The application of linear motor-driven stages as the feed drivers of CNC micro milling machine tools is growing. In addition to employ high speed and high precision equipment such as linear motor-driven stages, the precision of the machined contours is highly dependent on the capabilities of the servo controllers. In this paper, the design of a precise controller for a two-axis LMDS has been investigated for micro-milling applications. In such feed drives, disturbances such as friction, force ripples, and machining forces have adverse effects on the workpiece positioning precision due to the direct drive concept behind them. Therefore, in order to have an acceptable transient response and disturbance rejection properties, a two-degree-of-freedom proportional–integral–derivative controller was employed for each axis. To design this controller, the zero-placement method was used. To compensate disturbances and machining contour errors, the utilization of Kalman filter observers, neural networks, cross-coupled controllers, and different integration of them were studied. The controllers were experimentally examined for circular motions. An integrated controller consisted of a Kalman filter disturbance observer, a cross-coupled controller, and a well-designed two-degree-of-freedom proportional–integral–derivative controller resulted in a high contouring and tracking precision. The controller could also reduce the spikes caused by the friction at the motion reversal points such as the quadrants in circle trajectories.
Efficient actuation is an important requirement in electromechanical designs. Although hydraulic actuators are used extensively when high-magnitude forces are present in heavy machinery, they are not very energy-efficient. This paper aims to increase the efficiency of electro-hydraulic servo systems after introducing a controllable supply pressure and six mode of operation for different condition. This process allows for the system to have very low energy consumption whenever its environmental force agrees with its position reference signal. For this purpose, first, the electrohydraulic servo systems is modeled and a robust H controller is designed for each mode of operation. The resulting control system works based on applying each mode strategy at right time to save energy. The effectiveness of this method is tested by conducting experiments on a hydraulic test rig and presenting the experimental results.
In this paper, an application of the inverse method based on the artificial bee colony algorithm has been demonstrated for estimating unknown dimensions of a rectangular perforated fin. The analysis has been done to maximize the heat transfer rate for a given volume occupied by the fin. The perforated fin has been assumed to dissipate heat by virtue of natural convection and surface radiation. The least square mismatch between a given volume and an initially guessed one is used to define the objective function that in turn has been minimized using the artificial bee colony algorithm. A comparative study reveals the advantage of the artificial bee colony algorithm against other evolutionary and stochastic optimization methods for the present problem. Since, there exist multiple dimensions satisfying a given volume, so, the most optimal dimension has been identified on the basis of a heat transfer rate maximization criterion. The study reveals that a given amount of heat transfer rate can be achieved with multiple combinations of the fin surface area and even a particular value of surface area can result in different heat transfer rates.
The use of two-phase screw expanders in power generation cycles can achieve an increase in the utilisation of available energy from a low-temperature heat source when compared with more conventional single-phase turbines. The efficiency of screw expander machines is sensitive to expansion volume ratio, which, for given inlet and discharge pressures, increases as the expander inlet vapour dryness fraction decreases. For single-stage screw machines with low inlet dryness, this can lead to underexpansion of the working fluid and low isentropic efficiency. The cycle efficiency can potentially be improved by using a two-stage expander, consisting of a machine for low-pressure expansion and a smaller high-pressure machine connected in series. By expanding the working fluid over two stages, the built-in volume ratios of the two machines can be selected to provide a better match with the overall expansion process, thereby increasing the efficiency. The mass flow rate though both stages must be matched, and the compromise between increasing efficiency and maximising power output must also be considered. This study is based on the use of a rigorous thermodynamic screw machine model to compare the performance of single- and two-stage expanders. The model allows optimisation of the required intermediate pressure in the two-stage expander, along with the built-in volume ratio of both screw machine stages. The results allow specification of a two-stage machine, using either two screw machines or a combination of high-pressure screw and low-pressure turbine, in order to achieve maximum efficiency for a particular power output. For the low-temperature heat recovery application considered in this paper, the trilateral flash cycle using a two-stage expander and the Smith cycle using a high-pressure screw and low-pressure turbine are both predicted to achieve a similar overall conversion efficiency to that of a conventional saturated vapour organic Rankine cycle.
Friction stir welding is a novel joining process extensively used for welding of aluminum alloys. It is widely known that the process parameters involved in friction stir welding play a pivotal role in determining the final characteristics and microstructure of the joint. However, it is still unclear that what combination of process parameter values will lead to the optimum joint characteristics. Taguchi technique is a handy and efficient method that has been widely used for performing optimization in manufacturing engineering. In this paper, lap joint friction stir welding was performed on AA1100 and the process parameters were optimized using Taguchi L16 orthogonal design of experiments. Unlike previous studies on optimization of friction stir welding process in aluminum alloys, a more comprehensive approach has been taken towards the number of input and output parameters of the process. Process parameters considered in this study were tool rotational speed, tool traverse speed, tool tilt angle, and tool pin shape. The optimum design was obtained with reference to output parameters including hardness and grain size in the weld center zone, maximum working temperature, joint tensile strength, and elongation as well as the vertical and horizontal forces on the tool during the process. Analysis of variance was additionally performed to evaluate the significance of each design parameter on output parameters. Results gained from analysis of variance indicated that rotational speed and traverse speed were the most critical parameters in determining the weld mechanical properties as well as quality of the weld microstructure. Finally, to validate predicted optimum values based on Taguchi technique, confirmation tests were conducted, where an excellent agreement was observed between the predicted and experimental values, showing accuracy of the employed method and obtained results.
Two-step approach of validation is proposed to validate a numerical model, capable of accurate prediction of mixing power characteristics of a centrifugal mixer with vertical axis. Two sets of experiments and two sets of numerical simulations are presented—the first set to determine physical characteristics of the particles comparing the numerical simulations results with experimental data, and the second set to validate predicted behavior of anchor type vertical axis impeller for mixing of same particles. Zeolite particles were used for actual calculations. After determining shear modulus, coefficient of interaction, static friction coefficient, and rolling friction coefficient through optimization process based on numerical simulations with subject function of diameter and angle of repose derived from experiment, using these values in numerical simulation of impeller mixer mixing zeolite particles led to results, which were in good agreement with results of the second set of experiments. The obtained zeolite material parameter values can therefore serve as a solid basis for discrete elements method based numerical simulation of zeolite granular materials.
It is well established that the volumetric and isentropic efficiencies of reciprocating compressors used for household refrigeration are significantly reduced by suction gas superheating. Moreover, excessive levels of temperature may affect the reliability of some components, such as the electrical motor. This paper reports a modeling approach to predict the temperature distribution in the gas and solid components of an oil-free linear compressor. A simulation model based on the finite volume method was used to solve the heat conduction in the solid components and gas flow inside the compressor. On the other hand, the compression cycle in the cylinder was solved with a transient lumped formulation, but in a coupled manner with the remainder of the solution domain. The prediction of the suction gas superheating obtained with the model was in good agreement with the measurements, despite discrepancies being observed in some solid components and in the gas path along the discharge system. The model does not require any experimental calibration and hence is suitable to analyze different compressor designs. To illustrate this, the model was applied to predict the temperature distribution with respect to two design parameters.
Applying the independent metering circuit on the excavator is an effective way to reduce energy consumption and improve the performance of the actuators, e.g. the boom in the negative load circuit. This paper aims to improve the energy efficiency and the stationarity of the boom system based on the independent metering circuit using the strategy of flow and pressure accordance, pump and valve coordinate in dynamic and static. After studying the mechanic structure of the boom, principles of the system and elements characteristics, the four control strategies are designed to settle the problems in the traditional throttling system using mechanically connected orifices valves such as the load-sensing system and new coordinate challenges brought with the multivariable. Finally, experiments based on load sensing and independent metering circuit are implemented on a physical prototype. The experimental results show that the energy consumption of the boom system falls by 15% compared to the load-sensing system; the pressure pulsations of the pump when the boom starts to move reduce from 6.9 MPa to 1.7 MPa. Therefore, the independent metering circuit and the control strategy are good configuration for the boom actuator.
Binding of metal powders using electrochemically deposited binders provides a novel way of carrying metal additive manufacturing at ambient temperatures. In this paper, a mathematical model was developed to predict the hardness and the yield strength of electrochemically bound parts. In this work, an existing composite hardness model is modified to predict the deposit hardness. Experimental verification of the model was performed using brass and aluminum substrates with nickel as the binder under similar deposition parameters to verify that substrate effects were not involved in the measured hardness value. The film hardness values were then compared for deposits on both brass and aluminum substrates. The model was able to predict the hardness values on both substrates within 8% of each other thereby eliminating the substrate effects involved.
An integrated optimization framework for multi-cycle environmental stress screening tests and preventive maintenance scheduling is proposed. The proposed framework considers the improvement of product reliability through environmental stress screening tests and the associated screening cost, and the effect of preventive maintenance schedule on the maintenance cost as well. The environmental stress screening model is extended first to be applicable for multi-cycle environmental stress screening tests. The extended environmental stress screening model characterizes the product reliability function which survives the environmental stress screening test in terms of both the number of environmental stress screening cycles and the severity of screening stress. Afterwards, an integrated cost model is established by considering the cost of preventive maintenance, the cost of corrective maintenance, the cost of environmental stress screening test, and the cost due to failure of products in the environmental stress screening test. The application case study demonstrates the implementation procedures and the application effectiveness of the proposed approach. The application results show that, considering the cost due to environmental stress screening and the cost due to maintenance separately could lead to suboptimal decisions. For enterprises responsible for both environmental stress screening and maintenance, it is suggested to optimize the environmental stress screening test and maintenance scheduling jointly to minimize the overall cost.
Electroless nickel boron coatings were prepared from thallium and lead-free alkaline bath. The influence of surfactants on the properties of electroless nickel boron coatings was studied. Three surfactants namely sodium dodecyl sulfate, cetyltrimethyl ammonium bromide and 3-(N, N–Dimethylmyristylammonio) propanesulfonate were used. Morphology, microhardness, surface finish, topography and corrosion resistance of the coatings were evaluated. Electroless nickel boron coatings with addition of surfactant sodium dodecyl sulfate, cetyltrimethyl ammonium bromide and 3-(N, N-Dimethylmyristylammonio) propanesulfonate results in a smooth surface, with an average roughness value (Ra) of 0.220 µm for cetyltrimethyl ammonium bromide, 0.198 µm for sodium dodecyl sulfate and 0.174 µm for 3-(N, N-Dimethylmyristylammonio) propanesulfonate which are less than the Ra without surfactant addition (0.256 µm). The deposits had a microhardness value of 590 and 743 HV in the as-plated and heat-treated conditions, respectively. With addition of sodium dodecyl sulfate, cetyltrimethyl ammonium bromide and 3-(N, N-Dimethylmyristylammonio) propanesulfonate, a significant improvement in the microhardness is observed. Potentiodynamic polarization tests were carried out in 3.5 wt% NaCl to determine the real anticorrosion performance of the electroless nickel boron deposits. The entire experimental procedure, the results achieved, and their investigation are presented in this paper.
This study considers the effect of forging direction on the initial shape of sheet to create a stepped work piece. The purpose of this study is to consider rolling direction in 0°, decreasing the waste while producing workpieces and so decreasing total cost of process. To this end, the assumed workpiece was made of a low carbon and anisotropic st14 steel sheet. To find the most appropriate direction and the shortest modification steps for final shape, the expansion level of the sheet was first imaged in the rolling direction and then the piece was shaped by the geometry. This approach was based on the coupling between the simulation and Genetic Algorithm. A Genetic Algorithm based approach is developed to optimize dimensions through integrating a finite element code running to compute the objective functions for each generation. Those points with a few materials modified through Genetic Algorithm yielded better results.
Currently, the simulation of multi-phase rotary displacement machines in reasonable accordance with the experimental results is not possible. Clearance sealing, additional frictional losses, heat transfer and lubrication are among the various effects caused by the presence of a liquid, which would all have to be modelled. Moreover, complex processes, such as condensation and evaporation affecting the thermodynamic equilibrium, as well as expansion of the multi-phase gas-liquid-mixture would have to be included. With the purpose of achieving a better understanding of liquid-flooded screw expanders, this paper describes a theoretical evaluation of clearance sealing by means of a liquid, and the resulting frictional losses. The influence of different auxiliary liquids, namely water and oil, is examined. Thus, after introducing the expander geometry and the auxiliary liquids, the results of a thermodynamic analysis are presented. The multi-chamber model-based simulation tool KaSim, that has been developed at the Chair of Fluidics, is applied to analyze the maximum potential of clearance sealing. Subsequently, dry running and liquid-flooded screw expanders are compared, taking clearance sealing as well as frictional losses into account. On the one hand, the study demonstrates that the influence of liquid water on temperature is negligible. On the other hand, the results show that reasonable modelling of oil requires a consideration of temperature-dependent dynamic viscosity for this auxiliary liquid. Finally, an extension of the presented simulation approach is introduced.
Hydrothermal behavior in a water-to-air double-pipe heat exchanger is studied experimentally and numerically. To achieve fully developed conditions, the heat exchanger was built with additional lengths before and after the test section. Commercial code (ANSYS 14) is used for numerical section. In order to enhance rate of heat transfer, discontinuous helical fins is utilized. Results show that Nusselt number augments with the enhancement of Reynolds number and Prandtl number, which are calculated at bulk temperature. The use of square section helical fins also shows a higher heat transfer enhancement rate than that of the circular one. Thermal performance factor is an increasing function of the open area ratio.
The test rig for water-injected process-gas screw compressor is designed and established. The dry gas seal technology was adopted for the shaft seal of screw compressor and the test rig has the function of regulating and controlling the mass flow of injected water. The performance characteristics of process-gas screw compressor under different working conditions are investigated by experimental research. The effect of rotational speed, the injected water mass flow, and the discharge pressure on the performance of screw compressor including discharge temperature and power consumption were obtained. The experimental results show that the water injection could reduce the discharge temperature of compressor significantly and increase the capacity of screw compressor at the same time. There exists an optimum mass flow of injected water that could effectively reduce the discharge temperature and seal the clearance between the female and male rotor simultaneously. For the tested screw compressor prototype, the proper injected water-to-air mass ratio is about 2–3 L/m3. The additional power consumption caused by the injected water is small compared with the total shaft power. The established compressor test rig and the experimental results are helpful for the development and improvement on the performance of water-injected process-gas screw compressor.
The performance and safety of a retainer-type ball valve have been evaluated for use in a high-pressure pipeline to a district heating plant. The retainer-type ball valve is a developed valve improving the defects of the leaks that may occur in the general valves such as the floating ball valve or trunnion ball valve. To verify the valve design, a numerical analysis of the design has been applied to investigate safety factors and to determine the flow coefficients for the DN300 and DN400 standard sizes. The conditions used for the numerical analysis was based on the international standards ISO 5208, IEC 60534-2-3, and a high-pressure pipeline to a district heating plant. The structural analysis results comprise deformations, equivalent stresses, and safety factors, and the flow analysis results show the flow coefficient, the pressure distribution, the velocity vectors, and the flow patterns for each rotation angle. These results confirmed the characteristics and reliability of the retainer-type ball valve and, based on these studies, we proposed a retainer-type ball valve as a solution to solve the leakage problem.
This study investigates the air leakage ventilation phenomenon in a passenger car and examines its effects on the concentration of carbon dioxide in the cabin. A theoretical general equation (
Stillinger–Weber potential and Z-layer energy model were adopted in molecular dynamics simulation to study the ablation of silicon by water-jet-guided femtosecond laser, and comparison was made by ablating silicon with or without water-jet cooling in our simulations. Simulation results indicated that with water-jet cooling, the thermal-affected zone could be reduced in area, and the peak of density could disappear more quickly. It was therefore concluded that water-jet-guided laser could be used to considerably improve the ablation quality of silicon.
Designing twin-screw compressors to safely operate at higher than normal temperatures poses a challenge as the compressor must accommodate larger peak thermal distortions while maintaining efficiency at nominal operating conditions. This paper will present a case study of an oil-injected compressor tested at elevated discharge temperatures with original and revised clearances. A procedure is presented to use boundary conditions derived from a chamber model to approximate component temperature distributions that are then used to predict possible thermal distortions and the resulting effect on clearance gaps. The original and revised clearance designs are evaluated and performance penalties incurred due to the modifications are discussed.
In this study, an artificial neural network model was developed to predict the geometric shapes of different objects using image processing. These objects with various sizes and shapes (circle, square, triangle, and rectangle) were used for the experimental process. In order to extract the features of these geometric shapes, morphological features, including the area, perimeter, compactness, elongation, rectangularity, and roundness, were applied. For the artificial neural network modeling, the standard back-propagation algorithm was found to be the optimum choice for training the model. In the building of the network structure, five different learning algorithms were used: the Levenberg–Marquardt, the quasi-Newton back propagation, the scaled conjugate gradient, the resilient back propagation, and the conjugate gradient back propagation. The best result was obtained by 6-5-1 network architectures with single hidden layers for the geometric shapes. After artificial neural network training, the correlation coefficients (R2) of the geometric shape values for training and testing data were very close to 1. Similarly, the root-mean-square error and mean error percentage values for the training and testing data were less than 0.9% and 0.004%, respectively. These results demonstrated that the artificial neural network is an admissible model for the estimation of geometric shapes using image processing.
The film flow behavior in an oil–gas cyclone separator was experimentally studied to improve the separation efficiency in terms of the effect of the oil film on the cylinder wall. The oil film flow pattern was captured using a high-speed camera, and the cylinder wall was divided into seven regions to analyze according to the different oil film flow patterns. Along the cyclone cylinder height, the central part of the cylinder was the main flow area, in which droplet–wall collisions and oil film splashing were severe. Additionally, the oil film’s distribution characteristics under inlet velocities of 14.0, 16.0, and 18.0 m/s were compared, and the results showed that more splashing oil droplets were generated under higher inlet velocity. Moreover, changing the structure of the central channel and outer cylinder slightly changed the oil film’s area and flow pattern but exhibited a weak effect on the oil film thickness and re-entrainment. Then, an improved structure was proposed by adding a porous cylinder to the outer cyclone to avoid the generation of small splashing droplets from the oil film. The performance of the modified separator was measured in a real oil-injected compressor system, which demonstrated higher separation efficiency with no increase in static pressure loss. The separation efficiency increased by up to 2.7%, while the pressure loss decreased by up to 10%. Thus, the improved structure can improve the performance of oil–gas separators by changing the distribution and thickness of the oil film on the cylinder wall.
A study on new materials usage to produce fiber metal laminates is presented in this work. Amorphous polyvinyl chloride thermoplastic and aluminum 3550 sheets are used to fabricate the fiber metal laminates. Different surface treatments were carried out on the aluminum sheets and the fiber metal laminates were produced using the film stacking procedure. Flexural strength and modulus of the products and also shear strength of bonding were measured using three-point bending test, and their failure mechanisms were evaluated using optical microscope images. Also, the effects of aluminum layer and aluminum/composite laminates bonding on the dynamic properties of the fiber metal laminates were studied using Dynamic Mechanical Thermal Analysis. It was concluded that mechanical roughening of the aluminum sheet has the maximum effect on the aluminum/matrix bonding strength such that simultaneous fracture of composite laminates and aluminum layer in the bending condition was observed in the produced fiber metal laminates without any delamination.
Metal-to-metal contact type flange joints (bolted flange joint with metal-to-metal contact) have a constant gasket sealing stress during service, so it is extensively used for "zero leakage" design in petrochemical, chemical, or nuclear power industry. XP CEN\TS 1591-3 provides a calculation method for metal-to-metal contact flange joints but the gasket parameters needed in this calculation and their test methods are not given. To determine the gasket parameters of metal-to-metal contact type flange joints, the procedures of the compression–resilience test, the stress relaxation test, and the sealing test at different temperature were described here, and the main mechanical properties and sealing property of a metal-to-metal contact type gasket were obtained from these tests. The methods to determine the metal-to-metal contact gasket parameters were introduced. And then, the calculation for a DN80 PN5.0 metal-to-metal contact type flange joint was carried out with two methods, one was the method according to XP CEN\TS 1591-3, the other was finite element method. In these calculations, the assembly condition and service condition were considered. The results of the two methods coincided well. This showed the test methods and test results of metal-to-metal contact type gasket parameters suggested here were available. So, they could be applied for the calculation of metal-to-metal contact type flange joints.
In the present investigation, a systematic study has been undertaken with regard to the effects of tempering time on room temperature mechanical properties of P91 (X10CrMoVNNB9-1) steel. Samples cut from P91 (X10CrMoVNNB9-1) industrial pipe were normalized at 1040 ℃ for 40 min and then tempered at 760 ℃ for different tempering times starting from 2 h to 8 h. Detailed analysis of microstructure, particle size, inter-particle spacing, and secondary phase carbide particles of the tempered samples was conducted by secondary electron microscopy technique. Optical microscopy was also utilized to characterize the tempered samples and for the measurement of grain size. In order to reveal the various phases formed during tempering of P91 (X10CrMoVNNB9-1) steel, X-ray diffraction was carried out. To study the fracture surface morphology of tensile tested and impact tested specimen field-emission scanning electron microscopy was carried out. The effect of tempering time on the microstructural parameters revealed an increase in grain size up to 4 h of tempering and then decreased because of recrystallization. The coarsening of secondary phase carbide particles M23C6 was revealed with an increase in tempering time. As a consequence, yield strength, hardness, and ultimate tensile strength were observed to decrease with increase in the tempering time. However, a drastic change was observed in the yield strength, ultimate tensile strength, and toughness after tempering for 6 h. From the present study, it was concluded that optimum combination of yield stress, ultimate tensile strength, hardness, and toughness obtained after tempering at 760 ℃ for 6 h.
This paper presents a process metamodel-based artificial neural network full factorial experimental design and analysis to study the yield of lengthy hexagonal graphene grown by chemical vapor deposition. All of the process variables of chemical vapor deposition such as temperature, pressure, and gas flow rate under the study played a role in influencing hexagonal graphene length; the current study investigated their main effects and interactions. The metamodel-based analysis demonstrates that the hydrocarbon flow rate and the pressure are the most statistically significant factors that influence the length of hexagonal graphene. In particular, minimum and maximum values of the chamber pressure are not significant in terms of the concentrating effect they may have on the flowing mixture of gases with very small flow rate, i.e. 50 sccm. At the highest flow rate of 400 sccm, the chamber pressure stepped up to 764 Torr, which can support the growth reaction to the extent that the resultant hexagonal graphene length of 900 µm can be achieved. However, the two level effect of the flow rate can optimize the length to 990 µm and 1390 µm at 700 Torr and 764 Torr, respectively. In addition, the response surface graph confirms the factors of significance and adds that higher flow with lower pressure will consistently yield tall hexagonal graphene. We found that gas flow rate is the most significant of the control variables and only the optimum value of the gas flow rate of 225 sccm can ensure the growth of tall hexagonal graphene. We also found that the interaction of flow rate with temperature of the gases in the chamber is extremely significant to the quality of output. Outcomes of this investigation are beneficial for moving close to producing hexagonal graphene on production scale for future applications.
Electrochemical machining is a unique prevalent nonconventional manufacturing process used in different industries involving various process parameters, which greatly influence machining performance. Therefore, selection of proper and optimal parameters setting is a challenging issue. In this paper, differential evolution algorithm is applied to look for the optimum solution to this problem. Four parameters, i.e. voltage, tool feed rate, electrolyte flow rate, and electrolyte concentration; and two machining criteria, i.e. material removal rate and surface roughness (Ra) are considered as input variables and responses, respectively. The main purpose is to maximize material removal rate and minimize Ra to achieve better machining performance. In this way, comprehensive mathematical models have first been developed using response surface methodology through experimentation based on central composite design plan. Then, differential evolution algorithm has been utilized for optimizing the process parameters; both single- and multiobjective optimizations are considered, and optimal Pareto front is determined. Finally, optimization result of a trade-off design point in the Pareto front of Ra and material removal rate was also verified experimentally. This machined surface was examined with field-emission scanning electron microscope images. The results showed that the proposed approach is an effective and suitable strategy for optimization of the electrochemical machining process.
Internal cylindrical grinding is one of the most difficult grinding processes due to the very long zone of contact between the grinding wheel and the workpiece surface. Such conditions limit delivery of the grinding fluid into the grinding zone, as well as impeding the removal of chips from it. As a result, during the internal cylindrical grinding process, difficult thermal conditions occur in the machining zone which finally could lead to grinding defects. One of the most efficient and cost-effective ways of improving the grinding stability and repeatability is modifying the grinding wheel structure. As such, modifications usually do not require interfering with the construction of the grinding machine or its equipment, they are universal and, possibly, widely applicable. This article presents a modified grinding wheel with helical grooves shaped on its active surface. Such modification was developed to reduce the thermal load of the workpiece surface and the occurrence of thermal defects. The effectiveness of the proposed grinding wheel modification was examined experimentally in the reciprocal circumferential internal cylindrical grinding process of 45C steel. The goal of the described tests was to determine the influence of the suggested grinding wheel modification on the condition of the workpiece surface layer (the surface roughness and residual stresses). The test results obtained indicated that application of the modified grinding wheel has a positive influence on the residual stresses in the workpiece surface layer, resulting in better delivery of the grinding fluid into the area of contact between the wheel and the machined material. Moreover, a decrease of the Ra parameter value by approximately 7–19%, as compared to the results of the process carried out with the (unmodified) reference grinding wheel was indicated.
In this paper, the effects of Al2O3 nanoparticles suspended in the water-based fluid on the thermo-economic properties of a fin and tube heat exchanger are studied using fast and elitism nondominated sorting genetic algorithm. Nine design parameters are selected as design parameters, and the total annual cost and effectiveness are considered as the two objective functions. First, the effect of nanoparticle on the total annual cost versus effectiveness is obtained at different cold side mass flow rates, and the results are compared with the base fluid. The results show that nanoparticles have a significant influence on the total annual cost and effectiveness in a lower cold side mass flow rates. Next, the heat exchanger volume versus effectiveness for the optimum points is measured at different cold side mass flow rates. It is demonstrated that, adding Al2O3 nanoparticle to the base fluid for the fixed value of effectiveness, decreases the heat exchanger volume, and this reduction is more significant in the lower mass flow rates. The pressure drop and total heat transfer surface area versus effectiveness for the optimum points are also obtained with and without nanoparticle. An increase in the tube side pressure drop is revealed in the nanofluid. In addition, due to the increase in the overall heat transfer coefficient, the lower heat transfer surface area is required for the fixed value of effectiveness. Finally, variations of objective functions versus particle volumetric concentration for five typical optimum points are estimated. It is concluded that an optimal value for the volumetric concentration can be obtained, in which the effectiveness is highest.
Permeability index is a crucial productivity indicator of the lower zone in blast furnaces to maintain the operation, energy consumption, and hot liquid metal production rates during the ironmaking process. Blast furnace operation parameters such as coke-to-ore ratio, wall pressures and temperatures, flame temperature, top gas pressure, temperature and composition, hot blast pressure and temperature, sounding levels, etc. and also the level of hot liquid metal and slag in the bottom of furnace, influence the permeability phenomenon directly. Hence, fluctuations and instantenous variations of permeability index parameter should be avoided by controlling inadequate drainage cycles and operational factors to achieve more efficient and stable operation in the furnaces. In this study, permeability index parameter of the Erdemir Blast Furnace #1, located in Turkey, is modeled and experimental computing work is carried out to assess the operation performance of the furnace, depending on selected input parameters. The demanding artificial intelligence and soft computing techniques, artificial neural networks and adaptive neural fuzzy inference system, and a well-known statistical tool, autoregressive integrated moving average model are executed throughout the study using previous furnace data, received during one day of operation. Selected performance measures, coefficient of determination (R2) and root mean squared error, are used to compare the forecasting accuracy of proposed models. Consequently, the most satisfactory forecasting model of the study, adaptive neural fuzzy inference system, is proposed to be integrated into the plant control system as an expert modeler.
This paper investigates torsional vibration and pulsating noise in a dry screw compressor. The compressor is designed at Gardner Denver (GD) and is oil-free and use for mounting on highway trucks in the dry bulk industry. They are driven using a power take-off (PTO) transmission and gear box on a truck. Torque peak fluctuations and noise measurements are made and their sources are investigated and reported in this work. To accurately predict the torsional response (frequency and relative angular deflection and torque amplitude), the Holzer method is used. It is shown that the first torsional frequency is manifested as sidebands in the gear train meshing frequencies and this can lead to noise. Using measurement data and curve fitting it is deduced that the pulsating noise is a result of amplitude modulation and not frequency modulation. Sensitivity analysis of the drive train identifies the weakest link in the drive train that limits the first torsional frequency to a low value. Tuning options like increasing the stiffness or inertia of the weakest element and shifting the input speed to the right are presented and discussed. Finally, the effect of higher-order torsional modes on inter-lobe clearance distribution of the rotors is investigated.
Due to the influence of centrifugal force, accurate contact stiffness model of spindle–toolholder joint at high speeds is crucial in predicting the dynamic behavior and chatter vibration of spindle–toolholder system. In this paper, a macro–micro scale hybrid model is presented to obtain the contact stiffness of spindle–toolholder joint in high speeds. The hybrid model refers to the finite element model in macro-scale and three-dimensional fractal model in micro-scale. The taper contact surface of spindle–toolholder joint is assumed flat in macro-scale and the finite element method is used to obtain the pressure distribution at different speeds. In micro-scale, the topography of contact surfaces is fractal featured and determined by fractal parameters. Asperities in micro-scale are considered as elastic and plastic deformation. Then, the contact ratio, radial and torsional contact stiffness of spindle–toolholder joint can be calculated by integrating the micro asperities. Experiments with BT40 type toolholder–spindle assembly are conducted to verify the proposed model in the case of no speed. The reasonable intervals of spindle speed and drawbar force can be obtained based on the presented hybrid model, which will provide theoretical basis for the application and optimization of the spindle–toolholder system.
In twin-roll casting, as heat is transferred from melt to rolls, the melt is cooled, solidified and finally rolled to a specific thickness. Therefore, an efficient cooling system for the roll is very important for a stable operation of the process. In the present study, a composite roll with internal cooling channels was designed for twin-roll casting of magnesium alloy AZ31 by considering steady-state heat transfer between objects. The roll consisting of a steel core and a copper alloy sleeve was proposed to be assembled by thermal-shrinkage fitting. The fitting strength was examined by a series of stress analyses at stages of assembly as well as operation. The number of cooling channels and their cross sections were modified accordingly.
Analysis of the multivariable coupling relationship, detection of the features of the coupling, and quantification of different degrees of each variable for the coupling are important foundations for information modeling, key point identification, and fault tracing of complex electromechanical systems. It is significant to understand the reasons associated with system conditions exchange, and improve the abilities of accident prevention and safety control of the system. In order to study the multifractal properties of the multivariable coupling relationship of the production system in the process industry, coupling detrended fluctuation analysis (CDFA) was applied. The strength and sources of the multifractality were estimated by shuffling and phase randomization with confidence bands. Different degrees of each variable were qualitatively and quantitatively quantified by the Chi square test. Empirical results showed that the CDFA was suitable for analyzing the multivariable coupling relationship of complex electromechanical system, and the coupling exhibited an obvious multifractal feature. Long-range correlation and fat-tailed probability density function of variables are sources for the multifractality of the multivariable coupling relationship of production system in process industry. Some invariant values, such as the multifractality power and ranks of different degree of single variable for the coupling, were detected for a specific operation condition, which were meaningful for conditions identification and information quality control of complex electromechanical system in process industry.
In this paper, the implementation of the Adomian decomposition method is demonstrated to solve a nonlinear heat transfer problem for a stepped fin involving all temperature-dependent means of heat transfer and nonlinear boundary conditions. Unlike conventional insulated tip assumption, to make the present problem more practical, the fin tip is assumed to disperse heat by convection and radiation. Thermal parameters such as the thermal conductivity, the surface heat transfer coefficient and the surface emissivity are considered to be temperature-dependent. Adomian polynomials are first obtained and then a set of Adomian decomposition method results is validated with pertinent results of the differential transformation method reported in the literature. Effects of different thermo-physical parameters on the temperature distribution and the efficiency have been exemplified. The study reveals that for a given set of conditions, the stepped fin may perform better than the straight fin.
Turning with rotary tool is a newly developed alternative of the conventional turning process in which cutting edge of a round insert rotates about its axis, so that a continuously indexed cutting edge is fed into the cutting zone. In the present study, a longitudinal high-frequency vibration was superimposed to the rotary tool to analyze the cutting force and surface roughness of AA7075 during orthogonal cutting. However, due to contribution of wide ranges of factors in the vibratory-rotary turning process, the selection of optimal parameter setting is a challenge that is faced with this process. In the present work, an attempt was made to simultaneously minimize machining force (Fz) and surface roughness (Ra) through selection of the optimal setting of cutting velocity, feed rate, tool rotary speed in rotary turning, and vibratory-rotary turning operations. Here, grey relational analysis was used to find the optimal parameter setting in rotary turning and vibratory-rotary turning processes, separately. Then the obtained solutions were compared. Results indicated that applying axial vibration to the rotary tool turning significantly reduced both surface roughness and cutting force. From the optimization by the grey relational analysis method, it was obtained that for both rotary turning and vibratory-rotary turning operations, setting of 4 m/min cutting velocity, 220 r/min tool rotary speed, 0.08 mm/rev feed rate, and 0.3 mm depth of cut are the most-optimal solutions that causes minimum Fz and Ra, simultaneously. Also, the vibratory-rotary turning process had higher values of grey relational grade than the rotary turning process that implies outperformance of the vibratory-rotary turning with respect to the rotary turning process. The obtained results were then verified, compared, and discussed based on the mechanics of turning process.
To obtain more accurate flow characteristics of pump turbines, the method of large eddy simulation with wall-adapting local eddy viscosity model is applied in simulating several operating points in the pump mode. Firstly, based on the experimental validation, the method of large eddy simulation could better predict the external performance and internal flow characteristics in a pump turbine in the pump mode compared with the method of Reynolds-averaged Navier–Stokes with two-equation turbulence model shear stress transport k–. Then, flow characteristics under 1.00QBEP (best efficiency point), 0.91QBEP, 0.88QBEP, and 0.85QBEP operating points are investigated to find out the causes of the head drop in the energy-discharge curve through large eddy simulation. The detailed analysis reveals that the head drop at the point 0.85QBEP is related to the recirculation flow at the runner inlet. Finally, unsteady studies confirm that vortex movement at the runner inlet lead to the variation of the amplitudes and directions of the velocity, which generates the rotation of the separation vortices in the runner and stay vane channels.
This paper studies the effects of variable viscosity and periodic boundary conditions on natural convection double-diffusive flow past a vertical plate in a slip flow regime when suction velocity oscillates in time about a constant mean. The fluid viscosity is assumed to vary with temperature. The problem is governed by a nonlinear and coupled linear system of partial differential equations. Perturbation method is employed to solve the equations. The influence of flow parameters on fluid temperature, concentration and velocity, skin friction, and rate of heat transfer have been presented graphically. It is observed that increase in viscosity parameter for the binary mixture of carbon dioxide (Sc = 0.94) in air (Pr = 0.71) increase velocity near the plate. In addition, the mean skin friction increases with increase in viscosity parameter.
This paper studies the dynamic plastic response of thin quadrangular mild steel plates subjected to uniform and localized impulsive loading. For this, two new dimensionless numbers based on dimensionless governing equation of plates have been suggested. Four different effective parameters such as plate geometry, inertia of applied load, mechanical properties of material and strain rate sensitivity have been considered in suggested dimensionless numbers. The unknown coefficients of these numbers have been calculated by using singular value decomposition method. In order to illustrate the ability of empirical constitutive equations for predicting the maximum deflection, these equations are compared with different sets of experimental results that have been performed by various researchers. The comparison between the results of present empirical equations and the other theoretical and experimental ones shows that these models are more accurate than the other ones and are suitable to use for predicting the maximum deflection of all quadrangular mild steel plates subjected to uniform and localized loading.
In this study, the adhering failure of cemented carbide inserts during the heavy-duty cutting of large-scale, high-strength steel forgings is investigated. First, the heavy-duty cutting of high-strength steel forgings is simulated. According to the results, the maximum cutting temperature and force were approximately 950 ℃ and 42 KN, respectively. Next, the effects of these thermal-mechanical loading conditions on the material performance of the inserts are discussed. In addition, the adhering failure of the inserts is analyzed. Then, an insert-chip adhering model and the high-temperature strength of the insert material are used to illustrate the critical condition of the insert-chip adhering process via MATLAB simulations. Furthermore, the anti-adhering performance of the inserts is improved and an optimized insert design for the heavy-duty cutting process is constructed from the aspects of insert material, structure and coating. According to the results, the service lift of the heavy-duty cutting inserts XF8 was two times greater than that of conventional welded cemented carbide inserts. The cutting parameters of the large-scale forging process are also optimized using the orthogonal experimental method. The results of this study could be used to improve the anti-adhering performance, service life, and production efficiency of cemented carbide inserts intended for the cutting of large-scale forgings.
The overhead multiple outlets ventilation duct system of 18 m long is used to maintain the specified indoor thermal comfort environment for each railway passenger car. Therefore, the flow uniformity of the overhead ventilation duct system is very important for heating, ventilation, and air conditioning performance of a train. In this study, design optimization was conducted to increase the flow uniformity of the overhead ventilation duct system for a train by combining computational fluid dynamics and design of experiment methods. To perform the study, the flow uniformity of the base model was evaluated using numerical analysis whose reliability was verified. Design parameters of the overhead ventilation duct system were selected, and an effectiveness evaluation was performed for each design parameter by using 2 k factorial design. Based on the results of the effectiveness evaluation for the design parameters, optimum models having improved flow uniformity were designed using the response surface method. The performances of the optimum models were also evaluated by the same numerical analysis that was applied to the base model. The flow uniformity of the optimum models was improved by controlling the opening ratios of the perforated plates and guide vane shape. In addition, nonuniform flow components locally existing in the base model were suppressed.
The aim of this paper is to study the different shapes of nanoparticles on mixed convective steady flow over a rotating disk. For nanofluid, the copper nanoparticles of disk, cylindrical, and spherical shapes of different sizes and water as base fluid are considered. The physical problem is first modeled and then the governing equations are transformed into nonlinear ordinary differential equations. These equations are dimensionless using geometrical and physical flowfield-dependent parameters and solved analytically. A very good agreement is observed between the obtained results of the current study and previously published study in limiting cases. The shape effects on velocity profiles in radial, tangential, axial directions, and temperature distribution are displayed graphically with the reflection of specific range of nanolayer thickness and its conductivity. In addition, irreversibility due to heat and fluid friction is investigated that supports the heat transfer enhancement in renewable energy systems and industrial thermal management. For the analysis of the averaged entropy generation number, the results are shown in pie charts and tablet form. It is evident from the study that proper choice of nanoparticles will be helpful in controlling velocity and heat transfer. It is also observed that irreversibility process can be reduced by using nanoparticles, especially the spherical particles.
A numerical scheme for two-phase flow in gas liquid cylindrical cyclone is developed and its performance is investigated. A three-dimensional cyclone is simulated with computational fluid dynamic methods. After choosing a suitable mesh grid for the cyclone and checking grid independency, the effect of changing geometry parameters on the gas liquid cylindrical cyclone performance such as gas carry under and liquid carry over is investigated and finally the geometry is optimized to minimize both gas carry under and liquid carry over. Geometrical parameters have great effect on optimizing cyclone separators performance. Reynold’s stress model is used for turbulence simulation of the flow and two-phase flow is simulated using Eulerian–Eulerian approach. Optimized parameters are inlet nozzle width, inlet angle, inlet altitude relative to the bottom of the cyclone, cyclone main diameter, and liquid outlet diameter. Results show that gas carry under decreases with decreasing liquid outlet diameter of the cyclone, increasing main diameter of the cyclone, increasing inlet nozzle’s width, and decreasing nozzle’s inlet angle. The optimum point for gas carry under was given with changing inlet altitude relative to the bottom of the cyclone. The optimum point for liquid carry over was obtained with changing liquid outlet diameter, main diameter of the cyclone, inlet altitude, and inlet nozzle width and increasing inlet angle causes an increase in liquid carry over.
In this paper, the results of adding nanoparticles and applying non-uniform magnetic fields on a biofluid (blood) flow through a two-dimensional horizontal channel with a step are reported. Two magnetic fields with positive and negative gradients were applied. The control volume technique and two-phase mixture model in the numerical approach have been used to illustrate the hydro-thermal behavior of flow. Simulation results reveal that nanoparticles can significantly increase the Nusselt number and wall shear stress. Also, the wall shear stress, Nu, and recirculation length in the presence of a magnetic field with different gradients can be externally controlled. Based on the results, the negative gradient magnetic field increases wall shear stress and Nu in the affected region, unlike the positive gradient.
A new time–frequency analysis method, based on variational mode decomposition, was investigated. When a gear fault occurs, its vibration signal is nonstationary, nonlinear, and exhibits complex modulation performance. According to the modulation characteristics of the gear vibration signal arising from faults therein, a gear fault diagnosis method based on variational mode decomposition and envelope analysis was proposed. The variational mode decomposition method can decompose a complex signal into several stable components. The obtained components were analyzed by envelope demodulation. According to the envelope spectrum, gear faults can be diagnosed. In essence, the variational mode decomposition method can decompose a multi-component signal into a number of single component amplitude modulation–frequency modulation signals. The method is suited to the handling of multi-component amplitude modulation–frequency modulation signals. The simulated signal and the actual gear fault vibration signals were analyzed. The results showed that the method can be effectively applied to gear fault diagnosis.
In the oil and gas industry, the testing of auxiliary lubrication plants represents an important preliminary activity before the whole turbo machinery train (including the auxiliary lubrication plant) can be put in operation. Therefore, the employment of both efficient and accurate plant models becomes mandatory to synthesize satisfactory control strategies both for testing and normal operation purposes. For this reason, this paper focuses on the development of innovative real-time models and control architectures to describe and regulate auxiliary lubrication plants. In particular, according to the Bond-Graph modelling strategy, a novel lumped parameter model of the lube oil unit has been developed to properly optimize the behaviour of this unit if it is controlled. The code has been compiled and uploaded on a commercial real-time platform, employed to control the pressure control valve of the physical plant, for which a new controller has been developed.
The comparison between the data obtained from the simulated system and acquired from the physical plant shows good agreement and the good performance and reliability of the proposed model and control strategy. The modelling approach and the control strategy have been developed in collaboration with GE Nuovo Pignone S.p.a. while the experimental data were acquired in a plant located in Ptuj (Slovenia).
In general, welding of dissimilar metals is more challenging than similar metals. This paper presents the outcomes of a detailed experimental study carried out to investigate the effect of process parameters and their interactions during dissimilar welding between AISI 304 austenitic stainless steel and AISI 4340 alloy steel and proposes an approach for multi-response optimization of process parameters. Six different process parameters and three interactions amongst them are considered during gas tungsten arc welding and the results are analyzed to devise the significance and contribution of each parameter, interaction on the welded joint pertaining to tensile strength, toughness, distortion and fusion zone microhardness variation. Detailed experimental study and analysis showed that maximum tensile strength, toughness, or minimum distortion is obtained at different parametric combinations. Thus, in order to search a best process combination that optimizes multiple responses, analytic hierarchy process is applied with a modified approach to assign the relative importance of each alternative. The steps involved in the approach are also discussed and the optimum parametric combination is selected that maximizes the joint mechanical strength. Results show that maximum joint strength is achieved when ER 308 filler material, Ar + H2 shielding gas with moderate flow rate and suitable pre-heating as well as post-heating are used.
In order to investigate the performance of variable thickness scroll compressors, a detail mathematical modeling based on energy and mass balances is established in this two-part. In part I, the geometric modeling and thermodynamic modeling are developed. The profile based on circle involute, high order curve, and arc is built up using the base line method. The volume of working chambers from suction to discharge is defined. Thereafter, the evolution and derivative of the working chamber volume with respect to the orbiting angle are discussed. The energy and the mass balance for working chamber are described. Suction gas heating, radial and flank leakage, heat transfer between the working fluid, scroll wraps and plates are considered in the thermodynamic modeling. The established geometric modeling and thermodynamic modeling can provide better understanding of the variable thickness scroll compressor working process. The dynamical modeling and model validation are reported in part II.
Passive micromixers are one of the parts used for the mixing of two or more fluids in micro-electro-mechanical system devices, and they have been developed for various types. Fluid mixing in microscale devices is essential in microfluidic applications; however, it is difficult to mix fluids in microchannels due to the slowness of the molecular diffusion process at the microscale. In this study, optimization of the groove shape geometries of a micromixer using response surface design was performed, and the mixing performance was investigated through a numerical analysis applied with the passive scalar method. The most useful parameters were determined to be the geometric parameters of optimization, such as groove depth, groove length, distance between grooves, and groove angle. Response surface design, a design of experiments technique, was applied to the optimization procedure. The mixing index and pressure drop are important factors for evaluating the micromixer performance. Through the response surface design, this study aims to affect the groove shape of a passive micromixer. Consequently, it was concluded that the groove length and distance between grooves improved the mixing performance and decreased the pressure drop. In addition, optimal models were proposed for the passive micromixer.
In order to investigate the performance of variable thickness scroll compressor, a detail mathematical modeling based on energy and mass balances is established in this two-part. In part II, dynamic modeling and model validation are developed. Temperature, pressure, mass flow of working chambers, friction loss power of moving parts, efficiency, and shaft power are investigated by solving the mathematical modeling. The experimental rig for variable thickness scroll compressor based on involute of circle, high order curve and arc is set up. From the comparison of the simulated and measured data, it can be seen that the compressor model predicts the mass flow, discharge temperature, and shaft power very well. So the proposed mathematical modeling can accurately describe all the suction, compression, and discharge processes for variable thickness scroll compressor.
This article offers an overview of 11 grinding wheel construction modifications used in the peripheral grinding of flat, shaped, internal, and external cylindrical surfaces, when grinding wheels made of superabrasive grains are used (natural and synthetic diamonds, as well as mono- and microcrystalline cubic boron nitride). The text contains characteristics of grinding wheels with: bubble corundum grains, glass-crystalline bond, conic chamfer, zones of different diameters, a centrifugal provision of the coolant into the grinding zone, aggregate grains, zone-diversified structure, as well as impregnated (self-lubricating), multiporous, segment and "intelligent" grinding wheels. Each of the presented structural modifications were described by giving construction scheme, used abrasive grains, range of applications, advantages as well as disadvantages. Modifications of the grinding wheel construction allow for effective improvement of both the conditions and the results of the grinding process. A wide range of the known modifications allow for their proper selection depending on the required criteria of effective evaluation and taking into account the specific characteristics of superabrasive grains. As a result, it is possible to obtain positive influence on a number of technological factors of the grinding process. The described modifications of the grinding wheel structure can be also an inspiration and the basis for creating new solutions in this field.
This article offers an overview of 14 grinding wheel construction modifications used in the peripheral grinding of flat-shaped internal and external cylindrical surfaces, when grinding wheels made of conventional abrasive grains are used (Al2O3, sol-gel alumina, SiC, etc.). The text contains characteristics of grinding wheels with mixed grains, glass-crystalline bond, a centrifugal provision of the coolant into the grinding zone, aggregate grains, zones of different diameters, radial rough grinding zone, extended finish grinding segments, active surface macro- and micro-discontinuities, as well as multiporous, impregnated (self-lubricating), sandwich, sectional and segment grinding wheels. Each of the presented structural modifications was described by giving construction scheme, used abrasive grains, range of applications, advantages as well as disadvantages. Modifications of the grinding wheel construction allow for effective improvement of both the conditions and the results of the grinding process. A wide range of the known modifications allows for their proper selection depending on the required criteria of effective evaluation and taking into account the specific characteristics of conventional abrasive grains. As a result, it is possible to obtain positive influence on a number of technological factors of the grinding process. The described modifications of the grinding wheel structure can be also an inspiration and the basis for creating new solutions in this field.
At present, the changing structure, material and increasing device are used to suppress the vibration of motor in general. These methods increase system complexity in the different degree. So a novel vibration suppression method based on fractional order Proportional-Integral-Derivative (PID) controller is proposed in this article. First, the digital realization process of fractional order PID controller is illustrated in detail. Then the integer order PID controller and fractional order PID controller are, respectively, used to adjust the input current of inverter to control the 1.5 kW alternating current motor. The vibration frequency spectrums and stator current frequency spectrums in low-frequency and carrier frequency band are, respectively, studied by using the comparison and analysis methods. At the same time, the vibration frequency spectrum and stator current frequency spectrum of 15 kW alternating current motor are compared and analyzed. And the frequency spectrums near the rotating frequency of stator current of 1.5 kW and 15 kW alternating current motors are amplified to deeply analyze spectrum characteristics. The experimental results show that the fractional order PID controller has the characteristics of multi-point control by comparing with the integer order PID controller. It changes the frequency components of stator current, and then the electromagnetic torque is more stable. So, the fractional order PID controller can better suppress the vibration of alternating current motor. The proposed method can provide a new idea for vibration suppression of rotating machinery.
In current study, two kinds of nano-composites were prepared and the effect of input parameters on impact properties of desired hybrid nano-composites was investigated. Carbon fiber orientation, nano-clay content, and carbon nano-tube content were selected as input parameters in one set and carbon fiber orientation, nano-clay content, and nano-SiO2 content were the input parameters of the other set of prepared nano-composites. Taguchi design was used for design of experiments and analyzing results. The obtained results show that the maximum value of impact strength for both of nano-composites occurred in the design level 2 with 0 degree of fiber orientation, 1.5 wt% of nano-clay, 1 wt% of nano-SiO2, and 1 wt% of carbon nano-tube and the magnitude of impact strength for nano-clay/carbon nano-tube and nano-clay/nano-SiO2 was 6.6 kJ/m2 and 6.3 kJ/m2, respectively. From analysis of variance, it was clear that all of the input variables had reverse effect on impact response except the nano-clay. The carbon fiber orientation had the greatest effect and the effect of carbon nano-tube was higher than nano-SiO2 according to its probability value. Also mechanical plots show that, the optimum level of input variables of hybrid nano-composites reached higher values of impact strength compared with pure epoxy and binary nano-composites.
The primary crusher is essential equipment employed for comminuting the mineral in processing plants. Any kind of failure of its components will accordingly hinder the performance of the plant. Therefore, to minimize sudden failures, analysis should be undertaken to improve performance and operational reliability of the crushers and its components. This paper considers the methods for analyzing failure rates of a jaw crusher and its critical components application of a two-parameter Weibull distribution in a mineral processing plant fitted using statistical tests such as goodness of fit and maximum likelihood estimation. Monte Carlo simulation, analysis of variance, and artificial neural network are also applied. Two-parameter Weibull distribution is found to be the best fit distribution using Kolmogorov–Smirnov test. Maximum likelihood estimation method is used to find out the shape and scale parameter of two-parameter Weibull distribution. Monte Carlo simulation generates 40 numbers of shape parameters, scale parameters, and time. Further, 40 numbers of Weibull distribution parameters are evaluated to examine the failure rate, significant difference, and regression coefficient using ANOVA. Artificial neural network with back-propagation algorithm is used to determine R2 and is compared with analysis of variance.
In this paper, we consider an unreliable production system consisting of two machines (M1 and M2) in which M1 produces a single product type to satisfy a constant and continuous demand of M2 and it is subjected to random failures. In order to palliate perturbations caused by failures, a buffer stock is built up to satisfy the demand during the production unavailability of M1. A traditional assumption made in the previous research is that repairs can restore the failed machines to as good as new state. To develop a more realistic mathematical model of the system, we relax this assumption by assuming that the working times of M1 after repairs are geometrically decreasing, which means M1 cannot be repaired as good as new. Undergoing a specified number of repairs, M1 will be replaced by an identical new one. A bivariate policy
Nowadays, the demand for achieving cars with higher strength, lower fuel consumption, and better safety considerations propels automakers to produce parts with extremely high strength-to-weight ratios. This criterion is done through the hot-stamping process considered as a novel technology employed for producing high-strength steel parts with low springback, particularly appropriate for the vehicle body. In this paper, firstly, numerical simulation of the hot-stamping process of a blank consisted of boron-alloyed steel 22MnB5 (with commercial name of Usibor 1500) is performed. Secondly, effects of different design parameters including blank holder force, die radius, gap between the punch and die, and forming time on the final temperature distributions as well as springback of the part is investigated. Consequently, optimization has been performed using Taguchi L16 orthogonal array to obtain the parameters which minimize above-mentioned parameters as two objective functions. Obtained results are verified based on performing numerical simulation and comparison to a similar work in the literature. Accuracy of the results is also assessed via the technique of plotting normal probability graphs of both objective functions. Finally, via evaluation of contribution percentage associated with analysis of variance considering each design parameter, a discussion is done by proposing the optimum design.
The cartridge flow valves, used in heavy machine and equipment, have the advantages of low leakage, large flow capacity, simple structure, and ease of modulation. However, in order to reduce the influence of load variety on the flow through valve, a pressure differential compensator or a cartridge type flow sensor should be added to the proportional throttle valve. These methods have disadvantages of reducing the flow capacity of valve and increasing the throttling loss. To overcome these disadvantages, a low energy consumption, high controllable electro-hydraulic proportional flow valve which consists of a hydraulic transistor (Valvistor) and a small displacement hydraulic pump driven by a servo motor is proposed firstly in the world. As the pump flow is basically proportional to the pump speed and little influenced by load variety, the flow through main valve is proportional to pilot pump speed. In the research, it’s known that feedback throttle slot pre-opening will cause the decrease of the main valve flow as pressure drop increases. So, small orifices are used instead of the pre-opening of feedback throttle slot to reduce the influence of load variety on the flow through valve. Furthermore, a method of pressure differential changing with pilot pump rotational speed calibration is introduced to further mitigate the influence of pressure difference. In this paper, the mathematical dynamic model of the valve is also established and the stability criterion of valve is derived. The influence of valve parameters and the flow pulsation of pilot pump on valve flow performance is analyzed and simulated. In view of the pilot pump flow pulsation frequency being much higher than the valve natural frequency, the research shows that the influence of flow pulsation of pilot pump on valve flow performance is very little. The research work provides a new method for the large flow electro-hydraulic proportional control system.
This article deals with a second-order slip flow and magnetic field on boundary layer flow of micropolar fluid past a stretching sheet. Situation of nil normal flux of nanoparticles at the wall for the stretching flow is taken into account. By employing appropriate similarity transformation and non-dimensional variables, the governing non-linear boundary-value problems were reduced into coupled higher order non-linear ordinary differential equation. Then, numerical solution for velocity, angular velocity (microrotation), temperature, and concentration has been established. The equations were numerically solved using the function bvp4c from the matlab software for different values of governing parameters. Numerical results have been obtained and discussed for non-dimensional velocity, temperature, microrotation, the skin friction coefficient, and local Nusselt number using some fixed values of the governing parameters. The results indicate that the skin friction coefficient Cf increases as the values of slip parameter increase. However, the local Nusselt number –
This paper investigates the combined effects of buoyancy forces, homogeneous chemical reaction, thermal radiation, partial slip, heat source, Thermophoresis and Brownian motion on hydromagnetic stagnation point flow of nanofluid with heat and mass transfer over a stretching convective surface. The stretching velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point. Using similarity transformation, the governing nonlinear partial differential equations are reduced to a set of nonlinear ordinary differential equations which are solved numerically by employing by shooting method coupled with Runge–Kutta Fehlberg integration technique. Graphical results showing the effects of various thermophysical parameters on the velocity, temperature, nanoparticle concentration, local skin friction, local Nusselt number and local Sherwood number are presented and discussed quantitatively.
In this study, nanoparticle boron carbide was produced after the reduction of boron oxide with magnesium under the presence of carbon by using mechanochemical synthesis method. During the synthesis processing, microstructure and phase transformations of powders were performed by using X-ray diffraction (XRD), Fourier-transform infrared spectrum (FT-IR), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (HRTEM). At the end of 2 h, reaction products (MgO, B4C) were determined by XRD and FT-IR examinations. Nanoparticle B4C single-phase crystalline structure from the MgO/B4C composite powder mixture, which was the reaction product, was obtained by leaching process. With the increase in the synthesis period, starting material peaks diminished and Fe peak intensity became evident. After the HRTEM examinations, it was determined that synthesized B4C particles were within range of 10–200 nm especially in the activation of leaching process. Additionally, by using spot pattern analysis method, planes represented by B4C particles were calculated.
Austenitic stainless steel AISI 316L is used in many applications, including chemical industry, nuclear power plants, and medical devices, because of its high mechanical properties and corrosion resistance. Machinability study on the stainless steel is of interest. Toward sustainable manufacturing, this study also includes the power consumption during machining along with other machining responses of cutting force, surface roughness, and tool life. Turning on the stainless steel was performed using coated carbide tool without using cutting fluid. The turning was performed at various cutting speeds (90, 150, and 210 m/min) and feeds (0.10, 0.16, and 0.22 mm/rev). Response surface methodology was adopted in designing the experiments to quantify the effect of cutting speed and feed on the machining responses. It was found that cutting speed was proportional to power consumption and was inversely proportional to tool life, and showed no significant effect on the cutting force and the surface roughness. Feed was proportional to cutting force, power consumption, and surface roughness and was inversely proportional to tool life. Empirical equations developed from the results for all machining responses were shown to be useful in determining the optimum cutting parameters range.
Electro-polishing was used as an alternative to mechanical polishing for the cutting edge preparation of tungsten carbide (WC) ball nose end mills. High-quality cutting edge surfaces with roughness of magnitude 0.3–0.35 µm was achieved using the electro-polishing process. A direct current of 0.96 A was passed through an electrolytic cell containing the electrolyte sodium hydroxide with a concentration—2.5 mol/dm3. The ball nose end mill was suspended as the anode and a stainless steel (SS304) as the cathode. The ball nose end mill was electro-polished using the optimized parameters which was obtained through performing the preliminary experiments on tungsten carbide coupons of size D6 x 20 mm. The effects of electro-polishing on the surface texture of the ball nose end mill were determined using surface texture examinations. Machining tests were conducted on Ti6Al4V alloy to understand the growth of flank wear on the electro-polished ball nose end mills. After every 5 m of cutting distance, flank wear measurements were done for both the regular ball nose end mill and the electro-polished ball nose end mills. The results revealed that the electro-polished ball nose end mill reached a flank wear of 0.15 mm after a cutting distance of 550 m. This was significantly more than the cutting distance of the standard ball nose end mill of magnitude 350 m for the same amount of flank wear. This showed an increase in tool life of over 50%.
Detecting and locating small leaks in the water distribution networks save water and help in making critical decisions about the network and the infrastructure. In this work, inside-pipe pressure measurements are used to evaluate the local variation of the pressure around small circular leaks as compared to main pipeline pressure, for reliable leak detection. The technique is working for pressurized pipelines and may be used for liquids and gases. In addition, since large leaks are easy to find, the attention is given to detecting small leaks, which are difficult to be detected using the commercial acoustic methods; specifically with plastic pipes. The current study thereafter helps in characterizing the effective zone of pressure sensing around the leak. A pressure probe, mounted on a movable platform, moves inside a water-pressurized pipe very close to the wall in order to measure the pressure variation at the vicinity of the leak. The effects of pipeline pressure, leak size, and the clearance distance between the pipe wall and the pressure probe on the measured pressure drop around the leak are investigated. Results showed that direct pressure measurements inside the pipe can be effectively used for leak detection. The local pressure drop due to the small leak is very localized around the leak and captured within the leak diameter in the longitudinal direction and almost leak-like radius above the leak in the radial direction. As the line pressure increases, the measured pressure drop increases but the zone of pressure variation is still confined around the leak itself. If the sensor is moving over the leak, then the magnitude of the measured pressure drop is inversely proportional to the sensor speed inside the pipe.
This article is aimed at analysing the steady-state performance of four hydrostatic drives and compares their overall efficiency. The speed of the hydrostatic drives is controlled by speed controlled vane pump, variable displacement flow compensated pump, variable displacement pressure compensated pump and proportional direction controlled valve. Bondgraph simulation technique is used to model the hydrostatic drive. The relationships of the loss coefficients with the state variables obtained from the model are identified through experimental investigation. Using them, at different torque levels, the performances of the hydrostatic drives are studied on their slips, torque losses and the overall efficiencies and they are validated experimentally. It is found that hydrostatic drive using speed controlled vane pump exhibits the maximum efficiency, whereas the poorest efficiency is shown by the valve controlled system out of the four drives considered in the analysis.
This paper investigates the influence of a tapered cylinder nozzle (TCN) on pressure pulsations in a high-speed reciprocating compressor piping system. Numerical methods, the 3D frequency-domain finite element method (FEM) and the 3D time-domain computational fluid dynamics (CFD) were used to separately calculate gas column natural frequencies and pressure pulsations. With favorable agreement between model predictions and experimental data, it is concluded from predictions that an installed TCN changes both the values and distribution of frequencies because installation of a TCN filter can alter gas column structure in the piping system. The order of frequency dominated by cylinder nozzle response increases sharply as the TCN diameter ratio increases and the TCN length to diameter ratio decreases. Pressure fluctuations can be effectively attenuated in piping system under different functioning conditions, e.g. variable compressor speeds and variable discharge pressures.
In medical cosmetology, laser energy must be properly controlled to avoid unnecessary thermal damage of normal tissue due to excessive irradiation. When a laser source is applied to a specific target that is very close to the surface tissue, residual heat can damage the surface tissue even after the laser treatment is halted. This study aims to determine the proper conditions for the laser treatment and the prediction of the thermal damage of surface tissue after the laser is applied. An 810 nm diode laser was used to irradiate porcine liver and the surface temperature was measured using infrared thermography for different laser application processes. The Pennes bioheat transfer equation was solved using the ANSYS software package to simulate the surface temperature and thermal damage zone in laser surgery. The double ellipsoid function represented the laser source term in the heat transfer simulation. The results of the simulation were compared with the experimental data. Finally, a transient analysis of the estimations of thermal damage after laser surgery was conducted for different conditions of power, laser irradiation time, and laser depth under the surface of the porcine liver.
Process chamber is the core unit of chemical vapor deposition and etching, and the physical fields in it have fatal effect on process quality. It is significant and difficult for improving the process performance to regulate the fields’ profiles finely. Two design solutions for the profile regulation are proposed: controllable type and resistance type. A novel profile error feedback method is presented, and a simulation-based auto-design framework is established. The profile error feedback method is in a quasi-closed-loop-control mode. It starts from an initial guessed sequence of the design/control variables and predicts a better sequence via feedback of the profile error between the output-targeted profile and the expected one. It never stops until the profile error is narrowed in the preset tolerance. Three kinds of numerical experiments about the regulation of the thermal, fluid, and plasma profile are set to test the effectiveness and feasibility of the profile error feedback method and the two kinds of design schemes.
Gasketed bolted flange joints are used in process industry for connecting pressure vessels and pipes. Design procedures available in the literature mostly discuss structural strength, while sealing failure is still a big concern in industries. Similarly, limited work is found in the literature regarding performance of gasketed bolted joints under combined loading. A detailed 3D nonlinear finite element analysis is performed to study the strength and sealing of a gasketed bolted flanged pipe joint under different bolt-up strategy (Industrial and ASME) and under combined internal pressure and axial loading.
Friction drilling processes are used commonly in hot forming operations. This process is similar to drilling processes but without using chip. This process is used especially for joining thin-walled metal components. In this study, the drilling process using centerdrill is investigated both experimentally and numerically. The finite element analyses (FEA) were conducted using deform-3D software based on finite element method (FEM). In this study, an analytic model is developed, which calculate the process parameters as torque and axial power, heat transfer coefficient. A comparison was also made for temperature, torque and axial force obtained from experimental and numerical analyses. At the end of the study, while the torque and axial force values decrease with increasing of spindle speed, temperature values of centerdrill and workpiece increase with increasing of spindle speed. A good consistency between both experimental and FEA simulations was found during the centerdrill process.
Dry electrical discharge machining (EDM) is a modification of the oil EDM process in which the liquid dielectric is replaced by a gaseous dielectric. This study investigates the effects of different types of gas (air, nitrogen, and mixture of argon/air) on the machining characteristics of dry EDM of M35 workpiece material. A Taguchi L27 orthogonal array design was applied to investigate the effects of six control factors, including current, pulse on-time, duty factor, gas pressure, electrode rotational speed and specifically type of gas on machining responses, including material removal rate (MRR), surface roughness, and radial overcut. Also, the surface integrity was investigated in different dielectric mediums. Results show that the argon/air mixture can improve the MRR with respect to air and nitrogen. The best dimensional accuracy can be obtained by using nitrogen as the dielectric medium. Also, the machined surface with nitrogen has the fewest small drops and the microcracks in Aagon/air mixture is more than those air one. So, the argon/air mixture is the best dielectric with respect to nitrogen and air mediums for dry EDM of high-speed steel M35.
Numerical computations have been realized to explore and evaluate the laminar mixed convection heat transfer from a heated trapezoidal bluff body. Two different configurations of the trapezoidal bluff body viz. expanded and tapered considered and a comparison has been made at different operational parameters. The spectrum of physical control parameters considered as Reynolds number (Re) = 10–50, Richardson number (Ri) = 0–1, and Prandtl number (Pr) = 0.7 (air). A finite volume method implemented on the collocated grid arrangement has been employed for numerical computations. Overall drag and lift coefficients are found higher for a tapered body as compared to an expanded body. However, average Nusselt number is greater for the expanded body as compared to the tapered one. With increase in Re at a given Ri, total drag coefficient is found to decrease in steady regime, but it increases in time-periodic regime. On increasing Ri, drag and lift coefficients decrease in the steady regime for both geometries. A correlation expressing the functional relationship of average Nusselt number with Re and Ri for both geometries has been proposed. Critical Re at Ri = 0.5 for the expanded geometry is found to be between Re = 46 and 47, while for the tapered body it exists between Re = 35 and 36. Maximum heat transfer enhancement for the tapered body with respect to the expanded body at Ri = 0, 0.5, and 1 is found to be approximately 26, 24, and 21%, respectively.
In recent years, many explosion accidents of LPG (Liquefied Petroleum Gas) tank happen due to fires, temperature-pressure-stress coupled field parameters of LPG tank under fire change nonlinearly, which are affected by many factors, such as fire type and filling rate. In order to improve the computing efficiency, the Legendre wavelet function is combined with traditional finite element to construct the Legendre finite element, and the effect of every affecting factor on changing rule of coupled field of LPG tank under fire can be analyzed effectively. First, the basic property of Legendre wavelet is analyzed. Second, temperature–pressure–stress-coupled model of LPG under fire is constructed; the temperature-pressure-stress coupled Legendre wavelet finite element is established; and then the effect of every affecting factor on coupled field of LPG tank under fire is obtained. Results show that analysis precision based on Legendre wavelet finite element method can be improved effectively.
This paper presents experimental and analytical investigation of the dynamic inelastic response of rectangular metal plates subjected to liquid shock loading. A series of experimental results on fully clamped aluminum alloy and mild steel rectangular plates of different thickness and varying standoff distance of hammer is reported. The effect of varying both shock load and the plate material on the deflection is described. Also, an analytical procedure based on an upper bound solution is used to theoretically study the dynamic behavior of uniform impacted plates. In the present model, effects of strain rate and bending/membrane strain are assumed. The results of the analytical model and the experimental data have good agreement. So, this model can be useful for predicting deformation of rectangular plates under low impact loading.
Compared to non-cavitating flow, cavitating flow is much complex owing to the numerical difficulties caused by cavity generation and collapse. In the present work, cavitating flow around a two-dimensional Clark-Y hydrofoil is studied numerically with particular emphasis on understanding the cavitation structures and the shedding dynamics. A cavitation model, coupled with the mixture multi-phase approach, and the modified shear stress transport k- turbulence model has been developed and implemented in this study to calculate the pressure, velocity, and vapor volume fraction of the hydrofoil. The cavitation model has been implemented in ANSYS FLUENT platform. The hydrofoil has a fixed angle of attack of α = 8° with a Reynolds number of Re = 7.5 x 105. Simulations have been carried out for various cavitation numbers ranging from non-cavitating flows to the cloud cavitation regime. In particular, we compared the lift and drag coefficients, the cavitation dynamics, and the time-averaged velocity with available experimental data. The comparisons between the numerical and experimental results show that the present numerical method is capable to predict the formation, breakup, shedding, and collapse of the sheet/cloud cavity. The periodical formation, shedding, and collapse of sheet/cloud cavity lead to substantial increase in turbulent velocity fluctuations in the cavitation regimes around the hydrofoil and in the wake flow.
The drilling of metals produces undesired raised material which is defined as burr. It is important to minimize the burr size by modifying the drill geometry or selection of drilling parameters. Although, selection of optimal drilling parameters can be minimize the burr size, but it may be increases the overcut or decreases the material removal rate (MRR). In this paper, drilling parameters have been selected for minimal burr size and desired overcut and MRR. Four adaptive neuro fuzzy inference system (ANFIS) models have been designed based on experimental observation in drilling of copper. Outputs of ANFIS models are burr height, burr thickness, burr type and overcut of hole; While input parameters of drilling process are cutting speed, tool diameter and ratio of feed rate to diameter. Then the particle swarm optimization method has been used to select the optimum condition of input parameters to minimize the burr size in desired value of overcut and MRR. Results showed that the proposed models can be predict the outputs well and they can be used as adequate predictors and optimizer for achieving the drilling parameters which gives a type of burr with low value of burr height and burr thickness with desirable overcut and MRR.
In our article, inverse kinematic problem of a plasma cutting robot with three degree of freedom is solved using artificial neural networks. Artificial neural network was trained using joint angle values according to cartesian coordinates (x, y, z) of end point of a robotic arm. The Levenberg–Marquardt training algorithm was applied to educate artificial neural network. To validate the designed neural network, it was tested using a new test data set which is not applied in training. A simulation was performed on a three-dimensional model of MSC.ADAMS software using angle values obtained from artificial neural network test. It was revealed from this simulation that trajectory of plasma cutting torch obtained using artificial neural network agreed well with desired trajectory.
Drilling and completing wells through complex salt formation is technically challenging and costing. Field data demonstrates that well casings designed by traditional safety coefficient criterion occurring failure in deep salt formation though their safety factors are greater than 1. To reveal the failure mechanism, a probabilistic computational model coupled with salt formation, defective cement and worn casing is established and analyzed using Monte Carlo simulation method. On the basis of reliability theory, the results calculated by 5000 times simulations show that the traditional safety coefficient criterion has been unable to adapt to the safety assessment of well casings under salt creep conditions. To gain a sophisticated evaluation, a new assessment criterion is established and applied to assess the security of well casings under salt creep conditions. This study provides a new perspective for revealing the failure mechanism and solutions of evaluation on well casings under salt creep conditions, which may be an alternative method to study and predict the life of well casings in deep complicated formation.
This paper examines the flow field of a circular-arc gear pump operating at high pressures and high speeds by the commercial finite-volume-based code Fluent. The performance of circular-arc gear pump operating at high pressures and high speeds have been discussed. The mathematical model of the tooth profile is established. The pressures including gears mesh, outlet pressures, and outlet flow rate are studied under different rated outlet pressures and rotational speeds. There are dynamic pressures at clearance between chamber and tip circle of gear. Moreover, parts of radial leakages are prevented by dynamic pressures. The outlet pressures almost remain constant. However, there are strong pressure fluctuations in gears mesh under the high pressures and high speeds. The pressures are several times higher than the rated outlet pressure when the circular-arc gear pump operates at 10,000 r/min and 12,000 r/min. Gear meshing pressure fluctuations increase with the increase in rotational speeds. However, gear meshing pressure fluctuations decrease with the increase of outlet rate pressures. There are rotational speeds and outlet rate pressure critical points for gear meshing pressures, and the variation tendency of gear meshing pressures changes dramatically when it exceeds the critical points. Hence, the research results provide base model for circular-arc gear pump operating at high pressures and high speeds.
This paper attempts to review the implications of the sulphur oxides (SOx), nitrogen oxides (NOx) and nitrous oxide (N2O) emissions to the design of fluidised bed combustion (FBC) operations. The review focuses on how the knowledge of SOx and NOx emissions trends can be applied to influence the design of FBC operations. The effects of the emission trends of these noxious gases on the design operations for FBC such as temperature control, nozzle designs, sorbent selection design, air supply and control designs were reviewed. The implications of SOx, N2O and NOx emissions on the design of FBC systems rest primarily on the need to design the operational conditions of the system. The design for the precise location of the fuel feeding ports, secondary air feeding ports, limestone feeding ports and a prescribed size and quantity of sorbents to feed into the system was found to be crucial for reduction of these emissions. The emissions also have an impact on the design of the distributor plate of the system; reduction of the emissions necessitates good fluidisation and well-regulated temperature within the system. The review therefore concludes that there is a close nexus between the design and operation of FBC systems with NOx, N2O and SOx emissions.
This paper deals with the problem of conjugate heat transfer of a rotary disk which is uniformly heated. Computational fluid dynamics simulations are performed for different ranges of rotational Reynolds number (20,000–50,000) and heat flux (100, 200, and 400 kW/m3) on this surface. Two numerical approaches including multiple reference frame and sliding mesh are employed to simulate the interaction between rotary and stationary domains. It is shown that both methods yield satisfactory results, and an excellent agreement with the results obtained from the correlation available in the literature is also found. Furthermore, the effects of involved parameters on average and local convective heat transfer are investigated. Results show that the temperature profiles on the disk surface remain rather unchanged for all ranges of those parameters under study here. It is also shown that local Nusselt number decreases more steeply for higher ratios of fluid conductivity to solid conductivity.
Electrical discharge machining (EDM) is an extensively used method in the machining of electrically conductive materials. Recast or white layer formation is undesirable, but inevitable, result of EDM and needs to be understood and accurately determined to efficiently perform post-treatment processes for removing the recast layer caused by EDM process. In this study, recast layer thickness and surface roughness data obtained from experimental study were analyzed and a correlation between these two parameters has been established. Image-processing technique has been used for obtaining of recast layer thickness data. It was observed that the correlation between recast layer thickness and surface roughness increases remarkably with the increase of working current and pulse time. The correlation obtained in this study has the potential to predict the recast layer thickness on spark-eroded surfaces from simple surface roughness values instead of using the prevailing time-consuming and tedious etching and polishing method. The possible approximation of the recast layer thickness using a thermal model is also discussed.
Natural convection heat transfer from a hot vertical hollow brass cylinder has been studied experimentally and numerically. The governing equations of continuity, momentum and energy are discretised by using an implicit finite difference technique. The velocity and temperature profiles, boundary layer thickness, local and average heat transfer coefficient are obtained using the numerical simulation. The predictions of the numerical simulation are compared with the experiments conducted on a laboratory-scale apparatus and with the results obtained from analytical solutions available in literature. The numerical simulation results are obtained for two fluids; air and water vapour whereas the experiments are conducted for air only. The induced flow is laminar in both the simulation and the experiments. The dependence of boundary layer thickness on Prandtl number is discussed. The numerically obtained Nusselt number is found quite close to the analytical one. The results show the heat dissipation from the cylinder to surrounding fluid is higher for air than for water vapour. The various factors that affect the comparison of the experimental results with the numerical simulation are discussed.
In this paper, a high-temperature heat pump (HTHP) is developed and manufactured to replace the traditional oil-fired boiler heater for crude oil heating. It extracts thermal energy from waste hot water separated from the crude oil to provide high-temperature hot water to heat the crude oil. A prototype of the HTHP system is installed in the Jinzhou oil treatment station in Liaoning, China and the field test is conducted for about 6000 h. A typical 144 h of field testing data is analyzed to evaluate the performance of the designed HTHP system. It is observed that the temperature of hot water provided by the HTHP unit varies from 86 ℃ to 95 ℃ throughout the whole operating period and is sufficient for the crude oil heating (80–90 ℃). The heating capacity and power consumption of the HTHP system varies from 1350 to 1785 kW, and 171 to 197 kW, respectively. The overall system coefficient of performance ranges from 3.5 to 4.4 with an average value of 3.8. Based on the experimental results, a primary energy ratio is introduced to evaluate and compare the economics of the studied HTHP system and oil-fired boiler heater. The comparison shows that the energy consumed by the HTHP unit is only 57% of that consumed by the oil-fired boiler heater. If all traditional oil-fired boiler heaters are replaced by the HTHPs in the Jinzhou oil treatment station, the total yearly energy saving is around 1.12 x 104 tons of equivalent coal which equates to 1.76 x 104 tons of CO2 emissions.
The main purpose of this work is a numerical study on unsteady natural convection from outer surface of helical coils. Each heat exchanger consisted of a helical coil and a shell. The helical coil was mounted in the shell vertically. The cold water was in the shell and the hot water was flowing through the coil and was cooled by unsteady natural convection. A CFD code has been used for heat exchanger simulation. The analyses have been carried out for 27 helical coils with different geometries. The effect of helical coil geometry on natural convective heat transfer is investigated. All of continuity, momentum, energy, and turbulence equations are solved for both of fluids simultaneously, so there is no need to simplifying assumptions for boundary conditions. Results are compared with previous experimental researches. Statistical analyses have been done on data points of temperature and natural convection Nusselt number. It is revealed that shell-side fluid temperature and the Nusselt number of the outer surface of coils are functions of in-tube fluid mass flow rate, geometrical parameters of helical coils, and time. A new correlation is presented for calculating the temperature changes of bath fluid. Some other fluids are used as coil and bath fluids and results show that the presented correlation for bath temperature computing have an acceptable accuracy for them.
In this paper, after thermal and economic modeling of cogeneration plant, this system is optimized to find the optimal prime mover and their benefit for various cooling, heating, and electrical demand loads. To find the optimal prime mover and their benefit for each triple load, two new nondimensional design parameters including electric cooling ratio and nominal power ratio are defined. It is observed that, for example, for higher electrical and lower heating load demands, the gas engine is more profitable while for higher electrical and heating load demands, diesel engine is more profitable. In addition, some ranges of demand loads at which using CCHP plant is not profitable (in comparison with traditional system) are also obtained and presented. The optimum results obtained in NO SELL mode show that the highest values of actual annual benefit (AAB) are obtained for highest values of electrical load demand. This region corresponds with values of Hdmn/Qdmn (heating to cooling load demand ratio) in the range of 1.5–3.5. The highest values of AAB for SELL mode are obtained to be in the range of 0.5–3.5 for Hdmn/Qdmn (heating to cooling load demand ratio).
Aimed at overcoming high sensitivity to machining or mounting error of line-contact conjugate surfaces, a novel torus involute gear drive is proposed which can compensate large axial misalignments and possess good meshing characteristics without lead correction. The torus involute gear is essentially a special spur gear with continuous shifting in the second order. Based on the processing principle of the torus involute gears, their mathematical models are established according to the corresponding imaginary rack cutter. In order to provide the approach to choose proper designing parameters, geometry characteristics of the torus involute gear are investigated: condition equations of tooth undercutting for a convex torus involute gear and tooth pointing for a concave torus involute gear are formulated utilizing the developed mathematical models, and the approach to checking tooth flank interference is provided. Contact characteristics of the gear set is studied through tooth contact analysis and finite element analysis. The simulated results produce useful information about tooth contact pattern, stress distribution, and transmission errors of the gear set.
In this work, investigations have been made for surface roughness (Ra) improvement of vacuum moulding (VM) components by introducing barrel finishing (BF) on fused deposition modelling patterns at preliminary stage (i.e. before being used as master patterns). The Ra improvement will help to avoid/reduce post machining/finishing operations for green manufacturing. The VM master patterns were prepared using P-430 grade acrylonitrile butadiene styrene material on commercial fused deposition modelling setup. Further, Ra of VM master pattern prepared was improved by using BF process (as intermediate process). The controllable parameters of BF and VM process (namely, media weight, cycle time, vacuum pressure and grain size of refractory sand) were studied at three levels by using Taguchi L9 orthogonal array to explore their affects on Ra of the final cast components. The results of study suggest that media weight of BF and sand grain size of VM process contribute significantly for improving Ra.
This paper deals with vibration-fault diagnosis of spark plug of an internal combustion engine using wavelet analysis and support vector machine. In order to reduce the noises of the vibration signals, wavelet denoising technique was used. A performance comparison was made between different mother wavelets as well as different levels of decomposition in order to find the best cases for the system under study. The results showed that the maximum classification accuracies were obtained by 13 different wavelets, namely, db1_4, db1_5, db2_4, db3_4, coif1_4, coif1_5, coif2_4, coif3_3, coif3_4, coif3_5, dmey_2, dmey_4 and bior3.7_6. It was also demonstrated that db1, coif1, coif3 and dmey were valuable mother wavelets for this study. Moreover, the results indicated that the proposed approach can reliably be used for spark plug fault diagnosis.
A new vibration signal denoising method of hydropower unit based on noise-assisted multivariate empirical mode decomposition (NA-MEMD) and approximate entropy is proposed. Firstly, the NA-MEMD is used to decompose the signal into a number of intrinsic mode functions. Then, the approximate entropy of each component is computed. According to a preset threshold of approximate entropy, these components are reconstructed to denoise vibration signal of hydropower unit. The analysis results of simulation signal and real-world signal show that the proposed method is adaptive and has a good denoising performance. It is very suitable for online denoising of hydropower unit's vibration signal.
Impact forces are one of the mechanisms for grinding in mill. This takes place when the particles elevated by the lifters get into cascade motion and their fall on the load causes the breakage of other particles. The present paper aimed to study the impact forces in terms of variables like: mill speed, solid charge filling (ball filling), slurry concentration, and slurry filling. In this work, the influence of these operating parameters was investigated using a pilot mill. To this end, a copper ore was used to prepare slurry at different solid concentration. The tests covered a range of slurry filling from 0 to 2 with five different balls filling between 12% and 36% of mill volume and six different speeds between 60% and 85% of critical speed. The results delineate that the increase in the mill speed leads to a remarkable increase in the amount and frequency of the impact forces. Increasing the charge volume leads to decrease the maximum impact forces. The results show that with the increase in slurry filling and the resulting formation of a pool, the impact forces will decrease. Moreover, it is found that with the increase in slurry concentration, the slurry will act as a damper decreasing the impact forces.
In this study, the drying kinetics of cotton bobbin drying process in a pressurized hot-air convective bobbin dryer was investigated, and a drying model was introduced for the simulation of drying. Tests were conducted for drying temperatures of 70℃, 80℃, and 90℃; effective drying air pressures of 1, 2, and 3 bars; three volumetric flow rates of 42.5, 55, and 67.5 m3/h; and for three different bobbin diameters of 10, 14, and 18 cm. Optimum drying conditions were specified in terms of drying time and energy consumption. Results indicate that the total drying time depends significantly on the drying temperature, pressure, and volumetric flow rate. Results show that the minimum energy consumption is obtained for low values of drying air temperatures and pressures, and for moderate and high values of drying air volumetric flow rates. It was also found that the Page model is suitable for simulating the drying behavior of cotton yarn bobbins. Finally, results show that effective diffusion coefficient values are between 1.132 x 10–7 m2/s and 3.453x10–7 m2/s depending on the values of drying parameters.
Three grades of titanium alloy TITAN 15, TITAN 21, and TITAN 31 were machined using powder mixed electric discharge machining to study the effect of cryogenic treatment and its effect on tool wear rate (TWR). Thereafter, an attempt has been made to develop a mathematical model for predicting TWR using dimensional analysis using the outcome of the Taguchi model and thermo-physical properties of tool materials. The model shows the significant role of thermal conductivity on TWR in electric discharge machining of titanium alloys. The predicted values from the developed mathematical model were validated and were found to be in good agreement with the experimental results. Microscopic investigations on selected tool samples were performed using scanning electron microscope, energy-dispersive X-ray spectrometer, and X-ray diffraction. The results showed transfer of material on the tool surface from the workpiece, dielectric, and the powder.
During the start-up and shut-down phases of steam power plants many components are subjected to pressure and temperature transients that have to be carefully regulated both for safety and reliability reasons. For this reason, there is a growing interest in the optimization of turbine bypass controllers and actuators which are mainly used to regulate the plant during this kind of operations. In this work, a numerically efficient model for real-time simulation of a steam plant is presented. In particular, a modular Simulink™ library of components such as valves, turbines, and heaters has been developed. In this way, it is possible to easily assemble and customize models able to simulate different plants and operating scenarios. The code, which is implemented for a fixed, discrete step solver, can be easily compiled for a RT target (such as a Texas Instrument DSP) in order to be executed in real time on a low-cost industrial hardware. The proposed model has been used for quite innovative applications such as the development of a hardware-in-the-loop test rig of turbine bypass controllers and valve positioners. Preliminary experimental activities and results of the proposed test rig developed for Velan ABV are introduced and discussed.
This paper presents results of detailed nonlinear finite element analysis of gasketed bolted flange pipe joints of different sizes (1, 4, 5, 6, 8, 10, 20 in.) of 900# pressure class for achieving proper preload close to the target stress values with and without considering yielding at bolt and flange and gasket crushing recommended by ASME and industrial guidelines for optimized performance using customized optimization algorithm. In addition, two strategies torque control method and stretch control method are used which is a normal practice in the industry.
In this article bending control of rotating Euler–Bernoulli beam is considered. It is assumed that the fixed-free elastic beam is attached to a servomotor using a variance constrained controller, specifically output variance constrained controller for vibration suppression. Equations of motion of the system obtained via Hamilton's principle and Galerkin method are used. The resulting linearized state-space models obtained considering just one or three modes are used for control system design. Output variance constrained controllers are designed in order to control bending at the beam tip and beam rotation angle with different variance constraint magnitudes. Closed-loop responses are analyzed when they experience white noise perturbations. Comparisons between system having tighter variance constraint and weaker variance constraint are also performed. Finally, robustness of Output variance constrained controllers with respect to the modeling uncertainty (i.e. variation of number of modes) is examined.
The diffuser plays a significant role in the performance of a centrifugal pump, especially for a high-power centrifugal pump. Therefore, to improve the efficiency of a centrifugal pump, optimization of a vaned diffuser is proposed in this work. The steady simulations were carried out by solving the three-dimensional Reynolds-averaged Navier–Stokes equations with a shear stress transport turbulence model. The numerical head and efficiency were validated by the experimental results of the original pump, and the results show that the predicted performance of the numerical simulation is in good agreement with the experimental results. Four design variables of the diffuser including the diffuser inlet diameter D 3, diffuser inlet width b 3, diffuser inlet angle α 3, and diffuser wrap angle 2 were selected to design by the CFturbo 9.0. The diffusers under test were selected using the orthogonal experiment method using the orthogonal array L 16(44). The effect of the four variables on the pump’s efficiency was investigated by the predicted efficiency of 16 diffusers. A quadratic polynomial fitting function for the variables and efficiency was constructed using the response surface method. The optimal values were obtained by solving the response function with the multi-island genetic algorithm. Through the analysis of the range and quadratic regression, it was found that the diffuser wrap angle has the most significant influence on efficiency. The efficiency of the optimal pump increased by 8.65% compared with the original scheme. The velocity distributions in the diffuser inlet and volute were improved and became more uniform. The total pressure in the diffuser and volute of the optimal pump was higher than that of the original pump.
In order to reduce the manufacturing process variability and improve the production yield, it is important to predict the performance of manufacturing process. The adaptive neuro-fuzzy inference system (ANFIS) is a powerful network which can predict the output parameters of manufacturing process. However, design of ANFIS needs trial and errors to select the best structure. In this study, an imperialistic competitive algorithm has been used to determine the ANFIS architecture to reach minimum values of the prediction error. In order to evaluate the performance of this combined method, two illustrative examples of manufacturing processes have been used. Results indicated that the combined method has superiority in prediction of output, rather than previous developed ANFIS models and so it can be applied for modeling of the other manufacturing processes.
The stagnation point flow of a nanofluid towards a permeable stretching/shrinking sheet using the Buongiorno's model is studied. Numerical results are obtained using boundary value problem solver bvp4c in MATLAB for several values of the governing parameters. The numerical results show that dual (upper and lower branch) solutions exist for the shrinking case, while for the stretching case, the solution is unique. A stability analysis is performed to determine the physical realizable in practice of the dual solutions. It is found that the skin friction decreases when the sheet is stretched, but increases when the suction effect is increased. It is also found that increasing the thermophoresis parameter reduces the heat transfer rate at the surface, while increasing the Brownian motion parameter increases the mass transfer rate at the surface.
Design optimization of heat exchangers is a very complicated task that has been traditionally carried out based on a trial-and-error procedure. To overcome the difficulties of the conventional design approaches especially when a large number of variables, constraints and objectives are involved, a new method based on a well-established evolutionary algorithm, particle swarm optimization, weighted sum approach and a novel constraint handling strategy is presented in this study. Since the conventional constraint handling strategies are not effective and easy-to-implement in multi-objective algorithms, a novel feasibility-based ranking strategy is introduced which is both extremely user-friendly and effective. A case study from industry has been investigated to illustrate the performance of the presented approach. The results show that the proposed algorithm can find the near pareto-optimal with higher accuracy when it is compared to conventional non-dominated sorting genetic algorithm II. Moreover, the difficulties of a trial-and-error process for setting the penalty parameters are solved in this algorithm.
In reciprocating compressors, partial unloading stepless capacity regulation causes the power consumption to reduce in proportion to the decrease in capacity. To enable the widespread application of this method, it is necessary to analyse the changes in the mechanical status of a reciprocating compressor while its capacity is being regulated. This study focused on the rod reversal in a reciprocating compressor and evaluated the influence of capacity regulation. Based on a thermodynamic cycle model, the reversal angles for different capacities were calculated and compared for an M-type reciprocating compressor. The calculated results show that, for a compressor for which the designed reversal angles are sufficiently large to ensure good lubrication for pin and bushing assemblies, stepless capacity regulation can guarantee its safe operation.
Chemical kinetics modeling within the numerical simulations of turbulent reactive flows is a critical issue. In this study, first a large eddy simulation of a non-premixed planar methane jet flame with artificial neural network -based chemical kinetics is performed. To consider the effects of turbulence on the evolution of the thermo-chemical state space, the artificial neural network training patterns are obtained by solving the unsteady reaction-diffusion equations of linear eddy mixing sub-grid combustion model. The optimization procedure for selecting the optimum neural network architecture is discussed in detail. A flow field analysis and a comparison between a non-reactive jet with the same velocity boundary conditions with the flame jet are performed. It is shown that the non-reactive jet is more turbulent and vortical structures of the non-reactive jet occur closer to the jet exit compared to the flame jet. Second, in a first attempt to quantify the influence of different chemical kinetics methods, large eddy simulation computations are performed with other methods used to represent the chemical kinetics such as direct integration and look-up table. A comparative study is performed between the averaged, instantaneous and fluctuation profiles of the scalar field and flame structures obtained by each method. Although all large eddy simulation results are very close to each other, the main discrepancy is observed for CO mass fractions obtained by artificial neural network and look-up table-based chemical kinetics simulations. It is also shown that the averaged scalar field and the conditional averaged values of the flame are overestimated by look-up table based chemical kinetics large eddy simulation computations. Moreover, the potential savings of artificial neural network in computational costs in comparison with other chemistry approaches are illustrated.
The purpose of this study is to utilize Taguchi method, which can prove to be a handy and effective tool for determining minimum vibration response of rotor-bearing system set to avoid running at critical speed. In the study, three test cases considering different coupling type (elastic, jaw, and solid) and disc location (disc location A, B, and C) were conducted to observe behavioral changes of the shaft system considering vibration signatures. Each test case was conducted for three different shaft running speeds of 12, 18, and 24 Hz. To find the minimum peak amplitude values by experimenting different combinations of the rotor-bearing system set needs a lot of experiments for reaching solution. Moreover, the solution proves costly because of the time consumed in doing many experiments. This fact depicts the importance of an efficient optimization method to be used. Taguchi method can determine the design parameters, which have the greatest influence on the solution through a very limited number of experiments, for finding optimum set of rotor-bearing system. The method is performed using an iterative procedure to gain an optimum design.
The present work provides the computations of unsteady 3D synthetic jet ejected into a quiescent ambient. The
This paper presents a novel methodology applying Monte Carlo methods with delay-time analysis to test the effects of scheduled maintenance and inspection actions on factors affecting the operational efficiency of a marine system which is subject to degradation. The aim is to demonstrate how a Monte Carlo model incorporated into delay-time analysis can be used to predict the transition behaviour of a system under analysis. The model presented in this paper focuses on the effects on system failure probability and downtime of various maintenance and inspection policies. The impact on spare part requirements is also investigated.
A novel mathematical model for combustion of a single copper concentrate particle is presented. The model includes particle volatilization, fragmentation, smelting, and combustion phenomena. This model has been incorporated into a general computational fluid dynamics code to calculate flow field and particle trajectories needed to simulate the smelting process in flash furnaces. In this model, Lagrangian approach was used to handle solid particles and droplets of liquid fuel charged, while Eulerian framework was used to handle the gas phase flow field. The results show that the effect of particle fragmentation was remarkable in flash smelting process as compared with experimental data and should be considered in combustion modeling. Moreover, the flash smelting process simulation results show that the reaction shaft design should be optimized based on a combination of furnace dimension and type of concentrate burners.
In this study, milling operations were carried out using AISI 1040 specimens steel in dry cutting conditions. The cutting tools used in the experiment include P20 tool steel and they also have three different approach angles (45°, 60°, 75°) and rake angles (0°, –6°, –12°). In milling experiments, cutting parameters with a depth of cut of 1.5 mm, cutting speed of 193 m/min, and feed rate of 313 mm/min were selected. A comparison was presented between the force values which were obtained by measured value and predicted with numerical simulations, and then a good agreement was found between measured and predicted force values. As result of, it was observed that the rake and approach angles were effective in milling operations.
The effect of suction/injection on transient free-convective flow bounded by two infinite vertical parallel porous plates in the presence of thermal radiation is investigated numerically as well as analytically. The transient mathematical model has been solved using the implicit finite difference method while the steady state version of the physical situation has been solved using perturbation method. During the course of numerical computation, an excellent agreement was found between transient solution at large value of time and steady state solution. In addition, it was found that the time required to reach steady state is directly proportional to the Prandtl number of the working fluid for fixed values of other controlling parameters.
The problem of trajectory tracking for a class of nonlinear systems in the presence of un-modeled dynamics, parameter variations and even the actuator faults is investigated in this paper. A novel fault-tolerant control scheme is proposed by combining the nominal model-based controller and time-delay controller, which are adopted to achieve the real-time dynamic compensation and guarantee the robust stability of the controlled systems, respectively. Moreover, high-quality differential signals are unavailable in the presence of disturbances and measurement noise, which limit the performance of closed-loop systems in practice. Therefore, an extended state observer (ESO) is introduced to obtain high-quality differential signal estimations based on position measurements only. Furthermore, the effectiveness of the proposed novel control scheme is verified by testing in the spacecraft attitude tracking system.
In this paper an inverse numerical study of a conductive, convective and radiative rectangular fin is carried out with temperature-dependent thermal conductivity. At first, an implicit Runge-Kutta method-based solution is obtained for calculating the temperature distribution, and then an inverse problem is solved for estimation of unknown thermo-physical properties. The convection–conduction parameter, variable conductivity parameter and radiative parameter have been simultaneously predicted for satisfying a prescribed temperature distribution. This is achieved by minimizing a least squares-based objective function using a hybrid differential evolution-nonlinear programming optimization algorithm. The results obtained from the forward method are compared with Adomian decomposition and homotopy analysis methods which are found to be satisfactory. It is observed that many feasible combinations of parameters exist which satisfy the same temperature distribution, thus providing an opportunity for selecting any combination from the available alternatives. The effect of convection–conduction parameter on the temperature distribution is observed to be more than other parameters. A case study of different fin materials is also carried out for demonstrating the application of the present methodology.
Gasketed flange joints are usually subjected to internal pressure at high temperature. The most important requirement of flange joint is to provide leak-free joint under operating condition. In the present study, temperature-dependent nonlinear gasket properties of spiral-wound gasket at elevated temperatures are obtained experimentally and included in the analysis. The relaxation of gasket contact stress in both single and twin-gasketed joints at elevated temperatures is compared. It is observed that the ability to withstand internal pressure decreases with increase in temperature in both single and twin-gasketed flange joints. But, the twin-gasketed flange joint is found to withstand higher internal pressure than single-gasketed joint at a given bolt preload and temperature. The influence of gasket seating surface rotation on the distribution of gasket radial contact stress at elevated temperature is studied. The effect of elevated temperature on flange stresses of twin-gasketed joint is also examined.
This paper uses the variational iteration method to study nonlinear oscillator, and He’s amplitude–frequency formulation is adopted here as a good initial guess. In general, the ability of amplitude–frequency formulation to present reasonable and precision results makes it a reliable method, especially in oscillation systems. In addition, simplicity in the determination of the frequency of the system is one of the distinctive merits in this method. On the other hand, it is difficult to attain higher accurate solutions or higher order solutions in amplitude–frequency formulation. Thus, to overcome this hardship, one can select amplitude–frequency formulation as an initial guess in variational iteration method; this not only noticeably improves the accuracy and efficiency of variational iteration method (improved variational iteration method) but also accomplishing higher order solutions is feasible. Moreover, the more precise the frequency of the initial guess of variational iteration method, the more dominant the final results of variational iteration method. To show the ability and precision of this choice, some examples are presented and their results are compared to variational iteration method, amplitude–frequency formulation, energy balance method, and fourth Runge-Kutta’s numerical method. The resultant graphs and charts show an excellent agreement to this choice. In fact, the choice of amplitude–frequency formulation as an initial guess not only improves various aspects of the variational iteration method but also it distinguishes decline the relatively complex trend of calculating of initial guess compared to other ways.
It is important for fuselage assembly to align the skin panel onto the frame, i.e. to reduce the gaps and subsequently lessen the need for shimming, but conventional position control method cannot always meet the requirement. This study proposed a direct force control technology, which can be directly promoted to a full-rate production without making any dedicated assistance and complex finite element analysis. This strategy was based on a force sensor mounted on a flexible tooling locator to feed back the pressing force information to the controller system. To achieve a certain compressing status, the system was controlled to achieve a desired force rather than reach a specific position. After obtaining four ideal force values from an experimental study during a prototype trial-production, a force-size interval that provides a certain grey degree of confidence was proposed for the flexible tooling control system using a parameter estimation approach for small samples based on the grey distance measure. Compared with conventional position control method, force control technology can achieve better compressing status, since it enables a reduction of all gap values between the skin panel and the framework by 0.15 mm on average or even 0.2 mm at most in the same assembly process.
Fuel dispenser is an integrated fuel pumping and metering system for automotive refueling at the service station. In this paper, we develop a preset refueling mode for the dispenser. A frequency converter and the flow rate signal from the measurement transducer are utilized instead of the solenoid valve, which is used to control the flow rate in the traditional refueling mode. With variable speed pumping system, the rotational speed of the pump is adjusted to achieve the desired flow rate and head necessary for the application. All the experiments were operated on a real dispenser system. How the frequency influences the refueling accuracy is observed. Through choosing a suitable frequency, not only accuracy but also energy efficiency improves compared with the traditional refueling mode. It is able to provide a reference for authority to fill in gaps in low-quantity (less than 5 L) refueling.
In this article, the evolution of vapor film on the surfaces of hot objects immersed in a cryogenic superfluid helium liquid is considered. It is assumed that at the beginning of the process, a thin film of steam exists on the surface of the object that has a spherical shape. If the heat flux is greater than the critical heat flux, the growth of vapor film will continue, otherwise it will collapse. Survey and analysis of the previously mentioned problem has been done using numerical method and the main onjectives are as follows: (a) study the evolution of the vapor film immersed in superfluid helium on the surface of the hot ball and (b) the stability of vapor film immersed in superfluid helium on the surface of the hot ball.
Since the practical system in many real-world applications contains several different work stages and multiple failure modes it is a difficult task to analyze such system with the system state’s nonbinary characteristic. An efficient phased mission reliability analysis approach for systems with multiple failure modes is presented in this paper, which is called the extended multivalued decision diagram with multiple failure modes. To reduce the complexity and size of the model, the branch merging, nodes reduction, and phase fusion approaches are used and then an engineering case is given to validate the efficiency of model simplification. At end, the proposed method is illustrated and compared with the binary decision diagram approach through the example.
In this paper, steady, laminar, incompressible, and two-dimensional micropolar flow between a porous disk and a nonporous disk is considered. By introducing suitable similarity transformations, the problem is reduced to a set of nonlinear boundary value problems. Optimal homotopy asymptotic method is employed to obtain the series solutions for velocity and microrotation distribution. The accuracy of results is examined by the fourth-order Runge–Kutta numerical method. The results are presented to study the velocity and rotation profiles for different physical parameters such as: Reynolds number, vortex viscosity parameter, spin gradient viscosity, and microinertia density parameter. As a result, the magnitude of the injection velocity has strong influence on the flow velocities and the microrotation.
The aim of this article is to apply the collocation method for boundary layer in unbounded domain. The solution for velocity and temperature are computed by applying the collocation method. It does not need any perturbation, linearization, or small parameter versus homotopy perturbation method and parameter perturbation method. Also the determination of the auxiliary parameter and auxiliary function versus homotopy analysis method is not necessary. The use of a special technique to obtain solutions that are very close to the exact solution of the equation has been attempted. The idea is to transform the equations and boundary conditions into another set of variables. In comparison with previous studies, the solution shows that the results of the present method are in excellent agreement with those of the numerical methods. As an important result, it is depicted that approximation of the physical quantities f ''(0) and '(0) are more accurate in comparison with those obtained using homotopy perturbation method. Also, the results reveal that this method is more suitable for solution of boundary layer problems with infinite boundary values.
It is well known that simple proportional, integral, and derivative control yields poor tracking performance due to the friction- and flow-related nonlinearities in electrohydraulic servo-systems. Nonlinear effects are more significant in proportional valve having deadband and non-matched ports with potential application in systems with complex ground friction in off-road vehicles or complex inertia loads in simulators meant for pilot training. A feedforward-based controller has been designed here by performing a number of characterization experiments for achieving good tracking performance overcoming severe nonlinearities. An algebraic model of friction has been developed for including hysteresis beyond the static friction zone in a double-rod piston-cylinder arrangement. A proportional valve with non-matched ports and large deadband has been characterized in terms of command signal to flow gains for each metered port and a leakage coefficient. Also, a dynamic model for the valve with embedded control has been constructed. All these models have been integrated together to predict the piston-motion dynamics. A simple theoretical analysis with a fixed command excitation revealed that following the initial transients a sustained oscillation over a constant mean piston velocity could exist for low pump pressure and valve damping due to the flow-motion coupling. The bandwidth and damping coefficient of the valve flow have been estimated through a comparison between the predicted and experimentally measured piston displacement variation with time. Besides evaluating the feedforward using the algebraic friction model along with assuming incompressible flow and negligible valve leakage, the predictions of the complete model were used to ascertain the proportional, integral, and derivative gains to be implemented in real-time control. Up to 0.5 Hz sinusoidal excitation, the proposed control revealed excellent tracking performance. Controls with only proportional, integral, and derivative and proportional, integral, and derivative together with feedforward exhibited noticeable phase shifts, respectively, from frequencies 0.0625 Hz and 0.6 Hz. Hence, the proposed controller can be useful in low-cost, low-power, precision applications up to 0.5 Hz input excitations.
Melt viscosity is one of the main factors affecting product quality in extrusion processes particularly with regard to recycled polymers. However, due to wide variability in the physical properties of recycled feedstock, it is difficult to maintain the melt viscosity during extrusion of polymer blends and obtain good quality product without generating scrap. This research investigates the application of ultrasound and temperature control in an automatic extruder controller, which has ability to maintain constant melt viscosity from variable recycled polymer feedstock during extrusion processing. An ultrasonic modulation system has been developed and fitted to the extruder prior to the die to convey ultrasonic energy from a high power ultrasonic generator to the polymer melt. Two separate control loops have been developed to run simultaneously in one controller: the first loop controls the ultrasonic energy or temperature to maintain constant die pressure, the second loop is used to control extruder screw speed to maintain constant throughput at the extruder die. Time response and energy consumption of the control methods in real-time experiments are also investigated and reported this paper.
The preloading process is essential for circumferential bolted rotors with curvic couplings and preloading effects determining the rotor performance. A nonuniform clamp load of each bolt will destroy the periodicity of the rotor and affect its strength, stiffness, and stability. In this paper, the finite element method was adopted, the influence of elastic interaction on two types of preload methods (one by one and group) was investigated and the mechanism about elastic interaction was analyzed, and a method to achieve a uniform clamp force of spindle bolts was proposed. This method is based on displacement, and by ensuring equal relative displacements of each bolt and nut during the preloading process, the uniform clamp force can be obtained. The validity of the proposed method is experimentally verified.
In this study, the combined effects of velocity slip and convective heating, Brownian motion and thermophoresis on the magnetohydrodynamic stagnation point flow, and heat transfer of a power-law nanofluid over a stretching sheet is investigated. Using appropriate similarity transformation and the Runge–Kutta–Fehlberg fourth fifth order with shooting technique, the model nonlinear governing differential equations are obtained and solved numerically. The effect of variations of parameters on nanofluid velocity, temperature, concentration, skin friction coefficient, local Nusselt number, and local Sherwood number are presented and discussed. It is found that the skin friction coefficient is an increasing function of a power-law index n and a decreasing function of the slip parameter . Both local Nusselt number and local Sherwood number are increasing function of a power-law index. Increase in Biot number increases local Nusselt number but decreases the local Sherwood number. The results of the study are compared with the previously published result and are found to be in excellent agreement with it.
In this paper, the conveying behavior of a twin-screw multiphase pump is investigated when it pumps either pure water or gas–liquid mixtures with gas void fractions varying from 20% to 90%. A prototype of the twin-screw multiphase pump is developed and set up in a laboratory for this purpose. A theoretical model is established to evaluate backflow rates in the twin-screw pump clearances, total pump volume flow rates, and power consumptions at various pressure differences and gas void fractions. Results show that the predictions from the model agree well with experimental data. For pumping pure water, the power consumption increases by 45.3% when the pressure difference between inlet and outlet of the twin-screw multiphase pump increases from 0.6 to 1.0 MPa. However, the effect of the pressure difference on the total pump flow rate is negligible. For pumping air–water mixtures, the pressure difference has a significant effect on both power consumption and total volume flow rate of the multiphase pump. The pump power consumption increases by more than 40% when the pressure difference increases from 0.4 to 1.0 MPa. On the contrary, the pump volume flow rate decreases between 10% and 30% varying with the gas void fraction value. However, at the fixed pressure differences of 0.4 MPa and 1.0 MPa, the pump power consumption does not show much difference with the change of gas void fractions from 20% to 90% although the total pump volume flow rate reduces by 18.7% and 25.7%, respectively.
For the engineering design of large horizontal vessels with uneven multiple saddles, no clear specifications are given in design codes, especially with uneven settlements. In this paper, an analytical method based on three-moment theorem with settlements is introduced to evaluate the shear forces and bending moments at some critical cross-sections of a large horizontal pressure vessel supported on 10 saddles with uneven settlements. Zick’s stress analysis method for a horizontal vessel supported on two saddles is extended to the multiple saddle arrangements. It is found that as a result of varied cross-section and uneven saddle supports, the shear forces and bending moments are different at different saddle sections. Finite element calculations are also performed to prove the analytical solutions. Results show that for the vessel without settlements, the bending moments and reactions obtained by the three-moment equation method are slightly larger than those obtained by finite element method. Non-uniform deformation of the vessel at different saddles may be contributed to the differences of the two results. For the vessel with settlements, the bending moments and reactions at some saddles obtained by the three-moment equation method are quite larger than those obtained by finite element method. But if the actual axis settlement of the vessel is applied to the three-moment equation method, the two results are close to each other. Experiments are also carried out to verify the reliability of the proposed method.
A floating-type joint applies the entire bolt load to the gasket to generate sealing contact stress, and is prone to leak due to the bolt load loss. Different with the floating type one, a metal-to-metal contact type joint applies only part of the bolt load to the gasket to achieve seating stress, and applies the additional bolt load to the metal-to-metal contact to compensate for the unloading effects due to internal and external loadings. Due to this advantage, metal-to-metal contact type joints are gradually used in chemical industries, nuclear power industries, etc. A flange joint together with a metal-to-metal contact type gasket forms the metal-to-metal contact type joint studied in this article. A three-dimensional nonlinear finite element model is developed to highlight the complex behavior of the flange joint under bolting-up, pressure loading and thermal loading conditions. Despite the common perception that gasket stress in a metal-to-metal contact type joint stays constant, reduced gasket stress is concluded due to flange rotation and joint thermal expansion.
In this work, the cooling slope method is employed to produce the A356 feedstock in semisolid processing. This paper discusses the effect of temperature on the final microstructure of A356 aluminum alloy in this method. These temperatures are casting temperature, mold temperature, and cooling slope plate temperature. The dendritic primary phase in the conventionally cast A356 alloy is transformed into a non-dendritic one in ingots cast over a cooling plate at casting temperature of 600 ℃, 615 ℃, 625 ℃, 650 ℃, and 680 ℃, and at condition of using a cooling system or without it. After pouring, the melt which becomes semisolid at the end of the plate is consequently poured into cylindrical steel mold at temperatures of 25 ℃, 200 ℃, and 400 ℃. The cooling slope is adjusted at the angle of 50° with respect to the horizontal plane and 500 mm length. It is found that the pouring, plate, and mold temperatures affect the size and morphology of α-Al phase. The effects of these are 22% decrease on average grain diameter and 8.5% increase on the shape factor at the weakest case. The results illustrated that by modifying the temperature the hardness of the specimens is increased. The results indicated that the highest uniformity with the grain size of ~88 µm and maximum shape factor of 0.68 are related to pouring and mold temperature of 625 ℃ and 200 ℃, respectively using water cooling system.
This work deals with the prediction of unknown parameters and identifying feasible materials for satisfying a given temperature distribution in a rectangular fin geometry involving variable thermal conductivity and surface heat transfer coefficient. The unknown parameters which have been estimated in this work are the thermal conductivity, coefficient of variable conductivity and fin dimensions. For achieving the required objective, an inverse problem is solved by minimization of least squares error using a hybrid evolutionary-nonlinear programming algorithm. Due to correlated nature of the unknowns, many feasible combinations of materials have been found with varying dimensions, which is proposed to offer a wide range of flexibility in selecting the fin material. The present study is proposed to be useful in situations where only few discrete temperatures are available, as it helps to find out feasible materials alongwith relevant dimensions which will yield a prescribed temperature distribution.
Carbon black is produced from waste wood apple shell (WAS) material using pyrolysis at various carbonization temperatures (400 ℃ and 600 ℃) and used as reinforcement in thermoset polymer composite. The composites were prepared at 5, 10, 15, and 20 wt% filler loadings. The characterization of shell particles has been done through proximate, ultimate, and energy dispersive spectroscopy analyses. Tensile, flexural, and hardness tests were performed at different filler loadings. The results indicated that the strength of the polymer composite increased as filler loading increased to some extent and hardness property of the carbon black composite gives better result as compared to neat polymer composite. However, the filler–matrix bonding from tensile and flexural load was analyzed by scanning electron microscopy.
Optimal design of a combined cooling, heating and power (CCHP) generation system is presented in this paper. The goal of this study is to compare different outcomes which might be obtained during CCHP equipment selection due to following different scenarios: (1) when selecting the type of prime mover (PM, such as gas turbine or gas engine or diesel engine), what differences could be obtained when the selected nominal power of all PMs is similar (SNP) or they be selected non-similar (NSNP)? (2) What differences could be reached when selling electricity to the grid is feasible (SELL mode) or not (NO SELL mode)? (3) What differences are going to occur when PMs could run at variable partial load (VPL) during a year or constant partial load (CPL) during a year? Particle Swarm Optimization (PSO) method was applied to select the CCHP equipment by maximizing the relative annual benefit (RAB) as the objective function. Optimization results for our case study showed that NSNP-NO SELL-VPL scenario showed 15.41%, 10.80%, and 5.23% growth in optimum value of RAB in comparison with that for SNP-NO SELL-VPL scenario for gas engine, diesel engine and gas turbine, respectively. Furthermore, for our case study, NSNP-NO SELL-VPL scenario showed advantage over NSNP-NO SELL-CPL case, with 26.80%, 27.72%, and 13.60% higher RAB values when gas engine, diesel engine, and gas turbine were selected. Finally, differences were 12.37%, 23.76%, and 11.09% when SNP-NO SELL-VPL and SNP-NO SELL-CPL scenarios were compared.
Safe transportation of natural gas, mostly in liquid form such as liquefied natural gas to international market is very important. In the case of exterior material contact to liquefied natural gas, intensive boiling and exploding should be anticipated. This paper investigates the thermo-physical contact between a single drop of water (0 ℃ as a fluid with higher temperature) with liquid methane, which is similar to liquefied natural gas, at a very low temperature (–162 ℃). Heat transfer between water drop and liquefied methane results in rapid pressure increase in a vapor film. It causes the generation and rapid growth of methane vapor film which is a result of abrupt evaporation and causes liquid methane explosion. In this situation, the intense vapor explosion phenomena endanger the safety of system. A mathematical model for these phenomena has been developed by assuming saturation condition on interface surface. Then, the effects of the variation of different thermo-physical parameters on the vapor film growth have been investigated. The results show that in some cases, the vapor pressure pulse created in the film can reach more than three times the initial pressure, which can endanger the safety of system.
In this paper, the natural convection of a non-Newtonian Cu–water nanofluid between two infinite parallel vertical flat plates is investigated. The basic partial differential equations are reduced to ordinary differential equations which are solved analytically using homotopy perturbation method. The comparison between the results from homotopy perturbation and numerical methods are in good agreement which proves the capability of this method for solving this problem. The effects of the nanoparticle volume fraction, dimensionless non-Newtonian viscosity and Eckert number on flow and heat transfer characteristics are examined. The results show that as nanoparticle volume fraction increases, the momentum boundary layer thickness increases with the decrease in the thermal boundary layer thickness.
Despite the fact that spring energized C-rings are widely used in nuclear power plants for flange seal, few studies are carried out to highlight the complex mechanical behaviors of the C-ring. A three dimensional nonlinear finite element analysis is developed to examine the compression recovery performance of the spring energized C-ring. Through the analysis, it is found that the compression recovery curve of the spring energized C-ring can be simplified to three straight lines. Two dimensional parameters, including the inner lining thickness and spring wire diameter, are studied to determine their impacts on the spring energized C-ring. Relations between the compression recovery curve and spring wire diameter are concluded and expressed by specific equations. Moreover, the deformation and contact stress distribution of the C-ring are also studied. The validation of the finite element model is confirmed by the experimental method.
Piping is the main transportation method for fluids from one location to another within an industrial plant. Design and routing of piping is heavily influenced by the stresses generated due to thermal effects and high pressure of the operating fluid. In particular, pressurized fluids create critical loads on the supports and elbows of the pipe which increases the overall stresses in the piping. Moreover, long pipes operating under high temperature gradients tend to expand significantly. Therefore, designers and engineers usually provide an expansion loop in order to relieve the pipe from the critical stresses. However, expansion loops require extra space, supports, elbows, bends, additional steel structure that could adversely affect the operating cost. It is therefore necessary to optimize the geometry, the number of expansion loops, and the supports. Reducing the number of loops in one single system or reducing the length of the loop itself is always favored as long as stresses are within safe limits. Usually, the commercial software (PipeData) is used in the industry to get the dimensions of the expansion loop. However, this software is mostly based on empirical models that rely on past experience rather than engineering fundamentals. Accordingly, this paper conducts an optimization analysis concerning the expansion loop dimensions and the number of supports without compromising on the safety of piping. The design approach is conducted as per the guidelines of ASME B31.3 (Process Piping) code and uses the commercial software (CAESAR II) for stress calculations. A full comparison for the expansion loop dimension is conducted between the empirical approach and the optimization analysis using ASME B31.3 for one of the existing oilfield projects. Results indicate that optimization reduces the dimensions and the number of expansion loops as well as the total number of supports. This results in significant savings in the piping cost without any compromise on the safety.
Steps for studying pressure variation resulting from oscillatory flow in reciprocating compressors is the main subject of this article. These variations in pressure are referred to as "pulsation". Interacting between plant piping and equipment, possibility of resonance conditions, high vibrations, support degradation, and high risk of fatigue failures caused by dynamic forces and induced by the pulsation, are the most commonly observed problems.
In this article, stainless steel 316L lined carbon steel tubes are used to prevent flow-induced erosion corrosion in the reactor effluent air cooler during the process of refining. Finite element analysis was carried out to investigate the characteristics of stress, drawing force, and interfacial contact pressure during the cold drawing process. Process parameters such as drawing head size and liner diameter were optimized to produce maximum residual contact pressure at the interface of base tube and liner. The effect of working conditions on tube bonding strength was also studied. It was found that the lined tubes can function well in reactor effluent air cooler under combined loading of internal pressure and elevated temperature, i.e. the normal working condition. Finally examinations and testing were performed to meet the requirement of standards and codes.
The thermo-hydraulic investigations for triple concentric-tube heat exchanger with two-thermal communications have been experimentally carried out at steady state conditions. Water at different temperature was passed through the inner tube, the inner annulus and through the outer annulus. Experiments were performed at all possible flow arrangements for Reynolds number ranging from 2800 to 11,000 of hot water in inner annulus. Validations of experimental results have also been carried out with the established results. Experimental investigations have been carried out to measure the variations in temperature of fluid streams along the length of heat exchanger and variations of friction factor and of Nusselt number with Reynolds number.
This work addresses the engineering demands for precise interactive process planning for the manufacture of high precision in the manufacturing of 3D micro- and nanoproducts. It outlines the development of a digital tool based on a haptics-based human–machine interface. This interface is underpinned using an empirical model derived from a series of experimental results obtained from a focused ion beam machine through a series of experiments, which produced the surface topographies of a number of micro- and nanograting arrays; these were systemically analysed to provide an underpinning empirical database, which could be accessed via the haptic process planning system. On accessing these data, highly accurate geometrical models are then input into a haptics human machine interface to emulate the focused ion beam machining process as defined by the customised fabrication parameters. The haptic planning system predicts and simulates the shape and form of the finished product profiles as the haptic device is passed across a virtual substrate. Once the simulation is complete and the outputs verified by the user, the system then automatically outputs a stream file to drive the focused ion beam process to produce the surface topographies required. The simulation results reveal that compared with trial and error method, the haptics-based simulation method is a reliable way to plan and optimise the fabrication parameters in design and manufacture of micro- and nanogratings by focused ion beam machining cost-effectively. This could potentially provide substantial lead time and cost reductions associated with these currently inherently expensive unit cost products as well as demonstrate a novel tool not only for the planning of nanomachining cutting sequences but also for the interactive design of such products. This work also highlights the benefits of an empirical model as a means of underpinning and supporting real-time haptics interaction, something not possible using more numerical-based techniques.
A three-dimensional fluid–structure interaction model is proposed for the discharge valve movement in a rotary compressor. The compression chamber pressure measured by the experiment confirmed that the fluid–structure interaction model is able to predict the valve dynamic behavior precisely. To demonstrate that the fact of the discharge port being covered partly by the cylinder and the roller cannot be ignored in the valve model, another fluid–structure interaction model in which the discharge port is not covered and the cylinder shape is simplified to be cylindrical is also specially presented. In this simplified fluid–structure interaction model, the flow energy loss through the discharge valve is 68.8% of that in the fluid–structure interaction model, and the impact velocity of the valve reed impacting on the retainer is 2.9 m/s higher than that in the FSI model. It is found that the valve reed is obviously inclined because the discharge port is covered partly by the cylinder.
This paper studies heat transfer during rapid heat cycle injection molding process. Actually, the mold is heated and cooled with channels in which steam or water circulates. The purpose of this numerical study is to improve the design of heating/cooling system to ameliorate the quality of the polymer part and the cycle productivity. Transfers in mold, translating thermal phenomena are predicted by the finite volume method and the fractional area volume obstacle representation in cyclic transient regime. It was found that the steady cycle is obtained rapidly (after two or three cycles) for the rapid heat cycle molding process when compared to conventional injection molding. The mathematical modeling was developed to explore the effect of control temperature system characteristics on temperature uniformity of the cavity surface and thermal response efficiency. The three-dimensional simulation results show the limitations of the conventional system when compared to the conformal configuration. This research study also compares three conformal thermal control systems, and shows that the heating energy consumption can be greatly decreased (about 27%) with the amelioration of the temperature distribution by means of the improvement of the channel layout.
Finding leakage in valves is important to troubleshoot performance of internal combustion engines. Leakage can lead to a reduction in engine power and an increase in emissions. The main objective of the present study is to investigate relationship between valve leakage and the acoustic emission generated from the steady flow in the cylinder head of the internal combustion engine. The test rig is the cylinder head for a spark-ignited engine. The test rig simulates the valve leakage due to valve clearance. The valve clearance fault was artificially simulated by a very small lift in valve. The acoustic emission method was used to measure acoustic emission signals generated by valve flow. Characteristics of acoustic emission signals in the time and frequency domains are presented and explained. The effects of air pressure level, valve lift, and valve type on the acoustic emission signals are investigated. It is shown that acoustic emission energy and valve leakage parameters have a linear correlation. The results demonstrate the potential of the acoustic emission source identification in the practical situation of detecting valve leakage using the investigated relationship.
The paper deals with devising two different fuzzy inference systems to predict the hardness of copper/carbon nanotube nanocomposite. These composites are outstanding candidates for thermal management applications in electronic packaging due to the high conductivity of copper. Knowing the extraordinary properties of carbon nanotubes, it seems that copper-based composites reinforced with small amount of carbon nanotubes, resulted in improved mechanical properties. Hence, carbon nanotube reinforced copper matrix nanocomposites are fabricated by hot-press sintering of high energy ball milled copper/carbon nanotube powders. Different milling factors are investigated. Finally the Vickers hardness of sintered nanocomposites is reported. To simulate a predictive framework for current case study, two different machine learning algorithms are engaged. The first learning algorithm is the classic least square optimization method, which provides the requirements for fast adaption of the consequent parts of fuzzy inference system. The second method learning algorithm uses the rudiments of neural computing through layering the fuzzy inference system and using back-propagation optimization algorithm. Based on the experiments, the authors realize that the adopted fuzzy systems can effectively extract the knowledge required for predicting the hardness of copper/carbon nanotube nanocomposite.
In this article, we propose a new simplified sectional flexibility method to simulate multi-cracks in a beam. The crack is considered as a line spring model which is related to the ratio of crack depth to the beam height (a/h). The transfer matrix method was derived and employed to construct the eigenvalue system. The local adaptive differential quadrature method was applied to evaluate the natural frequencies of cracked beams. The results of natural frequencies are in excellent agreement with literature results. For identification of multiple cracks in a beam, the Newton–Raphson iteration method was applied to predict the locations and depths of cracks. Numerical results were compared with results of other investigators and this method was found to be more accurate.
A low cost powder flowability tester for industry has been developed at The Wolfson Centre for Bulk Solids Handling Technology, University of Greenwich in collaboration with Brookfield Engineering and four food manufacturers: Cadbury, Kerry Ingredients, GSK and United Biscuits. Anticipated uses of the tester are primarily for quality control and new product development, but it can also be used for storage vessel design.
This paper presents the preliminary results from ‘round robin’ trials undertaken with the powder flow tester using the BCR limestone (CRM-116) standard test material. The mean flow properties have been compared to published data found in the literature for the other shear testers.
This article details the integrated grinding process and internal cylindrical centrifugal dynamic burnishing. It presents the construction of a developed hybrid tool for cylindrical machining that makes it possible to perform the grinding cut and dynamic centrifugal burnishing in a single procedure. Moreover, it includes an analysis of the geometric structure of the machined surface of cylinders made from Incoloy® alloy 600, Inconel® alloy 800HT®, and Titanium Grade 2®. The obtained analysis results were compared with the results obtained for the referential material, 100Cr6 steel. The results of these experiments showed that with the application of hybrid tools, which combine the grinding process and dynamic centrifugal burnishing, it is possible to obtain considerable changes in the geometric structure of the shaped surfaces of workpieces from hard-to-cut materials.
Thermal behavior of optical fiber during the cooling stage of drawing process has been studied numerically. An optical fiber during the cooling stage of drawing process has been modeled as finite-length of the cylinder moving in still air at a constant drawing speed. A two-dimensional unsteady-state energy equation is solved using finite difference schemes. Two-dimensional steady-state boundary layer equations are solved using implicit finite difference method to estimate a convective heat transfer coefficient of air at the surface of fiber. The effects of drawing speed, diameter and fiber material on cooling rate of optical fiber are reported here. The average convective heat transfer coefficient of air around the surface of fiber has been estimated accurately and validated with the experimental results available in the literature. Results have shown that there is an increase in cooling rate of optical fiber with increase in drawing speed. The size of fiber has shown a significant effect on cooling rate of fiber at low drawing speeds. Present results are matching well with the analytical and experimental results available in the literature.
Maintainability is a design attribute of a product, and its relationship with the design factors is complicated. In consideration of the fuzziness and uncertainty of design factors that influences the product's maintainability indices, we propose a method based on fuzzy grey relational analysis to determine their prioritization in this paper. First, the evaluation methods of various design factors and how these factors affect product maintainability indices are analyzed. Then, the fuzzy grey relational analysis model of the relationship between the design factors and maintainability indices is set up, and the prioritization of design factors to maintainability indices is achieved. Finally, the proposed methods are applied on a subsystem of a manned spacecraft, which indicates that the proposed method can quantitatively analyze the influencing degree of the design factors to maintainability indices. This information can be used to guide maintainability indices evaluation modeling based on digital mock-up in the design phase and help to catch the major influencing design factors in maintainability design.
A modular fault diagnosis model of induction motor is proposed based on radial basis function neural network. The modular structure makes model configuration flexible, training time short and model convergence easier. The training algorithm of the fault diagnosis model is given. Through an example, factors of the affecting fault diagnosis model classification are analyzed, methods of feature extraction and feature enhance are discussed, and the algorithm of feature enhance is presented. Lastly, the construction, training and verification of the motor fault diagnosis model consisting of two sub-models are introduced. Research results show that because of adopting the modular model and using a sub-model to recognize a fault state, model training becomes easier. It is more important that the fault recognition ability and application flexibility of the fault diagnosis model proposed are improved obviously.
For reliability problems with arbitrary independent random variables, the variables are always transformed into normal variables for the convenience of reliability analysis. Usually, the probability density function (PDF) of normal variables do not always well reflect the real probability feature of the tail of the original PDF. Hence, non-negligible equivalent normalization error affects the accuracy of the computed reliability results, especially when the original probability of failure of the reliability problem is quite low. In order to tackle this problem, the paper introduces a modified estimation of the unified form of the maximum entropy PDF (MEPDF) of these variables. Since the modified MEPDF brings the benefits for getting a better approximation in the tails of the original PDF, during the reliability analysis, the paper uses the MEPDFs as the surrogate of the original ones and exploits the first and second order moment approach by resorting to facilitation brought by the unified form of the MEPDF. Lastly, the presented examples show that the proposed method achieves better accuracy of the computed reliability results.
Optimizing multiple responses received significant research attention. Nevertheless, most of the proposed approach ignored engineer’s preferences about factor settings as well as the mathematical relationship between quality responses and process factors. This research utilizes the weighted additive model in fuzzy goal programming for optimizing multiple responses in the Taguchi method. The mathematical relationships between each quality response and process factors are first formulated. Then, each of quality responses and process factors is represented by a proper membership function with desired preference settings. A general optimization model is finally proposed. Four case studies are provided for illustration; in all of which the proposed approach efficiently optimized multiple responses. Compared to previous techniques, such as fuzzy logic, grey relational analysis, and multiple response signal-to-noise approach, the proposed approach provides more reliable optimal factor settings, considers engineer’s preferences about process factors, and provides mathematical relationships that can enable process engineers predict process performance accurately. In conclusion, the proposed approach may provide process engineers great assistance in optimizing process performance in the manufacturing applications on the Taguchi method.
Multi-point thermoforming is a new flexible technique for manufacturing three-dimensional polymer sheet parts. The fixed die utilized in conventional thermoforming process is replaced by a multi-point die, which can be reconfigured rapidly and nearly cost-free. In the present study, the effects of the elastic conditions on the surface quality and shape accuracy of the formed workpiece have been investigated through experiments and numerical simulations. The results show that an elastic cushion with proper thickness and hardness can significantly improve the surface quality of the workpiece. It has also been found that the application of lubrication can improve the shape accuracy of the formed workpiece.
This paper presents an investigation of the influence of the orifice plate parameters and installation positions on the attenuation of gas pulsation in a reciprocating compressor piping system. The acoustic wave theory and transfer matrix approach were applied to establish the simulation model, in which the valve chamber was assumed to be the pipe–volume–pipe element. Based on the model, the effects of the size and installation positions of the orifice plate on the gas column natural frequencies and pressure pulsation amplitudes were analyzed for the discharge piping system of a two-stage reciprocating air compressor. A test rig was built to validate the simulation results. The gas column natural frequencies and pressure pulsation amplitudes at different locations of the piping system were measured to verify the model. A favorable agreement was noted, with a maximum error of 2.1% for the natural frequencies and 6.3% for the pulsating amplitudes. The influence of the orifice plate on the gas column natural frequency varied according to its position and parameters. The results showed that all orders of natural frequencies decreased slightly as the inner diameter of the orifice plate decreased when the orifice plate was installed downstream of the vessel. However, the distribution of the gas column natural frequency changed when the orifice plate was installed upstream of the vessel. The pressure fluctuations in the piping system could be attenuated substantially by placing an orifice plate of reasonable parameter downstream of the vessel, within a distance of 0.4 m. The degree to which the orifice plate could attenuate the gas pulsation varied under different operating conditions. However, its attenuation effect was more sensitive to the compressor speed than to the discharge pressure.
Computer simulation of machining processes can save cost, time, and lead to reach an effective predictive capability. In this paper, by using computer simulation, damping capability of the lathe tools under static and vibrational analysis at different tool overhang conditions is studied. A novel predictive model of the cutting tool is developed, in which damping capability of the tool is improved by using composite material with high damping capability. Epoxy granites with normal, rigid, and plastic structures were used as composite materials in modified model of tool holder. The all-metal model, model with holes in tool holder and the modified model filled up with the composite material, with the same geometry and dimensions are used.
A new type of water mist fire extinguisher was proposed to be used in the manned spacecraft. The goal of prototype is that it can extinguish class 8B fires on the ground and its mass is less than 2.5 kg. The prototype employed only water as suppression agents. In the extinguisher, a piston separated the water from nitrogen artificially, which dispels the influence of the gravity on discharging. It possesses some advantages, such as high reliability, easy refilling of water and nitrogen, long life span, and convenient maintenance. A pressure-swirl nozzle was employed to produce water mist. There was no part to keep the pressure constant at the nozzle’s entrance; the service pressure of nozzle was determined in the range from 6 to 15 MPa. In that scope, the variation of droplet size with pressure did not have a significant impact on suppression performance, and the suppression time increment due to velocity reduction was in the acceptable level. A series of tests were conducted to verify its performance. The vibration test presented that there was no nitrogen leakage and no obvious resonance happened, which meant it possessed high reliability. The fire suppression tests indicated that it can suppress different fire types of a certain scale. The simulation results showed that the spray performance is improved in the microgravity. Conclusion can be drawn that the prototype is feasible in the microgravity and it reached the requirements of the design.
In this study, we try to analyze the free nonlinear vibration of a stringer shell analytically. The nonlinear governing equation of the problem is derived. Homotopy perturbation method is applied completely to obtain the analytical solution of the problem. We try to provide engineers and designers to achieve the nonlinear frequency of nonlinear problems especially shell vibrations with an easy method. The effects of different parameters on the ratio of nonlinear to linear natural frequency of shells are completely studied. The homotopy perturbation method gives us an excellent agreement with numerical results for whole range of the oscillation amplitude. The first order of homotopy perturbation method leads us to highly accurate solutions as indicated in this paper.
Scroll expander is suitable for small-scale organic Rankine cycle system. In this article, a detailed mathematical model describing the stable and dynamic process of scroll expander is built, an experiment system is set up, and the performance of scroll expander is tested. The results show that the p–V diagram of simulation and experiment show good agreement. The volumetric efficiency of scroll expander increases with rotating speed, and the maximum value is 63% under the tested condition. The isentropic efficiency increases at low rotating speed but then decreases, and the maximum value is 36.4%. Both the stable rotating speed and stable time of scroll expander increase with the electric resistance; here the stable time is defined as the elapsed time when the scroll expander varies from one stable condition to another. Although the transient rotating speed varies periodically with running time when the scroll expander runs stably, the variable quantity can be ignored. The total efficiency of expander and system efficiency first increase with the rotating speed and then decrease, and the maximum values are 41% and 2.9%, respectively, when the Carnot efficiency is 21.2% and the maximum theoretical efficiency is 8%.
A thermochemical model of the flash smelting furnace has been developed to predict fuel and oxygen consumption. The principal assumption of the model was that all matte, slag, dust and gaseous phases in the furnace were in thermal and chemical equilibriums. The present model was validated through measured data of Shahr-e Babak copper complex. Good agreement between predicted and measured data was achieved. In this study, the effect of air enrichment grade and air preheat temperature on the fuel consumption and required air for the oxidation and combustion reactions were examined for both heavy oil and methane. The results of parametric studies show that the rate of fuel consumption changes remarkably with the variation of working parameters of flash furnace. It was also found that the concentration of SO2 increases with oxygen content in the air. The results of the present investigation can be used for process automation and optimization.
Reliable, safe and economic CO2 transport from CO2 capture points to long-term storage/enhanced oil recovery sites is critical for commercial deployment of carbon capture and storage technology. Pipeline transportation of CO2 is considered the most feasible and viable option for achieving this. However, in carbon capture and storage applications, there is concern about associated impurities and huge volumes of high pressure CO2 to be transported over distances that will likely be densely populated areas. On this basis, there is limited experience for design and economic assessment of CO2 pipeline. The Humber region in the UK is a likely site for building CO2 pipelines in the future due to large CO2 emissions in the region and its close access to depleted gas fields and saline aquifers beneath the North Sea. In this paper, various issues to be considered in CO2 pipeline design for carbon capture and storage applications are discussed. Also, different techno-economic correlations for CO2 pipelines are assessed using the Humber region as a case study. Levelized cost of CO2 pipelines calculated for the region range from 0.14 to 0.75 GBP per tonne of CO2. This is a preliminary study and is useful for obtaining quick techno-economic assessment of CO2 pipelines.
This article investigates the combined effects of diffusion-thermo and dual-phase-lags on unsteady double-diffusive convection flow in a vertical microchannel filled with porous material. The channel boundary plates are kept at asymmetric thermal as well as concentration conditions with velocity slip and temperature, as well as concentration jumps on the boundaries. The energy as well as concentration equations follow the dual-phase-lag heat conduction model. The method of Laplace transform was used to solve the resulting governing equations while the Laplace expressions are inverted by the Riemann-sum approach. The effect of different flow parameters on mass flux as well as mean chemical concentration and mean fluid temperature within the channel are investigated. It is interesting to remark that the mass flux increases within the channel as the porosity increases while the mean temperature of fluid can be increased by simultaneously growing the Dufour number and thermal retardation time ( T ).
Although the use of dry gas seals (DGSs) in process centrifugal compressors has become an industry standard since the 1980s end users are still facing operational issues related to premature failures which incur significant maintenance and operational costs. It has been recognized that the majority of the failures are due to a lack of properly conditioned seal gas and this has driven more recent development of Gas Conditioning Units (GCUs) to deliver appropriate quantities of clean, superheated gas to the seal at the required pressure. However, there are a large number of operating units where retrofit of a GCU represents significant cost and engineering challenge. The aim of this paper is to share some recent experience of a DGS reliability improvement program that does not involve retrofitting a GCU. A basic introduction to DGS operating principles and an overview of DGS design and control issues is also included with a focus on tandem seals in high-pressure natural gas compression applications.
The unsteady mixed convection stagnation-point flow of a nanofluid toward a vertical surface is investigated numerically. The external velocity impinges normal to the vertical surface, the surface temperature, and the surface volume fraction of nanoparticles are assumed to vary linearly with the distance from the stagnation point. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. A similarity solution is presented, which depends on the Prandtl number Pr, Lewis number Le, Brownian motion number Nb, and thermophoresis number Nt. The governing system of equations is first transformed into a dimensionless form, and then the resulting equations are solved numerically by using a fourth-order Runge–Kutta scheme coupled with a conventional shooting procedure. The features of the flow, heat, and mass transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. The quantitative comparison of skin friction and heat transfer rates with the published results for special cases is shown.
Many approaches have been taken to the condition monitoring of gas turbines including performance analysis, vibration monitoring and lubricant debris monitoring. Acoustic emission monitoring has the potential to provide information about turbine operation and faults as they occur and has two possible advantages over other techniques. Firstly, because acoustic emission is sensitive to minor changes which do not necessarily involve whole-body motion, it is potentially able to reveal faults at an early stage. Secondly, because acoustic emission propagates over the structure from the source(s) to the sensor(s), it has the capacity to locate the source of any fault signal without intrusion. This paper explores the nature of the acoustic emission signals generated in a laboratory-scale gas turbine in order to extract and select features of the signal under normal running conditions and to establish the physical source(s) of this acoustic emission. A series of tests with the turbine running normally, either idling with the speed being controlled by fuel and air flow, or under load at fixed fuel and air flow with the speed being controlled by the amount of load applied, provided a range of conditions of gas flow through the turbine. An ancillary set of simplified tests with the free power turbine impeller jammed or absent was used to help distinguish between components of the acoustic emission associated with standing waves in various parts of the turbine and turbulence around the impeller. The results provide the first systematic study of fluid-induced acoustic emission in turbines and, as such, offer a baseline interpretation for acoustic emission generation in turbines and fluid machinery generally. Specifically, the findings will be compared with measurements made on the same turbine with simulated blade faults in a future publication.
In this article, the magnetohydrodynamic stagnation point flow and heat transfer of an incompressible viscous nanofluid over a shrinking/stretching permeable sheet is investigated theoretically and analytically. The ambient fluid velocity, stretching/shrinking velocity of sheet and the wall temperature are assumed to vary linearly with the distance from the stagnation point. The similarity solution is used to reduce the governing system of partial differential equations to a set of highly non-linear ordinary differential equations which are then solved analytically using a very efficient technique, namely homotopy analysis method. Expressions for velocity and temperature fields are developed in series form and graphical results are presented to investigate the influence of various pertinent parameters. Here, three different types of nanoparticles, namely copper Cu, alumina Al2 O3 and titania TiO2 with water as the base fluid are considered. It is observed that, for all three nanoparticles, the magnitude of the skin friction coefficient and local Nusselt number increases with the nanoparticle volume fraction . The highest values of the skin friction coefficient and the local Nusselt number were obtained for the Cu nanoparticles compared to Al2 O3 and TiO2.
Transient mixed convective laminar boundary layer flow of an incompressible, viscous, dissipative, electrically conducting nanofluid from a continuously stretching permeable surface in the presence of magnetic field and thermal radiation flux is studied. The model used for the unsteadiness in the momentum, temperature, and concentration fields is based on the time-dependent stretching velocity and surface temperature and concentration. Similarity transformations are used to convert the governing time-dependent nonlinear boundary layer equations for momentum, thermal energy, and concentration to a system of nonlinear ordinary coupled differential equations with appropriate boundary conditions. The transformed model is shown to be controlled by a number of thermophysical parameters, namely the magnetic parameter, thermal convective parameter, mass convective parameter, suction parameter, radiation-conduction parameter, Eckert number, Prandtl number, Lewis number, Brownian motion parameter, thermophoresis parameter, and the unsteadiness parameter. Numerical solutions are obtained with the robust Nactsheim–Swigert shooting technique together with Runge–Kutta sixth-order iteration schemes. Comparisons with previously published work are performed and are found to be in excellent agreement. The effects of selected parameters on velocity, temperature, and concentration distributions and furthermore on skin friction coefficients, heat transfer rate (Nusselt number), and mass transfer rate (Sherwood number) are presented graphically. The current study has applications in high-temperature nano-technological materials processing.
Efficiency tests were conducted on two single-stage double-suction split-case pumps in a clean water distribution facility. Efficiency was monitored via two techniques, one established and the other proposed in this study. Measurements of the former were taken via the standard technique using a Yatesmeter that required time to calibrate and that probes be inserted into the clean water flow; the latter method was non-intrusive, being based solely on accelerometer measurements at key locations on the volute/split casing. Both techniques required some post-processing of data. Through comparison of the techniques, it is shown that for the pumps that were analysed it is possible to extract indicators within the vibration signatures that permit good correlation with efficiency data. In both cases only a few recorded measurement points were possible and the vibration indicator-based curve fitting technique was able to locate the best efficiency point more accurately than using the curve fitted to the Yatesmeter measured data. This short communication reports on the initial tests which are showing promising results.
Hazard and operability analysis is a decisive factor to evaluate safety and reliability of plants considering the propagated effects due to consecutive failures of known critical components. A good design and analysis practice increases the robustness of the considered system in different operating conditions; however, in the plant design process, the use of a model-based design approach is fundamental to increase speed, efficiency and reliability. In this work, a tool for the 1-D simulation of thermal hydraulic plants is presented and applied to the analysis of critical system for compressor and gas turbine units, e.g. the lubrication circuits. Different from known commercial products, the proposed tool is implemented to work in cooperation with PidXP™ (the GE Nuovo Pignone P&ID definition tool), and it is optimized for fixed step solvers in order to easily include the rotating machine control logics within the simulation environment (essential prerequisite for hazard and operability evaluations). All the above makes it suitable for the fast prototyping of real time code. Moreover, the proposed tool represents a general tool in the model-based approach, and it can be used as a Simulink™ library of components that have been optimized and specifically designed in order to make easier the automatic generation of simulation models from P&Id schemes and technical documentation, reducing errors associated to data transcription and operator misbehaviour. In this work, proposed approach and test bench on experimental data for validation purposes are shown.
In this paper, a new iso-parametric tool path generation technique has been presented for machining truncated free-form surfaces by means of re-parameterisation. Three methods of re-parameterisation have been discussed, namely, the Coons method, partial differential equation method and the newly developed ‘Boundary Interpolation method.’ Tool paths have been generated based on the iso-parametric curves produced by re-parameterisation. The complete mathematical formulations have been given and subsequently their applications have been studied through some typical cases. Case studies show that the Coons and Laplace partial differential equation have some drawbacks in generating tool paths when the surface boundaries are irregular but the new Boundary Interpolation algorithm gives smooth and efficient iso-parametric tool paths by eliminating the problems like overcrossing (in case of Coons method) and uneven distribution of iso-parametrics (in case of Laplace partial differential equation method).
This article is a contribution to the design of the hydraulic steering system with an accumulator of different parameters on suppressing water hammer. The accurate model taking account of the characteristics of the entrance of the hydraulic accumulator, which have great influence on the frequency characteristics of the accumulator is developed. In addition, this article proposes a more comprehensive distributed parameter model of the hydraulic steering system with an accumulator installed before the proportional directional valve, which takes into account both the relief valve and the pipeline between the hydraulic accumulator and the proportional directional valve. The dynamic characteristics of the hydraulic steering system were analyzed both in the frequency and time domain. The numerical simulation of water hammer which used a holistic unsteady-friction model has been performed by the method of characteristics and finite difference method with spatial interpolation using Fortran language. The law that the natural frequency of the accumulator which is equal or approximate to the frequency of water hammer in pipeline has good effect on suppressing water hammer is validated by analytical and numerical simulations as well as experimental results, for the design of the nominal volume and charged pressure of the hydraulic accumulator in the hydraulic steering system.
This study analyses the hydrodynamic and thermal behaviours of a fully developed natural convection flow in a vertical parallel-plate microchannel with suction/injection. The velocity slip and temperature jump at the walls are taken into account. The fully developed solutions of the velocity, temperature, volume flow rate, rate of heat transfer which is expressed as the Nusselt number and skin friction are derived analytically. The influence of each governing parameter on the microchannel hydrodynamic and thermal behaviours is discussed with the aid of graphs. Results show that as suction/injection on the channel surfaces increases, the volume flow rate increases and the rate of heat transfer decreases. In addition, it is observed that increase in the effects of rarefaction and fluid–wall interaction results in the increase in the volume flow rate and decrease in the heat transfer rate.
Silicon-based solar applications have tended towards the use of large, thin cells. However, an increased loss of materials occurs due to a high rate of destruction during the soldering and packaging processes. In this study, the effects of the presence of cracks on the thermal stress and stress intensity factor of the cells were explored for different aspect ratios of the soldering rods using an established finite element method. It was found that the residual stress in the cell was concentrated near the ends of the soldering rods, which coincided with the typical positions where breakage tended to occur on the cell. The residual stress on the cell increased with an increasing aspect ratio of the soldering rod. Cell damage due to cracking can be avoided by controlling the magnitude of the soldering rod’s aspect ratio.
Process analytical technology is considered to be a system for designing, analyzing, and controlling pharmaceutical manufacturing to ensure final product quality. This research, therefore, utilized the process analytical technology framework to improve the performance of tableting process. Two main responses are of main interest including hardness and weight. At initial factor levels, the <overline>x</overline> - s charts are established and found in control for both responses. However, the process capability index, Cpm , values are calculated to be 0.42 and 0.51 for hardness and weight, respectively. Moreover, the multiple process capability index, MCpm, is 0.46. These values indicate that the tableting process is incapable of producing quality tablets. The L27 is used for conducting designed experiments. The weighted additive model in fuzzy goal programming is then used to determine optimal factor settings. Confirmation experiments are then conducted at optimal factor settings. It is found that the Cpm values are calculated to be 2.13 and 1.85 for hardness and weight, respectively. The MCpm value significantly improved to 1.99, which means that the process is highly capable. Consequently, the T2 and the sample generalized variance control charts are established and further used for monitoring future production. In conclusion, the tools used in the process analytical technology framework are found effective for improving the performance of tableting process.
The performance of twin-screw pumps that are widely used in industry hinges upon a number of factors. In this research, a systematic approach is presented, encompassing the design optimization of a Type-A screw and the subsequent performance evaluation of a twin-screw pump. We first investigate the effect of involute meshing angle on the contact line properties of the Type-A screw, and carry out design optimization. We then formulate a flow field analysis of the twin-screw pump using the screw tooth profiles and spiral surfaces under the optimal involute angles obtained, and analyze the pressure field, velocity field and other characteristics of the pump. The influence of contact line on the pump sealing property is also assessed. Concurrent with the numerical study, experimental investigation is performed to evaluate the rotating speed and power of the pump, as well as their intrinsic relations with the flow, pressure and power of the screws. These studies reveal that under the optimal design of the screw, the pump performance can be significantly improved. The methodology of design and analysis outlined in this research can be applied to other screw pumps, and the results of parametric analysis involved can shed lights on the development of screw pumps in general.
The dynamic characteristics of suction valves for reciprocating compressor with a stepless capacity control system are studied in this article. The self-acting valve model that is applicable for stepless capacity control condition is derived. For the suction valve movement controlled by actuator, a simulation of the hydraulic and mechanical system is conducted. An experimental platform is setup, which is used to test the valve dynamic when it is controlled by actuator. The results from the mathematical model show that the valve impact speeds are influenced by the valve lift, Mach number of the flow in the valve clearance and the initial crank rotation angle of the valve closing process. The simulation results agree well with experimental results. The simulated maximum speed is about 0.53 m/s, and the maximum speed tested by experiment is about 0.58 m/s, both of which are much lower than the speed of the automatic valve (3 m/s). In addition, simulation results show that the maximum speed is at constant when the hydraulic piston stroke increases, which is much different from the automatic valve. It becomes apparent from the aforementioned results that with stepless capacity control system the dynamic characteristics of the suction valve are changed. The valve can be limited at a low speed, and the valve impact speeds to seat and stopper decrease significantly, which would be helpful for extending the life of the valve plate.
The dynamic characteristics of suction valves for reciprocating compressor with a stepless capacity control system are studied in this article. The self-acting valve model that is applicable for stepless capacity control condition is derived. For the suction valve movement controlled by actuator, a simulation of the hydraulic and mechanical system is conducted. An experimental platform is setup, which is used to test the valve dynamic when it is controlled by actuator. The results from the mathematical model show that the valve impact speeds are influenced by the valve lift, Mach number of the flow in the valve clearance and the initial crank rotation angle of the valve closing process. The simulation results agree well with experimental results. The simulated maximum speed is about 0.53 m/s, and the maximum speed tested by experiment is about 0.58 m/s, both of which are much lower than the speed of the automatic valve (3 m/s). In addition, simulation results show that the maximum speed is at constant when the hydraulic piston stroke increases, which is much different from the automatic valve. It becomes apparent from the aforementioned results that with stepless capacity control system the dynamic characteristics of the suction valve are changed. The valve can be limited at a low speed, and the valve impact speeds to seat and stopper decrease significantly, which would be helpful for extending the life of the valve plate.
This article presents the application of custom-designed poledioscope for dynamic measurement of thermally induced shear stress, as a technique for monitoring waviness of the microscale patterns created using CO2 laser, directly over optically birefringent polymers. Laser ablation experiments were conducted for three optical grade polymers: ethylene vinyl acetate, poly methyl methacrylate, and allyl diglycol carbonate under varying laser power and scanning speeds. A poledioscope, customized by incorporating beam splitter in place of rotating analyzer section of conventional polariscope, was used to assess the thermally induced shear stress on the materials in real time. The waviness of the profile of groove patterns was measured using a profilometer. The shear stress mapping and the profile waviness data recorded for range of laser processing parameters were further analyzed to determine that high thermally induced shear stress results in significant damage on waviness of the lased profile.
Multi-point forming is an advanced flexible manufacture technology, which has been used in many fields successfully. In order to provide a flexible method for forming a polymer, multi-point forming is applied to the manufacture of polycarbonate sheet. An optimized DSGZ constitutive model is established to describe the stress–strain relation of polycarbonate sheet, and its parameters are determined according to experimental data. The multi-point forming process of polycarbonate sheet is introduced briefly, and a simple calculating scheme of punch height is developed. Numerical simulations of spherical and saddle-shaped parts are carried out by dynamic explicit finite element analysis, and the effects of punch number and punch radius on the surface accuracy and shape accuracy are studied. The multi-point forming experiments of polycarbonate sheet are done, and the comparisons of shape error between experimental parts and objective parts are conducted, which show that the polycarbonate products have good surface accuracy and shape accuracy.
The velocity profiles on stepped spillways are analyzed using computational fluid dynamics simulations and large-scale laboratory experiments. Five different turbulence models are considered in the analysis: the Standard k-, the Realizable k-, the Renormalization group k-, the Standard k- and the Shear stress transport k- model. The computational fluid dynamics simulation results are compared with laboratory measurements from a large-scale physical model with flow velocities up to 15 m/s. It is indicated that the numerical model involving any of these turbulence models can satisfactorily simulate the velocity profiles. All five turbulence models performed satisfactorily well on large-scale stepped spillways. The k- models may be slightly better suited in the lower region, while the realizable k- model provided slightly better results in the upper part of the velocity profile. A power law with n = 5.09 also provides a useful first approximation with a limitation of the flow along stepped spillway with the Reynolds number of <inline-formula id="ilm1-0954408912472172">1.68 \times 10^6 \le </inline-formula>Re <inline-formula id="ilm2-0954408912472172"> \le 7.21 \times 10^6 </inline-formula>.
Thermal modeling and optimal design of combined cooling, heating, and power generation system are presented in this article. Selecting the type and number of prime movers, their nominal power and operational strategy, the heating capacity of backup boiler and storage tank, the cooling capacity of electrical and absorption chillers as well as electric cooling ratio (the ratio of electrical chiller capacity to the demand cooling capacity) were considered as nine design parameters. Three types of prime movers including gas turbine, diesel engine, and gas engine were studied in this article. Multi-objective particle swarm optimization algorithm was applied to obtain the maximum actual annual benefit and exergy efficiency simultaneously. Actual annual benefit included the energy, economy, and environmental parameters, therefore with adding exergy parameters, 4 E analysis of combined cooling, heating, and power system was performed. The combined cooling, heating, and power system could run in two operation modes, named economical and electricity tracking modes. In the former case, it was allowed to sell the excess electricity to the network and in the latter, it was not allowed to sell the excess electricity to the grid. It was observed that actual annual benefit for the gas engine was higher than two other cases in economical mode. In electricity tracking mode, the gas engine and gas turbine were more profitable. In addition, the trends of optimum values of design parameters versus actual annual benefit and exergy efficiency in economical mode were investigated and the results were presented. Finally, the results of applying the assumptions of constant and variable running load of prime movers during a year were compared.
Nowadays, the ever increasing need for higher accuracy, reliability and security in modern industries has given rise intensively to the use of multi-sensor data fusion method in fault diagnosis of industrial equipment. In this article, an effective and powerful method for precise fault diagnosis of planetary gearbox based on fusion of vibration and acoustic data using the Dempster–Shafer theory is presented. For this purpose, the vibration and acoustic signals in different modes of the gears were first received simultaneously by two separate sensors and then were transmitted from time domain to time–frequency domain using wavelet analysis. After signal processing, each sensor's data were transferred to a local classifier for primary fault diagnosis. Local classification was performed by artificial neural network classifier. The outputs of the local classification were used as the inputs into Dempster–Shafer rules for fusion of classifiers and achieving the final accuracy of the classification. In primary fault diagnosis, the accuracy of fault classification based on vibration and acoustic signals was obtained as 86% and 88%, respectively. After incorporating the outcomes of two sensors, the final accuracy of the classification was calculated as 98% which indicates a 10% jump compared to single-sensor mode. These results indicate the effectiveness of the data fusion method in condition monitoring and fault diagnosis of the equipment. Moreover, in this article, the capability of Dempster–Shafer theory in the fusion of uncertain data and the increase of accuracy in the classification was demonstrated to a quiet acceptable level.
In this study, design and manufacturing of a hermetic Stirling engine having rhombic-drive mechanism were presented. In the engine, rhombic-drive mechanism was used for less vibration and piston friction. An alternator was coupled with the rhombic-drive mechanism in the engine block to convert mechanical power directly into electricity. Due to the mechanical problems, engine performance was measured without alternator unit by coupling the rhombic-drive mechanism with a dynamometer. The tests were conducted at 400 °C and 500 °C hot-end temperatures at atmospheric pressure. The surface temperature of the displacer cylinder hot end was controlled by LPG flow. The maximum torque and power obtained were 1.26 Nm at 264 r/min engine speed and 41.7 W at 350 r/min engine speed, respectively, at 500 °C hot-end temperature. The variation of cyclic work obtained by the experimental study was compared with the theoretical results obtained by nodal analysis.
This study presents an experimental investigation of the cylindrical grinding process AISI 1040, AISI 8620, AISI 5140 and AISI 52100 steels with using helically grooved grinding wheels with of 15°, 30° and 45°. The main purpose of this experimental study is to investigate different angle grooved induced surface and dimensional quality, as well as one of the significant surface integrity parameters residual stress. The obtained results illustrate the significance of grooved angle in terms of measured output parameters. The experimental results showed that grinding with helically grooved wheels improves the ground surface finish. Consequently, the improvement ratios of the surface roughness, roundness and residual stress using a helically grooved grinding wheel for 45° were 28–73%, 47–137% for four steel and 4.4% for AISI 1040 steel, respectively. Moreover, the results from the analysis of the variance indicated that the materials and grinding wheels have a significant effect on both surface roughness and roundness.
The laminar boundary layer flow and heat transfer of Casson non-Newtonian fluid from a permeable horizontal cylinder in the presence of thermal and hydrodynamic slip conditions is analysed. The cylinder surface is maintained at a constant temperature. The boundary layer conservation equations, which are parabolic in nature, are normalised into non-similar form and then solved numerically with the well-tested, efficient, implicit, stable Keller–Box finite-difference scheme. Increasing velocity slip induces acceleration in the flow near the cylinder surface and the reverse effect further from the surface. Increasing velocity slip consistently enhances temperatures throughout the boundary layer regime. An increase in thermal slip parameter strongly decelerates the flow and also reduces temperatures in the boundary layer regime. An increase in Casson rheological parameter acts to elevate considerably the skin friction (non-dimensional wall shear stress) and this effect is pronounced at higher values of tangential coordinate. Temperatures are however very slightly decreased with increasing values of Casson rheological parameter. Increasing mass flow injection (blowing) at the cylinder surface causes a strong acceleration, whereas increasing suction is found to induce the opposite effect. The study finds applications in rheological chocolate food processing.
Inherent safety is a proactive approach for loss or elimination of hazard values and risk management. Expansion of safety relating to process and production in a supply chain in an uncertain environment has a critical effect on the competitive advantage of each food industrial organization. In this article, the fuzzy rating weights of each pair of the considered hazards and uncertain hazard values are described by linguistic expressions modelled by triangular fuzzy numbers. The fuzzy extent approach for the synthetic extent values of the pairwise comparison for handling fuzzy analytic hierarchical process is used to calculate the weight vector. The proposed fuzzy model is arranged in a hierarchical structure, so that the output of one interference system is used as an input for the second interference step. In the first of interference steps, the total hazard value for each identified process is calculated using the fuzzy algebra rules. In the second interference step, the inherent safety index for each process is determined on the basis of total hazard value, using the IF–THEN fuzzy logic rules. It is shown that the proposed fuzzy model is highly suitable as a decision making tool for making decisions about the inherent safety index of food industrial processes.
Contamination control in fluid power system is a challenge due to the fact that it has been one of the major reasons of wear, failure, and the related downtime. A novel hydraulic oil purifier proposed in this study is considered to be capable of removing the solid particle contaminant, moisture, and gas simultaneously, which consists of two parts: hydrocyclone separator and rotating packed bed (i.e. Higee). A hydrocyclone separator used to be applied to chemical industry is tried to be designed according to experiential parameters in a typical fluid power system for the first time. And then, the mathematical model of the hydrocyclone separator has been established. The distribution of the hydraulic oil and solid particles in swirling flow field inside the base hydrocyclone separator has been simulated with the help of computational fluid dynamics software Fluent. The effects of the cone angle and cylindrical length on the separation performance of the hydrocyclone separator have been subsequently investigated. Based on the simulation results, the hydrocyclone separator with 25° cone angle and 60 mm cylindrical length has been considered as the most satisfied configuration. Simulation analysis of the optimal configuration flow field reflects a relatively pleasant solid–liquid separation performance considered to be beneficial to controlling the contamination level of fluid power system. The research outcome will lay a foundation for the development of the new hydraulic oil purifier proposed in this study.
In this study, microwave drying behaviour of apple slices was investigated experimentally to determine the effect of microwave power on drying, energy consumption and colour quality. Microwave drying behaviour was simulated by a theoretical drying model. Suitability of several empirical and semi-empirical models in defining the microwave drying behaviour of apple slices was determined by statistical analysis. The experimental results show that the drying time, energy consumption and the colour quality of apple slices decrease considerably with an increase of microwave power. The modelling results indicate that theoretical model simulates microwave drying behaviour of apple slices very well and among the empirical and semi-empirical models, the Page model yields the best fit with the experimental data. The modelling results also show that the excess pressure inside the apple slices shows first an increasing trend and then begins to decrease as the moisture content takes lower values.
This article presents a numerical simulation of the thermodynamic process in the cylinder and dynamics of the self-acting valves for an air reciprocating compressor. The finite-volume method was employed to solve the compressible turbulent flow in the cylinder and through the valves. A single degree-of-freedom model was adopted to simulate the valve dynamics. The piston’s motion was defined by a user’s preset function, and the fluid-structure interaction between the gas flow and the valve dynamics was solved in a strictly coupled fashion. The technique of non-conformal interfaces was adopted to allow fluxes between adjacent zones with different mesh node locations. Based on the analysis of the characteristics of the flow through valves and the valve movement, sensitivity analysis on the valve impact velocity and the angle of inclination indicates that the valve impact velocity was more sensitive to the variation of the rotational speed and the valve lift while severe inclining motion occurs when the valves are installed in the radial direction. Instantaneous gas flow and force coefficients with the variation of valve displacement are also obtained according to the mass-flow rate across the valve and the gas force acting on the ring plate.
Circular sawing is a very flexible method used in natural stone processing. This method can be used in all sawing stages, such as tile production, cutting the slabs to size, shaping of cubic pieces, etc. Due to this feature, it is the preferred tool for stone processing. Thus, the investigation of sawing parameters affected on circular sawing performance is necessary. In this study, the effects of some sawing parameters (diamond concentration in segment, sawing depth, and saw blade diameter) on sawing performance (unit wear and unit energy) were investigated through the use of computer-assisted automatic circular sawing machine. Real marble samples, commercially named Afyon Violet, were used in the experiments. It was determined graphically that diamond concentration in segment, sawing depth, and saw blade diameter were very effective on unit wear and unit energy. The statistical analyses were also conducted to determine the effects of sawing parameters on unit wear and unit energy. Consequently, stone processors must take into consideration these sawing parameters in order to achieve more economical production.
A continuum model of the melting process in porous fibrous media is introduced. The fluid flow, heat transfer and phase change within the porous nonwoven web is numerically solved using computational fluid dynamics. Boundary conditions from an experimentally validated whole system model of a typical industrial machine, producing fibrous webs are incorporated. The presented model shows the capability to investigate the phase change during heating of the thermoplastic fibres during nonwoven web formation. Moreover, the fibres’ geometrical information and constitutive equations, describing the material behaviour are included. The approach considers the fibre thickness, sheath fraction, and thermophysical properties like melting temperature, latent heat of fusion and the liquid fraction, enabling the assessment of different fibre types and to determine the properties of the fabric. The model results reveal that the web porosity has the most significant effect on the melting process among the considered parameters. Thermal gradients that occur inside the web are due to the combined convection and latent heat of fusion effect, which stores heat to melt the fibres. The model is applicable to a wide variety of systems ranging from textiles, fibrous beds, ceramics, membranes and porous composite materials.
Driven by practical maintenance experience and the desire for higher component availability, this article presents a predictive maintenance policy for maximizing the availability of a batch of components (or single-component machines) in one repair cycle based on their real-time degradation signals, where the maintainability of preventive maintenance acts is explicitly correlated with the degradation levels accumulated before the preventive maintenance acts. The degradation correlated maintainability is modelled by a recently proposed proportional repair model. Within the proposed predictive maintenance policy, each component’s reliability is calculated and updated using its real-time degradation signals. The results from a numerical experiment based on a typical degradation model show that, for a batch of components whose maintainability of preventive maintenance acts is indeed correlated with the damage/degradation level accumulated before the preventive maintenance acts, it will lead to suboptimal preventive maintenance schedules if the effect of damage/degradation level on maintainability is ignored. In addition, the experimental results provide evidence of the superiority of the predictive maintenance policy over the corresponding preventive maintenance policy in terms of achieving higher average availability, by considering the real-time degradation signals of each individual component.
In this study, constructal theory is used to analyse the radial and branching configurations of highly conductive incomplete inserts embedded in a disc for cooling purposes. The thermal conductivities are considered temperature-dependent which are varied linearly and ascending. Applying the Kirchhoff transformation, the resulting nonlinear partial equations are transformed to linear ones which are more suitable to solve, analytically. Furthermore, the effect of temperature-dependency of the thermal conductivities is examined and compared with the case with constant thermal conductivities under different conditions where a decrease in heat resistance is observed. However, the effectiveness of this factor in decreasing the thermal resistance is dependent upon other parameters. The effect of considering variable cross-section for the highly conductive material is combined with the temperature-dependency of the conductivities where it is concluded that under certain circumstances where the effect of temperature-dependency of the conductivities is weak, the variable cross-section can be used to reduce the thermal resistance, efficiently. Finally, since the proposed analytical solution is accompanied with some approximations, the problem is also solved numerically to verify the solution where an acceptable agreement is observed.
Factory approval test (FAT) or shop run test is a unique opportunity to evaluate rotating machine performance before delivery to site. This note presents a new adaptive signal processing method to evaluate vibration measurement during FAT based on obtained noisy data. It is also a necessary step for machine reliability, fault diagnosis, future predictive maintenance, and condition monitoring.