Based on the grinding target profile of the rail and the grinding capacity of a single grinding stone, a numerical calculation method for rail grinding patterns that includes grinding angle and grinding power of each grinding stone of the GMC96 rail grinding train was designed and established. By means of this numerical method, the grinding pattern of each grinding pass was optimized and the rail head profile after grinding was calculated. Furthermore, a method for the evaluation of the grinding quality is provided. The results indicate that in multipass rail grinding, a sequence of grinding passes – where the greatest grinding effort is applied on the earlier passes, with the last pass applying reducing levels of grinding effort – produces the highest conformance to the target grinding profile. For example, when rail grinding is planned for two passes, applying 60% of the total grinding effort on the first pass and 40% on the second pass decreases the final grinding error by 7.3%.
A new approach has been developed to determine the dynamic amplification factors of railways. This approach employs a traditional multi-body dynamic model of vehicle–track interaction and a 3D explicit finite element model of wheel–rail rolling contact to treat the low- and high-frequency dynamics, respectively. Excitations are considered by contact surface unevenness and more specifically, by the power spectrum density of track irregularity for the low-frequency analysis and by the critical wheel flat, weld, and rail corrugation for the high frequency. For the 40-tonne axle load heavy haul railway simulated in this work, it has been found that the optimum fastening stiffness should be 150–200 MN/m; the dynamic amplification factors of the wheel–rail contact, fastening, and ballast forces are 1.94, 2.0, and 1.67, respectively, if the fastening stiffness of 200 MN/m is applied. Finally, new dynamic amplification factor formulae that include key parameters such as the fastening stiffness, speed, and axle load are proposed for the heavy haul railway design.
Rail wear is the most common defect that affects sharply curved metro rails, thus impacting their renewal periods. This article presents a stochastic model, based on a Weibull distribution, for the estimation of the renewal periods of sharply curved metro rails based on the analysis of the characteristics of rail wear. The model considers several heterogeneous factors to determine their effects on the deterioration process and is shown to be able to estimate the life expectancy of these rails in any wear state, as well as their remaining lives and renewal periods, with respect to these heterogeneous factors. The model is validated by a case study of the Beijing Metro, based on 10 years of rail wear inspection data and heterogeneous factor data of 200 sharp curves.
Maintenance and eventual renewal of a ballasted track constitute major operational costs for a railway network. Thus, significant benefits would accrue from a more robust track design having a longer service life and reduced maintenance requirements. This paper presents the results from a laboratory study and explores the potential to achieve this through improving the ballast grading and reducing the ballast shoulder slope. Cyclic loading tests were carried out on a section of track representing one sleeper bay in plane strain, in the Southampton Railway Testing Facility. A cyclic load representing a 20 tonne axle load was applied at 3 Hz for at least 3 million cycles, during which measurements of permanent and resilient vertical deflection were made. Certain interventions are found to result in lower rates of permanent settlement and different resilient ranges of movement. Supplementary measurements to determine longitudinal pressure, ballast breakage and attrition, and shoulder slope movement were used to explore the mechanisms responsible for the observed improvements in ballast bed performance. It is concluded that the use of finer ballast gradings and a shallower shoulder slope have the potential to reduce maintenance requirements.
In this study, the head hardening process was employed, by using a mixture of air and water under laboratory conditions, to improve the residual stress behavior of R260 grade rails . For this purpose, three types of specimens were selected. One group of rails was heated up to the austenite stage and then cooled for 20 s; the next group was heated up to the austenite stage and then cooled for 40 s and the third group was not exposed to any heat treatment. The hardness results showed that the specimens cooled for 40 s had excessive hardness; the specimens cooled for 20 s exhibited similar properties as that of R350HT rail standards, which are especially preferred in the lower radius of curvature bends in railways, but not that of R260. According to the analysis of residual stress, all samples had compressive residual stress, but the specimens cooled for 20 s had the highest stress value.
The traditional freight wagons employ I-beam sections as the main load-bearing structures. The primary loads they carry are vertical (from loading units) and axial (from train traction and buffers). Ease of manufacturing has played an important role in the selection of the I-beam for this role. However, with lightweighting increasingly becoming an important design objective, an evaluation needs to be done to assess if there are other existing or new section profiles (geometry) that would carry the same operational loads but are lighter. This paper presents an evaluation of 24 section profiles for their ability to take the operational loads of freight wagons. The profiles are divided into two categories, namely ‘conventional – made by wagon manufacturers (including the I-beam)’ and ‘pre-fabricated’ sections. For ranking purposes, the primary design objectives or key performance indicators were bending stress, associated deflection and buckling load. Subsequently, this was treated as a multi-criteria decision-making process. The loading conditions were applied as prescribed by the EU standard EN 12663-2. To carry out structural analysis, finite element analysis was implemented using ANSYS software. To determine the validity of the finite element analysis results, correlation analysis was done with respect to beam theory. Parameters considered were: maximum stress, deflection, second moment of area, thickness, bending stiffness and flexural rigidity. The paper discusses the impreciseness related to the use of beam theory since the local stiffness of the beam is neglected leading to an inaccurate estimation of the buckling load and the vertical displacement. Even more complicated can be the estimation of the maximum stress to be used for comparison when features such as spot welds are present. The nominal stress values computed by means of Navier equation lead to an inaccurate value of the stress since it neglects the variations in the local stiffness, which can lead to an increase in the bending stress values. The main objective of the paper is the applicability of particular section profiles to the railway field with the aim of lightweighting the main structure. Sections commonly adopted in civil applications have also been investigated to understand the stiffness and strength under railway service loads. The common approach reported in literature so far makes use either of the beam theory or topological finite element approach to determine the optimised shape under the action of the simplified loading conditions. Although the previous approaches seem to be more general, the assumptions made affect the optimisation process since the stress state differs from that attained under the actual service load in the real structure. In this paper, the use of complex shape cross sections and detailed finite element models allows to take account of the real behaviour in terms of stiffness distribution and local stress effects due to manufacturing features like welds. The structural assessment carried out with the detailed models also allows for the proper comparison among the considered sections. Analysis of the results showed that three out of the 24 section profiles have the highest potential to be fitted as the main load-bearing beams for freight wagons, with the pre-fabricated Z-section being the optimum of the three.
This study aims at identifying the roles and tasks of a train driver, who operates a highly automated high-speed passenger train, as well as the job requirements in terms of personnel selection criteria. To this end, two studies – a prospective task analysis and a prospective job analysis based on Fleishman – were conducted with two samples of experienced high-speed train drivers from Germany. The results show that cognitive information acquisition and continuous monitoring tasks require mental persistence and sustained attention, thus converting the train driver into a train operator. It is proposed that the future tasks and working conditions should be designed to strengthen the train operators’ share in tasks of information integration, strategizing, and decision-making. Thus, the detrimental effects of continuous monitoring tasks, which are well established across transportation industry domains, could be alleviated.
The critical examination of driver cognition and information processing is vital to ensuring an effective signal passed at danger (SPAD) prevention strategy. Although this need was identified in KiwiRail’s organisational strategy to reduce signal passed at danger risk, the why and how factors were not clearly described and robustly linked to deliver the necessary effects. With risk-triggered commentary driving programmes gaining recognition as valuable components and activities within the driver competency model, an opportunity to couple risk-triggered commentary driving with stabilised approach methodologies and procedures, adopted from aviation and modified for use on New Zealand’s railway network was subsequently identified. A driver subject matter expert group was formed, a literature review completed, guidance developed and new procedures trialled. This activity provided new opportunities to introduce error-tolerant system design, increase accuracy of driver signal action response and reduce signal passed at danger risk on New Zealand’s National Rail System by adopting and designing bespoke methodologies that support enhanced driver cognition and safe system design.
This paper supplements two previous papers written by the authors and addresses three issues arising from those papers. The three issues are follows: (1) the robustness of a crashworthy design in scenarios different from the design conditions, (2) the correlation of structural crashworthiness with passenger safety and (3) behaviour characterisation of vehicle materials in train collisions. The investigation of these issues provides an increased understanding of the research conclusions gained from a number of varied conditions, and targeting the development requirements in these three areas will promote crashworthiness applications in rail vehicles.
In the big data era, large and complex data sets will exceed scientists’ capacity to make sense of them in the traditional way. New approaches in data analysis, supported by computer science, will be necessary to address the problems that emerge with the rise of big data. The analysis of the Close Call database, which is a text-based database for near-miss reporting on the GB railways, provides a test case. The traditional analysis of Close Calls is time consuming and prone to differences in interpretation. This paper investigates the use of visual analytics techniques, based on network text analysis, to conduct data analysis and extract safety knowledge from 500 randomly selected Close Call records relating to worker slips, trips and falls. The results demonstrate a straightforward, yet effective, way to identify hazardous conditions without having to read each report individually. This opens up new ways to perform data analysis in safety science.
Structural railway transport elements are typically designed to work for at least 30 years without undergoing major maintenance. However, real-life operational conditions present behaviors different to the model predicted during the initial design phase, which affects the lifetime of the elements in question. This is the case of first-generation railway vehicles which operates in the city of Medellín, Colombia, as the bolster beam presented cracks after 12 years of operation, possibly due to undesired impacts between the bogie and the pivot of the bolster beam. Monitoring vibrational signals would give some sort of an insight into impact phenomena; however, herein lies the problem, as they are difficult to identify using only vibration signals, occurring during time events that take place in a speed-varying system. In this article, the authors present a technique that automatically detects impacts using multiple in-between time/frequency representations, ranking them according to their capacity to discriminate between impact events. Our results show that the best representation for this data was the Fractional Cepstrum Transform at order 0.5 (auROC = 0.961), which outperformed the best pure domain descriptor by least 4%.
Pier settlement causes deformation of bridge structures, and further distorts the track structures placed on bridge decks, which may greatly affect the service life of the tracks and safe operation of trains. This study analyzes track stresses and vehicle dynamic responses in train–track–bridge system with pier settlement and determines the pier settlement safe value for high-speed railways with China Railway Track System (CRTS) II slab tracks. First, a detailed train–track–bridge dynamic model is established based on the train–track–bridge dynamic interaction theory. Verified with field experimental results, the model is utilized to calculate the dynamic responses of the vehicle–track–bridge system with different pier settlement values. Finally, the safe value of the pier settlement in the CRTS II slab track railway line is determined according to the limit of the vehicle dynamic indicators and the structural stresses of tracks. The results show that the vertical acceleration of the car body is more sensitive to pier settlement among all the vehicle dynamic indicators. Structural stresses of tracks caused by pier settlement appear at the positions of the pier with settlement and its two adjacent piers. The effect of train loads on the track stresses is much smaller than that of the pier settlement. It is important to adopt the structural stresses of tracks as the evaluation criteria of the pier settlement safe value than the vehicle dynamic indicators. Taking the effects of the bridge pier settlement, the vehicle load, the prestress effect, and the self-weight into consideration, the pier settlement safe value for the high-speed railway lines with the CRTS II slab track is 11.5 mm.
Fault inspection plays an important role in ensuring the safe operation of freight cars. With the development of computer vision technology, vision-based fault inspection has become one of the principal means of fault inspection. A coupler yoke is an important component of the train’s connection system, and if the bolt goes missing, it would cause the separation of the train from the coupler, resulting in a serious accident. In this paper, we propose an automatic image inspection system to inspect the faults in coupler yokes during the operation of a freight train. Images of the coupler are acquired and the inspection process is divided into two parts: the localization part and the recognition part. In the localization part, we combine the normalized gradient magnitude with the histogram of gradients on six orientations to form the "Multiple Dimension Features", design a fast algorithm to compute the multi-resolution image features, and use a linear support vector machine to locate the position of the coupler yoke in an image. In the recognition part, we use Haar features to study the appearances of coupler yokes, propose a fast decision trees training method by pre-pruning non-effective features, and use AdaBoost decision trees as the final classifier to determine whether there is a fault. The two main parts above combine to create the whole inspection system, and experimental results show that this proposed method can achieve a fault inspection rate of 98.6% while the average processing time of an image is about 98 ms, which shows that our system has high inspection accuracy and a good real-time performance.
Static track inspection methods record the position and direction data through track surveys completed by trolleys that survey a track based on a track control network. The track inspection points must be measured in sections to decrease the likelihood of measurement errors. Certain track inspection points will be measured twice by adjacent stations, and different results will be obtained because of the measurement errors. To improve the regularity of the track, inspection point data from the sectional measurements must be processed, and differences in the results for the same inspection points must be eliminated. Therefore, this paper proposes a novel method referred to as the regularity for processing sectional measurement data (RPSMD) method, which overcomes the disadvantages of the currently available methods of processing inspection points via track-surveying trolleys and also improves the processing of nonoverlapping and overlapping inspection points. The adjustment criterion states that the difference value for the same adjusted overlapping points should be zero, and this criterion can be used to obtain the adjustment equation for each station. Using the adjustment equation, all station points can be corrected and the total regularity of the track points can be guaranteed. According to precisely measured ballastless tracks and their calculated three-dimensional coordinates, the RPSMD method and other available methods are verified by an experimentally designed precise mechanical device. The experimental results show that the accuracy of the nonoverlapping points adjusted by the RPSMD method is improved, and the accuracy is obviously higher than that obtained by the other available methods. Also, the accuracy of the RPSMD-adjusted overlapping points is much higher than that of the nonadjusted points.
In recent years there has been increased interest in developing a safer and more efficient railway system, as the railway has demonstrated the potential to become the most sustainable mode of transport. In Europe, significant investments have been made in order to increase the speed of both passenger and freight vehicles, but a good efficiency of railway transport can be achieved only if it is possible to ensure a high level of safety and reliability. These requirements can be achieved by adopting onboard diagnostic systems in order to increase the vehicle safety and to improve the strategies for a scheduled and corrective maintenance. This study shows the design and testing of an onboard monitoring system, which can be installed on different types of railway vehicles. The system is able to detect anomalies of the running behavior of vehicles and faults at the component level.
Rolling contact fatigue is a major problem connected with railway tracks, especially in curves, since it leads to higher maintenance costs. By optimising the top-of-rail friction, the wear and cracks on the top of the rail can eventually be reduced without causing very long braking distances. There are several research articles available on crack prediction, but most of the research is focused either on rail without a friction modifier or on wheels with and without friction control. In the present study, in order to predict the formation of surface-initiated rolling contact fatigue, a range of friction coefficients with different Kalker’s reduction factors has been assumed. Kalker’s reduction factor takes care of the basic tendency of creepage as a function of the traction forces at lower creepage. The assumed range covers possible friction values from those for non-lubricated rail to those for rail with a minimum measured friction control on the top of the rail using a friction modifier. A fatigue index model based on the shakedown theory was used to predict the generation of surface-initiated rolling contact fatigue. Simulations were performed using multi-body simulation, for which inputs were taken from the Iron Ore line in the north of Sweden. The effect of friction control was studied for different curve radii, ranging from 200 m to 3000 m, and for different axle loads from 30 to 40 tonnes at a constant train speed of 60 km/h. One example of a result is that a maximum friction coefficient (µ) of 0.2 with a Kalker’s reduction factor of 15% is needed in the case of trains with a heavy axle load to avoid crack formation.
Energy-efficient operation of trains in subway systems is regarded as one of the most effective strategies to cut down the operational cost. Most of the studies about the energy-efficient operation of trains aim to minimize the consumption of mechanical energy of trains. In this paper, an energy-efficient train control model is proposed under the practical billing system by introducing the traction efficiency. In addition, a numerical solution approach is presented to solve the energy-efficient driving strategy, which consists of the control sequences and the corresponding switching points. First, the authors analyze the energy-efficient control problem by applying the maximum principle, from which the energy-efficient control regime is proved to include the maximum acceleration, coasting, cruising with partial braking, and maximum braking. Second, the control sequences for one section are fully analyzed and an algorithm is presented to calculate the switching points with the energy consumption constraint. To obtain the solution to an interval with variable speed limits and gradients, the interval is divided into several sections, where the gradient and speed limit of each section are constants. A primary energy-efficient solution, which costs a longer trip time, is given. Then, energy units are assigned into multiple sections to shorten the trip time of the primary solution. Specifically, each energy unit is added into the selected section to achieve the maximum time reduction. Finally, the energy-efficient driving strategy at all sections will be obtained when the scheduled trip time of the interval is delivered. Some examples based on the practical data are conducted to illustrate that the proposed approach has a good potential on saving energy of trains.
The transmission of vibration through a passenger train seat to the seat pan and to the backrest has been measured in the fore-and-aft, lateral and vertical directions with 12 subjects using 0.5–40 Hz random vibration (with both single-axis and tri-axial excitation) and using simulated tri-axial train vibration. There were small differences in transmissibilities obtained using single-axis and tri-axial random vibration but greater differences in transmissibilities between tri-axial random vibration and simulated train vibration. Seat effective amplitude transmissibilities (SEAT values) were similar for single-axis and tri-axial random vibration but differed between tri-axial random vibration and simulated train vibration. The SEAT values measured using both tri-axial random vibration and simulated train vibration were well predicted from the seat transmissibilities measured using single-axis random vibration. It is concluded that either single-axis or tri-axial vibration excitation can be used when quantifying the transmissibility of a seat and identifying seat resonances. A SEAT value depends on the vibration spectrum in the vehicle and so the SEAT value for a train seat cannot be obtained using vibration unlike that in a train. A useful SEAT value for a train seat can either be measured (by simulating tri-axial train vibration in a laboratory) or calculated (from measurements of vibration in a train and measurements of seat transmissibility obtained using random vibration in a laboratory). The findings of this study may assist the optimisation of seat testing standards including the laboratory method for evaluating the transmission of vibration through the seats of railway vehicles defined in a current international standard.
Energy is becoming an increasingly important topic in all transport systems. However, when evaluating alternative methods for the optimisation of energy use, it is vital to obtain a thorough understanding of the energy flows within the system. While new systems generally have comprehensive automatic energy metering and monitoring of their components, there is much legacy infrastructure without this capability. This article develops a methodology to determine a breakdown of energy use for the Tyne and Wear Metro, the results of which are compared with other railway systems. This is complemented by an investigation into the energy consumption of stabled rolling stock.
Subgrade is a critical component of railway systems since it provides a stable platform for the track substructure. The implementation of quality assurance methods is very important during the construction of a new railway subgrade and in monitoring the working performance of operating railways. There are several indicators available to measure the compaction and mechanical performance of a completed subgrade system, including compaction degree (K), porosity (n), modulus of subgrade reaction (K30), basic bearing capacity (
This study investigates the mechanism of wheelset longitudinal vibration and its influence on wheel periodical wear. A longitudinal wheel/rail friction model was created after analyzing the characteristics of wheel/rail longitudinal friction that fit our study. This friction model is then incorporated into a vibration analysis of a wheelset coupled with a single-wheelset longitudinal dynamical model. The response of the single-wheelset system both considers the effects of track excitation and small randomly varying velocity, and the wheelset longitudinal random vibration process is held constant. Meanwhile, from the micro perspective, wheelset longitudinal vibration will cause changes of wheel/rail contact parameters mainly in the natural frequency which will cause periodical wear. Such wear is due to the natural frequency of wheelset longitudinal vibration being the same or doubled.
A numerical model based on the periodic-Fourier-modal method is proposed for the dynamic analysis of a train-floating slab track coupling system with random track irregularity. In the model, each vehicle of the train is modeled as a multiple-degree-of-freedom vibration system consisting of one car body, two bogies, four wheelsets, and two groups of spring-damper suspension devices. The floating slab track is modeled as a periodic-infinite structure with discrete supports and discontinuous slabs. Linear springs are used to couple the train and the track. In order to establish this numerical model, an efficient periodic approach named periodic-Fourier-modal method for solving the dynamic response of the floating slab track under a harmonic moving load is first developed. Based on this, a strategy is then proposed which can couple the moving train to the track with random irregularity and express the wheel–rail force as a superposition of a series of harmonic loads. With the solved wheel–rail force, the vehicle response can be directly calculated through vehicle dynamics, while track response can be calculated through the principle of superposition and the reuse of the initially proposed periodic-Fourier-modal method. Using this train–floating slab track coupling model, the solution of the dynamic response of the infinite track can be transformed to perform only within a single periodic range, which can save the calculation time significantly. The numerical results of the Beijing subway, based on the proposed model, are discussed in detail, and some important conclusions are drawn.
This paper presents a detailed investigation of out-of-round electric locomotive wheels through extensive measurement conducted at field sites. More than 2000 wheels, of seven types of locomotives widely used in China, have been measured since April 2013. The measurement results indicate that two types of freight traffic locomotives suffer serious polygonal wear problems with center wavelengths ranging from 160 to 315 mm. The dominating wavelength is 200 mm. Therefore, the investigations are mainly focused on the two locomotive types. The other types, which are taken for comparison, do not exhibit obvious polygonal wear. However, they exhibited more or less eccentricity. The effect of wheel re-profiling on the wheel polygon is also investigated and discussed. The dominating harmonic orders and center wavelengths after re-profiling are consistent with those before re-profiling at the correct circumstances, if the center wavelength of the polygonal wear is about 200 mm.
The support condition of railway sleepers has a significant effect on the mechanical behavior of railway tracks due to the passing of different trains. One of the important issues in this regard relates to existing unsupported sleepers on the railway tracks. These sleepers cause changes in the dynamic responses of railway tracks under a moving train. In the literature, the effects of train bogie patterns on the behavior of tracks with and without unsupported sleepers have not been completely investigated till now. Therefore, the present study investigates this issue using numerical analyses. In this regard, first, a finite element model of a railway track is utilized, and the results are verified and validated against those of previous studies. Then, equations of three vehicle models are derived and their interactions with the track model are investigated. These models include vehicles without bogies and vehicles with two- and three-axle bogies. During the numerical analyses, the effects of the unsupported sleepers on the dynamic performance of the track are studied. Finally, based on the achieved numerical results, many regression equations are derived between the train axle loads with rail bending moments, sleeper displacements, and support forces for tracks.
To prevent derailment such as flange-climbing derailment, precise understanding of the vehicle dynamics is important. In this study, the authors have developed a bogie rotational resistance test machine which has many innovative functions to understand the characteristics of railway bogies. The test machine can measure the rotational resistance of a bogie connected to a carbody. By using this machine, some distinctive characteristics of the rotational resistance have been clarified. As a result, a modified simulation model was constructed based on the test result, and it enabled a more accurate analysis of vehicle dynamics during the curve passage.
Application of active suspensions in high-speed passenger trains is gradually getting more and more common. Active suspensions are primarily aimed at improving ride comfort, wear or stability. Failure of these systems may not only just deteriorate the performance but it may also put vehicle safety at risk. There are not many studies that explain how a thorough study proving safety of active suspension should be performed. Therefore, initiating this type of study is necessary for not only preventing incidences but also for assuring acceptance of active suspension by rail vehicle operators and authorities. This study proposes a flowchart for systematic studies of active suspension failures in rail vehicles. The flowchart steps are solidified by using failure mode and effects analysis and fault tree analysis techniques and also acceptance criteria from the EN14363 standard. Furthermore, six failure modes are introduced which are very general and their use can be extended to other studies of active suspension failure. In the last section of the paper, the proposed flowchart is put into practice through four failure examples of active vertical suspension.
The longitudinal profile of a railway track excites a dynamic response in a train which can potentially be used to determine that profile. A method is proposed in this paper for the determination of the longitudinal profile through an analysis of bogie vertical accelerations and angular velocities resulting from the train/track dynamic interaction. The cross-entropy optimisation technique is applied to determine the railway track profile elevations that generate a vehicle response which best fits the measured dynamic response of a railway carriage bogie. Numerical validation of the concept is achieved by using a two-dimensional quarter-car dynamic model, representing a railway carriage and bogie, traversing an infinitely stiff profile. The concept is further tested by the introduction of a two-dimensional car dynamic vehicle model and a three-layer track model to infer the track profile in the longitudinal direction. Both interaction models are implemented in Matlab. Various grades of track irregularity are generated which excite the vehicle inducing a dynamic response. Ten vertical elevations are found at a time which give a least squares fit of theoretical to measured accelerations and angular velocity. In each time step, half of these elevations are retained and a new optimisation is used to determine the next 10 elevations along the length of the track. The optimised elevations are collated to determine the overall longitudinal profile over a finite length of railway track.
The phenomenon of track rigidity in desert areas due to sand dune movement and ballast contamination is one of the most important causes of ballasted railway track degradation and consequently increase in train-induced vibrations. In addition to looking at the existing methods for reducing the track rigidity such as using ballast mat and installing the under sleeper pad, this paper focuses on evaluating the dynamic behavior of railway track including ballast mixed with tire-derived aggregate in a field study. Based on prior laboratory tests done by the authors and latest researches, 10 volume percentages of tire-derived aggregate were adopted as maximum suitable amount to be mixed with ballast for decreasing the track rigidity and increasing its damping property maintaining the basic ballasted track capabilities. In this regard, in a test track located in central desert of Iran in Bafgh-Jandagh railway route, the ballast was mixed with 0, 5 and 10% of tire-derived aggregate by tamping machine in three different sections with 20 m lengths. Moreover, another test section in the same route with fully fouled ballast was considered as a critical bench mark. Many tests were carried out on the mentioned sections using impact test method. In the next stage, the operational modal analysis method was utilized to achieve the tested sections’ mode shapes, natural frequencies and damping ratios as well as geometrical attenuation from the recorded responses. By knowing the modal properties, numerical models of tracks were developed, and the effect of tire-derived aggregate as well as fouling on track stiffness was evaluated.
Rail weld geometry irregularity is one of the main excitation sources for vehicle–track coupled dynamic system, and it has a direct effect on the wheel–rail dynamic interactions, which are responsible further for the wheel–rail noise, railway component damages, and track deteriorations. In many previous studies, the rail weld irregularity was usually modeled as a single or composite concave cosine wave based on field investigations on traditional railway lines or researchers’ experiences. These investigations were mainly concentrated on the maximum value of the rail weld irregularity. However, the geometrical shape was usually ignored. In this paper, a series of rail weld irregularities measured on Beijing–Shanghai high-speed railway passenger-dedicated line in China are presented. Based on the analysis of the measured rail surface geometry in the weld zones, some typical theoretical models of the rail weld irregularity are established. Then, the effectiveness of the established rail weld irregularity models are demonstrated for dynamic evaluation of the rail weld irregularity in high-speed railways by comparison between the wheel–rail dynamic responses excited by the measured and the modeled rail weld irregularities, respectively. Finally, the influences of different rail weld irregularities on the wheel–rail dynamic interactions are investigated using the vehicle–track coupled dynamics model and the established rail weld irregularity models. The results are expected to be capable of providing references for the analysis and evaluation of the rail weld irregularity in high-speed railways.
Rail grinding is a special application of high-performance dry grinding, which combines a number of special characteristics, such as high feed speed, good surface roughness and waviness and a high material removal rate. Since beginning of the 20th century, rail grinding is used as a maintenance process and is essential for the increased rail life. In recent years, the surface roughness of railway tracks became increasingly important, especially with respect to the noise emissions. The rail grinding has a positive impact on the quality and life of the railway infrastructure, particularly on the driving comfort and safety. However, for the first weeks after the grinding, residents near railway lines have increased noise emissions from passing trains. This undesirable side-effect is a result of the rough surface left after the grinding process. Only through numerous train crossings are the generated roughness peaks gradually smoothed, whereby the noise emission is reduced. The wheel–rail contact is the dominant noise source at speeds between 50 and 250 km/h. Below those speeds, the propulsion noises outweigh and above 250 km/h the aerodynamic effects outweigh the wheel–rail contact noise emissions. In this paper, a newly developed rail grinding strategy is presented, which improves the roughness of the rail surface and, thus, delivers a reduction of noise emissions immediately after the grinding. The basic development of this new grinding technique was performed as a laboratory test, which will be presented in detail. Furthermore, for a better understanding of the process, the most important technological and kinematic variables are presented. The results of acoustic measurements on a track section, which has been ground with this new technology, will be presented.
The influence of contact surface upon the dynamic performance of a pantograph–catenary system is a question that has been highlighted by the increasing use of high speed railways. Using the mode-superposition method, we establish a pantograph–catenary-coupled dynamics model with consideration of the contact surface; we analyse the characteristics of the contact surface based on a large amount of measured data; and we determine the characteristic parameters according to their influence upon the system dynamic performance. The results show that the contact wire irregularity contains a periodic component formed by gravity and a random component formed by wear, local assembly errors, hardpoints and the like. Periodic and low-frequency random irregularities mainly lead to the increase in contact force amplitude at peak points with wavelengths submultiple of the tension length, span or dropper spacing. On the contrary, high-frequency random irregularity has a great influence upon the amplitude of all frequencies and is the main factor leading to the deterioration of the system dynamic performance. The contact strip wear surface achieves quadratic function fitting, and we propose two characteristic quantities of this surface, namely, shape parameter A, and wear depth B. The wear surface of contact strip enhances the periodic characteristics of pantograph–catenary system of each span, leading to the amplitude increase of the contact force in frequency with span submultiple wavelength. The bigger the absolute value of the shape parameter, the poorer the dynamic performance. According to the criteria of the contact force eigenvalues, we determine the threshold value of the contact strip shape parameter A, and the contact wire irregularity amplitude of each frequency. The threshold given in this paper can be used in the condition assessment of parts, and make judgements on whether a servicing is needed, which is part of the technologies for informationisation and intelligent high-speed train health management.
A high-speed railway train control system plays a key role in ensuring the safe operation of the trains. To ensure the safety of high-speed railway train control systems, it is vital to perform hazard analysis on them. In this context, this paper proposes a novel hazard analysis method which extends a previously reported system-theoretic hazard analysis method "system-theoretic process analysis." The proposed method improves the standard system-theoretic process analysis to capture the temporal relations between inadequate control actions leading to hazards. These temporal relations are crucial for investigating the causes of hazards. To depict the temporal relations of control actions of high-speed railway train control systems, a new temporal logic called "control action temporal logic" is proposed first. Then based on this temporal logic, a new control action relation model is added into the process of system-theoretic process analysis. This model depicts the relations (including temporal relations) between control actions. In order to identify both the inadequate control actions and their temporal relations, an algorithm is designed and used. Finally, the effectiveness of the proposed method is verified through the hazard analysis on the Chinese Train Control System level 3.
The pantograph-catenary subsystem is a fundamental component of a railway train since it provides the traction electrical power. A bad operating condition or, even worse, a failure can disrupt the railway traffic creating economic damages and, in some cases, serious accidents. Therefore, the correct operation of such subsystems should be ensured in order to have an economically efficient, reliable and safe transportation system. In this study, a new arc detection method was proposed and is based on features from the current and voltage signals collected by the pantograph. A tool named mathematical morphology is applied to voltage and current signals to emphasize the effect of the arc, before applying the fast Fourier transform to obtain the power spectrum. Afterwards, three support vector machine-based classifiers are trained separately to detect the arcs, and a fuzzy integral technique is used to synthesize the results obtained by the individual classifiers, therefore implementing a classifier fusion technique. The experimental results show that the proposed approach is effective for the detection of arcs, and the fusion of classifier has a higher detection accuracy than any individual classifier.
The application of Doppler-based LIght Detection and Ranging (LIDAR) technology for determining track curvature and lateral irregularities, including alignment and gage variation, are investigated. The proposed method uses track measurements by two low-elevation, slightly tilted LIDAR sensors nominally pointed at the rail gage face on each track. The Doppler LIDAR lenses are installed with a slight forward angle to measure track speed in both longitudinal and lateral directions. The lateral speed measurements are processed for assessing the track gage and alignment variations, using a method that is based on the frequency bandwidth dissimilarities between the vehicle speed and track geometry irregularity. Using the results from an extensive series of tests with a body-mounted Doppler LIDAR system on-board a track geometry measurement railcar, the study indicates a close match between the LIDAR measurements and those made with existing sensors on-board the railcar. The field testing conducted during this study indicates that LIDAR sensors could provide a reliable, non-contact track monitoring instrument for field use in various weather and track conditions, potentially in a semi-autonomous or autonomous manner.
Railway accidents place significant demands on the resources of, and support from, railway emergency management departments. Once an accident occurs, an efficient incident rescue plan needs to be delivered as early as possible to minimise the loss of life and property. However, in the railway sector, most relevant departments currently face a challenge in drawing up a rescue scheme effectively and accurately with the insufficient information collected from the scene of a train accident. To assist with the rescue planning, we propose a framework which can rapidly and automatically construct a 3D virtual scene of a train accident by utilising photos of the accident spot. The framework uses a hybrid 3D reconstruction method to extract the position and pose information of the carriages involved in an accident. It adopts a geographic information system and a 3D visualisation engine to model and display the landscapes and buildings at the site of a train accident. In order to assess and validate our prototype, we quantitatively evaluate our main algorithm and demonstrate the usage of our technology with two case studies including a simulated scene with an in-lab setting and a real train derailment scene from on-site pictures. The results of both are accountable with high accuracy and represent the ability of timely modelling and visualisation of a train accident scene.
This study describes the critical speed enhancement of the KTX-Sancheon, a Korean high-speed train, using measured wheel profiles. The wheel wear shape of the commercial high-speed train was measured according to mileage, and the relationship between conicity and mileage was investigated. The critical speed of the KTX-Sancheon power car was analyzed numerically with the measured wheel profiles. The suspension parameters were optimized to increase the critical speed of the KTX-Sancheon. As a result, the critical speed of the power car increased by 34.1% compared to its initial condition. The results are being used for a new design of the power bogie.
This study focuses mainly on the mechanism of wheelset longitudinal dynamics which has often been neglected. By analysing the process of wheel/rail rolling contact, taking into account of the wheelset longitudinal vibration, a wheel/rail longitudinal friction model combining an elastic spring and a viscous damper coupled with a friction element and incorporating both frequency and amplitude dependence is proposed to capture the characteristics of wheel/rail longitudinal vibration and the differences between small and large creepage. At small creepage, the characteristics of the wheel/rail longitudinal friction model are influenced by the excitation frequency and the amplitude of creepage. This influence is incorporated into a dynamical analysis of a wheel/rail longitudinal friction model coupled with a single-wheelset longitudinal dynamical model. The results show that once the wheelset longitudinal vibration has been stimulated under external excitation at small creepage, the wheelset longitudinal natural frequency will be dominant, with other frequencies making a very small contribution in comparison. This will cause a sudden increase in vibration amplitude, which may lead to wheel/rail nonlinear adhesion–slip vibration at large creepage.
An efficient three-dimensional dynamic track-subgrade interaction model has been formulated and then validated by field investigations at various field and traffic conditions including the effect of different train speeds and types of trains. The model contains a two-dimensional discrete support track model and three-dimensional computation-efficient finite element soil subgrade model. In the two-dimensional track model, the rail beam is modelled as an Euler-Bernoulli beam. The two-dimensional track model discretizes the tie and ballast as rigid bodies with designated spacing. The three-dimensional finite element subgrade model is simulated by plane-stress quadrilateral finite elements. The longitudinal direction of the subgrade model is expanded in the frequency domain and is assumed to be homogeneous. Therefore, the computing time could be largely reduced. A moving dynamic loading is applied on top of the rail. The model is capable of taking train speed variations and the profile change of the cross section into consideration. Multiple field instrumentation tests covering the two train types and different train speeds at the test site were then conducted to verify the accuracy of the dynamic track-subgrade interaction model. Testing site is located on the Amtrak's highest speed line (Northeast Corridor: 250 km/h) near Kingston, Rhode Island in the United States. A method to obtain the tie deflection from accelerometer data at Kingston was proposed and then validated at another site on the Northeast Corridor. Tie deflections measured in the field were compared with those predicted by the three-dimensional dynamic track-subgrade interaction model. It is concluded that this model can predict track performance accurately for the Kingston site.
The European FP7 project DynoTRAIN was set up in order to close important open points in the technical specifications for interoperability of the trans-European rail system and to contribute to European standards. This contribution targeted the reduction of cost of the process for the assessment of running dynamics characteristics that is required when seeking authorisation to place rolling stock in service according to the EU procedure. The project was divided into seven work packages. Work Package 7 was devoted to the issue of ‘regulatory acceptance’: the results had to be discussed with and presented to regulatory authorities in a way as to be acceptable for use by such authorities. An important part of this work addressed accuracy (and its quantitative counterpart, uncertainty) of the assessment process, which was widely recognised at the beginning of the project as a key issue that needed to be tackled to increase confidence in both experimental and virtual assessment processes. In this paper, the uncertainty framework that was developed in WP7 and its relationship with the work of other DynoTRAIN Work Packages is presented. An application of the concepts of the framework is given in the form of quantitative results regarding the accuracy of the current EN 14363 experimental assessment process for running dynamics characteristics.
Increased demand for railway transportation is creating a need for higher train speeds and axle loads. These, in turn, increase the likelihood of track degradation and failures. Modelling the degradation behaviour of track geometry and development of applicable and effective maintenance strategies has become a challenging concern for railway infrastructure managers. During the last three decades, a number of track geometry degradation and maintenance modelling approaches have been developed to predict and improve the railway track geometry condition. In this paper, existing track geometry measures are identified and discussed. Available models for track geometry degradation are reviewed and classified. Tamping recovery models are also reviewed and discussed to identify the issues and challenges of different available methodologies and models. Existing track geometry maintenance models are reviewed and critical observations on each contribution are provided. The most important track maintenance scheduling models are identified and discussed. Finally, the paper provides directions for further research.
To study the effect of car body-mounted equipment on the car body flexible vibration, a vertical rigid-flexible coupling model of a high-speed vehicle is established, which includes a flexible car body, rigid bodies for two bogie frames, four wheelsets, and the car body-mounted equipment. The car body is approximated by an elastic beam, with dimensions selected to give similar mass and vertical bending frequency to an existing car body. Model validation is then carried out by comparing results from numerical simulation and on-track test. Using frequency response analysis and ride comfort analysis, parametric studies are undertaken in order to investigate the respective effect of equipment mounting systems on the car body flexible vibration and ride comfort perceived by the passenger. It is found that the equipment behaves as a dynamic vibration absorber on account of its elastic connections to the car body. The stiffness, damping, mass, and installing position of the equipment have a significant influence on the car body flexible vibration. The optimal parameters of the dynamic vibration absorber are given, which can contribute much to the vibration absorption of the car body flexible vibration. Finally, extensive tests on a high-speed test vehicle are conducted to represent a part of results obtained in the numerical study, including modal tests on the car body, component tests on rubber springs used in the equipment mounting systems, and roller rig tests on the vibration absorption performance of the equipment. It is shown that the car body flexible vibration can be effectively suppressed by reasonably suspending the car body-mounted equipment.
A hanging tie is a form of railroad track distress that occurs when voids have developed beneath the ties due to uneven ballast settlement and improper maintenance practices. It will lead to an increase in dynamic impact loading on the top of the ballast thereby further deteriorating the track structure. This paper proposes a fast, nondestructive screening method to identify the hanging tie problem. The method utilizes a dynamic track model to characterize the track’s "moving deflection spectrum" under different tie-supporting scenarios. The model includes a moving dynamic load and ties with discrete supports. The moving deflection spectrum shows dynamic responses of the "track moving deflection" in the frequency domain. The modeling results indicate that a significant discrepancy exists in the moving deflection spectrum depending on whether or not there is a hanging tie condition. To validate this method, preliminary field tests were carried out on both Boston Metro and St. Louis Metro lines. Then the moving deflection spectrum generated by the model is compared with the moving deflection spectrum in the field tests as measured by the accelerometers installed on a high-rail vehicle. Results show that the method is effective in identifying the hanging tie problem and has great potential to be employed by the rail industry in the future.
To combat adhesion loss, sand is fired into the wheel–rail contact via a hose using compressed air typically from a storage hopper mounted to the under frame of the train. Many passenger trains in the UK are fitted with stepped braking controllers which range from 1 to 3 with a fourth step being ‘emergency braking’.1 Sand is fired automatically if wheel slip is detected from brake step level 2 upwards.2 Sand is automatically fired when the emergency brakes are applied irrespective of whether low adhesion/wheel slip has been detected.2 For adhesion loss in traction, sand can be applied at the driver’s discretion. Current railway standards2 govern the maximum permissible sand flow rate to protect against wheel/rail isolation of track circuits, but do not address the hose position. This results in a range of hose set-ups across different train types, some of which may not be effective at delivering sand. The work here was carried out using a full-scale laboratory rail–wheel test machine to find the position for the hose and sand flow rates that give optimum sand entrainment to the contact. It was found that ideally the hose should be aimed at the rail or nip and be as close to that contact as safely possible. The use of a 20 mm bore nozzle on the end of a 25 mm bore hose increased sand passing through the contact by up to 70% relative to widely used 25 mm bore hoses without a nozzle. Reduction in sand flow rate below the 2 kg/min threshold significantly reduced the amount of sand entering the contact. It was also shown that relatively small movements in the hose/nozzle from its ideal position and cross winds significantly reduced sand entrainment.
Condition monitoring systems are commonly exploited to assess the health status of equipment. A fundamental part of any condition monitoring system is data acquisition. Meaningfully estimating the current condition and predicting the future behaviour of the equipment strongly depend on the characteristic of the data measurement stage. Nowadays, condition monitoring has wide applications in the railway industry, and various monitoring approaches have been proposed for the inspection of wheel and rail conditions. In-service condition monitoring of wheels provides the real-time data required for maintenance planning, while in-workshop inspection is normally done at fixed intervals carried out periodically. In-service data acquisition can be divided into on-board and wayside measurements. In this paper, on the basis of these classifications, the existing data acquisition techniques for the monitoring of railway wheel condition are reviewed, and the state-of-the-art methods and required research are discussed.
With increasing train speed, it is necessary to study the relation between slab track vibration and travelling speed. In this paper, a wireless sensor network system is deployed on a typical ballastless slab track in China, which uses acceleration nodes to collect vibration information when the train is passing by at different constant speeds. Then, after comparing the denoising effects of a hard threshold method, a soft threshold method and a Bayes wavelet method, the Bayes wavelet denoising method is used to remove the noise, while the spatial variability characteristics of the signal are preserved. Finally, the wavelet energy spectrum is adopted to obtain the duration and energy of the non-stationary vibration data. The time–frequency function curve is obtained to further analyse the physical behaviour of the vehicle–track system. A hammering experiment is conducted to show the importance of the results. This work facilitates a better understanding of the track vibration characteristics for monitoring the status of the track.
To study the railway overhead wire's flexural wave motion that significantly affects the quality of current collection between pantograph and catenary, dynamic responses of a real catenary excited by different excitations are measured and analyzed by using a set of noncontact photogrammetric devices together with the finite-element simulation. Based on the measured and simulated results, the wave motion along the contact wire is investigated and some findings have been obtained. First, it is the first two dominant modal components in the catenary displacement responses that induce a beat phenomenon, and this beat phenomenon is increasingly obvious near the registration arm. Moreover, with the simulated displacement contour, catenary local vibration characteristics affected by the travelling wave can be clearly interpreted. Furthermore, the wave group velocity of contact wire in catenary is determined and verified to be approximately 139.18 m/s; in addition, treating the contact wire in the overhead wire system as an ideal string or a tensioned Euler beam will overestimate the corresponding group velocity with a relative error by about 13.21%.
Rail track longevity is a primary concern for the railroad industry in the US. Therefore, it is important to study the rail support system in detail. This includes understanding the interactions between the rail, the different fastening components, and the crosstie. Then evaluate the support system’s long-term performance. Over the past several years, the railroad industry in the US has been leaning toward implementing alternative solutions to the traditional hardwood timber crossties. Recycled plastic composite crossties present an appealing and effective solution due to their sustainably, environmental benefits, durability, and ease of installation. Several US manufacturers are currently offering commercial crosstie solutions using different recycled plastic composite materials. Thousands of composite plastic crossties are currently in service in a wide variety of railroad tracks. Researchers have investigated this material in the past; however, additional research is still needed to fully understand the rail support system and its long-term behavior. This paper presents an experimental investigation aiming to understand and assess the performance of the full rail support system: the rail section, fastening assembly, and recycled high-density polyethylene crossties. The study encompassed a comprehensive experimental investigation using static and cyclic test methods recommended by the American Railway Engineering and Maintenance-of-Way Association manual. The static tests addressed the performance of the rail support system when subjected to uplift forces and longitudinal loading in the direction of the rail track, e.g. breaking and traction forces. The dynamic test evaluated the long-term behavior of the rail support system while being subjected to repeated loading for three million fatigue cycles. The outcomes of this study showed great results; the crossties survived the fatigue loading with normal wear and minimal degradation, which highlights the potential of these materials if properly optimized and engineered.
The need for interoperability for rail operators across Europe has resulted in the development of the technical specifications for interoperability: requirements and regulations which include safety limits for train aerodynamics. Safety limits are calculated within guidelines, including environmental conditions, train speeds and ballast shoulder height. However, there are many cases on the European rail network which fall outside ballast shoulder height limits, raising questions about the suitability of the technical specifications for interoperability limits, where European homologation is a requirement. Ballast is a layer of crushed stone onto which the railway track is laid; a ballast shoulder is defined from the top of the ballast layer to the base of the track foundation or ground. This paper describes the detailed model-scale experiments carried out at the University of Birmingham’s moving model TRAIN rig facility to assess the influence of ground geometries on aerodynamic flow development around a train. The technical specifications for interoperability methodology was questioned in relation to whether modest changes to include a wider cross-section of ballast shoulder heights, more appropriate to actual operating conditions, would affect limit values in relation to safety. The influence of ballast shoulder height was investigated for three typical train types. The results showed a similar static pressure development for all the ballast shoulder heights tested. Passenger train results indicated that shallow ballast shoulders confine the aerodynamic flow within a smaller area, increasing the magnitude of slipstream velocities in respect to larger ballast shoulders. The largest slipstream velocities were found for the ground configuration with no ballast shoulder modelled. Measurements within the technical specifications for interoperability-specified range of ballast shoulder heights exhibited little difference in flow development. Analysis of maximum 1 s gusts, calculated using the current technical specifications for interoperability methodology, found values lie close to, but do not break, the existing limits. Increasing ballast shoulder height was shown to decrease values away from technical specifications for interoperability limits.
Over the past two decades, a rolling deflection measurement system aiming to continuously measure the track modulus has been under development at the University of Nebraska – Lincoln under the sponsorship of the Federal Railroad Administration. This system measures the relative vertical distance (referred to as Yrel) between the rail surface and the rail/wheel contact plane at a distance of 1.22 m from the nearest wheel to the sensor system. The aim of this study was to investigate the potential of using the Yrel measurement as an indicator of the track modulus for various rail foundation conditions. To meet this objective, a detailed finite element model capable of simulating moving loads and track modulus variation was developed. One of the unique contributions of this study is that it presents a comprehensive study of the Yrel–track modulus relationship by defining more realistic support conditions using discrete spring supports and by simulating the stochastic nature of the track modulus along a 160-m track length. The numerical model was employed to examine the accuracy of estimating the track modulus using the Yrel measurements when foundation stiffness is variable. Furthermore, the correlation between the statistical properties of the track modulus and Yrel was studied over different track segment lengths.
On 18 November 1996, a fire on Heavy Goods Vehicle shuttle No. ‘7539’, travelling from France to England, forced the train to stop at about 19 km from the French entrance. This paper presents the results of an analysis of the accident. The analysis covers the incident train’s journey from the French terminal until it stopped in-tunnel only. The approach has been to use a tunnel fire safety management system model as a ‘template’ for comparison with the ‘system’ at the time of the tunnel fire. Some findings have been highlighted. The model is intended to represent a ‘systemic’ approach to tunnel fire safety management.
In this study, the nonlinear damping characteristics of friction wedges in the secondary suspension of a freight wagon are investigated considering nonsmooth unilateral contact, multiaxis motions, slip–stick conditions, and geometry of the wedges. The parameters of the contact pairs within the suspension were identified to achieve smooth and efficient numerical solutions, while ensuring adequate accuracy. A simulation model of the friction wedge was formulated and analyzed, which revealed highly nonlinear dependence on vertical, roll, and lateral motions between the bolster and the side frames. The friction wedge model was integrated into the multibody dynamic model of a three-piece bogie to study the effects of wedge properties on hunting characteristics. The resulting 114-degrees-of-freedom wagon model incorporated constraints due to side bearings, axle boxes, and the center plates, while the wheel–rail contact forces were obtained using the FASTSIM algorithm. The simulation results were obtained to study hunting properties of the wagon in terms of critical speed and the predominant oscillation frequency, and the effects of wedge friction and geometry on stability characteristics of the freight car. The results showed subcritical Hopf bifurcation of dynamic responses of the wagon. Moreover, an increase in the wedge angle, friction coefficient, and springs free length resulted in a higher critical speed.
The purpose of this study was to analyze train driver injuries under secondary impact and to optimize the driver workspace to reduce the driver impact injury risk. The console–seat–dummy collision analysis model of train cab is established using MADYMO. The driver dynamic impact response and the driver injury results were obtained from the collision model. The optimization of driver workspace parameters was conducted to reduce the driver injury risk. Fifteen samples were chosen for numerical simulation based on the optimal Latin hypercube design; the polynomial response surface methodology was adopted to fit the relationship between the driver injury criteria and the workspace parameters. The driver injury results show that the driver injury is considerably severe. The optimization results indicate that the driver injury is minimal when factors A, B, C, and D are 356.6 mm, 404.6 mm, 145 mm, and 200 mm, respectively. Compared with the initial collision model, all six driver injury criteria after optimization decrease obviously and are well within the tolerance limits, respectively. The analysis of the optimization results and the results of computer simulation refined after the optimization confirm that the optimization results show good correlation with the injury results of the collision numerical model and the effectiveness of the optimization design in reducing the severity of the driver injury during a secondary impact.
Railway track switches, commonly referred to as ‘turnouts’ or ‘points,’ are a necessary element of any rail network. However, they often prove to be performance-limiting elements of networks. A novel concept for rail track switching has been developed as part of a UK research project with substantial industrial input. The concept is currently at the demonstrator phase, with a scale (384 mm) gauge unit operational in a laboratory. Details of the novel arrangement and concept are provided herein. This concept is considered as an advance on the state of the art. This paper also presents the work that took place to develop the concept. Novel contributions include the establishment of a formal set of functional requirements for railway track switching solutions, and a demonstration that the current solutions do not fully meet these requirements. The novel design meets the set of functional requirements for track switching solutions, in addition to offering several features that the current designs are unable to offer, in particular to enable multi-channel actuation and rail locking, and provide a degree of fault tolerance. This paper describes the design and operation of this switching concept, from requirements capture and solution generation through to the construction of the laboratory demonstrator. The novel concept is contrasted with the design and operation of the ‘traditional’ switch design. Conclusions to the work show that the novel concept meets all the functional requirements whilst exceeding the capabilities of the existing designs in most non-functional requirement areas.
While magnesium alloys have the attractive attributes of low density, the application of the metal in transportation industries has been restricted by its low stiffness and strength. The aim of this study was to examine the possibility of lightweight railway car body construction using magnesium alloys from the structural and manufacturing perspectives. Extruded members, making up a car body, were designed employing a gradient-based optimization algorithm. And then, numerical simulations were conducted to confirm the structural performance of the newly designed car body. In addition, one of the designed members was extruded and joined with another via friction stir welding in order to verify its fabrication potential. The work demonstrated that, with just 85% of the weight of an aluminium car body currently in operation, a magnesium-based railway car body can be potentially constructed by extrusion followed by friction stir welding for the next generation rolling stocks; that is to say, the weight saving amount is 10% of the total bare frame weight, or 2% of its total rolling stock weight.
The exact characterization of the wheel–rail normal contact situations is essential for its wear, fatigue, and guidance analysis. To simulate this contact, numerous input parameters are required. Many of them have to be estimated. The aim of this sensitivity analysis was to investigate the direct effects and interactions of the input parameters on the contact pressure distribution of a freight wagon wheel on a straight track. For this purpose, a finite element model was parametrized in such a way that all the parameters were continuous. This research demonstrates that the output parameters of the wheel–rail contact simulations have a broad deviation and the input variable with the most influence on the contact form and position is the lateral displacement of the wheelset. Nevertheless, the profile shape of the wheel and rail, the wheel radius, and the relative wheel–rail inclination are important input parameters as well, and also need to be considered for exact simulations of the wheel–rail contact. On the other hand, the deviation of material parameters of wheel and rail steel can be neglected.
Wear processes from mechanical braking, rail/wheel contact, the railway electrification system and re-suspended materials due to the turbulence of passing trains in tunnels and stations have been suggested to be the main contributors to particulate matter levels inside trains. In this study, onboard monitoring was performed on a commuter train stopping at underground and aboveground stations. The concentration and size distribution of particulates were monitored for both indoor and outdoor levels. The results show that the levels of PM10 and PM2.5 inside the train were about one-fifth of the outdoor levels. Significant increases in indoor particulate number concentrations were observed in tunnel environments and there was a slight increase when the doors were open. Differences in the size distributions of micro- and nano-sized particulates could be identified for different tunnels.
The wheel wear properties of heavy haul bogies running on the Da-Qin railway line were measured. The hollow and asymmetric wear are indicated. The wheel/rail contact geometry relationship was calculated on the basis of the measured wheel profiles. The dynamic simulation model using SIMPACK software for C80BF Gondola with ZK7 radial bogie and C80B gondola with ZK6 cross brace bogie was established. The hollow depth effect on wheelset attack angle and lateral force was quantified. According to the actual conditions of Da-Qin railway line, the hollow wear was predicted using a numerical method. Based on these results, the hollow wear maintenance standard was recommended. Finally, a field test for asymmetric hollow wear was described.
This paper presents a mechanistic model of the rail head lateral deflection with the aim of quantifying the distribution of the lateral wheel load in a concrete sleeper rail track. The model is developed based on observations of the field experimentation and the results of a three-dimensional validated finite element model. The input parameters of the model are primarily based on the design of the fastening system and the track structure. In the developed model, the rail head lateral deflection is divided into two components which are computed separately: rail base lateral deflection and rail head rotational deflection. The model considers the possible gap between the field-side shoulder and insulator, and assumes Coulomb Law of friction for the rail base interfaces. Based on an experimental design approach, the prediction of the mechanistic model is compared with that of finite element model as well as with field data.
The ballasted ladder track is a new type of longitudinal track. In this paper, to investigate its vibration reduction effect, both a laboratory test and in situ experiment were conducted. As the vibration sources, a newly designed drop weight impulse setup was employed in the laboratory test, and moving metro trains were employed in the in situ measurement. The vibration reduction effects of the ballasted track with ladder sleepers and regular concrete sleepers were compared. The results show that the ballasted ladder track can effectively decrease the peak value in the time domain and has the potential effect to control the environmental vibration in low frequencies. The shape of the sleeper can induce changes in the vibration field of the ballast.
The flow field and sound propagation around a three-coach 1/8th scale high-speed passenger train were obtained using a detached-eddy simulation and the Ffowcs-Williams and Hawkings acoustic analogy. The Reynolds number of flow based on the train height and speed was 2,000,000. The numerical results of the flow and aeroacoustic fields were validated using wind tunnel experiments and full-scale data, respectively. Features of overall sound pressure level, sound pressure level and A-weighted sound pressure level of typical measuring points are discussed. The sound propagated by a high-speed train is shown as a broadband noise spectrum including tonal component, where high sound pressure levels are concentrated on the low-frequency range from 10 Hz to 300 Hz. The inter-carriage gap is found to cause distinct tonal noise in contrast to the other parts of the train that cause a broadband noise. The negative log law has been used to study the influence of distance from the centre of track on the sound pressure level, where a good fit is shown at low-frequency ranges. The peak values of A-weighted sound pressure level from both full-scale experiment and simulation results occur at approximately 1 kHz, where simulation results show almost the same range as the experiment. The surface of each component of the train as well as the whole train are chosen as the integral surface for the Ffowcs-Williams and Hawkings computation of the far-field noise characteristics. It was found that the sound source generated by a high-speed train is mainly dipole, and the largest noise was obtained from the leading bogie. The results of this paper provide, for the first time, a better understanding of the aeroacoustic field around a three-coach train model, and the paper has the potential to assist engineers to design high-speed trains with aeroacoustic noise reduction in a better manner.
The primary purpose of this paper was to choose appropriate time integration methods for the simulation of nonlinear railway vehicle systems. The nonlinear elements existing in railway vehicle systems were summarized, and the relevant mathematical expressions were provided. A newly developed integration method, which is the corrected explicit method of double time steps, was implemented in five typical nonlinear examples of nonlinear railway vehicle systems. The Newmark method, the Wilson- method, the Runge–Kutta method, the predictor-corrector Adams method, the Zhai method, and the precise integration method were also employed for comparison purpose. Finally, the scope of application of these methods was pointed out . The results show that the Newmark method and the Wilson- method should not be applied to nonlinear railway vehicle systems as these methods result in errors. In contrast to the predictor-corrector Adams method and the precise integration method, the Runge–Kutta method with error control (RK45) is not applicable to the non-smooth problems although the RK45 possesses high accuracy. In addition, the application of the RK45 and the predictor-corrector Adams method with error control may result in spurious tiny oscillation in the vehicle system related to nonlinear vertical wheel–rail forces. The corrected explicit method of double time steps, the Zhai method, the standard Runge–Kutta method, the precise integration method, the RK45, and the predictor-corrector Adams method which possess tight error tolerances are recommended for nonlinear railway vehicle systems according to the requirements of accuracy and computational efficiency.
In this study, noise-source identification of a high-speed train was conducted using a microphone array system. The actual sound pressure level analysis of the noise source was performed using scaling factors between the real sound pressure and the beam-power output based on the assumption that the integrated area of the main beam-power lobe is equal to half that of the actual sound pressure of the noise source. Then, the scaling factors for the 144-channel microphone array were derived from analysis of the array response function, and a verification experiment was conducted using a known noise source, an air horn, located on a high-speed train moving at 240 km/h. After the verification test, noise-source identification of the high-speed train was conducted. Based on the resulting noise map of the high-speed train moving at 390 km/h, the main noise sources were determined to be the inter-coach spacing, wheels, and pantograph. The noise generated by the pantograph was then investigated in more detail. It was concluded that the pan head of the pantograph was the main noise source at a frequency of 1000 Hz.
The dynamic response of a high-speed rail experiencing heavy braking is investigated using the moving element method. Possible sliding of train wheels over the rails as the train decelerates is accounted for. The train is modelled as a 14-DOF system comprising a car body, bogies and wheel sets interconnected by spring-damping units. The railway track is modelled as an infinite Euler–Bernoulli beam resting on a two-parameter elastic-damped foundation. A convected coordinate system attached to the moving train is employed in the formulation of the governing equations. The effects of braking torque, coefficient of static friction between wheels and rail, initial train speed and the severity of railhead roughness (track irregularity) on the dynamic response of the high-speed rail, including the occurrence of the ‘jumping wheel’ phenomenon, are examined. The phenomenon describes the momentary loss of contact between the wheel and track. A combination of high braking torque, large static friction coefficient, high initial train speed and severe track condition promotes larger dynamic effects.
One of the most important safety-related tasks in the rail industry is an early detection of defective rolling stock components. Railway wheels and wheel bearings are the two components prone to damages due to their interactions with brakes and railway track, which makes them a high priority when the rail industry investigates improvements in the current detection processes. One of the specific wheel defects is a flat wheel, which is often caused by a sliding wheel during a heavy braking application. The main contribution of this paper is the development of a computer vision method for automatically detecting the sliding wheels from images taken by wayside thermal cameras. As a byproduct, the process will also include a method for detecting hot bearings from the same images. We first discuss our automatic detection and segmentation method, which identifies the wheel and bearing portion of the image. Then, we develop a method, using histogram of oriented gradients to extract the features of these regions. These feature descriptors are later employed by support vector machine to build a fast classifier with a good detection rate, which can detect abnormalities in the wheel. At the end, we train our algorithm using simulated images of sliding wheels and test it on several thermal images collected in a revenue service by the Union Pacific Railroad in North America.
To consider the rail pads of thermoplastic polyurethane elastomer (TPE), chloroprene rubber (CR), and ethylene propylene diene monomer (EPDM) that are usually used in the Chinese subway as test subjects, their static stiffness at temperatures of –40℃ to 70℃ was measured by a universal testing machine equipped with a temperature control box. Then, the influence of the temperature-dependent stiffness of the rail pads on the vertical vehicle-track coupled vibrations was investigated with application of a vehicle-track coupled dynamic model. It was found that the static stiffness of these rail pads exhibits a nonlinear variation with temperature. Their static stiffness is considerably sensitive to temperatures below 20℃, when the CR rail pad is the most sensitive. At temperatures above 20℃, their static stiffness slightly alters with increasing temperature. The temperature-dependent stiffness of these rail pads mainly affects the vertical vibrations of the vehicle system above the one-third octave center frequency of 31.5 Hz and the vertical rail vibrations near the center frequency of 63 Hz. Moreover, the influence of the low-temperature stiffness of rail pads at –40℃ to 20℃ is far greater than the effect of the high-temperature stiffness of rail pads at 20–70℃. Thus, TPE, CR, and EPDM rail pads have excellent high-temperature stability and adverse low-temperature sensibility.
Low-flatcar wagons represent a good alternative to freight truck transportation. In fact, the whole truck can be easily loaded on these wagons. However, due to the railway vehicle gauge, these vehicles present a particular design with an important impact on the dynamics of the trainset and on its derailment risk. The present work aims at analysing the dynamic behaviour of the trainset and the influence of the freight train composition on the derailment risk. Numerical simulations have been performed to identify the most critical conditions. Then, an experimental campaign has been carried out to evaluate the derailment risk associated to these conditions.
The aim of this paper is to study the optimization of the rail profile for heavy haul railways. A numerical model is developed, where the rail profile is parameterized as a generalized function for a series of independent variables. A well-designed formula, which characterizes the conformance between wheel and rail profiles around contact point for all possible wheel–rail contact situations, is considered as the objective function. During the construction of the objective function, a wheel–rail contact geometry algorithm is implemented to detect contact point positions quickly. Linear and nonlinear constraints are introduced in order to meet some necessary conditions. Then, the optimization of rail profile can be transformed into a typical mathematical nonlinear optimization problem with single objective, multivariables, and multiconstraints. In order to solve this problem effectively and efficiently, the sequential quadratic programming algorithm combined with Lagrange function, quasi-Newton method is employed. At each major iteration, a quasi-Newton approximation is made of the Hessian matrix of the Lagrangian function using BFGS updating method. This is then used to generate a quadratic programming subproblem whose solution is for forming the search direction for the iteration of independent variables. Finally, the R75 rail profile, prevalently used in China’s heavy haul railways, is optimized using the developed model to better match the LM wheel profile. A modified rail profile is put forward and compared with the original rail profile systematically in wheel–rail contact geometry relationship, vehicle–track dynamic behaviors, and wear developments. A vehicle–track coupling dynamics model and a wheel–rail wear prediction model are respectively established to conduct the comparative study. According to the calculation results, the optimized rail profile is proved to have superior performances and, thus, can be considered a better choice to match LM wheel for China’s heavy haul railways, which is of practical value for the design and preventive grinding of heavy haul rails. In addition, this application example validates the rationality of the developed numerical optimization model. It can also be used for the optimization of other rail profiles.
In this paper, hybridizing a heavy vehicle is developed. A switcher locomotive is considered for hybridization. Due to their low operational speed, the switcher locomotives require much lower power when compared to other types of locomotives. Besides, switcher locomotives have higher loss of energy due to their frequent starting and stopping. Hybrid-powered transit vehicles are considered to be excellent replacements for ordinary transit vehicles, since hybrid powered vehicles are equipped with more than one traction power sources. Therefore, a switcher locomotive’s driving cycle is derived from the measured field data and used to calculate and design the hybrid vehicle’s components. A "fuzzy controller" is used to plan a suitable controller for the designed hybrid locomotive. Comparisons show a substantial decrease, both in the fuel consumption and the pollutions of the designed hybrid switcher locomotive versus the conventional diesel-electric locomotives.
The amount of ballast particles surrounding a railway track significantly influences its resistance in all directions. As time goes by, with the development of high-speed trains, more attention has been paid to this issue owing to the increase in dynamic effects of rolling stock on track loading. The focus of the present study is on the investigation of the interaction between different surfaces (base, crib, and shoulder) of concrete sleeper and their adjacent ballast layer along with the related parameters under lateral impact loading condition. In this regard, by utilizing a pendulum loading test device, a number of lateral impact tests were conducted on an instrumented concrete sleeper in laboratory. On the basis of experimental results, the average contribution of base, crib, and shoulder zones in the total dynamic lateral resistance of sleeper was calculated as 48%, 23%, and 29%, respectively. Furthermore, in the lateral impact force domain of 13–28 kN, the sleeper–ballast dynamic friction coefficient at base and crib zones varied in the ranges 0.8–1.5 and 0.5–0.6. Moreover, a maximum impact factor of 2.5 was obtained for analysis and design purposes. It should be stated that the trend of laboratory results confirmed the common static friction coefficient of 0.8.
This paper presents an experimental study on dynamic performance of China Railway Track System (CRTS) series track systems using a full-scale test rig. The test rig has been constructed based on 55.17 m long full-scale nonballasted tracks composed of four typical CRTS track elements in high-speed railways. First, the dynamic characteristics of different nonballasted tracks are investigated by conducting wheel-drop tests, where a wheel-drop testing vehicle with a dropping wheelset is devised to provide the wheel-drop load. The vibration levels of different track systems are assessed by the root-mean-square acceleration per one-third octave band, and the vibration transmission characteristics of the CRTS series tracks are evaluated by transfer functions. Further, a mathematical track model is used to extract the dynamic stiffness and damping coefficient of the four types of nonballasted track systems based on the wheel–rail impact response. The vibration characteristics, the dynamic stiffness, and damping coefficient of different nonballasted track systems under various wheel-drop heights are compared and discussed in detail.
Railway track stiffness is an important track property which can help with the identification of maintenance related problems. Railway track stiffness can currently be measured using stationary equipment or specialised low-speed vehicles. The concept of using trains in regular service to measure track stiffness has the potential to provide inexpensive daily ‘drive-by’ track monitoring to complement data collected by less-frequent monitoring techniques. A method is proposed in this paper for the detection of track stiffness variation through an analysis of vehicle accelerations resulting from the vehicle–track dynamic interaction. The cross-entropy optimisation technique is applied to determine the track stiffness profile, which generates a vehicle response that best fits the measured vertical accelerations of a railway carriage bogie.
Numerical validation of the concept is achieved by using a two-dimensional half-bogie dynamic model, representing a railway vehicle, to infer a global track stiffness profile along a track. The track stiffness measurement algorithm is implemented in Matlab. This paper reports the results of the numerical simulations. The proposed method gives good estimates of the track stiffness. To the authors’ knowledge, this is the first time an optimisation technique has been applied to the determination of railway track stiffness.
In this study, the author uses parametric models to predict the track geometry-induced dynamic behavior of a vehicle. The characteristics of vehicle dynamics in these models are directly identified through the spatial as opposed to the frequency domain. One of the former’s merits is that we can identify the characteristics of vehicle dynamics with fewer observed points than when we use spectral analysis, making it easier to obtain fewer data set for identification. Another is that we can determine the parameters to represent dynamic behavior of a vehicle using statistical criteria. With these models, we can predict vertical acceleration of a vehicle and its wheel load as well as estimate track conditions by taking into account both ride comfort and operating safety.
A track circuit never reporting block failure means a track section is reported as vacant to a railway control system, even if it is occupied by a train. This is a wrong side failure which may cause an accident. A high-voltage impulse (HVI) track circuit based on the fast Fourier transform is currently in use in China to solve this problem, but it has been observed that when used in electric railway systems large inrush currents can lead to another track circuit failure mode, which is referred to as a transient reporting block (TRB) in this paper. The root causes and impact of TRB track circuit failures are analyzed and a solution to the TRB failure mode based on wavelet analysis is proposed. Computer simulations and onsite experiments are carried out and the results show that the proposed approach can accurately extract the feature frequency and then effectively avoid the TRB failure, even if the HVI track signal is disturbed by a significant inrush of traction-return current.
The actual European regulations for the acceptance of railway vehicles prescribe the measurement of not only accelerations but also contact forces exchanged at wheel–rail interface, in order to assess the level of running safety, track loading and vibration behaviour. It is important to point out that the standards do not prescribe any specific method to measure forces, or define the measurement of forces. The aim of this paper is to investigate the metrological properties of a dynamometric wheelset in order to determine the associated measurement uncertainty and to verify its readiness in the range of frequencies where the force analysis must be performed. With reference to a specific instrumented wheelset, a method for increasing the accuracy of the measure when critical running conditions (i.e. large values of the derailment coefficient Y/Q) are detected is proposed. The proposed method can be applied to any instrumented wheelset, but it is particularly effective on non-conventional wheelsets, where only few measurements are available and the classical methods cause large estimation errors.
The possibility of omitting rail expansion devices from the track configuration, when continuously welded rail is continued over temporary bridge decks, is investigated in detail. More specifically, the related rail track to temporary bridge interaction phenomena are analysed using finite element modelling. A first parametric analysis assesses the additional rail stresses due to moving trainloads and temperature variations, based on stipulations provided in the unit identification code 774-3R. In addition the model is expanded to a more complex structure that is able to simulate the buckling behaviour of the rail track using non-linear methods. Using this model, a second parametric study is performed in which only thermal loading is considered. This allows for determining the parameters, which are predominant in determining the critical buckling temperature of the rails, and for assessing the magnitude of the safety margin necessary, when it comes to thermal buckling of the rails and the temporary bridges. It can be concluded that, depending on the magnitude of two main factors, the lateral ballast resistance and the amplitude of the initial track misalignment, a considerable reduction of the track stability might arise. Therefore, a minimal characteristic lateral ballast resistance of 4 kN is recommended along with a maximal allowable misalignment amplitude of 7 mm has to be prescribed when thermal track buckling has to be considered in the design.
This investigation aims to find empirical equations that describe the rail–wheel normal (frictionless) contact characteristics. These equations can then be used to determine an equivalent Hertzian load to account for normal contact in the finite element analyses mandated by the Transnet RS/ME/SP/008 specification, without explicitly simulating the contact between two bodies. The standard is similar to UIC 510-5 and does not consider tangential contact. The normal contact problem is solved for the test case using nonlinear finite element methods as well as the boundary element method. Material plasticity was also investigated in finite element analyses with limited effect for contact away from the flange area. The data from boundary element analyses were fitted to a power law equation for each contact parameter. The equivalent Hertzian contact produced with the empirical equations is able to predict the normal contact parameters relatively accurately, producing a maximum error of 9.6% (excluding one area with a geometric anomaly).
Train simulation software is conventionally validated by checking simulation results against equivalent data collected from real train runs. It is typically expected that these results will be within 5–10% accuracy of the recorded data. However, such a large margin could allow errors in the programming to be overlooked, resulting in an inaccurate model. This paper presents a method for error checking and validating the kinematics of train simulators based on comparison with calculated results, which are found by solving the fundamental equations governing train motion. A typical train run comprises of a combination of two or more of the four stages: accelerating, cruising, coasting and braking. Each stage is considered as a separate scenario for which the equations must be solved, in order to find the running time, distance travelled and energy consumption of the vehicle. This validation method is applied to two train movement simulators currently used for research. Certain specific scenarios for which analytical solutions are available are run in each simulator. The differences from the analytical solution in each test case are quantified, allowing the simulators to be compared to each other and the exact solution.
This paper models the input signal amplitude of the main track and the small track of the adjacent jointless track circuit (JTC) when JTC is idle and the track circuit reader(TCR) received signal amplitude when JTC is occupied, based on the work mechanism of JTC and TCR. Based on the models, the relative impact of compensation capacitor on signal amplitude is obtained by simulation. The paper further proposes a calculation method for structure importance of compensation capacitors. Experimental results indicate that the rankings of structure importance are not affected by ballast resistance of JTC in this method. The results also show that the compensation capacitors closer to the receiving end are more important than those closer to the sending end. In addition, C2, C6, and C3 closer to receiving end are the most important and should be paid close attention during maintenance. The second, the first and the fifth capacitor from the sending end, have less impact on the JTC and TCR signal. This paper is helpful to determine the maintenance priority of each capacitor, optimize the maintenance strategy, and make better use of JTC.
Although it is accepted that system design affects train driver performance, the literature related to this phenomenon – in relation to urban railways and metro systems in particular – is scarce. Metro systems differ significantly from mainline railways, being closed systems, with shorter headways, a greater number of stations and more signals encountered. This paper aims to investigate the effects of design-related performance shaping factors on metro driver performance, by analysing historical incident records for the 2011–2013 period on the Tyne & Wear (T&W) Metro (UK). Bivariate statistical analysis has been used, to assess the potential inter-dependency of the performance shaping factors and other common causal factors, for various driver-related incident types. In addition to category A signals passed at danger incidents, station overruns, and incidents associated with station procedures have also been assessed. The results show the significant importance of the location (design) based performance shaping factors in incident propagation mechanisms in the Metro. The two years under investigation display increased consistency between driver-related incidents and locations, rather than time of day, or season. In addition, the highest correlation between incidents has been found in terms of locations. Deviations from a standardised T&W Metro station design were found to associate with either an increase or decrease in incident rates, depending on whether additional complexity or simplicity was introduced. Although the features of metro systems suggest improved route knowledge and system familiarity among drivers, the results show that this can actually lead to an unsatisfactory safety-related performance during non-routine operations, e.g. engineering works, or driving in sidings.
The energy-absorbing structure of a crashworthy railway vehicle was designed by combining the characteristics of thin-walled metal structures and aluminum honeycomb structures: finite element models of collisions involving energy-absorbing structures were built in ANSYS/LS-DYNA. In these models, the thin-walled metal structure was modeled as a plastic kinematic hardening material, and the honeycomb structure was modeled as an equivalent solid model with orthotropic–anisotropic mechanical properties. The analysis showed that the safe velocity standard for rail vehicle collisions was improved from 25 km/h to 45 km/h by using a combined energy-absorbing structure; its energy absorption exceeded the sum of the energy absorbed by the thin-walled metal structure and honeycomb structure when loaded separately, because of the interaction effects of thin-walled metal structure and aluminum honeycomb structure. For an aluminum honeycomb to the same specification, the composite structure showed the highest SEA when using a thin-walled metal structure composed of bi-grooved tubes, followed by that using single-groove tubes: that with a straight-walled structure had the lowest SEA.
Diesel-electric locomotives consume a significant amount of fuel in rail transportation systems. The power transmission system of these locomotives is similar to that of hybrid electric vehicles, so the available diesel-electric locomotives can be promoted to series hybrid locomotives by adding an energy storage source. In this study, the GM SD40-2 locomotive is considered as a case study and the series hybrid structure for this locomotive is designed and simulated by adding a lithium-ion battery pack. Additionally, control strategy plays an important role in reducing the amount of fuel consumed by hybrid electric vehicles. The fuzzy look-ahead control is applied as an online approach for fuel consumption reduction in railway transportation. A fuzzy controller modifies throttle position by accounting for the battery state of charge, the gradient and desired speed of the path ahead. The model developed in this study for train motion simulation considers the locomotive subsystems and satisfies the experimental fuel consumption data specified in the locomotive’s catalog. A simulation of a freight train with the GM SD40-2 locomotive on a local track showed considerable improvement of fuel economy when using series hybrid structure in conjunction with our proposed algorithm for diesel-electric locomotives.
Contact loss between the concrete underlayer and the subgrade caused by the differential settlement or stiffness of subgrade structure is a common distress, which deteriorates the mechanical properties of the track structure and adversely affects the safety and comfort for the operation on high-speed railway. The objective of this paper is to study the damage mechanism of prefabricated slab track subjected to such contact loss and to propose a critical value for the size of contact loss that would not jeopardize the safety of rail traffic and riding comfort of passengers. Thus, a vibration calculation model for the vertically coupled vehicle-J-slab track-subgrade system is established using finite element method, both of the short-wave irregularity and the German long-wave irregularity were taken into account to calculate the dynamic response of vehicle, track structure and subgrade with different contact loss areas and speeds scenarios. Based on the numerical simulation results, a critical value of contact loss area is proposed. When the actual contact loss area is smaller than the critical value, the welded joint irregularity is the dominant factor in the vehicle dynamic response; however, when the actual contact loss area is larger than the critical value, the track irregularity induced by contact loss under the concrete underlayer becomes the dominant factor. It is suggested that the contact loss area should be controlled under the critical value in order to ease or mitigate the dynamic response of the vehicle and track structure. The numerical simulation indicates the critical contact loss area is about 10 m2 for the short-wave irregularity case and 14 m2 for the long-wave irregularity case, thus it is suggested that the contact loss area underneath the concrete underlayer should not exceed 10 m2, which is consistent with the Swedish standard and the German standard on weak areas of subgrade compaction.
As the well-known difficulties are that feedback signals are not easy and economical measurement in practice for active control, this paper presents a study of state estimation for active control of independently rotating wheels (IRW) based on observers. The reduced-order observer and high-order sliding mode observer are used to provide reliable and accurate estimations of the wheel pair state and track curvature using practical sensors. This proposed method uses less sensors than the one of previous studies. Furthermore, lateral accelerator and yaw velocity sensors (gyros) are economical and available for active steering and stability control system to obtain the required feedback signals. The wheels’ relative rotational speed, track curvature and yaw angle of wheelsets are the feedback signals for IRW active control approach. Computer simulations are used to verify the effectiveness of proposed methods and assess control performance in stability and negotiation.
This work presents experimental assessment of the improvements to the horizontal ride quality of a railway vehicle equipped with a semi-active magneto-rheological (MR) suspension system. The assessment includes the development of a mathematical model and magnetic circuit analysis of the MR damper, the design and manufacture of MR damper, and field test on the railway. After evaluating the field-dependent damping force characteristics, the conventional passive dampers of the operational railway vehicle are replaced with the MR dampers to evaluate horizontal dynamic characteristics that directly indicates the ride quality of the railway vehicle. Various sensors are installed in the vehicle and a skyhook controller with semi-active condition is implemented to produce an appropriate input current for the generation of the desired damping force. Three periods of testing are undertaken on the railway bridge at 120 km/h and the measured data of acceleration level are recoded and presented. It is demonstrated from the measured results that the vibration can be effectively controlled by the proposed semi-active MR suspension system associated with the skyhook controller. Finally, from the vibration control responses the horizontal ride quality of railway vehicle is evaluated and presented in frequency domain.
In the National Spanish railway network, two types of track gauge with continuous welded rails are currently in use: the "Iberian" wide gauge (1668 mm) and the standard gauge (1435 mm). In order to improve links and freight traffic between different lines and with the rest of Europe, a dual gauge track with three rails was developed. This solution modifies the classical track configuration, so it is necessary to develop new methodologies and studies to understand its behavior. Among other loads applied on a continuous welded rail track, a considerable rise in temperature induces compressive stresses in the three rails that can lead to lateral track buckling. Moreover, on dual gauge tracks, the addition of the third rail increases the axial compression, which may lead to track instability. For this reason, a three-dimensional continuous welded rail model is developed in this study to be used for dual gauge track buckling analysis on straight tracks subjected to temperature load. The continuous welded rail dual gauge track model consists of beam, solid and spring elements, in which a non-linear behaviour of the ballast is considered. The results obtained may be used to predict the buckling capacity of the continuous welded rail on dual gauge tracks with respect to different parameters such as lateral resistance, lateral imperfections, sleeper spacing or torsional stiffness.
Aerodynamics of trains running inside tunnels change more significantly in comparison with open air scenarios. It has been confirmed that the lateral vibration as well as the aerodynamic drag of the trains is increased and the micro-pressure wave is produced at the tunnel exit when the trains are passing through tunnels. The aim of this article is to explore the impact of a high-speed train passing through a tunnel on the pantograph aerodynamics and the dynamic behavior of the pantograph–catenary interaction. The aerodynamic forces acting on the pantograph are investigated thoroughly by extensive numerical simulations as well as systematic field tests. To investigate the effects of the aerodynamic forces of pantograph on the quality of current collection, the numerical simulations of the pantograph–catenary dynamic interaction are conducted with our proposed model, taking into consideration the action of the aerodynamic uplift forces obtained by the numerical simulations on the pantograph. Then, a series of numerical simulations are also carried out to analyze the effects of the train speed and the blockage ratio on the aerodynamic uplift forces of the pantograph, on the contact forces, as well as on the displacement of the contact wire, while the train is passing through a tunnel. The results reveal that compared with the open air scenarios, the aerodynamic drag and uplift forces of the pantograph, the mean value of the contact force and the displacement level of the registration arm can considerably increase as the train runs inside a tunnel. Moreover, the statistical values of the contact forces and the displacement level of the contact wire become larger while the train is passing through the tunnel at different speeds. On the other hand, the quality of current collection decreases with the increasing of the blockage ratio.
Pantograph–catenary disconnection occurs quite frequently in high-speed situations. Pantograph arcing has a significant impact on the contact surfaces and power quality. This article focuses on the effect on the electrical characteristics of the four-quadrant converter of pantograph arcing. An arc model which combines Cassie’s arc model with Mayr’s arc model is built. This article mainly researches the influence of the pantograph arcing on the four-quadrant converter in different durations. Pantograph arcing leads to voltage pulse in voltage, as well as the harmonics in the current of the alternating current side. At the same time, the direct current voltage decreases when the arc occurs. Therefore, it can ultimately decrease the output torque and increase the torque pulsation of the motor.
The influence of different ground simulation systems on the air flow around a high-speed train with zero yaw angle is investigated. Force values, force development graphs, surface pressures, the underbody flow and the wake are studied in detail with Computational Fluid Dynamics, which is initially validated by wind tunnel testing. It shows that the stationary ground has severe deviations from the full moving ground on the aerodynamic performance due to the inaccurate pressure distribution on the underbody. This is mainly attributed to the high level of interaction between the underbody and the boundary layer development. In addition, a ground boundary layer separation bubble can be observed under the tail end of the train for the stationary ground on account of insufficient energy to overcome the increasing adverse pressure gradient. In order to guarantee a correct underbody flow, a partially moving ground is proposed, including the "3-moving ground" and the "1-moving ground". Such ground simulation systems are well compatible with the fixed rail tracks and the bottom support struts compared to the full moving ground. As a conceivable method to reduce the influence of the boundary layer, raising the high-speed train model with different ground clearances is also studied. Overall, the 3-moving ground is suggested to be the best choice for the ground simulation systems in high speed train wind tunnel testing.
A quick-hardening concrete track has been developed to convert old ballast tracks into concrete tracks on operating lines. This method has been utilized to convert urban railways since 1997. With recent increases in train traffic and speed, maintaining track irregularities within design criteria has become essential to ensuring safety. On quick-hardening tracks, track irregularities are predominantly caused by irregular settlement around construction joints. These construction joints are inevitable in quick-hardening concrete; however, they create discontinuous sections that can affect the stable running of trains and structural durability. In this study, full-scale tests were performed with quasi-static and repeated loading on both continuous and discontinuous sections in which the earth pressure acting on the trackbed, accumulated settlement, and elastic displacement were measured. The results obtained indicate that construction joints are disadvantageous in terms of load transfer, settlement, and displacement. Additional field observations conducted on the Seoul Metro Line corroborated the results of the full-scale tests. The overall findings strongly suggest that construction joints on quick-hardening concrete tracks would need to be reinforced.
Today, rail transport systems are widely used in the world. Because of the high consumption of energy in these systems, finding ways to optimize their energy consumption is important. One of the best ways to save more energy and prevent the losses of rail transportation is using the optimal speed profile. In this article, intelligent algorithms, involving ant colony optimization for continuous domain
The Eurocode 1 standard requires railway bridges to be checked against the hazard of resonance. To perform this task, the first natural bending frequency of a bridge span has to be computed. The analytical method based on the single-beam analogy is sufficiently accurate for simply supported beam-girder bridges. This paper proves the applicability of the method for through truss bridge spans with steel-and-concrete composite decks; this is despite the fact that the spans do not strictly comply with the assumptions of this method. The flexural stiffness of the bridge span is computed taking into account the joint action of the truss girders and the composite deck; the limited extent of span shear stiffness due to diagonal bracing is also considered. A uniform distribution of the span mass over the span length is assumed. The mass is computed based on geometrical characteristics of truss and deck members, taking into account gusset plates, stiffeners, connectors and fittings. The analytical method and finite element method are applied to find the natural frequencies of two through truss bridge spans with composite decks. Computed results are compared with frequencies recorded during bridge testing. Taking into consideration the joint action of the truss girders and the composite deck, as well as the limited shear stiffness provided by diagonal bracing, significantly improves the accuracy of the assessment provided by the analytical method. The natural bending frequencies computed for the two bridge spans fall within the range of 0.95–1.05 of the recorded values.
Free ends of insulated rail joints occur because gaps between the rails and endposts can be created due to pull-apart problems as the rails contract longitudinally in winter and by degradation of railhead material. Dynamic behaviour of gapped rail joints changes adversely compared to that of insulated rail joints. Thus, material degradation and damage of gapped rail joint components such as rail ends, joint bars, etc. are accelerated. Only limited literatures are available addressing the free end of rail effects at rail joints, targeting stress and pressure distributions in the vicinity of the rail joints. To understand clearly the material degradation and delamination process of gapped rail joints, a thorough analysis of failure of both insulated rail joints and gapped rail joints and subsequent damage of the railhead material is necessary to improve the service life of these joints. A new three-dimensional finite element analysis is carried out in this paper to assess damage to railhead material when gapped rail joints form. Both narrow (5 mm) and wide (10 mm) gaps are considered, using a peak vertical pressure load of 2500 MPa applied cyclically at one rail end, forming vertical impacts. Stress distributions and plastic deformations in the vicinity of gapped rail joints are quantified using finite element analysis data and compared with that of the insulated rail joints to show the effects of free rail ends. Residual stress and strain distributions indicate the damage to the railhead material. Equivalent plastic strain (PEEQ) quantifies the progressive damage to the railhead material at the rail ends. The free end of rail effects can be further illustrated by comparing PEEQ for insulated rail joints and gapped rail joints. The railhead material of 5 and 10 mm gapped rail joints is more sensitive to permanent deformation compared to that of the corresponding insulated rail joints. Therefore, free rail end joints pose an increased potential threat to rail operations in relation to crack initiation, damage and premature failure of railhead material.
Wheel–rail contact is more complex in railway a turnout than in ordinary track and, thus, necessitates an advanced model to simulate dynamic interaction and predict rail wear. The main aim of the present work is to assess the application of several wheel–rail rolling contact models in railway turnout. For normal contact problems, wheel–rail contact models based on four different methods are compared: Hertz theory, the semi-Hertzian method, CONTACT, and the finite element method. The assessment is based on the results of contact patch shape and size and contact pressure for several wheelset lateral displacements. The load is set to a constant and equal to static wheel load. Calculations are performed at the section of switch rail head with width 35 mm in CN60-1100-1:18 turnout; both standard and worn rail profiles are accounted for. For tangential contact problems, four corresponding methods are assessed, based on the calculation of creep forces, distribution of the stick/slide region and computational efficiency: Shen–Hedrick–Elkins theory, FASTSIM, improved FASTSIM based on semi-Hertzian method, and CONTACT. It is found that the normal contact problems solved by the semi-Hertzian method and CONTACT correlate well with the finite element method, and the tangential contact problems solved by improved FASTSIM and CONTACT are quite favorable. The conclusions of this work can provide some guidance for contact model selection in the dynamic simulation and wear prediction of railway turnout.
A sustained increase in heavy axle loads and cumulative freight tonnages, coupled with increased development of high-speed passenger rail, is placing an increasing demand on railway infrastructures. Some of the most-critical areas of the infrastructure in need of further research are track components used in high-speed passenger, heavy haul and shared infrastructure applications. In North America, many design guidelines for these systems use historical wheel loads and design factors that may not necessarily be representative of the loading currently experienced on rail networks. Without a clear understanding of the nature of these loads and how design processes reflect them, it is impossible to adequately evaluate the superstructure in order to make design improvements. Therefore, researchers at the University of Illinois at Urbana-Champaign are conducting research to lay the groundwork for an improved and thorough understanding of the loading environment imparted into the track structure using wheel loads captured by wheel impact load detectors. This paper identifies several design factors that have been developed internationally, and evaluates their effectiveness based on wheel loads using several existing and new evaluative metrics. New design factors are also developed to represent the wheel-loading environment in a different manner. An evaluative approach to historical and innovative design methodologies will provide improvements to designs, based on actual loading experienced on today’s rail networks.
The costs of fatalities and injuries from train accidents have a great impact on society. As part of our effort to understand the characteristics of past train accidents, this paper presents an analysis of significant train accidents occurring in China from 1954 to 2014. Rough set theory and associated rules approaches are applied in analyzing the collected data. The results show that although most derived rules are unique, some rules are worth noting. Collision accidents generally lead to more casualties than derailment accidents, and the most frequent cause of accidents is human error. Additionally, most train accidents occur during summer. These findings can provide railway leaders with lessons and rules learned from past accidents, thus facilitating the establishment of a safer railway operation environment in China.
Extending the use of continuous welded rails by eliminating the weak points (expansion joints) of a railway track especially in sharp curves, which has resulted in increasing the operational speed and axle load of rolling stocks, enhances the special attention to the issue of track lateral resistance. In this regard, the ballast layer interaction with sleepers plays a crucial role in providing the track lateral stability. In many railway projects supplying the appropriate ballast materials has encountered serious restrictions owing to the lack of qualified ore and also their long distance to the project’s site. With the development of steel industry, the quantity of production and accumulation of steel slag as a waste material has increased. In recent years, a great deal of attention has been paid to the use of this material as railway ballast. According to the physical and mechanical characteristics of steel slags, such as high specific gravity and the granular roughness respect to the limestone ballast, the usage of slag ballast can improve the track lateral stability. In this research, many field experiments were conducted on tracks with steel slag ballast and limestone ballast materials considering the same gradation. In this matter, several single tie push tests were carried out on both tracks with various ballast geometries. The ballast depth was considered as 30, 40, and 50 cm and the shoulder ballast width was equal to 30 and 40 cm. Moreover, the shoulder ballast height was chosen 0 and 10 cm. Consequently, the lateral resistance of both tracks was measured and compared in the same conditions. In overall, the obtained results confirmed a 27% increase in lateral resistance of track with steel slag ballast respect to that with limestone ballast.
Train-induced dynamic responses and loads in bridge pier systems are not well understood. In this study, five different piers from two separate railway bridges were investigated experimentally. The dynamic responses and loads at the bridge beam ends, pier tops, and pile caps were measured by considering various train speeds. The frequencies of the dynamic loads on pile caps were also analyzed. The results show that the induced dynamic response decreases significantly with the descending pier height. The train-induced vertical dynamic displacements are related to the axle loads and the stiffness of the pile foundation and foundation soils. The accelerations at pier tops and pile caps are very similar but noticeably less than those at beam ends. The train-induced vertical dynamic loads on pile caps increase with the total span length. The measured change of dynamic forces (Q) is approximately 20 – 30% of the measured peak loads (Q). In addition, the results show that the frequency (f) varies linearly with the train speed rather than with the bridge span length.
Although air springs are widely applied on high-speed electric multiple unit (EMU) trains, there is no accepted method to model the dynamics of these air springs. In this paper, a three-dimensional (3D)-coupled dynamics model of an air spring used on a high-speed EMU train was created through the derivation of thermodynamics equations and using a curve-fitting method. Experimental and simulated stiffness tests were performed to verify the accuracy of the 3D-coupled model, which was then implemented in the MBS vehicle dynamics model. The influence of the nonlinear behaviour of the air spring on the vehicle’s dynamic performance was analyzed by a dual-simulation approach using the 3D-coupled model of the air spring and the dynamics model of the vehicle. From the results, it can be concluded that the air spring can improve the vehicle’s vertical ride comfort, due to its ability to adjust the vertical stiffness and damping based on the level of vibration. However, the vehicle’s ability to negotiate curves is reduced due to an increase in the air spring’s lateral and longitudinal stiffness, a result of the lateral displacement of the car body. Furthermore, the operation of the leveling valve in the 3D-coupled model can slightly reduce the vehicle’s overturning coefficient, which is a phenomenon that the normal air spring models cannot simulate. Finally, the 3D-coupled model was applied to simulate a leakage process, which is a complex series of chain reactions, in the air spring system. The calculation results indicate that, even though the ride comfort is severely degraded by the leakage, the vehicle’s running safety can still be guaranteed.
Locomotive traction control behaviour and its dynamic impacts on rails and vehicles have not been comprehensively investigated in respect to transient conditions. Such transient traction behaviour could be more significant than steady state behaviour in determining dynamic traction performance and track degradation (i.e. squat/corrugation formation, etc.). In order to study this effect, detailed numerical simulations are performed to investigate a locomotive’s dynamic response to a change in contact conditions. In particular, creep response, vibration of the locomotive, and dynamic normal and traction forces are determined using a developed full-scale dynamics model of a locomotive. The model includes a detailed representation of the AC motor dynamics, which has not been considered in previous works. The results show that the detailed model is capable of simulating the dynamic fluctuations in creep and traction forces that are not considered in simpler models. Such transient responses may cause damage to the track and vehicle components.
The status inspection and maintenance actions on the mechanical components of freight trains are significant determinants of railway safety. Fastening bolts, as a key component, are widely used to transmit, connect and fasten various parts of freight trains. Their absence can degrade the original structure and lead to accidents. Recently, machine vision approaches have been widely used to inspect the status of mechanical components, thereby reducing costs and avoiding traffic accidents. This paper proposes a visual inspection system that is based on the machine vision approach and can be used to automatically inspect the status of fastening bolts on freight trains. To detect the presence/absence of a fastening bolt in a complex background, a hierarchical detection framework consisting in fault area extraction and fastening bolt detection is proposed. In the first module, a gray projection method is used to divide the fault area that contains the target from the complex background. Subsequently, a fastening bolt detector is designed to verify the candidate image regions. Several gradient-orientation-based features and a classifier can be used to perform the detection task. Experimental results show that the combination of a gradient orientation co-occurrence matrix and a support vector machine has the best classification performance. The proposed inspection system has the advantages of good real-time performance and high inspection accuracy; it achieves an accuracy of 99.96% with a speed of nine frames per second.
Railroad spikes represent a vital component of the rail track system, as they fasten the rail to the supporting crossties. Thus, it is important to understand its behavior and effect on the fastening assembly to mitigate any local failure, which, in turn, could lead to system deterioration or damage. Currently, alternative solutions to the traditional hardwood timber crossties are increasing being adopted by the railroad industry in the USA, with recycled plastic composite crossties being among the available alternatives. Their sustainably, environmental benefits, durability and ease of installation render them an attractive and competitive solution. Several research programs have studied this material and its fastening system in the past; however, additional research is required to fully understand the behavior of these materials and their interactions with the fastening system components. This paper presents an investigation that aims to understand and assess the performance of typical railroad spikes used for recycled high-density-polyethylene crossties. The study encompassed a comprehensive experimental investigation and analytical finite element modeling. The testing program evaluated railroad spikes using static testing methods recommended by the American Railway Engineering and Maintenance-of-Way Association (AREMA) manual. These tests addressed the rail spike pullout and lateral restraint for both screw and cut spikes. Finite element models were constructed and calibrated using the data obtained from the experimental program in order to extrapolate on the experimental results and predict the behavior of full-scale systems beyond the scale of the laboratory. The results observed in this study showed great promise, surpassing all the AREMA recommendations, which highlights the potential of these materials if properly optimized and engineered. Screw spikes exhibited a very good performance, surpassing the minimum recommendations by a significant margin (up to more than 200%) and are thus are highly recommended for future implementation.
Consistent increases in cumulative freight tonnages, combined with the move towards increased higher-speed intercity passenger rail operation, have placed greater demands on North American railroad infrastructure. Concrete sleepers and fastening system components are known to fail at a wide range of life cycle intervals when subjected to demanding loading environments. Such failures can cause track geometry defects, require repetitive maintenance procedures, and present critical engineering challenges. Rail seat deterioration, the degradation of the concrete material beneath the rail, has been identified through a survey of North American Class I railroads to be the most-critical engineering challenge for concrete sleepers. Shoulder/fastener wear or fatigue was identified by the same survey as the second-most-critical engineering challenge related to concrete sleepers. Lateral forces transferred through the fastening system are thought to be a primary cause of degradation of insulators. The objective of this study is to quantify the demands on the insulator through analysis of the transfer of lateral wheel loads into the fastening system by measuring the magnitude of the lateral forces entering the shoulder, a component of the fastening system adjacent to the insulator. The lateral load evaluation device (LLED) was developed at the University of Illinois in Urbana Champaign to quantify these forces. Data captured by the LLED will assist the rail industry in moving towards the mechanistic design of future fastening systems, by quantifying the lateral forces in the fastening system under representative loading conditions. Information gained through this study will also lead to a better understanding of the frictional forces at key interfaces in the fastening system. Preliminary results show that the transfer of lateral wheel loads into the fastening system is highly dependent on the magnitude of the lateral wheel loads and the frictional characteristics of the fastening system.
In most railway companies in China, the loss of nuts from rail fasteners is still found by visual inspections performed by maintenance workers; this approach cannot meet the continuing requirements to reduce maintenance costs and improve maintenance efficiency. In this paper, a computer vision system for detecting the loss of nuts from rail fasteners is proposed that is based on kernel two-dimensional principal component – two-dimensional principal component analysis (K2DPCA-2DPCA) and a support vector machine (SVM). The framework of this information-technology-based system is introduced, and the calculation method to find the positions where nuts are missing is also proposed. The K2DPCA-2DPCA feature extraction method and SVM used for feature classification in the computer vision system are described in detail. Finally, the combination of K2DPCA-2DPCA and SVM is compared with other feature extraction and feature classification methods in an experiment on the detection of the loss of nuts from rail fasteners. In this paper, it is found that the algorithm based on K2DPCA-2DPCA and a SVM is a better method for the computer vision system. It can identify the loss of nuts from a rail fastener with a high recognition rate and reach the maximum recognition rate using only a relatively small number of features. Furthermore, for the same number of training samples, the algorithm based on K2DPCA-2DPCA and SVM is also better than other algorithms for use in the computer vision system.
In this study, an improved physical parametric model with key in-service parameters was established and experimentally validated for a high-speed railway hydraulic damper. A subtle variable oil property model was built and coupled into the full model to address the dynamic flow losses and the relief-valve system dynamics. Experiments were conducted to evaluate the accuracy and robustness of the full damper model and simulation, which determined the damping characteristics over an extremely wide range of excitation speeds. Further simulations with in-service conditions and excitations were performed using the validated model, and the results revealed that improper key in-service parameters, such as improper rubber attachment stiffness, entrained air ratios and small mounting clearances, can greatly degrade the damping capability of a hydraulic damper. The obtained physical model includes all the influential factors that have an impact on the damping characteristics, so it will serve as a useful basic theory in the prediction of in-service performance, optimal specification and product design optimization of hydraulic dampers for modern high-speed rail vehicles.
This study investigates the effect of an internal dynamic excitation of the traction system on the dynamic performance of a high-speed train. First, a dynamic model of the traction system is developed that considers various complex factors such as the time-varying stiffness of meshing teeth pairs and the gear transmission error. The internal exciting force of the gear is taken to be the result of multiplying its meshing stiffness by its transmission error. Then a multi-body dynamics model of the motor car that includes the driving system is established. Furthermore, a field experiment at a high-speed rail line is performed. Based on the test data, the dynamic characteristics of a high-speed train are analyzed. The obtained results show that the internal dynamic excitation of the traction system can significantly influence the vertical vibration of the frame and gearbox; however, it has little effect on their lateral vibration. The sampling frequency has a major effect on the vibration amplitude of the gearbox; frequency spectrum results show that when the train runs at a high speed, the main vibration frequencies of the gearbox are the meshing frequency and its harmonic frequencies. It is demonstrated that it is necessary to take the internal dynamic excitation into account when assessing the dynamic performance of the gear transmission system.
The design and construction of a complex damping layer for rails is presented in this paper. A numerical procedure for the calculation of the loss factor of a compound track model using this treatment was developed. Through this procedure, guidelines on the selection of the optimal material and configuration among the commercially available and technologically feasible options were formulated. A vinyl ester resin-interpenetrating polymer network was chosen as the viscoelastic material for the damping layer, polyurethane epoxy resin as the material for the extra layer, and 3Cr13Mo steel as the material for the constraining layer. This study culminated in the construction of a prototype and the evaluation of its performance in the laboratory. Laboratory measurements on track demonstrated that the proposed damping approach can effectively mitigate rail vibration and noise radiation over the frequency range between 12.5 and 4000 Hz. The glue developed in this work was found to be highly reliable and efficient in reducing noise.
A method is proposed for the fatigue strength testing of the underframe of a railway vehicle car body. Fatigue strength testing of individual components of the draft gear is conducted under laboratory conditions. Loads on individual components equivalent to vehicle loads are accurately determined in these experiments. The response of the tested specimen is consistent with the partial response of the entire car body. The basic process of reproducing the vehicle’s load spectrum on the simulation test platform is analyzed in detail. The vibrational state of the car body under realistic track conditions is accurately simulated on the test platform, which allows the body to be subjected to random loads and provides a basis for the specifications of follow-up fatigue tests on the car body and its components.
The demand for freight rail transportation in North America is anticipated to substantially increase in the foreseeable future. Additionally, government agencies seek to increase the speed and frequency of passenger trains operating on certain freight lines, further adding to demand for new railway capacity. The majority of the North American mainline railway network is single track with passing sidings for meets and passes. Expanding the infrastructure by constructing additional track is necessary to maintain network fluidity under increased rail traffic. The additional track can be constructed in phases over time, resulting in hybrid track configurations during the transition from purely single track to a double-track route. To plan this phased approach, there is a need to understand the incremental capacity benefit as a single-track route transitions to a two-main-track route in the context of shared passenger and freight train operations. Consequently, in this study, the Rail Traffic Controller software is used to simulate various hybrid track configurations. The simulations consider different operating conditions to capture the interaction between traffic volume, traffic composition and speed differences between train types. A nonlinear regression model is then developed to quantify the incremental capacity benefit of double-track construction through exponential delay–volume relationships. Adding sections of double track reduces train delay linearly under constant volume. This linear delay reduction yields a convex increase in capacity as double track is installed. These results allow railway practitioners to make more-informed decisions on the optimal strategy for incremental railway capacity upgrades.
Three-dimensional random vibrations of a high-speed-train–bridge time-varying system with track irregularities are studied in this paper. The rail irregularity is regarded as a random process. By extending the pseudo-excitation method, three kinds of rail irregularity are transformed into a pseudo load vector of the coupled system. A finite element model is used to describe the bridge and a spatial multi-body mass–spring–damping model is adopted to represent a moving railway car. Monte Carlo simulations are implemented to validate the presented method. A detailed case study on the train–bridge coupled system is conducted; it is focused on the effects of three kinds of rail irregularity on the stochastic characteristics of the dynamic responses of the system. The effect of randomness on the level of safety and the riding comfort created by the coupled system are also discussed. The results demonstrate that track irregularities may have a greater impact on the transverse response of the coupled system than on the vertical responses.
The aim of this paper is to study the influence of rail flexibility when a wheel/rail wear prediction model that computes the material loss based on an energy approach is used. The wheel/rail wear model used in this investigation is a simplified combined wear hypothesis that is based on the frictional energy loss in the contact patch. In order to account for wear and its distribution in a profiled wheel surface, the contact forces, creepages and location of the wheel/rail contact points are first calculated using a fully nonlinear multibody system (MBS) and three-dimensional contact formulations that account for the rail flexibility. The contact forces, creepages and contact point locations are defined as nonlinear functions of the rail deformations. These nonlinear expressions are used in the wear calculations. The wear distribution is considered to be proportional to the normal force in the contact area. Numerical simulations are first performed in order to compare between the results obtained using the simplified wheel/rail wear model and the results obtained using Archard’s wear model with a focus on sliding when the track is modeled as a rigid body. This simplified wear model is then used in the simulation of the MBS vehicle model in the case of a flexible body track, in which the rails are modeled using the finite element floating frame of reference approach and modal reduction techniques. The effect of the rail deformation on the wear results are examined by comparing these results with those obtained using the rigid-body track model.
The design and integration of suspension parameters directly affects the riding quality of a rail vehicle. This study is intended to develop an approach to the optimization of suspension parameters of rail vehicles based on a virtual prototype Kriging model. To construct the virtual prototype Kriging model, a virtual prototype model of a rail vehicle and its suspension system was established based on a vertical model for its dynamics and using virtual prototype software. A virtual prototype Kriging model of a rail vehicle based on riding quality was also proposed, in which the training sample was obtained as different combinations of suspension parameters using the virtual prototype and dynamics simulations based on the design of experiments method. On this basis, an optimization model of the suspension parameters was established, in which the objective function was the Kriging model of the riding quality index. The optimized combination of suspension parameters was determined using the Multi-Island Genetic Algorithm. The dynamics simulation results before and after optimization for different rail profiles indicated that the riding quality was significantly improved, which demonstrated the universality and effectiveness of this approach.
An irregular geometry of the track can influence the safe passage of railway traffic. Therefore, maintenance activities on railways are mostly directed towards the correction of track geometry. It has been shown that unevenly supported and unsupported sleepers make major contributions to the effect of track geometry deterioration. In addition, irregular sleeper support conditions can contribute to ballast fouling, thus reducing its service life. Therefore, assessing the support conditions of the sleepers in a railway track is essential. This paper reviews methods that can be used for this purpose. Then, we propose a method for the assessment of sleeper support conditions and present results obtained in field investigations. The proposed method is based on sampling of the micro-tremor on sleepers and interpretation of obtained data. The obtained results prove that the proposed method is reliable and therefore usable in practice.
A computational procedure is developed in the present paper, allowing the prediction of the ballasted track profile degradation under railway traffic loading. In this procedure, an integration of the short-term and long-term mechanical processes of track deterioration is taken into account, using a track degradation model. This degradation model is incorporated into a finite element code where two modes of calculation are implemented: the "implicit mode" concerns the short-term track deterioration, in which the hypoplastic model is used for the ballast layer and the dynamic response to an instantaneous train axle passage is obtained to serve as input data for the "explicit mode", which concerns the simulation of long-term track deterioration, using the accumulation model for ballast layer. The whole procedure is illustrated on the prediction of the ballasted track profile degradation of a track section of 100 m. The results show a significant influence of the type of track geometry defects and the vehicle velocity on the evolution of track deterioration and the capability of the proposed procedure in reproducing the track profile degradation.
This paper models and analyzes the cable traction network (CTN) of a novel AC 110 kV-50 Hz cable traction power supply system (TPSS). First, we propose an equivalent model of the CTN that considers the charging current of the cables, in order to research the capacitance effect of the CTN. Then, three cases based on the novel TPSS are used to validate the proposed model, and to investigate the characteristics of the CTN. Simulation results show that the proposed model is effective in calculating both the charging current and the voltage on the cable system. Calculation results from case 2 show that the capacitance effect is mainly caused by the charging current flowing through the system's reactance, which consists of the reactance of the power system and the reactance of the main transformer. The reactance of the system, compensation coefficient and cable length can each influence the charging current and capacitance effect of the cable. Case 3 illustrates that the novel TPSS is very effective in supplying power and can greatly reduce the number of neutral sections; thus, it is suitable for application in future railway designs.
In trains with tread brakes, the coefficient of friction between the brake block and the railway wheel determines the stopping distance. The blocks have traditionally been manufactured from cast iron. Although these blocks have good braking capacity, their use is often restricted due to the squealing noise they emit. Tests of alternative composite block materials have been successful under summer conditions; however, in regions with snowy winters the use of such materials has been limited due to problems with braking capacity under snowy conditions. This research aims to develop a laboratory-scale test methodology for evaluating the braking capacity of tread brake materials under winter and snowy conditions. A pin-on-disc machine placed in a climate chamber was used for testing, and a block of standard cast iron was compared with blocks of standard composite materials. The results indicated that the blocks of standard composite materials generate a much smoother surface on the counter wheel and a significantly lower friction coefficient under snowy conditions. A second test series evaluated blocks of alternative composite materials, and a candidate material with low noise and a sufficiently high sliding friction coefficient was selected for further study. A third test series examining geometrical changes in the contact surface in terms of milled parallel tracks was performed; it revealed that the braking capacity under winter conditions can be increased by milling actions if the parallel tracks are properly oriented – in this case, at an angle of 45° to the sliding direction.
A nonlinear dynamic model for a rubber spring is created and subsequently used to describe the mechanical behavior of rubber mounts in the suspension system of a railroad vehicle. The characteristics of dynamic stiffness and damping relative to the applied displacement amplitude and frequency are investigated both through simulations and measurements. The model is one dimensional and is based on a superposition of elastic force, frictional force and fractional derivative viscous force. The amplitude dependence is represented by a nonlinear frictional component and a fractional derivative calculus approach is used to account for its frequency dependence. The fractional calculus approach considers previous responses in the current calculation, which results in the memory characteristics of rubber being considered. A linear elastic spring component is still needed to describe its static behavior. The least-squares technique is used to obtain model parameters from measurements, and an overall good agreement between the simulations and measurements is obtained. The model only has five parameters and represents a reasonable compromise between accuracy and computational effort, and thus, it is a suitable tool for railroad vehicle dynamics analysis and simulation.
The railway sleeper, an indispensable component of most railway tracks, is made in diverse materials and geometric forms. Apart from sparse information on their mechanical behaviour, little has been documented about how different sleepers perform as regards track settlement. Box tests have been undertaken to investigate the performance of sections similar in geometry or material composition to some sleeper types used in the railway industry. In tandem, the effects of ‘soft’ and ‘stiff’ under sleeper pads (USPs) were also investigated. Resulting permanent settlements showed that with no USP, the steel section performs better than other sleeper sections. The USPs have, in general, been shown to reduce settlement and more importantly negate the differences between different sleeper sections, suggesting that the sleeper–ballast interface is an important variable for track performance prediction.
A numerical method for the calculation of the frequencies of vibration of a car body on a high-speed electric multiple unit train with under-chassis-suspended equipment is proposed. In addition, the design of the parameters of the suspension system for the equipment is presented; it is based on the principles of mode matching, transmissibility matching, and consideration of the optimal vibration of both car body and equipment. It is shown that by tuning the suspension stiffness, the first vertical bending frequency of the car body displays a frequency-hopping phenomenon. The first vertical bending frequency of the car body can be enhanced by optimizing the suspension parameters, so as to suppress the vibrations of both the car body and the suspended equipment.
This study examines the economies of scale and the determinants of rolling stock maintenance costs for 24 urban rail transit operators. The estimates reveal significant returns to scale in maintenance for both per car and per car kilometre. The econometric analysis also provides statistically significant cost elasticities for wages and staff hours, suggesting substitution effects between factors. Staff outsourcing is found to significantly decrease costs, whereas higher levels of fleet availability at the peak and rolling stock failures increase it. The effect of the age of rolling stock and the network is negligible on rolling stock maintenance costs; however, the analysis reveals a downward trend in rolling stock costs among the metros in the CoMET and Nova consortia.
The construction of non-ballasted slab railway track on existing subgrade soils, or on embankments, is at an early stage of development on Chinese railways. Developing appropriate standards for the allowable amount of subgrade differential settlement that takes into account the dynamic response of the train–track system is one of a number of issues that need to be addressed. To inform the development of such standards, a model based on the theory of vehicle–track coupling dynamics, which considers the weight of the track structure, was created to investigate how differential settlement, in terms of the amplitude, wavelength and position of the settlement along the track, can affect various railway performance-related criteria, including ride quality, stability, vehicle safety and potential damage to the wheel of the train and the rail (i.e. forces at the wheel–rail contact and in the fasteners). The performance of the model was favorably compared with other widely used models described in the literature. The analysis of the study to inform design standards using the developed model demonstrated that the magnitude of the differential settlement influences passenger comfort the most compared with other performance criteria. For the considered CRTS I track, there exists a particular wavelength (8 m for the specific conditions considered) that results in all measures of performance being at their maximum values. Furthermore, the longitudinal position of the settlement waveform in relation to the joints between two concrete slabs, a factor which is not considered in design standards, was shown to influence component deterioration, passenger comfort and safety. The greatest propensity to cause component damage occurs when the beginning or end of the differential settlement waveform corresponds with the inter-slab joint of a concrete base. Accordingly, it is recommended that current design standards should be modified to specify appropriate combinations of amplitude, wavelength and position of the differential settlement to give acceptable measures of performance.
The stiffness and damping of railpads in a railway track are affected by changes in the temperature of the surrounding environment. This results in the rolling noise radiated by trains increasing as the temperature increases. This paper quantifies this effect for a ballasted track equipped with natural rubber railpads and also studies the behaviour of a cork-reinforced rubber railpad. By means of measurements in a temperature-controlled environment, it is shown that the shear modulus of the natural rubber increases by a factor of six when the temperature is reduced from 40 ℃ to –20 ℃. The loss factor increases from 0.15 at 40 ℃ to 0.65 at –20 ℃. The shear modulus of the cork-reinforced rubber increases by a factor of 10, and the loss factor shows the typical trend of transition between rubbery and glassy regions. The railpad stiffness estimated from decay rate measurements at different temperatures is shown to follow the same trend. Field measurements of the noise from passing trains are performed for temperatures between 0 ℃ and 35 ℃; they show an increase of about 3–4 dB. Similar results are obtained from predictions of noise using the measured dependence of pad stiffness.
The quality of track geometry is an important aspect in railway engineering, as it reflects any deviations and thus the actual condition of a track. Monitoring and prediction of a relevant geometry quality parameter provides an opportunity for effective maintenance, thus creating the advantages of extending the life of the asset, reducing maintenance costs and minimizing possession time requirements. Effective maintenance practice requires a good understanding of the behaviour of track structures over time and also prediction of its condition using only a few inputs. This paper presents a grey-system-theory-based model for predicting track irregularity. Three variants of the grey model are presented and their performances are compared with simple linear and exponential models. Regression models and the grey-system-theory-based models are used to obtain the standard deviation of the longitudinal level from a series of geometry inspection data. The overall performances of the models are evaluated in terms of the regression and prediction accuracies, and it is shown that a Fourier series modification of the grey model has the best performance and the minimum error. The contribution of this paper is the creation of a prediction model for track geometry quality, which is essential for planning and scheduling of preventive geometry maintenance.
This paper presents an analysis of railway research carried out in the UK, coupled with interview data from those with active experience of rail research. The aim of this work is to better understand the impact of research in order to identify key factors that influence successful implementation of outcomes, or present barriers to the development and adoption of rail innovation. The paper introduces the innovation context experienced by the rail sector, comparing it with other industries leading to a discussion of research gaps. Data was collected using interviews with industry research experts combined with an analysis of a sample of case studies, dating primarily from 1988 onwards. These data were assessed against three analytical frameworks: barriers and enablers, research process and research impact. Particular emphasis is placed on how research in the rail sector does not always follow the linear process typified by Technology Readiness Levels. The results of this exercise are then discussed leading to the conclusions including the definition of mechanisms that, if followed, could lead to maximising uptake of railway research.
The performance of the pantograph–catenary system plays a significant role in determining the reliability and safety of a high-speed train. With an increase in train speed, repeated separations between the pantograph and catenary result in an increased number of arcing events, which exacerbate the levels of damage on the pantograph–catenary system, leading to frequent train accidents. The arcing event is a complex phenomenon that is influenced by various factors, and involves interactions between the electromagnetic, thermal and airflow fields. The high temperatures generated by an arc result in ablation of material in the pantograph–catenary system, thus reducing its life expectancy. In order to investigate the mechanism of this damage to the pantograph–catenary system, a model of the arcing phenomenon is established and analyzed. In the proposed model, a set of arc plasma conservation equations are solved to determine the temperature distribution in the arc. The influences of different experimental conditions on the characteristics of the arc and the temperature distributions in the catenary wire and pantograph strip are calculated and discussed. Finally, the results obtained in the simulation studies are compared with realistic arc images recorded using a high-speed camera, and a good agreement is found.
This paper discusses the possibility of using computational fluid dynamics (CFD) to assess the influence of aerodynamic forces (aerodynamic uplift) on the mean contact force acting between a pantograph and the contact wire. The analysis consists of experimental tests and CFD simulations, performed in both wind tunnel and on-track scenarios. A method for the computation of the aerodynamic uplift and for the assessment of the contact force imbalance between the leading and trailing collectors is proposed. The method is based on the virtual work principle, and exploits both the numerical forces resulting from CFD analysis, and the Jacobian terms obtained from a kinematic analysis of the pantograph. The proposed model takes into account stationary phenomena, and it is fully validated by means of experimental results.
Tonal squeal noise (i.e. the high-amplitude singing of a railway wheel with pure tone components) is emitted by some trailing inner wagon wheels on heavy haul trains traversing 1000 m radius curves on the iron ore export line in South Africa. Field measurements have shown that the trailing inner wheels that squeal are subject to predominantly longitudinal creepage with little-to-no lateral creepage. The longitudinal creepage acting at the contact of the squealing wheels exceeds 1%, which supports the likelihood of creep saturation and subsequent squealing due to unsteady longitudinal creepage in the large-radius curves. Experimental modal analysis of the wheel types identified to be relevant to squeal has revealed that for each unstable frequency, two eigenmodes are likely to be important: one that has a large mode shape component at the wheel–rail contact in the circumferential direction and another that has a large mode shape component at the wheel–rail contact in the radial direction. A frictional self-excitation mechanism based on mode-coupling is favoured as being responsible for squeal excited in large-radius curves.
Transition zones are constructions intended to provide smooth passage of a train, when moving from a track supported on an embankment to a track on a stiff structure, such as a bridge, tunnel or culvert. The design of transition zones is based on creating a gradual stiffness variation between the free track and the stiffer structure. In the Netherlands, the standard transition zone design consists of placing a concrete approach slab before and after the structure. In the present paper, the performance of a typical transition zone is assessed, by means of numerical analysis. After validation of the results it is shown that the presence of a concrete slab, combined with the fact that the sleepers are hanging, causes a stress redistribution towards the free end of the approach slabs. This aggravates the long-term deformation of the soil and increases the differential settlement under normal train speed. A critical train speed is identified for the transition zone.
This paper deals with the effect of door width on the passenger flow time on Korean urban railways using analysis of covariance (ANCOVA) and regression analysis. All regression coefficients are statistically significant in both analyses. The ANCOVA results show that increasing the door width can be quite useful in reducing passenger flow time. Regression analysis, which controls for other independent variables, also shows a clear relationship between door width and passenger flow time. In an additional regression model, we consider the interaction between door width and the number of boarding passengers. This paper also compares flow times estimated through two different methods: laboratory experiments and live railway observation, and finds no significant difference between the two approaches.
Aerodynamic noise can be a significant problem in the operation of high-speed trains; its prediction is difficult to achieve in an industrial context. The aerodynamic and aeroacoustic behaviour of the flow past a simplified high-speed train bogie at scale 1:10 is studied in this paper; the utilized approach is a two-stage hybrid method that consists in computational fluid dynamics and computational acoustics studies. The near-field unsteady flow was obtained by numerically solving the Navier–Stokes equations with the delayed detached-eddy model and the results were used to predict the far-field noise using the Ffowcs-Williams – Hawkings method. The sound radiated from the same scaled bogie model was measured in an anechoic open-jet wind tunnel. The aeroacoustic characteristics of tandem wheelsets were also investigated for comparison purposes. It was found that the unsteady flow past the bogie is characterized by coherently alternating vortex shedding from the axles and more randomly distributed vortices of various scales and orientations from the wheels and frame. The vortices formed behind the upstream geometries move downstream due to convection and impinge on the downstream bodies, generating a highly turbulent wake behind the bogie. The noise predictions correspond fairly well with the experimental measurements for the dominant frequency of tonal noise and the shape of spectra. Vortex shedding from the axles generates tonal noise, with the dominant peak corresponding to the vortex-shedding frequency. The directivity exhibits a dipole shape for the noise radiated from the bogie. Compared with the wheelsets of the bogie, the noise contribution from the bogie frame is relatively weak.
High-density railway lines experience a high rate of deterioration on the running surface of the rails; it can be addressed by rail grinding in order to reduce the frequency of rail replacement. Rail grinding includes additional complex features beyond what is usually considered in conventional grinding. Although extensive empirical experience exists to describe rail grinding, it can still be considered to be an emerging field that is in need of predictive theoretical guidance. This paper presents a newly developed modeling approach that is intended to provide a theoretical understanding of the rail grinding process and allow the prediction of rail grinding behavior and performance. The modeling is a bottom-up approach that starts from individual cutting grains and builds up to the rail grinding train level. First, grain distribution modeling is used to build a uniform template for the grinding simulation, based on the assumption of spherical grains with normally distributed sizes. Second, one representative slice is extracted as a grinding surface with stable grains. Protrusion heights and spacing distances of the cutting grains are analyzed to obtain the features of the grinding surface. Then the spherical grains are transformed into decahedrons with arbitrary poses, so as to closely approximate the actual surface of a grinding wheel. Third, the interactions of the cutting grains are combined into a model of a single grinding wheel and compared to test results from a single-wheel test. This allows for the connection between the utilized grinding parameters and the grinding results to be isolated, which is validated with supporting experiments performed on a single wheel. The individual wheel relationships can be combined into a full multi-wheel grinding pattern for estimating the simulation results of a multi-wheel grinding train. Eventually, the comparison between the simulations and grinding tests is used to show the effectiveness of the predictive rail grinding modeling at the level of a rail grinding train.
The existence of zones along a railway line that have abrupt changes in the vertical track stiffness is a well-known phenomenon. It results in the need for constant maintenance activities to keep the quality of the track within an acceptable range; which, in turn, increases the operational and maintenance costs of the line. The causes of these zones are related to features in the superstructure and infrastructure of the line. This longitudinal variation results in the creation of longitudinal heterogeneity in the value of the vertical track stiffness. To deal with this problem, a new design is proposed in this paper that is focused on different infrastructure components. A three-dimensional finite element model of a section of railway track is developed in order to analyse the behaviour of both superstructure and infrastructure in response to the passage of railway loads. The proposed model, and hence the new design, is applied to a real Spanish high-speed rail line that is being constructed between Lemoa and Galdakao in the Basque Country. This line goes through an area with a complex topography and it is projected that about 70% of its length will occur in tunnels or on bridges. This characteristic is used to show the advantages and applicability of the proposed cross-section design to achieve a better homogeneity in the value of the vertical track stiffness and, therefore, to reduce the consequences (from a technical and economic point of view) of this variation on the operation of the line.
Travelling by rail is considered to be a safe option compared with other types of transport, in terms of the number of accidents. However, there are always opportunities to improve the current safety standards and industrial practices. The aim of this paper is to give a better understanding of the current modelling techniques that could support the design of new railway vehicle structures. The paper highlights the established practices in modelling of proof, fatigue and crashworthiness. It also reviews the state-of-the-art in the modelling of material behaviour, recommends practical modelling solutions that can be used in the railway industry, and demonstrates new modelling techniques for crashworthiness.
This paper investigates the energy absorption and dissipation pattern in train-to-train collisions. For this purpose, simplified scaled rail vehicle models were designed based on the energy-absorbing characteristics of honeycomb-based structures under static loading, and scaled tests were performed under dynamic loading. In this study, a one-eighth-scale model of train-to-train collisions for a three-car set was tested, and the corresponding displacement–time and velocity–time curves were obtained. The extents of energy absorption and dissipation were also calculated. Also, finite element simulations were conducted to simulate one-eighth-scale train collisions for three-car, five-car and eight-car sets. The finite element numerical simulation of scaled train collisions produced results that were consistent with experiment results. The simulation results also indicated that train sets do not significantly affect energy absorption and dissipation pattern. The energy-absorbing structure at the front of a train plays a major role in the collisions. Moving cars absorb slightly more energy than stationary cars in both the scaled test and finite element simulations.
In order to improve the dynamic performance of high-speed locomotives, an active control method for the movement of a suspended motor is proposed, in which a damper is replaced by an actuator. A simplified mechanical model of the flexible suspension system is established to study its dynamics and create an active control strategy. Then, a multi-body dynamic model of the locomotive is simulated to obtain the conditions for optimal control. The results show that a smaller damping of the lateral suspension is conducive to improving the dynamic performance of the locomotive; the system has a theoretical optimum damping ratio of between 0.1 and 0.3. A small level of damping results in a large lateral displacement of the suspended system, which cannot be allowed to occur due to space limitations. The optimal control is used with the aim of reducing the lateral vibration amplitude of the suspended motor system and bogie frame. The active control of the suspension system improves the lateral dynamic performance of the locomotive and effectively limits the lateral displacement of the suspended system relative to the bogie frame. Compared with a passive suspension approach, the lateral forces on the wheelset are reduced by up to 25% at speeds between 140 and 180 km/h on straight track, and the nonlinear critical speed is increased from 390 to 480 km/h.
To determine the optimal design of the rail profile for a curved segment of a heavy haul railway, an optimization method that considers the extent of rail wear over the entire design cycle was developed. The approach is based on wheel–rail rolling contact theory, vehicle–track dynamic theory and nonlinear programming theory. The changes in the rail profile were analyzed using an updating strategy that considers random irregularities in the railway track. The minimum average metal loss from the vehicle in terms of wear and grinding for the whole design cycle was regarded as the design objective, and discrete point coordinates on the rail were regarded as the design variables. A radial basis function was used to establish an approximate model, which formed an explicit function between design variables and design objectives. The optimization model was established on this basis, and a genetic algorithm was used to solve the optimization model for the optimized profile. The maximum passing gross load for the whole design cycle reached 150.74 x106 t, an increase of 139.73% compared with the standard profile, which achieved the purpose of prolonging the service life of the rail.
This paper presents qualitative and quantitative analyses of the action of points, a critical component of railway networks. They allow diagnostic and prognostic evaluations of the points using health monitoring systems, i.e. they allow the state of the system at a desired moment to be evaluated and the forecasting of the future condition of the system. The main objective is to increase the reliability, availability, safety and maintainability of these systems. A novel approach for maintenance management based on fault tree analysis is proposed. A binary decision diagram (BDD) approach is proposed for the qualitative analysis of the fault trees. The BDD obtains a Boolean expression for the fault tree. An optimal ordering of events is required in order to obtain an efficient conversion from a fault tree to a BDD, with the AND method being used for this purpose. Each event is classified based on its importance to the fault tree. It is studied using the Birnbaum and Criticality importance measures, using the Boolean expressions in order to perform accurate diagnostics and valuable prognostics on the state of the system. The presented approach allows the failure probability of the system to be determined along with importance measures obtained by considering variable time increments, e.g. shorter periods at the beginning and end of the life cycle of an event. A real case study on a set of M63 points is presented. The results provide useful information that can be used to support operations and the planning of maintenance tasks. The approach creates a methodology to establish effective maintenance planning, as it is a flexible and simple method that takes into account a nonlinear system that leads to an optimal allocation of resources. Finally, the conditions for an optimized online decision-making process are achieved.
Track geometry deteriorates with traffic flow, thus it needs to be regularly restored using tamping or other method. As the deterioration is mainly in the vertical direction this aspect has been widely studied and models for its analysis developed, however, the lateral deterioration of track is not as well understood. This research aims to develop a method that can be used to analyse and predict the lateral deterioration of railway track caused by traffic flows, and investigate the influences of different railway vehicles, running speeds, traffic types and wheel/rail contact conditions.
The goal of every public transport operator is to not only provide high-quality service, but also to minimize investment and operating costs. A significant proportion of the costs are associated with the acquisition, operation and maintenance of reserve vehicles. If the number of vehicles held in reserve is too high, an operator will incur economic losses because vehicles are underused. Conversely, if the number of reserve vehicles is too low, the quality of service will be reduced due to disruptions in the timetable. To determine the number of vehicles to hold in reserve, a coefficient of availability is commonly used. The coefficient of availability is determined by two parameters: reliability and maintainability. Both parameters have the same physical dimensions, the mean time between failures (MTBF) and mean time to repair, and they are expressed in hours. Vehicle wear, which results during the emergence of failures, is not very dependent on the time of operation but is strongly dependent on the distance travelled. It is therefore appropriate to use mean distance between failures (MDBF) instead of MTBF, because it better describes the reliability of vehicles. Using MDBF, however, means that the coefficient of availability is not considered, because MDBF and MTTR have different physical dimensions. This problem is solved by using a random vector that makes it is possible to determine the number of vehicles to hold in reserve based on the distance travelled and maintenance time. This original approach allows the acquisition of better and more authentic data necessary for an operator’s decision-making process. Therefore, the number of required reserve vehicles can be much better planned. Ultimately, this positively affects the quality of services and also the investment and operating costs of the operator.
A model of the vibration behaviour of a discontinuous slab track installed on a viaduct is presented. It is represented by a three-layer Euler–Bernoulli beam model subjected to a harmonic load. Analytical equations are derived using the receptance method, and they are used to determine the vibration properties of the system. Comparisons are made between the vibration behaviour under various parameter conditions of the Chinese CRTS I slab track and a typical floating slab track installed on a viaduct. Attention is focused on the mobility, vibration isolation and track decay rates. The results show that, as expected, the floating slab track generates significantly lower viaduct vibrations than the CRTS I slab track. A slab track fitted with a relatively stiff rail pad and soft bearing layer is recommended for consideration during the engineering design phase; appropriate choices can lead to the optimization of the vibration isolation performance of a railway track on a viaduct, thus avoiding the creation of excessive rail vibrations. It is also shown that the average response of the viaduct gives a more representative assessment of the vibration isolation effect than if the average force transmitted to the viaduct is used. Moreover, in terms of insertion loss, these results are relatively insensitive to the choice of viaduct parameters.
This paper describes the phenomenon of thermal conicity (TC) of railway wheels that occurs as the result of excessive thermal loads generated in the process of braking using brake blocks and then cooling to ambient temperature. The TC phenomenon is described using a standard BA004 railway wheel and load values derived from the TSI ‘Rolling stock’ guidelines. A methodology for determining the thermal loads created during braking is described, as well as the individual stages of the creation of a model based on the finite element method.
A design approach for a crash energy management (CEM) system for a N13-type railway passenger car used by the Turkish State Railway Company is developed in this paper. The components of the CEM system are honeycomb-structured boxes, primary energy absorbers, shear bolts, a sliding sill mechanism and a fixed sill mechanism that are located in the passenger-free space at the end of the passenger car. In order to investigate the benefits provided by the CEM system, a full-scale railway passenger car collision with a rigid wall is simulated by using dynamic/explicit finite element (FE) methods. The crushing force, secondary impact velocity, acceleration and velocity curves, and deformation modes are computed to allow a comparison of the crashworthiness performance of a passenger car equipped with the proposed CEM system with that of a conventional passenger car. Comparisons of FE analysis results show that a passenger car incorporating the CEM system has a superior crashworthiness performance to that of the conventional passenger car.
Signalling systems ensure the safe operation of the railway network. Their reliability and maintainability directly affect the capacity and availability of the railway network, in terms of both infrastructure and trains, as a line cannot be fully operative until a failure has been repaired. The purpose of this paper is to propose a data-driven decision support model that integrates the various parameters of corrective maintenance data and to study maintenance performance by considering different reliability, availability, maintainability and safety parameters. This model is based on failure analysis of historical events in the form of corrective maintenance actions. It has been validated in a case study of railway signalling systems and the results are summarised. The model allows the creation of maintenance policies based on failure characteristics, as it integrates the information recorded in the various parameters of the corrective maintenance work orders. The model shows how the different failures affect the dependability of the system: the critical failures indicate the reliability of the system, the corrective actions give information about the maintainability of the components, and the relationship between the corrective maintenance times measures the efficiency of the corrective maintenance actions. All this information can be used to plan new strategies of preventive maintenance and failure diagnostics, reduce the corrective maintenance and improve the maintenance performance.
Hydrogen used as an energy carrier is a promising alternative to diesel for autonomous railway motive power, but, globally, few prototypes exist. In 2012, the Institution of Mechanical Engineers held the inaugural Railway Challenge, in which the participating teams had to develop, design and construct a locomotive to run on 10.25 inch (260.35 mm) gauge track while meeting certain set design criteria as well as competing in operational challenges. The University of Birmingham Railway Challenge Team’s locomotive design is described in this paper. The vehicle is the UK’s first hydrogen-powered locomotive and is called Hydrogen Pioneer. The drive-system consists of a hydrogen tank, a 1.1 kW proton-exchange-membrane fuel cell stack, a 4.3 kWh battery pack and two 2.2 kW permanent-magnet traction motors. The development of the locomotive, from the original concept to the final design, and the design validation are all presented in this paper. The locomotive completed successfully all challenges through which the proof of the concept of a hydrogen-hybrid locomotive was established.
After defining energy sustainability, the authors developed a theoretical framework within which to examine relations among the vertical alignment of a heavy haul railway, the minimum energy consumption, the recoverable surplus energy, the symmetry of the grade and the line voltage stability. Thereafter, the review moved from on-board power generation, as in diesel electric locomotives, through positive and negative change agents, to external power generation, as in electric locomotives. The change agents included non-renewable liquid fuel availability; energy storage quanta, devices and systems; harmful emissions; throughput scalability; and the potential impact of hydrogen as a fuel. Ideal external generation visualises electric traction within an open system: comprising a smart grid supported by bulk electricity storage, to enable heavy haul railways to manage optimally their traction energy through symbiotic interaction with external generators, consumers and storage providers. The high cost of electricity distribution infrastructure, buoyant availability of diesel fuel, and challenges of up-scaling electrically hauled throughput tonnage, oppose that ideal. To conclude, system design will likely reflect the vertical alignment's potential to regenerate energy, its ability to recover fully instantaneously surplus energy, whether the train brake system supports electric braking priority, and whether there is equitable access to a smart grid.
With the latest developments in technology, the Automatic Train Operation (ATO) has been widely used in urban rail transit systems over the past decade. The control process used by the ATO system generally consists of two levels. The high-level control calculates the target speed according to the moving authority of the trains and the low-level control implements precise tracking on the target speed by controlling the traction and braking force. Most of the literature has only focused on the high-level control to optimize the train trajectory, but did not practically combine the low-level control of the ATO system. When the optimized trajectory is applied as the target speed, it will cause frequent switches between acceleration and braking for precise tracking and waste a lot of energy. Hence, this previous research may not be applied to practical ATO systems. In this paper, a numerical algorithm is proposed to solve the energy-ecient train control problem with a given trip time by distributing the reverse time to dierent segments. Then a method is presented for optimization of target speeds based on the ATO control principles, which guides the train to output optimized control sequences. The proposed approach is capable of avoiding the unnecessary switching and then eciently reduces the traction energy consumption of the train switches. Furthermore, case studies have been undertaken based on infrastructure data from the Beijing Yizhuang rail transit line, and the simulation results illustrate that the proposed approach results in good performance with regards to energy saving.
When analyzing a railway operation, multiple issues must be taken into account to obtain the best results in terms of safety, efficiency and flexibility. In this project, carried out in collaboration between CITEF and a European metro line, a tool has been developed and implemented. Based on the line data provided by the metro line, the signalling system (distance to go/speed signalling), the main characteristics of the rolling stock, etc., information can be obtained for modelling/modifying the line, changing or removing/inserting track circuits or even changing the maximum running speeds on those track circuits. Travel times, line frequencies, bottlenecks, and degraded conditions are also analyzed from the simulations, so that finally the best headway to be implemented on the line can be proposed for the user, who is able to know how to improve the main line features like capacity and frequency of trains. Integrating distance to go and speed signalling into the set of parameters, is another capability proposed. Fundamental information on the signalling system capacity can be obtained simply by running the algorithms designed for this task along with the changes in order to carry it out.
In this paper, novel control strategies are proposed to suppress the sloshing phenomenon in tank wagons. Surface liquid movement can cause additional oscillations in the car body, and consequently, the dynamic stability of the rail car experiences additional problems. Lateral and longitudinal surface movements of liquid are modeled and simulated. In the proposed methodology, part of the liquid is isolated in a tube in order to provide the essential inertia in passive and active vibration absorbers. The performance of different vibration-absorbing systems including the tuned mass damper, delayed resonator and nonlinear energy sink are evaluated in a variety of loading situations. Dynamic stability is measured in terms of Nadal’s criterion and the unloading quotient is determined as an auxiliary index and compared with limiting criteria. It is found that an appropriately designed and installed control system can passively absorb and locally dissipate a major portion of the kinetic energy of the car body, up to an optimal value of 65%.
The Iron Ore Line (Malmbanan) is a 473 km long track section located in northern Sweden and has been in operation since 1903. This track section stretches through two countries, namely Sweden and Norway, and the main part of the track runs on the Swedish side, where the owner is the Swedish Government and the infrastructure manager is Trafikverket (the Swedish Transport Administration). The ore trains are owned and managed by the freight operator and mining company LKAB. Due to the high axle load exerted by transportation of the iron ore, 30 tonnes, and the high demand for a constant flow of ore and pellets, the track and wagons must be monitored and maintained on a regular basis. The condition of the wagon wheel is one of the most important aspects in this connection, and here the wheel profile plays an important role. For this reason an automatic laser-based wheel profile monitoring system (WPMS) has been installed on this line using a system lifecycle approach that is based on the reliability, availability, maintainability and safety (RAMS) approach for railways. The system was prepared and installed and is being operated in a collaborative project between the freight operator and infrastructure manager. The measurements are used to diagnose the condition of the wheels, and to further optimize their maintenance. This paper presents a study of the concepts and ideas of the WPMS, and the selection, installation and validation of the equipment using a system lifecycle approach that is based on RAMS for railways. Results from the profile measurements and validation are shown. The system’s reliability during performance in extreme climate conditions, with severe cold and large quantities of snow, is presented. Then the benefits, perceived challenges and acquired knowledge of the system are discussed, and an improved V-model for the lifecycle approach is presented.
Significant increases in rail loads, as well as growing interest in providing higher-speed passenger rail services, is placing new and increasing existing demands on fastening systems and concrete sleepers. Consequently, there is a strong need to better understand the response of fastening systems and concrete sleepers to these significantly increased demands. This paper presents an experimentally validated three-dimensional (3D) finite element (FE) model of a fastening system and concrete sleeper that can be used to study and improve the design and performance of these systems. In this 3D FE model, the following mechanisms that are critical to the performance of fastening systems and concrete sleepers are included: frictional interaction between components of the fastening system; interaction between shoulders and concrete; and the plastic behavior of each component in the system. The FE model is validated using laboratory experimental tests, in which a lateral load is applied to a single concrete sleeper with two sets of fastening systems. The validated FE model is used to analyze the sleeper/fastening system under different loading scenarios involving various vertical and lateral load combinations. Both component stress and system deflection of the model are analyzed to investigate the system performance at the component and system levels. The results of the study show that FE modeling can be used to investigate the complex behavior of fastening systems and concrete sleepers.
A sustained increase in gross rail loads and cumulative freight tonnages on heavy haul railways, as well as increased interest in high- and higher-speed passenger rail development, is placing an increasing demand on railway infrastructure and its components. Rail seat deterioration (RSD) refers to the degradation of the material at the contact interface between the sleeper’s rail seat and the pad that protects the bearing area of the sleeper.
RSD continues to be identified as one of the primary factors limiting concrete sleeper service life, particularly in heavy haul operations. This paper includes results from two laboratory experiments that used test setups and protocols and were designed to isolate the abrasion mechanism. The first experiment was used to acquire quantitative and qualitative data related to the frictional properties of rail pad materials sliding on a concrete surface under various normal loads. The second experiment quantified the abrasion resistance of rail seat materials. Results confirmed that abrasion is a feasible RSD mechanism and that the frictional characteristics at the contact interface between the rail pad and concrete rail seat appear to have an impact on the transfer of forces and relative movement, and thus the abrasion mechanism. Also, the abrasion resistance of the rail seat’s surface can be improved by grinding off the top cement paste layer to expose a hard aggregate surface and also by applying an epoxy coating to the surface. Increasing the service life of railway track components will facilitate capacity building on heavy haul, mixed-traffic and passenger railways around the world by reducing maintenance costs and decreasing the demand for maintenance windows.
The key requirement to calculate the fatigue and wear levels of wheels and rails is to establish a method that can accurately represent the wheel/rail contact stress. Wheel and rail surfaces are composed of a series of surfaces each with a different curvature, which makes research on wheel/rail contact very difficult. In this paper, a wheel from a passenger train with a LM-type worn tread profile and a 60 kg/m rail are taken as the research objects in a study on the contact positions and static contact stress. An analytical model for accurately finding the contact position is established by building and solving wheel and rail profile equations. Furthermore, a slice-based model is established to calculate the contact stress of a contact point, especially for points on the profiles near the junction of two surfaces with different curvatures. The error created by using the slice-based model is corrected so as to make the calculation more accurate. An example, in which the axis load is 18 t, is analyzed. The maximum contact stress, deformation and contact spot size are calculated, and some useful conclusions are obtained. The research presented in this paper can provide a reliable foundation for future research on wheel and rail fatigue, friction and wear.
A new innovative method for track deflection and track stiffness measurement is described and used on the iron-ore line in Sweden. The method uses two different measurement systems of longitudinal level on one axle, and by comparing them in a new way it is possible to extract the unloaded level and the effect of the loading from the loaded longitudinal level. Displacement due to loading can also be interpreted as a track stiffness value if the wheel load is simulated or measured. With this method, a new approach to condition monitoring of track is created due to the possibility of monitoring stiffness and longitudinal level at the same time using a track recording car. The method has been used in an extensive measurement campaign on the iron-ore line in the north of Sweden. Many examples are given in this paper to illustrate different track defects on ordinary track, mainly on track section (bandel) 118. Hanging sleepers and mud-pumping places have been successfully located using the new method. The method has been used in both winter and summer conditions. We have found that the track stiffness/deflection level does not vary considerably with change of season. This result is explained by the design decision in the 1980s to use soft fastener pads, which seems to have been a very good decision.
This paper discusses the mechanism responsible for the formation of polygon-shaped wheels; the aim is to solve the problem of their occurrence on subway vehicles. This phenomenon occurs mainly as a result of wheel/rail vertical forces created by the vibration of the wheelset over several complete revolutions of the wheel. In addition, a relationship linking the phase angle between two adjacent vertices, the main vibration frequency and running speed of the polygonal wheel is derived. Then, considering a subway vehicle that is powered by a linear induction motor and applying the multi-body system dynamics model, the main frequency of the wheel/rail vertical force under various running speeds is investigated. Analysis of the speed and main frequency value of a subway vehicle covered in this study revealed that a polygonal wheel with nine vertices can be generated in the speed range 72 to 80 km/h.
Previous investigations have shown that an abrupt stiffness change in track support is often associated with accelerated rates of deterioration of track geometry, high maintenance demand and poor ride quality. However, at present, there is no detailed understanding of the mechanisms of the deterioration of track geometry at transition zones. This paper aims to use the discrete element method to investigate transition zones from a micromechanical perspective. A simple track transition model with dimensions 2.1 m x 0.3 m x 0.45 m was simulated by using PFC3D. In order to identify and evaluate appropriate mitigation methods, two kinds of transition patterns, including a single step change and a multi step-by-step change for subgrade stiffness distribution were tested. The influence of train direction, speed and axle load on the transition was also investigated. In addition, geogrid was used in the ballast layer to examine the effects of geogrid reinforcement. This paper provides insight into the factors that can cause or accelerate track degradation at the transition zones, in order to identify and evaluate appropriate mitigation design.
Slipstreams caused by high-speed train movement through the atmosphere pose a safety risk to passengers, trackside workers and track infrastructure. The improved delayed detached eddy simulation (IDDES) approach, an improved version of the detached eddy simulation method, is adopted in this paper to calculate the slipstream of a four-coach 1/25th-scale model of the CRH2 high-speed train. Slipstream velocities and pressures at various lateral distances from the centre of rail (COR) position and vertical distances from the top of rail (TOR) position at trackside are calculated. Numerical results are compared with measurements obtained in a full-scale test and good agreement is obtained, which verifies the effectiveness and potential of the less costly IDDES method. It is found that the velocity and pressure distributions are similar to those obtained using different train types but with different peak values related to the difference in shapes. The peak velocities in the slipstream along the length of the train are found at the tail and in the near wake region. The magnitude of the peak decreases with an increasing distance from the COR and shows a relatively high value at about two thirds of the train height from the TOR. The maximum pressure coefficients are found in the upstream and nose regions. The results show that the value of these coefficients decreases with an increasing distance from the COR and TOR. Based on the suggested safe slipstream velocity in China, the IDDES results show that for a CRH2 high-speed train at a speed of 350 km/h, the safe standing distance should be greater than 3.4 m in the lower part of the train’s slipstream (up to about half of the train height from the ground) and 2.4 m for the top part of the train’s slipstream (above half the height of the train from the ground).
Rail grinding is a key maintenance activity for Network Rail. It is performed at night through possession of the track, so process speed is critical. Increasing the metal removal rate (MRR) of the rail grinding operations would be a way to improve the time taken for this operation. The aerospace industry has recently seen advances in grinding technologies that have increased MRR. This work was aimed at assessing their best practice and its application to rail grinding operations.
Current Network Rail grinding operations include preventative and corrective re-profiling of the rail head. The majority of work performed in the UK is preventative re-profiling with current train speeds ranging from 1 to 10 mile/h. Opportunities exist to increase train speed and improve the productivity of this operation through the use of more advanced grinding technologies.
The most relevant aerospace technology is high efficiency deep grinding (HEDG). This approach uses: a high surface speed of the grinding wheel, superabrasive tooling, and high workpiece feed rates to remove material quickly from the cut-zone. Productivity improvements were identified by applying theory on power requirements (by assessing the specific grinding energy) and chip thickness of the grinding process. Computer CAD/CAM modelling was also performed to assess the effect of changing grinding techniques on potential gouging of the track infrastructure and/or interference with example trackside obstructions.
The work concluded that opportunities do exist to improve the current productivity of grinding operations. Utilizing HEDG technology theoretically provides a 100% train speed increase (utilizing the same power available with the current setup) for preventative re-profiling. This requires the application of high surface speeds of the grinding wheel and superabrasive technology. Further increases in train speed require increased spindle power. The chip thickness experienced by grinding grains is reduced for a peripheral grinding setup and high wheel surface speeds that is beneficial for wheel wear. The application of HEDG technology cutting on the periphery of the wheel provided optimum conditions during CAD/CAM simulation to avoid rail gouging, and any potential collision of the grinding stone with modelled trackside obstructions.
With the development of high-density intercity railway networks, substantial investments are now required, in terms of labor and machinery, in order to be able to conduct safety inspections. This results in high operational costs. High-capacity and high-speed operations have resulted in levels of damage and deterioration of railway system components that have surpassed all expected values. Thus, traditional methods of periodic inspection, though still necessary, are no longer sufficient to detect the rapid development of defects on railway systems. Therefore, the direct use of operational trains as inspection vehicles to detect defects in real-time has become a current trend in the development of inspection techniques. This study applies an inspection technique previously reported in the literature to on-site testing of track. The response to vibrations on railway bridges, track system components and track irregularities are also studied. The effects are analyzed using the Hilbert–Huang transform approach. It is shown that the proposed data analysis method can be used in conjunction with the routine operation of trains to create a method for the monitoring of track defects.
Sleepers play an important role in determining the performance of rail tracks. The level of this importance can be gauged by noting the large number of sleepers that are located on railway tracks (1700 sleepers per kilometer of main line track). Reducing the life cycle costs of railway sleepers, as a result of decreasing construction, maintenance and operation costs, can have a significant economic effect on the cost of operating track. In this regard, the use of novel materials to construct high-strength sleepers is of considerable interest. Blast furnace slag, especially iron slag, can be crushed and used as an aggregate in the concrete used to produce sleepers. In the present study, slag and limestone sand was used to create a slag-containing concrete that was subsequently used to produce sleepers. The results of laboratory tests on slag-containing concrete showed a 46% increase in compressive strength compared with non-slag-containing concrete. The ratio of tensile to compressive strengths of all the slag-containing concrete samples varied between 0.06 and 0.087, which is comparable to the range of 0.1 to 0.15 for non-slag-containing concrete. Negative moment tests performed on sleepers manufactured from slag-containing concrete required a 30% increase in the vertical load to initiate the first crack compared with a sleeper produced from non-slag-containing concrete. These preliminary results suggest that a new generation of high-strength sleepers can be created; the long-term efficiency of this type of sleeper will need to be confirmed by durability tests and practical use.
Preventing railway vehicles from derailing is an important issue for the rail industry. Also important is minimizing the outcome of a derailment by formulating post-derailment measures to limit the extent to which railway vehicles deviate from the track. In this paper, two kinds of post-derailment devices are designed and then validated using derailment experiments performed in the laboratory. The derailment experiments are performed on a derailment test bench designed by the Traction Power State Key Laboratory. To design the\ post-derailment devices, a half-car derailment test without any post-derailment device is conducted to understand the dynamic behaviour after a derailment. Then devices that can be mounted under the axle box to limit the lateral displacement of the vehicle during the derailment are designed on the basis of the observed dynamic behaviour. A theoretical analysis is used to derive the relationship between the mounting position and the initial conditions of the derailment. Finally, the two devices, which have different mounting positions, were verified in derailment experiments. The verification results indicate that a device with a reasonable mounting position can limit the lateral displacement of the vehicle and reduce the consequences of a derailment. Also, in order to avoid the fastener area, the distance between the device and the wheel needs to be larger than 180 mm.
The paper illustrates how damage patterns in the form of rolling contact fatigue (RCF) on wheels, can be employed to identify and improve underlying operational conditions. The focus is on RCF of locomotive wheels operating on the Iron Ore Line in northern Sweden and Norway. Seasonal changes and damage patterns are charted. Potential root causes for observed damage patterns are identified and investigated. Mitigating actions are proposed and the efficiency of implemented actions is quantified.
Railway turnout systems are one of the most important components of a railway’s infrastructure. Their geographically distributed nature makes failure detection, forecasting and maintenance planning extremely important. Prognostics, forecasting the time to failure in order to achieve effective maintenance planning, has attracted increasing attention from industry and researchers in recent years. The prognostic approach has great potential to achieve reduced costs and increased availability. However, the applicability of any engineering model requires economic and practical justifications. This paper presents an analysis of different prognostic methods for railway turnout systems. Five different sensors, installed in a real turnout system used on Turkish State Railways, are individually analysed by applying various prognostic methods. This paper aims to guide practitioners on the application of prognostics and health management technologies to railway turnout systems by discussing the advantages and disadvantages of using different sensors and prognostic methods.
With the development of subway systems, the utilization of regenerative braking energy has become an important issue. Focusing on the dynamic coordination of trains when regenerative braking energy is available, this paper proposes a new strategy, in which the regenerative energy generated by braking trains is used directly by accelerating trains. First, a mathematical model is formulated to optimize the metro timetable to maximize the utilization of regenerative braking energy. The model is a nonlinear integer programming problem that searches for the optimal headway and dwell time at each station. Furthermore, a simulated annealing algorithm is used to solve the optimal timetable. Finally, the Island Line of MTR (the mass transit system in Hong Kong) is taken as an example to illustrate the efficiency of the model and solution method. The results show that the utilization of regenerative braking energy can be improved by between 4 and 12% depending on the energy conversion rate. It is shown that a larger energy conversion rate results in a larger improvement.
Signal cables on Chinese heavy haul railways are often observed to have been burnt and damaged; this can cause the failure of signalling systems and can lead to accidents. In this paper, a theoretical analysis and laboratory-based test bench experiments are presented to investigate the cause and mechanism of this burning phenomenon. First, a laboratory simulation test bench is designed, to test actual cables under man-made conditions and intermittent conduction between the iron trough and. steel armour The phenomenon reproduced in the test shows good consistency with field observations and data on voltage and current levels is recorded for testing validation. A quantitative analysis of this phenomenon is carried out using Cassie and Mayr arc models on a high-current area and a zero-point-crossing area, respectively, with a comparison of the calculated and measured data being subsequently performed. Based on the characteristics of the test results, it is verified that a possible cause is an electric arc. Finally, solutions to mitigate the phenomenon are proposed, based on the analysis of the mechanism of the creation of the electric arc and how it damages the signal cables.
As fossil fuel resources decrease and their price correspondingly increases, finding a suitable alternative source of energy is a priority in all countries. This case study predicts the amount of energy that can be generated by photovoltaic cells mounted on the roof of a passenger coach moving on the Kerman–Tehran rail line in Iran under various conditions such as different months, hours and train speeds. The energy gain is calculated using an isotropic solar model and data on the levels of radiation incident on a horizontal surface at Kerman, Yazd, Esfahan, Qom and Tehran. These cities are located on the Kerman–Tehran rail route. The results show that departure time and speed of the train play a significant role in determining the amount of energy created by the photovoltaic panels.
The objective of this study is to investigate the effect of hardness and contact stress on wear and damage behavior of wheel and rail materials using a rolling-sliding simulation facility. Furthermore, the hardness matching and damage mechanism of wheel and rail materials are explored and clarified using several techniques. The wear weight of wheel rollers increases nearly linearly with the hardness ratio of rail and wheel rollers. However, the wear weight of rail rollers linearly decreases at the same conditions. An increase in the hardness of the wheel material results in the damage mechanism of the wheel roller changing from small pitting and adhesion wear to delamination wear. Then the rail roller shows severe shelling damage. Practically, the matching of the hardness of wheel and rail materials shows significant potential for alleviating wear and surface damage. An increase in the contact stress results in the wear of wheel and rail rollers becoming more severe. The damage mechanism changes from small shelling to serious delamination damage and oxidation wear. The main compositions of wear debris are the oxide Fe2O3 and martensite. Accordingly, decreasing the contact stress is an effective measure for alleviating wear and damage of heavy-haul wheel and rail materials.
This paper discusses the state-of-the-art procedures obtained in the research projects performed by Delft University of Technology and ProRail, together with other partners and experts, such as Netherlands Railways, to optimize the wheel/rail interface on the Dutch rail system. The wheel/rail interface has been the focus of a significant number of research projects and improvement measures in the Netherlands over the last 10 years. ProRail’s rails are subjected today to a ‘stress regime’, with high friction and loads from their operation, certainly since the introduction of new rolling stock and new rail types. This has resulted in cracks and premature loss of rail life due to rolling contact fatigue (RCF), particularly in curves and turnouts. Once damage occurs, it accelerates the degradation of track. This can be avoided by grinding that introduces artificial wear and moving more towards a ‘wear regime’, where initial cracks do not ‘survive’ and do not have the possibility to initiate and grow to form deep defects. Following this philosophy, a preventive gradual grinding strategy has been implemented to remove developing fatigue damage. Also, resistance to stress and avoidance of stress on the rails have been identified as possible strategies. This has led to various developments. A new ‘anti-head check’ rail profile (54E5) and use of new rail steels have led to reduced contact stresses and RCF initiation. Wheel/rail interface conditioning is being introduced to reduce noise and contact stress using on-train applicators. Wheel profiles have been optimized based on the new 54E5 profile and ongoing research focuses more and more on a holistic approach to wheel, rail and bogie design. This paper presents key projects and outcomes of the RCF research programme.
Many railway assets, such as wheels, suffer from increasing deterioration during operation. Good condition monitoring based on good decision-making techniques can lead to accurate assessment of the current health of the wheels. This, in turn, will improve safety, facilitate maintenance planning and scheduling, and reduce maintenance costs and down-time. In this paper, wheel/rail forces are selected as a parameter (feature) for the condition monitoring of wheel health. Once wheels are properly thresholded, determining their condition can help operators to define maintenance limits for their rolling stock. In addition, if rail forces are used as condition indicators of wheel wear, it is possible to use measurement stations that cost less than ordinary profile stations. These stations are located on ordinary tracks and can provide the condition of wheelsets without causing shutdowns or slowdowns of the railway system and without interfering with railway traffic. The paper uses the iron-ore transport line in northern Sweden as a test scenario to validate the use of wheel/rail forces as indicators of wagon and wheel health. The iron-ore transport line has several monitoring systems, but in this paper only two of these systems will be used. Wheel/rail force measurements are performed on curves to see how the vehicle negotiates the curve, and wheel profile measurements are done on tangent track not far away. The vehicles investigated are iron-ore wagons with an axle load of 30 tonnes and a loaded top speed of 60 km/h. The measurements are non-intrusive, since trains are moving and assets are not damaged during the testing process.
Subways, one of the most popular modes of the rapid transit systems, play an important role in maintaining the sustainability of transportation in large metropolitan areas. This study focuses on the optimum dimension of the internal diameter of subway tunnels that creates a space for train passage that is large enough to preventing collisions with electromechanical and wayside facilities and emergency walkways and is small enough to minimize costs. The discussion hinges around how a train in the worst-case situation of a super-elevated track with a minimum curve radius can pass through a tunnel equipped with wayside facilities without any accidents while satisfying all the economic aspects of the project. Limiting the speed of a train in response to the confined area between a train’s dynamic envelope and emergency walkways leads to extended travel times, excess wear on the wheel and rail and even changes in the amount of electricity consumed by the train. All the mentioned factors result in an operational cost and the total cost is achieved by summing up this cost and the construction costs for different tunnel diameters. An economic analysis is performed by comparing the costs of construction and operation for different tunnels against the benefits of passenger revenues. Generating net-present-value diagrams for tunnels with different internal diameters as a function of time shows that a double-tracked single-tube tunnel with an 8.40-m internal diameter is the optimum from both an economic point of view and being able to match technical specifications.
The conventional crosswind stability analysis of high-speed trains is based on a deterministic approach with the final output being a characteristic wind curve (CWC). The CWC only provides the dividing line between the safe state and failure state of vehicles, thus it cannot be used to evaluate the overturning probability of vehicles subjected to strong winds. To overcome this shortcoming of the conventional CWC, a fuzzy stochastic approach is proposed that can make an effective assessment of the operational safety of high-speed trains exposed to stochastic winds. According to this methodology, the uncertain parameters existing in the system such as stochastic winds and aerodynamic coefficients are modelled as basic random variables, and the failure of the structure is considered as a fuzzy random event. An algorithm for computing the unsteady aerodynamic loads of high-speed trains exposed to stochastic winds is created and then the aerodynamic loads are applied to a dynamic model of the vehicle system in order to investigate the dynamic response. Importance sampling is used to conduct an analysis of the crosswind stability of high-speed trains based on fuzzy random reliability theory. This finally leads to the substitution of the conventional CWC by probabilistic characteristic wind curves (PCWCs). The conventional CWC is shown to be over-conservative, while the PCWCs can provide more significant reference for the safe operation of high-speed trains.
To relieve the traffic pressure in a subway system, in reality, increasing train frequency, improving train capacity and applying express trains, are three practical organization strategies. In this paper, we compare these three strategies by using four evaluation indexes, including accumulated congestion degree, loading ratio, passenger volume and energy consumption in one direction during one hour. Moreover, in order to determine the optimal strategy, an ideal-point compromise approach is employed in this paper. Specifically, for investigating the passenger flow and energy consumption in aforementioned strategies, we provide variation models for passenger flow in a subway system with fuzzy passenger arrival rates and alighting ratios. By using the operational data from Beijing Yizhuang subway line, we conduct extensive case studies to illustrate the performance of different strategies.
In the rail industry, the important design parameters of rubber suspension systems are currently solely based on the loading part of the loading/unloading history, e.g. the load–deflection characteristics and fatigue requirement. Different energy levels and stress values are created for an identical load value during loading and unloading cycles in rubber-like materials. Hence, the performance of a rubber suspension can be substantially different during loading and unloading, which can lead to unexpected effects. An engineering approach is proposed to account for this so-called Mullins effect. Existing elastomeric models, widely used in rail vehicle design, can be modified to account for the unloading using this methodology. A typical rubber-to-metal bonded component, which is used in rail suspension systems, is selected for a verification study. It is shown that the predictions from the new approach are consistent with the results of the whole load/deflection history obtained in a laboratory experiment. In addition, if the unloading characteristics are not considered, results obtained from stress calculations can have a 20% margin of error. The proposed approach should be further verified using other types of rubber suspension systems.
The reasons for wear of a wheel to create a polygon-shaped wheel on metro trains are analysed in this paper. Analysis of wear data leads to the conclusion that it is mainly structural vibration of the wheelset that causes the wear that creates polygon-shaped wheels. After analysing the characteristics of the structure and vibration of the vehicle, a model that considers wheelset flexibility is established. We then analyse the effects of flexible deformation of the wheelset on vertical force, creepage and creep force in wheel/rail rolling contact, and find that the main wheel wear frequency is 35.98 Hz. As for the question of how many faces the worn polygon-shaped wheel displays, we propose that the nature of the wear to create the polygon-shaped wheel depends on the average running speed of the vehicle. This relationship accounts for the apparent contradiction of a fixed vibration frequency and variable vehicle speed leading to wear to create a polygon-shaped wheel, and shows how a multi-faced polygon can be caused by a low-frequency vibration between wheel and rail.
This paper presents a study of the parameters that influence the detection of squats when using axle box acceleration (ABA) measurements. The analysed parameters include the train speed, the location of the squat in the track relative to the sleeper, and the track design. The study is conducted relying on a validated finite element model. The ABA measurements are found to be highly influenced by train speed. To model this influence, a practical method is proposed to represent the relationship between the train speed and relevant characteristics of ABA (magnitude and frequency) at a given squat. Such practical relationships provide the opportunity to map the ABA signals when it proves impossible to run measuring trains at a constant speed (as is the case with any in-service railway vehicle). The parameter study also indicates that the major frequency characteristics of ABA at squats are strongly related to the natural frequencies of the track. This conclusion is validated by performing hammer tests on the railway track. It is suggested that a proper characterization of the tracks will lead to a better understanding of the ABA signals. Finally, it is claimed that the results presented in this paper can be used as a guideline to calibrate or improve squat detection algorithms based on ABA measurements on a track.
The Swedish iron ore company LKAB uses freight wagons with three-piece bogies to transport iron ore from its mines in Kiruna and Malmberget to the ports at Luleå and Narvik. A simulation model of the freight wagon is built using the multibody simulation code GENSYS. The objective is to investigate possible sources of rolling contact fatigue (RCF) of the wheels given the high level of observed damage. A parameter study is performed on the effects of vertical track stiffness and viscous damping that occur as a result of seasonal variations of the track condition. Another parameter study is carried out on the influence of the wheel/rail friction coefficient as in winter time the climate is very dry along most parts of the Malmbanan line. The impact of track gauge, track quality and cant deficiency on RCF is also studied. Comparing the calculated and observed RCF locations on wheels, attempts are made to find a relation between wear number and RCF damage. To detect the surface-initiated fatigue a so-called shakedown map is used. It is shown that RCF occurs on the tread of the inner wheels while negotiating curves with below an approximately 450 m radius. It is also shown that cant deficiency can be helpful for the vehicles to negotiate curves and to reduce the risk of RCF, however, on the other hand it may increase the track forces and in severe cases result in flange climbing. Lateral track irregularities and a large track gauge result in small contact areas and can lead to a higher risk of RCF. In cold dry climate conditions, as the water content in air drops significantly, the wheel/rail friction coefficient increases and when the material in the wheel begins to behave in a brittle manner, the risk of RCF is significantly increased, especially when the wear rate is not high enough to remove the initiated cracks.
Recent rail rollover derailments motivated this investigation. The wheel/rail forces under seven track/rail conditions were measured at a curve of a heavy haul line. The investigation indicated that combinations of reverse rail cant, weak rail restraint, poor truck steering and poor wheel/rail contact can increase the risk of a rail rollover derailment. This investigation reaffirms the findings from previous rail roll studies and further stresses three important issues related to track maintenance practice. First, track maintenance tasks that involve changing track gage or rail orientation can have the unintended consequence of causing adverse wheel/rail contact, resulting in large lateral forces. Rail grinding should be coordinated with the restoration of rail cant to correct wheel/rail contact patterns. Second, restoring and restraining only the high rail has a high risk of causing a rollover derailment from the low rail. Third, rail grinding cannot be properly conducted on a track that has weak rail restraint and variable levels of reverse rail cant.
A closed-form displacement response of track subjected to loads moving at variable speeds is proposed in this paper. The structure of the track is modeled as a Timoshenko beam of infinite length that is periodically supported by double-layer spring-damping elements. The frequency-domain displacement response of the track is simplified into the mathematical form of a summation rather than an integral. The transfer function for the track is expressed in the form of a transfer matrix. Various kinds of moving loads, such as single and series moving forces, masses and double-layer mass systems, are considered in calculations. For the verification of the theory, the displacement response of a simply supported beam subjected to masses moving at variable speeds is calculated and compared with reports in the literature on the same case. The obtained results indicate that the influence of the loads moving at variable speeds on the displacement response of the track cannot be ignored, and the displacement response of the track increases slightly with acceleration of the moving loads. Also, larger oscillations are generated by the interaction of the moving mass and the track.
This paper presents two types of extended Kalman filter (EKF) and two types of unscented Kalman filter (UKF) based on vertical railway vehicle models for parameters estimation of secondary suspensions. Due to track irregularities, the random vertical velocity of the track can be approximated as a zero-mean Gaussian white noise and it is used to excite the dynamic model of the railway vehicle. Under this approximation, the variance of the vertical velocity of the track, which is affected by the track roughness level and vehicle velocity, can introduce uncertainty into the system. Based on the random track irregularity, two cases are proposed to determine how the track irregularities enter the system. One case uses the vertical velocity and displacement of the track as inputs of the system and assumes that the state variables are corrupted by the Gaussian noises. The other case assumes that the vertical velocity of the track is the process noise of the system. Based on these two cases, two types of EKF and UKF are developed to estimate the parameters of the secondary suspensions. In order to study the performances of the proposed EKFs and UKFs, several simulation experiments using linear and nonlinear model are carried out that consider the uncertainties of the random track.
The use of continuous welded rail (CWR) track has solved many of the problems associated with tread surface discontinuities that occur in jointed tracks. However, due to the longitudinal expansion of the rails in CWR tracks being highly constrained, the generated compressive stresses in the rails can cause track buckling in the horizontal plane. Track buckling is a complex phenomenon, in which many factors are involved and around which there is much uncertainty. The objective of this paper is to present an analytical model that can be used to calculate the buckling load of a CWR track. This model accounts for the contributions of base, crib and shoulder ballast and includes the effect of vertical loading on each of these components. Moreover, a parametric study based on this model is developed, in order to understand how and the extent to which the considered factors affect track stability. The results of the study indicate that the characteristics of the existing misalignments in the track are the critical parameters involved in the phenomenon. In addition, maintenance operations that affect the ballast, such as tamping or surfacing, and the dimensions and material of the track sleepers are also important factors.
A railway vehicle is a complicated mechatronic system. Its mechanical structure and connections are key influences on its performance. When a railway vehicle runs at very high speeds its dynamic performance becomes of considerable interest. Therefore, the identification of the design factors that significantly impact on the vehicle’s running behavior, such as safety, stability, comfort and reliability, is a key step towards vehicle design optimization. The optimal design of a railway vehicle is difficult to perform using existing methods due to the complexity inherent in rail/track interactions. Thus, performing a sensitivity analysis of a railway vehicle can be seen as a bridge between performance analysis and an optimal design. This paper presents a sensitivity model that can be used to analyze the performance parameters of a railway vehicle in terms of variation of its design parameters. First, the railway vehicle is described as a multi-body system that can be broken down into its component parts and then, the dynamic behavior of the system is investigated. To simplify the model, a spring/damper connection is used in the classic Hertz nonlinear elastic contact model to represent the force in the normal direction at the wheel/rail contact point. Finally, based on the adjoint variable method, the equations that constitute the sensitivity model of the railway vehicle are derived and analysis software is developed. A case study shows the reliability of the proposed approach.
This paper proposes a practical method to predict the impact of foundation construction for a new high-speed rail line on running safety and riding comfort of an existing high-speed line. The presented numerical model consists of a bridge girder/pier finite element model, a pier-bearing platform-pile foundation-soil numerical model and a train/bridge interaction model that takes into account the dynamic interactions in the train/bridge/pier/soil system. The proposed method is used in an engineering case study. The results show that the foundation construction has an obvious influence on a nearby existing high-speed-line bridge. The differential settlement of piers leads to an increase in the bridge deflection, and generally the higher the train speed, the larger the deflection. The lateral displacement of the pier has a greater influence on the ride comfort than the vertical differential settlement, and an allowance of 20 mm is suggested for lateral displacement of the pier in a ballasted high-speed line.
Experimental evidence, as obtained from line tests, shows that, under some circumstances, the level of hunting motion experienced by a railway vehicle negotiating a curve can be higher than for the same vehicle running at the same speed on tangent track. Starting from this experimental observation, this paper aims to propose a physical explanation for the different hunting behaviour of a railway vehicle running in a curve. After presenting the available experimental evidence, a qualitative examination of the phenomenon is provided. A multi-body model of the vehicle running in a curve is defined and validated against line measurements. This model is then used to numerically evaluate the hunting behaviour of the vehicle in a wide range of curve radii relevant for high-speed lines. In this way, the experimental findings are extended to curve radius and cant deficiency values that were not observed in line tests, due to the use of a specific track section and to the range of speeds covered by the tests.
A new model is presented for the calculation of the rail extension, the friction created by sleeper fastenings and the temperature-induced stress for continuously welded rail (CWR) under free conditions and the calculation and analysis of temperature-induced stress when the temperature is changing and the rail is anchored. The mechanism for generating friction and the phenomenon of rail creep (extension) on site are used to establish a law that states that the friction force of the fasteners is distributed from the center of the CWR section towards the two ends in increasing scale; this observation is used to derive a formula for calculation of the distribution of the friction force in CWR fastenings. Formulas for calculating the temperature-induced stress and its distribution are also derived. The presented results show that the distribution of temperature-induced stress is cone-shaped in the absence of rail creep (extension), and with creep it presents a tangent and a cone shape in anchored sections. A comparison with the traditional temperature-induced stress distribution pattern in a rail of a tangent constitutes an argument against the established methods. The results reported in this paper should play an important role in guiding site maintenance activities.
An innovative control approach for a Maglev system, including a new structure of the Maglev line and a novel levitation control method, is proposed in order to solve the problem of vehicle–guideway coupling vibration. Compared with a traditional Maglev line, the magnetic tracks in the new line are divided into smaller pieces to allow decoupling of the levitation magnets from the flexible supporting beams (steel or concrete beams). The vibration states of the magnetic tracks are introduced into the control system by the state observer, and a controller is designed using the full state feedback method. The effects of various parameters on the stability of the system are investigated. Also, a hardware-in-loop test rig is built to verify the feasibility of the scheme. The following conclusions are drawn based on the obtained results: in the new system, the magnet is dual-decoupled from the carbody and the supporting beam; the relative position between the magnet and the supporting beam exerts a negligible effect on the responses of the track and magnet, this makes it feasible to obtain all the vibration states of the track and the magnet using a state observer; an increase in the mass of the track is conducive to the stability of the system and a low pad stiffness value produces a faster decay ratio of the vibration of the supporting beam; the system’s stability margin is improved as the damping ratio of the supporting beam increases.
An approach to optimize the wheel reprofiling of a high-speed electric multiple unit (EMU) train is presented; it has three functions as objectives: the critical speed of the train, the contact stress that affects the contact fatigue of wheel/rail wear and the diameter of the nominal rolling circle of the wheel. The vertical coordinates of the control points on the curve of the wheel profile are used as design variables and the upper and lower values of each control point are utilized as additional limiting conditions of the curve, with the height, thickness and contact angle of the wheel flange as well as the derivative of the curve acting as constraints on the geometry parameters. A multi-objective optimization model is established for the wheel reprofiling of a high-speed EMU train; three models are created: standard, worn and optimized wheel profiles. Comparisons of wheel/rail contact, running stability and curving performance of the vehicle are performed. It is shown that the wheel profile obtained from the reprofiling optimization model satisfies the constraints and its corresponding dynamic performance has a good agreement with that of a standard wheel profile with a 30 mm thick wheel flange. A performance close to that of a standard wheel profile can be obtained even though the worn wheel is not reprofiled to have the standard profile. Also, the amount of diameter reduction in the direction of the nominal rolling circle is reduced and service life-time is extended by employing the proposed wheel reprofiling approach based on the multi-objective optimization strategy.
This paper presents a high precision train speed calculation technique based on ground vibration information. This versatile method can calculate speeds for trams, intercity locomotives and high speed trains on any track/embankment arrangement. Additionally, it has high accuracy for sensors located up to 100 m from the track, thus allowing semi-remote, non-invasive monitoring of train velocities. The calculation method combines three separate speed calculation techniques to provide estimates for arbitrary train speeds, even for sensors placed at large track offsets. The first estimation technique involves the use of cepstral analysis to isolate key harmonics for use with speed calculation. The second method is similar; however, the combination of a running rms and a previously developed "dominant frequency method" are used. The third method uses an analytical vibration frequency prediction model in combination with regression analysis to calculate train speed. All three methods are combined into one calculation procedure, resulting in high accuracy estimates. To show the robustness and ability of the new method to calculate a wide range of train speeds, it is used to predict tram, intercity and high speed rail train passage velocities generated from a previously validated vibration prediction numerical model. More importantly, it is used to predict train speeds during field trials performed on operational railway lines in Belgium and in UK. The new method is shown to offer high performance for several train types and track setups (including abutment and tunnel cases).
The aim of this paper is to investigate the possibility of improving the ride quality of a two-axle railway vehicle with a single-stage suspension by means of passive suspensions employing an inerter device. The inerter is a mechanical one-port element that is analogous to a capacitor in electrical circuits. The goal is to improve the ride quality in both the vertical and lateral motions in response to track irregularities. Performance benefits for several simple passive suspension layouts are demonstrated and compared with the conventional scheme. The elastic effects of the damper and inerter device are then taken into consideration for practical purposes. The optimum parameter values of the damper, inerter and the parameters representing the elastic effects provide guidance for mechanical design purposes.
A railway track asset management strategy must ensure that the condition of the track stays at an acceptable level, ensuring passenger comfort and safety. The determination of an efficient and effective strategy is a complex problem that requires consideration of the interrelated processes of deterioration, inspection, maintenance and renewal. Railway traffic causes the track’s geometry to deteriorate through time. When the track’s geometry has been assessed and seen to have deteriorated, maintenance is scheduled to restore the track’s geometry using a tamping machine. Tamping involves lifting the track to the required position before inserting vibrating tines into the ballast either side of the sleepers and using them to pack the ballast below. This process causes damage to the ballast, causing a relative acceleration in future track geometry deterioration and decreasing the time between subsequent maintenance interventions.
This paper describes a Markov model that can be used to investigate the asset management strategy applied to a railway track section. The model predicts the way that the track section’s condition changes with time for a given asset management strategy, which is defined through the specification of a number of model parameters. The model is applied to a track section with a specified maintenance strategy and is used to investigate the track’s performance for that strategy. Parameters corresponding to asset management decisions that relate to inspection, maintenance and renewal are then changed in order to illustrate the effects of the decisions on the track’s life cycle. The Markov model provides a simple yet powerful means of investigating the effects of an asset management strategy on a railway track section.
The propulsion principle of the Transrapid maglev train is based on long stator linear synchronous motors. The stator winding in the guideway is divided into multiple segments that are individually switched on or off, with power being supplied to a given segment only as it is passed by the train. In commercial operation the power from substations is connected to the stator segments in one of two ways: change-step connection or three-step connection. Although each type of power supply has its advantages and application scope, the change-step connection is the central topic of interest in this study due to its salient features. When the train’s propulsion system uses this supply mode, the inverter control systems at the power stations must know exactly when the stator current begins to decline and the stator segment that it is supplying is about to change. Therefore, the timings to adjust the stator current are crucial to the operating system of a Transrapid train and should be determined from the dynamic conditions of the train. This paper aims to determine the timings for controlling the stator current. Based on calculated results, it is concluded that changing the power supply between stator sections can be smoothly performed using the proposed propulsion control system.
The aim of this paper is to define an evaluation method to quantify the index of motion sickness incidence (MSI) in railway motion conditions. This index is widely used in the literature to quantify illness symptoms that occur as a result of generic low-frequency motions (kinetosis). In fact, only one standard exists (ISO 2631) and it was defined for general motion and in particular for vertical acceleration motion conditions. No standards have been written that consider the conditions experienced in railway motion. This paper reports an evaluation approach that can be used to examine illness symptoms experienced during rail trips and involves indices and methods well-known in the rail industry. In particular the proposed approach involves the P ct index (EN 12299: Comfort index on curve transition) and some weighting curves for the filtering of accelerometer signals that are also specified in railway regulations (EN 12299, ISO 2631). The proposed method, that is consistent with a theoretical model that has been reported in the literature, allows the MSI index to be obtained as a function of travel time and/or track distance. The model is validated through a comparison with experimental data available in literature and with experimental data recorded for a tilting train during tests performed in Slovenia.
The material requirements for the frog of a turnout are quite complex. The crossing nose region of the frog represents a discontinuity in the track as the wheel needs to change from one rail to the other. This causes increased dynamic contact forces and slip between wheel and frog. The high contact pressures and slip can cause damage such as wear, rolling contact fatigue and severe plastic deformation in the frog. The material from which the frog is constructed plays a crucial role in the development of damage. On the one hand, a plastic material response can reduce the contact pressures by an adaption of the frog’s geometry. On the other hand, materials have a different resistance to wear, crack initiation and growth. To clarify the requirements for materials for the manufacture of frogs, five different steel grades used to create frogs that are in service in various railway turnouts were investigated. The chosen materials were ‘Hadfield steel’ (an Mn-13, abrasion-resistant grain-refined steel with 400 HV), bainitic railway steel, tempered steel 51CrV4 (DIN 1.8159) and maraging steel. They were investigated in the same conditions as they would experience in service, covering a variety of steel microstructures and macroscopic hardness values. To compare the materials’ responses to the high impact forces, their impact fracture toughness was measured and selected fracture surfaces were investigated with scanning electron microscopy. To compare their response to the cyclic loading, the materials were tested with respect to their monotonic tensile strength as well as fatigue strength by means of low cycle fatigue tests. Measurements of the fracture toughness KIC were performed on all materials to compare their fracture resistance. The achieved results can be used as input data for finite-element-based calculations of the local loading conditions in railway turnouts. Additionally, the comparison can help the choice of the best material for specific loading conditions, i.e. specific crossing geometries and track loading conditions.
The dispatching system of a high-speed railway system is the basis that guarantees trains that run at high speed, high density, are secure and have a good punctuality. The prediction of train operation conflicts is the main issue of train operation adjustment. In this paper, we propose the use of workflow nets and triangular fuzzy numbers to study the issues associated with predicting train operation conflicts. The linked lists for conflict prediction are built and used as tools to derive the train running states corresponding to the two operating modes of train workflow nets: the sequential mode and the alternative mode. Based on the current train running status and the triangular fuzzy numbers of times for future activities in train operation, the probabilities of all kinds of train operation conflicts that might occur can be obtained by comparing the possible end times of the workflow nets with the fixed deadlines. Hence, the prediction of train operation conflicts is realized.
In this paper, a method is presented for the calculation of the vibration created in buildings by the operation of underground railways. The method is based on the sub-modelling approach which is used to couple a model of a building on a piled foundation to another model that calculates the vibration generated in the soil in underground railway tunnels. The method couples a building on a piled foundation to the soil at discrete points by satisfying equilibrium and compatibility requirements at those points. The method results in efficient numerical calculations. A two-dimensional frame made of beam elements is used to model the building and its piled foundation. The elements are formulated using a dynamic stiffness matrix which accounts for Euler–Bernoulli bending and axial behaviour. Vibrations created by a train moving in an underground tunnel are calculated using the well-known pipe-in-pipe (PiP) model. The model calculates the power spectral density (PSD) of the displacement in the soil. The excitation mechanism is the roughness of the rail and the PSD is calculated for a train moving on a floating-slab track in an underground railway tunnel for a stationary process. The current version of PiP accounts for a tunnel embedded in a half-space. The building frame is coupled in this paper at 90° to the tunnel’s centreline. The main result of this paper illustrates the significant contribution of the building’s dynamics to the displacement wave field received by the building. The example presented in this paper shows a decrease of more than 20 dB in the displacement PSDs at frequencies larger than 10 Hz when accounting for the change in this wave field.
Communications-based train control (CBTC) is an emerging technology for urban rail transit systems. An integrated method for assessing the capacity of CBTC-system-installed urban rail lines is proposed in this paper. Based on the UIC Code 406 method, the new integrated method includes train movement simulation, timetable construction, test and optimisation. In order to achieve an accurate blocking time, this paper introduces three operational scenarios, namely: consecutive running of trains, entering a station and turn-back at a terminal station. A practical timetable is implemented and optimised by simulating and evaluating the capacity with UIC Code 406. This paper considers Beijing’s Yizhuang metro line in a case study. It is found that a speed limit on the line produces a greater impact on the capacity compared with dwell time and switch speed restrictions. Furthermore, it is noted that a capacity bottleneck can easily occur during the process of entering a station and also during a turn-back operation at a terminal station.
With the increases in traffic, axle loads and travelling speed, the dynamic monitoring of railway tracks and structures is becoming more and more important to ensure a high level of safety and comfort. This situation is particularly critical at transition zones where rapid changes of track stiffness occur. This paper presents a contactless system to measure track displacements and its application in an embankment/underpass transition zone, located on the Northern line of the Portuguese railway network where the Alfa Pendular tilting train travels at a maximum speed of 220 km/h. The system is based on a diode laser module and a position sensitive detector (PSD). The PSD receives the laser beam emission and the detection of the centre of gravity of the beam spotlight on the PSD area enables the calculation of the displacement. Before field application, static and dynamic laboratory validation tests were performed in order to evaluate the system performance for different laser to PSD distances, and an accuracy of 0.01 mm was achieved using data acquisition rates of up to 15 kHz. The optical measuring system proved to be an efficient and flexible way to measure absolute and relative rail displacements in the field, enabling the detection of track deformability differences along the transition zone, even for the passage of trains at high speed (220 km/h).
The high maintenance cost of high-speed wheels due to wear and rolling contact fatigue is a major problem in the commercial operation of high-speed trains in China. In order to understand the wear behavior of high-speed wheels and its influence on the motion stability of high-speed trains, the worn profiles and the work-hardening of the wheels of the CRH3 high-speed trains that operate on the Wuhan–Guangzhou line were monitored in different periods during service; in particular, the influence of hollow wear of the wheel on the lateral acceleration of the bearing-box was investigated in detail. A new wheel profile design method was suggested to reduce the hollow wear by seeking an optimization match of the wheel profiles, the vehicle’s suspension systems, and the wear behavior of wheels in service. The feasibility of the method was verified by numerical simulation using the operation conditions of CRH3 high-speed trains on the Wuhan–Guangzhou line. A new wheel profile was designed using this method. The wheel/rail contact performance and the vehicle’s dynamic behavior resulting from the designed new wheel were investigated in detail and compared with those of the original wheel. The wear behavior of the designed new wheel profile was predicted based on wear data measured on the original wheel. The results show that compared with the original wheel profile, the designed new wheel profile can improve the wheel/rail contact state, reduce the contact stress level, and lower the friction power of wheel and rail. The extent of hollow wear on the new wheel is significantly decreased and the vehicle has improved dynamic behavior when wheelsets with the designed new profile are used. Thus, the period before re-profiling is required can be effectively extended.
This paper studies the accuracy of rigid-wall (stonewall) and symmetric models in rail vehicle impact stability. The investigation is based on modelling results and theoretical analysis. The theoretical investigation consists of a mechanical description of the conservation of energy transformation and instability of train impact due to irregular structural collapse and loose coupling patterns. It is shown that an unstable response is a common consequence in vehicle impacts and the corresponding stiffness amongst cross-sections has a strong effect on collapse stability. The modelling investigation summarises impact simulations of a cab vehicle. This illustrates the pitfalls of the rigid-wall and symmetric models as follows: firstly, using a rigid wall in modelling could mask irregular deformations and lead to overestimated crashworthy performance behaviours; and secondly, symmetric impacts could lead to asymmetric deformations resulting in crucial irregular responses of rail vehicles being missed. This paper explores the irregular responses of rail vehicles in train collisions and highlights the relevant issues which might be overlooked when conventional static approaches are used in dynamic scenarios. It is anticipated that the paper will provide increased insight into impact mechanics of rail vehicles and promote a rethink about the influence of characteristic behaviours in dynamic responses resulting in a more accurate representation.
The safe operation of continuously welded rail depends on its ability to laterally resist forces generated by vehicles. In recent decades, considerable improvement has been made in increasing the lateral resistance and stability of track. This has been achieved by using elastic rail fastenings, increasing the height and width of the ballast shoulder, and modifying the shape of the sleeper. This paper deals with the effect of the vertical load on the lateral resistance and stability of a railway track using frictional sleepers (with a ribbed underside) in comparison with conventional sleepers (with a flat underside). The test results prove that the vertical load has a significant effect on the increase in the track’s lateral resistance in both types of sleepers; however, it is more effective in the tracks with frictional sleepers.
The rotation movement between bogie and carbody is studied using vehicle system dynamics theory and formulas for the rotation resistance factor are derived for different air spring states. Laboratory tests are conducted and the obtained results are compared with calculations. The rotation resistance factor for motor and trailer cars experiencing AW0 and AW4 loading conditions when air springs are in inflated, deflated and over-inflated states are considered so as to validate the proposed formulas and test and discuss error sources. The rotation resistance factor of the bogie is related to the rotation angle and speed. The faster the rotation speed, then the greater is the rotation resistance factor. The greater the rotation angle, then the greater is the rotation resistance factor. The maximum rotation resistance factor is 0.094 for a trailer car at a rotation speed of 1 deg/s and experiencing AW0 loading conditions and with the air springs in the deflated state. The maximum rotation resistance factor when the air springs are deflated is much greater than that when the air springs are in the inflated state for a rotation speed of 1 deg/s. The maximum rotation resistance factor obtained at a rotation speed of 1 deg/s is much greater than the one obtained at 0.2 deg/s. The over-inflated state of air springs has little influence on the rotation resistance of the bogie. The calculated results obtained when considering air springs in inflated and over-inflated states are slightly smaller than test results with a maximum difference of 0.02. For the deflated state of the air springs, the calculated and test results for a trailer car are equivalent and the calculated results are slightly larger than the test results for a motor car with a maximum difference of about 0.02. The theoretical formulas should consider the dynamic nature of stiffness properties and damping effect of air springs. The effects of other suspension components should also be considered. A laboratory test or field test after assembly is an essential requirement. The comparison of test and calculated results validates the proposed formulas and allows sources of error to be discussed.
The aerodynamic properties of a pantograph that is under consideration for application on Korean high-speed trains are experimentally investigated. The selected experimental models were one-quarter scale pantographs (a double-arm pantograph, single-arm pantograph and a periscope pantograph) with either a rectangular panhead or a panhead with an optimized streamlined shape. To increase the performance and the robustness of the pantograph, the drag coefficient and the fluctuation of the lift coefficient along the angle of attack are simultaneously minimized. In order to confirm the aerodynamic enhancement of the pantograph due to the optimized panhead, the aerodynamic forces are compared with those of a pantograph with a rectangular panhead. To investigate the aerodynamic force distribution of a pantograph, the aerodynamic forces of the lift and drag of the pantograph are measured in wind tunnel tests and analyzed in terms of the pantograph’s components. In addition, wake flows are examined based on variations of the shape of the panhead.
In a crosswind scenario, the risk of high-speed trains overturning increases when they run on viaducts since the aerodynamic loads are higher than on the ground. In order to increase safety, vehicles are sheltered by fences that are installed on the viaduct to reduce the loads experienced by the train. Windbreaks can be designed to have different heights, and with or without eaves on the top. In this paper, a parametric study with a total of 12 fence designs was carried out using a two-dimensional model of a train standing on a viaduct. To asses the relative effectiveness of sheltering devices, tests were done in a wind tunnel with a scaled model at a Reynolds number of 1 x 105, and the train’s aerodynamic coefficients were measured. Experimental results were compared with those predicted by Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations of flow, showing that a computational model is able to satisfactorily predict the trend of the aerodynamic coefficients. In a second set of tests, the Reynolds number was increased to 12 x 106 (at a free flow air velocity of 30 m/s) in order to simulate strong wind conditions. The aerodynamic coefficients showed a similar trend for both Reynolds numbers; however, their numerical value changed enough to indicate that simulations at the lower Reynolds number do not provide all required information. Furthermore, the variation of coefficients in the simulations allowed an explanation of how fences modified the flow around the vehicle to be proposed. This made it clear why increasing fence height reduced all the coefficients but adding an eave had an effect mainly on the lift force coefficient. Finally, by analysing the time signals it was possible to clarify the influence of the Reynolds number on the peak-to-peak amplitude, the time period and the Strouhal number.
This paper presents the development of a modular tool for the prediction of train braking performance. Particular attention is devoted to the accurate prediction of stopping distances, considering different loading and operating conditions, necessary to verify safety requirements prescribed by the European Technical Specifications for Interoperability of High Speed Trains (TSI-HS) and the corresponding EN regulations. Results are verified by considering, as a benchmark, the AnsaldoBreda EMU V250: a European train being developed for Belgium and The Netherlands’s high-speed lines. Technical information and experimental data were available for this train, directly recorded during preliminary supplier exercise. Validation results were encouraging, and allowed a more accurate identification of the pad friction factor influence on braking performance.
Experimental bird strike tests were conducted in which a 2.6-kg dead chicken was projected at a speed of 500 km/h to hit a raised aerodynamic brake wing. The brake wing was fabricated with a sandwich of composite material as its skin and polymethacrylimide foam as its core. Pre-test numerical analyses of bird strikes were performed using the LS-Dyna solver code, an Arbitrary Lagrangian Eulerian model of the bird, and a Lagrangian model of the brake wing. The numerical and experimental results were well correlated, confirming the validity of the finite element model and calculation approach. Finally, bird strikes were conducted on a brake wing extended to 75° and 90° to determine the difference between the two conditions on the basis of effective wind-drag area. Impact, failure after impact and high strength at impact properties were investigated for a composite of carbon and glass fibre laminate.
A reliability study based on a Bayesian semi-parametric framework is performed in order to explore the impact of the position of a locomotive wheel on its service lifetime and to predict its other reliability characteristics. A piecewise constant hazard regression model is used to analyse the lifetime of locomotive wheels using degradation data and taking into account the bogie on which the wheel is located. Gamma frailties are included in this study to explore unobserved covariates within the same group. The goal is to flexibly determine reliability for the wheel. A case study is performed using Markov chain Monte Carlo methods and the following conclusions are drawn. First, a polynomial degradation path is a better choice for the studied locomotive wheels; second, under given operational conditions, the position of the locomotive wheel, i.e. on which bogie it is mounted, can influence its reliability; third, a piecewise constant hazard regression model can be used to undertake reliability studies; fourth, considering gamma frailties is useful for exploring the influence of unobserved covariates; and fifth, the wheels have a higher failure risk after running a threshold distance, a finding which could be applied in optimisation of maintenance activities.
Frictional heat is generated when a train wheels pass over the rail. In addition heat is also generated by the use of an eddy current brake system. This generated heat causes a variation in the temperature of a rail’s surface; it accelerates the formation of both rolling contact fatigue and wear on the wheel/rail contact surface; and threatens the running safety of railway vehicles. The convective heat transfer characteristics on the surface of a rail when the train passes over it are very important in determining the temperature change of the rail. This paper reports experimental results of the convective heat transfer characteristics on a rail’s surface when a rolling wheel passes over the rail. A test model was created based on the configuration commonly used in a two-bogie car. The local and average heat transfer coefficients of the test section of the rail were obtained. The heat transfer results were extended to the real case using an analogy between the frequencies of the test wheel and train wheels. The results show that when the speed is less than 182 km/h, the intensity of convection heat transfer on the rail’s surface increases with an increase in the speed of the train, however, it decreases significantly when the speed is larger than 182 km/h.
Mineral oil and other lubricants are commonly applied to the gauge corner of high rails to avoid wheel/rail interface wear on railways. Although not directly applied to the top of the rail, these lubricants sometimes end up on this surface, and the relatively low coefficient of friction they produce can cause slipping or sliding at the wheel/rail interface during vehicle acceleration or braking. It has been reported in the literature that the application of traction fluid (a modern technique involving the use of a synthetic lubricant) produced a higher coefficient of friction than that of a conventional wheel/rail interface lubricant. In this study, tests were performed using traction fluid to evaluate its influence on a vehicle’s braking distance and other important performance elements from a practical point of view. The results of the braking performance evaluation carried out on a braking test stand showed that the braking distance increase with synthetic traction fluids was roughly one-half of that observed with conventional wheel/rail lubrication oil. This suggests the potential of using traction fluid as a wheel/rail lubricant.
Turnouts are critical components of track systems in terms of safety, operation and maintenance. Each year, a considerable part of the maintenance budget is spent on their inspection, maintenance and renewal. Applying a cost-effective maintenance strategy helps to achieve the best performance at the lowest possible cost. In Sweden, the geometry of turnouts is inspected at predefined time intervals using the STRIX / IMV 100 track measurement car. This study uses time series for the measured longitudinal level of turnouts on the Iron Ore Line (Malmbanan) in northern Sweden. Two different approaches are applied to analyse the geometrical degradation of turnouts due to dynamic forces generated by train traffic. In the first approach, the recorded measurements are adjusted at the crossing point and then the relative geometrical degradation of turnouts is evaluated by using two defined parameters, the absolute residual area and the maximum settlement, In the second approach, various geometry parameters are defined to estimate the degradation in each measurement separately. The growth rate of the longitudinal level degradation as a function of million gross tonnes / time is evaluated. The proposed methods are based on characterisation of the individual track measurements. The results facilitate correct decision-making in the maintenance process through understanding the degradation rate and defining the optimal maintenance thresholds for the planning process. In the long run, this can lead to a cost-effective maintenance strategy with optimised inspection and maintenance intervals.
Irregularities in railway tracks are a key factor influencing the safety of trains. In this paper, rail track is considered to consist of consecutive track maintenance units whose individual defect states can be quantified in terms of a track quality index. A Markov stochastic process approach is used to evaluate the deterioration of a maintenance unit. A hazard model is formulated using the heterogeneity of the maintenance units, and a matrix of the Markov transition probabilities is constructed. The parameters of the developed models are estimated via a maximum log-likelihood function. The prediction model is validated with track irregularity data measured using track geometry cars.
Simply supported pre-stressed concrete box-girder bridges are the most common bridge type found on high-speed railway and urban rail transit lines in China. A field experiment has been conducted on the Pixian Viaduct of the Chengdu–Dujiangyan Intercity Railway, where two kinds of simply supported pre-stressed concrete box-girder bridges with a standard span of 32 m are used, one single track and the other double track. Characteristics of the noise underneath the box-girder, far from the bridge, and near the bridge gap were measured and analyzed in the time and frequency domains during high-speed train passage, as was the vibration of the box-girder’s bottom plate. The variations of noise with distance and train speed at locations 1.5 and 9 m above ground level were measured and fitted using mathematical formulae. A simplified formula to predict near-field bridge-borne noise was proposed and verified. The peak bridge-borne noise frequency and its tonal characteristic at 50 and 63 Hz for the double-track and single-track box-girders, respectively, were interpreted in terms of bridge vibration and sound radiation efficiency, respectively. The vibration/noise transfer function and coherence were evaluated, showing that vibration resonance is more significant than acoustic coincidence and that the former is more important in terms of noise reduction.
In this paper, we propose a Distributed Architecture for Railway Traffic Control using Multi-Agent Systems called DARTCMAS. It has a hierarchical organizational model that consists of three main layers of diverse agents: "Train Agents" at the bottom, "Station Agents" in the middle and "Center of Traffic Control Agent" in the top layer. Any train in the railway traffic system is considered as an intelligent agent that has reactive, proactive and interactive properties, simultaneously. DARTCMAS considers local traffic control centers that are embedded in some selected stations as "Station Agents". Lastly, "Center of Traffic Control Agent" acts as a comprehensive monitoring and supporting reference. We define an internal architecture for each of the agents. Furthermore, two types of interactions among agents are developed: first, inter-layer interactions that represent communications between two adjacent layers in the organizational model of DARTCMAS; and second, intra-layer interactions that represent relations between the same agents type in a specific layer. Simulations have been performed using MATLAB and the "Java Agent DEvelopment framework" whose results show the effectiveness of the model.
The ballast pick-up (or ballast train-induced-wind erosion (BTE)) phenomenon is a limiting factor for the maximum allowed operational train speed. The determination of the conditions for the initiation of the motion of the ballast stones due to the wind gust created by high-speed trains is critical to predict the start of ballast pick-up because, once the motion is initiated, a saltation-like chain reaction can take place. The aim of this paper is to present a model to evaluate the effect of a random aerodynamic impulse on stone motion initiation, and an experimental study performed to check the capability of the proposed model to classify trains by their effect on the ballast due to the flow generated by the trains. A measurement study has been performed at kp 69 + 500 on the Madrid – Barcelona High Speed Line. The obtained results show the feasibility of the proposed method, and contribute to a technique for BTE characterization, which can be relevant for the development of train interoperability standards.
A mathematical model to estimate the dynamic coefficients of a moving freight train is given; an approach is used in which some train vehicles are represented by simplified calculation schemes and other vehicles are represented in detail by taking into account their design and the features of the transported cargo. The train motion along track of different shapes and in various operational modes (with constant and variable speeds) is modelled. Some simulation results are presented.
The initial geometry of a railway track continually degrades over its life-cycle. Changes in the track alignment give rise to variations in the dynamic axle load which accelerate track degradation, with consequences for maintenance and availability of the line. This behaviour is particularly evident at some critical locations that are associated with abrupt changes in the track’s vertical stiffness, such as transitions to bridges or other structures. In order to mitigate this problem, careful design and construction is required, for which several recommendations have been suggested in the literature. However, studies based on the maintenance records of existing high-speed lines have shown that the problem of track degradation associated with stiffness variations is far from being solved. This paper presents a short review on the design of transition zones. A case study on the design and construction of a transition zone on a new Portuguese railway line is analysed. Results of conventional laboratory and cyclic load triaxial testing on granular materials and in situ mechanical characterization of the layers are presented. Relevant aspects regarding the construction are addressed and discussed. The results obtained at the substructure level seem to indicate that the design of the transition zone was successful in minimizing settlement and achieving a gradual stiffness increase as a bridge is approached.
The operation of trams close to sensitive buildings can lead to concerns over ground-borne vibration and re-radiated noise. Vibration generated at the wheel/rail interface propagates through the track structure, through the ground and into buildings, where it may cause disturbance as perceptible vibration and/or re-radiated noise. This paper presents work undertaken to solve a re-radiated noise problem within the auditorium of the Royal Concert Hall, Nottingham, UK. The hall is situated alongside a crossover between two tracks of Nottingham’s Express Transit tramway. Initial measurements established the dominance of re-radiated noise over airborne noise. Simultaneous noise and vibration measurements were then used to establish the relative significance of the impulsive vibration generated at the various rail discontinuities of the crossover, compared with the essentially continuous vibration due to wheel/rail roughness. The results led to the selection of a new ‘lift-over’ crossing, together with an improved design of switch, as the basis for solving the problem. The paper includes descriptions of the experimental methods, together with a summary of the results. The new crossover design is described and the results of the commissioning measurements are presented as a final demonstration of the new lift-over crossing’s performance.
A 9-kN magneto-rheological (MR) damper for lateral suspension control of a railway vehicle is created in this paper. The twin-tube style is adopted in order to obtain a long damper stroke and guarantee the symmetry of the output damping force. A bypass MR valve with a radial flow path is utilised to control the generated damping force. Three-dimensional finite element analysis studies are performed to determine the magnetic field strength inside the MR valve region. The MR damper is mathematically modelled for the situation of a unidirectional fluid flow in the chamber and valve. The test results indicate that the MR damper can produce a considerable range of dynamic force and can operate as a fail-safe device. Sedimentation is detected in the damper; however, the response time is acceptable for real-world deployment.
The UK rail industry collects and analyses incident data to assess the risks experienced by passengers, the railway workforce and members of the public. The current analysis mainly compares current and historic incident rates and, for each type of incident, looks at the railway as a whole. However, changes to reduce risk are often made locally, at least at first, so a modelling approach is needed that is able to analyse local risk. In this paper we present a form of model that is able to make local risk estimates from incident data, using a case study – boarding and alighting incidents at stations. Using a Bayesian network (BN), we analyse the incident data with expert judgements about causal factors. The BN cannot be directly leant from data because the dataset contains no entries for the overwhelming majority of cases where the railway is used without incident. Instead, the incident data is analysed in the context of a model of the use of the railway, so that the prevalence of the causal factors in normal use can be compared with that in the incident data. The usage model is derived from multiple data sets; the use of a BN allows this to be done with approximations. Finally, we show how the model allows local risk to be estimated and consider the wider applicability of the techniques described.
Repeatable field tests to measure the vehicle response to unsteady crosswinds are not practical due to safety and economic reasons. Simulations are therefore necessary to gather information on the vehicle response to crosswind. However, in turn, these simulations need to be validated. This study presents results of measured quasi-static and dynamic responses of a stationary rail vehicle due to defined lateral carbody excitations imitating unsteady crosswind, which are reflected by multibody simulations. The vehicle responses are measured in terms of suspension deflections, lateral carbody accelerations and vertical wheel/rail forces. The vehicle dynamic response to a gust-like event results in an overshoot of wheel unloading. In general the measurements and simulations show good agreement. However, the simulations partly overestimate the responses slightly and an influence due to airspring levelling can be observed in the measured values of quasi-static load cases.
North American heavy haul railroads are experiencing growth in traffic demand and increasingly facing capacity constraints. A key factor influencing railroad operations is heterogeneity in train characteristics. Different train types can have substantially different operating characteristics including maximum speed, power-to-ton ratio and dispatching priority. This heterogeneity causes conflicts between trains that increase delays and reduce capacity. Dispatching simulation software was used to analyze the effect of various combinations of intermodal and bulk trains on a hypothetical, signalized, single-track line with characteristics typical of a North American freight railroad subdivision. This assessment studied the relationship between volume, heterogeneity and delay. Further work identified the key factors that contribute to the increased delays due to heterogeneity. The train characteristics of speed, acceleration, braking and priority were considered for their effect on the increased delays due to heterogeneity. Understanding these factors that affect delay allows for more effective network capacity planning and efficient rail operations. The results also suggest certain railway operating strategies that may reduce the delays caused by train-type heterogeneity thereby improving service reliability.
Increases in train length and axle loads have significantly increased in-train forces for heavy haul trains. These forces when combined with the rotation behavior of the coupler can exert an adverse effect on the operational safety of trains. This paper analyzes the rotation behavior of a coupler resulting from the application of a compressive force. A suitable free-rotation angle for the coupler and a stabilization mechanism are also presented. Simulations were performed using a dynamic model of a train consisting of three heavy haul locomotives and two couplers. The obtained results indicate that trains with free-rotation angles of the coupler of 6°have a better dynamic safety and lower levels of wheel tread wear than trains with an initial free-rotation angle of 8°. Variation of the locomotive’s structural parameters, including the secondary stop free clearance, the distance between front and rear stops and the distance between secondary stop and coupler pin, affects the maximum rotation angle of the coupler and, in turn, the operational safety of the train. The matching of the locomotive’s structural parameters and the free-rotation angle of the coupler should be considered when selecting a heavy haul coupler and buffer system so as to avoid safety problems caused by excessive rotation behavior of the coupler.
Rail joints are provided with a gap to account for thermal movement and to maintain electrical insulation for the control of signals and/or broken rail detection circuits. The gap in the rail joint is regarded as a source of significant problems for the rail industry since it leads to a very short rail service life compared with other track components due to the various, and difficult to predict, failure modes – thus increasing the risk for train operations. Many attempts to improve the life of rail joints have led to a large number of patents around the world; notable attempts include strengthening through larger-sized joint bars, an increased number of bolts and the use of high yield materials. Unfortunately, no design to date has shown the ability to prolong the life of the rail joints to values close to those for continuously welded rail (CWR). This paper reports the results of a fundamental study that has revealed that the wheel contact at the free edge of the railhead is a major problem since it generates a singularity in the contact pressure and railhead stresses. A design was therefore developed using an optimisation framework that prevents wheel contact at the railhead edge. Finite element modelling of the design has shown that the contact pressure and railhead stress singularities are eliminated, thus increasing the potential to work as effectively as a CWR that does not have a geometric gap. An experimental validation of the finite element results is presented through an innovative non-contact measurement of strains. Some practical issues related to grinding rails to the optimal design are also discussed.
This paper outlines work carried out to assess how, during winter months, adhesion may be influenced by contamination of the rail head by the salt/grit that is applied to road surfaces as a preventative method to stop ice formation. Twin-disc testing was carried out in which a mechanically formed oxide layer was produced on the disc specimens prior to assessing adhesion levels under realistic contact pressures and slips in the following conditions: dry, wet, dry salt and two salt/water solutions. Under dry conditions adhesion levels differ little from reference tests without an oxide layer, however, the presence of an oxide layer under wet conditions can be seen to further reduce adhesion from a reference level (0.2) to below 0.1. When salt is entrained into the contact it increases adhesion levels above that seen under wet conditions in the presence of an oxide layer, however, the presence of salt is most likely to affect the generation of rail head oxides in the first place and in turn influence adhesion.
Current rules of railway operations employed in the UK can be regarded as conservative. While the safety of passengers is a clearly an overriding paramount consideration, such rules may represent a drawback in that they reduce capacity. At present, with high and growing demand there is a clear need to increase railway capacity. While construction of new lines or significant augmentation of existing ones offer ways of providing increased capacity, there is a long gestation period and it is extremely expensive at a time of tight governmental budgetary constraints. A viable alternative is to investigate methods of increasing the productivity of the current infrastructure by understanding how the established rules of railway operation can be challenged without compromising the safety of the passengers. To accomplish this stated goal, a fault-tolerance-based approach to train controls at nodes (junctions and stations) is proposed. This paper introduces the concept of fault tolerance in the context of train operations at a classic railway junction, presents a dynamic, mesoscopic simulation model developed to represent the new control rules and discusses initial results from the application of this approach on capacity gains.
At present in the UK an elasticity-based approach is used to forecast changes in rail passenger demand resulting from changes in both the rail service offer and external conditions, with uplift factors calculated based on the proportional change in the level of explanatory variables over time. Changes in these explanatory variables may have differing effects on rail demand in different areas. This is currently controlled for via a limited segmentation of the market with different elasticities estimated for each segment, which inevitably limits the complexity of the variations which can be captured. This paper describes the use of geographically weighted regression (GWR) to enhance the modelling of such spatial variation. First, conventional cross-sectional demand models were calibrated covering major rail flows across the Great Britain. These models were then recalibrated using GWR to allow assessment of spatial variations in rail demand elasticities. Previous applications of GWR have almost exclusively focused on spatial data which have a single point location. This is not the case for rail flows, and this paper compares the results given by several different methods for defining point locations for flows. It also assesses different methods for approximating GWR results to simplify their application in real-life forecasting situations. The results show that the use of GWR can give a significant improvement in the fit of flow-based rail demand models, and that it is possible to spatially segment the UK passenger rail market based on the results from these models. In order to integrate such segmentations with the standard UK rail demand forecasting methodology it would, however, be necessary to extend the GWR methodology further to allow the calibration of GWR models on panel data.
From the viewpoint of engineering applications, the prediction of the failure of railway axles plays an important role in preventing the occurrence of fatigue fractures. Combining a nonlinear damage accumulation model, a probabilistic S-N curve, and a one-to-one probability density functions transformation technique, a general probabilistic methodology for modeling damage accumulation is developed to analyze the time-dependent fatigue reliability of railway axle steels. The damage accumulation is characterized as a distribution in a general degradation path, which captures a nonlinear damage accumulation phenomenon under variable-amplitude loading conditions; its mean and variability change with time. Moreover, a framework for fatigue reliability assessments and service life prediction is presented based on the estimation of the evolution and probabilistic distribution of fatigue damage over time. The proposed methodology is then validated by experimental data obtained for a railway axle (45 steel and LZ50 steel). The time-dependent reliability is analyzed and demonstrated through probabilistic modeling of cumulative fatigue damage, and good agreement between the predicted results and the experimental measurements under different variable amplitude loadings is obtained.
Optimum allocation and efficient utilisation of track possession time are becoming important topics in railway infrastructure management due to increasing capacity demands. This development and other requirements of modern infrastructure management necessitate the improvement of planning and scheduling of large-scale maintenance activities such as tamping. It is therefore necessary to develop short-, medium- and long-term plans for performing tamping on a network or track section within a definite time horizon. To this end, two key aspects of infrastructure maintenance planning are considered in this paper, deterioration modelling and scheduling optimisation. An exponential deterioration function is applied to model the geometry quality of a series of 200 m segments of a 130 km line section, and an empirical model for recovery after tamping intervention is developed. These two models are subsequently used to generate a methodology to optimise a schedule for tamping intervention by minimising the total cost of intervention including the cost of track possession while geometry quality is ascertained to be within a desirable limit. The modelling considers two types of tamping interventions, preventive and corrective, with different intervention limits and tamping machines. The result of this paper suggests a tamping plan which will lead to optimum allocation of track possession time while maintaining the track geometry quality within specified limits.
It is not uncommon for conventional ballasted railway track systems to have unsupported sleepers due the uneven settlement of the ballast or subgrade. In order to investigate the possible implications of unsupported sleepers, this paper describes the development of a dynamic finite element model which includes wheel/rail friction. The developed model was used to investigate the behavior of a section of existing track on the ballasted Shuohuang heavy haul railway line in China. The investigation showed that the maximum displacement of the rails and sleepers increases significantly with the number of consecutive unsupported sleepers. Furthermore, the magnitude of the displacement between an unsupported sleeper and the ballast is likely to greatly exacerbate ballast/sleeper attrition and reduce the fatigue life of the hanging sleeper. An increase in the number of unsupported sleepers amplifies these effects. In addition, it was found that the sleepers adjacent to unsupported ones carry an additional load resulting potentially in their increased wear and additional damage to the substructure. To better understand the wider implications of the presence of unsupported sleepers on track performance, the stability, safety (in terms of derailment) and potential for rail and substructure damage were computed as a function of the number of unsupported sleepers (one to four) and compared with specifications. The results showed that the number of unsupported sleepers has a significant adverse impact on all four measures. However, while the effects on stability, safety and rail damage were within the limits suggested in specifications, even when four sleepers were modeled, the potential for substructure failure within a typical design life of the railway system was identified.
This paper investigates a significant reduction in environmental noise attributable to changes in the Network Rail grinding strategy employed within GB. It also considers how these findings could inform noise mapping and action plans required by the Environmental Noise Directive (END). Acoustic track quality (ATQ) is a measure of the surface roughness of the running rails and is proportional to wayside rolling noise levels during the passage of a train. Levels of ATQ have been determined for approximately 1100 km of track on GB’s East and West Coast mainlines from wayside noise measurements made during the pass-by of Network Rail’s New Measurement Train and data collected by an under-carriage microphone system fitted to this train. The results show a substantial apparent reduction in rail surface roughness and associated wayside noise levels since a similar study was undertaken in 2004. While these findings require further verification they are supported by initial direct rail head roughness level measurements which also show low levels of roughness. The results of the study show how a maintenance rail grinding strategy can potentially reduce wayside noise levels across large parts of a railway network. While the measure of track quality used to evaluate the benefits of a maintenance rail grinding strategy is specific to GB’s method for calculating railway noise, the results also provide insight into the potential benefits of maintenance rail grinding on networks outside of GB. In addition the results demonstrate the importance of including a track quality parameter, such as ATQ, in any prediction methodologies for rail noise used in noise mapping exercises, such as those being undertaken as part of the END.
Fault inspection is a key part of ensuring safe operation of freight trains. The development of machine vision technology has resulted in vision-based fault inspection becoming the principal means of fault inspection. An angle cock is an important component in the brake system, and a fault in it could lead to a serious accident. In this paper, we propose an automated vision method to inspect for missing handles on an angle cock during operation of a freight train. Images of the angle cock are acquired and they are analyzed using a proposed gradient encoding histogram and support vector machine that combine to create a detection system. Experimental results show that we achieved a fault detection rate of 99.8% using the proposed system, which represents a good real-time performance and high detection accuracy.
The goal of the research presented in this paper is to design and incorporate new technologies into railway bogie-mounted sensors. It is often impossible to connect the mounted systems to physical wires due to their location in an inaccessible position or the distance to the energy source. Therefore, another power source must be used to solve this problem. Energy harvesting technology is an increasingly popular solution that extracts energy from the ambient environment and transforms it into electrical energy. Using piezoelectric transducers, it is possible to transform the vibrations experienced by the bogie into energy that can be used to power the sensors. A prototype with multiple piezoelectric transducers has been designed, built and subjected to tests to validate the technology. The experimental results for all of the different configurations tested and levels of energy collected are presented.
The theory and practice of train-induced aerodynamic pressure loads on surfaces near to the tracks is compromised by an incomplete understanding of trains operating in short tunnels, partially enclosed spaces, and next to simple structures such as vertical walls. Unique pressure-loading patterns occur in each case. This work has been carried out to obtain a fundamental understanding of how these loading patterns transition from one to the other as the infrastructure becomes more confined. It also considers the impact of the results on two separate European codes of practice applying to tunnels and other structures. A parametric moving-model study was undertaken, transitioning from the open air to single and double vertical walls, partially enclosed spaces, short single-track tunnels and a longer tunnel. The train model was based on a German ICE2, and was fired at 32 m/s past the structures. Multiple surface pressure tappings and in-flow probes were used, providing the opportunity to assess the three-dimensional nature of the pressure and velocity fields. The experiments successfully mapped the transition between the three loading patterns and isolated the geometric changes. Further loading patterns were discovered relating to the length of the train, the length of the tunnel and the distance from the tunnel entrance. The three-dimensional nature of the pressure was related to the length of the tunnel and the distance from the tunnel entrance. Issues surrounding the lack of provision in codes of practice for short tunnels were discussed.
High-speed passenger trains can cause destructive vibrations on bridge structures. The possibility of resonance is particularly related to the bridge superstructure’s natural frequency and the frequency of moving loads, which is characterized by the train type and its speed. In this study, a multimode dynamic analysis has been performed for a variety of superstructures, span lengths, train speeds and train types. Numerical analysis has been applied to evaluate different girder support conditions such as simple, two-span continuous and three-span continuous. In addition, the train/structure interaction is included in the analytical models. The results are presented in terms of moment dynamic load factors for a practical range of the superstructure’s fundamental frequency, which include various superstructure types such as concrete, prestressed concrete and steel. Different high-speed trains are considered moving at various speeds to capture the configuration for highest responses. This study provides a set of diagrams for initial estimation of high-speed railroad bridge bending moment response. Proposed diagrams will help bridge designers to avoid an uneconomic bridge system in early design stages.
A moving block philosophy is increasingly being implemented as part of communications-based train control (CBTC) systems in mass transit operations. Due to its complexity and safety criticality, it is difficult to develop formal methods to support the design of specific schemes. An innovative framework, based on topology mathematics, for supporting CBTC moving block system development is proposed in this paper. Within the new framework, the moving block train control logic is transformed into topological spaces representing the movement authority for trains. Using this approach, the verification of logic and safety properties can be performed by automatic assessment of the topological space. Within the paper the essential characteristics of moving block systems, train behaviour and static track-side infrastructure are analysed. As a result of this analysis, topological units are formed to represent train movement trajectory and standard railway network elements. Four calculation methods: dividing, trimming, covering and integrating, are described as standard unit operations. Finally, a case study is implemented to demonstrate how the method is advantageous for CBTC scheme layout development. It is found that the approach is able to bridge the gap between traditional, highly abstracted, formal methods and the specific safety-critical railway scheme designs.
An inconvenient consequence of the UIC health and safety criterion for allowable pressure changes in railway tunnels is highlighted. It is shown that the criterion limits allowable speeds in long tunnels with large changes of elevation much more than it does in equivalent tunnels with small changes in elevation. The constraint is especially strong for trains travelling uphill, but it can also exist for trains travelling downhill. Possible ways of avoiding the problem without reducing speed are considered and are found to be practicable in some cases. However, they are of uncertain suitability because they rely on exploiting a particular feature of the safety criterion in a manner that is unlikely to have been intended when it was mandated. In addition, attention is drawn to an ambiguity inherent in the application of the criterion to certain types of tunnel. Suggestions are made for simple modifications to the criterion and comparisons are made with conditions experienced routinely in commercial aviation.
Railway bridges form one of the major railway asset groups with more than 35,000 bridges on the UK rail network. Additionally, the bridge structures are old with more than 50% of the population constructed over 100 years ago. Due to the unique nature of each bridge and their varied means of construction, the decision as to what type of maintenance actions should be performed and when to perform them is a complex problem. Models can be formulated to predict the future condition of assets along with the effect that interventions such as servicing, repair and element replacement will produce. This can be used to support this decision making process. This paper demonstrates a Markov modelling approach to predict the condition of individual bridge elements. For each bridge element the degradation process is determined by examining the maintenance records and analysing the times that each element takes to deteriorate to the point where maintenance of a certain severity classification is required. By combining the elemental models, an overall bridge model is formed which can be used to investigate different maintenance strategies. The model is capable of accounting for a bridge’s current condition, material, route criticality, structural arrangement and environment. The maintenance, opportunistic maintenance and renewal strategy can also be varied in the model along with the service frequency, inspection frequency and repair delay time. Using the model the whole life costs can be predicted for any of the selected maintenance strategies.
The use of state-of-the-art technology to collect and analyse data has significantly improved the effectiveness of safety studies. Currently, despite the fact that there are many safety systems deployed at railway crossings, only limited research has been conducted to evaluate which of these systems is the most effective in terms of costs and safety. This paper demonstrates a way to evaluate safety at railway crossings using a twin-pronged approach: a driving simulator and traffic simulation software. A number of outputs have been observed from a driving simulator, such as driver compliance rate, vehicle speed profile, acceleration profile, initial braking position and final braking position. The compliance percentage at passive crossings (67 and 72% for a stop sign and rumble strips, respectively) has lower compliance rates compared with active crossings (97 and 93% for flashing red light and in-vehicle audible warning, respectively) at an 80 km/h approach speed. Using a statistical analysis it is shown that speed and acceleration profiles can be used to differentiate the effectiveness of active and passive crossings. These indicators are interpreted and used as input to a traffic simulation, which assists in determining which safety device is more efficient. By integrating driving simulator and traffic simulation models, this approach can be applied to evaluate and compare safety performance without the need to install costly test beds at real railway crossings.
A two-dimensional (2D) finite element model has been developed for simulation and analysis of train/turnout vertical dynamic interactions at a common crossing. The model has been validated through field measurements and simulation results obtained using a three-dimensional (3D) multi-body system (MBS) model. The dynamic behaviour of three turnouts on the Dutch railway network was simulated using the 2D model. The simulation results were compared with measured data collected from the instrumented crossings containing corresponding turnouts. It was observed that the values of the vertical acceleration of the crossing nose obtained from the simulations were in good agreement with the measured values. The 2D model was verified by adapting the more intricate 3D MBS model established in the VI-Rail software. The vertical geometry of the rail used in the 2D model was obtained using the wheel trajectory from the 3D model. It was observed that the dynamic wheel forces in the two models were close to one another. From these results it was concluded that the 2D model is able to simulate train/turnout interactions with a good accuracy and thus it can be used instead of complex time-consuming numerical simulations.
In this paper, the effect of track spacing on the aerodynamic performance of a stationary double-stacked freight wagon passed by a high-speed passenger train is investigated using large eddy simulation (LES). The passenger train is a 1/20th scale model of an ICE2-shaped high-speed train and consists of nose, two coaches, inter-carriage gap and tail. Based on the speed and height of the passenger train, a flow Reynolds number of 2 x 105 is used in the simulation studies. To isolate the effect of the mesh resolution computations are performed using three different meshes: coarse, medium and fine, consisting of 3.2 x 106, 6.9 x 106 and 9.0 x 106 nodes, respectively. The results are also validated with available experimental data and a good agreement is demonstrated. The aerodynamic loads on the freight containers and passenger train are obtained during a passing process. High side force values are generated on the freight containers when the passenger train approaches followed by a sudden reduction when the nose of the passenger train passes the freight wagons. There is also a reduction in the side force when the tail of the passenger train passes the freight wagon followed by a significant increase when the wake flow hits the freight wagon. Similar behavior is observed for the lift and drag coefficients. The effect of track spacing is investigated by performing simulations at three different track spacing values: 3.5, 4 and 4.5 m. The results show that a reduction in track spacing generally increases the aerodynamic forces on both the freight wagon and passenger train.
Signalling block occupancy is triggered by the wheelset of a rail vehicle ‘shunting’ the track circuit. The main cause of loss of shunting is the many materials that can be present on the rail head. These include iron oxides, leaves, ballast dust, oil, as well as products deliberately applied to the rail/wheel such as grease, friction modifiers, lubricants and sand. These may lead to an indication that a signal block is unoccupied when a train is actually present. Friction modifiers (FMs) are being increasingly used for reduction of noise, lateral forces, wear, rolling contact fatigue, etc. The Kelsan® high positive friction (HPF) solid stick FM is applied directly to the wheel tread creating a thin film. Although no effects have been observed during field operation, the intention in this work was to build on previous studies and evaluate conductance across a wider range of contact conditions as studies have shown that loss of shunt is more common with light axle loads where films could have a greater effect. The testing was performed at a contact pressure of 470 MPa (equating to a 4.9 tonne axle load). An HPF stick was spring loaded against the rotating wheel disc to generate a FM film at the contact. Tests were run to measure the impedance across the discs using a modified TI21 track circuit. Static testing was also performed using discs with a pre-generated HPF film. Analysis of the results showed that the application of HPF friction modifier had no significant effect on the measured level of impedance. The highest impedance levels were recorded under pure rolling (0% slip) where FMs were not being applied. In cases where the application of FM increased impedance, the recorded impedance values were still lower than the highest values measured in the absence of a FM. This is of key relevance as several light rail operators coast their trains.
A three-dimensional equilibrium model of a wheelset is created that takes the geometrical contact and non-linear creep force between the wheel and rail into account. This model can thus be used to study derailment conditions during flange climbing. To ensure the validity of Nadal’s criterion at small and negative angles of attack, the effects of the angle of attack and friction coefficient on an "equivalent friction coefficient", which is defined as the ratio of the lateral creep force to the normal force, are studied. Using the results of the wheelset equilibrium equation, two curve-fitted formulas for the equivalent friction coefficient are generated in terms of the angle of attack and friction coefficient using, respectively, the Shen–Hedrick–Elkins creep theory and FASTSIM approach. A derailment criterion is proposed based on the curve-fitted equivalent friction coefficients, which takes the angle of attack, friction coefficient and contact angle into consideration. The effectiveness of the proposed criterion is verified through numerical comparisons with wheelset equilibrium equations for different contact angles and friction coefficients, and through experimental comparisons with scaled tests made by Japanese National Railways and full-scale field testing at the Transportation Technology Center, Inc.
Despite the increasing trend for high-fidelity train simulator procurement in the rail industry, current research suggests that simulators are extremely underutilised, which points to ineffective integration arising from one or more disconnects in the management layers. This paper presents a study that set out to: profile the design of driver learning frameworks; investigate how simulators were being integrated; and determine key criteria for simulator acceptance. Data were collected from 61 industry end-users, mostly train drivers, in six rail organisations, and analysed thematically. The findings revealed three Rs that reflected perceptions of poor integration and comprised the dominant end-user evaluation criteria for simulator utility; these were: (i) Reality; (ii) Relevance; and (iii) Reliability. This paper explores the problem of ineffective integration by using and applying a Robocop allegory, in order to disentangle the dynamic shared between the systemic and cultural influences of the organisation, when new technology is introduced in a highly regulated environment. The paper concludes by presenting three prime directives, triangulated from the study and current literature, to transcend the issues impeding the path of effective simulator integration in rail, and overcome the ‘Robocop problem’ as it applies to this industry.
The maximum air velocity created by a moving train inside a tunnel is obtained using an artificial neural network approach. A neural network model is developed to represent a single train travelling in a single tunnel. A set of non-dimensional groups, which are known to influence the induced flow characteristics, is used for the training of the neural network. Various test runs are compared with the results of the authoritative software, Subway Environmental Simulation. The presence of ventilation shafts within a tunnel is included in the model by defining an aerodynamically equivalent single tunnel using major head loss characteristics of different parts of the system. This approach eliminated the requirement to train the neural network for a large number of possible tunnel/shaft configurations.
Aerodynamic drag is approximately proportional to speed squared so the drag of slower moving freight trains has received less attention than that of higher-speed passenger trains. Key results of wind tunnel tests of European container trains were published in 1989 and are the basis for most assessments of drag of European container trains (American container trains usually have far higher drag due to double-stacking containers or transporting complete semi-trailers and were studied in research programmes at a similar time). The research reported here concerns a reappraisal of the European results and of more recent results obtained from the application of computational fluid dynamics modelling and the results of real-world and wind tunnel testing of the aerodynamics of container wagons. The paper presents empirical equations that can be used to predict the energy savings associated with different container loading scenarios within a fixed length train and the energy required for carrying aerodynamic features such as baffles or fairings. Illustrative examples are provided using data measured during freight operations. The effect on drag of side winds and their speed distributions are included as are representative vehicle speed profiles. Most previous authors have ignored both side winds and end effects; it is shown that the effects of these are opposite but of similar magnitudes so the results of these authors remain valid.
Fidelity evaluations are an important part of simulation design. They identify any gaps in fidelity, help establish the simulator’s overall validity, and their outcomes may significantly enhance the correspondence between the simulated environment and the real world. However, fidelity evaluations are easily overwhelmed by the technical focus in the simulator commissioning and acceptance processes, and too often, are overlooked or undermined in favour of remaining within the scope of the original specification. This article presents a fidelity evaluation that was applied to a railway safety research simulator after it was deployed for operational use. The evaluation was stratified according to the physical, functional and task-based strands of fidelity, and undertaken in a collaborative research approach that integrated the relative domain, task, simulation and human factors-based expertise of a team of evaluators. Furthermore, the evaluation also examined the simulator’s tractability in terms of its intended users (researchers), and investigated the scope for scenario development. The findings revealed several opportunities for improving the fidelity of the simulator for research (and training) applications, but also identified a number of critical deficiencies in its underlying architecture. This paper discusses the outcomes of the evaluation in terms of the fidelity expectations of the developer and user, and the tension encountered when trying to adjust these post-deployment. Lastly, it provides some clarification between what to improve and what can be improved, when the proverbial train has, for all intents and purposes, left the station.
In this article, the stability limit of the undisturbed motion of a simple railway motor bogie whose traction motors are fully suspended on the bogie frame is analysed. Under appropriate assumptions, equations of motion for the vehicle system are deduced by considering the lateral and yaw motions of the bogie frame, wheelsets and traction motors. Using root locus analysis, eigenvalues and eigenvectors of the equations are calculated, and a stability assessment for determining the bifurcation point is proposed. The vehicle speed at the bifurcation point is defined as the bifurcation speed where the equilibrium position of the vehicle system loses stability. Parametric studies are undertaken in order to investigate the respective effects of the traction motor's parameters on the stability of the vehicle system. It is found that the stiffness, damping and mass properties of the traction motor have significant influences on the bifurcation speed. There exists an optimum natural frequency for the motor suspension, below which a relatively high bifurcation speed is obtained. Finally, the effect of the bogie's parameters on the optimum natural frequency is investigated, and it is shown that the optimum natural frequency is significantly affected by the primary and secondary suspensions, and the wheel/rail contact conditions.
Part 1 of this paper reports results from the extensive full-scale slipstream measurements carried out as part of the AeroTRAIN project, and in particular concentrates on the ensemble analysis of this data. This paper concentrates on the analysis of maximum gusts, in order to make suggestions for modifications to the current technical specifications for interoperability (TSI) methodology. The very large data set obtained for one particular high-speed train type (the S-103) enabled the variation of slipstream gusts with vehicle speed and wind speed to be determined. It was also possible to carry out a statistical analysis of the gusts that enabled the standard uncertainty of the TSI gust parameter to be determined. It was shown that for most trains the maximum gusts occurred in the near wake of the train, but for double-unit trains the maximum gusts could occur around the gap between the units and for locomotive/coach combinations the maxima could occur around the nose of the locomotive or at the discontinuity between the train and the locomotive. Perhaps the most significant result, which could allow a considerable simplification of the TSI methodology, was that if both trackside and platform measurements for a particular train were plotted against height above the rail, then, with very few exceptions, they fell onto one curve, which implies that a trackside measurement could replace the current required platform measurement.
This paper describes a series of extensive and unique full-scale measurements of the slipstreams of trains of various types that were carried out as part of the EU-sponsored AeroTRAIN project, together with the analysis of the experimental data. These experiments were carried out with the fundamental aim of seeking to reduce the complexity of the current technical specifications for interoperability (TSI) testing methodology. Experimental sites in Spain and Germany were used, for a range of different train types – high-speed single-unit trains, high-speed double-unit trains, conventional passenger units and locomotive/coach combinations. The data that was obtained was supplemented by other data from previous projects. The analysis primarily involved a study of the ensemble averages of the slipstream velocities, measured both at trackside and above platforms. The differences between the flows around different train types were elucidated, and the effect of platforms on slipstream behaviour described. A brief analysis of the effects of crosswinds on slipstream behaviour was also carried out. Through a detailed analysis of slipstream velocity components, the detailed nature of the flow around the nose and in the near wake of the train was investigated, again revealing differences in flow pattern between different trains. Significant similarity in the far wake flows was revealed. These fundamental results form the basis for the detailed discussion of the proposed TSI methodology that will be presented in Part 2 of this paper. Overall the results enable the nature of the flow field around trains to be understood in far greater detail than before, and also allow the developments of a revised TSI methodology which is more efficient than current practice.
Special trackwork, including turnouts and crossing diamonds and their components, plays a vital role in railway infrastructure by providing route flexibility to trains as they travel across a network. As the interest in shared rail corridors involving heavy-axle-load freight traffic and high-speed-rail passenger traffic grows, special trackwork represents a significant challenge due to diverging loading characteristics and design priorities. This paper presents an overview of the issues related with special trackwork for shared rail corridors, as well as an in-depth analysis of the relevant research to date. The relevance of different shared operation types and research needs are also presented. This study can be used to assist in the planning of new passenger services on freight rail lines, or vice versa, in the USA, and may also be relevant to shared rail corridor development in other countries.
The measurement and improvement of track quality are key issues in determining the time at which railway maintenance must be performed and its cost. Efficient track maintenance ensures optimum allocation of limited maintenance resources which has an enormous effect on maintenance efficiency. Applying an appropriate tamping strategy helps reduce maintenance costs, making operations more cost-effective and leading to increased safety and passenger comfort levels. This paper discusses optimisation of the track geometry inspection interval with a view to minimising the total ballast maintenance costs per unit traffic load. The proposed model considers inspection time, the maintenance-planning horizon time after inspection and takes into account the costs associated with inspection, tamping and risk of accidents due to poor track quality. It draws on track geometry data from the iron ore line (Malmbanan) in northern Sweden, used by both passenger and freight trains, to find the probability distribution of geometry faults.
The maintenance and renewal activities of wheelsets account for a large proportion of the whole-life costs for railway rolling stock. These activities are influenced by a large number of factors including depot constraints, wheel surface damage, fleet availability and vehicle design. If these factors are not managed efficiently it can have significant implications on a vehicle’s service provision, track damage, environmental and whole-life costs. Therefore, the development of an effective wheelset management tool will support the optimisation of maintenance and renewal regimes, thereby increasing wheelset life and reducing costs. Further development of the Vehicle Track Interaction Strategic Model has enhanced the rolling stock modelling capabilities of the tool through the development of the Wheelset Management Model (WMM). This model aims to assist in the strategic planning of wheelset maintenance and renewal activities and thereby allowing users to examine the benefits and cost impact of a range of different scenarios to optimise wheelset management strategies. This paper describes the capabilities of the WMM and illustrates how the model can be used to optimise a fleet’s maintenance strategy through the application of a realistic industry case study. The implications of different wheelset maintenance regimes on wheelset life and costs were examined. Finally, the paper presents how the tools can be used to investigate whole-system costs and demonstrate the impact of wheelset maintenance on track costs.
The availability of a reliable speed and travelled distance estimation is relevant for the efficiency and safety of automatic train protection and control systems. This paper investigates the main features of an innovative localization algorithm that integrates tachometers and inertial measurement units. Nowadays, the estimation is performed by an odometry algorithm that relies on wheel angular speed sensors. The objective is to increase the accuracy of the odometric estimation, especially in critical adhesion conditions, through sensor fusion techniques based on Kalman filter theory. The Italian company ECM S.p.A. has supported the project, providing a custom inertial measurement unit based on micro electro-mechanical system sensors for the on-track testing of the algorithm. The preliminary results show a significant improvement of the position and speed estimation performances compared to those obtained with SCMT (Italian acronym for ‘Sistema Controllo Marcia Treno’) algorithms, currently in use on the Italian railway network. A wide set of simulated test results, showing the improvement of the estimation process, is presented and discussed. An accurate train navigation that scarcely relies on information from the infrastructure will open a road map for the development of a more and more effective and efficient exploitation of the railway infrastructure.
Rail curve lubrication using wayside gauge face lubrication systems is widely used by the railway industry. It provides cost-effective solutions to reduce rail/wheel wear, energy consumption, costs and noise. Research efforts on cost-effective friction management solutions for the Australian heavy haul industry have been limited. Therefore, the performance measures necessary for the evaluation of effective gauge face lubrication practice have not been developed. Currently, there are no specific performance measures available for heavy haul rail curve lubrication. Also, the performance of in-rail lubrication seems to be poor in most cases. Appropriate performance measures should be implemented that can accurately demonstrate the actual performance of the lubrication. This paper is focused on the development of effective performance measures based on lubrication theory, maintenance regime, field testings of different wayside lubrication equipment technology and different greases currently used on heavy haul lines. Extensive field tests have been conducted on the Queensland Rail Network’s North Coast Line, which is a dedicated coal line. Data were collected and analysed for the development of performance measures and cost-effective lubrication decisions. The presented performance measures and illustrative examples could be used by other types of railway networks for enhancement of rail/wheel asset life, asset availability, reliability and safety along with reduction of costs.
Railroad crossings represent a significant danger in railroad transportation systems. Each year thousands of accidents occur that involve trains and other vehicles at unprotected railroad crossings, resulting in hundreds of fatalities and injuries. Additionally, derailments occur on average once every 6 h across the United States due to mechanical failures and improperly maintained track, endangering property and lives. The lack of electrical infrastructure in remote areas is a primary barrier impeding the installation of safety enhancements such as warning light systems and track health monitoring sensors that could reduce the frequency of such accidents. Providing on-demand power by harvesting energy from deflecting railroad track during the passage of trains is a promising approach compared with the cost of installing electrical power lines or the lack of robust solar and/or wind power solutions. This paper discusses the design and development of several power harvesting devices capable of scavenging power from the vertical deflection of railroad track. The design of a cam-based generator device driven by the train wheels is also discussed. Simulation and testing results on these devices are also presented in this paper.
The measurement and improvement of track quality are key issues in determining both the restoration time and cost of railway maintenance. Applying the optimal tamping strategy helps reduce maintenance costs, making operations more cost-effective and leading to increased safety and passenger comfort. In this paper, track geometry data from the iron ore line (Malmbanan) in northern Sweden, which handles both passenger and freight trains, are used to evaluate track geometry maintenance in a cold climate. The paper describes Trafikverket’s (Swedish Transport Administration) tamping strategy and evaluates its effectiveness in measuring, reporting and improving track quality. Finally, it evaluates the performance of the maintenance contractor and discusses the importance of the functional requirements stated in the outsourcing contracts.
In this paper, we propose the use of workflow nets to study the issues associated with deriving the running states of trains. Triangular fuzzy numbers are introduced to express the train’s activity times and to aid in the modelling using workflow nets of the running processes of high-speed trains. A workflow net links all the activities of a train’s running processes into a sequence called a train running workflow net for high-speed trains. The main job of a triangular fuzzy number workflow net is triangular fuzzy number operation. The principles of this operation are discussed in this paper. The connotations of the two modes of operation of train running workflow nets—sequential mode and alternative mode—are also analysed. In addition, methods for calculating the time duration during which a triangular fuzzy number workflow net operates, both in sequential mode and alternative mode, for high-speed trains are proposed and proved. Train activity times and running status can be forecast by executing the proposed triangular fuzzy number workflow nets.
This paper addresses the effect of formation length and service frequency on the determination of train timetables. The case of inter-city rail transport is considered since the planning of through journals allows the problem to be significantly simplified. Based on the analysis of passengers’ generalized travel expense, the law of passenger boarding choice considering the schedule delay cost is studied and extended. Then the law of boarding choice under the condition of the generalized travel cost is found. The law states that the distribution of the expected boarding time of passengers on every train is sequential, continuous and symmetric and the attractiveness range of each train is uniform. A maximum profit model with elastic demand is solved using an analytic method. A numerical example is provided to show the effects of train formation and service frequency on passenger demand and objective functions as well as the train schedule with different balance factors. Two operator service strategies (i.e. a short train and high service frequency mode or a long train and low service frequency mode) are analysed in depth.
The accuracy of multi-body simulation results relies on the model building process and the accuracy of the model parameters. A more widespread use of vehicle dynamic calculations in the acceptance process would be possible if the validation of the model was secured. This paper proposes a methodology for an objective and direct identification of the values of the parameters of a rail vehicle model, using the results of the stationary tests defined in the acceptance process of railway vehicles (EN14363). The methodology also takes into account the variability of the measuring process by providing a probabilistic estimation of the identified parameters. The methodology is validated using an example of a virtual wheel unloading test (simulation). Four significant model parameters can be accurately calculated: vertical primary and secondary suspension stiffness, stiffness of the anti-roll bar, and height of the null moment point (the lateral/roll coupling effect of the air spring). Finally, a reduction method is shown which decreases the uncertainties of the identified parameters by up to 50%.
This paper investigates, with the help of a mathematical model, the impact of traffic composition on the economic profitability of a new railway corridor. The model permits, for various exploitation scenarios (mixed traffic operation, dedicated passenger operation, dedicated freight operation), first, the calculation of the economic profitability of each scenario (net present value (NPV) and the internal rate of return of the investment), and second, the selection, on the basis of demand for passenger and/or freight to be transported via rail on the new corridor, the exploitation scenario that presents the highest economic profitability. The obtained results show that the basic criterion for the selection of the optimum scenario concerns the characteristics of transportation demand (type of goods and volume transported) and, second, the topography of the landscape. Specifically, for average demand values, mixed exploitation scenarios present the highest NPV, whereas for high demand values, dedicated operation scenarios are the most profitable. Furthermore, the dedicated freight operation scenarios presents a higher NPV compared with passenger operation scenarios when the ratio of the demand of the number of passengers to freight tonnes approaches 1:3 (traffic train composition percentage of 50:50), this favours mixed operation scenarios.
This paper reports on the development of high-speed railway systems in China. In addition, with respect to the characteristics of the high-speed train system, the relationship between various coupled systems that can affect train operation are analysed, including interactions between two vehicles, between a track and train, a pantograph/catenary and train, and airflow and a train. On the basis of this research, problems pertaining to the dynamics arising from high-speed operations are studied and the necessity for a study of the system dynamics of high-speed trains—considering all these interactions—is discussed. A theoretic framework for the analysis of the dynamics generated by coupled systems in high-speed trains is presented and the modelling methods for these coupled systems are outlined.
This paper describes a novel connection system which allows fast, safe and reliable coupling and uncoupling of two sections of a freight wagon body as part of a bimodal transport system. The connection system allows the time for loading and unloading a truck trailer to be reduced to almost one-half of the current duration. The connection system is composed of a cylindrical clamping pin with three conical shoulders at one end and an axial slide. A crank mechanism in a cylindrical guide is used to lock the clamp. The crank is connected to the pin and symmetric piston rods are connected to the moving clamp, other auxiliary members constrain the clamp.
Computer simulations are utilised to study the energy used by heavy haul trains and the amount of energy that can be generated from dynamic braking of these trains; these studies allow the potential for the application of hybrid locomotives to be evaluated. An in-house written software package is used to perform simulations on the energy balance between energy usage and the energy generated from dynamic braking for heavy haul operations on two typical track routes in Australia. The simulation results show that the energy generated from dynamic braking can contribute up to 30% of the energy used in locomotive traction. Detailed analyses show that the locomotives can operate at an average power that is much less than full power, and an energy hybridisation potential factor is defined, with the maximum factor reaching a value of 63%. This factor indicates the considerable potential for using hybrid locomotive traction in heavy haul applications.
The effects of current density and polarity on the tribology characteristics of the contact between an aluminium/stainless steel composite third rail and a copper-impregnated carbon collector shoe are studied using a modified pin-on-disc apparatus. In particular, friction coefficient, temperature rise and wear volume loss of the friction pair are measured. The chemical constituents of worn surfaces are investigated using energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that with increasing current density the temperature of the contact area increases, the contact surfaces oxidize, the tangential force and friction coefficient decrease, and the wear volume loss of the friction pair increases. Oxidation degree and the wear volume losses of collector shoes with a positive polarity are larger than that of collector shoes with a negative polarity. Water molecules adsorbed by the sliding contact surface of the friction pair decompose into hydroxyl and hydrogen ions under the influence of the electric field; subsequently, the hydroxyl ions migrate to the anode where they generate oxygen. The anodic oxidation reaction at high temperature weakens the bond between the grains in the surface layer of the positive friction pair, and aggravates the wear of material, which in turn changes the friction and wear characteristics of the friction pair.
Three different train configurations with different numbers of cars are analysed in order to investigate the effect of the train length on wake structures. The train geometry considered is the aerodynamic train model and the different versions have two, three and four cars. Due to the different lengths of the trains, the boundary-layer thickness will be different at the tail of each configuration. The flow is simulated using detached eddy simulation, and coherent flow structures are extracted via proper orthogonal decomposition and dynamic mode decomposition. As a result of reconstruction of the flow field using coupling of the mean flow and the first fluctuating proper orthogonal decomposition mode, it is found that the dominant flow structure in the wake is the same for all three cases. However, this structure has different frequencies and wavelengths depending on the boundary-layer thickness in front of the separation. It is shown that the frequency decreases as the boundary-layer thickness increases for these train configurations.
The wheel–rail contact force is an essential parameter in many aspects in railway mechanics, for instance, in rolling contact fatigue analysis. Since the wheel–rail contact force cannot be measured directly, instrumented wheelsets have been developed to collect the radial strains at certain positions on the wheel web. In this paper, an inverse method to estimate the wheel–rail contact force history based on strain measurements is discussed. In the proposed method, the contact force is determined by minimizing the least-squares discrepancy between measured radial strains and corresponding computed strains from a three-dimensional finite-element model of the wheel. The inverse method is compared with the existing method based on direct extraction of the contact force from combinations of measured strains using Wheatstone bridges. Using synthetic data, it is found that the proposed inverse method is insensitive to the eigenmodes of the wheel, as opposed to the existing method. In addition, noise reduction by using Tikhonov regularization and by choosing proper sampling rates are discussed.
In this paper, the quantification of the external noise sources in high-speed trains is discussed. A thorough understanding of the underlying causes of noise generation in high-speed trains is needed to develop effective noise control measures. However, because high-speed trains produce a complex array of sounds, it is very difficult to determine each individual source of noise. In this study, the delay-and-sum beamforming method, which uses microphone arrays, was used to separate the noise sources and analyze the sound characteristics of high-speed trains. A new microphone array with 96 microphones was designed to measure the noise produced by high-speed trains. Performance verification tests were conducted to ensure the reliability of the results obtained from the array. Then, the system was used to measure the sounds produced by Korean high-speed trains traveling at speeds between 150 and 300 km/h. Sound maps were then produced using the beamforming technique. The study determined that the majority of the noise produced by the high-speed trains originated from the front nose, bogie, pantograph and inter-coach spacing. Finally, the beampower spectra of the aerodynamic noise sources originating in the front nose, pantograph and inter-coach spacing were deduced from frequency conversion. From these results, the aerodynamic noise characteristics of the major sources of noise in high-speed trains were determined.
In this paper, a step-shaped trench was introduced for the attenuation of train-induced vibration levels on trackside buildings. In order to evaluate the effectiveness of the proposed type of trench in comparison with a standard rectangular trench, a two-dimensional finite element model was developed under plane strain conditions using the ABAQUS software. The validity of the preliminary model of the track including a rectangular-shaped trench was confirmed by a close agreement of obtained results with those of previous studies. The effectiveness of the step-shaped trench compared with the rectangular type was studied in open and in-filled forms in terms of decreasing the effects of ground-borne vibrations on trackside structures. The obtained results for open and in-filled step-shaped trenches respectively showed 21% and 26.2% decreases in the maximum amplitude reduction ratio with respect to the common rectangular trench. Moreover, in the case of a real train moving loads, the proposed trench shape further decreased the values of peak particle velocity, root mean square and particle velocity decibel on a trackside structure compared with the values obtained for a rectangular-shaped trench.
The ladder track used by the Beijing subway which can be subjected to rail corrugation is considered in this paper. Dynamic models of the vehicle and the ladder track are developed to analyse the track vibration behaviour. Using these models the effect of the most significant ladder track parameters on track vibrations are analysed in the frequency and time domains. Using experimental and numerical results the vibration frequency of the rail that is responsible for rail corrugation is determined. Based on the results of the parametric study, an optimisation of the mechanical properties of the ladder track to reduce or eliminate the track vibrations at the corrugation frequency and ultimately to reduce the chance of rail corrugation is performed using a genetic algorithm-based approach. The results of the optimisation are presented and discussed.
Transition zones corresponding to the passage from railway tracks on embankment to natural ground or settlement free structures are frequently problematic for maintenance. Changing stiffness of the track and differential settlements are the main causes for the degradation of tracks and foundations at transitions. This paper presents a methodology to predict the settlement of the track due to train loading, applicable to transition zones. The methodology is based on dynamic calculations using a (non-linear) train–track interaction model and an incremental settlement model. Important non-linear aspects in dynamic models for railway transitions are the loss of contact between the sleepers and the ballast and the non-linear constitutive behaviour of the ballast. The settlements are calculated paying attention to the factors that most influence the long-term behaviour of ballast, such as the amplitude of the applied dynamic force and the number of loading cycles. The importance of the dynamic loading from the trains and of the constitutive models used for the trackbed layers is analysed.
This paper proposes the design of an aerodynamic braking device for a high-speed train. The design is based on the parameters of the high-speed train and the working principles of airplane wings. The proposed device is a unidirectional opening model driven by hydraulics. The prototype uses hard-wired signals to transmit braking commands on eight levels. The important characteristics of the device include a synchronous action and a fault-oriented security design. Its functions include service braking, gradual braking, emergency braking and self-checking. Simulation results show that deceleration in the high-speed zone between 250 and 500 km/h can be improved by between 8 and 60%. When the train runs at 500 km/h, the braking deceleration rate can be improved by 0.12 m/s2. The simulation results are found to agree with wind tunnel test results. The braking characteristics are also investigated using a test bed, which mimics the aerodynamic load exerted on the prototype when the train is running between 0 and 550 km/h. It is clearly demonstrated that the proposed principle of the aerodynamic braking system is feasible and its design scheme is reasonable. The aerodynamic braking device can survive a 50,000 N aerodynamic load, and the time taken to achieve the maximum braking capacity, which is the time taken to take the brake panel from its closed position of -5° to the maximum angle of 75°, is less than 3 s. The proposed prototype therefore offers an important step in the design of practical systems.
The underfloor flow field of three different 1:50 generic high-speed train models hauled through a water towing tank at a speed of 4 m/s (Reynolds number = 0.24 x 106) over smooth ground, rough ground, and ground with sleepers is measured by means of two-component particle image velocimetry. The reference train model, consisting of four cars, features inter-car gaps and two bogies per car. These features are removed and all gaps are closed to create the smooth train configuration whereas the rough train configuration has all the gaps but no bogies. The lowest underfloor flow velocities and velocity gradients at the ground are observed for the smooth train model on the ground with sleepers. Furthermore, the measurements reveal that any additional irregularity of the underbody leads to regions characterised by flow acceleration in the otherwise Couette-like flow and this increases the possibility of ballast flight. Therefore, it is concluded that a smooth underbody can lower the risk of ballast flight. The results obtained for the reference train model are compared with those of a full-scale measurement. It is shown that the results of the water towing tank experiments with the scaled train model reflect the main characteristics of the underfloor flow of the full-scale measurements.
This paper deals with selected problems encountered in the real-time operation of a passenger railway station. Delays to incoming trains can negate a valid timetable and track assignment plan. In such situations the dispatcher has to flexibly solve problems related to potential train routing conflicts. This paper models the dispatcher’s decision-making process using a mathematical programming approach. Inputs to the mathematical programming model reflect potential delays to incoming trains. Outputs from the model concentrate mainly on solving the following problems: first, which platform track is assigned to an arriving train, and second, how long connecting trains are allowed to wait for the delayed incoming train. The objective function applies a multi-criteria approach with two goals: to reduce the influence of the delays on departing trains (i.e. to minimise the deviations from the valid timetable), and, at the same time, to minimise the inconvenience caused to passengers. The proposed model can be used to support the dispatching control of real-time traffic or as a part of a railway station simulation model.
Tread braking of railway wheels results in the kinetic energy of the train being dissipated into the wheel and blocks in the form of heat. This heat is further conducted into adjacent structures, notably the cold rail, and also transferred into the surroundings by convection and radiation. Heat partitioning between wheel and block is, for short time periods, controlled by local thermal interactions at the contact point and by the conductive properties of the bodies. However, for a metro train that performs longer periods of intermittent braking (or for drag braking) convective and radiation cooling properties of the components come into play. In the present study, results from brake rig tests and from in-field testing of a metro train are presented and used to calibrate a simulation model. It is found that the cooling level of the wheels of the metro train is substantially lower than for the wheels of a freight wagon. Moreover, it is found that the first axle on the metro train is exposed to higher cooling levels than the remaining axles. In a numerical example, temperatures of tread braked wheels are calculated using the new findings for a metro train, and the results obtained are compared with wheel temperatures as calculated assuming freight wagon conditions.
This paper shows the importance of modelling the components of the suspension when performing dynamics simulations of a railway vehicle. Focusing on the air spring secondary suspension, a process to define an accurate component model is proposed based on a combination of laboratory tests and model identification techniques. Six models for the air spring secondary suspension are discussed and assessed based on comparison with experiments.
A hot mixed asphalt layer can be inserted between the ballast and subgrade layers in the foundations of rail tracks to improve the stress and strain distributions in these layers and also reduce track vibrations and level of damage in the track’s superstructure. These phenomena depend on various parameters such as the manner of operation of the railway and the mechanical characteristics of the foundations. This study is devoted to the derivation of analytical equations that describe the tensile strain on the asphalt layer and compression stress in the subgrade layer in terms of these parameters. A series of numerical analyses have been performed using the KENTRACK simulation code in which the railway axle load, asphalt thickness, ballast modulus and California bearing ratio of the subgrade were varied. The obtained values of the maximum tensile strain in the asphalt and compression stress on the subgrade were analysed using a least squares method in order to extract correlation equations that consider the maximum tensile strain in the asphalt layer and compression stress on the subgrade layer in terms of the varied parameters. A comparison of the obtained simulation results with measured data reported in the literature shows a good agreement between the results.
As a general rule, the multi-body simulation models used by railway vehicle designers consider the wheelsets to be fully rigid, thus leading to possible errors when calculating the critical speed of the vehicle under study. This article suggests a wheelset model that takes into account wheelset flexibility for the study of dynamic stability. The model is simple to implement, easily parameterised, and can be applied to both conventional and variable gauge wheelsets. The parameters corresponding to wheelset flexibility that most influence the critical speed of high-speed and variable gauge vehicles are also analysed.
Ultrasonically detected ‘squat-type’ rail defects are becoming increasingly common on railways throughout the world. On the London Underground (LU) these defects are found on three lines. Focussing on the difference between these lines and others on the LU network has identified vehicles with modern AC traction characteristics as a common theme found only on problem lines. Metallurgical analysis of the defects found that the mechanisms for generation and growth are not consistent with conventional rolling contact fatigue, with evidence of significant thermal input. The defects are only found on open sections. The areas most susceptible to the defects are those where low-speed running is more common. A mathematical model of the traction package has been used to examine the forces and thermal input generated at the wheel–rail interface with modern wheel-spin control systems under wheel slip and adhesion recovery conditions. The outputs have been analysed to assess whether sufficient forces and temperatures are generated to explain the observed rail damage. The results suggest that under certain circumstances wheel-spin recovery generates sufficient rail surface energy for martensitic transformation. Additional modelling suggests that thermal input from wheel-spin aids crack propagation and that regions of slightly degraded (wet as opposed to leaf or oil contaminated) rail adhesion are sufficient to initiate these flaws.
This paper demonstrates an enhanced Brute Force algorithm application for optimising the driving speed curve by trading off reductions in energy usage against increases in delay penalty. A simulator is used to compare the train operation performance with different train control system configurations when implemented on a section of high-speed line operating with two trains, including differences in journey time and train energy consumption. Results are presented using six different train control system configurations combined with three different operating priorities. Analysis of the results shows that the operation performance can be improved by eliminating the interactions between trains using advanced control systems or optimal operating priorities. The algorithm is shown to achieve the objectives efficiently and accurately. Control system configurations with intermediate levels of complexity (e.g. European Train Control System Levels 2 and 1 with in-fill) when coupled with the optimisation process have been shown to have similar performance to the more advanced control system.
This is the first part of a two-part paper that describes the results of an experimental investigation to measure the aerodynamic pressure forces on structures in the vicinity of railway tracks. The investigations were carried out in order to obtain a fundamental understanding of the nature of the phenomenon and to obtain data for a variety of railway infrastructure geometries of particular relevance to the UK situation, in order to provide material for a National Annex to the relevant Eurocode. The experiments were carried out on the moving model TRAIN Rig, with models of three different sorts of trains with different nose types, and a variety of infrastructures types: vertical hoardings, overbridges, station canopies and trestle platforms. The transient loads that were measured had a characteristic form: a positive pressure peak followed by a negative pressure peak. In general the magnitudes of the two peaks were different, and varied with infrastructure type and position, as well as with train type. As would be expected, the more streamlined the train, the lower were the magnitudes of the pressure transients. A comparison of the experimental results was made with a variety of existing model- scale and full-scale data and a broad consistency was demonstrated, within the limits that the rather different experimental conditions in the various cases would allow. An analysis of the scaling of these pressure transients was carried out, and it was shown that whilst there was a reasonable coalescence around a theoretical formulation, the complexity of the flows involved meant that a general scaling formulation could not be achieved. Part 2 of this paper will consider the application of the results to the development of revised standards formulations.
The temperature rise of wheels and blocks due to frictional heating during railway tread braking along with the transfer of heat through the wheel–rail contact is studied in this paper. In particular, heat partitioning between block, wheel and rail for stop braking cycles is considered. The wheels are of interest because they are a limiting factor for railway tread braking systems. Two types of thermal models are employed to investigate the maximum temperatures over the wheel tread. In a circumferential (plane) model of wheel, block and rail, the heat transfer problem is studied by use of a finite element formulation of the two-dimensional time-dependent convection–diffusion equation. The hot spot phenomenon is simulated by introducing a prescribed wheel-fixed contact pressure distribution between wheel and block. In an axisymmetric (axial) model of wheel, block and rail, the lateral movements of the wheel–rail contact are studied. A general result is that the cooling effect provided by the rail is important when local temperatures on the tread are considered, but not when studying bulk temperatures created in a single stop braking event. Furthermore, it is found from the lateral movements of the wheel–rail contact that slow oscillations result in maximum temperatures over the wheel tread that are somewhat lower than for travelling on straight track (rolling at the rolling circle).
To simplify construction, reduce weight and improve mechanical properties, a sandwich panel substitution process is performed on corrugated sheets in the floor and roof of a rail vehicle car body. A requirement based selection is used to design the sandwich panels with the corrugated sheet mechanical characteristics as boundaries. Car body stiffness is evaluated by modal analysis. The derived panels reduce the mass of the car body by 600–700 kg. Results show the varying importance of the longitudinal, transverse and shear properties of the floor and roof panels, as well as how efficient the corrugated sheets actually are.
The vertical dynamic actions transmitted by railway vehicles to the ballasted track infrastructure are evaluated taking into account models with different degrees of detail. In particular, this matter has been studied from a two-dimensional finite-element model to a fully coupled three-dimensional multibody finite-element model. The vehicle and track are coupled via a nonlinear Hertz contact mechanism. The method of Lagrange multipliers is used for the contact constraint enforcement between the wheel and rail. Distributed elevation irregularities are generated based on power spectral density distributions, which are taken into account for the interaction. Due to the contact nonlinearities, the numerical simulations are performed in the time domain, using a direct integration method for the transient problem. The results obtained include contact forces, forces transmitted to the infrastructure (sleeper) by railpads, and envelopes of relevant results for several track irregularities and speed ranges. The main contribution of this work is to identify and discuss coincidences and differences between discrete two-dimensional models and continuum three-dimensional models, as well to assess the validity of evaluating the dynamic loading on the track with simplified two-dimensional models.
Models that can predict the correct logistics actions that need to be taken to ensure the availability of spare parts during maintenance of railway vehicles are of considerable interest. Since the occurrence of defects is a random phenomenon it is not possible to know in advance what spare parts will be required at any point in time. This situation requires the creation of a stochastic model that can incorporate uncertainty. Deterministic and stochastic models of maintenance logistics are based on the assumption of a non-zero stock level of spare parts. Carrying an extensive inventory of parts requires a large financial outlay and it is still often the case that a required spare part is not immediately available and has to be obtained. This paper shows, provided certain conditions are met, that it is possible to create cost-effective maintenance procedures even if the required spare part is not immediately available. Thus, the amount of money locked up in stock can be effectively regulated, thus reducing operating costs.
Leaves on railway tracks affect the level of adhesion between the wheel and rail, especially in autumn. When crushed by wheels, leaves form a tarnished, low level of adhesion layer that sticks to the railhead and often requires mechanical removal. A Stockholm local traffic track with a long history of adhesion problems was subjected to field tests on railhead contamination. On five occasions under different conditions, spaced over a year, the friction coefficient was measured using a tribometer and samples of the rail were taken. The techniques of electron spectroscopy for chemical analysis and glow discharge optical emission spectrometry were conducted to determine the composition of the top layer of rail contaminants and hardness was measured using the nano-indentation technique. The tarnished layer contains much higher contents of calcium, carbon and nitrogen than do leaf residue layers and uncontaminated samples. These high element contents are generated from the leaf material, which chemically reacts with the bulk material. The hardness of the tarnished layer is one-fifth that of the non-tarnished layer of the same running band. A chemical reaction occurs from the surface to a depth of several microns. The thickness of the friction-reducing oxide layer can be used to predict the friction coefficient and extent of leaf contamination.
High-speed trains push air to the front, sides and over the top to form a train slipstream. The extension of the slipstream to the side, top and wake flow depends on train speed, train shape, ambient conditions and the environment in which the train operates. In this paper, the slipstream and wake flow of a 1/20th scale model of a simplified five-coach ICE2-shape train running in two different environments; in open air and when passing a platform, were obtained using large-eddy simulation (LES). The flow Reynolds number was taken to be 300,000; based on the speed and height of the train. The effect of the platform height on the train slipstream was investigated by performing simulations on a platform of different heights: 20, 60, 90 cm. To investigate the effect of mesh resolution on the results, two different computations were performed for the case of the flow around the train running in the open air using a different number of mesh nodes; a fine mesh consisting of 18,000,000 nodes and a coarse mesh consisting of 12,000,000 nodes. The results of the coarse mesh simulation were deemed to be comparable to those from the fine mesh simulation. The LES results were also compared with full-scale data and a good agreement obtained. A number of different flow regions were observed in the train slipstream: upstream region, nose region, boundary layer region, inter-carriage gap region, tail region and wake region. Localized velocity peaks were obtained near the nose of the train and in the near wake region. Coherent structures were formed at the nose, roof and inter-carriage gaps of the train. These structures spread in the slipstream and extend a long distance behind the train in the far wake flow. The maximum slipstream turbulent intensity was found in the near wake flow. The results showed that there is a significant effect of the platform height on the slipstream velocity and nose and tail pressure pulses. However, there is only a minor effect of the platform height on the static pressure along the body of the train compared with that on the nose and tail pressure pulses. In general, the slipstream velocity in the lower region of a train running in the open air was found to be larger than that around a train passing a platform. This has been related to the effect of the underbody complexities of the train.
The combination of low-frequency lateral and roll motions experienced in tilting trains can provoke motion sickness. The incidence of sickness depends on vehicle design and subject demographics. Vehicle design affects the location of the centre-of-roll, which influences passenger perception of motion. Age and gender have large influences on susceptibility to sickness, but little is known about the effects of ethnicity and body size. This study investigated the influence of both the vertical position of the centre-of-roll and subject characteristics (ethnicity, weight, stature and sickness susceptibility) on sickness caused by fully roll-compensated lateral oscillation. It was hypothesised that sickness would be greater when full compensation occurred at the head than when full compensation occurred at the seat. Sixty subjects experienced a 0.2-Hz lateral oscillation combined with ±7.3° of roll, so that the lateral acceleration was fully compensated at either the seat surface or 800 mm above the seat (i.e. average head height). Illness ratings and symptom scores were recorded every minute for 50 min (i.e. during a 5-min acclimatisation period, a 30-min exposure period and a 15-min recovery period). Although the mean illness ratings were greater when full compensation occurred at the head than at the seat, the difference was not statistically significant. Weight and stature were not associated with motion sickness, but illness ratings were much greater in Asian subjects than in European subjects. It is concluded that differences in susceptibility between Asians and Europeans have a greater effect on motion sickness than the height of the centre-of-rotation during roll-compensated lateral acceleration.
This study investigates the dynamic response of a locomotive drive system experiencing wheel/rail saturation adhesion. A dynamic locomotive model is created and then integrated with electromechanical and control systems to simulate the vibration in the component parts of the drive system. The model is used to investigate the drive system’s sensitivity to resonance effects. The obtained results show that the wheel/rail stick-slip state can experience both longitudinal vibrations and self-excited vibrations in the drive system. Different parts of the drive system are excited by the two types of vibrations; however, in both cases the main frequencies are multiples of the natural frequency vibration of the drive system. It is necessary to select an appropriate value for the motor suspension rubber stiffness if structural resonances of the drive system under wheel/rail saturated adhesion are to be avoided.