion, flexion and synthesis postures. The parameters of nominal model as well as their perturbation range are identified by the forgetting factor recursive least square method. The weighting functions are constructed accordingly. The results show that the uncertain model of synthesis posture can represent the magnitude-frequency characteristic at low frequency, while, for high frequency, the uncertain models composed by the weighting function of synthesis posture and the corresponding nominal model are feasible. These provide effective approaches for hand exoskeleton force control issues.
Early in the design process, designers attempt to explore in the wide design space to generate a number of feasible solutions and decide the best concept scheme with a high degree of uncertainty according to customer demands. A strategy that can assist designers in exploring and ascertaining design solutions within this vast space is therefore crucial. However, existing product design tools mainly focus on the detailed design phase and due to lack of effective design tools, it is often difficult for human designers to explore in wide multi-disciplinary solution spaces. Therefore, this paper proposes a cognitive process-based approach for assisting designers achieving intelligent conceptual design. By analyzing designers’ thinking characteristics, a design meta-thinking model is defined and a simulation model which is composed of divergent thinking and convergent thinking is put forward. Case-based reasoning and genetic algorithm are applied to stimulate divergent thinking to associate and produce feasible concept solutions. Furthermore, multiple-attribute decision-making method based on intuitionistic fuzzy number is employed to stimulate convergent thinking to obtain the best solution from generated conceptual candidate solutions. Finally, a case study is implemented on a turbo-expander. The result of this example demonstrates that the proposed approach can provide an intelligent manner to perform conceptual design. Meanwhile, a computer-aided design prototype system is developed based on this framework.
Effect of carbon nanotube emulsified fuel in a single-cylinder water-cooled four-stroke diesel engine was studied. CNT were produced by indigenous flame synthesis method. Water diesel emulsion was prepared in the proportion of 78% diesel, 20% water, and 2% surfactant with a HLB balance of 8. Tween 80 and Span 80 were used as surfactants. CNT in the mass fraction of 50 ppm, 100 ppm, and 150 ppm were blended in the water–diesel emulsion. CNT were dispersed in the water for 35 min with the help of ultrasonicator set at frequency of 40 kHz and ultrasonic power of 120 W, subsequently added in diesel, surfactant mixture to produce CNT blended water diesel emulsion. A mechanical homogenizer was used to produce emulsion at the speed of 3000 r/min for 25 min. The experimental investigation was carried out using single-cylinder diesel engine coupled with eddy current dynamometer and equipped with data acquisition system. An AVL Di-gas analyzer and AVL smoke opacity meter has been used to measure the exhaust emissions. Experiment was conducted at a constant speed of 1500 r/min from no load to full load for all fuel specimens. A comparative study involving combustion characteristics, brake specific fuel consumption, brake thermal efficiency, NOx, CO, HC, CO2 were recorded for pure diesel, water diesel emulsion and CNT-emulsified fuel. The results have shown significant improvement in engine performance, combustions attributes and reduction in emissions using CNT-emulsified fuel.
The pushing chain mechanism is a novel telescoping mechanism used to push objects from one position to another rapidly. For obtaining a long telescoping distance, this mechanism adopts a helicoids case which can store links as many as possible. In order to analyze the dynamic properties and the pushing stability of the pushing chain, the dynamics models of its extraction from the helicoids case and engagement with the sprocket are established. Meanwhile, the dynamics model of the extended chain during the pushing process is deduced. A numerical simulation of the full dynamics model is performed using MATLAB. The simulation results show that the drive forces influenced by the polygon effect transit from drastic oscillations to smooth fluctuations. The traction force acted on the chain in the helicoids case drops down to zero gradually with time. The links of the extended chain have a transverse vibration around the pushing line and the amplitudes reach a maximum at the middle. However, the pushing velocity rises quickly at the initial stage and begins to stabilize with small fluctuation. The pushing chain mechanism has good pushing stability and high-speed performance.
This paper focuses on the hardness distribution in the AA2014-T6 ring specimens upset under rigid dies. Three different types of lubricants namely soap, boric acid and vaseline were employed as lubricants and the friction factor corresponding to the lubricant employed was evaluated using standard ‘Ring compression test’. The strain distributions obtained from the simulation studies were used to predict the hardness inside the ring specimen. The hardness measured experimentally was validated with the predicted hardness and it was found that the errors in the predicted results were less than 10%. The hardness variations inside the upset metallic ring specimens were compared with the deformed solid cylinders to understand the behavior of differential strain hardening. It can be reported from the experimental and predicted results that the hardness is not uniform inside the deformed ring specimen and it varies at the bulge head; on the surface and along the neutral plane.
Forced convection of water–Cu nanofluid in a two-dimensional microchannel is studied numerically. The microchannel wall is divided into three parts. The entry and exit ones are kept insulated while the middle one has more temperature than the inlet fluid. The whole of microchannel is under the influence of a magnetic field with uniform strength of B 0. Slip velocity and temperature jump are involved along the microchannel walls for different values of slip coefficient such as B = 0.001, B = 0.01, and B = 0.1 for Re = 10, Re = 50, and Re = 100. Navier–Stokes equations are discretized and numerically solved by a developed computer code in FORTRAN. Results are presented as the velocity, temperature, and Nusselt number profiles. Moreover, the effect of magnetic field on slip velocity and temperature jump is investigated for the first time in the present work. Larger Hartmann number, Reynolds number, and volume fraction correspond to more heat transfer rate; however, the effects of Ha and are more significant at higher Re.
This study focuses on a step-length control method to investigate piecewise type nonlinearities such as multi-staged clutch dampers in a practical system. In general, step-length control techniques are employed to overcome at least two difficulties with respect to examining the nonlinear dynamic responses of a physical system. Such techniques first reduce the calculation time, which increases the efficiency of simulation in many case studies. Then, the employment of step-length control resolves strongly stiff problems which often occur in the asymmetrical piecewise type nonlinearities. In order to overcome these difficulties, this study suggests a newly developed step-length control method based on the employment of two different adaptive step sizes from prior steps to the next steps, when simulation is conducted using an arc-length continuation method. The simulation results using the step-length control method show much improvement with respect to reducing the calculation times and number of steps compared with the ones without step-length control method. Thus, this study provides clear understanding of the objectives of using step-length control such that it increases the efficiency of simulation as well as resolves the convergence problems in a nonlinear dynamic system.
The main focus of this paper is how the concept design phase of the product development process can be improved by using an objective data-driven approach in selecting a final concept design to progress further. A quantitative new test-bed ‘Product Optimisation Value Engineering’ (PROVEN) is presented to critically assess new and evolving powertrain technologies at the concept design phase. The new test-bed has the ability to define a technology value map to assess multiple technical options as a function of its attributes, whose precise values can be determined at a given cost. A mathematical model that incorporates a highly adaptable, data-driven and multi-attribute value approach to product specification and conceptual design is developed, novel to the concept design process. This creates a substantially optimised product offering to the market, reducing overall development costs while achieving customer satisfaction.
A numerical investigation has been performed to make a comparative study of clogging and detachment behavior of an elongated bubble during adiabatic flow through a uniform and diverging cross-sectional microchannel. The adiabatic gas–liquid two-phase flow has been numerically solved using volume of fluid approach in a finite volume code. Simulations have been made to investigate the effects of wall wettability, surface tension, and flow velocity on the bubble dynamics for both the configurations of microchannel. The net pressure drop across the bubble in the diverging channel has been calculated analytically and the results have been compared with numerical results. In both types of channels, the bubble shape goes through a transient stage followed by a steady and stable shape. The change in bubble shape during transient phase depends on the surface wettability, flow velocity, and the confinement of the channels. The bubble attains the symmetrical shape earlier in diverging channel. The formation of liquid film between the bubble and the wall plays an important role in the clogging behavior and movement of the bubble. Wall wettability has less impact on the pressure drop characteristics in the diverging channel.
The redundant manipulator has been broadly applied to various fields including industrial manufacturing, surgical manipulation and space exploration by providing high accuracy, flexibility, and efficiency. Particularly, the technology is capable of improving the assembling precision while simplifying the operation in complicated environments, and therefore of intense interest in industrial settings. For manipulator design, space occupation optimizing is a critical step and parameters of the flexible area, the shape and size of workspace have been commonly employed to evaluate the optimizing performance. In this paper, by combining the Fourier transform with the convolution theorem, we presented a workspace density function of redundant manipulator to describe the shape and size of workspace and flexibility. The workspace density function is an evaluation criterion to select the optimal geometric parameters for the manipulator. Based on the workspace density function shown in the simulation results section, the optimal design parameters were obtained. The approach presented in this paper holds the potential to improve the redundant manipulator design.
Sensorless monitoring technology based on motor current signature analysis is a nonintrusive and economical technique to monitor motor-driven equipment. Sensorless monitoring technology can be applied to a centrifugal pump system. This technology is also based on the motor current signature of centrifugal pump load; however, systematic research regarding motor current signature in overall normal operation points which is the applied basic for sensorless monitoring technology has been rarely performed. As such, we partially examined the motor current signature of a centrifugal pump load by experimental observation, theoretical analysis, and numerical simulation. Results show that stator current is a sinusoidal alternating current that strictly follows sine law associated with the cycle of the fundamental frequency of supply power. The trend of the root mean square and peak–peak of current is the same as flow–shaft power characteristics; hence, this trend could be used as indicator of the pump operational point monitor. The frequency characteristics of a centrifugal pump, such as blade passing frequency, rotation frequency, and broadband noise, could be reflected as sidebands around the fundamental frequency. The stator current spectrum is composed of fundamental frequency component, harmonics component, and noise. The fundamental frequency component is directly related to the pump load in which changes associated with the law of fundamental frequency component are relatively similar to flow–shaft power characteristics. Harmonics component and noise are caused by load fluctuation in which the amount of energy of these two components exhibits a lower value at the preferred operation point. By contrast, the amount of energy likely increases when pump operation is at an unstable operation point. These results further indicate that motor current signature analysis is a feasible and cost-effective method to monitor centrifugal pump operation status. Therefore, motor current signature analysis can be applied to monitor-related flow phenomena.
The design of a highly efficient pulse tube cryocooler (PTC) is a subject of recent research activities. The PTC performance depends on various operating and design parameters. Regenerator is one of the very important components of the PTC which decides the low temperature that the PTC can attain. Efficiency of regenerator should be high enough, 96% or above, in order to reach very low temperature while the pressure drop in the regenerator is one of the parameters which needs to be analysed in detail. In the present work, theoretical and experimental investigations are carried out on two different single stage U type PTC. The volumes of regenerators and pulse tubes, in both the cases are kept same while the length to diameter (L/D) ratios of regenerators are changed. Investigations are carried out on these PTC with respect to pressure drop in the regenerator and net refrigeration effect obtained from the PTC at 80 K. The pressure drop increases from 0.29 bar to 2.07 bar with an increase in L/D ratio from 1.93 to 9, resulting in decrease in refrigeration effect from 6.1 W to 1.7 W at 80 K with 300 W input power. The study is further extended to understand the effect of coarse size stainless steel mesh size in the regenerator. Coarse size meshes filled up to 60% of regenerator length improved the refrigeration effect from 1.7 W to 2.8 W; however, further filling degrades the performance of the PTC. The experimental results are compared with theoretical results obtained by Sage software and Isothermal model.
Conventional beam pumping units have occupied an important position in oilfield equipment due to such characteristics as simple structure, high reliability, simple operation, easy maintenance, and so on. In fact, there are about 90,000 sets of beam pumping units in China. However, the unbalanced structure of the beam pumping units cannot be entirely eliminated because of the inherent geometry and mechanical properties of four-bar linkage, that is the electromotor equivalent torque ripple cannot be absorbed or eliminated by counterweight in up-and-down travels, which causes the electromotor to work under greatly changed load rate with low power factor and high energy consumption. The mechanical relationship of a conventional beam pumping unit was derived first, and then parameters of a basic structure were optimized through dynamic optimization. On this basis, the hydraulic hybrid solution was proposed, and a secondary balance was conducted on the optimal pumping unit electrometer’s load torque. Computer simulation model was established to carry out a system dynamic analysis and the results showed that the scheme can reduce the motor load torque ripple, improve motor load rate and power factor, and reduce motor power effectively. It may bring tremendous decrease of electricity cost and have great significance for oilfield equipment energy saving, oil extraction cost reduction, and promotion of petroleum products’ competitiveness.
Existing knowledge provides important reference for designers in mechanical design activities. However, current knowledge acquisition methods based on information retrieval have the problem of inefficiency and low precision, which mainly meet the requirement for knowledge coverage. To improve the efficiency of knowledge acquisition and ensure the availability of design knowledge, this paper proposes a knowledge push service method based on design intent and user interest. First, the design intent model, which is mainly the formal expression of the target function of conceptual design, is built. Second, the user interest model that consists of domain themes and operation logs is built, and an automatic updating method of user interest is proposed. Third, a matching method of design knowledge based on design intent, and a sorting algorithm of knowledge candidates based on user interest are proposed to realize personalized knowledge active push service. Finally, a prototype system called Personalized Knowledge Push System for Mechanical Conceptual Design (MCD-PKPS) is implemented. An illustrative case demonstrates that the proposed method can successfully improve the efficiency and availability of knowledge acquisition.
The elasticity and geometrical errors of precision elements are one of the major factors affecting vibration responses in geared transmission systems. In this study, the influences of assembly error and bearing elasticity on the spur gear dynamic behavior are analyzed. A lumped parameter model for spur gear pair is formulated by representing the bearing elasticity with infinitesimal spring elements and tooth stiffness time function as rectangular waveform. The nonuniform tooth contact load is also considered. The severity of assembly error is assumed to be sufficiently small such that no partial loss of tooth contact occurs. A harmonic balance method is applied to the resultant second-order partial differential equation governing the gear pair dynamic behavior. The variations of dynamic transmission error and tooth contact load with respect to mesh frequency for a set of bearing stiffness are analyzed. The influences of bearing stiffness on the dynamic transmission error are also evaluated. The variation of actual cross angle, an indicator on the tooth meshing state, is examined with respect to nominal cross angle and bearing stiffness. The analysis shows that the presence of bearing elasticity and assembly error can degenerate tooth contact significantly, and hence the appropriate specifications of bearing and mesh stiffness are critical at gearbox design stage. The analysis demonstrates that the proposed lumped parameter model can provide detailed contact information like finite element model, but it avoids finite element model’s prohibitive computation burden and can be completed easily and be computed quickly.
The control purpose of an electro-hydraulic force control (EHFC) system is to real time replicate the force exerted on a structure in laboratory so as to simulate loads that cannot otherwise be generated naturally. In contrast to electro-hydraulic position control system, the tracking performance of EHFC system is always limited. To enhance the force replication accuracy of EHFC systems, a feedforward inverse controller integrating filtered-x LMS adaptive algorithm is presented in this paper. The proposed controller comprises a feedforward inverse controller and an adaptive controller. The feedforward inverse controller working as an inner loop is firstly established by directly cascading the designed parametric inverse transfer function to the EHFC system with proportional integral controller and the inverse transfer function is obtained with the implementation of system identification and zero magnitude error tracking technology. Then, the adaptive controller employing the filtered-x LMS algorithm acting as an outer loop is further combined with the feedforward controller to deal with the error occurred in the inverse model design procedure. Therefore, the proposed controller is an easy-to-implement strategy and can effectively enhance the force replication performance for both phase delay errors and amplitude mismatch errors. Finally, a series of experiments are carried out on a real EHFC test rig by means of xPC target technology, and the experimental results indicate that the proposed controller has a relatively better tracking accuracy compared with the proportional integral controller and the feedforward controller. It is also worth noting that the proposed controller can also be extended to other servo control systems where high accuracy tracking performance is required.
In this paper, periodic and hybrid trichiral structure is developed as the raft in a floating raft system to enhance isolation performance in the medium and high-frequency range. Firstly, wave propagation in the periodic trichiral structure is analyzed through Bloch theorem. Further study of the hybrid trichiral structure, consisting of multilayer of cells with different geometry, demonstrates that the stop band of this assembly is the superposition of the band gap generated by individual cells. This feature can be used to extend the stop band without affecting the performance in other frequencies. Vibration transmission of the floating raft system is studied through frequency response function based substructuring method. Numerical examples indicate that the sound power radiated from the foundation can be greatly attenuated in the stop band of the periodic trichiral raft. Based on the feature of hybrid structure, an optimization scheme with respect to the trichiral raft is developed with the aim of minimizing the radiated sound power of the system. The proposed modeling and optimization method can be extended to design other regular raft structures with great flexibility.
It is important to diagnose the bearing fault to prevent the serious accident of equipment. This paper introduces a bearing fault identification scheme based on envelope power spectrum analysis, linear discriminate analysis and continuous hidden Markov model. First the envelope power spectrum features are extracted from amplitude demodulated vibration signals from fault bearings. Then, linear discriminate analysis is employed to reduce the feature dimensions, which are helpful for improving the computing speed and diagnosing accuracy. At last, the new linear discriminate analysis features are input into continuous hidden Markov model to train the models under different conditions, respectively. In bearing fault identification, test data are input into the pretrained continuous hidden Markov models, and the bearing state can be detected by the output of continuous hidden Markov model. To validate the effectiveness of the proposed method, experimental samples of four bearing conditions at different fault sizes and loads are utilized to test the continuous hidden Markov model and back-propagation neural network. The result shows that continuous hidden Markov model and linear discriminate analysis-based method have higher accuracy and efficiency than back-propagation neural network.
A mathematical model of three-dimensional nonequilibrium condensing wet-steam flow is established in Eulerian form, based on conservation laws for a mixture of steam and water droplets. The method of moments is introduced in modeling the droplet spectrum. To describe the nonequilibrium condensing process, models for classical nucleation and enhanced droplet growth are applied. A special high-order implicit scheme is constructed for this condensing flow model. Tables based on IAPWS-IF97 formulae are used in solving the thermal properties of wet steam. The numerical results for a two-dimensional supersonic nozzle and a low-pressure steam turbine stage are compared with experimental data. The good agreement indicates the effectiveness of the condensation model and numerical scheme.
In order to enhance performance of automotive suspension with embedded-permanent-magnet magnetorheological (MR) damper, V-model developing flow of electronic control unit was adopted to study control system of the suspension. First of all, rapid control prototyping (RCP) system of suspension with embedded-permanent-magnet MR damper was built up based on real-time simulation platform D2P; control algorithm of fruit fly optimization algorithm– proportional-integral-derivative was designed and experiments of RCP simulation were carried out. Moreover, model of suspension with embedded-permanent-magnet MR damper was built with the instruction of magnetic field composition theory. On these bases, hardware in the loop simulation (HILS) platform was built up and HILS experiments were carried out as well. Finally, bench tests were carried out, whose results, together with simulation results, indicated that the controlling system of suspension with embedded-permanent-magnets MR damper in the given research could enhance automobiles’ ride performance and the designed control strategy and algorithm were good.
A novel hybrid manipulator is proposed and its kinematics and dynamics are analyzed systematically. First, a 3D prototype of the hybrid manipulator is constructed and analyzed. It is composed of a 5-DoF parallel manipulator with two equivalent composite universal joints and three fingers. Second, the kinematics formulae are established for solving the displacement, velocity and acceleration of the parallel manipulator and the finger mechanisms. Third, the dynamics formulae are derived for solving the dynamic active and constrained forces of the parallel manipulator and the finger mechanisms. Finally, a numerical example is given for solving the kinematics and the dynamics of the hybrid manipulator and the analytic solved results are verified by the simulation mechanism.
The selection of slewing bearings is based on the static load-carrying capacity. In this sense, manufacturers provide selection curves in their catalogues. However, little information is given about their origin. This work develops new and more versatile selection curves for four contact point slewing bearings, with a clear explanation of their background, scope and limitations. The new curves take into account the two possible static failure types, the ball-raceway contact failure and the bolted joint failure.
Traditional compound pendulum jaw crushers have many disadvantages such as low efficiency and uneven broken materials. This paper proposes a new biaxial compound pendulum jaw crusher to solve these problems. This paper presents the kinematic and dynamic performance of the new crushers, introduces its structure and layout features, derives the equations involving position, velocity, acceleration and kinetics, describes a workspace of the jaw crusher, analyzes the travel characteristic values and crushing force of movable jaw plates, and optimizes its structural and motion parameters through a multi-objective genetic algorithm. After the optimization process, the novel jaw crusher has little force on each hinge and large force on movable jaw plates. Specifically, the forces in the X-direction are 120,300 N for hinge C, 120,200 N for hinge D, and 195,000 N for hinge N; the forces in the Y-direction are 167,100 N, 162,800 N, and 197,900 N accordingly, while the breaking force of the movable jaw plate is 229,600 N. Experiments have been conducted. The results have clearly shown that the new biaxial compound pendulum jaw crusher has many advantages over conventional ones, such as the high crushing efficiency, even crushing, and large crushing force.
Graph theory has been applied to gear train analysis and synthesis for many years, and it is an effective and systematic modeling approach in the design process of gear transmission. Based on more than 100 references listed in this paper, a review about the graph-based method for kinematic and static force analysis, power flow, and mechanical efficiency computation is presented. The method is based on the concept of fundamental circuit corresponding to a basic epicyclic gear train. A 1-dof epicyclic gear train and a two-stage planetary gear train are used to illustrate the application of this method. Besides, isomorphism identification in the synthesis process and enumeration of 1-dof epicyclic gear train graphs are surveyed particularly. Also, the computerized methods for detection of redundant gears and degenerate structures in epicyclic gear trains are reviewed, respectively.
In this study, large amplitude free vibration behavior of a pretensioned Euler–Bernoulli beam is investigated both theoretically and experimentally. The Hamilton's principle is used to derive the beam governing equation of motion. By implementing the Galerkin's method and assuming the clamped–clamped boundary condition, the partial differential equation is converted to an ordinary nonlinear differential equation. Because of the large coefficient of the nonlinear term, the new homotopy perturbation method proposed by He, is modified to solve the governing nonlinear equation. Comparing the first- and the second-order approximate solutions of the modified homotopy perturbation method (MHPM) and those available in the literature demonstrates that the second-order MHPM leads to a more accurate solution which is valid for a wide range of the vibration amplitudes. The results have been validated by the experimental tests and the MHPM method. Also, the results show that an increase in the vibration amplitude and/or the pretension load increases the fundamental resonance frequency ratio. Besides, it would decrease with increasing the beam slenderness ratio.
The initial loss of tension in individual bolts after initial tightening obviously affects the level and the stability of the clamp load in bolted joints. A high-precision instrument to analyze the clamp load loss was developed. In this instrument, an Atlas Copco’s high performance spindle with an accuracy of ±2.5% under the conditions of one million duty cycles was used to tighten the test bolts and nuts. A rotary torque-angle transducer was integrated in the tightening spindle to measure the tightening torque. KMR force washer with a repeatability of < ±1% was applied to monitor the clamping force in real time. Using this instrument, the design of experiment analysis was performed to determine the effect of variables on the initial loss of tension. Those variables included the joint materials, the fastener class, the gasket grade, the lubrication, the surface roughness, the tightening speed, and the number of repeated tightening. The results showed that the tightening speed and the number of repeated tightening had a significant effect on the initial loss of tension. Moreover, a process criterion of eliminating plastic deformation was proposed to minimize the initial loss of tension. The findings presented in this paper will be expected to enhance the reliability and the safety of bolted assemblies, especially in critical applications.
The two-dimensional contact problem for an elastic body indenting an elastically similar half plane resulting in double contacts is important for various applications. In this paper, a generic quasi-static two-dimensional symmetric double contact problem with nonsingular end points between two elastically similar half planes, under the constant normal and oscillatory tangential loading, is analyzed. The classical singular integral equations approach is utilized to extract the pressure and shear functions in the contact zones; subsequently boundary conditions at end points are applied and a new side condition is derived and titled "the consistency condition" for symmetric double contacts. This condition is necessary for determining the extent of the contact and stick zones. Next, this analytical approach is applied to the symmetric indentation of a flat surface by two rigidly interconnected wedge-shaped punches.
The present work proposes a design procedure along with guidelines for the choice of initial clearance of a typical rotating gas turbine seal in a secondary air system. The basis for the design is to prevent seal rubbing against stator, by ensuring that the centrifugal and thermal growths of the seal are within the safe operating limits. As a case study, a six-tooth straight-through rotating labyrinth seal configuration is considered with wide ranging seal parameters, namely the seal inner radius (25–700 mm), speed (1000–5000 rad/s), temperature (200–650 ℃) and pressure ratio (1.1–2.5). By means of an iterative process, which involves computational fluid dynamics and finite element analysis techniques, and with a choice of initial clearance, an extensive database is generated. The results are presented in terms of non-dimensional variables, namely seal clearance ratio, centrifugal growth ratio, thermal growth ratio, operating clearance ratio due to centrifugal growth and operating clearance ratio due to thermal growth. It is found that the value of clearance ratio depends significantly on the dimensionless radial position. For a seal clearance ratio of 0.01, at 3000 rad/s, the leakage flow rate gets reduced by 18 and 4%, respectively for pressure ratios of 1.1 and 2.5, when the centrifugal growth alone is considered. When both centrifugal and thermal growths are considered, the percentage reduction becomes about 70% for the same seal operating at 3000 rad/s and 204 ℃, and it is as high as 95% at 426 ℃.
Freight trains play a vital role in cargo transportation in the world. The freight cars need to be redistributed for marshalling according to different destinations in the hump yard. Humans are usually employed to uncouple the freight cars in the marshalling yard. However, the work environment is difficult to work in, because of its potential danger and the effects of the surrounding environment can have a very serious impact on human’s health. A wheeled robot is developed to replace humans to finish the uncoupling task. It has four degrees-of-freedom with flexible motion. Based on the D-H method, the kinematics, including the forward and the inverse kinematics, is firstly analysed. The dynamic analysis is then studied by Newton–Euler equations. The workspace is lastly investigated to verify its operational space such that the coupler can be easily reached by the robot manipulator. Those characteristic analyses provide a basis for motion planning and real-time control of the robot.
Allocation of resources in cloud manufacturing is one of the key points of cloud manufacturing technology. To optimize cloud manufacturing resource management, it is indispensable to improve the process and efficiency of scheduling by matching jobs with resources according to the size of the job and establishing a four-level structure for resources based on the enterprise level, workshop level, primitive cell and service level. A resource scheduling model containing four indicators of cost, time, quality and risk with their own mathematical expressions is proposed. We also simulate the model with a new swap-shuffled leap-frog algorithm (SSFLA). Finally, we test the algorithm with different example scales and different end conditions and compare it with particle swarm optimization (PSO) and genetic algorithm (GA). The result shows that SSFLA performs well in convergence speed and robustness and does much better than PSO and GA. This algorithm provides an alternative choice for allocation of resources in cloud manufacturing model.
Design knowledge reuse is regarded as an effective strategy for design organizations to develop products with shorter time and less effort. However, existing design reuse approaches primarily focus on reusing the geometrical information of similar parts, with a wealth of contextual knowledge behind detailed design results lost. This paper presents an affordance-integrated approach for the reuse of detailed design knowledge, which can be employed to help designers determine the values of geometrical design parameters. First, this paper introduces an affordance-integrated model, called the structure-behavior-affordance, to represent the detailed design information. Then an affordance-based approach is proposed to help designers reuse the detailed design knowledge, which is also integrated with commercial CAD tools. Finally, the proposed approach is implemented as a detailed design knowledge reuse system and a turbocharger shell fixture is adopted as an example to illustrate the proposed design knowledge reuse approach.
Fuel and other subassemblies in fast breeder reactor are handled through a combination of small rotatable plug, large rotatable plug and transfer arm. Rotation of the plugs is facilitated through large slewing bearings. These bearings are subjected to heavy loads and moments. Manufacturing errors on the rolling elements and races influence the load sharing among the elements. As a result, higher load acting on a rolling element causes excessive local deformation and unacceptable indentation. The higher load can also cause excessive sub-surface shear stress and fatigue failure of rolling races. Too stringent tolerances demand sophisticated machines, whereas liberal tolerances mean compromise on the performance and life of the bearing. There are no established methods for design of slewing bearings that include the influence of manufacturing errors. Hence, an attempt has been made to find the influence of manufacturing errors on load distribution among the rolling elements using finite element method. It is observed that size error on the ball and waviness error (waviness spacing and height) on the raceway are the two influencing factors on load distribution. To study the influence of waviness error on the raceway, three sectors of bearing simulating waviness spacing of 10.8°, 18° and 36° with different waviness (peak-to-valley) height of 30 µm, 50 µm and 75 µm are analysed. It is observed that waviness height has larger influence on the load distribution among bearing balls when compared to waviness spacing.
Magnetic abrasive finishing (MAF) is an advanced machining process efficiently used for finishing of hard-to-machine materials. In this method, material removal takes place through nano-/microindentations in the presence of a controllable magnetic field generated via a permanent or an electronic magnet. Understanding the material removal mechanisms of the process is of particular importance for achievement of a high-quality surface with minimum surface defects. Therefore, in this work a numerical-experimental study was performed toward this issue using the extended finite element method (X-FEM). In this regard, the MAF operation was simulated as an indentation and sliding process of a sharp abrasive and the prevailing material removal mechanisms were obtained during MAF of BK7 optical glass. The constitutive material model for the specimen was defined according to the elastic-plastic-cracking model, which takes into account the tensile cracking and compressive yielding behavior of brittle materials. The X-FEM analysis revealed that both microcutting and microfracture mechanisms exist during MAF process of brittle materials depending on the process parameters. Among various parameters, magnetic particles size and abrasives size were the most influential factors affecting the dominant mechanism of material removal. The obtained numerical results were then validated experimentally by using scanning electron microscopy (SEM). The SEM observations revealed good performance of X-FEM analysis in prediction of material removal mechanisms during MAF of brittle materials.
The trellis supports of plants significantly affect their mechanical properties. Because trellises are usually used in grape plantations, their mechanical properties were measured in these systems. Vibrational grape harvesting was simulated using a finite element method. The major component of the vibration system is primarily represented by an elastic wire, and the green plants act as a mass with damping properties. The harvester ‘excitation’ was assumed to be sinusoidal with defined parameters. The real acceleration was measured during operation. The measured and calculated results correlated well. The process of detaching the crops can be determined using the calculated tearing force. This method helps to determine the dimensions of the trellis system and characterise the harvester’s operation.
Designing an optimal configuration for a reconfigurable robot to complete a task is an important issue. This paper proposes an optimization approach for a lattice distortable reconfigurable robot to pursue the best configuration with the least number of modules, and the robot configuration obtained by the approach has enough workspace reachability and structure strength to perform the specific task. This approach is carried out in two steps. In the first step called mechanism design, after establishing the mathematical models by the product of exponential formula for 12 types of lattices, based on the given task workspace, a configuration of an actuator with the least number of lattices is obtained by configuration synthesis method using the genetic algorithm. In the second step called structure design, the K-nearest neighbor method is explored to recognize the removable modules that have the minimum contribution to the overall strength of the robot. Then, an optimal topology configuration of the reconfigurable robot with the least number of modules is obtained by removing the removable modules. A computation example of the configuration optimization of a hexapod robot walking with the tripod gait is performed, and the results show the effectiveness of the proposed optimization approach.
The present work accounts Timoshenko beam theory followed by Ritz approximation and an iterative technique to deal nonlinear free vibration problems of cracked Functionally Graded Material (FGM) beams based on neutral surface location. Using neutral surface as a reference rather than the midsurface reduces the complexity of nonlinear problems. It is assumed that crack always remains open. Analysis is carried out for clamped-clamped and clamped-free boundary conditions. Nonlinear frequencies and mode shapes corresponding to first three mode of vibration are obtained for the first time for different crack parameters, amplitudes of vibration and material indexes. The accuracy of the present solution is verified by comparing some of the obtained results with existing solutions. It can be concluded that present results are not only accurate but the methodology is very simple and easy to perform.
The idea of taking inspiration from nature, and in particular from living systems, in the design of technological systems is fairly widespread and originated much research work. However, while in the field of materials this approach allowed the construction of systems of high complexity but at the same time inexpensive and able to be mass produced, the idea that, in a wider context, natural systems are necessarily optimized seems not to be justified. Optimization must not be confused with evolution: after Darwin we understand that there is no finalism in evolutionary processes, and that the mechanism producing the ‘design’ of living organisms cannot result in optimal designs to fulfil any given task, but can only cause a continuous adaptation to the environment. Similarly unfounded seems to be the idea that machines and devices, necessarily better that those obtained by using the traditional design approach, can be designed by taking inspiration from nature. The trial-and-error approach, supported by the principles of bionics, represents a setback with respect to the application of scientific principles to technology which so much contributed to the technological advancement in the modern world.
This paper investigates the traffic-related effects of a proposal to increase the speed limit from 40 mile/h to 50 mile/h, for heavy goods vehicles greater than 7.5 tonnes, on single carriageway roads. A ‘microscopic’ single carriageway traffic simulation is developed by combining the ‘enhanced intelligent driver model’ with a single carriageway gap-acceptance passing model. Fuel consumption estimates are made using engine characteristic maps and a ‘fuel optimal’ gear selection scheme, where vehicle trajectories from the traffic simulations are taken as input drive-cycles. Traffic congestion and fleet fuel consumption are specifically addressed, though implications regarding passing behaviour and traffic safety are also noted. Results indicate that the proposed 50 mile/h heavy goods vehicles speed limit would reduce traffic congestion by over 37% and increase fleet fuel consumption by approximately 0.5 L/100 km.
Sliding friction between the teeth is recognized as one of the main reasons of power losses in transmission as well as a potential reason of vibration and noise. A new approach is proposed to accurately calculate the sliding friction power losses in involute helical gears considered modification and geometric deviations resulting from the manufacturing processes, assembly errors, and deflections of support structures based on the simulation of gear mesh under light and significant load. Firstly, the paths of contact points on the pinion tooth surface are obtained from tooth contact analysis. Tooth surface load distributions and loaded transmission errors in one mesh period are obtained from loaded tooth contact analysis. Secondly, tooth surface load distributions are converted into the normal forces of tooth surface points of contact, loaded transmission errors are brought to the calculation formulas of sliding velocity, and the sliding friction coefficients of tooth surface points of contact are calculated by a non-Newtonian thermal elastohydrodynamic lubrication model. Substituting the sliding velocities, the normal forces, and the sliding friction coefficients into the power calculation formulas gives the sliding friction power losses of tooth surface points of contact. By the soft MATLAB, the values of the sliding friction power losses are integrated and the sliding friction power loss in helical gears from engagement to disengagement is obtained. Finally, an example of this approach is shown in the end. The results indicate that it is very necessary to consider the influence of loaded transmission errors for calculation of sliding friction power losses.
The design and performance of a new valving mechanism for portable pressurized spraying devices is described, where the propellant in the device is a safe gas (so-called compressed gas) propellant rather than the current liquefied gases all of which are either volatile organic compounds or greenhouse gases. The valve sprays a fixed volume of liquid when the spraying actuator is depressed, as is essential used medical sprays, such as pressurized metered dose inhalers and nasal sprays, and also for automatic (wall-mounted) aerosol delivery systems for air-fresheners, insecticides and disinfectants. For ‘compressed gas’ aerosol formats, there is no flash vaporization of propellant so that pumping liquid from a metering chamber and atomization to form a spray must be achieved entirely by designing some means of using the pumping action of the gas in the container to act upon the liquid in the metering chamber. The new design utilizes a loosely fitting spherical piston element and a simple arrangement of a concentric housing and a moveable valve stem, such that liquid flow paths between the different elements are automatically closed and opened in the correct time sequence when the valve stem is depressed and released. Spraying data show excellent repeatability of liquid sprayed per pulse throughout the lifetime of device and drop sizes that are acceptable for devices such as air-fresheners and nasal sprays. The valve has only one additional component compared with liquefied gas metered valves and can be straightforwardly injection moulded. As will be explained, previous attempts failed due to expense, complexity and unreliability.
In this study, the elastoplastic analysis of thin-walled tubes under cyclic bending and internal pressure is presented. A simple method is presented and verified. In order to predict ratcheting or shakedown behavior in the cyclic loading, von-Mises yield criterion as the yield surface and Chaboche’s nonlinear kinematic hardening model are used. The stress–strain variation is obtained with the help of return mapping algorithm. The present solution is in good agreement with experimental results. Shakedown or ratcheting behavior of the tube under various combinations of applied constant internal pressure and cyclic curvature is considered, Bree’s interaction diagram is obtained and the boundary between shakedown and ratcheting zone is determined.
Solar trackers are devices that improve the efficiency of photovoltaic collectors increasing the area exposed to direct radiation of the sun. The main drawback of these kinds of devices is that they have to consume certain energy in order to move the collectors following the sun trajectory. This work presents the detailed design of a mechanism with parallel kinematics architecture able to accurately follow the sun motion, which has been designed with the aim of minimizing the energy consumption during its operation.
This paper presents experimental and numerical investigation into the underwater sound radiation characteristics of a free-floating stiffened metal box covered with three different kinds of covering layers and subjected to mechanical excitation. One box is bare while the other three are, respectively, covered with solid covering layers, chiral covering layers, and chiral covering layers filled with expanded polystyrene (EPS) foams. The equivalent elastic modulus of chiral covering layer is obtained by the homogenization theory. The finite element method and boundary element method are used to calculate the underwater sound pressure. The measured and numerical results are illustrated and the sound insulation mechanisms of three covering layers are discussed. The measured results agree with the numerical results well. The covering layers can obviously reduce the underwater sound radiation of floating structures. Compared with the solid covering layer, the chiral covering layer is less effective in suppressing the sound radiation in the low-frequency range but more effective in the medium- and high-frequency range. The chiral covering layer filled with EPS foams shows the best performance, which is more effective in suppressing the sound radiation both in the low-frequency range and in the medium-frequency range. The EPS foams have a high contribution to the added damping of the chiral covering layer.
Future generation gas turbine combustors for power production are expected to have the capability of operating on a variety of different types of fuels. Energy systems running on different fuels produce flames with different burning behaviors, combustion dynamics, and pollutant emissions than when using conventional fuels. To ensure the implementation of new energy sources for future power generation units, which is critical for the US energy sector, lab-scale studies at high pressures and temperatures are being performed at many different locations throughout the world. Although many of these authors in the past present their results from the use of a high-pressure combustor, none have made their design methodology available to the public. Therefore, this paper presents a design of an optically accessible high-pressure combustor facility based on a 500 kW power and 1.5 MPa capability, which is the representative pressure of a gas turbine. Finite element analysis was extensively used to predict window and wall thicknesses needed to withstand these extreme conditions. Based on stress analysis quartz windows were designed with a thickness of 48 mm and a thickness of 8.61 cm was selected for the stainless steel combustor. Follow-up on testing using the high-pressure gas turbine combustor using various different types of fuels, diluents, and injectors have provided repeatable data on the capability of the combustor design to withstand the extreme environment conditions.
As an efficient manufacturing method for gears, shaping technology developed for non-circular helical gears will greatly break through the dilemma of their applications; especially for those gears with part of pitch curves being concave, being not able to be hobbed. Two fundamental linkage-models for external non-circular helical gears were built based on the meshing theory of non-circular gears in this article. According to four linkage methods in plane and two kinds of additional rotation in vertical direction, eight shaping strategies and their practical linkage-models (1)–(8) were developed. Taking a three-order elliptic helical gear as an example, the kinematic characteristics of the eight practical linkage-models were analyzed, which reveals that equal arc-length of gear billet (models (3) and (4)) have the highest accuracy under a given efficiency. The dynamic characteristics of models (3) and (4) were analyzed, which shows that model (4) (equal arc-length of gear billet and additional rotation on shaper cutter) is better in performance, and is an optimal one. The optimal linkage-model was demonstrated to be valid by a virtual shaping, and be able to shape those non-circular helical gears with part of pitch curves being concave. Moreover, the accuracy among every gear tooth is uniform. The theory developed and the results of the virtual shaping were illustrated with a shaping experiment. The train of thought and the results will be useful for any external non-circular helical gears with free pitch curves.
The dynamic analysis of wind turbine drive train is presented in this paper. A typical wind turbine drive train consists of a rotor, gearbox and generator. The dynamic modelling of epicyclic gearbox that exists in wind turbine is challenging due to the fact that it has both rotating and orbiting gears. The dynamic equations of motion are obtained based on the rigid multibody modelling with discrete flexibility approach by Lagrange’s formulation. The dynamic model accounts for the time varying gear tooth mesh stiffness, linear stiffness of bearings and torsional shaft stiffness. The aerodynamic torque that a wind turbine drive train subjected to, is modelled based on the simplified method for load calculation in wind turbine, Danish Standard DS472. The characteristic load value acting per unit length at the two-thirds length of the blade is used for calculating the total load of the torsional moment. The vibration signals that are obtained from wind turbine drive train are nonlinear and nonstationary in nature. This is due to the fact that the applied torque load on drive train is nonlinear and nonstationary in nature. The coupled dynamic model of 18 degrees of freedom is solved for responses in time and frequency domains for some nonstationary wind load realizations. The dynamic responses of the system, contact forces between gear tooth pairs in time and frequency domains are obtained numerically. The study envisages that this dynamic model of wind turbine drive train is very useful for subsequent studies on condition monitoring.
In a concentration solar system, large temperature differences occur between the hot- and cold-junction of thermoelectric module due to concentration technology. Therefore, the nonlinear temperature dependence of the Seebeck coefficient, the electric conductivity, and the thermal conductivity of thermoelectric materials should not be neglected in performance evaluation of thermoelectric generator. Herein, a discrete numerical model, with advantage of low-computational expense, high accuracy, and broad application scope, is built to design the thermoelectric generator in a concentration solar system. Temperature-dependent material properties and contact resistance are both incorporated in the discrete numerical model. Besides, an experiment is carried out to measure the performance of Bi2Te3 thermoelectric generator operating under various temperature differences (T). Finally, the discrete numerical model-calculated results are compared to the experimental data and the theoretical results computed by the commonly used constant properties model. Results show that the variation between the constant properties model-calculated output power and the measured one is less than 4% with T lower than 59 K and rises to 12.6% with T up to 251 K, while the error between the discrete numerical model-calculated output power and experiment remains lower than 2% even when T is above 251 K.
Fault detection and isolation are critical for safety related complex systems like aircraft, trains, automobiles, power plants and chemical plants. In order to realize a robust and real time monitoring and diagnosis for these types of multi-energy domain systems, this paper presents a novel scheme that integrates bond graph modeling for fault signatures establishment, and a multivariate state estimation technique-based empirical estimation for residual generation followed by a Sequential Probability Ratio Test-based residual evaluation for monitoring alarm. Once a fault is detected and alerted, a synthesized non-null coherence vector is created, and then matched with the pre-designed fault signatures matrix to isolate possible faults. To identify the effectiveness of the proposed methodology, a simulation for pneumatic equalizer control unit of locomotive electronically controlled pneumatic brake is conducted. The experimental results show that satisfied performance of fault detection and isolation can be obtained with lower miss alarm and timely response, which make it suitable for complex systems modeling and intelligent maintenance.
Continuous monitoring of diesel engine performance is critical for early detection of fault developments in an engine before they materialize into a functional failure. Instantaneous crank angular speed (IAS) analysis is one of a few non-intrusive condition monitoring techniques that can be utilized for such a task. Furthermore, the technique is more suitable for mass industry deployments than other non-intrusive methods such as vibration and acoustic emission techniques due to the low instrumentation cost, smaller data size and robust signal clarity since IAS is not affected by the engine operation noise and noise from the surrounding environment. A combination of IAS and order analysis was employed in this experimental study and the major order component of the IAS spectrum was used for engine loading estimation and fault diagnosis of a four-stroke four-cylinder diesel engine. It was shown that IAS analysis can provide useful information about engine speed variation caused by changing piston momentum and crankshaft acceleration during the engine combustion process. It was also found that the major order component of the IAS spectra directly associated with the engine firing frequency (at twice the mean shaft rotating speed) can be utilized to estimate engine loading condition regardless of whether the engine is operating at healthy condition or with faults. The amplitude of this order component follows a distinctive exponential curve as the loading condition changes. A mathematical relationship was then established in the paper to estimate the engine power output based on the amplitude of this order component of the IAS spectrum. It was further illustrated that IAS technique can be employed for the detection of a simulated exhaust valve fault in this study.
The presented publication demonstrates an accuracy assessment method for machine tool body casting utilizing an optical scanner and reference model of the machine tool body. The process allows assessing the casting shape accuracy, as well as determining whether the size of the allowances of all work surfaces is sufficient for appropriate machining, corresponding to the construction design. The described method enables dispensing with the arduous manual operation of marking out as well as shortening the time of aligning and fixing the casting body for machining. For the experimental setup, four rotary indexing table castings were investigated according to the method principles. The geometric accuracy of each casting was examined by comparing their scans with the computer-aided design model, and the machining allowances were evaluated to determine casting qualification for machining. The nominal volume of material to be removed was established and subsequently optimized to reduce the volume to be machined. Thus, a rapid method of aligning a casting in a machine tool according to the planned optimized distribution of machining allowances was developed. For the set of measured castings, it was proven that their poor geometric quality precluded the possibility of further machining according to standard marking out instructions. However, by following the presented methodology, it was possible to successfully process the entire set while reducing the overall volume of the material removed by 4.5–9.6%, as compared with nominal values. The obtained results ultimately confirmed that manual marking out could be eliminated from the casting assessment process.
In this paper, a hybrid serial–parallel forging manipulator was put forward, which is composed of a planar five-bar mechanism and a two-limb parallel mechanism in series. Forging manipulator’s DOF properties and motion principle were analyzed by means of screw theory. The position solution of the main motion mechanism of manipulator was derived in the grasping stage, which was used to solve input displacements of lifting and pitching hydraulic cylinders depending on the requirements of forged piece’s lifting height and pitching angle. Dimensional optimization of the manipulator’s main motion mechanism is carried out based on position equations, resulting in that the gripper carrier’s lifting motion was decoupled from the horizontal motion. The analytical expression between driving forces of each hydraulic cylinder and external load was derived by solving the first-order derivative of position equations and using principle of virtual work. The results showed that for the parallel-link manipulator, when gripper carrier is horizontal, driving force of lifting hydraulic cylinder is only related to forged piece’s gravity but not to gravitational moment. The mechanism of this phenomenon was also further studied. Experimental model with ratio 1:20 of forging manipulator’s lifting mechanism was developed, and kinematic and static experiments were conducted on it to verify the dimensional optimization results and the conclusion was obtained by the statics.
As an index of maintaining low fuel consumption, the digging force of an excavator is affected fully by the performance of the hydraulic actuators including boom cylinder, stick cylinder, and bucket cylinder. The seals are used widely in a fluid power system to prevent fluid leakage. However, wear induces changes in the diameter of the seal's cross-section area, having an effect on the sealing capability of seals. This article proposes a model for performance degradation induced by wear of a hydraulic actuator of an excavator. The model in this article describes the physical process of performance degradation of a hydraulic actuator by analyzing piston response when wear occurs. The model includes a dynamic model of a hydraulic actuator, a model of squeezing stress and deformation of a compressed elastomeric O-ring seal, a wear model of a seal, and a leak rate model. These models can be used for deducing the laws of performance degradation of a hydraulic actuator of an excavator and for predicting the useful life of a key component such as the seal. Finally, based on the established model, simulation results of a hydraulic actuator’s response are provided.
This paper proposes conceptual designs of multi-degree(s) of freedom (DOF) compliant parallel manipulators (CPMs) including 3-DOF translational CPMs and 6-DOF CPMs using a building block based pseudo-rigid-body-model (PRBM) approach. The proposed multi-DOF CPMs are composed of wire-beam based compliant mechanisms (WBBCMs) as distributed-compliance compliant building blocks (CBBs). Firstly, a comprehensive literature review for the design approaches of compliant mechanisms is conducted, and a building block based PRBM is then presented, which replaces the traditional kinematic sub-chain with an appropriate multi-DOF CBB. In order to obtain the decoupled 3-DOF translational CPMs (XYZ CPMs), two classes of kinematically decoupled 3-
The working state of the five hundred-meter aperture spherical telescope (FAST) is solved using the step-wise assignment method. In this paper, the mathematical model of the cable-net support structure of the FAST is set up by the catenary equation. There are a large number of nonlinear equations and unknown parameters of the model. The nonlinear equations are solved by using the step-wise assignment method. The method is using the analytical solutions of the cable-net equations of one working state as the initial value for the next working state, from which the analytical solutions of the nonlinear equations of the cable-net for each working state of the FAST and the tension and length of each driving cable can be obtained. The suggested algorithm is quite practically well suited to study the working state of the cable-net structures of the FAST. Also, the working state analysis result of the cable-net support structure of a reduced model of the cable-net structure reflector for the FAST is given to verify the reliability of the method. In order to show the validity of the method, comparisons with another algorithm to set the initial value are presented. This method has an important guiding significance to the further study on the control of the new type of flexible cable driving mechanism, especially the FAST.
A globe valve is a common device that performs flow control in a pipe system. The flow capability of the globe valve is estimated by a flow coefficient. To improve the control capability of the globe valve, a cage is utilized to adjust the flow coefficient in the valve. For example, if one feels like decreasing the flow coefficient, then a cage with numerous passageways will be considered rather than replacing a smaller valve and pipe. A double cages design is also employed to reach the same purpose. The flow coefficient of the valve is associated with passageways in the cage. Provided that the relationship between the total cross-sectional area of passageways and the flow coefficient is known, then one will be able to design another cage with required and re-allocated passageways to control the variation of flow coefficient. The objective of this study is to use computational fluid dynamic technique to predict the relationship. Furthermore, one can change variation of flow coefficient in a globe valve using a new designed cage with re-allocated passageways. Again, the change of the cage on the flow coefficient can be validated by computational fluid dynamics again. This approach would be useful for a valve engineer to design a cage to control the flow capability in a globe valve.
In this paper, we consider the design and analysis of an X–Y parallel piezoelectric-actuator-driven nanopositioner with a novel two-stage amplifying mechanism, where the mechanical design is optimized to achieve a large stroke and high-natural frequency for the purpose of high-performance servomechanism. The parallel kinematic X–Y flexure mechanism provides good geometric decoupling. The kinematic and dynamic analysis shows that the proposed design has a large work space and high bandwidth, which is further verified by finite-element analysis. The analysis results demonstrate that the designed nanopositioner has a large workspace more than 200 µm and a high-natural frequency at about 760 Hz. Furthermore, the dynamical model of the nanopositioner, including the dynamics of the PZT actuators, is also generated from the perspective of input/output transfer functions, and the parameters are identified by frequency-response experiments, which can be used for nano precision servomechanism.
The heart of gerotor motors is a gear-set. The gear-set consists of an inner gear which is rotating and orbiting in contact with an outer gear. Wear in these contacts is investigated experimentally and with a numerical implementation of an Archard based wear model in combination with a load sharing concept. The model utilizes the symmetry of the motor and is based on a three-scale approach to estimate the wear on the gears. The global model calculates contact forces, relative surface velocities and contact radii in the contacts between inner and outer gear. The calculations performed on the local scale are used to collect information about the influence of the surface roughness on lubricant film thickness. The wear depth is calculated on a semi-local scale, involving only one tooth on the outer gear. In partial elastohydrodynamic lubrication, load is carried by the part of the conjunction where there is direct contact between the mating surfaces and by the lubricant pressure. In the wear model, wear only occurs as a direct consequence of contact between the mating surfaces. Experimental results are compared with the model predictions for equivalent running conditions. The wear predicted by the model agrees with the experimental results. For this reason, it is concluded that wear in the gerotor motor is dominated by the wear mechanisms which are considered in the tribological model.
Energy storage devices are an essential part of hybrid and electric vehicles. The most commonly used ones are batteries, ultra capacitors and high speed flywheels. Among these, the flywheel is the only device that keeps the energy stored in the same form as the moving vehicle, i.e. mechanical energy. In order to connect the flywheel with the vehicle drive line, a suitable means is needed which would allow the flywheel to vary its speed continuously, in other words a continuously variable transmission (CVT) is needed. To improve the efficiency and speed ratio range of the variators, a power spilt CVT (PSCVT) can be employed. This paper discusses the kinematics of PSCVT used to connect the flywheel to the driveline. A methodology describing the characteristic equations of speed ratio, power flow and efficiency of the PSCVT for various types including power recirculating and multi regime in both directions of power flow has been presented. An example of a PSCVT for a flywheel energy storage system (FESS) is computed using the derived equations and the results compared.
Testability demonstration plays an important role in assuring the testability capability, which can decrease the fault diagnosis time and accelerate the maintenance actions. However, testability demonstration test with classical planning method has the problems of large fault sample size, high test cost, and long test period. A new testability demonstration planning method is proposed, which takes the component level data from both virtual and physical demonstration tests as prior information. Owing to the limitations of the testability modeling technology and relevant programming tools, the virtual testability prototype of the system level cannot be established and the virtual testability test data is not totally credible. So a data conversion method based on the information entropy theory is proposed to convert the component level virtual and physical test data into equivalent system test data, in which the data credibility is taken into consideration. The equivalent system test data is then used to get the prior probability density function of the testability indexes with an empirical Bayesian method. Then, a testability demonstration planning method of Bayesian posterior risk criteria is presented. Finally, the fault detection rate demonstration tests of a flight control system and a heating controller are taken as examples to verify the proposed method. The results show that the introduction of prior test data can effectively decrease the sample size and the credibility of the virtual testability test data can affect the test plan.
In this paper, static response of a sandwich cylindrical shell under elasto-plastic deformation is investigated. The faces are made of some isotropic materials and the core is made of an orthotropic material both with linear work hardening behavior. The faces are modeled as thin cylindrical shells obeying the Kirchhoff-Love assumptions. The core material is modeled as a special orthotropic solid in which its in-plane stresses are assumed to be negligible. The Prandtl-Reuss plastic flow theory and von Mises yield criterion are used in the analysis. The governing equations are derived using the principle of virtual displacements. Using Ritz method, the equations are solved for deformation components. After verification of the results, the analysis is extended by changing the values of different parameters.
This paper introduces a novel parallel mechanism having Schönflies motion. The mechanism consists of only two RRPaR-type limbs. After a short description of its structure, its position analysis is conducted and its screw-based kinematic model is derived. Next, its singularity analysis is performed via Grassmann line geometry and then its optimal kinematic characteristics are examined with respect to workspace size and isotropy property. The results show that the proposed parallel mechanism has a very high potential to be used as a manipulator or a haptic device. A prototype of this mechanism was developed and tested to corroborate its performance.
A novel 3-UP3R parallel mechanism with six degree of freedoms is proposed in this paper. One most important advantage of this mechanism is that the three translational and three rotational motions are partially decoupled: the end-effector position is only determined by three inputs, while the rotational angles are relative to all six inputs. The design methodology via GF set theory is brought out, using which the limb type can be determined. The mobility of the end-effector is analyzed. After that, the kinematic and velocity models are formulated. Then, workspace is studied, and since the robot is partially decoupled, the reachable workspace is also the dexterous workspace. In the end, both local and global performances are discussed using conditioning indexes. The experiment of real prototype shows that this mechanism works well and may be applied in many fields.
This study presents film thickness and friction measurements of the refrigerant R1233zd (E-1-chloro-3,3,3,trifluoropropene-1) in a tribological contact. For the film thickness, optical interferometry technique with glass–steel contact is used in a ball-disc configuration, whilst for the traction measurements (Stribeck and traction curves), a contact ceramic ball–steel disc is used. In both cases, the Wedeven Associates Machines-5 tribometer is employed. An attempt to model the film thickness results is also carried out. The model gives a reasonably good prediction with respect to the experiments.
With the wide application of multi-layer interference fit in many engineering fields, as for key component in the wind turbine generator, wind turbine’s shrink disk uses interference fit to transmit rated torque and axial force. In order to ensure the work reliability of shrink disk during the actual operation, the paper presents a more precise method on the design calculation of contact pressure on the mating surfaces with interference fit. In accordance with the order from the inside to the outside, the contact pressure of spindle-to-sleeve surface can be calculated based on the rated load required to transmit. Combining with Thick-wall Cylinder Theory and Lame Equation, taking into account the impact of fit clearance, the checking method of the bushing was used to calculate the contact pressure on mating surface of bushing-to-inner ring; and the stress analysis of the inner ring was used to calculate the contact pressure on mating surface of inner ring-to-outer ring. At the same time, the effects of frictional coefficient, fit clearance, and other design parameters on theoretical results were also analyzed. The pressure distribution of each mating surface was obtained by Abaqus software simulation, which showed that the results from improved method was closer to simulation results and had higher accuracy than traditional method by comparing the results with three different methods. Finally, the test was designed to verify whether the shrink disk could bear the load or not on the test platform of shrink disk, and the results indicated that it could meet the requirements of given loadcase.
The nonlinear vibrations of the tapping-mode atomic force microscopy probe are investigated due to both nonlinearity in tip–sample contact force and curvature of the microcantilever probe. The nonlinear equations of motion for vibrations of the probe are obtained using Hamilton’s principle. In this work, the contact force is considered to be more dominant while previous works only consider Van der Waals force. The nonlinear contact force is expanded using a Taylor series to provide a polynomial with coefficients that are functions of the tip–sample distance. The outcome of this work allows the proper distance to be chosen before scanning to avoid instability in the response. Instability regions must be avoided for accurate imaging. The results show that initial tip–sample distance has a major effect on the stability of the frequency response and force response curves. For analytical investigation, the mode shapes of the atomic force microscopy probe are derived based on the presence of the nonlinear contact force as a boundary condition at the free end of the probe. The frequency response curve is obtained using the method of multiple scales. The results show that the effects of the nonlinearities due to probe geometry and contact force can be minimized. Minimizing the effects of nonlinearities allows for less cumbersome and calculation intensive software packages for atomic force microscopies. This research shows that one possible method of decreasing the nonlinearity effect is increasing the excitation force; however, this can increase the contact region and is not the best solution for canceling the nonlinearity effect. The superior method which is the major contribution of this paper is to find the optimal initial tip–sample distance and excitation force that minimize the nonlinearity effect. It is shown that at a certain tip–sample distance the quadratic and cubic nonlinearities cancel each other and the system responds linearly.
Tendon-based transmission has significant advantages in the development of a surgical robot, which is fully magnetic resonance imaging compatible and can work dexterously in the very limited space inside magnetic resonance imaging core. According to the requirements of magnetic resonance imaging compatibility, a novel 6 degrees of freedom tendon-based surgical robot composed of three independent modules is developed in this paper. After a brief introduction to the robot, the direct and inverse kinematic equations are deduced by applying the concept of screw displacements, and the reachable workspace of the robot is calculated. As to the static force analysis, we apply the principle of virtual work to derive a transmission between the equivalent joint torques and the tendon forces. By the use of the pseudoinverse technique, a systematic method is developed for the resolution of redundant tendon forces.
A shape control system based on a wavelet radial basis function network for a Sendzimir mill (ZRM) and fuzzy control are developed to improve the shape control performance of a conventional ZRM system. The conventional shape recognition system for a ZRM adopted an incomplete multi-layer perceptron neural network system that was constructed two decades ago. The poor shape recognition of this system leads to actuator saturation and shape control performance deterioration. Therefore, the full automatic operation of a ZRM is often stopped, and manual input need to be performed. This affects the quality, causes a decline in the productivity of the steel strip and an unnecessary waste of manpower. In this paper, a wavelet radial basis network is developed to replace the multi-layer perceptron network and consequently improve shape recognition performance. A modified fuzzy controller is also constructed to prevent actuator saturation that occurs in a conventional shape control system owing to the use of a fixed gain-based fuzzy controller. A comparative simulation based on the data measured from an actual ZRM plant demonstrates the efficacy of the proposed shape control system.
In this study, vibration of double-walled carbon nanotubes (DWCNTs) conveying fluid placed in uniform magnetic field is carried out based on nonlocal elasticity theory. DWCNT is embedded in Pasternak foundation and is simulated as a Timoshenko beam (TB) model which includes rotary inertia and transverse shear deformation in the formulation. Considering slip boundary conditions and van der Waals (vdW) forces between inner and the outer nanotubes, the governing equations of motion are discretized and differential quadrature method (DQM) is applied to obtain the frequency of DWCNTs for clamped–clamped boundary condition. The detailed parametric study is conducted, focusing on the remarkable effects of small scale, Knudsen number, elastic medium, magnetic field, density, and velocity of conveying fluid on the stability of DWCNT. Results indicate that considering slip boundary conditions has significant effect on stability of DWCNTs. Also, it is found that trend of figures have good agreement with the previous researches. Results of this investigation could be applied for optimum design of nano/micro mechanical devices for controlling stability of DWCNTs conveying fluid under magnetic fields.
A unique mechanism is investigated in this paper to show the working principles of a novel hypocycloid twin-rotor piston engine (HTRPE), which provides the basis for the structural design, kinematic and dynamical analysis necessary to realize the engine. As a critical system for the HTRPE, the differential velocity mechanism is examined first by decomposing it into two non-uniform motion mechanisms and one hypocycloid mechanism, which allows an evaluation of different options of design parameters. Then analytical expressions are derived to calculate the rotor angular velocities and the relative angular velocities of pairs of rotors for a detailed performance analysis. Based on the results of this analysis a prototype HTRPE is proposed and benchmarked with both a conventional reciprocating and a Wankel engine. It is shown that the new engine outperforms the other two engines in key engine features including combustion gas force transmission, volumetric change of working chambers, power frequency, piston velocity and displacement, demonstrating that HTRPE is very promising as a more energy efficient engine due to its high compactness and power density, and consequently lightweight design.
A pre-curved bimetallic strip that is applied with a force in an axial orientation, i.e. along its chord line, exhibits nonlinear force–displacement characteristics. For thin bimetallic strips, whereby the radius of curvature is large compared to the thickness of the strip, the non-linearity tends to be tangent related. The new theoretical formula introduced here was correlated to the results of a set of force–displacement tests, and a good overall fit of the theory to the test data was achieved. The formula put forward in this work enables the evaluation of large chord line displacements but is limited to the permissible stress limits of the material. This work can also be directly applied to thin shallow arc beams of a single material. The application of this work is in the field of bimetallic force–displacement actuators.
This study conducted a loaded tooth contact analysis of a modified curvilinear gear set with localized bearing contact based on finite element analysis. The contact stress and transmission errors under load were examined. First, a mesh generation program was developed according to the mathematical model of a curvilinear gear generated using a male fly cutter. A finite element model containing one contacting tooth pair was built, and the mesh density at the contact-sensitive area was adjusted to attain a reasonable finite element model for estimating the contact pressure. Adequate mesh density at the possible contact region predicted by tooth contact analysis was defined based on the theoretical Hertzian contact stress and the calculated contact ellipse. A finite element model containing five tooth pairs was developed and applied to examine the contact stress and transmission errors under load of the modified curvilinear gear set. Finally, numerical examples were provided to demonstrate the contact stress and transmission errors under load for various design parameters and loads.
In this paper, a remote continuous adjoint-based acoustic propagation (RABAP) method is proposed for low noise turbofan duct design. The goal is to develop a set of adjoint equations and their corresponding boundary conditions in order to quantify the influence of geometry modifications on the amplitude of sound pressure at a near-field location. The governing equations for the 2.5D acoustic perturbation equation solver (APE) formulation for duct acoustic propagation is first introduced. This is followed by the formulation and discretization of the remote continuous adjoint equations based on 2.5D APE. The special treatment of the adjoint boundary condition to obtain sensitivities derivatives is also discussed. The theory is applied to acoustic design of an axisymmetric fan bypass duct for two different tone noise radiations. The 2.5D APE is further validated using comparisons to an experiment data of the TURNEX nozzle geometry. The implementation of the remote continuous adjoint method is validated by comparing the sensitivity derivative with that obtained using finite difference method. The result obtained confirms the effectiveness and efficiency of the proposed RABAP framework.
Twin pinion gear pumps are used widely in industrial hydraulics and as fuel-delivery pumps for aero engines. The kinematics of the pumping action leads to high-flow rates into and out of the meshing gears, and at the high speeds used with aerospace fuel pumps cavitation can occur. One-dimensional ‘lumped parameter’ models are often used to analyse this type of pump. These methods rely on an accurate description of the volume trapped by the meshing teeth and the flow areas during the meshing cycle. Typically, multiple computer-aided design models have to be created to calculate these values during the meshing cycle. This paper presents a mathematical method for calculating these parameters based on a parametric definition of the gear and inlet and outlet porting. Green's theorem is used to allow line integrals around the periphery of the tooth spaces to be used to calculate the volumes and flow areas. Winding numbers are used to calculate the inflow and outflow areas that are formed by the intersection of the trapped volume and the side area porting. The method is validated against computer-aided design model data. This method is well suited for incorporation in an optimisation algorithm since the geometry is defined parametrically.
Stability and the string stability of a platoon of adaptive cruise control (ACC) vehicles using a constant spacing are investigated. Due to realistic design and execution, negative effect of tracking lag parameter on the stability is examined. An efficient analytical approach is presented in order to obtain a sufficient stability condition in the domain of the control parameters. The stability criterion is examined using a partial differential equation (PDE) approximation using large number of vehicles subjected to the time lags in vehicle dynamics and heterogeneity in the control laws, which allows asymmetry in the use of front and back information. The string stability analysis is performed to evaluate the disturbance attenuation. Finally, an example of multiple vehicle platoon control is presented, which demonstrates the effectiveness and the robustness of the proposed method.
This study investigates the applicability of distorted models in predicting the frequencies and responses of coated thin plates. The significance of this study is that it provides the necessary scaling laws and structure size applicable intervals, which guide the design of distorted models. By comparing the effect of different coating thickness and different coating forms (single-sided coating and double-sided coatings), the direct use of a governing equation is employed to establish the scaling laws between the model and the prototype. Both complete and partial similarity is discussed. Then an aluminum-coated steel plate, which is commonly used, is analyzed as an example. Establishment of the structure size applicable interval is discussed, which should keep the same first-order natural characteristics (natural frequency and vibration mode). Applicable intervals of the distorted model under different orders are also obtained by using a numerical method. The applicability of the scaling laws and applicable intervals of coated thin plates are verified. The analytical results indicate that distorted models which satisfied the structure size applicable intervals can predict the characteristics of the prototype with good accuracy. This study provides a theoretical foundation for the design of scaled-down models of coated structures.
Time-varying mesh stiffness is a significant excitation source within gear systems. Split gear (or laminated gear, phase gear) is an interesting design using equally phased gear-slices, which can remarkably reduce the mesh stiffness fluctuation like helical gears but completely avoid the axial force. This work examines a split gear pair to address the suppression of the mesh stiffness fluctuation and rotational vibration thereof, especially the relationship between the key design parameters including the number of slice, contact ratio, and damping, and the parametric vibration. For these aims, this work develops a purely rotational model, based on which the multi-scale method is employed to determine stability boundaries. The results imply that the unstable zones are related to the mesh phase determined by the number of slices and contact ratio, and these zones can be diminished by the damping. The analytical predictions are numerically verified by Floquet theory.
In this paper, a framework for computer-aided type synthesis of parallel mechanisms (PMs) is described and the integrated type synthesis software based on the GF sets theory is developed for the first time. The objective of the software was to automate and facilitate type synthesis of PMs. The GF sets theory introduced in our earlier works is an effective type synthesis approach with high execution level. This approach is implemented in a software tool. Algorithms for number synthesis of PMs, decomposition of GF sets, and limbs design method are developed. The computer-aided type synthesis software shows intelligence and self-learning ability of a certain level. Guided by the software, users can complete type synthesis of PMs smoothly with some complex calculations done by the software. The validity of the proposed software is verified through a design example. The design cycle and cost of machinery products using PMs will be reduced with help of the software.
Dynamic behavior of mechanisms with clearance joints often exhibits nonlinear dynamic characteristics due to the collisions between the journal and bearing. However, previous studies could not quantify the complexity of the dynamic response. In this paper, based on the Poincaré map and correlation dimension, a fractal method is proposed to evaluate the complexity of nonlinear dynamic response of mechanisms with clearance joints. Motion equations of mechanical systems with clearance joints are described. A slider–crank mechanism is employed to demonstrate the efficiency of the fractal method and to discuss the influence of the clearance size and crank speed on the complexity of the dynamic response.
Gait generation plays a significant role in the quality of locomotion of legged robots. This paper presents the development of multi-phase dynamic equations and optimal trajectory generation for a seven-link planar-biped robot walking on the ground level with consideration of feet rotation in the double support phase. The main contribution of this paper is to increase the stability margin at the phase transition time for simultaneous feet rotation in double support phase by introducing a new style of feet rotation. First, the derivation of the dynamics equations, which is a challenging problem due to the existence of the holonomic constraints, is performed using the Lagrangian formulation. Then, an analytical solution to inverse kinematics is proposed to determine the angles of each joint. A multi-objective genetic algorithm-based optimization technique is proposed to obtain the key parameters in trajectory generation so that the zero moment point tracks a predefined stable trajectory and additionally minimizes the power consumption, which is subjected to actuators’ powers limitations. The effect of the hip height on the total power consumption is also investigated. The numerical simulations demonstrate the effectiveness of the proposed method.
With the development of small unmanned air vehicles, the urge for building the experimental facilities has emerged for the research on the low Reynolds number aerodynamics. In this paper, a five-component internal sting balance with the capacity of 10 N for forces and of 0.5 N·m for moments, which is to be installed in a close-circuit low Reynolds number wind tunnel for small unmanned air vehicle tests, was verified to investigate the interaction effect of its different components. Experimental setups and a sequence of evaluated procedures were designed to implement the application of different range of loads with pitch and roll angle coupled so as to investigate the interaction effect of different components by covering the full load range of sting balance. The sting balance was successfully verified with the designed experimental setups and procedures. Evaluation results showed that the interaction effect between balance components enhanced the measurement error and deteriorated the measurement precision. Moreover, it was also found that both precision and error depended on the loads. Relative error analysis revealed that the average relative error of all components was less than 2.1%. Hysteresis test showed that all balance component exhibited little hysteresis property except that side force component exhibited a mild hysteresis at lower load range.
The linear rolling guideway is composed of rail, carriage, rolling balls, and other accessories and contains a large number of rolling interfaces between the rolling balls and the grooves. For such a complex nonlinear mechanical system, it is very significant to obtain the statics deformation and vertical stiffness under different loads for the structural design of guideway and mechanical analysis of Computer Numerical Control (CNC) machine tool. Therefore, the focus of this study is on the development of statics modeling techniques of the linear rolling guideway by analytical and finite element methods, considering the rolling balls contact. First, an accurate statics analytical modeling method was proposed by using the Hertz contact theory and revision of experiment results. Then, on the basis of considering contacts between rolling balls and grooves, the precise finite element modeling was studied. To improve the efficiency of analysis, the full finite element model of guideway was replaced by the component finite element model. At last, the created analytical and component finite element models were applied to analyze the effects of load and preload on the statics characteristics of single ball and the whole guideway system. The proposal of current study may provide a reference to create the precise dynamics model of linear rolling guideway.
In engineering applications, many control devices have been developed to reduce the vibrations of structures. Active tuned mass damper system is one of these devices, which is a combination of a passive tuned mass damper system and an actuator to produce a control force. The main objective of this paper is to present a practical procedure for both deterministic and probabilistic design of the active tuned mass damper control system using multi-objective genetic algorithms to mitigate high-rise building responses. For this purpose, extensive numerical analyses have been performed, and optimal robust results of the active tuned mass damper design parameters with their effectiveness in reducing the example building responses have been presented. Uncertainties, which may exist in the system, have been taken into account using a robust design optimization procedure. The stiffness matrix and damping ratio of the building are considered as uncertain random variables; and using the well-known beta distribution, 50 pairs of these variables are generated. This resulted in 50 buildings with different stiffness matrices and damping ratios. These simulated buildings are used to evaluate robust optimal values of the active tuned mass damper design parameters. Four non-commensurable objective functions, namely maximum displacement, maximum velocity, maximum acceleration of each floor of the building, and active control force produced by the actuator are considered, and a fast and elitist non-dominated sorting genetic algorithm approach is used to find a set of pareto-optimal solutions.
The contact area and the negative friction velocity slope on dynamic instability of spherical joint are theoretically investigated. The contact area may be influenced by the various loading and design conditions between a ball and socket. The non-conformal contact is adopted for the static and dynamic derivations. This contact geometry is selected as the major design parameter in this study. The numerical results reveal that the smaller contact area produces the higher propensity of modal instability.
A hybrid lower extremity exoskeleton SJTU-EX which adopts a scissor mechanism as the hip and knee flexion/extension joint is proposed in Shanghai Jiao Tong University to augment load carrying for walking. The load supporting capabilities of a traditional serially connected mechanism and the scissor mechanism are compared in detail. The kinematic influence coefficient method of the kinematic and dynamic analysis is applied in the length optimization of the scissor sides to minimize the transmitting errors between the input and output motions in walking and the load capacities of different scissor mechanisms are illustrated. The optimization results are then verified by the walking simulations. Finally, the prototype of SJTU-EX is implemented with several improvements to enhance the working performances.
Cycloidal gears make up the main working unit of hydraulic gerotor machines. In the article, a question of a more efficient application of plastics in building the gears is discussed. The discussion is based on a numerical strain analysis which was done by means of the finite elements method. The stress and deformation values in the operating cycloidal gears were specified. The numerical analysis was carried out in two stages in order to determine the optimum gear tooth profile. The profile depends on the tooth height and on the tooth correction coefficient. At the first stage, the optimum tooth height coefficient was calculated. Having determined the optimum value , the analysis was continued, and at the second stage, the optimum correction coefficient v for the gears at an earlier selected constant value was defined. The analysis results were useful in selecting parameters for determining the geometrical characteristics of the cycloidal gears. The parameters were then used in defining the most suitable tooth profile for the hydraulic machine featuring the cycloidal gears.
This paper describes the design optimization of a tunnel ventilation jet fan through multi-objective optimization techniques. Four design variables were selected for design optimization. To analyze the performance of the fan, numerical analyses were conducted, and three-dimensional Reynolds-averaged Navier–Stokes equations with a shear stress transport turbulence model were solved. Two objective functions, the total efficiency of the forward direction and the ratio of the reverse direction outlet velocity to the forward direction outlet velocity, were employed, and multi-objective optimization was carried out to improve the aerodynamic performance. A response surface approximation surrogate model was constructed for each objective function based on numerical solutions obtained at specified design points. The non-dominated sorting genetic algorithm with a local search procedure was used for multi-objective optimization. The tradeoff between the two objectives was determined and described with respect to the Pareto-optimal solutions. Based on the analysis of the optimization results, we propose an optimization model to satisfy the objective function. Finally, to verify the performance, experiments with the base model and the optimization model were carried out.
This paper proposes a method to accurately predict thermal errors in spindles by applying experimental modifications to preliminary theoretical models. First, preliminary theoretical models of the temperature field and the thermal deformation are built via mechanism analysis, which is based on the size of the spindle and the parameters of the bearing. Then, thermal basic characteristics tests are conducted at two different initial temperatures. Finally, the results of the thermal basic characteristic tests are evaluated, and the preliminary theoretical model is modified to obtain the final model. A simulation of axial thermal deformation under different speeds is conducted by finite element analysis. It shows that the relationship between the axial thermal deformation and the speed is approximately linear. The model is validated via some experiments on the spindle of a numerical control lathe. The results indicate that the proposed model precisely predicts the spindle’s temperature field and multi-degree of freedom thermal errors.
The interference fit can improve the fatigue performance of mechanical joints and is widely used in aircraft assembly. In this paper, specimens of lap plates and several interference fit sizes were designed, and then the interference fit hi-lock bolt insertion was carried out in an experimental test. Using the commercial finite element software ABAQUS, a two-dimensional axisymmetric finite element model was established to simulate the bolt insertion process. The finite element model was validated by comparison of experimental results and finite element prediction for insertion force and protuberance height. After the interference fitted bolt insertion, the changing characteristics of the non-uniform hole expansion and protuberance were presented with increases in interference fit size. Under low level of interference fit, the tensile hoop stress was produced mainly on the hole wall, and changed into compressive hoop stress when interference fit size is larger. The maximum tensile hoop stress point on faying surfaces went away from the hole wall with interference fit size increasing.
In a wayside acoustic defective bearing detector system, bearing faults are detected through the analysis of the acoustic signal generated by the bearings of a passing vehicle. As vehicles pass by with high speeds, the acoustic signal recorded by the stationary microphone is disturbed by the Doppler effect. The reduction of the frequential structure disturbance of signals facilitates the efficient diagnosis of bearing faults. This study proposes a Doppler effect reduction scheme for the removal of the frequential structure disturbances of Doppler-shifted signals in the acoustic defective bearing detector system. First, the parameters, including the initial speed and the initial acceleration of the vehicle, are estimated by the acceleration-based Dopplerlet transform via the matching pursuit algorithm. Second, the time vector for resampling is calculated according to the estimated initial speed, the initial acceleration in the first step, the sound speed, and the measured geometric parameters of the ADBD system. Finally, the distorted signal is resampled through spline interpolation. Simulation and experimental cases are used to validate the effectiveness of the proposed scheme. Compared with the steady-motion-based method, the proposed scheme can better capture the true time-varying nature of Doppler-shifted signals. Moreover, this scheme is also robust to noise.
Robust design methods for topology optimization have received significant attention from researchers in recent years. There are various attempts in past to handle the manufacturing uncertainty of the topologically optimized components. In the present work, same issue is dealt by introducing a method of probabilistic distribution of material. Here, help from Karhunen–Loeve expansion of stochastic process, coupled with Monte Carlo method is taken. The proposed method retains the uncertainty characteristic of the specific manufacturing processes such as etching, e-beam lithography, laser micro machining, and milling. Hence, this method offers larger flexibility to the designer. The simulation for manufacturing uncertainty is utilized to determine the optimal tolerance range of the factors for robust and targeted performance, which is almost nonexistent in the literature. The methodology for tolerance range selection is capable to incorporate uncertainty of multiple factors simultaneously. In this method cross array design of experiment approach is used to analyze the effect of tolerance of each factor. The overall process for manufacturing uncertainty and tolerance range selection is illustrated using four benchmark problems. The chosen factors for considered structural problems are force, elasticity, volume fraction, and aspect ratio. Various combinations of tolerance ranges are used to simulate the performance of the optimized structure, which is expressed in terms of robustness and targeted values of compliance, and maximum deflection. Based on the simulated results of signal-to-noise ratio and mean values of performance, the combinations of tolerance range are suggested that gives a high level of robustness or targeted performance accuracy. To indicate the uniqueness of proposed approach, the obtained response for performances is compared with already available response for performance in literature for generalized approach. Current work is advantageous compared to usual robust design, and provides the performance for a specific scenario at each possible combination of tolerance ranges.
The purpose of this work is to present the numerical evaluation of the sound transmission loss of some simple panel configurations and to compare them to the theoretical and experimental data found in existing literature. The numerical evaluations are carried out through the commercial software VA-One®. Specifically, single and double panels of different materials and configurations are investigated and thus the possibility to build good predictive numerical models is verified. The panels refer to the common automotive and aerospace configurations. An analysis of foam lined panels is presented, too. The numerous test cases can be considered as benchmarks for the simulations obtained with the statistical energy analysis. The agreements are very good and thus, statistical energy analysis represents a mature predictive methodology for this kind of simulations. Nevertheless, some care is always needed to select among the different simulation strategies for given specific configurations. The results are eventually cross-compared in order to highlight the configurations which are more promising for further investigations; this has been done by introducing a dimensionless frequency.
This paper focuses on optimal design of an interval type-2 fuzzy logic system (IT-2FLS) to cope with uncertainty issue of training set and noisy data. Content of the solution is depicted based on the proposed algorithm to optimally design an IT-2FLS from a dataset, named OD-T2FLS. The major concept of the OD-T2FLS is a combination of a useful method of clustering data space to establish a type-1 fuzzy logic system (T-1FLS) and an appropriate way to transform the T-1FLS into an IT-2FLS as well as to optimally adjust parameters of the IT-2FLS. Firstly, an improved algorithm to establish an adaptive neuro-fuzzy inference system (ANFIS), named IM-ENFS, is presented. Based on the given dataset, clustering in the join input–output data space is realized to establish a cluster-data space. Using the IM-ENFS for this cluster-data space, together with the cluster-data space optimized, an ANFIS having a role as an optimal T1-FLS is also established. Parameters of the optimized T-1FLS are then used to build the initial structure of IT-2FLS. Subsequently, this IT-2FLS is optimally adjusted based on the well-known genetic algorithm. Finally, to demonstrate the effectiveness of the proposed OD-T2FLS, experiments including magnetorheological fluid damper are realized based on two different statuses of data sources, with and without noise.
In this paper, two kinematic structures with optimized spherical wrist modules are proposed for the practice of tele-echography through a new slave holder robot for a remote ultrasound diagnostic application. The medical gestures, performed during an ultrasound examination, are analyzed using two different techniques. The results are used in the definition of the robot kinematic structure specifications. The proposed medical robot is formed by two modules, a spherical displacement orientation module and a translation module, to control the interaction force between the probe and the patient. Multicriteria optimization is proposed and is applied to two spherical structures: one serial and one parallel. Workspace size and kinematic performance, in addition to the index of compactness of the manipulator, are considered in the optimization. The efficiency of the optimized kinematic structures across their workspace is studied and compared to determine which one is more adapted to the tele-echography application.
Powder-mixed electrical discharge machining (PMEDM) is the technique of using dielectric fluid mixed with various types of powders to improve the machined surface output. This process is fast gaining prominence in electrical discharge machining (EDM) industry. The objective of this investigation is to determine the ability of tantalum carbide (TaC) powder-mixed dielectric fluid to enhance the surface properties of stainless steel material during EDM. The properties investigated are the micro-hardness and corrosion characteristics of the EDMed surface. Machining was conducted with 25.0 g/L concentration of TaC powder in kerosene dielectric fluid. The machining variables used were the peak current, pulse on time and the pulse off time. The effects of these variables on the micro-hardness of the EDMed surface were determined. Corrosion tests were also conducted on the samples that exhibited higher hardness. Results showed that the EDMed surface was alloyed with elements from the TaC powder. The highest micro-hardness obtained with PMEDM is about 1,200 Hv. This is about 1.5 times that obtained without TaC powder in the dielectric fluid. The loss in weight during corrosion test was found to be 0.056 µg/min for the PMEDM which was much lower than the lowest value of 10.56 µg/min obtained for the EDM without powder dielectric fluid.
The science of biomimetics seeks to gain inspiration from nature for the development of new engineering solutions. This article reviews some of the work done to understand fatigue-resistant structures in nature. Evolution has created materials and components which are highly resistant to cyclic loading, using a number of interesting strategies: (i) careful control of geometry to minimise stress concentration; (ii) sophisticated use of fibre composites taking advantage of anisotropy, fibre insertions at joints and functional grading, to create structures with no weak interfaces; (iii) hollow, tubular components with optimised fatigue strength taking account of all possible failure modes, and; (iv) continuous monitoring and repair of fatigue cracks in service. In each case an attempt has been made to quantify the potential improvement and to outline the possibilities for future transport applications.
The traditional deterministic finite element updating only deals with a single specified structure. However, it is conceivable that uncertainties such as the geometric tolerances and physical properties of the material, will lead to the variability of the structural behaviors for a panel of nominally identical structures. In this case, we have to resort to the stochastic finite element updating approach to handle the problem. Based on the stochastic perturbation method, a new framework of stochastic finite element updating using data from modal test is proposed in this paper. The efficiency of updating is improved through dividing the updating procedure into two independent parts: the deterministic part updating and the stochastic part updating. The Bayesian statistical method is employed to improve the estimation accuracy of stochastic part updating. Two numerical examples are used to demonstrate the effectiveness and the efficiency of the proposed method.
Material tailoring in functionally graded isotropic hollow rods of arbitrary cross section under torsion is studied. The purposes of material tailoring pursued in this paper are divided into two categories. In the first category, we find the variation of the volume fractions of constituents of a functionally graded member under torsion to obtain an appropriate distribution of shear stress over the cross section. In the second category, the torsional rigidity of a rod with a pre-defined mass is maximized by appropriate determination of the variation of constituents of the functionally graded material. Hollow rods are studied in this paper since they have higher torsional rigidity compared to solid members with the same mass. Meshless numerical methods are used for torsional analysis of the cross sections. Moreover, numerical optimization methods are used for material tailoring of the rods. Several examples with different cross sections are presented to investigate the usefulness of the proposed technique on achieving the mentioned purposes.
The conventional approaches for electromagnetic shielding structures’ design, lack the incorporation of uncertainty in the design variables/parameters. In this paper, a reliability-based design optimization approach for designing electromagnetic shielding structure is proposed. The uncertainties/variability in the design variables/parameters are dealt with using the probabilistic sufficiency factor, which is a factor of safety relative to a target probability of failure. Estimation of probabilistic sufficiency factor requires performance function evaluation at every design point, which is extremely computationally intensive. The computational burden is reduced greatly by evaluating design responses only at the selected design points from the whole design space and employing artificial neural networks to approximate probabilistic sufficiency factor as a function of design variables. Subsequently, the trained artificial neural networks are used for the probabilistic sufficiency factor evaluation in the reliability-based design optimization, where optimization part is processed with the real-coded genetic algorithm. The proposed reliability-based design optimization approach is applied to design a three-layered shielding structure for a shielding effectiveness requirement of ~40 dB, used in many industrial/commercial applications, and for ~80 dB used in the military applications.
Due to the fact that the complexity of loads and uncertainties of random variables affect the reliability of defective casings, with consideration to the disadvantages of the deterministic approach, in this paper a probabilistic assessment method is employed based on previously established safety evaluation criteria for casings with corrosion defects in thermal recovery wells. In addition, Monte Carlo simulation is proposed to analyze the casing reliability under different remaining strengths. Sensitivity analysis is then performed to rank the influence of various variables for casing failure, and finally the influence law of the main parameters on the maximum Von Mises stress of defective casing is summarized.
The failure of cutting tools significantly decreases machining productivity and product quality; thus, tool condition monitoring is significant in modern manufacturing processes. A new method that is based on singular spectrum analysis and Mahalanobis distance are combined to extract the crucial characteristics from spindle motor current to monitor the tool's condition. The singular spectrum analysis is a novel nonparametric technique for extracting the properties of nonlinear and nonstationary signals. However, because the components are not completely independent, the original singular spectrum analysis eventually leads to misinterpretation of the final results. The proposed method is used to overcome the weakness of the original singular spectrum analysis. The singular spectrum analysis algorithm is adopted to decompose the original signal and the useful singular values that correspond to the tool condition can be extracted. The Mahalanobis distance of the singular values is proposed as a feature that can effectively express the tool condition. The experiments on a CNC Vertical Machining Center demonstrate that this method is effective and can accurately detect the tool breakage in mill process.
Unwanted vibration in cam-follower systems causes increased forces, noise, wear, and operating costs. This paper proposes a novel method to design high-speed cam profiles for vibration reduction by using command smoothing technique. Using system natural frequency and damping ratio, the technique reduces vibrations by intelligently smoothing any basic profiles. Furthermore, an example is given to express the design process and to verify the effectiveness of the method. The displacement, velocity, acceleration, and jerk properties of the proposed profile are demonstrated to show the excellent smoothness, which benefits high-speed cam follower systems. The comparisons of vibration properties between the smoothed profile and 3-4-5 polynomial profile are explored and quantified. The smoothed profile will induce zero vibration at the design operating speed and produce a low level of vibration around it. Experimental results obtained from a rectilinear control plant validate the simulated dynamic behavior and the effectiveness of the profile created by using command smoothing.
Bolted joints are widely used in modern engineering structures and machine designs due to their low cost and reliability when correctly selected. Their integrity depends on quantitative representation of the contact pressure distribution at the interface during design. Because of the difficulty in reaching and assessing clamped interfaces with traditional experimental methods, presently bolted joint design and evaluation is based on theoretical analysis, with assumptions to quantify pressure distribution at the clamped interface, which may not represent their true operating conditions. The present work utilises a non-intrusive ultrasonic technique to investigate and quantify the pressure distribution in bolted joints. The effect of variation in plate thickness on the contact pressure distribution at bolted interfaces under varying axial loads is investigated. While it was observed that the contact pressure at the interface increases as the applied load increases, the distance from the edge of the bolt hole at which the distribution becomes stable is independent of the applied load on the bolted joint. However, the contact pressure distribution was observed to vary with the plate thickness. Although the variation in the peak value of the average contact pressure distribution in bolted joints does not depend on the plate thickness, the distance from the edge of bolt hole at which the value of the distribution becomes stable increases as the plate thickness is increased. It was also observed that the edge of the bolt head affected the position of the peak value of the contact pressure distribution at the interface, though its effect was dependent on plate thickness. Furthermore, a model based on a Weibull distribution has been proposed to fit the experimental data and a good correlation was observed.
Based on nonlocal piezoelasticity theory, dynamic stability of double-walled boron nitride nanotubes (DWBNNTs) conveying viscose fluid is studied by incorporating Euler–Bernoulli beam theory, Timoshenko beam theory, and cylindrical shell theory. The surface stress effects are considered based on Gurtin–Murdoch continuum theory. The DWBNNT is embedded in visco-Pasternak medium and the nonlinear van der Waals forces between the inner and outer surface of the DWBNNT is taken into account. Using von Kármán geometric nonlinearity, the governing equations are derived based on Hamilton’s principle. In order to obtain the dynamic instability region of DWBNNT, incremental harmonic balance method is applied. The detailed parametric study is conducted, focusing on the combined effects of the nonlocality, surface stress, fluid velocity, and surrounding medium on the dynamic instability region of DWBNNT. Furthermore, dynamic instability region of Euler–Bernoulli beam theory, Timoshenko beam theory, and cylindrical shell theory are compared to each other. Numerical results indicate that neglecting the surface stress effects, the difference between dynamic instability region of three theories becomes remarkable.
The present work deals with the study of vibration and stability analysis of a functionally graded spinning shaft system using three-noded beam element based on the Timoshenko beam theory. Material properties are assumed to be graded in radial direction according to power law gradation. In the present analysis, the mixture of aluminum oxide (Al2O3) and stainless steel (SUS304) has been considered as functionally graded material where metal (SUS304) content decreases towards the outer diameter of the shaft. The functionally graded shafts has been modeled as a Timoshenko beam, which contains discrete isotropic rigid disks supported by flexible bearing. The functionally graded shaft has been modeled based on first-order shear deformation beam theory with transverse shear deformation, rotary inertia, gyroscopic effect, strain and kinetic energy of shafts by adopting three-dimensional constitutive relations. The derivation of governing equations of motion has been obtained using Hamilton’s principle. Three-noded beam element with four degrees of freedom per node has been used to solve the govering equations. In this work, the effects of both internal viscous and hysteretic damping have also been incorporated in the finite element model. Various results have been obtained such as Campbell diagram, stability speed limit, damping ratio, and time responses for functionally graded shaft and also compared with conventional steel shaft. It has been found that the responses of the functionally graded spinning shaft are significantly influenced by material properties, radial thickness, power law gradient index, and internal (viscous and hysteretic) damping. The obtained results also show the advantages of functionally graded shaft over conventional steel shaft.
Remote center of motion (RCM) mechanism, widely used as a wrist of minimally invasive surgery robot, is a kind of minor-mobility mechanism with part of it rotating around a fixed point distal from it. However, there is no physical revolute joint at that point. In this paper, kinematics of mechanisms with two remote centers of motion or multiple remote centers of motion (multi-RCM) are researched. The relationship between geometrics and kinetic characteristics of RCM mechanisms is found. Mechanisms with multi-loop kinematic chain are developed and are used to synthesize multiple RCM mechanisms. This type of dimension synthesis method proposed to design multi-RCM mechanisms just needs the initial condition of fixed positions of the frame and remote centers. A synthesis example and a potential application are presented. The synthesis method of multi-RCM mechanisms is effective in constructing new type of mechanisms.
This paper presents the design and validation of a lower limb exoskeleton robot for post-stroke patients at the early stage of neurorehabilitation. Instead of the usual walking gait, the popular exercise, recumbent cycling, is adopted to provide a safe and comfortable movement training to the patients who lost active motor abilities due to a very low muscle power. The exoskeleton robot mounted on a commercial wheelchair possesses two pairs of hip and knee joints on the right and left legs, respectively, and each joint has one degree of freedom actuated by a custom-made linear actuator in the sagittal plane. Additionally, two passive ankle joints are added to provide a limited range of motion for human comfort. The hip and knee joint motion profiles were calculated based on a simplified kinematic model of the recumbent cycling modality, and implemented through the motor position–velocity–time trajectory. Clinical trials were conducted on six stable post-stroke patients with a low muscle power under the supervision of a skilled therapist. The preliminary results validated the functionality and feasibility of the new exoskeleton robot and showed a promising application of the recumbent cycling modality in robot-assisted neurorehabilitation.
In this paper, a robust output feedback tracking control scheme for uncertain robot manipulators with only position measurements is investigated. First, a quasi-continuous second-order sliding mode (QC2S)-based exact differentiator and super-twisting second-order sliding mode (STW2S) controllers are designed to guarantee finite time convergence. Although the QC2S produces continuous control and less chattering than that of a conventional sliding mode controller and other high-order sliding mode controllers, a large amount of chattering exists when the sliding manifold is defined by the equation
To effectively reject the gyroscopic effects and moving-gimbal effects of the double gimbal magnetically suspended control moment gyroscope (DGMSCMG) and to avoid high control effort, this paper proposes a novel control method based on modal decoupling strategy. Modal controller is employed to realize the modal separation of the translation and rotation modes of the magnetically suspended rotor (MSR). Then the dynamic coupling among the two rotation modes of the MSR system and the two rotational motions of the gimbal servo systems have been decoupled by using differential geometry theory. Dynamic compensation filters have been designed to improve the decoupling performance and the system stability without large control resource. Compared with the existing channel decoupling method, the presented one can not only realize the separate control of stiffness and damping of the MSR but also simplify the control system design significantly. The simulation results verify the effectiveness and superiority of the proposed method.
The passive response of the rider’s body to bicycle oscillations is experimentally studied by means of laboratory tests. Lumped element models of the rider’s body are developed and the relevant stiffness and damping parameters are identified from experimental results. The biomechanical model of the rider is coupled with the benchmark model of the bicycle and open-loop stability analysis is carried out. Results show that the stiffness and damping parameters of the waist do not strongly affect bicycle stability. Uncontrolled arm stiffness has a very detrimental effect on stability and destroys the self-stabilization mechanism. Arm damping has a more complex effect and reduces the self-stability region.
This paper presents a key geometric errors identification method for machine tools based on matrix differential and experimental test. An error model for a machine tool was established by regarding the three-axis machining center as a multi-body system. The sensitivity coefficients of the machining error with respect to the geometric errors were determined using the matrix differential method, and the degree of influence of the geometric errors on the machining accuracy under ideal conditions was discussed. Using the 12-line method, 21 geometric errors of the machine tool were identified, allowing the three-dimensional volumetric error distributions of the machine tool to be mapped. Experimental results allow the degree of influence of the geometric errors on the machining accuracy under actual conditions to be confirmed. Finally, the key geometric errors affecting the machining accuracy were identified by a combination of matrix differential and experimental test. This paper provides guidance for the machine tool configuration design, machining technology determination, and geometric error compensation.
In this paper, the motion equivalent chain method is proposed and then applied to the type synthesis of a class of 2R2T parallel mechanism. The equivalent serial chains are synthesized for a specific 2R2T motion pattern based on screw theory. Feasible limb structures that provide a constraint couple and a constraint force are enumerated according to the reciprocity of the twist and wrench systems. Several motion equivalent single loop chains are constructed with the equivalent serial chains. Using motion equivalent single loop chains to replace the equivalent serial chains, a class of 2R2T parallel mechanisms is obtained based on the foundation of motion equivalent single loop chain structures.
The present article investigates heat transfer phenomenon in an aerospace radiating fin, analytically. Radiating extended surfaces are widely used to enhance heat transfer between primary surface and the environment. The performance of such a surface is significantly affected by variable thermal conductivity; especially in the case of large temperature differences happened in the actual aerospace applications. To study the effect of thermal conductivity variation, linear length-dependent function of thermal conductivity, is considered. In this study, two newest and popular analytical methods, differential transform method and optimal homotopy asymptotic method are used to evaluate the temperature profile and efficiency of radiating fin. For this purpose, after deriving and dimensionalizing the radiating fin heat transfer equation and briefly introducing these two methods, they are employed to solve the radiating fin problem. The obtained results are compared with the numerical ones to verify the accuracy of the proposed methods and choosing the better one between them, which is exclusive for this paper. Then, the effects of thermal conductivity and thermo-geometric radiating fin parameter on temperature profile and fin’s efficiency are completely discussed, which can help materials science researchers to design more compact and efficient radiating fin for using in aerospace and satellite applications.
Steady and transient heat convection in axisymmetric stagnation point flow with momentum and thermal slip effects are studied numerically for different flow parameters. The thermal response to time-dependent wall temperature variations in surface cooling and heating processes is analyzed in terms of temporal variations in the heat transfer coefficient, thermal jump, and fluid temperature at the surface. The transition time from an initial to a final steady state is also investigated over a range of slip factor and decay/growth rate of the wall temperature. A criterion in the form of a relation between Prandtl number and the specific heat ratio that characterizes the variation of the convective heat transfer coefficient with the slip factor is established. The results presented show that the convective heat transfer coefficient is less influenced by transient conditions as rarefaction increases. Higher Prandtl number flows are more influenced by transients. The transition time is found to increase with slip and decrease with the decay/growth rate of the wall temperature and is most influenced at relatively low values of both slip and decay/growth rate of the wall temperature.
In this paper, a novel tuning strategy for the fractional order proportional integral and fractional order [proportional integral] controllers is proposed for the permanent magnet synchronous motor servo drive system. The tuning strategy is based on a genetic algorithm–wavelet neural network hybrid method. Firstly, the initial values of the control parameters of the fractional order controllers are selected according to a new global tuning rule, which is based on the genetic algorithm and considers both the time- and frequency-domain specifications. Secondly, the wavelet neural network is utilized to update the control parameters based on the selected initial values in an online manner which improves the capability of handling parameter variations and time-varying operating conditions. Furthermore, to improve the computational efficiency, a recursive least squares algorithm, which provides information to the wavelet neural network, is used to identify the permanent magnet synchronous motor drive system. Finally, experimental results on the permanent magnet synchronous motor drive system show both of the two proposed fractional order controllers work efficiently, with improved performance comparing with their traditional counterpart.
The performance of bolt-nut connections can be improved by enhancing fatigue life of the connections. This can be accomplished by reducing the stress concentration in the threads of the connection. This investigation consists of two parts. In this part (part I), load distribution in threads of some ISO bolts is computed by three-dimensional numerical simulation and Stockley-proposed relations. The results show a close agreement between Stockley relations and the simulations for nearly all bolt sizes. The results indicate that stress concentration is nearly constant regardless of the bolt size. It is also found that the load percentage carried by the first thread varies from 35% for M6 and reaches to 58% for M20 and M30 ISO bolts. The results suggest that the rate of load distribution changes at a point of inflection, i.e. the rate after the inflection point diminishes as the bolt size decreases, whereas before this point, the trend of the rate is reversed. In part II (to be submitted separately), various techniques are employed for the reduction of stress concentration and enhancement of fatigue life of the connections. The techniques are evaluated by numerical simulations and fatigue tests.
This paper presents a numerical method for analyzing the pseudo-rigid-body model of compliant mechanisms based on finite elements and the principle of minimum potential energy. The proposed method represents the links of pseudo-rigid-body model with truss elements. As a result, the pseudo-rigid-body model is modeled into a compliant system that consists of finite elements and springs. The static equilibrium position of the pseudo-rigid-body model can be obtained by minimizing the potential energy function of this compliant system. A comparison between the proposed method and the MinPE method is presented. Lastly, a case study is provided to demonstrate the application of this method in the automated analysis of pseudo-rigid-body models. This numerical method paves the way for introducing the topology optimization techniques into the synthesis of flexure-based compliant mechanisms.
In this work, bolt and nut geometries are modified for the improvement of fatigue life of the bolt–nut connections. The modifications are aimed at reducing the stress concentration at the thread roots by factors such as reducing the shank diameter, making axial hole in bolt, stepping the nut and their combinations. The effect of modifications is studied by experiment and simulation. The experimental results show that all types of modifications considered result in an improvement in the fatigue resistance of bolt–nut connections but to different extents. However, the effects of the two latter types are more significant. The most improvement is achieved for the case when all types of modifications are combined together. In this case, fatigue life can be increased by almost 100%. Numerical results also show that all types of modifications lead to the reduction of stress concentration.
A torsional vibration dynamic model is established with the commercial software ADAMS to predict the torsional vibration characteristics of a compound planetary power-split hybrid electric vehicle. By calculating and simulating the built model in ADAMS, the natural frequencies and corresponding modes are obtained. The results agree well with previous work, which derives the conclusions by solution of the system dynamics equations of hybrid driveline. Moreover, the main factors that influence the torsional vibration of the powertrain under the excitation of engine and electric motors are analyzed by the forced vibration analysis. The calculated results show that the low frequencies occur mainly in the torsional vibration of wheels and vehicle, while the high orders are related to the torsional vibration of differential, sun gears and planets. The results also show that the amplitude of torsional vibration of driveline is the lowest when the damping and stiffness of torsional damper are 15 Nms/rad and 618 Nm/rad respectively, the halfshaft stiffness is 2760 Nm/rad and the rotational inertial of engine is 0.42 kgm2. The research can be used to support the further development of the power-split hybrid electric vehicle.
Damage prognosis of high-speed blades is very important for industrial turbomachinery. Nowadays, vibration monitoring using blade tip-timing methods is becoming promising. However, its main drawback is blade tip-timing signals are subsampled. Very few works have been done on damage prognosis using subsampled blade tip-timing signals. This paper investigates a novel method of blade damage prognosis based on kernel principal component analysis and grey model. Firstly, a nonaliasing reconstruction algorithm of subsampled blade tip-timing signals is proposed based on the Shannon theorem and wavelet packet transform. Secondly, kernel principal component analysis is done on the damage feature space and a damage index is defined by Mahalanobis distance. Then a grey model (1) model is proposed for damage prognosis. In the end, an experimental setup is built and a long time testing is done for collecting samples. The experimental results validate the superiority of the proposed method.
XY compliant parallel manipulators (aka XY parallel flexure motion stages) have been used as diverse applications such as atomic force microscope scanners due to their proved advantages such as eliminated backlash, reduced friction, reduced number of parts and monolithic configuration. This paper presents an innovative stiffness centre based approach to design a decoupled 2-legged XY compliant parallel manipulator in order to better minimise the inherent parasitic rotation and have a more compact configuration. This innovative design approach makes all of the stiffness centres, associated with the passive prismatic (P) modules, overlap at a point that all of the applied input forces can go through. A monolithic compact and decoupled XY compliant parallel manipulator with minimised parasitic rotation is then proposed using the proposed design approach based on a 2-PP kinematically decoupled translational parallel manipulator. Its load–displacement and motion range equations are derived, and geometrical parameters are determined for a specified motion range. Finite element analysis comparisons are also implemented to verify the analytical models with analysis of the performance characteristics including primary stiffness, cross-axis coupling, parasitic rotation, input and output motion difference and actuator nonisolation effect. Compared with the existing XY compliant parallel manipulators obtained using 4-legged mirror-symmetric constraint arrangement, the proposed XY compliant parallel manipulators based on stiffness centre approach mainly benefits from fewer legs resulting in reduced size, simpler modelling as well as smaller lost motion. Compared with existing 2-legged designs with the conventional arrangement, the present design has smaller parasitic rotation, which has been proved from the finite element analysis results.
A new meshing relationship for gear drive to characterize the conjugation geometry is studied in this paper based on conjugate curves. Conjugate curves are described as two smooth curves always keep continuous and tangent contact with each other in given contact direction under motion law. The general principle of curve meshing is developed for the given spatial or plane curve. The meshing equation along arbitrary direction of contact angle is derived. The properties of geometric and motion of the contact of conjugate curves are discussed. According to the equidistance-enveloping method, tubular meshing surfaces are proposed to build up circular arc tooth profiles, which inherit all properties of conjugate curves. The geometry design and mathematical model of the gears are established. Three types of contact pattern of tooth profiles are generated: convex-to-convex, convex-to-plane and convex-to-concave. A calculation example for convex-to-concave tooth profiles of gears is provided. Theoretical and numerical results demonstrate the feasibility and correctness of proposed conjugate curves theory and it lays the foundation for the design of high performance gear transmission.
A sleeve and its matched spindle are key components of a cotton picker, whose performances affect picking cotton efficiency directly. To enhance the sleeve strength and wear resistance, it is desired to add coatings on the inner surface of the sleeve. In this paper, influences of the coatings on the mechanical performances of the sleeve are investigated with fluid–structure interaction method. Mechanical performances of the sleeve are studied at the varied elastic modulus, Poisson's ratio, and thickness of the coating and different operating conditions. The numerical results show that both the amplitude and position of the von Mises stress and strain of the coated sleeve depend on the varied elastic modulus, Poisson's ratio, and thickness of coating. The coating effect on the sleeve is significant at a big eccentricity ratio or high rotational speed of the spindle.
The development of high performance coatings for the protection against erosion requires understanding of their complex failure mechanisms occurring during solid particle impact. In the present work, a numerical analysis is carried out to study the effect of particle diameter, particle velocity, and coating thickness on erosion damage of gas turbine blade coating caused by solid particle erosion. For this purpose, the performance assessment of turbine blade coating is done using scanning electron microscopic testing. Furthermore, simulation of the impact of a solid particle on a plate is performed by finite element method using the commercially available software ABAQUS. In particular, the following values of the particle diameter (dP ), the particle velocity (VP ), and coating thickness (tC ) have been analyzed: 20 µm ≤dP ≤80 µm, 80 m/s ≤VP ≤120 m/s and 5 µm ≤tC ≤12 µm. The results demonstrate that in erosion of gas turbine blade coating the particle velocity is 1.6 times more effective than the particle diameter and 7.3 times more effective than the coating thickness.
To improve the performance and reliability of gas turbine like an aeroengine, the multi-object multi-discipline (MOMD) reliability optimization design of high press turbine (HPT) blade-tip radial running clearance (BTRRC) was first accomplished based on the mechanical dynamic assembly reliability (MDAR) theory and distributed collaborative response surface method (DCRSM). Four optimization models of MDAR were developed based on the features of assembly machinery and the thought of DCRSM, which are, respectively, called as the direct reliability optimization model (denoted by M1), the multilayer reliability optimization models (denoted by M2), the direct reliability optimization model-based probabilistic analysis (denoted by M3), and the multilayer reliability optimization model-based probabilistic analysis (denoted by M4). Through the MDAR optimization design of BTRRC by the four standard optimization models, some conclusions are drawn as follows: (1) the DCRSM is proved to be effective and feasible for MOMD MDAR optimization design with high computational efficiency and precision; (2) all the reliability optimization results of BTRRC and assembly objects satisfy the requirements of optimization design, and the optimized BTTRC variations are reduced by about 10% and obey the normal distribution, which are quite promising in improving the design and control of HPT BTRRC; (3) in computational efficiency, the computing time of M1 and M3 is far less than those of M2 and M4, meanwhile M3 and M4 are superior to M1 and M2; (4) in computational accuracy, M1 and M2 are better than M3 and M4, as well as M2 and M4 are higher than M1 and M3 theoretically. The presented study does not only fulfill the HPT BTRRC dynamic assembly design from a probabilistic optimization perspective and improve the performance and reliability of gas turbine engine, but also provides a promising approach and four valuable optimization models for MDAR optimization design. Besides, the present efforts are of great significance in enriching the theory and method of mechanical reliability design.
The numerical analysis of an external gear pump with cavitation effects has been validated with experimental data obtained by applying Time-Resolved Particle Image Velocimetry. The effect of inlet and outlet pressure on volumetric efficiency has been studied numerically. First, the Particle Image Velocimetry method was used to analyze the two-dimensional velocity field in the middle plane of the suction chamber of the gear pump. The main improvement, with respect to previous similar analysis is the use of alginate micro particles as tracers. It is seen that the two-dimensional model is able to characterize the flow field of the real pump in the region of the inlet chamber in which cavitation is expected. In a previous study, it was seen that a cavitation cloud acted as a virtual contact point at low pressure, being responsible for an increase on the volumetric efficiency. The first set of simulations represents the pump working with high outlet pressure. Now, the cavitation cloud is not present and cavitation no longer helps to improve the efficiency of the pump. The second set of simulations represents the pump with an inlet loss factor, which implies a mean inlet pressure below atmospheric conditions. This allows cavitation clouds to propagate upstream. Despite the larger cavitation clouds, volumetric efficiency only drops at high operating velocities, when some clouds become trapped between gears and casing and are transported to the pressure side.
Big-end bearing knock is considered to be one of the common mechanical faults in internal combustion engines (IC engines). In this paper, a model has been built to simulate the effects of oversized clearance in the big-end bearing of an engine. In order to find a relationship between the acceleration response signal and the oversized clearance, the kinematic/kinetic and lubrication characteristics of the big ending bearing were studied. By adjusting the clearance, the impact forces with different levels of bearing knock fault can be simulated. The acceleration on the surface of the engine block was calculated by multiplying the simulated force spectrum by an experimentally measured frequency response function (FRF) in the frequency domain (and then inverse transforming to the time domain). As for experimentally measured vibration signals from bearing knock faults, the signal processing approach used involved calculating the squared envelopes of the simulated acceleration signals. The comparison to the experimental results demonstrated that the simulation model can correctly simulate vibration signals with different stages of bearing knock faults.
This paper aims at designing a pure translational parallel mechanism constructed by UPU (universal-prismatic-universal joint) kinematic limbs. First, the typical problem of unexpected rotations is pointed out from analyzing the typical 3-UPU parallel mechanism, and the reason for unexpected rotations of parallel mechanism constructed by UPU kinematic limbs is analyzed. Then, in order to design a pure translational parallel mechanism constructed by UPU without the unexpected rotations, the 2-UPU single loop is chosen as the basic structure to construct the 4-UPU translational parallel mechanism. Each 2-UPU single loop can be used to constrain a rotation about an axis of the linear complexes, which defined the unexpected rotations. Therefore, a novel type of 4-UPU pure translational parallel mechanism with redundant actuations is proposed. Since the existence of redundantly actuated kinematic limb, this proposed parallel mechanism possesses analytical forward kinematics, and its singularity can be avoided completely. Finally, the workspace and fault-tolerant performance are analyzed. When the proposed 4-UPU parallel mechanism is located in a fault-tolerant configuration, the moving platform can still possess movable ability to realize the given task even if one kinematic limb is in locked-joint failure mode, and the fault-tolerant workspace is obtained.
Dynamic analysis of finger seal can be performed by finite element method or equivalent model based on lumped mass method now available, which is difficult in meeting both the acceptable calculation time and accuracy simultaneously. For this reason, interactions between finger elements are considered and the equivalent dynamic model based on distributed mass method is proposed in this article. Seal dynamic performances are obtained by using this model to calculate the equivalent parameters, air leakage flow, and the contact behavior between finger seal and the rotor. The work to be presented here concerns the mapping of dynamic behavior of the finger seal with a stack of three finger elements, including the dynamic displacement responses of finger elements, the leakage clearances, and the contact pressures between the finger elements and the rotor, as well as the leakage flow rate and the wear rate. The results calculated by the equivalent model presented in this study are evaluated by comparison with the published experimental data and results from the model based on lumped mass method, which shows that the equivalent model based on distributed mass method is far superior to that based on lumped mass method because the calculations are in good agreement with the experimental results.
A systematic study of the packer rubber contact pressure under a fixed-displacement load is conducted to gain further insight into the packer seal mechanism. A Y221-114 double rubber packer is investigated using the finite element software ANSYS, where a design of experiments method is utilized to study the effects of the friction coefficient. The results show that the friction coefficient of the packer and the tubing had the greatest effect on contact pressure than other factors. Decreasing the rubber friction coefficient is conducive to forming the double rubber seal and increasing the maximum contact pressure working range. However, there is additionally a slight decrease in the value of maximum contact pressure. The results of the study provide valuable insight into the importance of packer design optimization.
The mechanical properties of a weldment structure are influenced by the level of residual stress generated during fusion welding process. The experimental determination of residual stress is cumbersome and not free from measurement errors. A sophisticated numerical model is relatively easy approach to predict residual stress due to the advancement of high performance computational technology. However, the integration of all process physics to make a sophisticated numerical model is ever demanding. The present work is motivated in that direction and involves a finite element based numerical model for simulation of welding-induced residual stresses. A thermal model using adaptive volumetric heat source has been used to estimate temperature distribution. Subsequently, the thermal history is used to perform stress analysis for butt welded plates using three different fusion welding processes. The material behaviour is assumed as elasto-plastic in nature. The calculated results and their trend have been validated with experimental results available in open literature.
In this paper, a flexure-based scanner driven by a differential piezo force is proposed for a fully bidirectional operation. The differential piezo force is generated by piezo-driven actuation mechanisms that are arranged antagonistically. The scanner consists of a target platform, a double compound linear guide mechanism, and two identical actuation mechanisms that are piezo-driven mechanical amplifiers that magnify the displacement of a stack-type piezo actuator. The actuation mechanisms are symmetrically mounted on both sides of the target platform, and generate antagonistic pull forces. The difference in the pull forces causes the motion of the target platform. Due to its symmetric structure, the proposed scanner can conduct a bidirectional motion along the positive and negative directions. Through design and analysis, the scanner is manufactured, and then the bidirectional motion and control performance of the scanner are demonstrated.
The type synthesis of four-degree-of-freedom parallel mechanisms using valid arrays and the valid topology graphs with digits is studied. First, the 12 contracted graphs without any binary links for type synthesis of the four-degree-of-freedom parallel mechanisms are constructed. Second, a complicated derivation of topology graphs with digit is transformed into a simple derivation of array, many valid arrays are derived, and many invalid arrays and invalid topology graphs with digit are determined and removed from the arrays using a compiled program. Third, many valid topology graphs with digit with various basic links are derived from the valid arrays, and the 46 different four-degree-of-freedom parallel mechanisms are synthesized using the valid topology graphs with digit and arrays, in which eight existing four-degree-of-freedom parallel mechanisms are included. Finally, the degree of freedoms of synthesized parallel mechanisms are calculated to verify the correction and effectiveness of type synthesis approach using valid arrays and the valid topology graphs with digit.
Efficient laser forming modeling for industrial application is still in the developing stage and many researchers are in the process of modifying it. Conventional three-dimensional finite element models are still expensive on computational time. In this paper, a finite element model adopting a shell-solid coupling technique is developed for the thermomechanical analysis of laser forming process. In the shell-solid coupling method, an additional shell element plane is utilized to transfer heat flux and displacement from the solid elements to the shell elements. The effects of the additional interface shell element thickness on temperature distribution and final distortion are investigated. The presented shell-solid coupling method is evaluated by the results of three-dimensional simulations and experimental data.
The farfield acoustic radiation efficiency and power of a flexible rectangular plate coupled to a relatively stiffer beam are investigated. A numerical model based on a modal method that consists of a plate with sliding edges surrounded by four stiff beams is studied. Assuming that each beam is a heavy mass, a plate with clamped edges is realised, and this model is verified. This model is then extended to a beam-stiffened plate. If the bending stiffness of the excited beam is large, the radiation efficiency increases in the corner- and edge-mode frequency regions and is higher than that of the clamped plate in terms of the averaged response for randomly selected excitations. The reason for this effect is that the corner and edge areas that radiate sound are broader because the behaviour of the plate is governed by the motion of the stiff beam. This is explained in terms of the wavenumber and the wavelength of a stiff beam and a flexible plate. It is shown that this is true only when the excitation is applied to the beam, and the radiation efficiency is similar if the plate is excited. In addition, it was found that the radiation power decreases with increasing beam stiffness because the vibration of the plate actually decreases. In addition, it was shown that the variation in the radiation efficiency of the beam-stiffened plate is smaller when the beam is excited than when the plate is excited.
This study investigates the radial aerodynamic forces that may develop inside the centrifugal compressor and the turbine volutes due to pressure variation of the circulating gas. The forces are numerically predicted for magnitudes, directions, and locations. The radial aerodynamic forces are numerically simulated as static forces in the turbocharger finite element model with floating ring bearings and solved for nonlinear time-transient response. The numerical predictions of the radial aerodynamic forces are computed with correlation to earlier experimental results of the same turbocharger. The outcomes of the investigation demonstrate a significant influence of the radial aerodynamic loads on the turbocharger dynamic stability and the bearing reaction forces. The numerical predictions are also compared with experimental results for validation.
This paper presents vibration control of a mixed-mode magnetorheological fluid-based mount system using a new robust fuzzy sliding mode controller. A novel model of controller is built based on adaptive hybrid control of interval type 2 fuzzy controller incorporating with a new modified sliding mode control. The interval type 2 fuzzy is optimized for computational cost by using enhanced iterative algorithm with stop condition, and a new modified switching surface of sliding mode control is designed for preventing the chattering of the system. The controller is then experimentally implemented under uncertain conditions in order to evaluate robust vibration control performance. In addition, in order to demonstrate the effectiveness of the proposed controller, two fuzzy sliding mode control algorithms proposed by Huang and Chan are adopted and modified. The principal control parameters of three controllers are updated online by adaptation laws to meet requirements of magnetorheological mount system which has two operation modes: flow mode and shear mode. It is shown from experimental realization of three controllers that the proposed control strategy performs the best under uncertain conditions compared with two other modified controllers. This merit is verified by presenting vibration control performances in both time and frequency domains.
A new sharpness algorithm has been proposed for improved integrity and human auditory perception, considering the complete sound transfer functions of the concha, middle ear, and inner ear. A new algorithm-based design procedure has been employed to evaluate the sharpness of a direct injection diesel engine noise. Normal components of the vibration velocities of the engine block surface were calculated using flexible multi-body dynamic analysis, verified by the engine bench tests and then extracted to simulate the structural radiated noise via standard boundary element codes. The acoustic response results revealed that considerable sound power levels existed in the main frequency ranges of 1550–1900 Hz and 2350–2800 Hz. After the engine block was modified and bench-tested, it was found that the sharpness of the measured engine noise was reduced by 6.47%. This has validated the new algorithm and the new algorithm-based design procedure which made the engine sound lower-pitched.
The paper deals with the investigation of nonlinear static and dynamic behaviors of electrostatically actuated carbon nanotubes with different geometries and boundary conditions. The deflection and pull-in properties are studied in detail in the presence of DC and combined DC + AC electrostatic voltages accompanying the interatomic interactions. The considered nano system can be applied in a wide range of nanoelectronics devices such as nano switches, nano resonators, nano transistors, nano capacitors and random access memories. Moreover, a useful mathematical model of the nano sensor application of the studied nano system to sense the stiffness of the nano particles is presented.
A rotor system with double time delays supported by the high-speed self-acting gas-lubricated bearings with three-axial grooves is modeled to implement active delay control of the system. The differential transformation method is employed to solve the time-dependent compressible gas Reynolds equation due to its rapid convergence rate and minimal calculation error. Based on the precise integration method, a calculation method is proposed to analyze the dynamic responses of a gas bearing-rotor nonlinear system with time delays. The motion analysis of the self-acting gas-lubricated bearing-rotor system with double time delays is implemented by the orbit diagrams, the time series, and the phase diagrams. The influence of time delays and feedback control gains on the dynamic responses of the bearing-rotor nonlinear system is analyzed. The numerical results show that the amplitude of the responses of the system with time delays control is reduced, the motion is more stable and good control effect is achieved when the chosen feedback control gains match the time delays of the bearing-rotor system.
In this paper, a prototype of jumping robot with flexible feet is proposed to surmount obstacle efficiently. A six-bar adjustable mechanism for regulating jumping height and distance as well as a self-righting mechanism for uprighting after falling down are presented. The jumping height, jumping distance and energy conversion efficiency (ECE) are analyzed and tested, respectively, through dynamics modeling and jumping experiments. Taking advantage of flexible feet whose parameters are optimally designed, both the ground impulse acting on the robot and external kinetic energy relating to the movement of robot’s center of mass increase, so the performance of jumping height and distance as well as ECE of the robot with flexible feet is better than that of the one without flexible feet. By reducing leg mass and take-off angle as well as increasing stored energy, the external kinetic energy is enlarged, and ECE of the robot with flexible feet could be further improved. Meanwhile, simulation results show that the existing jumping robots which adopt four- or six-bar jumping mechanism are capable of enhancing jumping height and distance as well as ECE by exploiting flexible feet.
Microorganisms or micro-robotic swimmers employ traveling waves as a common swimming mechanism involving time-irreversible deformations of their outer surface. Normally, the deforming surfaces constitute of multiple spatial waves, some standing and others propagating forward or backward. A unique technique is developed here to experimentally decompose a waving surface into its spatial wavelengths in each time instance by processing a sequence of photographs. This information is curve fitted to yield the phase velocity, frequency, and amplitudes of the propagating and receding waves of each component. The significance of the harmonic decomposition is demonstrated using an experimental macro-scale swimmer that utilizes small amplitude circumferential waves. A numerical image processing and curve-fitting procedure is shown and a theoretical model is also developed to account for the hydrodynamic effects of multiple wavelengths. The theoretical results fit well with the experimental data at low speeds, although the contribution of higher harmonics was small in experiment, but the higher harmonics are clearly visible and successfully identified. Still, the importance of the multiharmonics analysis for swimmers, which utilize traveling waves mechanisms, found both in nature and in man-made machines, was formulated and partially verified.
A planar reconfigurable linear (also rectilinear) rigid-body motion linkage (RLRBML) with two operation modes, that is, linear rigid-body motion mode and lockup mode, is presented using only R (revolute) joints. The RLRBML does not require disassembly and external intervention to implement multi-task requirements. It is created via combining a Robert’s linkage and a double parallelogram linkage (with equal lengths of rocker links) arranged in parallel, which can convert a limited circular motion to a linear rigid-body motion without any reference guide way. This linear rigid-body motion is achieved since the double parallelogram linkage can guarantee the translation of the motion stage, and Robert’s linkage ensures the approximate straight line motion of its pivot joint connecting to the double parallelogram linkage. This novel RLRBML is under the linear rigid-body motion mode if the four rocker links in the double parallelogram linkage are not parallel. The motion stage is in the lockup mode if all of the four rocker links in the double parallelogram linkage are kept parallel in a tilted position (but the inner/outer two rocker links are still parallel). In the lockup mode, the motion stage of the RLRBML is prohibited from moving even under power off, but the double parallelogram linkage is still moveable for its own rotation application. It is noted that further RLRBMLs can be obtained from the above RLRBML by replacing Robert’s linkage with any other straight line motion linkage (such as Watt’s linkage). Additionally, a compact RLRBML and two single-mode linear rigid-body motion linkages are presented.
The deformable fluid actuators available on the market, i.e. pneumatic muscles and pneumatic springs, are designed to mainly exert compressive or tensile forces. This paper deals with a novel fluid deformable actuator, with three membranes, called BiFAc3, whose particular feature is the ability to exert both tensile and compressive forces. The structure of the actuator is based on three cylindrical coaxial nonisotropic membranes connected to two end plates, whose original shape allows the independent supply of the three internal chambers. The first part of the paper deals with the internal structure and the geometry of the actuator, describes the operating principle and presents a prototype. The second part presents a modelling methodology that can be used to design and analyse the actuator in dynamic applications. The mathematical model of the actuator is based on three different levels of complexity which correspond to three consecutive design stages. The model has been experimentally validated: it is a useful tool for the choice of the actuator’s geometrical dimensions, in order to satisfy specific applicative requirements.
The present paper summarises an attempt of proposing a simple formula suitable for estimating the fatigue strength of welded connections whose weld beads are inclined with respect to the direction along which the fatigue loading is applied. By explicitly considering the degree of multiaxiality of the nominal stress state damaging the weld toe, such a formula is directly derived from the so-called Modified Wöhler Curve Method (MWCM). The MWCM is a bi-parametrical critical plane approach which postulates that, independently from the complexity of the assessed load history, fatigue strength can accurately be estimated by using the stress components relative to that material plane experiencing the maximum shear stress range. The accuracy and reliability of the proposed design technique were checked against a number of experimental results taken from the literature and generated by testing steel plates with inclined fillet-welded attachments. This validation exercise allowed us to prove that the devised formula can successfully be used in situations of practical interest to design against fatigue welded joints whose welds are inclined with respect to the direction along which the cyclic force is applied.
The utilization of variable pitch or helix cutters is an effective means to prevent chatter vibration during milling. In this paper, a frequency-domain solution to efficiently predict the stability for variable helix cutters milling is presented. This method is based on the principles of variable pitch model developed by Altintas and only considers the zero-order approximation of time-varying directional cutting constants. After discretizing the axial depth of cut into finite elements and modeling each element as a variable pitch cutter, time-varying regenerative delays in the case of variable helix cutters are transformed into multiple constant regenerative times. The chatter free axial depth of cut is solved from a stability expression in which the regenerative delay terms are approximated by the Taylor series expansion, whereas the spindle speed is identified from regenerative phase delays. Compared with time-averaged semidiscretization method, the accuracy and efficiency of the proposed technique has been verified. The results show that the proposed method has high computational efficiency. It is suited to calculate optimal geometries of milling tools and beneficial for application.
The dynamic characteristics of the machine tool will change greatly in the whole working process, which must be considered in design and control stage, and the model based on single state cannot predict these position-dependent variations. In this paper, a variable-coefficient linear dynamic model is established by employing two unfixed nodes, so that the explicit representations of the mass, stiffness matrices with respect to position parameters are set up. Sensitivity method is used to analyze the sensitive position parameters that affect the eigenvalues of the system greatly. The variations of the frequencies and frequency response functions with respect to position parameters are also calculated. Experimental validations are conducted to verify the accuracy of the model and some limitations are discussed.
A hot runner system can provide many advantages to plastic injection mold engineers for improving product quality. In edge gate systems in particular, the gate traces can appear on the side of products rather than the top. However, it is difficult to establish hot runner systems using edge gates because of their structural differences from conventional gate systems. This article presents the entire process of preparing a 48-cavity plastic injection molding system with edge gates. This process consists of 48-cavity injection mold design, structural analysis, verification of design plans, filling analysis of multi-cavity, cooling channel design on the basis of cooling analysis, fabrication of the mold system, and test injection. All presented computer-aided engineering analyses were conducted using ANSYS and MoldFlow.
The idea of utilizing a finely dispersed water-in-air mixture has been proven to be a feasible technique to produce very high cooling rates. The accuracy of numerical simulation program for conjugate heat transfer methodology is verified with the Mark II transonic high pressure turbine stator which is cooled by internal convection through radial round pipes, and different turbulence models and transition models are employed to analyze the influence on results. On the basis of it, the mist cooling is simulated under typical gas turbine operating conditions for internal convective cooling to discuss the improvement of cooling performance. Though the results indicate that mist cooling can decrease the temperature of boundary layer without impact on the temperature of the mainstream and the thickness of boundary layer, the cooling capacity is limited by inadequate evaporation of mist. Considering the distribution of thermal stress and mist evaporation, a compound cooling blade of film cooling with trailing edge ejection is acquired which is modified from the blade of Mark II internal convective cooling; the effects of various parameters including mist concentration and mist diameter on the improvement of cooling performance are investigated, meanwhile the impact of curvature on cooling efficiency and mist trajectory is analyzed finally.
The chemically recuperated gas turbine cycle testing platform was designed and built based on theoretical research and experimental study, which included the dual-stage flash evaporation, the diesel steam reformer, and the dual-fuel combustion system. In this paper, an experimental study on the oil (C7H16) prereforming performance is analyzed and the relative increment of the equivalent calorific value is 46.2%. Combustion characteristics are calculated with oil and reformed gas and the results show that main combustion zone temperature drops from 2280 to 1910 K, which leads the ultra-low NO emissions of 1.8 ppm. The flame is stable using reformed gas and the wall temperature is low, but the nonuniformity of outlet is relatively high. Thermal efficiency of combustion is more than 99% even at low load condition.
In this article, we propose a hybrid particle swarm optimization method and obtain the optimal solutions of the synthesis of mechanism. We study the mathematics on the four-bar linkage and its objective function on the optimization process and conduct the numerical experiment for four cases of movement of mechanical linkage bars (coupler curves). The result of synthesis of mechanism is not only shown to be in better accuracy but also properly matches the designated mechanical coupler bar curve.
This work examines analytically the forced convection in a channel partially filled with a porous material and subjected to constant wall heat flux. The Darcy–Brinkman–Forchheimer model is used to represent the fluid transport through the porous material. The local thermal non-equilibrium, two-equation model is further employed as the solid and fluid heat transport equations. Two fundamental models (models A and B) represent the thermal boundary conditions at the interface between the porous medium and the clear region. The governing equations of the problem are manipulated, and for each interface model, exact solutions, for the solid and fluid temperature fields, are developed. These solutions incorporate the porous material thickness, Biot number, fluid to solid thermal conductivity ratio and Darcy number as parameters. The results can be readily used to validate numerical simulations. They are, further, applicable to the analysis of enhanced heat transfer, using porous materials, in heat exchangers.
This article presents a method for designing a planar guide device that can guide sliders to move along a straight-curved rail and can eliminate the backlash between the slider and the rail throughout the whole range of the slider travel. The guide device has many sliders and each slider has three rollers that can separately roll on both sides of the rail. The straight-curved rail is composed of straight sections, connection sections, and circular-arc sections. For each slider, the three normal lines through the contact points between the rollers and the rail must always intersect at a common point, which is an instant center. Using this as a basis, the side profiles of the straight-curved rail can be determined. To avoid infinite jerk of the slider motion, the pitch curve of the connection section should consist of a transition curve, which is interposed between the straight line and the circular arc.
This study investigates the flow through round orifices with cross flow at the inlet. Emphasis is placed on the change in tangential velocity component for orifices with low L/D. A definition of velocity pick-up is developed based on the orifice exit to cross-flow tangential velocity ratio. Steady, incompressible, and 3D computational fluid dynamics models with the SST k - turbulent model are employed to calculate orifice flows with different geometrical and flow conditions. Stationary orifices and axial orifices in a rotating disk are considered. Computational fluid dynamics solutions are compared with experimental results and published correlations for discharge coefficients, and good agreement is generally demonstrated. It is found that the non-dimensional velocity pick-up depends strongly on the ratio of characteristic times for flow to travel across the orifice in the tangential direction and that for the flow to pass through the orifice. A correlation of velocity pick-up as a function of this ratio is given.
A vehicle suspension system with inerters is proposed and its dynamic model is established to analyse its dynamic performance. The structure of the suspension with inerters is also constructed and its form and structural parameters are optimized. Then the rack-and-pinion inerter and the bench test system of suspension are designed. Based on the simulation, bench test is conducted. It has shown that theoretical research is consistent with the test results. Moreover, the structure of the suspension with inerters is so simple, that it can be easily achieved. Consequently the passenger comfort is greatly enhanced and the comprehensive performance of the car has been coordinated. Therefore, simulated analysis and experimental tests in this paper can provide evidence for further research on suspension with inerters.
This work presents a numerical study of natural convection in a laterally heated cavity filled with an electrically conductive fluid (Pr = 0.0321) in the presence of an external magnetic field and an internal heat source. The finite volume method with the SIMPLER algorithm is used to solve the system of equations governing the magnetohydrodynamics flow. The influence of volumetric heating SQ on the flow structure and on the heat transfer within the cavity for Gr = 104, 105, and 106 was examined. The effects of aspect ratio (A = 1, 0.5, and 2), Prandtl number (low Prandtl number fluids), and magnetic field (Ha = 0 to 100) were determined in the steady state with internal heat generation. Two orientations of the magnetic field were considered in order to have better control of the flow. The strongest stabilization of the flow field with internal heat generation is found when the magnetic field is oriented horizontally.
This paper presents the effect of oblique impact angle on low velocity transient dynamic responses of delaminated composite pretwisted shallow conical shells. An eight-noded isoparametric quadratic plate bending element is employed in the finite element formulation incorporating rotary inertia and effects of transverse shear deformation based on Mindlin’s theory. The modified Hertzian contact law which accounts for permanent indentation is utilized to compute the contact force, and the time-dependent equations are solved by Newmark’s time integration scheme. A comparative study is carried out on torsion stiff, cross-ply, and bending stiff laminates to investigate the effects of triggering parameters like angle of twist, plate displacement, striker’s velocity, and displacement for graphite-epoxy composite laminate subjected to low velocity oblique impact at the center.
A multidisciplinary design optimization (MDO) system is established to reduce solid particle erosion of an axial induced draft fan with sweep and lean. The method improves the erosion resistance of the fan blade in the aerodynamic design stage through a change of blade sweep and lean. The multidisciplinary design optimization approach takes the place of the traditional time-consuming design method by automatic calculation of the flow field, stress distribution, dynamic frequencies, and erosion distribution for blade, controlled by an optimization strategy. A multi-objective particle swarm optimization (MOPSO) algorithm combined with radial basis function approximation model is employed for finding a compromise between the conflicting demands of high efficiency and low average erosion rate with constraints on the pressure ratio and structural responses for the blade. The Navier–Stokes solver, finite element method (FEM) is used to predict the aerodynamic performance and mechanical performance of the blade, respectively. Particle paths in a viscous flow are calculated using the Lagrangian method and Tabakoff rebound model. And then Tabakoff erosion model is used to predict erosion of the blade surface. Several representative designs are selected along the Pareto front to verify using computer aided engineering tools. A compromise solution is used to analyze in detail. Compared with the reference design, the optimal design increases the / 0 slightly by 0.53%, while decreases the avg / avg0 markedly by 13.7%. The result shows that the optimized blade favors a reduced total pressure due to its forward sweep. The decrease of the avg/ avg0 is attributed to a reduced impact velocity and impact angle. The analysis of variance technique indicates that the blade lean has a direct impact on performances with respect to efficiency, erosion, and von Mises stress of the blade, and the blade sweep law near hub has an immeasurable influence on blade von Mises stress. As a conclusion, it can be drawn that the proposed approach may open a new opportunity for the design of axial fan to reduce erosion damage of blade taking other disciplines into consideration. Meanwhile, the multidisciplinary design optimization system can be extended to other turbomachinery and erosion-resistant design fields.
A nonlocal sinusoidal plate model for micro/nanoscale plates is developed based on Eringen’s nonlocal elasticity theory and sinusoidal shear deformation plate theory. The small-scale effect is considered in the former theory while the transverse shear deformation effect is included in the latter theory. The proposed model accounts for sinusoidal variations of transverse shear strains through the thickness of the plate, and satisfies the stress-free boundary conditions on the plate surfaces, thus a shear correction factor is not required. Equations of motion and boundary conditions are derived from Hamilton’s principle. Analytical solutions for bending, buckling, and vibration of simply supported plates are presented, and the obtained results are compared with the existing solutions. The effects of small scale and shear deformation on the responses of the micro/nanoscale plates are investigated.
Complex nonlinear and nonstationary signals can be adaptively analyzed by the Hilbert–Huang transform through empirical mode decomposition and the Hilbert transform to generate the instantaneous energy. The instantaneous energy was able to display the local characteristics of the signals and had good time–frequency analysis capability, it is therefore widely applied to the analysis of vibration signals in the field of gear fault diagnosis. However, only a few extracted intrinsic mode functions through empirical mode decomposition can reflect fault feature or closely related to the faults but others are irrelevant. Therefore, the fault feature of the instantaneous energy for all intrinsic mode functions was not obvious and the accuracy of diagnosis was low. Aimed at solving this problem, a fault leading rate evaluation algorithm was proposed that can select those intrinsic mode functions, which reflect fault features (it was called the dominant intrinsic mode function) from all intrinsic mode functions. In the paper, this algorithm was applied to gear fault feature extraction. By calculating the instantaneous energy of the dominant intrinsic mode function the method could accurately extract gear fault feature and improve the accuracy of diagnosis. Both simulated signals and experimental signals of a Klingelnberg bevel gear were analyzed to verify the effectiveness and correctness of the algorithm.
This paper presents a new parameter identification method of the Stribeck friction model based on limit cycles. A single degree of freedom mass spring system driven by a belt is studied, and the Stribeck friction model is established between the mass and belt. Limit cycle oscillation will occur when the system is unstable. The limit cycle curve is described by some main shape characteristic parameters using the modified Freeman chain code method. Thus, the Stribeck friction parameters can be identified by using the ergodic search method to minimize the Euclidean distance of the theoretical and identified limit cycle shape characteristic parameters. The parameter identification method based on limit cycles is different from the traditional identification methods. It only needs the displacement and velocity responses of the system instead of the measurement of the friction force or motor voltage/current. All of these works can provide the reference for the research work of the friction parameter identification.
This article presents the partial dynamic balancing of a 6-DOF (degree of freedom) haptic device. At first, the motion of the 3-DOF rotational part is decoupled with the motion of the 3-DOF translational part, because the former has no effect on the baseplate, so it can be considered as a whole and only discusses the 3-DOF translational part in the process of calculating dynamic balancing. The main feature of this mechanism is that the system is symmetric about the Cartesian coordinate, so the dynamic balancing of the 3-DOF translational part can be simplified to the dynamic balancing of 1-DOF translational part. The conditions of shaking force balancing can be obtained by keeping the linear momentum constant, and the conditions of shaking moment balancing can be get by minimizing the rate of the angular momentum. Finally, simulation examples are given to verify that the centre of mass of the partial dynamically balanced mechanism is fixed, and the global reaction forces on the baseplate are zero, and the global reaction moments on the baseplate decrease about five times at all times and for arbitrary trajectories.
For accurate modeling and optimization of the air-powered engine, the basic model of the air-powered engine’s working process was established at first. Experiments on a prototype modified from an internal combustion engine were carried out to verify the air-powered engine’s feasibility and the basic model’s validity. Based on the experimental results, a balanced valve was designed. Afterward, the virtual prototype with the newly designed valve system was built and relative simulations were conducted to analyze the dynamic performances of the air-powered engine. Results show that the valve controlling model is easy to achieve parameterization. The output performance of the designed valve is superior to that of a solenoid valve. Furthermore, the inertia moment of the flywheel is analyzed to balance the starting performance and speed fluctuations. At last, orthogonal design and gray relation analysis were utilized to optimize the valve timing parameters, and optimized values of the cam rise angle and the cam return angle are proposed. This research can provide theoretical supports to the new air-powered engine prototype’s design and optimization.
Ninety-degree (normal) bleed slots have been used to stabilize the terminal normal shock in the throat of a mixed compression supersonic inlet. In this study, a quasi-one-dimensional bleed flow rate model, consisting of a constant-area channel with a pair of normal slots symmetrically located along the upper and lower endwalls, is developed. The bleed flow rate is shown to be a function of the terminal normal shock position within the slot. Some key factors, such as the bleed discharge coefficient, taken from the Bragg model, were derived from the basic laws of conservation for a one-dimensional simplification. Furthermore, numerical simulations based on Reynolds-averaged Navier–Stokes equations were performed to analyze the flow characteristics around the bleed slots. The predictions of the bleed flow rate model agree well with computational fluid dynamics results. This method may be helpful to predict the stability of the terminal normal shock in mixed compression supersonic inlets.
Hydraulic actuators are widely used in various kinds of industrial applications. High-power density is key parameters for engineering applications especially for quadruped robots applied in the outdoor environment. Therefore, an increasing number of advanced robots are equipped with hydraulic actuators. In this paper, to compensate the inherent nonlinearities and enhance the performance of the quadruped robot, a hybrid fuzzy controller composed of fuzzy logic controller and Proportion Integration Differentiation controller is evaluated both in simulations and experiments. The control strategy is developed based on the accurate mathematical model. The Matlab Simulink and Fuzzy Logic Toolbox are implemented to accomplish the simulations under flexible loads. Single hydraulic actuator and single leg experiments are accomplished on the specific platforms. Both the simulations and the experimental results indicate that the fuzzy Proportion Integration Differentiation control strategy is capable of fulfilling the specific position tracking under diverse loads. Compared with the conventional Proportion Integration Differentiation controller, the fuzzy Proportion Integration Differentiation controller provided a desirable performance under heavy load with comparatively little response and settling time. Results show that the fuzzy Proportion Integration Differentiation control strategy can effectively achieve the objective of enhancing position tracking robustness under flexible loads and improve the performance of quadruped robot.
In this paper, first, the dynamic behavior of a nonlinear friction driven oscillator subjected to harmonic external excitations and supported by limited power supply is studied. Dynamic analysis of the system through the variation of excitation frequency reveals that the system has chaotic motion near the fundamental natural frequency. After analyzing the dynamic response of the system, the control of chaotic motion of this system using tuned liquid column dampers (TLCD) and magneto-rheological tuned liquid column damper (MR-TLCD) are analyzed. Time-delay feedback control strategy is used in order to have real-time semi-active vibration control of the block with MR-TLCD. Simulation results show the high performance of both of the proposed methods for chaos elimination and improving the system operation. It is also concluded that the system transient time in semi-active control using MR-TLCDs and based on the new proposed control strategy is less than conventional TLCDs.
A-axis is an essential assembly in the five-axis CNC machine tools, and its positioning precision directly affects the machining accuracy and surface quality of the parts. Considering the influence of parameters perturbation and uncertain cutting force on the control precision of the A-axis, a nonlinear dynamics model of the A-axis system is established, which reveals the relationships among the drive torque, the load torque, the motion direction and the system parameters. Then, two adaptive sliding mode controllers (ASMC) are designed. The first one is based on the bipolar sigmoid function, which can adjust the switching gain and the boundary layer thickness adaptively, then, equilibrium between the tracking error and the chattering can be achieved. The second one is a compound adaptive controller constituted by the traditional sliding mode controller (TSMC) and an internal controller that is based on the hyperbolic tangent function. When the state trajectory comes into the boundary layer, the TSMC will be replaced by the internal controller, thus, the adaptive controller can continuously switch between these two controllers, which can effectively eliminate the high-frequency chattering in the TSMC. Stability of these two controllers is guaranteed by the Lyapunov theory. Experimental results demonstrate the effectiveness and feasibility of the proposed ASMC, which can smooth the input chattering and reduce the tracking error by 16.62% and 21.44%, respectively.
Because the collision avoidance function is indispensable for providing safe and easy operation of human-operated robotic systems, this paper deals with the collision avoidance control for a human-operated mobile robot in unknown environments. A typical four-wheeled mobile robot with infrared distance sensors for detecting obstacles is considered. The robot cannot move in an arbitrary direction owing to a nonholonomic constraint. Therefore, we propose a simple control approach in which a human operator’s control input is modified in real time to satisfy the nonholonomic constraint and avoid collision with obstacles. The proposed controller has steering- and brake-like functions that are adjusted according to the distance sensor information. The stability of the proposed control system is analyzed with a linear model. The effectiveness of the proposed method is confirmed by experiments in which several operators control the robot in an environment with obstacles.
Numerical simulation and physical modeling performed on small-scale ingots made from pure lead, having a hole drilled through their centerline to mimic porosity, are utilized to characterize the deformation mechanics of a single open die forging compression stage and to identify the influence of the lower V-die angle on porosity closure and forging load requirements of large cast ingots. Results show that a lower V-die angle of 120° provides the best closure of centerline porosity without demanding the highest forging loads or developing unreasonably asymmetric shapes that may create difficulties in multi-stage open die forging procedures.
Exact natural frequencies of functionally graded beams are determined using plane elasticity theory. The analysis yields infinitely many frequencies. For verification purposes, a comparison with the existing beam theory results is performed and a close agreement is observed for slender members. The elasticity solutions are general in the sense that they are valid for slender members as well as short and thick structural elements. Both flexural and axial free vibration mode shapes are presented for top and bottom surfaces and the effect of the beam thickness is discussed. The exact results presented herein can be used as benchmarks for future research of free vibration behavior of short and thick functionally graded material beams.
The mathematical model of the temperature system under the mode of the proportional throttle valve control and the variable frequency pump control is established, respectively. A compound control strategy that consists of a compensation controller and a sliding-mode predictive feedback controller is designed. The compensation controller, which takes the change of the wind speed as parameter, is used to eliminate the impact on the system caused by the change of the working conditions (wind speed); the sliding-mode predictive feedback controller is used to solve the problems in the system such as time delay, time-varying parameters and disturbance. In order to solve the problem of temperature disturbance caused by the mode switch between pump control and valve control and the oil-rich combustion phenomenon in the high-temperature case, a method takes the ramp signal in which the slope is adjustable as a temperature setting signal is proposed. The experimental results show that the designed strategy obtains a satisfactory control performance and can achieve the temperature control with fast response time and no overshoot. In addition, it takes the ramp signal in which the slope is adjustable as the temperature setting signal can achieve the undisturbed switching control of the temperature and prevent the oil-rich combustion effectively.
Mathematical modeling, simulation, and optimum design of equivalent one degree-of-freedom high-speed cam mechanisms used for internal combustion engines are investigated in this study. The dynamic equation governing the dynamic behavior of a typical high-speed cam–follower system of an internal combustion engine has been simplified using dimensionless analysis method. The resulting model is then used to find the optimum cam shape to reduce the residual vibrations in the follower part of the system. The Lagrange multipliers method is utilized to minimize the sum of squared error (deviation from the cam profile) over one period under continuity and smoothness constraints.
In this work, concurrent linear springs placed in the system that performs small in-plane oscillations around the stable equilibrium position are considered. New theorems defining how they can be replaced by two mutually orthogonal springs are provided. The same concept is applied to find two mutually orthogonal linear viscous dampers that can replace a system of concurrent linear viscous dampers. The directions of such springs and dampers correspond to the principal stiffness and damping axes, respectively. So far unknown invariants related to the sum of stiffness coefficients and damping coefficient of the original and equivalent systems are presented. A few examples are given to illustrate the use and benefits of this approach. In addition, it is shown how the concept of two mutually orthogonal springs can be beneficially used for analysing problems concerned with oscillations of a particle on elastic frames.
When machining workpieces with complicated and intricate shapes by wire electrical discharge machining, the workpiece height usually varies along a machining path. To ensure a stable and efficient machining, the machining parameters must be appropriately tuned based on the estimated workpiece height. Though an offline workpiece height estimation model can be established by traditional support vector regression with a satisfactory accuracy, the offline model is unable to cover all possible machining conditions. In this paper, least squares support vector machine is proposed to build up online a workpiece height estimation model. Due to the use of equality constraints in the formulation of least squares support vector machine, all data points are treated as support vectors, thus sparsity is lost as compared with traditional support vector machine. For online applications, a low computational load as well as a limited memory storage are required for an online algorithm. To meet the requirements of online workpiece height estimation, two measures are thus adopted. One is the use of a projection method which measures the relevance of a new data point with existing basic vectors by calculating its residue. The residue is used as criteria for admission of the new data point as a new member of the basic vector set. The other is the restriction on the size of the basic vector set. Removal of an insignificant basic vector is determined by its contribution to the model, which is measured by its coefficient in the model (or support value). Experimental results show that, by online learning, the estimation model can achieve an estimation error less than 2 mm at smooth parts of a workpiece. Based on the estimated workpiece height, proper machining parameters can be set and a stable machining can be achieved.
Concurrent linear springs belonging to systems that perform small out-of-plane oscillations around a stable equilibrium position are considered with a view to obtaining equivalent systems of three mutually orthogonal linear springs. Theorems defining their stiffness coefficients as well as their position, i.e. the position of the principal stiffness axes for which the potential energy does not contain mixed terms, are stated and proven. So far unknown invariants related to the sum of original and new stiffness coefficients are provided. In addition, the equivalent system of three mutually orthogonal dampers is obtained for any system of out-of-plane concurrent linear viscous. The theorem defining their damping coefficients and their directions, collinear with the principal damping axes for which the dissipative function does not contain mixed terms, is provided. The corresponding invariant for damping coefficients is presented, too. An ellipsoid of displacement and an ellipsoid of stiffness are discussed. Three illustrated examples are given.
This paper proposes an approach to evaluating the product assembly precision in different assembly sequences, considering the effect of joint surface deformation. Three assembly variation sources, including manufacturing variation, assembly clearance and joint surface deformation, which have effect on the final assembly precision are analyzed. Based on finite element analysis, a hybrid genetic algorithm and back-propagation neural network model is built to predict the assembly variations, which are caused by the joint surface deformation under different assembly conditions and different parameters of the joint surface. An assembly variation propagation model is built, and a product assembly precision evaluation approach is proposed to identify the feasible assembly sequences, and the optimal assembly sequence considering the effect of the joint surface deformation. Finally, a case study is given to verify the proposed approach.
The von Mises yield criterion is combined with an equilibrium equation to provide a semi-analytical plastic collapse solution for a thin hollow disc inserted into a rigid container and subject to thermal loading. A numerical method is only necessary to sequentially solve several simple transcendental equations. The state of stress is plane and the temperature field is uniform. The main distinguished feature of the solution is that all basic thermo-mechanical properties are temperature-dependent. The objective of the paper is to show the effect of temperature-dependency of these properties on plastic collapse.
We describe efforts to improve the accuracy of fatigue damage estimation methods of narrowband non-Gaussian random loading. The available analytical solutions are reviewed and briefly summarized, and the reasons for the occurrence of computational errors during nonlinear transformation-based methods are determined. The computational errors are mainly due to inconsistencies in the statistical moments above fourth order. A new approach is proposed for the evaluation of rainflow fatigue damage. This approach avoids the problem of transformation-based methods and provides accurate estimation for fatigue damage of narrowband leptokurtic non-Gaussian random loading. Additionally, the applicability of the proposed method to Gaussian random loading is investigated. Finally, two examples are carried out and comparisons are made to more commonly used methods to demonstrate the capabilities and brevity of the proposed algorithm.
Large gears for wind turbine gearboxes require high performances and cost-effective manufacturing processes. Heat distortion in the heat treatment phase and the consequent large grinding stock are responsible for high manufacturing costs due to reduced productivity. A research project aimed at the identification of new materials, manufacturing and heat treatment processes has been performed. Air quenchable alloy steels, combined with a specifically developed case hardening and heat treatment process, have been identified as an interesting solution, both from the point of view of cost effectiveness, thanks to reduced distortions and grinding stock, and for the environmental sustainability. The research project has been completed by the manufacturing of a full-scale gear, on which the whole process has been validated. Nevertheless, in order to judge the applicability of these steels to large gears, data from specific tests on the performances against typical gear failure modes, like bending and contact fatigue, are necessary as well. Single tooth fatigue bending tests and disc-on-disc contact fatigue tests have therefore been performed on two innovative materials, respectively, a high hardenability steel and a bainitic structure steel, and on a reference traditional case hardening steel. The results of these tests, which provide useful data for gear designers, are presented and discussed in this paper.
The present study proposes a dynamic numerical solution for deflections of curved beam structures. In order to extract characteristic equations of an arch under an in-plane constant moving load, an analysis procedure based on the Euler–Bernoulli beam theory considering polar system is conducted. A prismatic semicircular arch with uniform cross section, in various boundary conditions, is assumed. Radial and tangential displacements, as well as bending moments are obtained using differential quadrature method as a well-known numerical method. In addition to parametric studies, a curved steel bridge as an actual application is analyzed by the mentioned method. By using this differential quadrature technique, the function values and some partial derivatives are approximated by weighting coefficients. Convergence study is carried out to demonstrate the stability of the present method. In order to confirm the high level of accuracy of this approach, some comparisons are made between the results obtained by selected methods such as differential quadrature method, Galerkin method, and finite element method. The results show that in the structural problems with specific geometry, using differential quadrature method, which is independent of domain discretization, is proven to be efficient.
A compact retrieval system without moving parts was designed to lift and transport residuals in storage tanks to a higher elevation. The key component of the retrieval system, a curve reverse flow diverter (CRFD) with a vortex diode, was machined into a stainless steel disk to enable the entire system to be compact. The compact retrieval system can be installed in storage tanks through an existing narrow mounting hole. The pumping performance of the retrieval system was examined in terms of the effects of curve reverse flow diverter configurations, lift height, compression pressure, and suction pressure. Results reveal that the vortex diode with higher swirl resistance does not enhance the pumping capacity of the retrieval system. The pumping capacity of the retrieval system increased with increasing compression pressure and decreased with increasing lift height and suction pressure. During the compression phase of the retrieval system, the empty factor qc was found to be linear with the Euler number Eu . The compact retrieval system can resolve the difficulty to retrieve high-level radioactive residuals in storage tanks without radioactive leak and frequent maintenance.
Microscale biaxial accelerometers are required to be sensitive to applied accelerations and manufacturable by means of microelectromechanical systems technology. In order to meet these requirements, a compliant realization of biaxial accelerometers, dubbed simplicial biaxial accelerometers, has been proposed, as reported in this paper. Notched joints, to realize what is termed -joints in the parallel-robots literature, are employed and then improved by the introduction of Lamé-shaped hinges serving as flexible joints. The sensitivity of the simplicial biaxial accelerometers in estimating accelerations is investigated and validated by means of finite element analysis. The sensing system is embedded in the simplicial biaxial accelerometers, with piezoresistive sensing technology adopted in the instrumentation design. Using the principles of piezoresistive sensing, the electronic layout is developed for the accelerometer. Through the piezoresistive analysis implemented on the finite element model of the simplicial biaxial accelerometers, the matrix that maps voltage signals into acceleration signals is derived. By virtue of both the structural and electronic designs, the accelerometer is observed to be sensitive to accelerations in its plane, but fairly insensitive to accelerations in any of the other four directions of the rigid-body motion. Finally, prototypes were fabricated with microelectromechanical systems technology to test the microfabrication feasibility of the structure and measurement system of the accelerometer. Test results are the subject of a forthcoming paper.
There is a requirement for improved 3D surface characterisation and reduced tool wear, when modern computer numerical-controlled (CNC) machine tools are operating at high cutting velocities, spindle speeds and feed-rates. This research project investigates vibration-induced errors on a CNC vertical machining centre under dynamic conditions. A model of the machine structural dynamics is constructed using the Finite Element Method (FEM) for the comprehensive analytical investigation of the machine vibration behaviour. The analytical model is then validated against the measured results obtained from an experimental modal analysis (EMA) investigation. A correlation analysis of the simulated and experimental modal analysis results is undertaken in order to improve the accuracy of the model and minimise modelling practice errors. The resulting optimised model will need further sensitivity analysis utilising parametric structural analysis and characterisation techniques in order to identify a potential for vibration reduction using passive methods.
A lot of endeavors regarding the development of slider–crank mechanism in the ship’s propeller have been made and continue to be investigated. This paper presents the position control of a slider–crank mechanism, which is driven by the piston cylinder actuator to adjust the blade pitch angle. An effective motion control strategy known as the computed torque control can ensure global asymptotic stability. However, it is essential for this control scheme to have a precise and accurate system model. Moreover, large amounts of changes in the output and even instability of process are caused by a small amount of measurement or process noise, when the derivative gain is sufficiently large. Accordingly, in order to compensate any parameter deviation and disturbances as well as minimizing errors, we have presented a genetic algorithm-based computed torque control system which adjusts the proportional-derivative gains. Computer simulations are performed which reveals that asymptotically stability is reached and it confirms the effectiveness and high tracking capability of the proposed control scheme.
The contact angles formed at the position of each ball in ball screws are conventionally assumed to be a constant value in determination of contact stiffness. In this study, instead of being treated as pre-assumed constants, the contact angle is formulated as functions of the position angle of balls to reflect their distribution dependent on the operation condition and design parameters. After establishing a proper transformed coordinate system according to the ball screw mechanism, the variable contact angles and normal forces of the ball screw are predicted. Then the contact stiffness obtained by numerical calculations is validated by experiment and several characteristics arising from the variable contact angle will be discussed.
Water hydraulic axial piston motor (WHAPM) is one of the key components in water hydraulic system. It is essential to identify the desired engineering materials and material combinations for improving the WHAPM, which are featured by strong wear and erosion resistance. As the candidate materials of friction pairs in WHAPM, the tribological characteristics of 30 wt% carbon fiber-reinforced PEEK (PEEK + CA30) sliding against 17-4PH precipitation-hardening stainless steel under fresh water lubrication were investigated. The friction experiments were conducted on MCF-10 ring-on-ring test rig. With the help of metallographic microscope, an attempt was made to approach the tribological properties of friction pair. The experimental results showed that the ideal sliding velocity is also about 1 m/s when the applied load is between 200 and 600 N. It can be concluded that the slipper designed based on the principle of residual pressure coefficient bearing with auxiliary supporting area is an effective way to decrease the actual pv value in the prototype of WHAPM. The research outcomes will lay the foundation for the design of key friction pairs in the water hydraulic components and system.
Optimization of a highly conductive insert embedded into a heated rectangular chip has been lately investigated. The role of the insert was to gather the heat current within the chip body and remove it to a minimum temperature heat sink. The central goal of this paper is to invoke several reconsiderations, which result in excessive reduction of the peak temperature in the heated chip in comparison with the lowest peak temperature existed in the archival literature. It is proved that for the configuration under study with its bottom surface receiving a heat flux, the branching patterns of the insert must be avoided, in case the appropriate revisions in the architecture (width, location and cross section area) of the simple branchless patterns are considered. An analytical solution for predicting the peak temperatures in the chip is also addressed. It is demonstrated that under the same volume fraction and thermal conductivity of the cooling insert, the peak temperature is reduced to 2.9°C, which is 94% below the lowest temperature existed in the archival literature, which was around 50°C.
Traditional techniques for balancing long, flexible, high-speed rotating shafts are inadequate over a full range of shaft speeds. This problem is compounded by limitations within the manufacturing process, which have resulted in increasing problems with lateral vibrations and hence increased the failure rates of bearings in practical applications. There is a need to develop a novel strategy for balancing these coupling shafts that is low cost, robust under typically long-term operating conditions and amenable to on-site remediation. This paper proposes a new method of balancing long, flexible couplings by means of a pair of balancing sleeve arms that are integrally attached to each end of the coupling shaft. Balance corrections are applied to the free ends of the arms in order to apply a corrective centrifugal force to the coupling shaft in order to limit shaft-end reaction forces and to impart a corrective bending moment to the drive shaft that limits shaft deflection. The aim of this paper is to demonstrate the potential of this method, via the mathematical analysis of a plain, simply supported tube with uniform eccentricity and to show that any drive shaft, even with irregular geometry and/or imbalance, can be converted to an equivalent encastre case. This allows for the theoretical possibility of eliminating the first simply supported critical speed, thereby reducing the need for very large lateral critical speed margins, as this requirement constrains design flexibility. Although the analysis is performed on a sub 15 MW gas turbine, it is anticipated that this mechanism would be beneficial on any shaft system with high-flexibility/shaft deflection.
We developed a shape-design optimization method for the thermo-elastoplasticity problems that are applicable to the welding or thermal deformation of hull structures. The point is to determine the shape-design parameters such that the deformed shape after welding fits very well to a desired design. The geometric parameters of curved surfaces are selected as the design parameters. The shell finite elements, forward finite difference sensitivity, modified method of feasible direction algorithm and a programming language ANSYS Parametric Design Language in the established code ANSYS are employed in the shape optimization. The objective function is the weighted summation of differences between the deformed and the target geometries. The proposed method is effective even though new design variables are added to the design space during the optimization process since the multiple steps of design optimization are used during the whole optimization process. To obtain the better optimal design, the weights are determined for the next design optimization, based on the previous optimal results. Numerical examples demonstrate that the localized severe deviations from the target design are effectively prevented in the optimal design.
The vernier-gimballing magnetically suspended flywheel can generate control moment in radial directions by tilting the spinning rotor to rotate around the radial axes. In order to reduce the extra tilting torque caused by the uniform distribution of flux density and the magnetic coupling among different channels, a novel 3 degrees of freedom conical permanent-magnet-biased magnetic bearing is proposed in the paper. The axial and radial stators are both designed with the normal directions of the midst faces directing to the centroid of the rotor, so as to decrease the extra torque by shortening the length of torque arm. A novel structure of radial X and Y stator poles separated by nonmagnetic material is proposed, and the upper and lower conical stators are designed to be mirror structures with each other, so that the magnetic coupling can be reduced. The mathematical model of the proposed permanent-magnet-biased magnetic bearing is constructed by methods of equivalent magnetic circuit and finite element. Calculations and simulations are carried out on the suspension force, extra tilting torque, and force coupling. The results show that with the conical structure, the extra tilting torque can be decreased from 10.83 Nm to 0.11 Nm when the rotor tilts around X axis for 1°. The magnetic forces among X, Y, and Z directions are almost decoupled even when the rotor shifts in some direction. All the results prove that the novel permanent-magnet-biased magnetic bearing is suitable for application in vernier-gimballing magnetically suspended flywheel.
A 2D plane strain finite element program has been developed to investigate very high cycle fatigue in wind turbine roller bearings due to rolling contact. Focus is on fatigue in the inner ring, where the effect of residual stresses and hardness variation along the depth is accounted for. Both classic Hertzian and elastohydrodynamic lubrication theories have been used to model the pressure distribution acting on the inner raceway and results are compared according to the Dang Van multiaxial fatigue criterion. The contact on the bearing raceway is simulated by substituting the roller with the equivalent contact pressure distribution. The material used for the simulations is taken to be an AISI 52100 bearing steel and linear elastic behavior is here assumed. The effect of different residual stress distributions is also studied, as well as the effect of variable hardness along the depth, relating its values to the fatigue limit parameters for the material. It is found that both for Hertzian and elastohydrodynamic lubrication contacts, the Dang Van criterion predicts that fatigue failure will first occur in the subsurface region and that, regardless of the specific pressure distribution used, the hardness distribution can have a significant influence on the safety against failure for bearings subjected to very high cycle fatigue loading.
Flycutting is a major machining process for flat-surface machining, which is a typical intermittent-machining process. This paper is dedicated to study the influence of the intermittent-machining force on the workpiece surface generation. In the present study, some defects are identified on the machined surface and found to be corresponded to the tool-tip vibration by the dynamic analysis and the surface-generation simulation. A theoretical model is proposed to capture the dominant factor based on the characteristic. It reveals that the defects are attributed to the changing period of the intermittent-machining force and the dynamic performance of the machine tool. Hence, a surface-generation model is proposed to take account of the tool-tip vibration and the changing of the cutting locus. The simulation results have been found to agree well with the experimental results.
A diagnostic method of inspecting structural integrity using vibration, which is generated and monitored by piezoelectric transducers, is presented. When damage occurs in structures, the flexural-wave propagation characteristics change because of discontinuities in structural properties. To monitor this change, frequency-dependent variation of the wavenumber is measured from the piezoelectrically actuated harmonic vibration of a structure. The theoretical model was proposed to analyze the wave propagation and standing-wave pattern in the structure. Its prediction was compared to the measured vibration response on the basis of which the theoretical model was verified. Using the predicted response, the sensitivity of the potential energy to damage is obtained. With damages of different sizes and locations induced on the beam, the change in the wavenumber and equivalent dynamic stiffness was obtained from the measured transfer functions. The location and size of damage was identified from the damage index accurately. The correlation coefficient between the sensitivity of the potential energy and the variation of the dynamic stiffness was used in estimating the damage index. Analysis of the flexural-wave propagation from piezoelectric actuation allowed continued and precise structural health monitoring.
The rolling element bearing is one of the most extensively used components in various rotating machinery, and it is therefore critical to develop a suitable online rolling element bearing fault-diagnostic framework to improve a rolling element bearing system’s failure protection during conditional operations. In this paper, a hybrid fault-feature extraction method by detecting localized defects and analyzing vibration signals of rolling element bearings via customized multi-wavelet packet transform is proposed, in which the swarm fish algorithm has been utilized for the minimization of signal residual to determine the adaptive prediction operator. With good properties of concurrent symmetry, orthogonality, short support and high-order vanishing moment, the multiple wavelet functions and scaling functions are defined for the hybrid fault-feature extraction, which match the diverse characteristics of hybrid fault and extract coupling features, and the proposed lifting scheme-based multi-wavelet packet transform is highly effective. Then, the proposed method is validated by rolling element bearing experimental results, which show that this approach can effectively extract the hybrid fault features of inner race and rolling element.
Structural synthesis of kinematic chains is one of the most creative and important stages in mechanical design. It provides a number of optional structure types when new mechanisms are created. In this paper, a new algorithm for structural synthesis of planar simple and multiple joint kinematic chains has been proposed by subsequently adding single-kinematic-chain method. By this algorithm, the structure of multiple joint kinematic chains with specified degree-of-freedom, the number of links, and total multiple joint factors P can be synthesized in batch. When P = 0, the structure of simple joint kinematic chains with specified degree-of-freedom, and the number of links can also be generated. Finally, structural synthesis examples of planar simple and multiple joint kinematic chains have been studied to show effectiveness of this algorithm.
To forecast the dynamic responses of closed high-speed precision press accurately, a 3-degree-of-freedom (DOF) dynamic model of mass-spring damping is proposed in this work. This model operates by using the centralized parameter method. Considering the instantaneity of impact load, we employ impulse simulation to simulate the periodic impact working conditions of a JF75G-200 high-speed press using both 2-DOF and 3-DOF models. Simulation data on the dynamic responses of the press are acquired and compared with the results from on-site measuring. The proposed 3-DOF dynamic model of mass-spring damping has been proven by our simulation and test to be reliable as well as effective for detecting the dynamic responses of the press.
This paper deals with a non-linear mathematical model for simulation and analysis of a dynamic behaviour of a rotor-bearing system. The model is used for the simulation of plane motion of a centre of rotor’s cross-section which makes the model convenient for the analysis of vibrations generated in a rolling bearing as well as for the analysis of accuracy of the revolution of rotor supported on a rolling bearing. The model takes into account the following quantities: internal radial clearance, external radial load and unbalanced load. Differential equations of a motion are derived using Lagrange’s equations. The contacts between the balls and the rings are considered to be non-linear with a stiffness derived by the Hertzian theory of an elastic contact. The proposed model enables direct determination of local contact deformations which significantly reduces needed computations and CPU time. The results obtained by the model are used to reconstruct phase-space trajectories and Poincaré maps and to calculate the largest Lyapunov exponent in order to establish the stability of rotor-bearing system motion. A computer program is developed based on the mathematical model for the simulation and analysis of a dynamic behaviour of a rotor-bearing system.
An improved transverse shear stiffness for vibration and buckling analysis of functionally graded sandwich plates based on the first-order shear deformation theory is proposed in this paper. The transverse shear stress obtained from the in-plane stress and equilibrium equation allows to analytically derive an improved transverse shear stiffness and associated shear correction factor of the functionally graded sandwich plate. Sandwich plates with functionally graded faces and both homogeneous hardcore and softcore are considered. The material property is assumed to be isotropic at each point and vary through the plate thickness according to a power-law distribution of the volume fraction of the constituents. Equations of motion and boundary conditions are derived from Hamilton’s principle. The Navier-type solutions are obtained for simply supported boundary conditions, and exact formulae are proposed and compared with the existing solutions to verify the validity of the developed model. Numerical results are obtained for simply supported functionally graded sandwich plates made of three sets of material combinations of metal and ceramic, Al/Al2O3, Al/SiC and Al/WC to investigate the effects of the power-law index, thickness ratio of layer, material contrast on the shear correction factors, natural frequencies and critical buckling loads as well as load–frequency curves.
Equal channel angular pressing is one of the most prominent procedures for achieving ultra-fine grain structures among the various severe plastic deformation techniques. In this study, the effect of superimposing ultrasonic vibration on the punch during the equal channel angular pressing process was investigated by finite element model. Two different 2D plane strain models were considered in the simulations. In the first model, the die and the punch were considered as rigid bodies and in the second model, the punch was considered as an elastic body. Both models showed reduction in the forming force. These models also showed that this force reduction depends on the vibration amplitude and the die velocity. However, the amount of reduction was lower in the second model because the amplitude of 10 µm at the working surface of the punch reduced to 1.25 µm in forming situation while in the first model remained constant i.e. 10 µm. It was shown that this amplitude reduction during forming is more realistic in comparison with constant vibration amplitude. The reduction of amplitude depends on the work material and punch material and in this study they are AL1100 and Ti-6Al-4 V, respectively. By using a 3D finite element model and an elastic punch also showed that the second model is more realistic if compared with experimental data.
This paper presents kinematic analysis of a 3-degree of freedom parallel mechanism for hexapod walking-operating multifuctional robot. Each leg of the robot consists of three limbs: universal joint – prismatic joint chain (1-UP) and universal joint – prismatic joint – spherical joint chain (2-UPS) and at the end of the leg there is passive spherical joint to adjust to the uneven ground. In this paper, first the forward kinematic model is built and it shows that the model has close-form solution. Then the work space is discussed in which the robot feet trajectories can be projected. It can be shown that the current trajectories of the feet only take very small work space. After that force analysis is performed and the results show that the payload capability of the mechanism is very high. Experiments of the prototype show that the robot can walk easily with more than 150 kg loads while the step size is more than 0.5 m.
Soft magnetic composites (SMCs) can be described as soft magnetic powders covered by electrically insulating layers. In this work, iron powders with high purity and organic-silicon epoxy resin were chosen for good magnetic properties, thermal stability, and mechanical properties, respectively. The effect of amount of resin, different annealing temperatures on the microstructure, and performance of SMCs was investigated. Results show that organic-silicon epoxy resin has excellent properties as dielectric coating materials for coating iron powders and maximum heat-resistant temperature is about 400 °C. According to magnetic properties and flexural strength analysis, the optimum annealing temperature of organic-silicon epoxy resin-coated composite is 200 °C. Furthermore, the finite element analysis indicates that the strength of the whole composites is related to the adhesion of resin and iron and the strength of resin itself.
In order to study the vibration reliability of hydraulic turbine-generator unit, the nonlinear dynamic equation of the main shaft system of hydraulic turbine-generator unit is established by the finite element method. Then the nonlinear vibration characteristics of the system are analyzed and the excitation frequencies of the system are obtained by the method of multiple scales. Based on the criterion that the absolute values of difference between the natural frequencies and excitation frequencies of the system should be less than specific values, the hybrid probabilistic, nonprobabilistic, and fuzzy reliability model of the system based on nonlinear vibration is constructed. By the hybrid reliability model, the reliability of system can be calculated. Finally, an example is presented.
Sandwiched hollow sphere structure may have the potential to provide better ballistic impact protection as compared with monolithic plate based on the same weight and impact area. In the previous study of a sandwiched hollow sphere structure by the authors, a novel unit cell was created as a basic building unit of the structure, the tumbling effect was observed for significant impact energy absorption, and the existence of an optimal yield stress or hardness was proved for maximizing the impact energy absorption. However, the impact energy absorption ability of the sandwiched hollow sphere structure may also relate to many other factors. In this study, the diameter relation between the incoming projectile and the spheres in the sandwich core, the projectile initial impact velocity, and the sphere arrangement in the sandwich core are examined. It is revealed that the first layer sphere diameter should be comparable to the diameter of the incoming projectile, the diameter of spheres in different layers in one sandwich core should either decrease or increase monotonically, and there exists a critical impacting speed, at which the sandwiched sphere structure is most effective for impact energy absorption, etc. All these findings make the sandwiched hollow sphere structure a promising new member to the passive armor family.
In order to enhance the efficiency of the hydraulic system, one new-type hydraulic transformer is presented in this paper. First, the basic structure and the principle of the new-type hydraulic transformer are explained. Then, the mathematical models including both the inner and outer loops are analyzed. Moreover, two kinds of control methods are discussed corresponding to the two loops, respectively. Furthermore, the proposed strategies are translated into the simulation languages, and the simulation is made in Simulink. Finally, the prototypes of new-type hydraulic transformer and the test rig are constructed to test the performance. Both the simulated and experimental results show that the new-type hydraulic transformer can be used in the practical condition, and the proposed control algorithm is suitable.
A theoretical study based on dimensional analysis and fractal geometry of crack profiles is proposed to establish the relation between their fractal dimension D (1 < D < 2) and the parameters defining the fatigue crack propagation rate. The exponent m of the Paris’ law is found to be an increasing function of the fractal dimension of the crack profile, m = 2D/(2 – D). This trend is confirmed by a quantitative analysis of fractographic images of titanium alloys with different grain sizes (different roughness of crack profiles), by a new experimental test and by an indirect estimation of D from crack growth equations accounting from crack-size effects in steel and aluminum. The present study can be considered as the first quantitative analysis of fractographic images aiming at relating the morphological features of cracks to their kinetics in fatigue.
Planar twist channel angular extrusion (PTCAE) is a new severe plastic deformation method to produce bulk ultra-fine-grained materials which is based on conventional equal channel angular extrusion by applying additional planar twist strain in deformation zone of ECAP process and simultaneously imposing larger strain and increasing severe plastic deformation methods efficiency. Plastic deformation characteristics of PTCAE method were analyzed through finite element analysis using Deform 3D V.5 software, processing loads and values of effective strain in different directions of sample were studied for different planar twist angles (α) in comparison with the results of conventional ECAP with the same channel dimension and arc of curvature angles. Die and punch were assumed as rigid bodies, whereas the billet, with dimensions of 10 mm x 10 mm x 70 mm was considered to be deformable pure aluminum. The processing conditions such as friction coefficient, ram speed, mesh size and other factors were held constant to make comparison between the different processing conditions possible. The results indicated that more strain values with more uniform distribution may be achieved after PTCAE method in comparison with the conventional ECAP method. Also, it is observed that in α = 20, the equivalent strain distribution is homogenous approximately in both of vertical and horizontal directions of the cross-section of the sample. Therefore, PTCAE can be considered as a promising severe plastic deformation technique for future industrial applications which can be installed on any standard extrusion equipment without any additional required facilities that are essential in other new severe plastic deformation methods and can be used instead of ECAP process significantly and beneficially.
Metal contact seals are widely used in mechanical equipment, and such sealing performance is directly influenced by the interfacial micro-contact state. In this paper, the surfaces with random roughness are simulated by an exponential autocorrelation function and root-mean-square roughness. The model of metal surface micro-contact is established. The influences of the external loads on the interfacial separation, contact area and maximum interfacial stress are investigated by means of Hertz contact theory. Calculations and investigations are carried out for a concrete sealing interface. The variations of the interfacial separation, contact area and interfacial stress with the external applied loads are investigated with the two surfaces of the same and different root-mean-square roughness, respectively. Meanwhile, the concrete variation curves are obtained. Furthermore, the obtained variation curves are analysed in detail.
This paper examines the squeal propensity associated with the rigid motion of a brake pad. For the description of the rigid motion, the brake pad is analytically modeled as a composite annular sector plate with both the back plate and friction material rigid. The friction material is subject to friction contact with a rotating disc. The vibration modes of the rigid pad consist of the six rigid modes including three rotation and three translation modes coupled with contact stiffness. The analytical formulation for the dynamic motion of the composite rigid pad is presented. From the numerical calculation, the rigid pad modes are shown to be coupled with one another and thus generate the modal instability in both finite element full model and simplified pad model. It is suggested that the squeal propensity of the rigid pad modes can be estimated by using the simplified pad model and controlled by the certain design modification such as the contact area.
Output force or velocity polytopes are usually used as an index of the manipulability of robot. This paper discusses the relationship between the actuator force and the variation of the output force capacity polytope and proposes the output force capacity polytope method for the selection of actuator forces of a three degrees of freedom excavating manipulator with the requirement that the output force on the end effector is a set of all possible forces rather than a single force. In this paper, the method to calculate capacity polytope is introduced with the consideration of gravity effect. With the concept that the required output force space should be within the output capacity polytope, the output force capacity polytope approach for selecting actuator forces is proposed.
With the wide use of complex helical surfaces in screw components, it becomes more and more urgent to investigate efficient ways for the design and manufacture of components of this kind. This study establishes the mathematical model of helical surface based on discrete points on its axial section profile using cubic spline curve fitting method, and presents a theoretical approach to calculate the tool path for the whirling process which aims to produce the helical surface through enwrapping movements of standard cutters inserted in the tool ring. The approach is implemented in MATLAB environment focusing on the calculation of the cutter location points. After that, the theoretical machining error is analyzed focusing on the scallop height, which can be divided into axial and cross-sectional errors. Finally, a case study is provided, together with numerical simulation demonstrating the validity of the proposed approach.
The resonance demodulation technique has been widely employed in vibration signal analysis. In order to construct a proper bandpass filter, the prior knowledge, i.e. the resonance frequency band of the mechanical system is required in the traditional demodulation method. However, as the collected vibration signal is often tainted by the background noise and interferences often with unknown frequency contents, it is difficult to identify the center frequency and the bandwidth of the filter. This paper introduces a clustering-based segmentation method to determine these parameters automatically. Envelope analysis is then applied to demodulating the vibration data. According to the simulated cases, the proposed approach is robust to Gaussian noise and interferences. Its effectiveness is further validated by applying it to detect rolling bearing faults based on experimental data.
Unsteady cavitation flows in a centrifugal pump operating under off-design conditions are investigated by using a numerical framework combining the re-normalization group k– turbulence model and the transport equation-based cavitation model. The reliability and accuracy of the numerical model are demonstrated by the satisfactory agreement between the experimental and numerical values of the pump performance. Under partial discharge, the frequency spectra of the pressure fluctuation at the impeller inlet become more complex as the pump inlet pressure decreases. The maximum amplitude of pressure fluctuation at the blade leading edge for cavitation flow is 2.54 times larger than that for non-cavitation flow because of the violent disturbances caused by cavitation shedding and explosion. Under large discharge, the magnification on the maximum pressure amplitude is 1.6. This finding indicates that cavitation has less influence on pressure fluctuations in the impeller under large discharge than under partial discharge. This numerical simulation demonstrates the evolution of cavitation structure inside the impeller.
A novel bellows-type flow regulator was designed with the ability to maintain a steady thrust level and to adjust the thrust of a liquid rocket engine. The flow regulator showed good performance not only in maintaining the flow rate despite changes in the pressure difference across the flow regulator, but also in adjusting the flow rate in response to a changing shaft angle. A mathematical static model of the flow regulator was developed. A design criterion for ideal performance of the flow regulator was derived by theoretical analysis of the mathematical model. It was established that the main design parameters of the flow regulator affecting flow rate maintenance were the number and the width of ports in the 2nd throttle. The static characteristics predicted by the mathematical model show good agreement with experimental results, thus validating the mathematical model.
The key factor for underwater petroleum pipeline flange connection tool is its 20 bolts synchronous lead-in nuts. The alignment accuracy of bolts and nuts is critical for bolts lead-in nuts. In order to analyze the accuracy and design issues of the pipeline flange connection tool, the robot kinematics modeling method is adopted. Using the multi-body kinematics theory to homogeneous transformation matrix, the error model of deepwater pipe flange connection tool is established through total differential of the machinery pose transformation matrix. The error model of the tool is established by computer simulation, and the effect of the structure parameters on the bolt end pose error is analyzed. Based on the method of error matching design, the error in the deepwater pipe flange automatic connection tool is determined. Considering the specific structure of the connection tool, the adjusting mechanism for bolt angle error is also designed. Therefore, the hardware compensation of bolt angle error is achieved successfully, and it improves the positioning accuracy of the bolt end. Tests on bolt lead-in prototype are conducted. The experimental results show that the bolt could successfully lead into the nut and confirm the accuracies of the error model and design of the pipeline flange connection tool.
The drilling of deep wells has to face problems to suppress stick-slip vibrations, especially for tough formations. Such problems induce frequent tool failures and poor well quality. Torsional impact drilling is an emerging drilling technology for improving the productivity of oil and gas by mitigating the stick-slip vibration. In this paper, a high-frequency torsional impact generator has been developed in order to investigate this drilling technology. Mechanism of torsional impact as a means of stick-slip mitigation is studied. Structure and operating principle of the tool have been presented. The finite element analysis approach is utilized in the analysis of applicability of the impact unit which is most significant for the tool. The analysis indicates that the impact unit operates successfully. An experimental apparatus is developed to examine the applicability of the proposed numerical method to the analysis of the impact unit. Laboratory tests with different impact frequency are conducted with the apparatus. It is verified that the impact system operates regularly, and high-frequency torsional impacts are generated. In addition, impact parameters of the apparatus which will be helpful to the study of the high-frequency torsional impact drilling are obtained.
Instability of the interface between two immiscible fluids representing the so-called Kelvin–Helmholtz instability problem is studied using smoothed particle hydrodynamics method. Interfacial tension is included, and the fluids are assumed to be inviscid. The time evolution of interfaces is obtained for two low Richardson numbers Ri = 0.01 Ri = 0.1 while Bond number varies between zero and infinity. This study focuses on the effect of Bond and Richardson numbers on secondary instability of a two-dimensional shear layer. A brief theoretical discussion is given concerning the linear early time regime followed by numerical investigation of the growth of secondary waves on the main billow. Results show that for Ri = 0.01 , at all Bond numbers, secondary instabilities start in the early times after a perturbation is imposed, but they grow only for Bond numbers greater than 1. For Ri = 0.1 , however, secondary instabilities appear only at Bond numbers greater than 10. Finally, based on numerical simulations and using an energy budget analysis involving interfacial potential energy, a quantitative measure is given for the intensity of secondary instabilities using interfacial surface area.
In this paper, the laminar boundary layer flow of an electrically conducting micropolar fluid about a spinning cone with Hall current, Ohmic heating, and power-law variation in surface temperature is studied analytically. The governing equations are transformed into a dimensionless system of four nonlinear coupled partial differential equations. These equations have been solved analytically subject to the relevant boundary conditions by employing homotopy analysis method. The convergence of the obtained series solutions is carefully checked. Graphical results are presented to investigate the influence of the magnetic parameter, the Hall parameter, and the Eckert number on the axial velocity, the tangential velocity, the microrotation, and the temperature. For near the cone surface, the magnitude of microrotation velocity increases for free convection regime and decreases for forced convection regime as magnetic parameter increases, but the behavior is completely reversed as one moves away from the cone surface. Besides, in the immediate vicinity of the cone, the effect of increasing the Hall parameter is to increase very slightly the magnitude of microrotation velocity for free convection regime, while the magnitude of microrotation velocity decreases for forced convection regime as the Hall parameter increases, but the converse is apparent as one moves toward the edge of the boundary layer.
Traditional Euler angle-based methods for the kinematic and dynamic modeling of spherical joints involve highly complicated formulas that are numerically sensitive, with complex bookkeeping near local coordinate singularities. In this regard, exponential coordinates are known to possess several advantages over Euler angle representations. This paper presents several new exponential coordinate-based formulas and computational procedures that are particularly useful in the modeling of mechanisms containing spherical joints. Computationally robust procedures are derived for evaluating the forward and inverse formulas for the angular velocity and angular acceleration in terms of exponential coordinates. We show that these formulas simplify the parametrization of joint range limits for spherical joints, and lead to more compact equations in the forward and inverse dynamic analysis of mechanisms containing spherical joints.
Typical parallel mechanisms suffer from parallel singularity due to kinematic coupling of multichains. This paper investigates how to remove parallel singularities by using redundant actuations. First, actuation wrenches and constraint wrenches forming the full direct kinematic Jacobian matrix are derived. After briefly addressing conditions for their constraint singularities, Grassmann–Cayley algebra is employed to identify parallel singularities. Then, employing Grassmann line geometry, the locations and the minimum number of redundant actuators are identified for the parallel mechanisms to have parallel singularity-free workspace. Three different types of 3-degree-of-freedom parallel mechanisms such as planar, spherical, and spatial parallel mechanisms are given as exemplary devices.
Low-temperature heat sources such as waste heat and geothermal energy in the range from 100 °C to 200 °C are widely available and their potential is largely untapped. Stirling engines are one possibility to convert this heat to a usable power output. Much work has been done to optimise Stirling engines for high-temperature heat sources such as external combustion or concentrated solar energy but only little is known about suitable engine layouts at lower temperature differences. With the reduced temperature difference, changes become necessary not only in the heat exchangers and the regenerator but also in the operating parameters such as frequency and phase angle. This paper shows results obtained from a third-order simulation model that help to identify beneficial parameter combinations, and explains the differences of low and high-temperature engines.
Zero-stiffness structures have the remarkable ability to undergo large elastic deformations without requiring external work. Several equivalent descriptions exist, such as (i) continuous equilibrium, (ii) constant potential energy, (iii) neutral stability and (iv) zero stiffness. Each perspective on zero stiffness provides different methods of analysis and design. This paper reviews the concept of zero stiffness and categorises examples from the literature by the interpretation that best describes their working principle. Lastly, a basic spring-to-spring balancer is analysed to demonstrate the equivalence of the four different interpretations, and illustrate the different insights that each approach brings.
Electrodynamic suspension exploits repulsive forces due to eddy currents to produce positive stiffness by passive means, without violating the Earnshaw stability criterion. Systems employing this principle to levitate a rotor radial and/or axial degrees of freedom are called electrodynamic bearings (EDBs). Since the eddy currents can be induced either by using alternating current supplied electromagnets or by the relative motion between a conductor and a constant magnetic field, the research on EDBs has developed many different configurations. The present paper reviews the literature on electrodynamic passive magnetic bearings to analyze the evolution of this technology toward completely passive, stable, rotor levitation, and to compare the EDBs performance with other common magnetic bearing technologies. Radial and axial EDB technologies are reviewed attempting to create an organized connection between the works and to discuss some critical issues that still preclude the use of EDBs in industrial applications.
A numerical investigation of turbulent forced convection in a three-dimensional channel with periodic ribs on the lower channel wall is conducted. The lower wall is subjected to a uniform heat flux condition while the upper wall insulated. This study was conducted to investigate the forced convection, flow friction, and performance factor in a horizontal air and air/mist cooled rectangular duct, with various shaped ribs. Calculations are carried out for square ribs (case A), triangular ribs (case B), and trapezoidal ribs (case C and case D) cross sections over a range of Reynolds numbers (8000–20,000), constant mist mass fraction (6%), and fixed rib height and pitch. To investigate turbulence model effects, computations based on a finite volume method are carried out by utilizing three turbulence models: the standard k-, Omega Reynolds stress, and shear stress transport turbulence models. The predicted results from using several turbulence models reveal that the shear stress transport turbulence model provides better agreement with available measurements than others. It is found that the average mist cooling enhancement is about 1.8 times. The air/mist provides the higher heat transfer enhancement over air with trapezoidal-shaped ribs (38°, case C).
Concerning the problem of large rotating machinery like wind turbine which runs in low speed and non-stationary state, this research mainly focuses on separating fault trend feature from non-fault feature and the method of state deterioration evolution based on bi-spectrum. Firstly, the experimental signal such as low-speed startup vibration signal of rotor test rig in the normal state and a plurality of unbalanced state have been collected. Bi-spectrum method is applied to extract fault feature which submerged in complex background noise. On the basis of bi-spectrum analysis, the fault feature evolutionary matrix is defined to represent the state of equipment deterioration. The eigenvalues of fault feature evolutionary matrix are computed and fitted to a normal distribution curve, from which the mean value and variance are taken as fault feature parameters. Fault feature parameters are verified effectively by experiments. Finally, depending on fault feature parameters, graphical representation of state deterioration evolution is established. It is beneficial to provide guidelines for equipment deterioration trend. This method is applied to analyze the real vibration signal of wind turbine with the type of WD646/600 KW, and actual equipment condition verified the effectiveness of the proposed method.
A bond pull test is used to determine the strength of the bond of an electronic interconnect to a circuit board. A standard test consists of clamping and pulling the interconnect with a pair of microscopic jaws. In a successful test, the maximum pulling force registered by the jaws will be the failure load of the interconnect to circuit board bond. However, if the interconnect itself deforms before the bond has failed, then this would constitute an unsuccessful test. This paper reports on a theoretical analysis of the optimal geometry for gripping of a cylindrical interconnect. Upper and lower-bound plasticity models have been used to determine the jaw proportions that will maximize the load for the deformation of the interconnect and that should, therefore, be most likely to allow successful measurement of the bond strength. This theoretical analysis is compared to 2D and 3D non-linear finite element calculations. The 2D finite element models are axi-symmetric approximations of a pull test on a cylindrical interconnect. 3D finite element models take into account the actual jaw geometry and allow simulation of both clamping and pulling stages. The maximum calculated pull forces for both 2D and 3D simulations are in good agreement with the plasticity theory. Preliminary validation of the theory and finite element results has been accomplished through experimental clamping and pulling tests on cylindrical metal rods.
A novel type of lower extremity exoskeleton with series-parallel topology was described. Position analysis of a simplified leg was conducted to provide a basis of the kinematic accuracy reliability. Considering both assembly-machining errors and driving errors, the fuzzy reliability of kinematic accuracy was obtained based on the fuzzy probability theory. With a set of optimized length parameters and joint ranges of motion given, the fuzzy reliability of space distribution and the average fuzzy reliability were respectively calculated and shown in figures. These analyses of kinematic accuracy reliability provide a unique method to judge, analyze, and design exoskeleton mechanisms.
The paper describes the development of an innovative robotic gripper. To increase grasping stability without using too much space or causing control complexity, a three-phalanx underactuated finger is embedded in the gripper. This research mainly focuses on the mechanical design, kinematic, and static analyses of the robotic gripper. The results obtained through both simulation and experiments show good correlation with the analytical results. The preliminary experimental grasping results demonstrate that this robotic gripper with an embedded finger can successfully perform various activities of daily living.
This paper deals with an electromagnetic damper, which is composed of a permanent-magnet direct current motor, a ball screw, and a nut, as an active actuator. The main objective pursued in the paper is to study the active electromagnetic suspension system (AEMSS) considering hybrid control strategy (the hybrid control strategy is a linear combination of skyhook and groundhook control strategy). For this purpose, the nonlinear equations of the electric circuit of the AEMSS should be developed. Supposing linear conditions, the coefficients determination of the hybrid control strategy is carried out in the frequency domain using the genetic algorithm in order to improve the vehicle performance and energy regeneration simultaneously. Afterwards, the achieved coefficients are used to examine the designed AEMSS in the actual conditions for an actual road profile. The simulation results demonstrate that the designed AEMSS has the desired performance while energy can be regenerated from the road excitation and transformed into electric energy. Furthermore, it has been shown that the designed AEMSS regenerates energy during the ascent and descent of a bump and consumes energy near the top of the bump.
Solid lubricated bearings are commonly used in space mechanisms and other appliances, and their reliability analysis has drawn more and more attention. This paper focuses on the performance degradation analysis of solid lubricated bearings. Based on the vibration and friction torque signal of solid lubricated bearings, Laplace wavelet filter is adopted to process vibration signal and feature vector is constructed by calculating time-domain parameters of filtered vibration signal and original friction torque signal. Self-organizing map is then adopted to analyze the performance degradation based on extracted feature vectors. Experimental results show that this method can describe performance degradation process effectively.
The small flowrate and the diaphragm’s short life are two shortcomings of the diaphragm compressor. This paper presents a new generatrix of the cavity profile of a diaphragm compressor to increase cavity volume and decrease diaphragm's radial stress. To verify the design theory, the radial stresses on the oil side of the diaphragm in the cavities with the new and traditional generatrices were tested, and the experimental radial stresses agreed with the theoretical values. As the most important evaluation criteria of the cavity profile, the volumes of the cavities with different generatrices and the radial stress distribution of the diaphragm within were investigated under various design conditions. The results showed that the volume of the cavity with the new generatrix was about 6.5% larger than that with the traditional generatrix under the same design condition. Otherwise, with the same cavity volume and radius, the maximal radial stress of the diaphragm in the cavity with the new generatrix decreased by 10.3% stably, compared to that in the cavity with a traditional generatrix. Likewise, in the diaphragm’s centric region where the additional stress caused by the discharge holes occurred, the maximal radial stress of the diaphragm in the cavity with the new generatrix decreased about 11.5%.
Aluminum honeycomb core is one of the most sought after material for the sandwich panel for light weight applications. While the aluminum face sheet is isotropic, the honeycomb core assumes orthotropic characteristics due to its configuration and strenuous load transfer paths. It is now well established that stiffness, dynamic, and low velocity impact response of the honeycomb core sandwich panel are critically dependent on the elastic constants of the core. An attempt is made to determine the elastic constants of orthotropic core through finite element approach simulating the load transfer and fixity boundary conditions likely to be prevalent in the unit cell of the honeycomb core. The cell wall thickness and the cell shape dictated by plastic bending limitations have also been simulated to determine their influence on the elastic constants. Further, the cell wall thickness and the bend radius have been varied and their influence on orthotropic elastic constants has been determined. The results of the study have been compared with analytical solutions proposed by researchers. The finite element procedure evolved is a simple, efficient, and quick solution methodology to accurately predict elastic constants of honeycomb core depicting the exact cell size and shape.
The high-frequency corrosion fatigue behavior of extruded AZ31 magnesium alloy was investigated in different environments: air, gear oil and 3.5% NaCl solution. Compared with that in air, the corrosion fatigue limits were degraded by approximately 3.52% and 58.91%, respectively, and the corrosion fatigue lives were shortened by about 13.43% and 89.36%, respectively. In the same environment, the high-frequency fatigue limits are all higher than those tested at low frequency. The specimen geometrical shape plays a certain factor on stage characteristics of S–N curves. Compared with that of arc transition specimens, the stress sensitivity of line transition specimens is only reflected in a relatively high cycle fatigue life region. Different environments influence the corrosion failure kinetics processes (the crack initiation mechanism), but do not change the fatigue fracture mechanism of the alloy, and the higher loading frequency only accelerate the crack nucleation processes.
The determination of heat transfer coefficient plays an important role in optimal designing of heat transfer equipments as it directly affects the heat surface area and thereby the weight and cost of the equipment. Thus, prediction of heat transfer coefficient with minimum error reduces the exhaustive experimental work. Therefore, the prime objective of the present work is the application of computational intelligence methods for improving the prediction accuracy of heat transfer coefficient in flow boiling over tube bundles. The adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) are applied to predict the flow boiling heat transfer coefficient as output, taking pressure, pitch of the bundle, heat flux, mass flux and vapour quality as input. The performance of different derivatives of neural network such as multilayer perceptron, general regression neural network and radial basis network (RBF) is studied with varying the parameter. The ANFIS is tested with different types and number of membership functions for the prediction of flow boiling heat transfer coefficient. These methods are found to be better for predicting the flow boiling heat transfer coefficient than conventional correlations.
Using a sampling-based reliability-based design optimization method, we present a shape reliability-based design optimization method for coupled fluid–solid interaction problems. For the fluid–solid interaction problem in arbitrary Lagrangian–Eulerian formulation, a coupled variational equation is derived from a steady state Navier–Stokes equation for incompressible flows, an equilibrium equation for geometrically nonlinear solids, and a traction continuity condition at interfaces. The fluid–solid interaction problem is solved using the finite element method and the Newton–Raphson scheme. For the fluid mesh movement, we formulated and solved a pseudo-structural sub-problem. The shape of the solid is modeled using the Non-Uniform Rational B-Spline (NURBS) surface, and the coordinate components of the control points are selected as random design variables. The sensitivity of the probabilistic constraint is calculated using the first-order score functions obtained from the input distributions and from the Monte Carlo simulation on the surrogate model constructed by using the Dynamic Kriging method. The sequential quadratic programming algorithm is used for the optimization. In two numerical examples, the proposed optimization method is applied to the shape design problems of solid structure which is loaded by prescribed fluid flow, and this proves that the sampling-based reliability-based design optimization can be successfully utilized for obtaining a reliable optimum design in highly nonlinear multi-physics problems.
Cerebellar model articulation controller neural networks is one of the computational intelligence tools that can be applied for modeling, classification, and control. Proportional velocity controller is a servo-type controller, which is commonly applied to motion control systems. This paper presents a novel combination of cerebellar model articulation controller neural networks and optimal proportional velocity controller. A simple mathematical model for applying and studying cerebellar model articulation controller is introduced, and a study of its parameters is presented individually. The effect of parameters variation on cerebellar model articulation controller performance is identified. Learning algorithms highly affect the cerebellar model articulation controller behavior even when the parameters are optimized, and proper selection of the learning scheme must be taken under consideration. Three different learning algorithms are studied for evaluating transient and steady-state cerebellar model articulation controller responses. The results showed that the change of cerebellar model articulation controller generalization size and scale of the control signal has a marked effect on the performance of cerebellar model articulation controller. Furthermore, the constant learning rate algorithm gives the best overall performance.
For the structural systems with both epistemic and aleatory uncertainties, in order to analyze the effects of different regions of epistemic parameters on failure probability, two regional importance measures (RIMs) are firstly proposed, i.e. contribution to mean of failure probability (CMFP) and contribution to variance of failure probability (CVFP), and their properties are analyzed and verified. Then, to analyze the effect of different regions of the epistemic parameters on their corresponding first-order variance (i.e. main effect) in the Sobol’s variance decomposition, another RIM is proposed which is named as contribution to variance of conditional mean of failure probability (CVCFP). The proposed CVCFP is then extended to define another RIM named as contribution to mean of conditional mean of failure probability, i.e. CMCFP, to measure the contribution of regions of epistemic parameters to mean of conditional mean of failure probability. For the problem that the computational cost for calculating the conditional mean of failure probability may be too large to be accepted, the state dependent parameter (SDP) method is introduced to estimate CVCFP and CMCFP. Several examples are used to demonstrate the effectiveness of the proposed RIMs and the efficiency and accuracy of the SDP-based method are also demonstrated by the examples.
In this study, bending of composite open conical shell panels subjected to various distributed mechanical loads with various types of orthotropy is investigated. The stiffness coefficients are assumed to be functions of the meridional and circumferential coordinates in panels, which are produced by various methods for the realistic applications. In the first case of orthotropic open conical shell panels, the orientation of fibers are assumed to be in the meridional and circumferential directions. The stiffness coefficients of this type of fiber-reinforced panel are usually assumed to be constant. It is shown that due to the geometry of the conical surface, thickness of laminate will be changed along the meridional direction. The effect of stiffness variation on the response of panel is considered for the first time. In the case of open conical shell panel, which is fabricated by molding the prepreg layers around a conical-shaped mandrel, angle between fibers and meridional lines and, consequently, stiffness coefficients are assumed to be functions of the circumferential coordinates. In the third type, open conical shell panel can be made by cutting from a filament wound circular conical shell. In this case, thickness and ply orientation are functions of the shell coordinates. In this article, different path definitions for variable stiffness filament wound shells are considered. The inclusion of this geometric complicating effect in static analysis will add considerably to the complication and cost of a solution scheme. This article presents some results to show when these assumptions have a significant effect on the end result. The governing equations are based on the first-order shear deformation theory. The governing equations are discretized at whole domain grid points, and the boundary conditions are implemented exactly at boundary grid points using the generalized differential quadrature method. Application of the generalized differential quadrature to the governing equations, solution domain and boundary conditions leads to a system of algebraic equations. Various combinations of clamped, simply supported and free boundary conditions are implemented. It is found that the present method can accurately analyze fiber-reinforced open conical shell panels with various types of orthotropy.
We propose a 3-degree of freedom gravity compensator for the neck of a robotic face. The neck of the face robot is configured with yaw-pitch-pitch-roll rotations. Since the yaw rotation is made parallel to gravity, only the pitch-pitch-roll rotations are considered for gravity compensation. The 1-degree of freedom gravity compensator is located at the first pitch joint. A 2-degree of freedom gravity compensator equivalent to the existing gravity compensator is proposed and applied to the second pitch and roll rotations. A parallelogram is adopted between the first and second pitch rotations. One end of the 2-degree of freedom gravity compensator is attached at the parallelogram and the other is fixed at the face. Wires are used to realize a zero-length spring for all gravity compensators and all springs are located at the base for compact design. Experimental results for gravity compensation show that gravitational torques were effectively counterbalanced by the proposed 3-degree of freedom gravity compensator.
After earthquakes, residual inter-story drifts greater than 0.5% in buildings may indicate a complete loss of the structure from an economic point of view. Recently, research efforts have been extended to the utilization of superelastic shape memory alloy materials for the smart control systems that can automatically reduce the plastic deformation of the structure subjected to strong seismic loading. Superelastic shape memory alloys are unique metallic alloys that undergo substantial inelastic deformations and regain their original conditions when applied loads are removed, thus alleviating the problem of permanent deformation. The frame structures make the best use of such shape memory alloy’s recentering capability if the superelastic shape memory alloy segments used to replace the steel segments are installed at the part where large deformation is likely to occur. The primary focus of this study is on the seismic response of special steel concentrically braced frames and buckling-restrained braced frames, utilizing superelastic shape memory alloy braces. In order to examine the comparative residual inter-story drift response of both braced frames, 3- and 6-story buildings were designed in accordance with current code specifications, and then nonlinear time-history analyses for two seismic hazard levels were conducted on 2D analytical frame models. The braced frames with superelastic shape memory alloy bracing systems were also compared to those with conventional steel bracing systems. Overall, analysis results show that the superelastic shape memory alloy bracing systems are more effective in decreasing residual inter-story drifts than the conventional steel bracing systems.
Rule induction as a method of constructing classifiers is of particular interest to data mining because it generates models in the form of If-Then rules which are more expressive and easier for humans to comprehend and check. Several induction algorithms have been developed to learn classification rules. However, most of these algorithms are based on ‘crisp’ data and produce ‘crisp’ models. This paper presents FuzzySRI, a novel algorithm based on the techniques of fuzzy sets and fuzzy logic for inducing fuzzy classification rules. The algorithm possesses the clear knowledge representation capability of rule induction methods and the ability of fuzzy techniques to handle vague information. Experimental results show that FuzzySRI can outperform other fuzzy and non-fuzzy learning systems in terms of predictive accuracy, comprehensibility, and computational efficiency. It is also shown that FuzzySRI can be successfully applied to an industrial application concerning the automatic identification of machine faults.
Two-lane, "microscopic" (vehicle-by-vehicle) simulations of motorway traffic are developed using existing models and validated using measured data from the M25 motorway. An energy consumption model is also built in, which takes the logged trajectories of simulated vehicles as drive-cycles. The simulations are used to investigate the effects on motorway congestion and fuel consumption if "longer and/or heavier vehicles" (LHVs) were to be permitted in the UK.
Baseline scenarios are simulated with traffic composed of cars, light goods vehicles and standard heavy goods vehicles (HGVs). A proportion of conventional articulated HGVs is then replaced by a smaller number of LHVs carrying the same total payload mass and volume. Four LHV configurations are investigated: an 18.75 m, 46 t longer semi-trailer (LST); 25.25 m, 50 t and 60 t B-doubles and a 34 m, 82 t A-double. Metrics for congestion, freight fleet energy consumption and car energy consumption are defined for comparing the scenarios. Finally, variation of take-up level and LHV engine power for the LST and A-double are investigated.
It is concluded that: (a) LHVs should reduce congestion particularly in dense traffic, however, a low mean proportion of freight traffic on UK roads and low take-up levels will limit this effect to be almost negligible; (b) LHVs can significantly improve the energy efficiency of freight fleets, giving up to a 23% reduction in fleet energy consumption at high take-up levels; (c) the small reduction in congestion caused by LHVs could improve the fuel consumption of other road users by up to 3% in dense traffic, however in free-flowing traffic an opposite effect occurs due to higher vehicle speeds and aerodynamic losses; and (d) underpowered LHVs have potential to generate severe congestion, however current manufacturers’ recommendations appear suitable.
A reliable prediction method is very important to avoid a catastrophic failure. This paper presents a novel method for machinery condition prognosis, named least squares support vector regression strong tracking particle filter which is based on least squares support vector regression combing with strong tracking particle filter. There are two main contributions in our work: first, the regression function of least squares support vector regression is extended, which constructs a bridge for the application of combining data-driven method with a recursive filter based on extend Kalman filter; second, an extend Kalman filter-based particle filter is studied by introducing a strong tracking filter into a particle filter. The strong tracking filter is used to update particles and produce importance densities which can improve the performance of the particle filter in tracking saltatory states, and finally strong tracking particle filter improves the prediction performance of least squares support vector regression in predicting saltatory states. In the experiment, it can be concluded that the proposed method is better than classical condition predictors in machinery condition prognosis.
The latest trend in the cell phone component industry to use aluminium and magnesium alloys has resulted in the advanced processing technologies. Semi-solid forming process that is advantageous for the mass production of thin parts with complex shapes have been of interest as a promising tool for near net-shape manufacturing. This study describes a semi-solid forming process for the development of a 1 mm-thick cell phone case by using the rheological material prepared by electromagnetic stirring equipment. Thus, a new type of die design for indirect rheoforging was proposed to efficiently control the primary α-Al phase particles in the thin part under rheological conditions. Their microstructure and mechanical properties were investigated and compared to parts produced without electromagnetic stirring. Those products fabricated by electromagnetic stirring had better mechanical properties and globular microstructures than those fabricated without electromagnetic stirring. Several processing parameters such as punch velocity (30 mm/s), punch pressure (75–250 MPa), stirring time (10 s), and solid fraction (0–20%) were used. The optimal condition that resulted in a defect-free component with the improved mechanical properties was explained and discussed.
The forward displacement analysis of spherical parallel mechanisms is a nonlinear problem and has attracted the attention of many researchers. A method is proposed to analyze the forward displacement of a 3-RPR spherical parallel mechanism. Firstly, based on spherical geometry and spherical trigonometry theory, a mathematical model is derived for the forward displacement analysis of the spherical parallel mechanism. After simplifying the mathematical model, the kinematical equations are then solved using the resultant elimination method. Using this method, one can obtain the three variables representing the position and pose of the moving platform directly. Finally, a numerical example is presented and Autodesk Inventor software is used to verify all the real solutions. The method of mathematical modeling, equation simplification, resultant elimination presented in this paper can be extended to solve similar problems effectively.
Gate valves, which are widely applied in pneumatic conveying systems, are vulnerable to erosion by particles. It is thus important to investigate the erosion in gate valves from the perspective of fluid analysis, and then to predict and improve their lifetimes. The effects of valve geometry and gas–solid flow conditions on valve erosion are investigated. Since a gate valve usually operates fully open to let fluid pass through, the geometry is simplified as a cavity. As gate valves are always placed horizontally in industrial situations, investigated cavities are placed horizontally, and the erosion damage to the bottom half of the aft wall (surface T), which is most likely to be eroded, is studied. A computational fluid dynamics (CFD) based two-way Eulerian–Lagrangian procedue is used to predict the erosion severity. The simulation procedure is validated by comparing the CFD results with those obtained from experiments of a pipe and an elbow, and also with the erosion region of a damaged valve. For convenience, the total erosion ratio, defined as the ratio of the mass eroded on a particular surface to the total particle mass passing through the pipe inlet during the same time, is introduced. The results show that the total erosion ratio of surface T is largely independent of the mass flux ratio, pipe diameter and cavity depth. Meanwhile, the total erosion ratio increases with cavity width and particle diameter, while it decreases with inlet velocity. According to the fitted results, a simple erosion formula is proposed and validated by the CFD results in another 16 orthogonal experiments. Furthermore, the formula is improved for various values of Brinell hardness of carbon steel and sharpness factors of particles.
Electrical runout is a bottleneck problem of eddy current sensor, which is caused by the maldistribution/variation of material electromagnetic properties of measurement target. However, extraction methods of electrical runout in eddy current displacement measurement remain ambiguous. Here, a 2D finite element model for the influence analysis of conductivity and permeability of ferromagnetic material on coil impedance of eddy current sensor is reported, which will be beneficial for detecting material properties and guiding manufacturing process. The relationships between the real and imaginary part of coil impedance with the varied material conductivity, relative permeability and the lift-off, which indicates the detecting distance, are investigated. When the conductivity, relative permeability of ferromagnetic material and the lift-off vary within a certain range, the relationships between the real and imaginary part of coil impedance are all nearly linear. This paper further shows that the character of distribution of resistance and reactance in diagram under different material properties and same measuring distance is linear. Furthermore, these lines under different measuring distances are parallel. Also the character under different measuring distances and same material property is linear, but these lines under different material properties are diffuse with same intercept. Altogether, the study shows that this method based on redesign of signal processing and its circuit is feasible and instructive in separating electrical runout from the output of eddy current sensor.
Wind tunnel balance is one of the most important measurement equipments in aerodynamic testing. In this paper, a new six-component piezoelectric balance is developed to measure the dynamic impact loading force in the wind tunnel. The arrangement mode of the triaxial piezoelectric load cells is confirmed based on the theory analysis. Furthermore, the mathematical model is established according to the calibration experimental results. Support vector machine is proposed to develop the piezoelectric balance calibration. It is an effective method to predict the model using small samples and reduce the duration of the calibration. The results of prediction are compared to the conventional calibration and the dynamic step response. The linearity and repeatability of the balance are within 0.2% and 0.5%, respectively, and the interference error has been reduced using the support vector machine method. The experimental results have shown that the four supports arrangement mode can reduce the area of attack and enhance the measuring range of the balance. The dynamic characteristics of the piezoelectric balance performed by the step response test show that the designed balance is feasible to measure the dynamic impact airloads in a wind tunnel.
The paper presents kinematic and dynamic investigations of the main press forming mechanism of a thermoforming machine. A multibody analysis of this press forming mechanism, which lifts and rotates a press bed, was carried out. Press bed lifting, which is necessary to form the component, is performed by means of a first rod and toggle mechanism. Press bed rotation to eject the formed component is produced by means of a second rod and must be appropriately shifted. These rods are oscillating followers driven by cams, making it possible to precisely define trajectories as a function of the motor shaft rotation angle.
Analysis is performed by numerically solving the equations of motion. Cam synthesis on the basis of the oscillating followers’ trajectories makes it possible to obtain cam profiles in order to evaluate pressure angles and check that there is no undercutting. System dynamics is investigated in order to evaluate motor torque and analyse internal stresses on the hinges. In addition, some experimental results and those obtained with the dynamic model are compared. Performance improvement of the actual machine is carried out by modifying the trajectory of the press bed by means of a numerical code at the purpose developed. This approach is more convenient than the use of a commercial multibody code, which is not specifically built for parametric studies.
Vibration signals are usually affected by noise, which is in turn related to the measurement and data processing procedures. This paper presents a new subband adaptive denoising method for detective impulsive signatures based on minimum description length principle with improved normalized maximum likelihood density model. The threshold of the proposed denoising method is determined automatically without the need to estimate the noise variance. The effectiveness of the proposed denoising method over VisuaShrink, BayesShrink and minimum description length denoising methods are given through simulation and practical applications.
The efficient and easy computational implementation of multibody dynamic formulations is an important issue. In this paper, a parametric generalized coordinate formulation is proposed as a new approach to formulate joint constraint equations. By introducing the parametric generalized coordinates in the constraint equations, the complexity of the equations is significantly reduced. The number of arithmetic operations required to compute the derivatives of the constraints is drastically decreased depending on the type of joint involved (i.e. especially when the proposed method is applied to joints having lower degrees of freedom). Furthermore, the second derivatives of the constraint equations tend to have a large portion of zero sub-matrices, which simplifies the system matrix of the governing equations and allows for application of efficient sparse matrix techniques. Although the proposed approach has the drawback of a larger set of coordinates than a conventional Cartesian coordinate approach resulting in slightly less efficient computation, a systematic and easy formulation is achieved, which may relieve the implementation complexity for program developers. The dynamic analysis of a multibody slider-crank system is carried out to demonstrate the validity of the proposed formulation.
Vibration analysis of axially moving functionally graded plates with internal line supports and temperature-dependent properties is investigated using harmonic differential quadrature method. The plate is subjected to static in-plane forces while out-of-plane loading is dynamic. Stability of an axially moving plate, traveling at a constant velocity between different supports and experiencing small transverse vibrations are considered. The series of internal rigid line supports parallel to the plate edges are considered together with various arbitrary combinations of boundary conditions. Material properties of the plate are assumed temperature-dependent which is a non-linear function of temperature and differ continuously through thickness according to a power-law distribution of the volume fractions of the plate constituents. Two types of micromechanical models, namely, the Voigt and Mori–Tanaka models are considered. Based on the classical plate theory, the governing equations are obtained for functionally graded plate using the Hamilton’s principle. In the frame of a general dynamic analysis, it is shown that the onset of instability takes place in the form of divergence. The plate may experience divergence or flutter instability at a super critical velocity. Results for dynamic analysis of isotropic and laminated plates are validated with available data in the existing literature, which show excellent agreement. Furthermore, some new results are presented for vibration analysis of functionally graded material plates to study effects of the location of line supports, material properties, volume fraction, temperature, loading, aspect ratio and speed.
Extreme Learning Machine (ELM) is a novel single-hidden-layer feed forward neural network with fast learning speed and better generalization performance compared with the traditional gradient-based learning algorithms. However, ELM has two issues: the hidden node number of ELM needs to be predefined and the random determination of the input weights and hidden biases lead to ill-condition problem. In this paper, a two-stage evolutionary extreme learning machine (TSE-ELM) algorithm was proposed to overcome the drawbacks of original ELM, which used an improved artificial bee colony (ABC) algorithm to optimize the input weights and hidden biases. The proposed TSE-ELM algorithm was applied on the UCI benchmark datasets and rolling bearing fault diagnosis. The numerical experimental results demonstrated that TSE-ELM had an improved generalization performance than traditional ELM and other evolutionary ELMs.
In this work, a model of a rider and snowboard is presented. The snowboard is modelled as two rigid one-dimensional sections connected by a frictionless pin-joint linked by a torsional stiffness and the rider by a mass at a fixed height above the snowboard, which can move longitudinally. The model is simplified to allow the fundamental behaviour of the snowboard and rider to be investigated for a number of manoeuvres used by learners. The behaviour of the rider is shown to be related to the angle of lean and it is conjectured that the rider might attempt to achieve consistency of response by moving their centre of mass longitudinally. The response of the model in open-loop is difficult to control, and to overcome this, two control loops are designed for the lateral velocity and yaw angle of the snowboard. The model is shown to recreate a number of manoeuvres that are used to help people to learn to ride snowboards.
A ball joint is an automobile component that connects control arm to knuckle part. The ball joint can also be installed in linkage systems for motion control applications. This work describes a simulation strategy for a ball joint analysis, considering the manufacturing process. The manufacturing process can be divided into plugging and spinning processes. The dynamic analyses for the caulking process, made of plugging and spinning, are sequentially performed. Then the interested responses are selected as the stress distribution generated between the ball and bearing and the gap displacement. In this work, DAFUL software, using an implicit integration method, is introduced to calculate the responses. In addition, optimization problems that minimize the stress distribution and axial displacement are solved, by adopting the Kriging metamodel.
The main advantage of polychromatic sets-based assembly tolerance representation model is that the number of feature types to be processed is larger. However, the number of recommended assembly tolerance types generated by the model is somewhat large for the same feature surfaces. Furthermore, the model cannot be directly applied to further assembly tolerance analysis and synthesis due to the fact that the information of degrees of freedom cannot be processed in polychromatic sets. To further reduce the number of recommended assembly tolerance types and to lay foundation for further assembly tolerance analysis and synthesis, a spatial relation layer is introduced into the polychromatic sets-based model and an assembly tolerance representation model based on spatial relations for generating assembly tolerance types is proposed. The proposed model is hierarchically organized and consists of part layer, assembly feature surface layer, spatial relation layer and assembly tolerance type layer. Each layer is defined with an adjacency matrix, respectively. By the mapping from spatial relations to assembly tolerance types, the number of recommended assembly tolerance types generated by the mapping from feature surfaces to assembly tolerance types is able to be further reduced. In addition, the information of degrees of freedom can be attached in the elements of adjacency matrices when recommended assembly tolerance types are generated by spatial relations so that the proposed model can be directly applied to further assembly tolerance analysis and synthesis. The effectiveness of the proposed model is demonstrated by an approach for generating assembly tolerance types and a practical example.
The viscous, incompressible and laminar flow around rectangular cross sections is simulated via a Cartesian-Staggered grid finite volume method for various of aspect ratios. Simulations were carried out for a range of 10–150 Reynolds number and aspect ratios of 0.5–4. In the present work, The Great-Source Technique is used to satisfy directly the no slip condition. The grid is refined in the same size in the back and front regions of the body, but for increasing computation accuracy, the region of rectangular section has been refined more. Because of widespread application of rectangular cross sections and less attendance on it than circular sections, especially in laminar flow and low Reynolds, the aim of this study is to investigate the range of harmonic instability and estimation of its critical Reynolds number. For this purpose, The shedding frequency and The variation of lift and drag coefficients with time and Reynolds numbers have been analyzed for various of aspect ratios. The results show that increase in aspect ratios leads the rise in critical Reynolds number.
The three-dimensional pressure- and shear-driven flow phenomena in a circular recess of hydrostatic rotary table in heavy-duty computer numerical control machines is very complicated and has not been fully explored. Navier–Stokes equations have been applied through the whole flow region using a finite volume approach to explore this complicated flow phenomena, including the influences of feeding Reynolds number (Rei), sliding Reynolds number (Res) and the recess geometry on flow behaviors. A test rig based on a particle image velocimetry was built to compare experimental and numerical results, finding a good agreement for stationary cases. The results show that the flow patterns in the recess are very complex and four three-dimensional vortices exist at Rei = 448 and Res = 74.6. Four flow states are defined according to the structure of the vortices. Different sectional profiles of the streamlines and velocity vector fields are examined to reveal the mechanism of pressure- and shear-driven flow interactions. The results of influences of recess geometry on flow states and pressure patterns are intended to contribute to represent a database in view of the hydrostatic rotary table theoretical modeling.
In order to realize non-contact transportation of a heavy load object that is more than 3N at a stable speed, a new hybrid suspension transportation utilizing both ultrasonic and aerostatic suspension is put forward. The resonant frequency of the hybrid suspension system, the fixed position of transducer and the matching impedance are analyzed using ANSYS software, Eular–Bernouli beam theory and equivalent circuit principle of transducer, respectively. Several physical parameters that influence the driving ability of traveling wave are also analyzed. Based on the optimal results obtained, the prototype of hybrid suspension is designed and manufactured in the experiment. The experimental system result shows that the hybrid suspension utilizing both ultrasonic and aerostatic suspension can realize non-contact transportation of heavy load objects at the stable speed and experimental results coincide well with the theoretical analysis results. The test result shows that the transport speed of suspended objects under hybrid suspension is larger than that only under ultrasonic suspension. A 75 x 60 mm object of 432 g, with surface density of 96 kg/m2, is transported at the stable speed of 4.2 cm/s when excitation voltage is 300 V and inlet pressure is 0.15 MPa.
This paper deals with an experimental investigation to measure the frictional pressure drops for two-phase flow boiling in a micro-channel with a hydraulic diameter of 500 µm. First, the experimental study is performed under the test conditions: heat fluxes ranging from 100 to 400 kW/m2, vapor qualities from 0 to 0.2, and mass fluxes of 200, 400 and 600 kg/m2s. Then, the frictional pressure drop during flow boiling is estimated using two models: the homogeneous model and the separated flow model. The experimental results show that the two-phase multiplier decreases with the increase of mass flux. In addition, the measured pressure drops are compared with those from a few correlation models available for macro-scales and mini/micro-scales. Finally, the present paper proposes a new correlation for two-phase frictional pressure drops in mini/micro-scales. This correlation model is developed based on the Chisholm constant C as a function of two-phase Reynolds and Weber numbers. It is found that the new correlation satisfactorily predicts the experimental data within mean absolute error (MAE) of 3.9%.
This paper is concerned with the vibration characteristics of an embedded nanoplate-based nanoelectromechanical sensor made of polyvinylidene fluoride (PVDF) carrying a nanoparticle with different masses at any position. The nanoplate is surrounded by elastic medium which is simulated as Pasternak foundation. The PVDF nanoplate is subjected to an applied voltage in the thickness direction. In order to satisfy the Maxwell equation, electric potential distribution is assumed as a combination of a half-cosine and linear variation. Adopting the nonlocal Mindlin plate theory, the governing equations are derived based on the energy method and Hamilton’s principle which are then solved by Galerkin method to obtain the natural frequency of the nanoplate. A detailed parametric study is conducted to elucidate the influences of the nonlocal parameter, external electric voltage, position and mass of nanoparticle, temperature changes and dimension of nanoplate and elastic medium. Results indicate that the frequency is increased as the nanoparticle comes closer to the center of the nanoplate; also increasing mass of the nanoparticle decreases the frequency of the system. This study might be useful for the design of PVDF nanoplate-based resonator as nanoelectromechanical sensor.
In this paper, we focus on the design requirement of a high-precision magnetic resonance imaging-compatible robot for prostate needle-insertion surgery, which is actuated by five ultrasonic motors to achieve the goal of needle posture adjustment and prostate puncture. After a brief introduction to the robot, the direct and inverse kinematic equations are deduced. In order to show the relationship of the velocity between the actuators and the end effector, the Jacobian matrix is derived by formulating a velocity closed-loop equation for each limb. The kinematics is carried out by minimizing a global and comprehensive dimensional synthesis conditioning index subject to transmission angle and range of motion of the mechanism constraints. The dimensional parameters are obtained for achieving a good kinematic performance throughout the entire task workspace by an example, and finally the reachable workspace of the robot is calculated.
Rolling element bearings are widely used in modern machinery and play an important role in industrial applications. Tough environments under which they work make them subject to failure. The classical strategy is to collect bearing vibration signals and denoise the signals to detect fault features by using signal processing techniques. Although the noise is reduced with this strategy, the fault features may be weakened or even destroyed as well. Different from the classical denoising techniques, stochastic resonance is able to extract weak features embedded in heavy noise by utilizing noise instead of eliminating noise. The single stochastic resonance, however, fails to extract the fault features when the signal-to-noise ratio of the bearing vibration signals is very low. To address this problem, this paper investigates the enhancement methods of stochastic resonance and develops a cascaded stochastic resonance-based weak feature extraction method for bearing fault detection. Two sets of vibration signals collected respectively from an experimental bearing and a bearing inside a train wheel pair are utilized to demonstrate the proposed method. The results show that the method is superior to the other enhancement methods in extracting weak features of bearing faults.
In this paper, a method based on coordinate equivalence was presented to investigate the characteristic parameters of angular contact ball bearing such as contact angle and contact force between ball and raceways subjected to the combined radial, axial and moment loads, with considering the effects of centrifugal force and gyroscopic moment in high-speed conditions. The radial, axial and angular displacements are solved based on Newton–Raphson method rather than as the known variables. The method simplifies the procedure involved in determining derivatives for Newton–Raphson method. The results show good agreement with existent model and can be used to analyze the bearing performance, especially for high-speed condition. It was also shown that the inertial loads resulting from the high-speed condition have significant effect on the contact angle and contact force between ball and raceways and have to be considered in the bearing design and performance analysis.
In the course of expansion in turbines, steam first supercools and then nucleates to become a two-phase mixture. The fluid then consists of a very large number of extremely small droplets which are carried by and interact with the parent vapour. The formation and subsequent behaviour of the liquid phase cause problems which lower the performance of the wet stages of steam turbines. To treat such flows the general conservation equations governing the whole field are combined with those describing droplet nucleation and growth and the set treated numerically. The article examines the solution of throughflows of nucleating steam in a turbine stage using a time-marching technique. The treatment which is the refinement of an earlier one has been applied to the flow in a turbine stage. Comparisons are presented between the results of theoretical solutions and direct measurements upstream and downstream of the nucleating stage and the agreement obtained is good.
In this paper, an experimental characterisation of a particle impact damper (PID) under periodic excitation is investigated. The developed method allows the measurement of damping properties of PID without the supplementary use of a primary structure. The passive damping of PID varies with the excitation frequency and its design parameters. The nonlinear damping of PID is then interpreted as an equivalent viscous damping to be introduced in a finite element model of a structure to predict its dynamic response. The results of numerical simulations are in good agreement with those of experiment and show the relevance of the developed method to predict the dynamic behaviour of a structure treated by PID’s.
The improvement of direct human–robot physical interaction has recently become one of the strongest motivation factors in robotics research. Impedance/admittance control methods are key technologies in several directions of advanced robotics such as dexterous manipulation, haptics and telemanipulation. In this paper, we propose a control scheme and a design technique for stabilising shared impedance/admittance-based bilateral telemanipulation under varying time delay. The proposed scheme introduces delay-adaptive non-linear damping to stabilise the impedance model. A modified version of the tensor product model transformation is applied to determine the tensor product type polytopic linear parameter varying (LPV) representation of the impedance controlled interaction model, such that the value of the actual time delay becomes an external parameter rather than an inherent property of the system. The main benefit of the proposed approach is that the model form it produces is amenable to the immediate application of modern, linear matrix inequality (LMI)-based multi-objective synthesis methods. The viability of the proposed methodology is demonstrated through a single DoF force reflecting tele-grasping application. The results are also confirmed through laboratory experiments which help to further highlight the perspectives of this novel approach.
In this study, a finite volume method for the steady thermoelastic analysis of the functionally graded materials is presented. The method is validated in a benchmark case from the published paper. By incorporating the variation of material properties in the discretization process, the method is able to avoid discontinuous distributions of stresses. Two different formulations for the calculation of variable gradients are assessed. The numerical results show that the least square method achieves better performances than the Gaussian method but least square method costs slightly more iteration and computer memory under different mesh types. Then the method is applied to analyze thermoelastic problems of the functionally graded circular rotating disk under different conditions. The effects of thickness, material properties, reference temperature and temperature difference between the inner and outer surfaces on the thermoelastic performance of the disk have been studied.
This article develops a new output feedback tracking control scheme for uncertain robot manipulators with only position measurements. Unlike the conventional sliding mode controller, a quasi-continuous second-order sliding mode controller (QC2C) is first designed. Although the QC2C produces continuous control and less chattering than conventional sliding mode and other high-order sliding mode controllers, chattering exists when the sliding manifold is defined by the equation s = ⋅ = 0. To alleviate the chattering, an adaptive fuzzy QC2C (FQC2C) is designed, in which the fuzzy system is used to adaptively tune the sliding mode controller gain. Furthermore, in order to eliminate chattering and achieve higher tracking accuracy, quasi-continuous third-order sliding mode controller (QC3C) and fuzzy QC3C (FQC3C) are investigated. These controllers incorporate a super-twisting second-order sliding mode observer for estimating the joint velocities, and a robust exact differentiator to estimate the sliding manifold derivative; therefore, the velocity measurement is not required. Finally, computer simulation results for a PUMA560 industrial robot are also shown to verify the effectiveness of the proposed strategy.
This paper investigates the dynamic behavior of microcantilevers under suddenly applied DC voltage based on the modified couple stress theory. The cantilever is modeled based on the Euler–Bernoulli beam theory and equation of motion is derived using Hamilton’s principle. Both analytical and numerical methods are utilized to predict the dynamic behavior of the microbeam. Multiple scales method is used for analytical analysis and the numerical approach is based on a hybrid finite element/finite difference method. The results of the modified couple stress theory are compared with those from the literature as well as the results predicted by the classical theory. It is shown that the modified couple stress theory predicts size-dependent normalized dynamic behavior for the microbeam while according to the classical theory the normalized behavior of the microbeam is independent of its size. When the thickness of the beam is in order of its material length scale, the difference between the results given by the modified couple stress theory and those predicted by the classical theory is considerable. As the beam thickness increases, the results of the modified couple stress theory converge to those of the classical theory.
Nonlinear vibration and instability of embedded double-walled carbon nanocones subjected to axial load are investigated in this article based on Eringen's nonlocal theory and Timoshenko beam model. The elastic medium is simulated as Pasternak foundation and the van der Waals forces between the inner and the outer layers of double-walled carbon nanocones are taken into account. Using von Kármán geometric nonlinearity, energy method and Hamilton’s principle, the nonlocal nonlinear motion equations are obtained. The differential quadrature method is applied to discretize the motion equations, which are then solved to obtain the nonlinear frequency and critical fluid velocity of viscous-fluid-conveying double-walled carbon nanocones. A detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, thickness-to-length ratio, temperature change, apex angles, elastic medium and van der Waals forces on the dimensionless frequency and critical buckling load of double-walled carbon nanocones. The results show that the small-size effect on the nonlinear frequency is significant and cannot be neglected; also, the nonlinear frequency and critical buckling load decrease with increasing the cone apex-angle.
The oblique circular torus (OCT) and its main geometric properties are introduced. Intrinsic vector calculation is utilized to mathematically describe the OCT. The coordinate-free approach leads to the algebraic equation of an OCT in a privileged Cartesian reference frame. The OCT equation is used to confirm a theorem of Euclidean geometry. In a broad category of OCT, through any point five circles can be drawn on the surface, namely the parallel of latitude and four circular generatrices whose planes pass through the OCT center of symmetry. In the special case of a right circular torus, the Villarceau theorem is verified. Next, consider the four RRS open chains whose S spherical-joint centers move on the same OCT and their possible in-parallel assemblies in single-loop RRRS chains. From a category of the foregoing RRRS chains, a new derivation of the amazing Bennett 4R linkage is proposed. Two kinds of Bennett linkages are further verified and each kind contains two enantiomorphic or symmetric linkages. Four types of Bennett linkages associated with one OCT are established by uniquely specifying the link twist as an acute value. Two cases of special type, rectangular and equilateral configurations, are also confirmed.
Based on the three-dimensional design platform, this article conducted parametrization of blade leading and trailing edge positions, and analyzed the influence of different position parameters on mixed-flow pump hydraulic performance and internal flow with model test and numerical simulation. The results showed that the hydraulic efficiency of a mixed-flow pump increased slightly when the position parameter h of the blade leading edge on the hub increased, and increased significantly when the position parameter t of the blade leading and trailing edge positions on the shroud increased. However, with t increasing, the growth rate of decreased. Numerical simulation has shown that by selecting a proper value of t, the impeller energy conversion capacity can be effectively improved, and the distributions of static pressure and total energy can be more uniform in the flow passage. Meanwhile, with t increasing, blade angle on the blade trailing edge decreased. Correspondingly, the absolute velocity in the outlet zone decreased, and the hydraulic loss in the outlet zone also decreased, which is beneficial to improving hydraulic efficiency of the mixed-flow pump. Within the value range of 7–9°, with different combinations of position parameter t1 of the blade leading edge on the shroud and position parameter t2 of the blade trailing edge on the shroud, the mixed-flow pump hydraulic efficiency and blade wrap angle show a linear positive correlation, suggesting that an increase in could significantly improve impeller energy conversion capacity. Compared to t1, t2 has a more significant influence on and . Thus, the value of t2 should be carefully attended to during design process.
Several dynamic models are proposed for the contact analysis of a tensioned beam with a moving oscillator. Depending on whether the strain and stress used to derive the equations of motion are nonlinear, four models are established to analyze the beam deflections and the contact force between the beam and moving oscillator. We find that the differences in the contact forces and deflections computed with the models become large as the beam tension and moving velocity decrease and the natural frequency ratio of the oscillator to the beam increases. The nonlinear model derived with nonlinear strain and stress is desirable for an accurate analysis.
This article aims at modeling, analysis and design of a passive vibration isolation system using a magnetic damper with high efficiency and compactness. The experimental set-up was developed for a single degree-of-freedom vibration isolation system, where the damper consists of two elements: an outer stationary conducting tube made up of copper and a moving core made up of an array of three ring-shaped neodymium magnets of Nd–Fe–B alloy separated by four block cylinders made of mild steel that are fixed to a steel rod. The generation of eddy currents in the conductor and its resistance causes the mechanical vibration to dissipate heat energy. The vibration response of the system is obtained starting from a low-frequency range. The proposed magnetic damper achieves a maximum transmissibility value less than two for a natural frequency that is less than 10 Hz and the excitations at higher frequencies are successfully isolated. Numerical and experimental studies were carried out for a range of system parameters which show that isolators based on magnetic damping could be very effective for passive vibration isolation. Further, a theoretical model for an active isolation system is proposed in order to reduce the transmissibility at resonance. It is envisaged that the combined active–passive eddy current damper could be effectively used for vibration isolation.
This article describes the theoretical analysis and experimental verification of the influence of variations of leakage flow as well as ideal flow on delivery pressure ripple in a balanced vane pump. The analytical model for simulating the delivery pressure ripple of the pump is simplified. It is composed of only the ripple of the ideal flow based on the theoretical pump displacement determined from geometrical pump dimensions, the leakage flow variation dependent on the pump dimensions including clearances and pump-operating conditions, an oil chamber volume in the pump and the impedance of a hydraulic circuit with a throttle valve set close to a pump outlet. The purpose of this study is to predict the pump delivery pressure ripple at the design stage of the vane pump. This article reveals that the delivery pressure ripple can be theoretically predicted through the calculations of the leakage flow as well as the ideal flow. The waveform of the delivery pressure ripple calculated agrees well with the measured one. The leakage flow variation significantly affects the delivery pressure ripple and it can be also calculated accurately from the pump dimensions including the clearances and pump-operating conditions. In addition, the components of the leakage flow are clarified and their effects on the delivery pressure ripple are investigated.
In this paper, a new kind of six-parallel-legged robot is presented. It is designed for drilling holes on the aircraft surface. Each leg of the robot is a 3-DOF parallel mechanism with three chains: 1UP and 2UPS. The three prismatic joints are active joints and can be controlled either by position or by force. First, the task process and the gait plan are discussed and then, according to the requirement, the control method is introduced. After that, the mechanism topology patterns under different working conditions are studied and the control mode of each motor is determined. Then the kinematical model is built up, based on which the position control curves can be obtained. The simulation result shows that the robot can walk pretty well on the fuselage surface and that the actuation forces are quite smooth. Furthermore, the first prototype has been manufactured and some experiments such as walking and manipulation have been done.
Dynamic modeling and mechanics analysis of a novel pneumatic muscle driven parallel mechanism for imitating human pelvis (PMPMHP) is investigated. The PMPMHP has some advantages for both parallel structure and pneumatic muscle actuator. To begin with, the kinematic model of the PMPMHP is introduced and the dimensions of the PMPMHP are optimized by using genetic algorithm. Then, the dynamic model is developed on the basis of Newton–Euler method and ideal gas law. After that the workspace, singularity and stiffness of the PMPMHP are analyzed. At the end, simulation results indicate the feasible operation performances of the PMPMHP. This mechanism can be further utilized either for rehabilitation therapy of human pelvises or for humanoid robot design of the pelvis part.
Multi-rigid-body system dynamics can be used to investigate the dynamics of a mechanical system of rigid bodies while the finite element method is often utilized to model the quasi-static elastic deformations of an elastic structure. However, neither of these two methods can resolve the real dynamics of a mechanical system when both rigid displacements and elastic deformations coexist. Therefore, this article proposes a meshing method to simulate the mechanical system with uniform mass point movements. To split the specified solid structure into a set of regularly distributed dynamic units, one can assume that the mass density of the structure is evenly distributed within the whole concrete volume and the elasticity and damping of the material are isotropic. Then the whole solid structure of each component can be divided into a number of tetrahedrons the vertexes of which are the points with the mass parameters. The original distances between every pair of adjacent points are supposed to be identical, and the stiffness and the damping coefficients are introduced to formulate the internal and external dynamics of the adjacent mass points. To illustrate the correction and effectiveness of the method, the dynamics problems of a number of regular elastic bodies are investigated with large rigid displacements accompanying elastic deformations. Computer simulations demonstrate that this method is especially useful for real mechanical systems where the rigid displacements and elastic deformations coexist.
A mathematical model of the acoustic emission signal during a grinding cycle is proposed for the monitoring of material removal in precision cylindrical grinding. Acoustic emission signals generated during precision grinding are sensitive to forces in grinding and present opportunities in accurate and reliable process monitoring. The proposed model is developed on the basis of a traditional grinding force model. Using the developed model, a series of experiments were performed to demonstrate the effectiveness of the acoustic emission-sensing approach in estimating the time constant and material removal in grinding. Results indicate that acoustic emission measurements can be used in the prediction of material removal in precision grinding with excellent sensitivity.
Dynamic analysis of a functionally graded piezoelectric spherical shell under the effect of mechanical-electrical-thermal shocks is carried out. Thick spherical shell is transversely isotropic and material properties are assumed to be graded in the radial direction according to a power law function. The governing partial differential equations are obtained in terms of displacement, temperature and electric fields and expressed in the form of series form in space and time domains using the polynomial differential quadrature method coupled with finite difference method, respectively. A comparison of numerical results with the static and dynamic results is presented that shows an excellent agreement. Numerical results for different material parameters are calculated and presented graphically in order to show the effect of material grading parameter, thermal gradient, electric potential and thickness of the sphere on the distribution of stress, displacement, temperature and electric fields.
Stability is indispensable to haptic interfaces for the simulation of a large variety of virtual environments. On a multi-degree of freedom (multi-DOF) haptic device, the passivity condition must be satisfied in both end-effector and joint space to achieve stable interaction. In this study, a conservative passivity condition is utilized for the stability such that guaranteeing the passivity at all joints is a sufficient condition for the passivity and then stability of the whole haptic system. An optimal posture control algorithm is developed to satisfy this passivity condition and maximize the stability performance of a redundant haptic device. The algorithm optimally adjusts the device postures, which are estimated by a Golden Section Search algorithm. The proposed control algorithm was experimentally implemented on a virtual sphere by using a 7-DOF redundant haptic device. Z-width stability metric was used to evaluate the performance of the proposed algorithm. The results show that the optimal posture control approach significantly improves the stability of the redundant haptic devices.
Bolted joints are widely used in aero-engines. One of the common applications is to connect the rotor disks and drums. An analytical model for the bending stiffness of the bolted disk–drum joints is developed. The joint stiffness calculated using the analytical model shows sound agreement with the calculation obtained based on finite element analyses. The joint stiffness model is then implemented into the dynamic model of a simple rotor connected through the bolted disk–drum joint. Finally, the whirling characteristics and steady-state response of the jointed rotor are investigated to evaluate the influence of the joint on the rotor dynamics, where the harmonic balance method is employed to calculate the steady-state response to unbalance force. The simulation results show that the joint influence on the whirling characteristics of the rotor system can be neglected; whereas, the presence of the bolted disk–drum joint may lead to a decrease in the rotor critical speeds due to the softening of the joint stiffness. The proposed analytical model for the bolted disk–drum joints can be adopted conveniently for different types of rotor systems connected by bolted disk–drum joints.
The main aim of this research work is to study the influence of adhesive properties on the formability of adhesive-bonded steel sheets. The adhesive properties were varied by having two different adhesives, epoxy based and acrylic based, and by changing the hardener to resin ratios. The deep drawing quality cold rolled steel and stainless steel (SS 316L) sheets were used as base materials. The epoxy and acrylic adhesives show improved elongation with increase in hardener to resin ratio. This is because of changeover of resin-rich formulation to hardener-rich formulation, making the sample more ductile. The adhesive-bonded blanks show improved elongation as compared to double sheets, which is due to the presence of adhesive delaying the onset of necking. With increase in hardener to resin ratio of both the adhesives, the elongation of individual sheets has improved. This is due to the improvement in elongation of adhesives with increase in hardener to resin ratio. The strain hardening exponent (n) of adhesive-bonded blanks has improved with increase in hardener to resin ratio in all the regions of deformation. The limit strain of deep drawing quality and SS 316L sheets constituting adhesive-bonded blanks shows improvement with increase in hardener to resin ratio. The adhesive-bonded blanks with interface bonding exhibit better limit strain as compared to the case without interface bonding.
A new algorithm is proposed for solving the time-dependent Navier-Stokes equations in a sequential uncoupled manner. The algorithm, known as PISO (Pressure Implicit with Splitting of Operators) is extended to the Smoothed Particle Hydrodynamics (SPH) context (PISO-SPH). The algorithm consists of one prediction and two correction steps, based on a full Navier-Stokes equation, therefore, a modified Poisson equation is derived which makes the algorithm more stable with less pressure fluctuations. The proposed PISO-SPH method is applied to solve a number of benchmark problems including both unsteady and steady state test cases. Comparing the results with analytical solutions and other numerical methods, it is shown that the proposed method is accurate and straightforward for the simulation of incompressible fluid flows.
Creating effective locomotion for a legged robot is a challenging task. Central pattern generators have been widely used to control robot locomotion. However, one significant disadvantage of the central pattern generator method is its inability to design high-quality walks because it only produces sine or quasi-sine signals for motor control as compared to most cases in which the expected control signals are more advanced. Control accuracy is therefore diminished when traditional methods are replaced by central pattern generators resulting in unaesthetically pleasing walking robots. In this paper, we present a set of solutions, based on testings of Sony’s four-legged robotic dog (AIBO), which produces the same walking quality as traditional methods. First, we designed a method based on both evolution and learning to optimize the walking gait. Second, a central pattern generator model was put forth to enabled AIBO to learn from arbitrary periodic inputs, which resulted in the replication of the optimized gait to ensure high-quality walking. Lastly, an accelerator sensor feedback was introduced so that AIBO could detect uphill and downhill terrains and change its gait according to the surrounding environment. Simulations were performed to verify this method.
The theoretical analysis of corrective characteristics of three kinds of polishing methods for mid-frequency errors was studied, which was aimed to confirm the possibility that computer control optical surfacing and computer control active-lap can be replaced by bonnet polishing in the machining process. The first step was to calculate the removal functions of three kinds of polishing technologies and use fast Fourier transform to figure out the frequency spectrum of each method. After that, according to the frequency spectra, curves of cut-off frequencies related to the working ranges of spatial frequencies errors were obtained. It revealed that the affected scope of spatial frequencies is determined by the polishing method, diameter size of polishing tool and shape of removal function. Moreover, only low-frequency errors could be modified and mid-frequency errors could not be corrected or created by computer control active-lap, and computer control optical surfacing can correct part of the mid-frequency errors and low-frequency errors in the polishing process, but at the same time can produce some new mid-frequency errors; as for bonnet polishing, it can be computer control active-lap-like in smoothing which only modified and created the low-frequency errors or computer control optical surfacing-like which corrected and created the mid-frequency errors in local polishing. Otherwise, the efficiency of bonnet polishing is higher than the other two methods. As a result, seen from the point of correction ability of mid-frequency or polishing efficiency, bonnet polishing could replace computer control active-lap and computer control optical surfacing for finishing two polishing stages by only one tool, which is significant to extending the application of bonnet polishing in optical manufacturing.
Impulse noise is one of the most hazardous and annoying types of noise, which is present in the working and community environment. A-weighted equivalent sound pressure level, describing most types of noise, appears not to be the appropriate descriptor, especially not for high-impulsive and high-energy impulsive noise. However, this descriptor is often used as a basis for impulse noise evaluation, when combined with appropriate adjustment terms. But despite of objective character of such evaluation, care should be taken regarding certain facts, especially the source of impulse noise, its environment and time of measurement. In this article, the relationships between all these influential parameters have been investigated in detail. Today, on the other hand, a sophisticated sound level meter offers the possibility of simultaneous measurement of many acoustical descriptors. By combining some of these descriptors with some analytical investigations, as shown in this article, more useful information concerning impulse noise can be obtained. In this article some of them are used for more detailed analysis of impulse correction, according to some international standards.
The bar fine-cropping, the first and one of the most important metal-forming procedure, separates the work-piece into accurate products and billets. The aim of this article is to investigate the influence of different main motor rotational frequencies on a new fine-cropping system. Five different rotational frequencies are applied to both the numerical simulations and the fine-cropping experiments. The numerical and experimental results show that good agreement is achieved by combining the average stress triaxiality under different stress states: the equivalent plastic strain, the fatigue-crack propagation path analysis and the micrograph fractography observation. Additionally, the cross-section quality of cropped billets and the final cropping time is also investigated. The results show that the cross-section quality and the final cropping time of the new fine-cropping are greatly influenced by the main motor rotational frequency, especially the frequency close to 33 Hz.
This study focuses on the slip prediction in a cable-drum system using artificial neural networks for the prospect of developing linear motion sensing scheme for such mechanisms. Both feed-forward and recurrent-type artificial neural network architectures are considered to capture the slip dynamics of cable-drum mechanisms. In the article, the network development is presented in a progressive (step-by-step) fashion for the purpose of not only making the design process transparent to the readers but also highlighting the corresponding challenges associated with the design phase (i.e. selection of architecture, network size, training process parameters, etc.). Prediction performances of the devised networks are evaluated rigorously via an experimental study. Finally, a structured neural network, which embodies the network with the best prediction performance, is further developed to overcome the drift observed at low velocity. The study illustrates that the resulting structured neural network could predict the slip in the mechanism within an error band of 100 µm when an absolute reference is utilized.
It is proved that hyperelastic honeycomb coatings can attenuate underwater blast loads impinged on the ship hull. The crush behavior of a unit tube cell of the coating made of rubber material is investigated in this study. A series of tests are conducted to investigate the crush dynamic behavior of the tube under low velocity impact loads. Numerical analyses are carried out to explore the impact process of the rubber tube and the role of some dynamic parameters, thereby serve as a reference in the design of new coating. Some characteristics, such as the geometric imperfections, nonlinear elasticity and material viscosity, are analyzed. The results of simulation and experiments show that the geometric imperfections not only attenuate the shock force in the buckling and the force plateau stages, but also enhance the shock force in the densification stage greatly and promote the global peak force initiation, while the material viscosity enhances the force plateau and attenuates the shock force in the densification stage greatly. These effects are illustrated and quantified with the aid of experiments and numerical calculations.
Time-varying mesh stiffness is a periodic function caused by the change in the number of contact tooth pairs and the contact positions of the gear teeth. It is one of the main sources of vibration of a gear transmission system. An efficient and effective way to evaluate the time-varying mesh stiffness is essential to comprehensively understand the dynamic properties of a planetary gear set. According to the literature, there are two ways to evaluate the gear mesh stiffness, the finite element method and the analytical method. The finite element method is time-consuming because one needs to model every meshing gear pair in order to know the mesh stiffness of a range of gear pairs. On the other hand, analytical method can offer a general approach to evaluate the mesh stiffness. In this study, the potential energy method is applied to evaluate the time-varying mesh stiffness of a planetary gear set. Analytical equations are derived without any modification of the gear tooth involute curve. The developed equations are applicable to any transmission structure of a planetary gear set. Detailed discussions are given to three commonly used transmission structures: fixed carrier, fixed ring gear and fixed sun gear.
Bearing performance degradation assessment is meaningful for keeping mechanical reliability and safety. For this purpose, a novel method based on kernel locality preserving projection is proposed in this article. Kernel locality preserving projection extends the traditional locality preserving projection into the non-linear form by using a kernel function and it is more appropriate to explore the non-linear information hidden in the data sets. Considering this point, the kernel locality preserving projection is used to generate a non-linear subspace from the normal bearing data. The test data are then projected onto the subspace to obtain an index for assessing bearing degradation degrees. The degradation index that is expressed in the form of inner product indicates similarity of the normal data and the test data. Validations by using monitoring data from two experiments show the effectiveness of the proposed method.
Since 1994, two main meshless methods have been developed and widely used: these are the element free Galerkin method and the meshless local Petrov-Galerkin method. Both methods solve partial differential equations by posing a numerical approximation to the solution using the moving least squares technique. Using Bernstein polynomials as the shape functions of Galerkin weak form-based methods improves the numerical approximation achieved at boundaries without losing accuracy inside the domain.
This article introduces a new semi-analytical nonlinear finite element formulation for thin cylinders according to a continuum-based approach. A comparison between the continuum-based approach and the classical approach for the buckling behavior of isotropic and orthotropic perfect cylinders validates the results. The classical approach is defined according to thin shell theories based on the von Karman approximation. A mathematical modeling for geometry imperfection of cylinders is derived according to a continuum-based approach whose results are compared with the results of the classical approach for imperfect cylinders. The influence of neglecting some nonlinear terms in the classical approach for perfect and imperfect cylinders on the buckling path is investigated. In the buckling analysis, two methods, i.e. the perturbation and load disturbance methods, which undertake to switch to the post-buckling path, are compared to each other.
This article presents numerical and experimental simulation of three-dimensional conjugate heat transfer problem in mini-scaled thermal storage system. The conjugate problem includes melting process of phase change material in the presence of natural convection during laminar flow of heat transfer fluid through circular minichannel. The paraffin wax is used as a phase change material while the water is used as a heat transfer fluid. The main objective of this study is to investigate the effect of the phase change material natural convection during the melting process on the heat transfer fluid thermal characteristics as well as the impact of the natural convection on the melting performance itself. The thermal characteristics are represented by local Nusselt number (Nu) and local surface temperature. The melting performance is evaluated by fusion time and liquid fraction profile. Two inlet temperatures and velocities of the heat transfer fluid are adopted to highlight the effect of the natural convection. Combination of the inlet temperatures and velocities of the heat transfer fluid forms four cases: case_1 (at Tf, in = 353 °K, Vf, in = 1 m/s), case_2 (at Tf, in = 453 °K, Vf, in = 1 m/s), case_3 (at Tf, in = 353 °K, Vf, in = 0.1 m/s), and case_4 (at Tf, in = 453 °K, Vf, in = 0.1 m/s). Experimental test rig was constructed to verify the computational results and good agreement between both results was achieved. The study shows that the heat transfer fluid encounters an erratic thermal behavior during the phase change material melting process. For example, the local surface temperature experiences dramatic increase and decrease at certain sections of the channel length. The magnitude of this temperature inconsistency interrelates closely to the strength of natural convection impact, and this can expose the minichannel (which has short length) to severe wall thermal stress. The local Nu experiences improvement in some section of the channel and at the same time it suffers from drastic deterioration in its value particularly at the channel end at which the convection current accommodates. The case with the lowest inlet velocity and the highest inlet temperature has the smallest fusion time at expense of the largest heat transfer fluid bulk temperature gradient before reaching the fusion time. The study is considered as a benchmark and helpful guidelines in the design of small-scaled thermal storage systems of phase change material.
A common assumption about fluid power systems is that the outlet pressure ripple is a primary source for air-borne noise. Fluid pressure fluctuations are caused by flow ripples generated by positive displacement units that are the prime power movers in these systems. The present research aims to leverage previous efforts in the topic of noise generation in hydrostatic units, formulating a method to predict air-borne noise for a particular reference machine. A numerical model has been developed to gain knowledge on the mechanisms of noise generation in external gear machines. The simulated noise sources are then applied to the structure in order to predict the propagation of noise to the surroundings. Also, experimental activity based on an innovative method of interpretation of noise measurements is also accomplished in order to better characterize the dependency between fluid-borne noise and air-borne noise. Measurements are made of total sound power level as well as sound pressure level at representative points to better understand the acoustic performance of external gear machines at a wide variety of operating conditions.
The use of variable pitch or helix cutters is a known means to prevent chatter vibration during milling. In this article, an alternative method based on an improved semi-discretization method is proposed to predict the stability of variable pitch or variable helix milling. In order to consider the effect of distributed system delays attributed to helix variation, the average delays were calculated for each flute after the engaged cutting flutes were divided into a finite number of axial elements. Meanwhile, a straightforward integral force model, which can consider the piecewise continuous regions of the cutting that describe the helix angle is used to determine the cutting force. Through comparisons with prior works, time-domain simulations, and cutting tests, the proposed approach was verified. In addition, the method was applied to examine the effect of tool geometries on stability trends. Several phenomena for certain combinations of pitch and helix angles are shown and explained.
This article proposes a numerical approach for the modeling and prediction of wear at revolute clearance joints in flexible multibody systems by integrating the procedures of wear prediction with multibody dynamics. In the approach, the flexible component is modeled based on the absolute nodal coordinate formulation. The contact force in the clearance joint is applied using the continuous contact force model proposed by Lankanrani and Nikravesh and the friction effect is considered using the LuGre friction model. The simulation of wear is performed by an iterative wear prediction procedure based on Archard’s wear model. The radial basis function neural network technique is employed to deal with the pin-on-disc experimental data for obtaining the wear coefficient used in the wear prediction procedure at different contact conditions. The comparison of the wear predicted at the clearance joint in the rigid and flexible planar slider-crank mechanisms demonstrates that the proposed approach can be used to model and predict wear at revolute clearance joints in flexible multibody systems, and the wear result predicted is slightly reduced after taking the flexibility of components into account.
A computational model taking into account the radial interference was first presented for determining the distribution of contact forces, static load-carrying capacity and fatigue life of a double row pitch bearing, which was subjected to the combined radial, axial and tilting moment loadings. The relation between the radial interference and the contact force distribution was analyzed. The static load-carrying capacity curves were established and the effect on the static load-carrying capacity by the change of the radial interference, coefficient of raceway groove curvature radius and initial contact angle was analyzed. The results show that with the increase in the radial interference, the maximum contact load decreases first then increases, and the basic rating fatigue life of the bearing increases first and then decreases. The radial interference value in the range of 0–0.05 mm has little effect on the static load-carrying capacity of the bearing. With the increase in the coefficient of raceway groove curvature radius and the decrease in the initial contact angle, the static load capacity of the bearing decreases.
The forces acting on the actuator used in a reciprocating capacity control system are analyzed in this article. The dynamic response of this system is influenced significantly by hydraulic pressure and reset spring force. The performance of dynamic response is tested under different hydraulic pressures and reset springs. The results show that the influence of reset spring force on the downward speed and displacement of actuator is more inconspicuous than the hydraulic pressure, but the reset speeds decrease obviously when the reset spring force is small (SPR2 and SPR3). The maximum downward displacement decreases and the consuming time increases with the decrease in the hydraulic pressure. The maximum downward speed of actuator decreases with the decrease in hydraulic pressure which influences the reliability and life of this system. Therefore, the performance of dynamic response and operating lifetime needs to be considered simultaneously during the design of partial stroke press-off inlet valve capacity control systems.
This work presents the application of a first-order perturbation method to evaluate the eigensensitivity of brake carriers when local geometric alterations arise. This method can be applied both to establish dynamic acceptance conditions of manufacturing-related errors (concept of ‘eigenacceptance’) and to assess the variation of eigenfrequencies and eigenmodes when design variations are done (concept of ‘eigendesign’). As an application of the first concept, the adequacy of the proposed method has been tested in the eigensensitivity of the rest of ingate caused by the manufacturing process; and with regard to the eigendesign concept, an easy-to-use methodology for the redesign of brake carriers has been developed and correlated.
In this research, a magnetorheological fluid-based damper to attenuate vibration due to unbalanced laundry mass from a front-loaded washing machine is proposed and optimally designed with experimental validation. First, rigid vibration mode of the washing machine due to an unbalanced mass is analyzed, and an optimal positioning of the suppression system for the washing machine is figured out. In order to attenuate vibration from the washing machine, several configurations of magnetorheological damper are proposed considering available space and the required damping force of the system. Based on the Bingham rheological model of magnetorheological fluid, damping force of the proposed magnetorheological dampers is then derived. An optimal design problem for the proposed magnetorheological damper is constructed considering its zero-field friction force and the maximum damping force. The optimization objective is to minimize the zero-field friction force of the magnetorheological damper while the maximum value of damping force is kept being greater than a required value. An optimization procedure based on finite element analysis integrated with an optimization tool is employed to obtain optimal geometric dimensions of the magnetorheological dampers featuring different types of magnetorheological fluid. Optimal solutions of the magnetorheological dampers are then presented and the optimized damper is figured out. In addition, performance characteristics of the optimized magnetorheological damper are presented and discussed.
The study of rotor dynamic stability of hydraulic turbine system has become extremely important because of the increasing capacity, size, and inertia of large turbines. Crown clearance and band clearance in hydraulic turbines will influence the rotor dynamic characters of turbine shaft system. In this article, the character of the turbine shaft system under different clearance parameters is studied in order to observe how the clearance parameters influence the stability of hydraulic turbine. The relationship between the hydraulic turbine stability system and the turbine clearance structure is also analyzed. In this study, the force on the turbine rotor induced by fluid flow in clearances is described with the analytical solution of Reynolds equation obtained in the article, in which the fluid flow is considered to be incompressible and isothermal. And, the rotor dynamic character of the turbine system is calculated by NewMark direct integral method and non-linear forces obtained from Reynolds equation are implemented. Finally, principles related to the clearance parameters influencing the rotor dynamic character of turbine system are summarized.
Circumferential impulse microturbine is a key component of the micro-electro-mechanical system and provides power to the latter. An innovative concept of microturbine power generation system was presented, and prototype improved circumferential impulse microturbine power generation systems were developed, and their output performances were tested. It is validated that the system can operate at a high speed in a dynamic equilibrium state using rolling bearings, and it is found that the output power and rotational speed of a six-blade turbine hollow-cup coil structure is higher than the output power and rotational speed of a six-blade turbine iron-core coil structure. The maximum output power of the eight-blade turbine hollow-cup coil power generation system is 1.1 W, and the maximum turbine rotational speed is 55,000 r/min. The maximum output power of the eight-blade turbine hollow-cup coil system increases up to 25% when compared to the six-blade turbine hollow-cup coil system and increases up to 83% when compared to the six-blade turbine iron-core coil system.
This paper presents an activity concerning the modelling and control of a system adopted to perform shear tests on seismic isolators. The test rig consists of a hydraulic actuation system that drives a sliding table mounted on linear bearings. The system is characterized by non-linearities such as hydraulic proportional valve dead zone and frictions. A non-linear model is derived and then employed for parameter identification procedure. The test rig needs a suitable controller able to guarantee the desired table displacement in presence of unknown reaction force of the device under test. The proposed approach consists of a feedforward control integrated with a feedback one. The feedforward control law takes the form of a non-linear inverse model of the system. In this way, it is possible to obtain the desired target without affecting the stability of the test rig. The feedback control has the function to compensate for tracking error due to the model uncertainties and the unknown isolator reaction force. Therefore, the feedback control is not required to compensate for the large non-linearities: in this manner, it is possible to obtain good tracking results without the increasing of the feedback control gain that would change the stability properties of the plant. Numerical simulations have been performed in order to evaluate the goodness of the designed control with and without the specimen under test. Experimental tests show that the controlled system simulations are able to predict the controller performance. The experimental results also confirm that the performance of the proposed controller fully satisfy the standards concerning the testing procedure of seismic isolators.
There is a requirement for improved three-dimensional surface characterisation and reduced tool wear when modern computer numerical control (CNC) machine tools are operating at high cutting velocities, spindle speeds and feed rates. For large depths of cut and large material removal rates, there is a tendency for machines to chatter caused by self-excited vibration in the machine tools leading to precision errors, poor surface finish quality, tool wear and possible machine damage. This study illustrates a method for improving machine tool performance by understanding and adaptively controlling the machine structural vibration. The first step taken is to measure and interpret machine tool vibration and produce a structural model. As a consequence, appropriate sensors need to be selected and/or designed and then integrated to measure all self-excited vibrations. The vibrations of the machine under investigation need to be clearly understood by analysis of sensor signals and surface finish measurement. The active vibration control system has been implemented on a CNC machine tool and validated under controlled conditions by compensating for machine tool vibrations on time-varying multi-point cutting operations for a vertical milling machine. The design of the adaptive control system using modelling, filtering, active vibration platform and sensor feedback techniques has been demonstrated to be successful.
This study reports on the kinematic analyses of four translational parallel manipulators (3RPC, SPS + 2RPC, RPPR + 2RPC and RPPR + 2PPP) articulated with linear actuators. They are based on serially connected chains which are connected with cylindrical (C), prismatic (P), revolute (R), spherical (S) and universal (U) joints. Of these manipulators, the one which is a fully decoupled, fully isotropic and singularity-free translational parallel manipulator (RPPR+2PPP) offers a one-to-one correspondence between its input and output displacement. This makes its forward and inverse position analyses simpler with a set of linear equations to be solved. Although the other manipulators have coupled kinematics, they still have simpler forward kinematic equations over other well-known translational parallel manipulators reported in the literature. We also employ screw theory to undertake the velocity and acceleration analyses. The primary contribution of this manuscript is to show how the 3-RPC translational parallel manipulator can be gradually modified in order to obtain a fully isotropic, fully decoupled and singularity-free translational parallel manipulator.
This article performs a theoretical and experimental analysis of a twin-shaft test rig in which the two unbalanced rotors are nonlinearly coupled through the flexibly mounted housing of a squeeze-film damper bearing, as in a real aircraft engine. The research aims are two-fold: to validate recently developed fast computation methods and to achieve an insight into the effect of the ratio between the rotor speeds on the overall vibration response. The experimental data correlated reasonably well with the theoretical analysis. The correlation was best when the speed ratio was equal to a ratio of large integers (in its most reduced form). When the speed ratio was a ratio of two low integers, the predicted response was found to be particularly sensitive to the arbitrary initial phase angle between the rotors.
The Voigt-type of dynamic vibration absorber is a classical model and has attracted considerable attention in many years because of its simple design, high reliability and useful applications in the fields of civil and mechanical engineering. Recently, a non-traditional type of dynamic vibration absorber was proposed. Unlike the traditional damped absorber configuration, the non-traditional absorber has a linear viscous damper connecting the absorber mass directly to the ground instead of the main mass. There have been some studies on the design of the non-traditional dynamic vibration absorber in the case of undamped primary structures. Those studies have shown that the non-traditional dynamic vibration absorber has better performance than the traditional dynamic vibration absorber. However, when damping is present at the primary system, there are very few studies on the design of non-traditional dynamic vibration absorber. This article presents a simple approach to determine the approximate analytical solutions for the <inline-formula id="ilm1-0954406213481422"><inline-graphic xlink:href="10.1177_0954406213481422mml-inline1"/>H_\infty</inline-formula> optimization of the non-traditional dynamic vibration absorber attached to the damped primary structure subjected to force excitation. The main idea of the study is based on the dual criterion suggested by Anh in order to replace approximately the original damped structure by an equivalent undamped structure. Then the approximate analytical solution of dynamic vibration absorber’s parameters is given by using known results for undamped structure obtained. The comparisons have been done to verify the effectiveness of the obtained results.
Stack-type piezoelectric actuators, which usually consist of several ceramic layers connected in series, are widely used in piezoelectric direct-drive servo valves (PDDSV). However, poor pulling force capacity of this kind of actuators affects the performances of the direct-drive servo valves. This article presents a new type of PDDSV, whose spool-driving mechanism is composed of a set of independent parts that are not fixed together but are in contact with each other. This multi-body contacting spool-driving mechanism provides bidirectional movement of the spool by a preloaded stack-type piezoelectric actuator and a driving disc spring. This prevents the stack-type piezoelectric actuator from bearing the pulling force due to the inertia and friction of the spool. Design of the proposed servo valve is illustrated in detail and its characteristics are also predicted. Based on a nonlinear dynamic model of the multi-body contacting spool-driving mechanism, a comprehensive dynamic simulation model of the proposed PDDSV is established. Static and dynamic characteristics of the proposed PDDSV have been studied experimentally and good agreements between experimental and simulation results are observed. The dynamic performances of the proposed PDDSV are compared with the existing piezoelectric servo valves, which demonstrate that the proposed PDDSV has satisfactory dynamic characteristics for high-frequency applications.
This article compares both new and commonly used boundary conditions for generating pressure-driven water flows through carbon nanotubes in molecular dynamics simulations. Three systems are considered: (1) a finite carbon nanotube membrane with streamwise periodicity and ‘gravity’-type Gaussian forcing, (2) a non-periodic finite carbon nanotube membrane with reservoir pressure control, and (3) an infinite carbon nanotube with periodicity and ‘gravity’-type uniform forcing. Comparison between these focuses on the flow behaviour, in particular the mass flow rate and pressure gradient along the carbon nanotube, as well as the radial distribution of water density inside the carbon nanotube. Similar flow behaviour is observed in both membrane systems, with the level of user input required for such simulations found to be largely dependent on the state controllers selected for use in the reservoirs. While System 1 is simple to implement in common molecular dynamics codes, System 2 is more complicated, and the selection of control parameters is less straightforward. A large pressure difference is required between the water reservoirs in these systems to compensate for large pressure losses sustained at the entrance and exit of the nanotube. Despite a simple set-up and a dramatic increase in computational efficiency, the infinite length carbon nanotube in System 3 does not account for these significant inlet and outlet effects, meaning that a much smaller pressure gradient is required to achieve a specified mass flow rate. The infinite tube set-up also restricts natural flow development along the carbon nanotube due to the explicit control of the fluid. Observation of radial density profiles suggests that this results in over-constraint of the water molecules in the tube.
This article presents the design and fabrication of a monolithic compliant microgripper. This research has mostly focused on the process of design, the finite element analysis, the fabrication method and use of a genetic algorithm method to solve the nonlinear kinematic equations and estimate the proper dimensions of the design. This new architecture of the microgripper enables it to apply a variable force to a wide range of micro-objects handled in microassembly, micromanipulation and also in biomedical applications such as artificial fertilization. The microgripper was designed to be normally open. Two shape memory alloy actuators close the jaws. To achieve the tasks, the most proper size has been considered to be 8 x 8 mm, with thickness of 250 µm. Polyethylene terephthalate has been used as the structural material. It is not brittle and is less sensitive to shock compared with silicon-based grippers; furthermore, its fabrication cost is less and it does not lose precision.
Transmission components are the main mechanical elements in a machine system, the accuracy level of the transmission system is one of the major sources of the machining error of multiaxis machine tools. This article investigates motion error analysis, volumetric motion error model for transmission system and the accuracy allocation method for multiaxis machine tools during the early design stage. For this purpose, a transmission system volumetric motion error model, which is based on the motion error matrix and screw theory, is derived for mapping transmission components’ error parameters to the volumetric motion errors of machine tools. The volumetric motion error matrix combines motion errors along the machine tools’ kinematic chains. Subsequently, the volumetric motion error model is expressed as a volumetric motion error twist, which is formulated from the volumetric motion error matrix. Additionally, the transmission system volumetric motion error twist model is used as design criteria for accuracy optimum allocation, with constraints on the twist magnitude and design variable limits. Then, design optimization is performed by using a multiobjective nonlinear optimization technique to minimize the manufacturing cost and volumetric motion error twist pitch. To solve this multiple objective optimum problem, this study proposes an approach integrating Lagrange multiplier and gradient descent operator with non-dominated sorting genetic algorithm-II (NSGA-II). Modified non-dominated sorting genetic algorithm-II searches for an allocation scheme Pareto optimal front. Consequently, VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) determines the best compromise solution from the Pareto set. Finally, a numerical experiment for the optimal design of a numerical control machine tool is conducted, which highlights the advantages of the proposed methodology.
A novel continuous adjoint-based acoustic propagation method is proposed for low-noise turbofan duct design. A fan bypass duct tonal noise propagation model that is verified by comparison with an analytical solution of the modal radiation from a semi-infinite duct with the shear layer is enhanced with its continuous adjoint formulation, having been applied to design the bypass duct. First, this article presents the complete formulation of the time-dependent optimal design problem. Second, a continuous adjoint-based acoustic propagation method for two-dimensional bypass duct configurations is derived and presented. This article aims at describing the potential of the adjoint technique for aeroacoustic shape optimization. The implementation of the unsteady aeroacoustic adjoint method is validated by comparing the sensitivity derivative with that obtained by finite differences. Using a continuous adjoint formulation, the necessary aerodynamic gradient information is obtained with large computational savings over traditional finite-difference methods. The examples presented demonstrate that the combination of a continuous-adjoint algorithm with a noise prediction method can be an efficient design tool in the bypass duct noise design problem.
CNT hetero-junctions offer the possibility of being used in micro-electromechanical systems and nano-electromechanical systems. However, in the present work, nonlocal axial buckling analysis of linear CNT hetero-junctions based on Euler–Bernoulli beam (EBB) model is investigated. In order to mathematically model a linear CNT hetero-junction, a CNT with two segments is considered. The constitutive equations are derived based on the Eringen's theory for various boundary conditions, namely clamped–clamped (C–C), clamped–pinned (C–P) and pinned–pinned (P–P). An analytical approach is applied to obtain the dimensionless buckling load of the CNT hetero-junctions. A detailed parametric study is conducted to elucidate the influences of the small-scale coefficient, homogeneity parameter, boundary conditions and CNT length of each segment on the axial buckling of the linear CNT hetero-junctions. The results indicate that the length of each segment and homogeneity parameter have a significant effect on the buckling load of the CNT hetero-junctions and should therefore be considered in its optimum design. Furthermore, the results are in good agreement with the previous researches.
To investigate the rotor-bearing dynamics and solve the unstable synchronous vibration problem under partial admission conditions in axial steam turbines, a three-dimensional computational fluid dynamics model of the governing stage for a 350 MW turbogenerator unit was established. Steam force under different partial admission cases was calculated. Results show that the uneven steam force in the horizontal direction was fairly as strong as that in the vertical direction. The maximal horizontal steam force was about 40% of the high intermediate pressure cylinder rotor weight. Synchronous vibration faults caused by partial admission may occur in practice. The finite element model was further built to analyze the rotor-bearing dynamics under partial admission conditions. Large fluctuation of the synchronous vibration was observed during the variation of control valve sequence. Finally, the effect of bearing elevation on the rotor-bearing dynamics was studied. The sensitivity of bearing load varies for different bearing elevations. An effective solution to the unstable synchronous vibration faults caused by partial admission was achieved by optimizing the distribution of bearing elevation. A relevant case was presented through practical test.
For extending the frequency bandwidth greatly and controlling the vibration characteristic variables precisely, the electro-hydraulic high-frequency vibrator controlled by the parallel design of a two-dimensional valve (named as 2D valve) and a standard servo valve is preserved. The frequency of the vibrator is proportional to the product of the rotary speed of the spool of the two-dimensional valve and the switching numbers between grooves in the spool and windows in sleeve in one circle, so that it is convenient to extend the working frequency range by coordinating these parameters. In this study, the load is considered to be an elastic force and the relationships between the characteristic variables of the vibration and the control parameters are investigated using the analytic method. For the solution to the expression of the bias of the vibration, the electro-hydraulic vibration system is considered to be equivalent to a symmetrical hydraulic cylinder controlled by a single slide valve with a neutral pre-opening, which is determined by the throttling area of the two-dimensional valve. For the waveform of the vibration, the system is assumed to be a hydraulic cylinder controlled only by the two-dimensional valve and the effect imposed by the parallel servo valve on hydraulic cylinder is treated as an external load. The equations of the waveform superimposed on the bias are finally solved using the analytic method, where the expressions of the vibration amplitude are derived. It is found that coupling relationships exist between the characteristic variables of the vibration and the control parameters, where the vibration amplitude is not only determined by the axial displacement of the spool of the two-dimensional valve but is also reciprocally proportional to the rotary speed of the spool of the two-dimensional valve. While the bias is only dependent on the ratio of the throttling area of the parallel servo valve to that of the two-dimensional valve, the working frequency is exclusively dependent on the rotary speed of the spool of the two-dimensional valve and the vibration amplitude is almost independent of the throttling area variation of the parallel servo valve. The experimental system is built to verify the analytic results of the relationships between characteristic variables and control parameters. It is demonstrated that the theoretical analysis is consistent well with measured results and it is also verified that by means of proposed multiple control to the hydraulic vibrator, the vibration can be sustained at the level of high accuracy.
Sliding bearing pair is one of the important friction pairs within water hydraulic axial piston pump, which can result in significant influences on the pump’s performance. Generally, owing to the characteristics of low viscosity and poor lubrication of water, the sliding bearing will operate under condition of dry or mixed lubrication, leading to a severe adhesives wear and material softening. In order to investigate the flow field of the sliding bearing in hydrodynamic condition, the effects of the water film pressure distribution, load carrying capacity changing with radial clearance and width–radius ratio of the sliding bearing pair have been simulated through MATLAB. And a suitable material combination of the sliding bearing pair was selected though a custom-manufactured friction and wear test rig. Based on the theoretical and experimental studies, an appropriate structure of the sliding bearing within water hydraulic axial piston pump was designed. The loading experiments for the developed water hydraulic axial piston pump assembled with two different flanges have been conducted at a water hydraulic component test rig. The experimental results revealed that the volumetric efficiency and noise characteristics of the pump are remarkably improved when the sliding bearing work under hydrodynamic lubrication condition in comparison with dry lubrication condition. The research results have laid the foundation for the development and improvement of the water hydraulic axial piston pump.
This article proposes a closed-loop control scheme based on joint-angle feedback for cable-driven parallel manipulators (CDPMs), which is able to overcome various difficulties resulting from the flexible nature of the driven cables to achieve higher control accuracy. By introducing a unique structure design that accommodates built-in encoders in passive joints, the seven degrees of freedom (7-DOF) CDPM can obtain joint angle values without external sensing devices, and it is used for feedback control together with a proper closed-loop control algorithm. The control algorithm has been derived from the time differential of the kinematic formulation, which relates the joint angular velocities to the time derivative of cable lengths. In addition, the Lyapunov stability theory and Monte Carlo method have been used to mathematically verify the self-feedback control law that has tolerance for parameter errors. With the aid of co-simulation technique, the self-feedback closed-loop control is applied on a 7-DOF CDPM and it shows higher motion accuracy than the one with an open-loop control. The trajectory tracking experiment on the motion control of the 7-DOF CDPM demonstrated a good performance of the self-feedback control method.
The energy conservation principle has been applied to derive the formulation of the frequencies of free transverse vibration of beams for a given mode shape. For uniform beams with a tip mass and with either a clamped/free or a clamped/sliding or a hinged/sliding constraint, under various loads, such a centrifugal force, axial acceleration and concentrated force, the mode shape functions for the free uniform beams have been employed to develop empirical formulae, which are capable of predicting their frequencies. The predictions show a good agreement with those given by finite element analysis.
Analysis and design of resistive shunt circuits for piezoelectric damping of beam structures is often based on a representation in terms of the single target vibration mode of the beam, neglecting spill-over effects from the out-of-bandwidth or residual vibration modes. In this article, a solution format is derived for the complex-valued natural frequency of the beam with a shunted piezoelectric laminate transducer, where the influence from the residual modes is taken into account by a quasi-static representation. This explicit solution format contains system parameters that directly represent the authority of the transducer and the spill-over from residual modes, and it recovers the short- and open-circuit frequencies as limit solutions. Furthermore, the frequency solution format provides the basis for design expressions for the optimal resistance and the corresponding attainable damping of the beam. The accuracy of the explicit frequency solution format is verified by comparison with numerical results. It is found that the complex-valued natural frequency of the first vibration mode of a beam with a piezoelectric laminate transducer shunted to a resistance is estimated with sufficient accuracy for engineering design purposes.
Object of this paper is the performance analysis of a six degrees of freedom measuring device based on a modified Stewart platform structure. Because of the device studied in this work represents a novel application of a Stewart like platform, an investigation about its performance has been done, in order to evaluate both behaviour and characteristics of this device in different geometrical configurations. In particular, sensitivity analysis has been carried on about geometrical characteristics and displacements amplitude. To calculate the sensitivity, the inverse kinematic equations of the device have been obtained.
A time-domain finite volume approach is presented for predicting the transmission loss of muffler including thermal effects with non-uniform sound speed field and density field, in which the acoustic wave equation in heterogeneous media is solved by using unstructured finite volume method with the temperature field specified or solved by some commercial code. An improved time-domain impulse method based on the absorbing boundary condition is applied to predict the acoustic attenuation characteristics of mufflers. The approach is validated by numerical simulations of a simple expansion chamber muffler and a complex muffler with five chambers. The predicted results agree well with the corresponding experimental ones and numerical ones obtained by finite element method with commercial code SYSNOISE. The results of both mufflers under different thermal conditions indicate that the temperature distribution has a significant influence on transmission loss. According to the analysis of a complex muffler with ideal medium, it is shown that the variation of working conditions can obviously affect density and sound speed distributions but have little influence on transmission loss. On the other hand, the obtained transmission loss with the solved temperature field deviates much from the one with specified uniform temperature field.
This study investigates the performance of particulate-filled thermoplastic fluoropolymer coatings under both dynamic impact tests and static indentation tests. An instrumented impact testing rig was used to measure the impact energy, impact velocity, acceleration and impact force during the impact tests. Coating samples with different thicknesses of coating layers and steel substrate were impact tested to investigate the effect of coating and substrate thickness on the impact response and damage to the coatings. The data obtained from the dynamic tests were used to calculate the Meyer hardness values of the coating and compared with the Meyer hardness results obtained from Brinell indentation tests on the coating. The Meyer index m was similar under dynamic impact and static indentation testing conditions. The Meyer hardness calculated from the impact tests does not change markedly as a function of depth of penetration normalised to the thickness of coating, whereas the Brinell hardness increases with the depth of penetration to coating thickness ratio. For a given value of indentation strain, the Meyer hardness calculated from the maximum force measured in the impact test is approximately 2.5 times that resulting from the Brinell test. This reflects the fact that the higher strain rate in the impact test would give rise to a higher flow stress and thus hardness.
The problem of machining titanium is one of the ever-increasing magnitudes due to its low thermal conductivity and work-hardening characteristic. In the present work, experimental studies have been carried out to obtain the optimum conditions for machining titanium alloy. The effect of machining parameters such as speed, feed, depth of cut and back rake angle on cutting force, and surface roughness were investigated. The significance of these parameters, on cutting force and surface roughness, has been established using the analysis of variance. The degree of influence of each process parameter on individual performance characteristic was analyzed from the experimental results obtained using the grey relational grade matrix. The back rake angle was identified as the most influential process parameter on cutting force and surface roughness. The cutting speed is identified as the most significant parameter for the turning operation according to the weighted sum grade of the cutting force and surface roughness.
Whilst machining heat is generated by the friction inherent into the sliding of the chip on the rake face of the insert, the temperature in the cutting zone of both the insert and the chip rises, facilitating adhesion and diffusion. These effects accelerate the insert wear, ultimately undermining the tool life. Therefore, a number of methods have been developed to control the heat generation. Most typically, metal working fluids are conveyed onto the rake face in the cutting zone, with negative implications on the contamination of the part. Many applications for instance in health care and optics are often hindered by this contamination. In this study, microfluidics structures internal to the insert were examined as a means of controlling the heat generation. Conventional and internally cooled tools were compared in dry turning of AA6082-T6 aluminium alloy in two 33 factorial experiments of different machining conditions. Statistical analyses supported the conclusion that the chip temperature depends only on the depth of cut but not on the feed rate or on the cutting speed. They also showed that the benefit of cooling the insert internally increases while increasing the depth of cut. Internally cooled tools can therefore be particularly advantageous in roughing operations.
The aim of this note is to obtain a flow rate equation for subsonic Fanno flow, which has a form similar to the flow rate equation for isothermal flow. When pipe dimensions and the proper values of pressures and temperatures at two sections along a pipe, namely P1, P2, T1 and T2 are given, the mass flow rate is obtained by simple substitution into the obtained formula. However, only three of the above four quantities are independently given, since the steady Fanno flow problem involves three first-order differential equations. Therefore, the problem has three degrees of freedom. The theory in this note shows an algebraic equation that determines the fourth quantity by using the given three quantities. The method for finding the mass flow rate and state variables of the gas in the pipe are substantially simplified compared with the commonly distributed method. The relative difference of mass flow rates between the subsonic Fanno and isothermal flows is smaller than 1% in practical combinations of P2/P1 and the pipe-friction parameter fL/D.
Nonlinear vibration and instability of a smart piezoelectric microtube made of poly-vinylidene fluoride embedded in an elastic medium is investigated. The tube conveys an isentropic, incompressible fluid flowing in a fully developed irrotational manner. This smart microtube is modeled as a thin shell based on the nonlinear Donnell's shell theory. Effects of mean flow velocity, fluid viscosity, elastic medium modulus, temperature change, imposed electric potential, small scale and aspect ratio on the vibration behavior of the microtube are analyzed. The results indicated that increasing mean flow velocity considerably changes the nonlinearity effects on instability of embedded piezoelectric polymeric microtube so that small scale and temperature change effects become negligible. It has also been found that stability of the system is strongly dependent on the imposed electric potential. The system studied in this article can be used as sensors and actuators in sensitive applications.
To enhance the forced convection heat transfer of turbulent air stream inside the different corrugated channels, a numerical study has been conducted to explore the effect of electrohydrodynamic actuator. In this regard, a two-dimensional numerical approach has been developed to evaluate the average Nusselt number and friction factor. The results obtained show that, while the thermal enhancement factor without electrohydrodynamic is best with trapezoidal corrugation for flows in the low Reynolds number regime, the addition of electrohydrodynamic works best with rectangular corrugation.
Analysis of a flexible manipulator as an initial value problem, due to its large deformations, involves nonlinear ordinary differential equations of motion. In the present work, these equations are solved through the general Frechet derivatives and the generalized differential quadrature (GDQ) method directly. The results so obtained are compared with those of the fourth-order Runge–Kutta method. It is seen that both the results match each other well. Further considering the same manipulator as a boundary value problem, its governing equation is a highly nonlinear partial differential equation. Again applying the general Frechet derivatives and the GDQ method, it is seen that the results are in good match with the linear theory. In both cases, the general Frechet derivatives are introduced and successfully used for linearization. The results of the present study indicate that the GDQ method combined with the general Frechet derivatives can be successfully used for the solution of nonlinear differential equations.
A new involute-helix gear drive, which is point contact with convex and concave circular-arc tooth profiles, is proposed in this article. The basic principle characterized by the advantages of involute and circular-arc gears is put forward. Based on the theory of conjugates curves, generation and mathematical model of this new transmission are presented. The separability of center distance on involute-helix gear is discussed and meshing characteristic of point contact is also analyzed. Finally, the three-dimensional solid model of a gear pair is developed to demonstrate the properties of this new transmission.
Reliability prediction of highly safe mechanical systems can be performed using classical tail modeling. Classical tail modeling is based on performing a relatively small number of limit-state evaluations through a sampling scheme and then fitting a tail model to the tail part of the data. However, the limit-state calculations that do not belong to the tail part are discarded, so majority of limit-state evaluations are wasted. Guided tail modeling, proposed earlier by the author, can provide a remedy through guidance of the limit-state function calculations toward the tail region. In the original guided tail modeling, the guidance is achieved through a procedure based on threshold estimation using univariate dimension reduction and extended generalized lambda distribution and tail region approximation using univariate dimension reduction. This article proposes a new guided tail modeling technique that utilizes support vector machines. In the proposed method, named guided tail modeling with support vector machines (GTM-SVM), the threshold estimation is still performed using univariate dimension reduction and extended generalized lambda distribution, while the tail region approximation is based on support vector machines. The performance of guided tail modeling with support vector machines is tested with mathematical example problems as well as structural mechanics problems with varying number of variables. GTM-SVM is found to be more accurate than both guided tail modeling and classical tail modeling for low-dimensional problems. For high-dimensional problems, on the other hand, the original guided tail modeling is found to be more accurate than guided tail modeling with support vector machines, which is superior to classical tail modeling.
A new type of canned motor pump with extensive application value is designed, researched, and developed in this article. In order to grasp the characteristic of the internal flow field of the pump, the internal flow field is simulated numerically by using FLUENT software with the standard k– turbulence model, SIMPLEC algorithm, and multiple reference frame model. The distribution of the pressure and velocity of the flow in the canned motor pump is analyzed in different working conditions. Moreover, the head and efficiency of the pump is predicted based on the simulation results, which show that the head and efficiency of the canned motor pump in small flow rate will be better. The performance of the canned motor pump can be improved by appropriately increasing the outer diameter of the impeller and the base diameter of the volute. The results of the numerical simulation are in accord with theoretical analysis, which verifies the correctness of the numerical simulation. The investigations have important theoretical guiding significance for the design of the canned motor pump.
This article reports dissolution, regeneration, and characterization of cellulose using an ionic liquid, namely 1-butyl-3-methylimidazolium chloride (BMIMCl). During dissolving process, BMIMCl takes much less time to dissolve cellulose with high degree of polymerization (DP = 4500) than other solvent system, lithium chloride/N,N-dimethylacetamide (LiCl/DMAc). Regenerated cellulose film from BMIMCl–cellulose solution is characterized by viscosity, thermo gravimetric analyzer, X-ray diffraction, pull test, and transmittance test. Compared with LiCl/DMAc–cellulose, BMIMCl–cellulose solution has lower viscosity and its film has lower Young's modulus and yield strength. From thermo gravimetric analyzer and X-ray diffraction experiment, BMIMCl–cellulose film has impurity and X-ray diffraction pattern similar with those of LiCl/DMAc–cellulose film. BMIMCl–cellulose film exhibits higher transmittance. The ionic liquid recovery test verifies that BMIMCl is highly recoverable with 99%, which proves that BMIMCl is a green solvent. Through the bending displacement test, the BMIMCl–cellulose film shows a good actuation behavior of electro-active paper.
A three-dimensional computational fluid dynamics model with the thermal phase change model is used to investigate the thermal–hydraulic characteristics of a steam generator with and without quatrefoil tube support plates. The two types of modeled designs are a unit pipe with and one without tube support plates. The computational fluid dynamics simulations capture the boiling phenomena, vortex and recirculation distributions, and the periodic characteristics of the circumferential wall temperature in the regions surrounding the tube support plates. The cross-flow energy responsible for flow-induced vibration damage in the region of the U-bend tubes is obtained with the aid of these localized thermal–hydraulic distributions. A comparison between the key parameters of the unit pipe models with and without tube support plates clearly reveals the influence of tube support plates in guiding flow behavior and alleviating flow-induced vibration damage for a steam generator’s U-bend tube bundle. Therefore, this computational fluid dynamics model can provide technical support for optimizing tube support plate design and improving the thermal–hydraulic characteristics of steam generator.
Modeling of complex processes often leads to complex mathematical relationships between inputs and outputs, which do not reflect the influence of the independent variables on the output parameters. In this article, an innovative technique based on neural networks is presented to extract fuzzy linguistic rules for modeling some processes using some input–output data. In this way, genetic algorithm is used both for optimal structure design of those group method of data handling-type neural networks and for subsequent optimization of sub-bounds of fuzzy singleton antecedents to further optimize the obtained fuzzy rule base. Three different input–output data tables related to some complex problems of a nonlinear mathematical system, an explosive cutting process and the probability of failure estimation of a two mass-spring system are modeled by some fuzzy rules, using the technique discussed in this article.
This article presents analytical solutions for buckling analysis of functionally graded plate based on a refined plate theory. Based on the refined shear deformation theory, the position of neutral surface is determined and the governing stability equations based on neutral surface are derived. There is no stretching–bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The closed-form solutions of buckling load are obtained for rectangular plates with various boundary conditions. The accuracy of neutral surface-based model is verified by comparing the obtained results with those reported in the literature. Finally, parameter studies are carried out to study the effects of power law index, thickness ratio, and aspect ratio on the critical buckling load of functionally graded plates.
In order to carry out the experimental investigation on control of flow over airfoil, one form of the Gurney flap and one form of the vortex generator were designed. The comparative study is performed for different scenarios such as clean airfoil, clean airfoil with Gurney flap, clean airfoil with vortex generators and clean airfoil with both Gurney flap and vortex generators. Wind tunnel test shows that: (a) the lift at linear regime with the same attack is greatly increased by using a Gurney flap; (b) the stall performance is remarkably improved by using vortex generators; and (c) the lift at both linear and stall regimes are both improved by using combined Gurney flap and vortex generators, and drag is slightly increased at linear regime and greatly reduced at stall regime. In other words, the proper combination of Gurney flap and vortex generators can result in remarkable improvement of aerodynamic performance of an airfoil, and it is an ideal combinational control style.
This article describes the design methodology for a network of robotic Lagrangian floating sensors designed to perform real-time monitoring of water flow, environmental parameters, and bathymetry of shallow water environments (bays, estuarine, and riverine environments). Unlike previous Lagrangian sensors which passively monitor water velocity, the sensors described in this article can actively control their trajectory on the surface of the water and are capable of inter-sensor communication. The addition of these functionalities enables Lagrangian sensing in obstacle-encumbered environments, such as rivers. The Ishikawa cause and effect design framework is used to ensure that the final system synthesizes the diverse operational and functional needs of multiple end-user groups to arrive at a broadly applicable system design. A summary of potential applications for the system is given including completed projects performed on behalf of the Department of Homeland Security, Office of Naval Research, and the California Bay-Delta Authority.
That motor sport is synonymous with advanced manufacturing is probably true of the upper echelons such as F1, WRC and ALMS. However, at privateer level, many of the advanced manufacturing technologies, and to an extent many of the more traditional manufacturing technologies, are beyond reach due to a combination of cost and low production volumes. One technology that has the potential to make the transition from the upper echelons to the privateer level is rapid casting technology. Rapid casting combines the advantages of traditional casting, including greater flexibility during the design stage and a more effective structural behaviour, with the requirement for low production numbers synonymous with motor sport. The low-volume element is achieved through the use of rapid prototyping technology to fabricate the high quality and complex patterns used in investment casting with lower cost and shorter leading times. A potential application was investigated through the presented case study. This involved the use of rapid casting, based on the direct rapid prototyping approach, to design and manufacture an upright for a single-seater race car. The use of advanced computer-aided design/computer-aided manufacture techniques and rapid casting technology resulted in an upright that is structurally efficient (<160 MPa main load cases), has low weight (~900 g) and a reduced number of component parts.
Aimed at solving the problems of radial fluid pressure imbalance, bigger flow ripple and shorter service life that exists in traditional gear pumps, a new type of gear pump based on the principle of harmonic gear drive is put forth, where the function for pumping fluid is achieved by mutual engagement between flexible gear and rigid gear. The structural composition, principle and features of the new gear pump are described in this article. The new pump has two higher pressure cavities arranged symmetrically, which counteracts the fluid pressure and the pump could work longer. Its displacement is two times that of the conventional gear pump and the total discharge is bigger. Flow pulsation, vibration and noise in the new pump are evidently diminished, which make the operation smooth. The new gear pump has superiority in performance and could guide the development in gear pump technology.
In order to improve levitation capability and stability of ultrasonic standing wave, a novel levitation device was presented, which adopted concave spherical surface on the emitter and the reflector. Using ANSYS software, the acoustic field generated by the concave spherical emitting surface was analyzed and the formation of ultrasonic standing wave was simulated. Based on the simulation result, the distribution and maximum acoustic pressure under different radius of concave spherical surface on the emitter and the reflector were ascertained. Through the MATLAB simulation, the optimal structural parameter and levitation position were predicted. Based on the optimization result, the prototype of standing wave levitation device was designed and manufactured. In the laboratory, the radiation force was tested and levitation experiments were also carried out and the actual levitation position was in accordance with the simulation results. When the distance between the emitter and the reflector equaled to about 34.9 mm, three steel balls of 3 mm diameter could be levitated at the same time in three disparate nodes position, the levitation capability and stability were demonstrated to be enhanced largely.
It has been a significant and challenging issue to determine the elastic deformation of parallel manipulators for their precision analysis and control. A new method is proposed and studied for solving the elastic deformation of some parallel manipulators with linear active legs using computer-aided design variation geometry. First, an original simulation mechanism of a parallel manipulator is constructed; each of the vectors in the force transformation matrix of the parallel manipulators is constructed by this simulation mechanism. The active/constrained wrench and their pose are determined based on the Newton–Euler formulation. Second, the elastic deformed dimensions of the active legs are determined based on the elastic deformation equation and the active/constrained wrench. Third, a new simulation mechanism of this parallel manipulator is constructed by replacing the original dimensions of active legs with the deformed dimensions of active legs and the elastic deformations of parallel manipulators are solved using the pose difference between the original and new simulation mechanisms. Finally, two parallel manipulators are illustrated and their elastic deformations are solved and verified by both analytic approach and finite element method.
Angulated-straight element is proposed by combining pantograph element and Hoberman element. It is prepared to construct scaling mechanisms for geometric figures. Angulated-straight element is a kind of scissor-like element that moves along a fixed angle in radial direction, coined radial-scaling element. To explore the advantages of this new element, scaling characteristics of the radial-scaling element are proposed, such as configurations, kinematic characteristics and scaling ratio. Scaling characteristics of hybrid-radial-scaling element are also investigated to enlarge the scaling ratio of radial-scaling element. All configurations of angulated-straight element are synthesized by a rotation method presented in this article. The kinematic characteristics and scaling ratios are analyzed and compared between angulated-straight element and Hoberman element. Synthesis methods of scaling mechanisms for geometric figures are presented by combining the geometric characteristics and design parameters of regular polygon and regular polyhedron. The result shows that shapes and combinations of linkages determine the scaling characteristics of the radial-scaling element. Scaling characteristics analysis of scaling elements is a useful basic theory for choosing and constructing scaling mechanisms. Types of scaling mechanism are enriched. These scaling mechanisms have a certain value of application.
A numerical model is formulated to analyze the tooth contact dynamic load distribution and dynamic transmission error of a pair of spur gears under the influence of bearing elasticity and gearbox assembly errors. In the proposed model, the deformation of the tooth is computed by applying a combination of finite elements and contact mechanics. The elasticity of the bearings is represented with infinitesimal linear spring elements, while the shafts and gears except the teeth that are in engagement are assumed to be rigid bodies. Applying those assumptions, three sets of highly coupled governing equations representing the meshing teeth flexible behavior, gear-bearing assembly translation dynamics and gear rotation dynamics are derived. The resultant model is then used to predict the dynamical behaviors of the geared rotor system, tooth contact dynamic load, and dynamic transmission error. A set of parametric studies is also performed to analyze the gear dynamic response.
In this study, anti-lock brake system control using sliding-mode controller is investigated. Different alternatives for the switching function and the sliding surface, involved in the structure of the sliding-mode controller, are explored. It was aimed to reach a better controller performance with less chattering and robustness to actuator imperfections. Regarding applicability, tire force response was modeled as a uniformly distributed uncertain parameter during controller designs. Controllers are simulated for both constant and varying coefficient of friction roads, with optimized design parameters. The effects of actuator first-order dynamics and transportation delay, which come up in practical implementations, were considered. The sliding-mode control structure which employs derivative switching function with integral sliding surface is originally proposed in this study. It is found to produce less chattering and provide more robustness, which could not be achieved side by side using former designs.
Helmholtz resonators and their modifications are commonly applied for suppressing unwanted sound, including acoustic oscillations in chambers of propulsion and power systems. Sound absorption characteristics of Helmholtz resonators can be enhanced and controlled with a use of thermal stratification in porous insets inside resonators. A simplified lumped-element model for thermoacoustically augmented Helmholtz resonators is developed in this article. Sample calculations illustrate effects of temperature gradients, porosity, positions of porous insets, and locations of resonators inside chambers.
The design of compact and inexpensive mechanical drives and gearboxes can take advantage from the use of custom rolling bearings in which the rolling elements are directly in contact with the shaft and the housing containing them. The custom construction is particularly convenient for the case of roller bearings, either cylindrical or tapered, because these elements are easily manufactured and provide a remarkable loading capacity. Starting from the standard load rating equations available in the literature (ISO standards), this paper develops a step-by-step design procedure for the geometric optimization of radial bearings with cylindrical rollers. The procedure includes constraints on the geometry and leads to the optimal bearing with the maximum static and dynamic load ratings compatible with the space available.
Gurson–Tvergaard–Needleman model is widely used to describe the three stages of ductile tearing: nucleation, growth and the coalescence of micro-voids. The aim of this article is to study the relationship between volume fraction of voids and the fracture strain f. The effects of the volume fraction of nucleation, fN, and the critical volume fraction, fc, were analysed. These parameters play crucial roles in the process of ductile damage. A phenomenological analysis is carried out to study the relationship between the different void volume parameters and the fracture strain f. A method is proposed for the determination of fN and fc, knowing the experimental fracture strain f. The experimental parameters are extracted from the load–diametric contraction curve of an axisymmetric notched tensile bar test AN2.
A new method is presented in this article to determine loads on all rollers in a cylindrical roller bearing. By introducing a pair of nonlinear springs for contact of each roller with its inner and outer races, the equations of equilibrium of the multi-component system are established by means of the virtual work principle. A set of linear complementary equations are deduced and solved using the Lemke algorithm for gaps and contact forces between all potentially engaged components. An iterative scheme is employed to effectively deal with the nonlinearity of the Hertzian contact between non-conforming bodies. Numerical results for a 19-roller cylindrical bearing, having various combinations of roller sizes, show that the proposed method is convergent and accurate. With this method, effects of uneven roller sizes caused by manufacturing errors, on load distributions can be accurately and efficiently determined. The proposed method can be extended to deal with other types of manufacturing errors such as uneven roller angular spacing, eccentricity, ovality, friction, etc., which are of significant interest to the bearing manufacturers.
In the present work, a multi-fault classification of gears has been attempted by the support vector machine learning technique using the vibration data in time domain. A proper utilization of the support vector machine is based on the selection of support vector machine parameters. The main focus of this article is to examine the performance of the multiclass ability of support vector machine techniques by optimizing its parameters using the grid-search method, genetic algorithm and artificial bee colony algorithm. Four fault conditions were considered. A group of statistical features were extracted from time domain data. The prediction of fault classification is attempted at the same angular speed as the measured data as well as innovatively at the intermediate and extrapolated angular speed conditions. This is due to the fact that it is not feasible to have measurement of vibration data at all continuous speeds of interest. The classification ability is noted and it shows an excellent prediction performance.
With increasing popularity in high-speed machining due to its high efficiency, there is a vital need for more accurate prediction of dynamic behaviors for high-speed motorized spindles. The spindle units integrate tools with built-in motors hence a comprehensive model is required to include the multi-physics coupling property. This article presents an integrated model which consists of four coupled sub-models: state, shaft, bearing, and thermal model. Using the variational principle, a state model for the motor-spindle system is generated, which can describe the running state of the spindle, and provide electrical parameters to study the motor heat generation for thermal model and the unbalanced magnetic force for shaft dynamic model. The thermal model is coupled with the bearing and shaft dynamic model through bearing heat generation and thermal displacement. Thus, the entire model becomes an integrated electro-thermo-mechanical dynamic model. The proposed integrated model is investigated by a solution procedure and validated experimentally, and it shows that the model is capable of accurately predicting the dynamic behaviors of motorized spindles. The coupling relationship among the electrical, thermal, and mechanical behaviors of the system becomes clear from the simulation and experimental results, and some feasible methods to improve the dynamic performances of the system are obtained.
Kiln burners for industrial tile production are usually fuelled by methane gas. However, the interest towards the use of coal or synthesis gases is rapidly increasing, mainly due to the opening of important markets in developing countries. The widely variable chemical composition of these fuels demands the gas burner to be adapted on case-by-case basis, since the firing parameters are strictly fixed, to guarantee the required temperature distribution within the kiln. In this context, computational fluid dynamics analysis represents a very convenient alternative to the traditional design based on experiments. In this article three-dimensional numerical predictions are presented for a syngas-fired burner. Three different fuels, two burner layouts and two burner nominal power are considered. Temperature, velocity and oxygen mass fraction distributions are discussed, and general design lines for low lower heating value gas burners are extracted.
There has been a rapid increase in the demand for biogas applications in recent years, and dry low NOx and dry low emission gas turbine combustors are promising platforms for such applications. Combustion instability is the most important drawback in dry low NOx gas turbine combustors and has, therefore, attracted considerable research interest lately. As a fundamental study towards the use of biogas in dry low NOx and dry low emission gas turbine combustors, this article investigates the influence of CO2 in surrogate biogas on combustion instability. Tests were conducted using a dry low NOx type, a dual lean premixed gas turbine combustor. For a dual flame with dual swirl, the pilot fuel mass fraction affects the flame structure, and the flame structure, in turn, determines the temperature distribution in the combustion chamber and the combustion instability. The effects of the pilot fuel mass fraction, which is an important parameter of the combustor, and the CO2 dilution rate, which is a major contributor of biogas combustion, on the combustion characteristics and instability are investigated through dynamic pressure signal and phase-resolved OH* images. Combustion instability decreases for higher CO2 dilution rates, whose effects depend on the pilot fuel mass fraction. The instability reaches its maximum at a pilot fuel mass fraction of 0.3. Tests confirm that combustion instability diminishes with CO2 dilution, as it reduces the perturbation in the heat emission, and the flame speed decreases resulting in a greater flame surface or volume. Further, investigation of the Rayleigh Index, which represents the coupling strength of the heat release fluctuation and the natural frequency, shows that CO2 dilution weakens the coupling strength, resulting in less combustion instability.
A new multi-pass hot shape rolling was designed based on a three-dimensional analysis of channel section beams in hot rolling by the finite element method. A complete production line in industry containing 13 passes in forming the section including break-down, intermediate, and finishing sequences is modeled. The output geometry and power consumption predicted by this simulation were verified against the practical data and the measured values of the production line of Zobahan Esfahan Company. Then, a sample caliber design process to achieve a specific cross section is prepared. The minimum possible number of passes consistent with the parameters affecting the spread is the main strategy of the new caliber design. Again this new caliber design is simulated using an explicit finite element code. The geometry and dimensions of the exit cross section, the separation force, roll torques, and the power consumption in each stage are calculated. Comparison of the new roll pass parameters and that of the conventional ones in industry is made to demonstrate the advantages of the new caliber design.
Surface texturing has proved to be a very useful tool for expanding the behaviour under hydrodynamic and elastohydrodynamic regimes instead of mixed or boundary lubrication regimes, and therefore for reducing the friction coefficient under high-load low-speed conditions. This article presents the texturing of different copper test-samples using photolithography and chemical etching to measure the friction coefficient using a point contact machine. The effects of texture size, texturing density, the initial roughness of the samples and the operating conditions have all been studied. Some combinations of texturing density and texture size achieve up to 30% reduction in the friction coefficient. Taking into account experimental data, artificial neural networks are used as a tool for both predicting and optimising the friction coefficient on the textured surface for any given operating condition.
Under severe operating conditions, the thermal effects and various deformations play an important role in determining the performance of misaligned plain journal bearings. However, the thermal effects and various deformations are rarely considered simultaneously in most studies on the misaligned plain journal bearings. In this article, a comprehensive thermoelastohydrodynamic model of the misaligned plain journal bearings is developed that involves the synthetic solution of the generalized Reynolds equation, three-dimensional energy equation, and heat conduction equations of the solids. Based on this model, series of simulation results are provided to examine the influence of the thermal effects and deformations on the behavior of the misaligned plain journal bearings. In addition, the comparisons between the thermohydrodynamic and complete thermoelastohydrodynamic model are also presented for different misalignment angle and magnitude. Results show that the thermal effects and various deformations should not be ignored because of their significant influence on the film thickness, film pressure as well as other bearings characteristics.
This article focuses on the synthesis of a steering mechanism that exactly meets the requirements of Ackermann steering geometry. It starts from reviewing of the four-bar linkage, then discusses the number of points that a common four-bar linkage could precisely trace at most. After pointing out the limits of a four-bar steering mechanism, this article investigates the turning geometry for steering wheels and proposes a steering mechanism with incomplete noncircular gears for vehicle by transforming the Ackermann criteria into the mechanism synthesis. The pitch curves, addendum curves, dedendum curves, tooth profiles and transition curves of the noncircular gears are formulated and designed. Kinematic simulations are executed to demonstrate the target of design.
Residual life estimation occupies an important place in modern mechanical design and condition-based maintenance programs. Condition monitoring information can reflect the health status of the individual device, and the effective use of this information can help continuously predict the individual residual life. In this study, an exponential degradation model is developed to describe the degradation characteristics of devices for residual life estimation. This model is based on a gamma-prior Bayesian updating approach and an acceptance–rejection algorithm. With the gamma distribution representing the degradation rate differences among individuals, the real-world data can be described flexibly. By aid of Bayesian updating approach, the model can be updated with both the historical data and real-time monitoring signals. Furthermore, on the basis of the updated model and by means of acceptance–rejection algorithm, the residual life distribution can be computed without redundant computation. Consequently, the residual life can be estimated using the results of the residual life distribution. Finally, the proposed method is applied to real-world vibration-based degradation signals resulting from the accelerated fatigue testing of conical roller bearings. The results show that this method can avoid redundant computation and effectively estimate and update the bearing’s residual life. Therefore, the engineering value and general application of this novel method has been validated.
In this study, the cylindricity error was integrated into the tolerance analysis of precision rotary assemblies using Jacobian–Torsor model. The contact method was developed to rapidly determine the actual fitting clearance through the virtual assembling of the mating cylindrical parts using Monte Carlo simulation. By modifying the expressions of small displacement torsors of the cylinder pairs, the actual fitting clearance between the bore and the shaft was taken into account, which overcame the shortage of Jacobian–Torsor model that the form error cannot be processed. The effects of the cylindricity error and the number of lobes on the actual fitting clearance and the functional requirements were analyzed in detail. The results show that the cylindricity error has significant influence on the actual fitting clearance and the final functional requirements, and it should not be ignored in the tolerance analysis for precision rotary assemblies.
This article describes a double action hydraulic power take off for a wave energy converter of inverse pendulum. The power take off converts slow irregular reciprocating wave motions to relatively smooth, fast rotation of an electrical generator. The design of the double action power take off and its control are critical to the magnitude and the continuity of the generated power. The interaction between the power take off behavior and the wave energy converter;’s hydrodynamic characteristics is complex, therefore a time domain simulation study is presented in which both parts are included. The power take off is modeled using AMESim;®, and the hydrodynamic equations are implemented in MATLAB;®; simulation is used to predict the behavior of the complete system. The simulation results show that the design of the double action hydraulic power take off for wave energy converter of inverse pendulum is entirely feasibility and its superiority has been verified by the preliminary experiments, especially compared with the existing single action power take off system.
Homotopy perturbation method is a novel approach that provides an approximate analytical solution to differential equations in the form of an infinite power series. In our previous work, homotopy perturbation method has been used to evaluate thermal performance of straight fins with constant thermal conductivity. A dimensionless analytical expression has been developed for fin effectiveness. In this study, homotopy perturbation method has been applied to convective straight fins considering thermal conductivity of the fin material is a function of the fin temperature. Former expression for fin effectiveness has been rearranged. The fin efficiency and the fin effectiveness have been obtained as a function of thermo-geometric fin parameter. The results have revealed that homotopy perturbation method is a very effective and practical approach for a rapid assessment of physical systems even if the energy balance equations include terms with strong nonlinearities. The resulting correlation equations can assist thermal design engineers for designing of straight fins with both constant and temperature-dependent thermal conductivity.
This article attempts to analyze the complicated vibrational behavior of the Euler–Bernoulli beam exposed to saturated nonlinear boundary condition through proposing an innovative precise equivalent function. In this direction, the beam vibrational response is attained by way of a new effective analytical method namely Hamiltonian approach. Despite all the procedures based on perturbation methods that deadzone or saturation dead-band parameter is omitted during integration, this study indicates that how using Hamiltonian approach, the impact of dead-band parameter is taken into account leading to higher accuracy of the approximated solution. Finally, the precision of the proposed equivalent function is evaluated in comparison with the numerical solutions, giving excellent results.
Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 x 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.
In this study, various cooling liquids considered as alternatives to water were investigated for cutting performance of diamond sawing disc utilized in cutting process of natural stones. In experiments, four various cooling liquids such as water, Ace-Cool, boron oil and liquid soap and two different natural stones (Blue Pearl and Nero Zimbabwe) were used. Down-cutting mode was selected for cutting experiments. In experiments, power consumption, cutting forces, specific energy, diamond segment wear and diamond crystal failures were determined. Power consumption of diamond sawing disc was measured through an energy analyzer and cutting forces through a three-directional dynamometer (ESIT). Specific energy values were calculated through an analytical method on the basis of the resulting power consumption and cutting forces. Besides, diamond segment wear was measured through a laser device (KEYENCE) and diamond crystal failure in cutting process was analyzed through scanning electron microscopy on the basis of cooling liquids. Results of the study show that various cooling liquids proposed as alternatives to water increase significantly cutting performance of the diamond sawing disc. While maximum cutting performance was achieved with a mixture of water and boron oil, minimum performance was achieved through use of water.
Dynamic six-component force measurement is of great significance in the area of aerodynamics. Although a large number of previous experiments had been carried out to study the static characteristics of wind tunnel balance, these test methods are difficult to apply to the dynamic measurement. In this article, a new mechanical device is developed to simulate the hatch open motion with wind loads, and then the dynamic loads is measured by the novel piezoelectric balance. Owing to the dynamic motion characteristics of nonlinearity, nonstationarity, and internal coupling, an effective control system, measuring principle and signal processing method have been proposed. A combined wavelet analysis and EMD adaptive algorithm with multi-sensor data fusion method is studied to process the complicated force signal. In addition, the inertial force of the hatch is eliminated and a force curve changing with angle and time has been obtained. Furthermore, dynamic experimental results demonstrate that the mechanical system and signal processing method can effectively control the hatch open motion and extract the feature of six-component force.
Life prognostics are an important way to reduce production loss, save maintenance cost and avoid fatal machine breakdowns. Predicting the remaining life of rolling bearing with small samples is a challenge due to lack of enough condition monitoring data. This study proposes a novel prognostics model based on relative features and multivariable support vector machine to meet the challenge. Support vector machine is an effective prediction method for the small samples. However, it only focuses on the univariate time series prognosis and fails to predict the remaining life directly. So multivariable support vector machine is constructed for the life prognostics with many relative features, which are closely linked to the remaining life. Unlike the univariate support vector machine, multivariable support vector machine considers the influences among various variables and excavates the potential information of small samples as much as possible. Besides, relative root mean square with ineffectiveness of the individual difference is used to assess the bearing performance degradation and divided the stages of the whole bearing life. The simulation and run-to-failure experiments are carried out to validate the novel prognostics model. And the results demonstrate that multivariable support vector machine utilizes many kinds of useful information for the precise prediction with practical values.
Precise cable drive has been developed as an alternative transmission element to gears, belts and pulleys, chains and sprockets in electro-optical tracking system. The analytical method is developed to predict the transmission backlash of precise cable drive to enable designers to better assess the precision performance in the design study phase. Slip angle of precise cable drive is studied, and the effect of the rotational velocity and inertia of cable on the force equilibrium of contact region is considered. The deformation of cable in slip region and free region is calculated respectively and theoretical formulation of transmission backlash for precise cable drive system is carried out. Parametric sensitivity is investigated to evaluate the relationship between the transmission backlash and precise cable drive parameters including preload tension, load tension, friction coefficient, center distance and output drum radius. Experimental setup is built and the transmission backlash is tested. Effect of preload tension on the transmission backlash is tested. Results show that the experimental value and the theoretical curve of the transmission backlash fit well, which validates the theoretical method developed in this article.
In performing tasks requiring less than 6 degrees-of-freedom (DOF), lower mobility robots having a parallel structure are effective. This work investigates an asymmetric type 4 degrees-of-freedom parallel mechanism having Schönflies motions. This mechanism would be useful for multi-purpose tasks because it incorporates a transmission linkage with appropriate output modules. The mobility analysis, kinematic modelling, and singularity analysis for the mechanism are performed. Optimal design parameters with respect to both the workspace size and kinematic isotropy are identified by employing composite global design index. In addition, to cope with the singularity problem, a new design involving redundant actuation is suggested. And dynamic simulations are conducted to reaffirm its high potential in real manufacturing applications.
The objective of this research is to examine the influence of low frequency pulsed electroforming process parameters, such as current, pulse-on time, pulse-off time, and electrolyte temperature, to obtain good thickness uniformity. For this purpose, a pulsed electroforming system was designed and made. Three level, four-parameter experiments were designed using Taguchi method. The effect of parameters and optimal parameters combination were obtained through signal-to-noise ratio (S/N), analysis of variance (ANOVA) and Pareto ANOVA method. Also the regression analysis was performed to obtain a predictive model. The results demonstrated that current has a dominant effect on thickness distribution and pulse-on time, temperature and pulse-off time affect thickness distribution, respectively. Optimum electroforming process parameters were determined and experimental tests were conducted to verify the optimized parameters. The results showed the effectiveness of the proposed optimization method.
A method for modeling and calculation of natural frequencies of a belt span and transverse vibration displacement of a point in the belt span for an accessory drive system is presented in this article. In the model, the belt between two adjacent pulleys is simplified as an axial moving visco-elastic string, and the relation between stress and strain for the belt is modeled with standard visco-elastic constitutive model. The calculated natural frequencies from the axial moving string model are compared with estimated results from the pulley–string belt coupled model. It is shown that the natural frequencies can be obtained directly from axial moving string model. An experiment is carried out for getting the natural frequencies of a belt span and the transverse displacement of a point in a belt span in a generic engine front end accessory drive system. The measured natural frequencies and transverse displacements are compared well with calculated results, which validate the modeling and calculation methods presented in this article. Based on the axial moving visco-elastic string model, the influences of elastic stiffness and damping of a belt on the transverse deflections of a point in one belt span are investigated. It is shown that the transverse deflections of the belt decrease with the increasing of the elastic stiffness and damping of belt.
Automated conceptual design often shows significant promise for generating conceptual solutions automatically through searching and synthesizing known principle solutions for a desired function. However, existing automated conceptual design systems lack an efficient heuristic search strategy and a knowledge-based planning mechanism, which lead to less chance of finding promising principle solutions within a limited time. This article proposes a novel semi-heuristic planning approach for automated conceptual design which comprises two successive steps, i.e. DESIGN PLAN and DESIGN COMBINATION. During the stage of DESIGN PLAN, the planning-graph technique is employed to extract a design plan from a planning graph, which is composed of various principle solution clusters. Under the guidance of the design plan, in the second stage, DESIGN COMBINATION combines compatible principle solutions from the principle solution clusters in the design plan until finding promising conceptual solutions. A prototype system and design case illustrate that the proposed semi-heuristic planning approach can successfully achieve an automated conceptual design synthesis.
The mass production of printed electronic devices can be achieved by roll-to-roll system that requires highly regulated web tension. This highly regulated tension is required to minimize printing register error and maintain proper roughness and thickness of the printed patterns. The roll-to-roll system has a continuous changing roll diameter and a strong coupling exists between the spans. The roll-to-roll system is a multi-input-multi-output, time variant, and nonlinear system. The conventional proportional–integral–derivative control, used in industry, is not able to cope with roll-to-roll system for printed electronics. In this study, multi-input-single-output decentralized control scheme is used for control of a multispan roll-to-roll system by applying regularized variable learning rate backpropagating artificial neural networks. Additional inputs from coupled spans are given to regularized variable learning rate backpropagating artificial neural network control to decouple the two spans. Experimental results show that the self-learning algorithm offers a solution to decouple speed and tension in a multispan roll-to-roll system.
A new analytical formulation is presented to study the steady-state creep in short fiber composites using complex variable method. In this new approach, both the fiber and matrix creep at low stresses and temperatures. To analyze the crept fiber, a plane stress model was used. Important novelties of the present analytical method are determination of displacement rates with proper boundary conditions in the crept fibers and also using the complex variable method in creep analyzing. It is noteworthy that the method can be useful to study the creep behavior in polymeric matrix composites due to their high capability of creep. Moreover, another significant application of the present method is to study on the creep or elastic behavior of carbon nanotube polymer composites. Finally, the results obtained from the present analytical method (complex variable method) show a good agreement with the existing experimental results.
The sealing performance of V-insert clamp used in automobile exhaust pipes was examined for various applied torques by a specially designed pneumatic testing system. Axial clamping forces of V-insert clamp were evaluated through a clamping performance test. In the clamping performance test, increase in the torque showed gradual increase in the axial clamping force for all gaps between exhaust pipes that were considered. Slight increase in the torque resulted in relatively high axial clamping force. In the sealing performance test, when applied pressure was 50 kPa, the leak was not present in all applied torques due to no pressure change as a function of time. For 100 kPa, the leak was observed for applied torques of 3 N-m and lower. When V-insert clamp was used to join the pipes together, at least the applied torque of 4 N-m was needed in order for V-insert clamp to effectively function in the exhaustion system. Therefore, it can be concluded that V-insert clamp showed sufficient sealing performance to support the applied pressure of up to 100 kPa within the exhaustion system when relatively high torque was applied.
Uncertainties in material models and their influence on structural behavior and reliability are important considerations in analysis and design of structures. In this article, a methodology based on the evidence theory is presented for uncertainty quantification of constitutive models. The proposed methodology is applied to Johnson–Cook plasticity model while considering various sources of uncertainty emanating from experimental stress–strain data as well as method of fitting the model constants and representation of the nondimensional temperature. All uncertain parameters are represented in interval form. Rules for agreement, conflict, and ignorance relationships in the data are discussed and subsequently used to construct a belief structure for each uncertain material parameter. The material model uncertainties are propagated through nonlinear crush simulation of an aluminium alloy 6061-T6 circular tube under axial impact load. Surrogate modeling and global optimization techniques are used for efficient calculation of the propagated belief structure of the tube response, whereas Yager’s aggregation rule of evidence is used for multi-model consideration. Evidence-based uncertainty in the structural response is measured and presented in terms of belief, plausibility, and plausibility-decision values.
This article reports the result of an investigation into the effects of surface modulus, residual surface tension and bioliquid density on the vibration frequency of bioliquid-filled microtubule. Results show that influences of surface modulus and residual surface tension on the vibration frequency of bioliquid-filled microtubule are different. The influence of surface effect on the vibration frequency of bioliquid-filled microtubule is dependent on the vibration mode of microtubule and the bioliquid density in the microtubule.
In spherical-mechanism kinematics, instantaneous pole axes play the same role as, in planar-mechanism kinematics, instant centres. Their locations only depend on the mechanism configuration when spherical single-degree-of-freedom mechanisms are considered. Such a property makes them a tool to visualize and/or to analyse the instantaneous kinematics of those mechanisms. This article addresses the singularity analysis of single-degree-of-freedom spherical mechanisms by exploiting the properties of instantaneous pole axes. An exhaustive enumeration of the geometric conditions which occur for all the singularity types is given, and a general analytical method based on this enumeration is proposed for implementing the singularity analysis. The proposed analytical method can be used to generate systems of equations useful either for finding the singularities of a given mechanism or to synthesize mechanisms that have to match specific requirements about the singularities.
The shape complexity of aerospace components is continuously increasing, which encourages researchers to further refine their manufacturing processes. Among such processes, blown powder direct laser deposition process is becoming an economical and energy efficient alternative to the conventional machining process. However, depending on their magnitudes, the distortion and residual stress generated during direct laser deposition process can affect the performance and geometric tolerances of manufactured components. This article reports an investigation carried out using the finite element analysis method to predict the distortion generated in an aero-engine component produced by the direct laser deposition process. The computation of the temperature induced during the direct laser deposition process and the corresponding distortion on the component was accomplished through a three-dimensional thermo-structural finite element analysis model. The model was validated against measured distortion values of the real component produced by direct laser deposition process using a Trumpf DMD505 CO2 laser. Various direct laser deposition fill patterns (orientation strategies/tool movement) were investigated in order to identify the best parameters that will result in minimum distortion.
An electro-hydraulic shaking table is a useful experimental apparatus to real-time replicate the desired acceleration signal for evaluating the performance of the tested structural systems. The article proposes a combined control strategy to improve the tracking accuracy of the electro-hydraulic shaking table. First, the combined control strategy utilizes an adaptive inverse control as a feedforward controller for extending the acceleration frequency bandwidth of the electro-hydraulic shaking table when the estimated plant model may be a nonminimum phase system and its inverse model is an unstable system. The adaptive inverse control feedforward compensator guarantees the stability of the estimated inverse transfer function. Then, the combined control strategy employs an improved internal model control for obtaining high fidelity tracking accuracy after the modeling error between the estimated inverse transfer function using adaptive inverse control and the electro-hydraulic shaking table actual inverse system is improved by the improved internal model control. So, the proposed control strategy combines the merits of adaptive inverse control feedforward compensator and improved internal model control. The combined strategy is programmed in MATLAB/Simulink, and then is compiled to a real-time PC system with xPC target technology for implementation. The experimental results demonstrate that a better tracking performance with the proposed combined control strategy is achieved in an electro-hydraulic shaking table than with a conventional controller.
The internal-meshing rotary compressor can be applied to the CO2 transcritical refrigeration cycle due to its simple structure, self-balanced initial mass, and high pressure endurance. Because of the different fluids transmitted by compressor and pump, the design method of the internal meshing rotary pump cannot be entirely and directly employed. In order to simplify the further study of the internal-meshing rotary compressors, the essential profile equations for the inner and outer rotors are derived and explicitly formulated based on the equidistant curve of curtate epicycloid and the multi-section circular arc, respectively. Then, the relationship between the meshes of the inner and outer rotors, the position of the instantaneous center, the meshing range of the tooth tip arc, and the modification of the profiles are discussed. These basic geometric theories are expected to lay the principles for the design of the compressor of interest.
Based on the mechanism of four-fold rigid origami, this study proposes a type of deployable truss structures that consist of repetitive basic parts and retain full cyclic symmetry in the folding/deployment process. On the basis of the irreducible representations and the great orthogonality theorem, symmetry-adapted analysis using group theory is described to identify the symmetry of mobility and kinematic behavior. Equivalent three-dimensional pin-jointed frameworks are employed for the symmetric structures. To verify that the structures can be foldable while retaining their full symmetries, numerical simulations on a series of structures with different symmetries and geometries are carried out. An artificial damping is introduced to stabilize the nonlinear folding behavior with singularity. Symmetry-adapted mobility analysis reveals that the structures of this type can be continuously folded with one degree-of-freedoms. Numerical simulations using the nonlinear iterative method accurately predict the folding behavior, as the results agree very well with the theoretic value.
The aim of this study is to model and optimize the cutting conditions for the cutting force (Fc) and average surface roughness (Ra) that result from the machining of high-alloy white cast iron (Ni-Hard). The hard turning experiments were carried out on a CNC lathe with ceramic and CBN inserts. Cutting tool material, cutting speed, feed rate and depth of cut were chosen as the cutting conditions (control factors). Taguchi’s L18 orthogonal array was used for design of experiment. Optimum levels of the cutting conditions were determined using signal-to-noise (S/N) ratio, which was calculated for machining output variables (Fc and Ra) according to the ‘the-smaller-the-better’ approach. The effects of the cutting conditions on machining output variables were evaluated by the analysis of variance. The analysis of variance results showed that the depth of cut and feed rate were the most significant factors on Fc and Ra, respectively. Besides, the optimal cutting conditions for main cutting force and surface roughness were found at the different levels.
This article provides a feature ranking criterion for multi-class support vector machine classification. In the proposed criterion, feature effectiveness is estimated for individual features by their contributions to class separability in the kernel space. Class separability, measured by cosine similarity, is defined by an objective function that consists of within-class and between-class separabilities. Feature ranking is achieved for individual features by sorting their effectiveness scores. The proposed criterion is validated on University of California Irvine benchmark datasets and also applied to pitting diagnosis for a planetary gearbox. The experimental results demonstrate that the proposed criterion of feature ranking is computationally economic and effective.
In spline couplings, torque is theoretically transmitted by all teeth, supporting the same loading level. In practice, due to manufacturing and mounting errors, not all teeth transmit the same amount of torque and as a result an overloading condition may occur. In traditional design practice, this uneven load sharing between teeth is often neglected or taken into account by means of a simplified approach. In this article, a theoretical method, non-finite element method based, is developed in order to determine both exact number of engaging teeth and shared forces in involute spline couplings with parallel offset errors. The described process consists of an iterative procedure, in which algorithm is divided into three main modules: the first one aims to calculate geometrical parameters, the second one analytically determines both deformation and stiffness of teeth and the third one calculates the actual number of engaging teeth and the shared load. The algorithm has been benchmarked against finite element method results, showing a very good agreement.
In this article, we extend the finite element formulation proposed by Buckham et al.2 to include the effects of rotary inertia in isotropic circular rods (or cables). In developing our model, we first express the angular velocities in terms of the time derivatives of the Frenet frame and use this definition to determine the contributions of rotary inertia. A salient feature of this model is that only six variables representing the absolute position vectors are used as nodal coordinates. Galerkin’s weighted residual approach is used to complete the discretization.
Steam fraction in riser tubes of boilers is a critical process variable which impacts the life of the tubes and could lead to tube rupture, long boiler down time, and expensive repairs. Unfortunately this parameter is difficult to measure by hardware sensors. This article presents a new neural network softsensor for estimation and monitoring steam mass and volume fractions in riser tubes. First, conventional data were collected from a target industrial boiler. The data are then used to develop a detailed nonlinear simulation model for the two phase flow in the riser tubes and risers and downcomers water circulation. The model output is verified against the collected field data. Next, the boiler nonlinear model is used to generate data covering a wide rage of operating conditions for training and testing the neural network. The input of the neural network includes the heating power, the steam flow rate, the water feed rate, the drum level, and the drum pressure. The neural networks predict the mass steam quality and the steam volume fractions. The softsensor achieves a root mean square error on the test data less than 1.5%. The predicted steam quality is then compared with the critical limits to guide the operators for safe and healthy operation of the boilers. The developed softsensor for estimation of the steam quality has simple structure and can be implemented easily at the operator stations or the application servers.
The umbilical cable tensioner is a core component of deep-water oil and gas development, and it can lay and recover the umbilical cables to ensure the transmission of communication signals, electric signals or liquid injection. The displacements of tensioner’s clamping hydraulic cylinders, which are not synchronized as the nonlinear electro-hydraulic control system, results in the occurrence of the crawler mechanism’s stuck phenomenon or cause umbilical cable deformation or even cause damage by the extrusion in the umbilical cable’s clamping process. To ensure synchronous clamping, the structure scheme of umbilical cable tensioner, crawler mechanism, clamping mechanism and the hydraulic system of synchronous clamping control is designed in this study. This article also analyzes the function of structure parameters and hydraulic cylinders’ displacement, speed and acceleration, and builds the synchronous clamping mechanical model to reveal crawler mechanism’ clamping law. The study proposes the control strategy including the fast moving stage, the working stage and the pressuring stage based on proportional–integral–derivative control, and analyzes the characteristics of synchronous clamping control by building the synchronous clamping experimental platform in the lab environment. The experimental data shows that the tensioner’s hydraulic cylinders have excellent synchronous clamping performance and the theoretical analysis is feasible. The research has important guiding significance for the tensioner design, and provides theoretical support for the laying of the deep-sea umbilical cables.
In this article, procedure and efficiency of the reduced-basis approach in structural design computation are studied. As a model order reduction approach, it provides fast evaluation of a structural system in explicitly parameterized formulation. Theoretically, the original structural system is reduced to obtain a reduced system by being projected onto a lower dimensional subspace. However, in practice, it is a time-consuming process due to the iterations of adaptive procedure in subspace construction. To improve the efficiency of the method, some characteristics are analyzed. First, the accuracy of the subspace is evaluated and computational costs of procedures with different approaches are studied. Results show that the subspaces constructed by greedy adaptive procedures with different beginnings have the same accuracy. It is instructive that accuracy of the subspace is guaranteed by adaptive procedure. And the computational costs depend on the number of iterations in adaptive procedure. Thus, a modified adaptive procedure is proposed to reduce the computational costs and guarantee the accuracy. The modified adaptive procedure begins with experimental design methods to obtain a set of samples rather than a single sample and ends with the adaptive procedure. The start set of samples are selected by the following experimental design methods: 2k factorial design, standard Latin design and Latin hypercube design. By being integrated with the experimental design, the modified adaptive procedure saves computational costs and retains the same accuracy as traditional procedure does. As an example, the outputs of a vehicle body front compartment subjected to a bending load are illustrated. It is proved that the proposed procedure is efficient and is applicable to many other structural design contexts.
In this article, the effect of the deformed interface on the hydro-viscous drive characteristics was investigated through a three-dimensional fluid simulation and experiments. The main parameters such as pressure field, velocity field, and torque transferred by the oil film were simulated in FLUENT software in the light of the principle of the computational fluid dynamics. The results found that the dynamic pressure and velocity of the oil film goes up gradually along the radial direction, and the dynamic pressure at zone with groove is much higher than that without groove due to the hydrodynamic effect. After the interface deforming, the dynamic pressure decreases; while the torque transferred by the oil film increases slightly. Furthermore, a special hydro-viscous drive test-bed was developed to verify the correctness and validity of the theoretical results.
In this article, a novel 4-RRCR parallel mechanism is introduced based on screw theory, and its kinematics and singularity are studied systematically. First, the degree of freedom analysis is performed using the screw theory. The formulas for solving the inverse and direct kinematics are derived. Second, a recursive elimination method is proposed to solve the Jacobian matrix based on the algebra operation of reciprocal product. Then, three kinds of singularity, i.e. limb, platform, and actuation singularities are analyzed. Finally, the analysis proves that the proposed mechanism possesses two advantages of simple forward kinematics and no platform singularity.
Rotor dynamics and flow characteristics are computed for a honeycomb seal and a corresponding labyrinth seal. Firstly, rotor dynamic parameters, such as amplitude and frequency of vibration are calculated. Then these parameters are used for unsteady fluid flow computation. Numerical results indicate that the rotor vibration can reduce sealing performance and result in additional aerodynamic force on rotor. Further, the aerodynamic forces tend to reduce the self-excited vibration of rotor, and this effect becomes more apparent with the increase of pressure difference. Vortex in seal cavities is deemed to be the primary cause of the above mentioned results. The differences between the two types of seals are presented in this article. Finally, authors conclude that suitable structure design of honeycomb and labyrinth seals, or their combination can minimize rotor vibration.
In this article, transition angle, a new concept for predicting failure mode in orthotropic materials, has been proposed. This angle is introduced as a transition angle from fiber fracture mode to matrix one of orthotropic part. Theoretical calculation of this angle is performed using the concept of microcracks in crack tip damage zone. In order to ensure about the consistency of the proposed approach with the nature of the fracture phenomena in wood, the results obtained from theoretical method are put into contrast with those obtained from practical testing. Transition angle is usable in introducing a safe domain for an angle in loading vector to fiber direction at laminated composite materials and prevents catastrophic failure.
The maintenance strategies optimization can play a key role in the industrial systems, in particular to reduce the related risks and the maintenance costs, improve the availability, and the reliability. Spare part demands are usually generated by the need of maintenance. It is often dependent on the maintenance strategies, and a better practice is to deal with these problems simultaneously. This article presents a stochastic dynamic programming maintenance model considering multi-failure states and spare part inventory. First, a probabilistic maintenance model called hidden semi-Markov model with aging factor is used to classify the multi-failure states and obtain transition probabilities among multi-failure states. Then, spare parts inventory cost is integrated into the maintenance model for different failure states. Finally, a double-layer dynamic programming maintenance model is proposed to obtain the optimal spare parts inventory and the optimal maintenance strategy through which the minimum total cost can be achieved. A case study is used to demonstrate the implementation and potential applications of the proposed methods.
Wind turbine gearbox operates under a wide array of highly fluctuating and dynamic load conditions caused by the stochastic nature of wind and operational wind turbine controls. Micropitting damage is one of failure modes commonly observed in wind turbine gearboxes. This article investigates gear micropitting of high-speed stage gears of a wind turbine gearbox operating under nominal and varying load and speed conditions. Based on the ISO standard of gear micropitting (ISO/TR 15144-1:2010) and considering the operating load and speed conditions, a theoretical study is carried out to assess the risk of gear micropitting by determining the contact stress, sliding parameter, local contact temperature and lubricant film thickness along the line of action of gear tooth contact. The non-uniform distributions of temperature and lubricant film thickness over the tooth flank are observed due to the conditions of torque and rotational speed variations and sliding contact along the gear tooth flanks. The lubricant film thickness varies along the tooth flank and is at the lowest when the tip of the driving gear engages with the root of the driven gear. The lubricant film thickness increases with the increase of rotational speed and decreases as torque and sliding increase. It can be concluded that micropitting is most likely to initiate at the addendum of driving gear and the dedendum of driven gear. The lowest film thickness occurs when the torque is high and the rotational speed is at the lowest which may cause direct tooth surface contact. At the low-torque condition, the varying rotational speed condition may cause a considerable variation of lubricant film thickness thus interrupting the lubrication which may result in micropitting.
Space deployable mechanisms have been widely employed in modern spacecraft, and the dynamic performance of such mechanisms has become increasingly important in the aerospace industry. This article focuses on the dynamic performance of a deployment mechanism with clearance considering damping, friction, gravity, and flexibility. The modeling methods of revolute joint with clearance, close cable loop, and lock mechanism of a typical deployable mechanism are provided in this article. Based on these proposed methods, the dynamics model of a space deployable mechanism with clearance is established using the multi-body program ADAMS. The effects of clearance, damping, friction, gravity, and flexibility on the dynamic performance of a deployable mechanism in the deploying and locking processes are studied using simulations. The results reveal that the deployable mechanism exhibits evidently nonlinear dynamic characteristics, thus validating the significance of clearance, damping, friction, gravity, and flexibility in system dynamic performance.
In this article, an optimal design problem of spur gear drive with a fixed load factor is formulated as a nonlinear optimization model. Three methods are presented to find the globally optimal design scheme on the structure of the spur gear pair. By suitable variable transformation, the constructed model is first converted into a linear program with mixed variables. By developing an algorithm of global optimization for solving a binary linear programming with mixed variables, all global optimal solutions are found for the original design problem. Taking into account the modification of the contact ratio factors, a specific global optimization method is provided to optimize the design of spur gear drive with soft tooth flank in a continuous variable space. On the basis of enumeration of the discrete variables and utilization of the monotonicity in the optimal model, another global optimization method is designed to search for the global optimal solutions in the mixed variable space, which does not depend upon whether the modification of contact ratio factor exists or not. Case studies are employed to demonstrate the validity and practicability of the constructed model and the proposed methods.
In this study, the performance of a typical bubbly water ramjet was investigated by the application of computational fluid dynamics method at different vessel velocities up to 80 knots for a range of air mass flow rates up to 0.9 kg/s. For this purpose, the validity of presented method was preliminarily examined for a converging–diverging nozzle. Then, a designed ramjet with discrete injection configuration was studied at different operating conditions. It was proved that the injection process significantly increases the amount of generated thrust up to 10 times more than the thrust of a single-phase water ramjet. The results suggest that for optimum operation of the ramjet, specific values should be assigned for both inlet and mixing chamber diameters with respect to outlet diameter. Furthermore, it seems that the modification of mixing chamber profile can effectively improve the performance, as the generated thrust of model with throat-like chamber surpasses that for conventional model up to more than two times. Finally, in order to rectify the contradiction of results obtained in previous literatures on the dependency of thrust on vessel velocity, a meaningful relation was derived between the generated thrust of the ramjet with the advance velocity at different air mass flow rates.
In many modern continuous production lines of steel sheets, a twist roll machine is used to change the strip direction for shortening the production line. A twist roll machine typically consists of a cylindrical body on which some guide rollers are mounted in rows to gradually change the traveling direction of the strip when passes over the guide rollers. In this article, quality of the sheets after exiting an industrial twist roll machine is first investigated. The amount and distribution of wear on the guide rollers are also assessed by measuring and comparing diameter at different sections of selected worn and new guide rollers. The specific wear rate as well as friction coefficient for guide rollers made of two different popular polymers is measured by pin-on-disk wear tests. Details of the strip path on the twist roll machine as well as contact between the strip and all the guide rollers are specified, and stress distribution in strip and the guide rollers is studied by finite element analysis. Effects of the guide rollers material and arrangement, the bridle rolls tension, and width and thickness of the strip on the amount and distribution of wear on the guide rollers as well as the elasto-plastic response of the strip are studied. The results are utilized to propose techniques for reducing defects on the sheet and the guide rollers, and finite element simulations show the effectiveness of these techniques.
This article presents a cutting force model for the milling of Inconel 718 whose machinability is considered to be very poor. The Johnson–Cook constitutive material model is used to determine the flow stress of Inconel 718 while the shear angle is determined based on a shear plane model assuming that the total energy on the shear plane plus the energy on the rake face is minimum. The temperature in the machining region is determined by using an iterative process. Finally, the cutting forces on each tooth of the milling cutter are calculated from its chip load considering the oblique cutting effects. The model is then verified by comparing the model predictions with the experimental data under the corresponding conditions, which shows a relatively good agreement with an average percentage error of 10.5% along the feed and normal directions.
The journal and the shaft shoulder of large-scale spindle are usually worn for insufficient lubrication or the entering of dust. Then, the large-scale spindle is necessary to be immediately repaired. Based on the repairing feature of the large-scale spindle and the main problem of the traditional repairing method, a planetary grinding equipment was developed. The working principle and the structure characteristic of the planetary grinding equipment were analysed. Furthermore, the spindle of the large-scale fan rotor was repaired in situ using the planetary grinding equipment. It was found that the repaired spindle has good dimension precision and surface roughness. A feasible technology was provided for the repairing of the large-scale spindle in situ using this machining method.
In this article, particle image velocimetry was used to measure the two-dimensional flow field for vortex gripper. The vortex gripper was divided into two parts for respective research, including vortex cup and the gas film gap. In the part of vortex cup, the tangential velocity increases gradually, and the velocity decreases intensely in the vicinity of the vortex cup’s wall after it reaches maximum. In addition, the velocity decreases gradually with the increase of the gas film gap. In the part of gas film gap, the tangential velocity increases to maximum along the radial direction first; after the air flows into the gas film gap due to the viscous impedance, it decreases gradually. When the gas film gap’s thickness is smaller, the velocity almost decreases to zero at the external edge of the skirt. However, when the gas film gap increases to a certain thickness, the velocity does not decrease to zero, and the flow air still keeps a certain speed out of it. The velocity decreases gradually with the increase of the gas film gap. The radial velocity in the vortex cup and the gas film gap is of very small order of magnitude comparing with the average velocity and tangential velocity. The analysis of the Reynolds number shows that the flow in the vortex cup is the turbulent flow, and at the part of the gas film gap, the Reynolds number increases with the increase of the gas film gap, and the flow changes from the laminar flow to the turbulent flow. Through the particle image velocimetry experiment, the vortex gripper’s internal flow structure is studied. It is the theory support of the computational fluid dynamics simulation study for vortex gripper and the structure optimization in the future work.
Topology optimization is a popular method to optimize the material for structural components. For minimum compliance problem, the effectiveness of the obtained topology is characterized by its compliance value. Here, compliance value depends on many factors. Due to uncertainties in these factors, desired compliance value is difficult to achieve. The sensitivities of these factors have already been investigated by researchers. Present work focuses on the selection and the significance of tolerance of these factors. The tolerance of input factors like applied force, volume fraction, aspect ratio of material domain and modulus of elasticity are selected to investigate the effect on compliance. To select tolerance range, the concept of inner and outer orthogonal arrays proposed by Taguchi is employed along with solid isotropic microstructure with penalization method of topology optimization. Different tolerance ranges are selected for each factor and tolerance combinations are generated using inner array. Thereafter outer array is used to create replications of a particular combination. For each replicate, compliance value is simulated using solid isotropic microstructure with penalization method. Based on statistical analysis of obtained values, significant factors are identified and optimal tolerance ranges are selected. In similar way, maximum deflection values are also simulated for analysis. Proposed methodology is applied on four different benchmark problems. The presented approach provides the effect of each possible set of tolerance on performance functions, which are compliance and deflection values. This work will be helpful to designers to select optimum tolerance of factors to achieve desired compliance value and performance for a topologically optimized structure prior to manufacturing in the realistic environment.
Feature selection has been used to achieve dimension reduction in the field of fault diagnosis. This article introduces a multi-criterion fusion framework for feature selection that takes into account three aspects of features: effectiveness, correlation, and classification performance. This framework enables a more comprehensive evaluation of features than does a single criterion. The proposed framework is implemented using five effectiveness criteria and a correlation criterion. It is used to diagnose eight failure modes of a planetary gearbox. The experimental results demonstrate that the proposed multi-criterion framework outperforms many well-studied single criteria.
In this study, the transfer matrix method is used to predict bending critical speeds of hydrogenerator shaft lines. A computer routine was developed for the calculations and this code is applied to two industrial hydrogenerators. The obtained results are compared with the data/guarantees from the equipments’ manufacturers. It is concluded that the present approach is a useful tool for rotor dynamics analysis at early design phases of hydrogenerator shaft lines.
A new method which employs pole placement technique of modern control theory to tune proportional–integral–derivative parameter for simultaneously achieving multi-axis matched dynamics and single axis stability is addressed in this article. This method has the advantage of simplicity in tuning, intuition in principle, and easy in program. Four different cascade proportional–integral–derivative control structures are investigated for applying the matching method appropriately and better understanding of its limitation. The deduction that the feedback gain ratios of position to speed loop of the same type interpolation axes imposed with the same desired poles are approximately equal is obtained. Experimental results show that the servo feed system designed or tuned by the proposed method can easily achieve matched dynamics. Furthermore, this method can be also employed to multi-axis motion system which is composed with both linear and rotating axes.
Extensive researchers have conducted several experiments in the past for selecting the optimum parameters in machining nickel based alloy – Inconel 718. These experiments conducted so far are dealt with dry machining and flooded coolant machining of nickel alloy Inconel 718. In this research study, the usage of refrigerated coolant is also dealt with and it is compared with dry machining and flooded coolant machining. Cutting speed, feed and depth of cut are considered as the machining parameters. The effectiveness of the refrigerated coolant in machining the heat resistant super alloy material Inconel 718 with respect to these machining parameters are described in this article. The machinability studies parameters were generated with surface roughness and flank wear. The performance of uncoated carbide cutting tool was investigated at various cutting condition under dry, flooded coolant and refrigerated coolant machining. The relationship between the machining parameters and the performance measures were established and using analysis of variance significant machining parameters determined. This article made an attempt to Taguchi optimization technique to study the machinability performances of Inconel 718. Taguchi approach is an efficient and effective experimental method in which a response variable can be optimized, given various control and noise factors, using fewer experiments than a factorial design. Taguchi’s optimization analysis indicates that the factors level, its significance to influence the surface roughness and flank wear for the machining processes. Confirmation tests were conducted at an optimal condition to make a comparison between the experimental results foreseen from the mentioned correlations.
A split cam design is proposed to solve the problem of assembly of the single piece cam in the flexible raced bearing of an earlier proposed novel harmonic drive system, which shows better torque characteristics and capacities in comparison to the conventional one of same size with oval-shaped strain wave generating cam. The cam profile has circular arcs at two working zones at 180° phases. The proposed profile shape is identified as the cause of trouble in assembly if the cam is made single piece. The split cam is made of two identical pieces having circular arc edges. These pieces constitute the cam in assembly after putting it inside the inner race of the flex bearing and adjusted by an adjuster. The design, kinematics, and the assembly method of the proposed split cam are presented in this article. The split cam arrangement not only solves the assembly problem but also gives a scope of fine adjustment of center distance (eccentricity). Such an adjustment is not possible in conventional oval wave generating cam. Stresses in flex gear cups assembled with both type cams at load and no-load conditions are estimated using finite element method. Some results are verified experimentally. Although the flex gear cup with the proposed split cam experiences lower stresses at load transmitting active gear contact zones, it shows higher stresses at some non-active zones (where teeth are free of load). It is apparent from results that stresses at those non-active zones do not increase substantially with the increase in torque, as they are away from active zones.
The conjugated straight-line internal gear pair, including a pinion with straight-line profile and an internal gear with profile conjugated to the pinion profile, is the key components to the conjugated straight-line internal gear pumps. Truninger [Truninger gear pump. Patent 3491698, USA, 1970] pointed that this kind of gear pairs leads to a very small trapped volume, which is 10 times smaller than that of the conventional involute internal gear pumps. Therefore, it can yield significant reduction in noise levels of the pumps. However, to the authors’ knowledge, there is no research on the design of these gear pairs until now. First, our study describes the straight-line profile of the pinion mathematically with definitions of some geometric parameters. Second, according to the theory of gearing, the mathematical models of the rack-cutter and the conjugated internal gear are derived. Then, the condition to avoid overcutting is obtained for the generation of the pinion by a rack-cutter. Finally, the condition to avoid interference in the internal gear pair is derived as a non-linear equation system and an algorithm is developed to find a numerical solution. Two examples are presented to demonstrate how to determine tooth numbers of the internal gears for avoiding interference. It is hoped that the study in this article should be helpful to the designers of the conjugated straight-line internal gear pairs. Moreover, it could provide a prepared knowledge for the researchers to investigate the performances of the fluid power gear machines, pumps, and motors, with the conjugated straight-line internal gear pumps.
In this study, variations of local heat transfer coefficient are obtained in subcooled flow boiling conditions for water/TiO2 nanofluid in a vertical and horizontal tube. The results for the base fluid are compared with the predictions of the well known Shah correlation and Gnielinski formula for laminar and turbulent flows for single-phase forced convection and also with Chen correlation for subcooled flow boiling. A good agreement between the results is realized. At the subcooled regime, heat transfer coefficient of nanofluid is less than that of the base fluid and it decreases by increasing nanoparticle concentration for both of the channels; however, addition of the nanopraticles into the fluid causes that the vapor volume fraction increases.
Univariate dimension-reduction integration, maximum entropy principle, and finite element method are employed to present a computational procedure for estimating probability densities and distributions of stochastic responses of structures. The proposed procedure can be described as follows: 1. Choose input variables and corresponding distributions. 2. Calculate the integration points and perform finite element analysis. 3. Calculate the first four moments of structural responses by univariate dimension-reduction integration. 4. Estimate probability density function and cumulative distribution function of responses by maximum entropy principle. Numerical integration formulas are obtained for non-normal distributions. The non-normal input variables need not to be transformed into equivalent normal ones. Three numerical examples involving explicit performance functions and solid mechanic problems without explicit performance functions are used to illustrate the proposed procedure. Accuracy and efficiency of the proposed procedure are demonstrated by comparisons of the estimated probability density functions and cumulative distribution functions obtained by maximum entropy principle and Monte Carlo simulation.
In this study, transverse nonlinear vibration and instability analysis of a viscous-fluid-conveyed single-layered graphene sheet (SLGS) subjected to thermal gradient are investigated. The small-size effects on bulk viscosity and slip boundary conditions of nanoflow through Knudsen number (Kn), as a small size parameter is considered. Viscopasternak model is considered to simulate the interaction between the graphene sheet and the surrounding elastic medium. Continuum orthotropic plate model and relations of classical plate theory are used. The nonlocal theory of Eringen is employed to incorporate the small-scale effect into the governing equations of the graphene sheet. Differential quadrature method is employed to solve the governing differential equations for simply supported edges. The convergence of the procedure is shown and the effects of flow velocity, temperature change and aspect ratio on the frequency of the single-layered graphene sheet are investigated. Moreover, the critical flow velocities and the instability characteristic are determined. It is evident from the results that the natural frequency of nanosheet increases with rising temperature.
The tapping mode is one of the mostly employed techniques in atomic force microscopy due to its accurate imaging quality for a wide variety of surfaces. However, chaotic microcantilever motion impairs the obtention of accurate images from the sample surfaces. In order to investigate the problem the tapping mode atomic force microscope is modeled and chaotic motion is identified for a wide range of the parameter's values. Additionally, attempting to prevent the chaotic motion, two control techniques are implemented: the optimal linear feedback control and the time-delayed feedback control. The simulation results show the feasibility of the techniques for chaos control in the atomic force microscopy.
This article analyzes the effect of electrostatically actuated flexible microvalves on the output performance of electrostatic micropumps. The existence of microvalves affects the pressure rise and volumetric efficiency of micropumps. The effects of valve volume on the pressure rises of pumps with single and double cavities are predicted by integrating energy minimization with the analytical solutions for circular membrane deflection under uniform pressure. Outlet valve resistance is analytically specified as well. The micropumps could achieve their maximum volumetric efficiency in the case of zero back pressure. However, the design of the inlet valve leads to gas trapping in the inlet valve during discharge. In such a situation, the volumetric efficiency of the pumps drops along with the increase of pressure rise. Moreover, the flexibility of valve plates yields a much lower voltage than the cavity actuation for the valve closing and the breakdown voltage of the dielectric layer on the valve body, thereby enhancing the reliability of the microvalves.
In this study, mixed convection in vertical and inclined parallel plate microchannels, has been investigated. The flow is steady, laminar, and incompressible and the walls are at constant temperature. A FORTRAN program has been written to solve the governing equations with wall velocity slip and temperature jump boundary conditions, and the results have been presented for Reynolds numbers of 25, 50, and 100, Knudsen numbers of 0, 0.005, 0.02, and 0.09, Richardson numbers of 0, 1, and 1.77, and microchannel inclination angles of 10°, 30°, 50°, and 90°. Results showed that wall velocity slip, friction coefficient, centerline velocity, and heat transfer rate decreases with increasing the Knudsen number. Increasing the Richardson number, for a given Reynolds number, decreases the microchannel centerline velocity because of the increasing of wall adjacent velocity, which is due to the promotion effect of natural convection. Also, the friction coefficient and Nusselt number increases with channel inclination angle.
This article presents the parametric study of pull-out radius of steam generator shell nozzle junction for fast breeder reactor. An efficient finite element modeling for shell nozzle junction has been presented in which shell elements are employed to idealize the whole region. In shell nozzle junction, pull-out region is an important part, so that region is taken and studied with different radius of curvature. The pull-out radius varies from 40 to 80 mm. Five models are taken into consideration and each with different radius of curvature. The optimized stress values for all the models are presented here.
Accurate fault prognosis is of vital importance for condition-based maintenance. As to complex mechanical systems, multiple sensors are often used to collect condition signals and the observation process may rather be non-Gaussian and non-stationary. Traditional hidden semi-Markov models cannot provide adequate representation for multivariate non-Gaussian and non-stationary time series. The innovation of this article is to extend classical hidden semi-Markov models by modeling the observation as a linear mixture of non-Gaussian multi-sensor signals. The proposed model is called as a multi-sensor mixtured hidden semi-Markov model. Under this new framework, modified parameter re-estimation algorithms are derived in detail based on the complete-data expectation maximization algorithm. In the end the proposed prognostic methodology is validated on a practical bearing application. The experimental results show that the proposed method is indeed promising to obtain better prognostic performance than classical hidden semi-Markov models.
We study dynamic fragmentation of metallic structures using the cracking particles method with obscuration zone. The cracking particles method is an efficient meshfree method for modeling dynamic fracture. Fracture is modeled by a set of crack segments. The cracking particles method does not require the representation of the crack topology. To avoid numerical fracture observed in discrete approaches, we employ obscuration zones proposed by Mott in his analytical work of fragmentation theory. We also study the influence of initial imperfections with different stochastic input parameters on the results.
Heavy goods vehicles exhibit poor braking performance in emergency situations when compared to other vehicles. Part of the problem is caused by sluggish pneumatic brake actuators, which limit the control bandwidth of their antilock braking systems. In addition, heuristic control algorithms are used that do not achieve the maximum braking force throughout the stop. In this article, a novel braking system is introduced for pneumatically braked heavy goods vehicles. The conventional brake actuators are improved by placing high-bandwidth, binary-actuated valves directly on the brake chambers. A made-for-purpose valve is described. It achieves a switching delay of 3–4 ms in tests, which is an order of magnitude faster than solenoids in conventional anti-lock braking systems. The heuristic braking control algorithms are replaced with a wheel slip regulator based on sliding mode control. The combined actuator and slip controller are shown to reduce stopping distances on smooth and rough, high friction (μ = 0.9) surfaces by 10% and 27% respectively in hardware-in-the-loop tests compared with conventional ABS. On smooth and rough, low friction (μ = 0.2) surfaces, stopping distances are reduced by 23% and 25%, respectively. Moreover, the overall air reservoir size required on a heavy goods vehicle is governed by its air usage during an anti-lock braking stop on a low friction, smooth surface. The 37% reduction in air usage observed in hardware-in-the-loop tests on this surface therefore represents the potential reduction in reservoir size that could be achieved by the new system.
Recently, the locomotion of a microrobot wirelessly actuated by electromagnetic actuation systems has been studied in many ways. Because of the inherent characteristics of an electromagnetic field, however, the magnetic field of each coil in the electromagnetic actuation system induces magnetic field interferences, which can distort the desired electromagnetic field, preventing the microrobot from following the desired path. In this article, we used two pairs of Helmholtz coils and two pairs of Maxwell coils in a two-dimensional electromagnetic actuation system. Generally, the two pairs of Helmholtz coils generate the torque for the rotation of the microrobot and the two pairs of Maxwell coils generate the propulsion force of the microrobot. Both pairs of Helmholtz and Maxwell coils have to work to simultaneously align and propel the microrobot in a desired direction. In this situation, however, the electromagnetic fields produced by the Helmholtz coils can interfere with those produced by the Maxwell coils. This interference is closely dependent on the position of the microrobot in the region of interest inside the electromagnetic coils system. This means that the alignment direction and propulsion force of the microrobot can be distorted according to the position of the microrobot. Therefore, we propose a compensation algorithm for the electromagnetic field interference using the position information of the microrobot to correct the magnetic field interferences. First, the interference of an electromagnetic field obeying the Biot–Savart law is analyzed by numerical analysis. Second, a position-based compensation algorithm for the locomotion of a microrobot is proposed. Various locomotion tests of a microrobot verified that the proposed compensation algorithm could reduce the normalized average tracking error from 5.25% to 1.92%.
In this article, a concept of an application for a Fibre Bragg Grating sensor grid for Structural Health Monitoring the foremast of STS Dar Mlodziezy is presented and discussed. Research presented in this article are related to characteristics of the foremast of STS Dar Mlodziezy during her normal operation. The main goal of the research was to determine the strain/stress level of the foremast above the topmast crosstrees where three steel jib stays are mounted. To achieved this goal during the research special attention was paid to setting the sails and to taking in the sails.
A general algorithm for the kinematic synthesis of Geneva mechanisms with curved slots is introduced here, when a suitable displacement program is given with the aim of avoiding the typical shock-loading problems of conventional Geneva mechanisms. Moreover, the effects of the design parameters are analyzed through significant numerical examples. These parameters are: number of driving cranks; number of slots; imposed displacement program; and pin radius of the driving crank for the Geneva mechanism.