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The gear transmission system is one of the essential subsystems of railway vehicles. The wheel polygonalization can affect the gear transmission system's condition monitoring and fault diagnosis, causing fatigue failure of the gear system and influencing driving safety. Therefore, to explore the mechanism of the wheel polygonalization in the gear system, this paper develops a Lagrangian form dynamic model of a railway vehicle with a gear transmission system. The model validation uses the data from the field test. The analysis explores the influence of the wheel polygonal fault on the gear transmission system under the traction condition. The results indicate that the wheel polygonal fault has amplitude/frequency modulation effects on the time/frequency response of the gear system. Also, the wheel polygonal fault causes the envelope of the speed curve to fluctuate periodically at a low frequency under traction conditions. The waveform asymmetry is gradually apparent as the traction continues. In the non-resonant region, the statistical analysis of the rotational speed fluctuation illustrates that the order of the wheel polygonal fault has more impact on the rotational speed fluctuation than the amplitude. Besides, in the resonance region, the eigenvalues of the system determine the magnitude of the amplitude. [ABSTRACT FROM AUTHOR]

The fatigue life of coil springs is usually predicted with a stationary Gaussian vibration load and deterministic structural parameters. However, the obtained fatigue life is inconsistent with the observed fatigue life of fractured springs which varies within a wide range. The work aims to propose a method to predict the fatigue life of the coil spring by considering the time-varying vibration load, i.e., root mean square (rms) varies with time and the uncertainties of geometric parameters. First, a synthetic method for time-varying vibration loads is proposed. The time-varying load is decomposed into multiple stationary Gaussian short samples represented by their power spectral density (PSD). These PSDs are synthesized according to the distribution characteristics of spectral values, in which data that are non-Gaussian are processed with the Johnson system. Second, the influence of parameter uncertainties in the coil spring is studied by a Monte Carlo analysis of the stress frequency response function. Finally, the fatigue life is calculated and compared with the results predicted by using the measured stress. The results show that the synthetic spectrum has almost the same damage potential as the measured time-varying load. In comparison with results predicted from the measured stress, the synthetic spectrum gives much better estimates of the fatigue life of the coil spring than the average spectrum. Parameter uncertainties of coil springs significantly affect fatigue life and should be taken into account. [ABSTRACT FROM AUTHOR]

Ensuring the safety of the railway vehicles over bridges shaken by earthquakes is a practical issue in the seismic design of railway bridges. To improve the vehicle's running safety on railway bridges during earthquakes, the stopper (or bump-stop) between the bogie and the car-body of the vehicle was modified as a fuse-type element, i.e., it was designed to break under large impact due to earthquake occurrence. The efficacy of the fuse stopper was illustrated by a full-scale vehicle-track shake table test. The fuse stopper element was introduced to the vehicle-bridge interaction model, whose accuracy was also demonstrated by comparison with the test results. The fuse stopper was designed to remain intact under service level earthquakes (SLE) to avoid frequent replacement or repair, while it should fuse to improve vehicle safety on a group of bridges under design basis earthquakes (DBE). The bridge group includes 24 simply-supported bridges with pier heights ranging from 6m to 60m, covering the most simply-supported bridges in the China railway network. A total of 10 ground motion records were used in the analysis to account for the uncertainty of ground motions. Through vehicle-bridge incremental dynamic analysis (IDA) simulation, the optimal fusion strength of 188 kN and the extended gap of 0.04 m were proposed for the fuse stopper at DBE intensity, in which the bridge group can achieve derailment-free. The design procedure of the fuse stopper may provide a cost-effective way to improve the vehicle's running safety on a group of bridges during earthquakes. [ABSTRACT FROM AUTHOR]

This study describes the low damped carbody oscillations of the HEMU-430X, a high-speed electric-multiple-unit experimental train of Korea. The HEMU-430X had already undergone a kind of hunting problem in the test period, but it was effectively suppressed through several measures and the test was finished successfully. However, recently, the HEMU-430X again experienced the similar but slightly different problem after its wheel profile was changed to XP55, which is widely used in high-speed trains in Korea. In this paper, the eigenbehavior and system damping ratio are analyzed using a linearized vehicle model to more systematically investigate the cause of the carbody oscillation of the HEMU-430X. The results show that the bogie lateral movement coupled with carbody upper sway has the least damping ratio in the case of the HEMU-430X and the magnitude of yaw directional constraints of the bogie plays an important role in causing the carbody oscillation. Parametric studies for suspension, equivalent conicity and creep coefficients are carried out. A solution is suggested and it is validated using field tests. [ABSTRACT FROM AUTHOR]

Current research papers use simulated load spectrums to assess bogie frames' fatigue life but seldom consider traction and braking loads. Traction and braking loads play important roles in predicting fatigue life in high-speed and heavy haul operational scenarios. Hence, there is a research gap in terms of the consideration of longitudinal load spectrums while assessing bogie frames' fatigue life. This paper presents research about this topic. A virtual prototype technique available in literature has been extended for this purpose; it uses multibody dynamics and finite element techniques to simulate the behaviour of bogie frames under real operational service loads. As a result, the special simulation methodology has been developed in this work and it includes the unique integration of simulation approaches that includes train dynamics, locomotive dynamics with the consideration of a traction control algorithm and the adopted fatigue life calculation method. This paper gives numerical examples of a rigid-flexible coupled dynamic railway vehicle model subjected to longitudinal forces. Road Environment Percent Occurrence Spectrum (REPOS) load spectrums of the bogie frame were developed from a whole-trip train simulation on a real route. The spectrums are then used to predict locomotive the bogie frame's fatigue life. The results of the bogie frame fatigue life evaluation performed in this paper show that fatigue lives at the roots of traction rod seats under longitudinal load spectrums are shorter than their fatigue life under vertical load spectrums. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomer is a new kind of intelligent material that mainly incorporates micron-sized ferromagnetic particles into a polymer. A dynamic vibration absorber that is based on the controllable shear modulus of magnetorheological elastomer is widely used in vibration systems. In the study, a flexible carbody model with a magnetorheological elastomer dynamic vibration absorber is established. A design method of a semiactive dynamic vibration absorber that is based on magnetorheological elastomer is introduced, and the operational principle of the semiactive dynamic vibration absorber is also discussed. To improve the vibration absorption performance of the magnetorheological elastomer dynamic vibration absorber, via multiple regression analysis, the optimal design frequency expressions for both the rigid vibration and the elastic vibration of the carbody are fitted. Parameter determination for the magnetorheological elastomer dynamic vibration absorber is investigated in detail. Then, the effects on the rigid vibration and the elastic vibration with the magnetorheological elastomer vibration absorber both with the passive vibration absorber and without a vibration absorber are analyzed. Finally, Sperling's riding index is used to evaluate the feasibility and the performance of the magnetorheological elastomer dynamic vibration absorber in a practical application. The results demonstrate that the vibration of the carbody can be effectively reduced by using the magnetorheological elastomer dynamic vibration absorber instead of the dynamic vibration absorber without the magnetorheological elastomer. The magnetorheological elastomer dynamic vibration absorber that is modified by the optimum frequency provides superior vibration reduction performance and improves the riding quality of the railway vehicle. [ABSTRACT FROM AUTHOR]

Nowadays, rail transport is a very important part of the transportation network for any countries. The demand for high operational speed makes hunting a very common instability problem in railway vehicles. Hunting leads to discomfort and causes physical damage to carriage components, such as wheels, rails, etc. The causes of instability and derailment should be identified and eliminated at the designing stage of a train to ensure its safe operation. In most of the earlier studies on hunting behaviour, a simplified model with a lower degree of freedom were considered, which resulted in incorrect results in some instances. In this study, a complete bond graph model of a railway vehicle with 31 degrees of freedom is presented to determine the response of a high-speed railway vehicle. For this purpose, two wheel–rail contacts grounded on a flange contact and Kalker's linear creep theory are implemented. The model is simulated to observe the effects of suspension elements on the vehicle's critical hunting velocity. It is observed that the critical hunting speed is extremely sensitive to the primary longitudinal and lateral springs. Other primary and secondary springs and dampers also affect the critical speed to some extent. However, the critical hunting velocity is insensitive to vertical suspension elements for both the primary and secondary suspensions. Also, the critical speed is found to be inversely related to the conicity of the wheel. [ABSTRACT FROM AUTHOR]

This study aims to provide a process for the development of a train collision model that can evaluate the performance of buffers in the coupling system of railway vehicles. The model development process is completed by testing the buffer systems, analyzing the test results, and generating empirical models based on the analyzed results. In the analysis, it is shown that the behavior of the rubber buffer and the high-capacity buffer is well reproduced by the empirical models. A simulation model developed from the process is not only able to produce response behaviors of the buffers that are close to the test results, but is also able to estimate the maximum energy within a 2% error for the rubber buffer and a 4% error for the high-capacity buffer. The validated model can be used in extended systems – when multiple trains are connected through buffer systems – to evaluate the applied force or the absorbed energy on buffer systems, to optimize the configuration of the coupling systems or to evaluate the performance of the buffers under different collision conditions. [ABSTRACT FROM AUTHOR]

Many structural elements are exposed to load conditions that are difficult to model during the design phase, such as environmental uncertainties, random impacts, and overloading, amongst others, thus increasing unprogrammed maintenance and reducing confidence in the reliability of the structure in question. One way to deal with this problem is to monitor the structural condition of the element. This approach requires supervising several signals coming from critical locations and then performing an accurate condition estimation of the element in question based on the data collected. This study implements a method to diagnose and evaluate the reliability of the bolster beam structure of the railway vehicle during a fatigue test. The results show that multidimensional monitoring not only diagnoses the element accurately but also results in correct estimation of reliability. [ABSTRACT FROM AUTHOR]

The conflict requirement between high-speed stability and curving trafficability has been always a critical issue of train. This article proposed an innovative stiffness variable magnetorheological elastomer rubber joint, which contains two sets of electromagnetic coil, magnetorheological elastomer, and three iron flanks to overcome the conflict requirement. To characterize the proposed magnetorheological elastomer rubber joint, an MTS machine was used to test the field-dependent property, the amplitude-dependent performance, and the frequency-dependent response. The test results verified the stiffness variation capability of the proposed magnetorheological elastomer rubber joint. After the characterization, the magnetorheological elastomer rubber joint was then embedded onto a train model. In the simulation, different curve tracks and different train speeds were simulated to evaluate the effectiveness of the magnetorheological elastomer rubber joint on reducing the angle of attack. Additionally, the critical speeds of the train models were tested and compared when the magnetorheological elastomer rubber joint was working in softened and stiffened mode, respectively. The simulation results demonstrated that the magnetorheological elastomer rubber joint can offer soft and hard wheelset positioning stiffness under different requirements so that both the high-speed stability and curve trafficability of the train can be guaranteed. [ABSTRACT FROM AUTHOR]

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 Medellı'n, 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 (auROC0.961), which outperformed the best pure domain descriptor by least 4%. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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-θ 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-θ 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Vibration in trains constitutes one aspect of the physical environment that can cause discomfort to passengers. In order to assess the vibration, a variety of techniques have been developed and used. The general approach is to acquire acceleration at the passenger–train interface, and to then process these acceleration signals in order to calculate human comfort. However, the comfort index so calculated is independent of the seat characteristics and human parameters. Thus, a human biodynamic model with dynamic seat characteristics is necessary in order to perform true comfort analysis. The biodynamics of human subjects has been a topic of interest over the years, and a number of mathematical models have been established. However, there are only a few studies incorporating biodynamic models in railway applications. So, the present work proposes to evaluate Sperling’s Ride Index for a low–medium speed railway vehicle and further to calculate root mean square acceleration of different body parts, as per the International Organization for Standardization (ISO) 2631 guidelines, through bond graph technique. Car body flexibility is also incorporated using modal expansion of a free–free beam. Physiological effects of the vibrations on the human body were analyzed using the criteria specified in ISO 2631. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Speed and safety are two key objectives in the operation of a railway. On double-line railways, such as the Estrada de Ferro Vitoria Minas (EFVM), a critical situation occurs when a train changes between lines, this should occur at the maximum allowed speed. However, the iron ore trains consisting of GDE-type wagons that operate on the EFVM perform this operation at 60 km/h, which is 5 km/h less than the maximum speed allowed under normal operating conditions. Thus, the brakes need to be applied over a long distance before the turnout in order to reduce the speed. A number of field tests were conducted in order to determine the actual maximum safe speed for traffic on a crossover (or turnout). This paper presents the results of computer simulations using NUCARS®. The GDE wagons and the characteristics of the track geometry were modeled. Several cases were simulated, with variations of parameters of the wagons, such as side bearing clearance and wheel profile. The results of the computer simulations were compared to the results from the field tests. Good correlation was found between them, indicating that the maximum speed of the GDE wagons running on the turnout might be open to review. [ABSTRACT FROM AUTHOR]

A new analytical formula to describe the vertical stiffness of a rolling lobe spring has been established; the equation incorporates the rate of change of the effective area of the spring. Two rolling lobe air springs were studied by performing analytical calculations, and the results were verified by comparisons to finite element simulations and experimental data. The analytical formula can be used to qualitatively predict the vertical stiffness of a rolling lobe air spring. Precise prediction of the value of the vertical stiffness can be obtained using the formula in cases where the reservoir volume is not very large. The influence of geometric parameters on the vertical stiffness of a rolling lobe air spring has been studied using the proposed formula and a guideline for its design has been obtained by plotting a cause–effect chart. [ABSTRACT FROM AUTHOR]

Starting from the knowledge of flush air data-sensing systems developed in the aerospace field, a system able to evaluate the crosswind velocity (absolute and angle) from pressure measurements performed on a train’s surface has been studied and developed. The crosswind evaluation algorithm is based on a neural network and is created and tested using pressure measurements carried out during wind tunnel tests on a scale-model of a railway vehicle. The number and positions of pressure taps on the surface of the train’s leading car are optimized, in terms of the sensitivity and robustness of the measurement system. The system is calibrated and validated using steady and quasi-steady wind tunnel tests on a scale model of a train. The designed neural network gives a maximum error of about 1 m/s for the modulus and 1° for the angle of the relative velocity. [ABSTRACT FROM AUTHOR]

The lateral dynamic features of a railway vehicle are investigated using two similar wheel/rail contact models: the Vermeulen–Johnson and the Shen–Hedrick–Elkins models. The symmetric/asymmetric bifurcation behaviour and chaotic motions of the railway vehicle are investigated in great detail by varying the speed and using the ‘resultant bifurcation diagram’ method. It is found that multiple solution branches exist and they can lead to more steady states in the dynamic behaviour of the railway vehicle. The coexistence of multiple steady states can lead to jumps in the amplitude of oscillations, resulting in problems for safe operation of the vehicle. Therefore, it should be avoided in everyday operation. Furthermore, the creation of multiple solution branches suggests that the critical speed of a vehicle should be determined from a comprehensive analysis of the various kinds of possible excitations and numerous tests. [ABSTRACT FROM AUTHOR]

The self-alignment of independently rotating wheels (IRWs) with inverse tread conicity cannot be realized simply by using a nonlinear concave wheel profile. A novel wheel profile design method is proposed to solve this problem that is based on the static guidance characteristic of a single isolated wheelset. The procedure is based on a desired lateral geometric force function with respect to the lateral displacement of IRWs with inverse tread conicity. The method focuses on the trajectory of the center of gravity under the wheel/rail contact constraint. A numerical process description and design example are provided and the resulting design is checked using forward contact analysis and the multi-body dynamics analysis software SIMPACK. A lateral restoring force that is proportional to the lateral displacement can be obtained using the proposed design method for the wheel profile. [ABSTRACT FROM AUTHOR]

This paper introduces new validation metrics that may be used for the validation of models of railway vehicles. The proposed validation metrics are based on a comparison between the cumulative distribution functions of selected parameters obtained by simulation and measurements. A model of a freight railway vehicle has been developed and the proposed validation metrics were used in model validation. The results of the validation were compared with the results of validation metrics used in the ‘DynoTRAIN’ project. It was shown that the proposed metric is more severe than the metrics used in the project; a result of it comparing the complete domains of the cumulative distribution functions and not only the selected characteristic values. [ABSTRACT FROM AUTHOR]

The damping ratios of suspension systems on a railway vehicle were estimated in terms of the free-decay responses obtained by applying the logarithmic-decrement method to data obtained in wedge tests. The characteristics of the free-decay responses were measured both for motor and trailer cars experiencing either the tare loading (AW0) or crush loading (AW3) condition and either inflated or deflated air springs. The considered cases included bouncing, pitching, rolling and lateral motions. A dynamic model was established and the simulation results were compared with the experimental results. For the vertical cases, the time cycles and displacement amplitudes of the free-decay response are related to the state of the air springs and the vehicle load. The damping ratio of the secondary suspension for inflated air springs is about three to five times higher than for when the air springs are deflated. For the primary suspension, it is two to four times higher. Also the heavier the carbody loads, the much more severe is the divergence. Furthermore, the damping ratios have their largest values for the pitching modes, followed by the bouncing modes and finally the rolling modes. For the lateral cases, the free-decay responses have similar characteristics to those of the vertical responses but with smaller amplitudes. All the tests show good agreement with one another, and the primary and secondary suspensions show similar regularities. The simulations show a good agreement with the test results and highlight that the initial velocity has only a limited effect on the test results. [ABSTRACT FROM AUTHOR]

This study developed a post-derailment dynamic model of railway vehicles to investigate their post-derailment dynamic behavior when travelling on a railway bridge during an earthquake. The model is composed of three parts: multi-body dynamic model of the railway vehicle, a collision detection model, and a contact force model. The dynamic model considered all the various kinds of contacts that may occur during the derailment, such as wheel/track slab contacts, wheel/fastener contacts, and brake-disc/rail contacts. A collision detection model that was based on the tight-fitting oriented bounding box trees approach was adopted to detect the collision situations during the derailment. The contact force model was used to calculate the contact force based on a Hertz spring-damper and the Coulomb friction law. Using this model, the post-derailment dynamic behavior of railway vehicles travelling on a railway bridge experiencing earthquake excitations was investigated. First, a seismic response analysis of the railway bridge was conducted in order to obtain the seismic response of the railway bridge; it was subsequently used as the input to the post-derailment dynamic model. Then the derailment postures of the vehicle and contact situations were fully analyzed to understand the post-derailment dynamic behavior of railway vehicles during the earthquake. The obtained results show that the brake disc adopted in the model has the ability to limit the deviation of the wheelsets after the derailment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

The wheelset on a railway vehicle experiences the problem of hunting motion, the onset of which occurs when travelling above the associated critical speed. This is known as a flutter-type self-excited oscillation resulting from non-conservative contact forces acting between the wheels and rails. Traditional methods for preventing hunting motion while running on a straight rail include using bolsters, yaw dampers, or stiffer supports. However, these methods decrease the running performance on a curved rail. To enhance the running performance on both straight and curved rails, we propose using a gyroscopic damper. Until now, a gyroscopic damper has been theoretically and experimentally shown to increase the critical speed for hunting motion. This control method does not need state feedback control, but is not a passive control method, because the gyroscope is rotated by an additional actuator provided separately from the traction motor. In practice, the weight increase from the additional actuator has been a problem in applying this control method. In this study, using the traction motor itself as a passive gyroscopic damper, a new stabilization control mechanism is proposed that eliminates the need for an additional actuator to rotate the gyroscope. An analytical model of a single railway vehicle wheelset was introduced at a scale corresponding to the experimental equipment. From the eigenvalue analysis, it was found that the critical speed increased with an increase in the rotor speed of the gyroscopic damper. Experiments were conducted using a simple apparatus consisting of a roller rig and a two-degree-of-freedom wheelset with a gyroscopic damper that has a mechanism equivalent to what is proposed. The results experimentally validate the proposed passive gyroscopic damper for the stabilization of hunting motion. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

The geometric filtering phenomenon is first analyzed with a simplified vertical vehicle model. Analytical solutions obtained with this model show that geometric filtering phenomenon consists of ‘wheelbase filtering’ and ‘bogie spacing filtering’ effects. The wheelbase filtering effect occurs when there is neither car body bounce nor pitch response at certain track wavelengths, whereas the bogie spacing filtering effect occurs when there is a null in either the car body bounce or pitch response at particular track wavelengths. Then, the correlated frequency response function for railway vehicles is defined to assess the effect of geometric filtering upon the resonant frequencies of a flexible car body. It is found that if the car body’s first bending frequency coincides with the peak values of bounce acceleration transmissibility, that is, it is near the null pitch response frequencies, resonant vibration of the flexible car body will happen. Finally, to suppress the resonant vibration of the flexible car body, it is proposed to use a dynamic vibration absorber (DVA) suspended under the car body underframe. The DVA parameters are optimized according to car body bending frequency and the null pitch frequency. The optimal DVAs show very good performance and robustness in suppression of the car body resonant vibration. [ABSTRACT FROM AUTHOR]

Although press fit joints are very important in railway engineering, few authors have investigated the strength of press fit joints in terms of their application in railway vehicles. This study analyses the tribological parameters that influence the strength of press fit joints, especially the contact pressure and the static friction coefficient. This research was targeted towards the control of the friction coefficient value to obtain the required strength of a press fit joint in conditions close to the minimum contact pressure that results in less prestressed press fit joints. To estimate press fit joint strength, this study examines the use of minimum and maximum values of the friction coefficient as recommended in the literature considering wide tribological conditions, as well as the experimentally determined friction coefficient values for specific tribological conditions. The study also points out the discrepancy between current railway standards and engineering practice considering the inspection of wheel set press fit joint strength. [ABSTRACT FROM PUBLISHER]

In this article, a two-degree-of-freedom model for the disc brake system is set up by considering the vertical motion of the brake unit and the pitch motion of the bogie frame, and the sliding friction interface between the brake lining and disc is included in the model. Using the Hurwitz determinants, an algebraic criterion for determining the Hopf bifurcation point of the system is proposed. The vehicle speed at the Hopf bifurcation point is defined as the critical speed where the equilibrium position of the disc brake system loses stability and the limit cycle emerges. In order to investigate the stability of the disc brake system, parametric studies are undertaken. It is shown that the mass of brake unit, vertical damping of primary suspension, friction coefficient, and brake normal force between the lining and disc have significant influences on the critical speed. The instability of the system may not occur if the parameters are properly designed. The limit cycle arisen due to the loss of stability of the equilibrium position is studied using the numerical integration method. It is found that once the brake system loses its stability at a certain speed, the stick—slip motion occurs and the limit cycle oscillation will last until the vehicle comes to a standstill. It is also known that the frequency of limit cycle is significantly affected by the mass and suspended stiffness of the brake unit but is not related to the vehicle speed in the braking process. [ABSTRACT FROM AUTHOR]

To improve ride comfort in railway vehicles, the suppression of vertical bending vibration and rigid-body-mode vibration in the car body is essential. In this paper, a system is proposed that aims to reduce bending and rigid-body-mode vibration simultaneously by introducing damping control devices in the primary and secondary suspensions. The technique involves a control system of primary vertical dampers and air springs; the former are used to suppress the first bending mode vibration; the latter, to suppress the rigid-body-mode vibration. The results of both simulations and vehicle running tests on the Sanyo-Shinkansen line demonstrate that this system reduced vertical vibrations in the bogies and the car body using the sky-hook control theory. In the running tests in particular, the system reduced the vertical vibration acceleration PSD peak value in the first bending mode to almost 20 per cent and in the rigid body mode to almost 50 per cent compared with the case when the system was not used. As a result, the ride quality level LT (a widely used index of ride comfort in Japan) decreased by at least 3 dB, indicating greater ride comfort. [ABSTRACT FROM AUTHOR]

To study the influences of carbody vertical stiffness on vehicle ride quality, a vertical model of railway passenger vehicles, which includes the carbody flexible effects and all vertical rigidmodes, is built.With the model and the covariance method, the requirements for the carbody bending frequency are researched.The results showthat when the stiffness of a carbody decreases to certain frequencies there are significant vibrations in the carbody, although structural damping provided by a fully equipped carbody will help attenuate the vibration to some extent. A simple way to avoid resonant vibration is to increase the bending frequencies of a carbody: the higher the vehicle running speed, the higher carbody stiffness could be required. However, there are practical limitations to such an increase and the method used in this study can readily obtain the lowest bending frequency required by vehicle ride quality. Finally, the geometric filtering phenomenon and its influences on the carbody resonant flexural vibration are analysed. Results show that it is this phenomenon rather than the natural vibrations of bogie bounce that most strongly influences the resonant flexural vibration of a railway carbody. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the generation and propagation of ground vibrations induced by railway traffic, more specifically in the case of urban vehicles. The complete vehicle—track—soil model is developed according to an uncoupled approach: the vehicle—track subsystem is first simulated so as to provide the ground forces which, in turn, are applied to the model of the soil. The vehicle—track model is built with the help of the home-made C++library [ABSTRACT FROM AUTHOR]

This paper analyses the influence of mechanical loads on railway vehicle solid wheel reliability. Reliability calculations is carried out according to the specifically set methodology — reliability is calculated according to the data about working loads and critical stress distribution. The influences on solid wheel reliability that are analysed are the following: standard deviation of lateral force distribution and mathematical expectation and standard deviation of the vertical force. [ABSTRACT FROM AUTHOR]