Showing papers in "Vehicle System Dynamics in 2023"

Optimization of vibration absorbers for the suppression of rail corrugation in the sharp curved section with Cologne-egg fasteners

Abstract: Rail corrugation in the sharp curved section with Cologne-egg fasteners is suppressed by vibration absorbers, in which the suppression mechanism is unclear and the optimization method of the vibration absorber needs to be further investigated. Firstly, the complex eigenvalue and dynamic transient methods are adopted to investigate the vibration inducement of rail corrugation and influence law of vibration absorber on the rail corrugation. Then, the optimization methods of absorbers are studied from the perspectives of the connection stiffness, connection damping and different installation methods of absorbers. Results show that vibration inducement of rail corrugation in the sharp curved section with Cologne-egg fasteners includes the friction-induced oscillation of the entire system and feedback oscillation of undulatory wear. The installation of the vibration absorber can effectively weaken the impact of the vibration inducement, thereby inhibiting the rail corrugation. When the vertical and lateral connection stiffness are 120 MN·m−1 and 60 MN·m−1 respectively, the vertical and lateral connection damping are 100 kN·s·m−1 and 50 kN·s·m−1 respectively, the vibration absorber has the best effect of suppressing rail corrugation. Moreover, the continuous installation on both rail webs can be adopted to achieve the better inhibitory effect of the absorber.

A multi-objective optimisation method of rail combination profile in high-speed turnout switch panel

Abstract: This paper presents a multi-objective optimisation method considering the switch and stock rail profiles in the switch panel. Based on the non-uniform rational B-spline (NURBS) theory, a parameterised model of the measured turnout profile is constructed to determine the variables. This study selects the vehicle dynamic performance and wheel-rail contact damage as the objective function to establish a multi-objective optimisation mathematical model that is solved using NSGA-II. Overall performances of the measured profile and the optimised profile are compared and evaluated for two aspects, dynamic performance and wheel-rail contact damage. The following are the conclusions: The maximum lateral vibration acceleration of the axle box is reduced from 2.64–2.09 m/s2, which has a 20.83% decrease. Concerning wheel-rail contact damage, the maximum wear index is reduced from 13.46–11.47 N, the reduction is 14.78%. At the same time, the cumulative surface rolling contact fatigue (RCF) is reduced from 8.29×10−5–7.38×10−5. This article can provide a profile repair method for worn turnouts, which can maximise the comprehensive performance of the turnout within a limited amount of grinding, and can reduce the wheel-rail contact damage of the turnout while taking into account driving stability.

A minimal model to study self-excited vibrations of a tram wheelset in curves with small radius of curvature

Abstract: A wheelset of a rail vehicle may experience stability issues in curves with a small radius of curvature, which are typical for tramway networks. Accompanied self-excited vibrations of the wheelset might be a potential mechanism of adverse wheel polygonization, although a possible relationship between the two phenomena is not addressed here. A basic 2-DOF model, representing a wheelset with non-driven, independently rotating resilient wheels, has been derived from the analysis of simulation results with a more detailed system model to understand the reasons for a possibly unstable motion in a uniform curve. It has been found that a dominating motion in the regime with a negative gradient of the lateral creep force–creepage characteristics is necessary for possible self-excitation but is not sufficient for the considered parameter range. The combination and interaction of the lateral oscillations of the resilient wheel and laterally elastic wheelset axle is essential for amplification. Resulting stable limit cycles can be observed, and influences on corresponding amplitudes are discussed. The lateral flexibility of the wheelset axle appears as an important influence.

Enhancing the trade-off between ride comfort and active actuation requirements via an inerter-based passive-active-combined automotive suspension

Abstract: Ride comfort is an important indicator to evaluate the dynamic performance of automotive vehicles. One method for improving ride comfort is to incorporate an active actuator into the passive suspension. However, the improvement is closely linked with the required actuation power and force. Increased actuation requirements may lead to higher energy consumption and a larger actuator size. To enhance the trade-off between ride comfort and active actuation requirements, a new design approach for searching for the optimal passive-active-combined suspension across many different mechanical component layouts incorporating an inerter is proposed in this paper. Compared with traditional designs where the suspension is limited to a few special layouts, via this approach the optimal passive part among all network possibilities with pre-determined numbers of each element type (springs, dampers and inerters), and optimal controller parameters of the parallel active actuator can be identified. Considering a quarter-car model, with a benchmark combined active-passive suspension in which the passive part is a spring-damper, the optimal inerter-based suspension can reduce the active force by more than 48% and regenerate 6 W more average power in the active part while achieving the same ride comfort. Note that in this case, two constraints are always considered: the road-holding ability (as indicated by the dynamic tyre load) and suspension travel of the identified suspension will not be worse than those of the benchmark suspension. The optimal trade-off obtained with this approach serves as a powerful tool in the automotive suspension design as it provides guidance on the following three aspects: the optimal ride comfort, the minimum power consumption and the feasibility of specific actuation requirements, where the second point is obtained in conjunction with the power conservation theorem proposed in this paper which proves that the total power consumed by the passive and active parts will not vary with changes in the passive part and active controller parameters.

Motorcycle steering torque estimation using a simplified front assembly model: experimental validation and manoeuvrability implications

Abstract: Steering torque constitutes the primary motorcycle control input for the lateral dynamics; consequently, estimating it is important. Conventionally, this is done with complete motorcycle models, requiring significant identification effort. The simplified models in the literature only describe the steering torque under specific cases.This work defined a steering assembly model with few parameters to estimate the steering torque analytically for stationary and transient manoeuvres.The model equations followed from existing motorcycle models through simplifying hypotheses; transfer functions describing the roll response and the Lane Change Roll Index (LCRI) were obtained from these equations. Measured steering torque signals from different datasets, including diverse motorcycle classes, were used as the reference for validation.A good agreement resulted between the estimated and measured torques, in the time and speed-acceleration domains and in terms of LCRI. When using the roll as the motorcycle response, manoeuvrability was highest at lower frequencies. The scooter was the most manoeuvrable; the sports and touring motorcycles were the least manoeuvrable at low and high frequencies, respectively. Concerning design parameters, the front-wheel spin inertia and front twist stiffness influenced manoeuvrability the most.The model allows recreating the steering torque signal for new and pre-existing datasets using commonly measured signals; the signal can describe the riding style and the effort required. Few parameters are required, facilitating its use and reducing the computational burden, allowing its use for steering assistance systems.

Influence of damping characteristics of mesh–type high damping rail pad on the vehicle–track dynamic performance and rail surface roughness

Abstract: The rail pad damping is a critical parameter to evaluate its vibration reduction capacity, which has essential research significance. The mesh–type high damping rail pad (MTHDRP) is proposed for the first time in this paper, and the differences in damping performance between MTHDRP and traditional rail pads (PTRP and GRP) are compared and studied. It is concluded that the MTHDRP has the highest damping coefficient than any other rail pads. The dynamics model calculation has discovered that the increase of the rail pad damping coefficient can not only effectively decrease the vibration acceleration, wheel–rail force, and derailment coefficient, but also is beneficial for both vehicle safety and stability and track structure protection. The field test shows that the acceleration of the rail, clip, iron pad, and track bed in the MTHDRP laying section is significantly lower than that in the PTRP laying section, and the rail surface roughness improves significantly after the rail pad is replaced with the MTHDRP for half a year.

Trajectory-following and off-tracking minimisation of long combination vehicles: a comparison between nonlinear and linear model predictive control

Abstract: In this paper, we compared the linear and nonlinear motion prediction models of a long combination vehicle (LCV). We designed a nonlinear model predictive control (NMPC) for trajectory-following and off-tracking minimisation of the LCV. The used prediction model allowed coupled longitudinal and lateral dynamics together with the possibility of a combined steering, propulsion and braking control of those vehicles in long prediction horizons and in all ranges of forward velocity. For LCVs where the vehicle model is highly nonlinear, we showed that the control actions calculated by a linear time-varying model predictive control (LTV-MPC) are relatively close to those obtained by the NMPC if the guess linearisation trajectory is sufficiently close to the nonlinear solution, in contrast to linearising for specific operating conditions that limit the generality of the designed function. We discussed how those guess trajectories can be obtained allowing off-line fixed time-varying model linearisation that is beneficial for real-time implementation of MPC in LCVs with long prediction horizons. The long prediction horizons are necessary for motion planning and trajectory-following of LCVs to maintain stability and tracking quality, e.g. by optimally reducing the speed prior to reaching a curve, and by generating control actions within the actuators limits.

Predictive maintenance in railway systems: MBS-based wheel and rail life prediction exemplified for the Swedish Iron-Ore line

Abstract: A successful predictive maintenance strategy for wheels and rails depends on an accurate and robust modelling of damage evolution, mainly uniform wear and Rolling Contact Fatigue (RCF). In this work a life prediction framework for wheels and rails is presented. The prediction model accounts for wear, RCF, and their interaction based on the output from MBS simulations to calculate the remaining life of the asset, given in mileage for wheels and MGTs for rails. Once the model is calibrated, the proposed methodology can predict the sensitivity of the maintenance intervals against changes in operational conditions, such as changes in contact lubrication, track gauge, operating speeds, etc. The prediction framework is then used in two operational cases on the Swedish Iron-Ore line. The studied cases are, the analysis of wheel life for the locomotives, and the analysis of rail life for gauge widening scenarios. The results demonstrate the capabilities of the MBS-based damage modelling for predictive maintenance purposes and showcase how these techniques can set the path towards Digital Twins of railway assets.

Out-of-round railway wheels and polygonisation

Abstract: Out-of-roundness in railway wheels, in particular polygonal wear resulting in regular, multi-lobed, out-of-round wheels, has become a significant problem in recent years. It is of concern to railway operators due to the increased noise and vibration it can cause. This polygonisation is caused by cyclic wear but the exact mechanism leading to this type of wear is not fully understood. It appears to be the result of dynamic linking between a resonance or other periodic excitation in the coupled vehicle–track system and the existing wear at the wheel. This paper reviews the developing body of research being carried out in many countries by research groups, manufacturers and operators. Some examples of polygonisation on different types of railway vehicles are reported including feight trains, urban transit trains and high-speed trains. The main theories for the formation mechanisms are presented and the current measurement methods, computer simulation techniques and the effects and potential mitigation methods are reviewed. In parallel, the mechanisms and consequences of discrete wheel tread irregularities, such as wheel flats and material fall-out due to rolling contact fatigue cracking, are addressed.

A quasi-steady-state minimum lap time simulation of race motorcycles using experimental data

Abstract: In this work, the minimum-lap-time problem is investigated using a quasi-steady-state model. The prior research approach has been modified by introducing experimentally based controls’ constraints to consider some effects of vehicle inertia and human physical limitations. The differences between the theoretical and recorded experimentally g-g diagrams are analysed, and a semi-empirical g-g diagram is proposed as an approximation for the usage of most motorcycle riders. The effect of the braking technique (optimum and using front brake only) is discussed on a variable radius ‘U’ trajectory example. A new system of OCP state equations is proposed, and optimal trajectories are computed for several test scenarios for open and closed-loop tracks. The simulation result for the closed-loop track is compared with the experimental data from a GPS-based data acquisition system. The standard and proposed approach are compared, and conclusions are drawn.

Trend analysis of rail corrugation on the metro based on wheel–rail stick-slip characteristics

Abstract: According to the actual metro situation, the vehicle-track rigid-flexible coupling numerical model was established, and the wheel–rail stick-slip characteristics on straight and curve tracks were analysed. Meantime, the stick-slip characteristics under the negative friction condition and its influence on corrugation were studied. The results show that for the straight track without irregularity or with long wavelength irregularity, the reason for the occurrence or further development of corrugation may be related to the saturation of transverse adhesion coefficient; for the straight track with short wavelength irregularity, the further development of corrugation may be related to the saturation of longitudinal adhesion coefficient. Both the inside and outside wheel–rail interfaces on the curve track have the trend of stick-slip vibration, and the existence of short wavelength irregularity will aggravate the intensity of stick-slip vibration. The fixed defect on rail surface will lead to the same phase rail wear at the same position, give the same phase periodic stick-slip vibration. The overall dispersion rates of longitudinal and transverse adhesion coefficients at the inside wheel–rail interface are greater than the corresponding values at the outside, which indicates that the inner rail is more prone to stick-slip vibration with large intensity.

Dynamic characteristics analysis of gear transmission and its support bearings of high-speed train on the curve

Abstract: The gear transmission in high-speed trains is crucial for transmitting the traction torque. Its dynamic characteristics impact the system's reliability and safety. Additionally, the gear transmission and its support bearings can be affected by wheel-rail interactions, particularly on curves with larger centrifugal forces. To address this, a spatial vehicle-track coupled dynamics model that considers the complete power transmission path and mechanical structure of the gear transmission is proposed. The model considers factors such as time-varying mesh stiffness, dynamic transmission error (DTE), time-varying support stiffness, and internal interactions of the gearcase bearing. Results indicate that when a high-speed train passes through a curve, the derailment coefficient and lateral force of the wheelset are less on the right curve due to the lateral component of the mesh force, but the opposite occurs on the left curve. The centrifugal effect affects the contributions of the lateral and vertical motions of the gear pair, which are balanced by the torsional motions of the components in the power transmission path. Additionally, the internal interactions between the rolling elements and races are intensified due to track irregularity and gear engagement, but the centrifugal effect of the pinion can be ignored.

An optimal control approach to the computation of g-g diagrams

Abstract: The so-called g-g diagram is widely employed to assess the performance of road vehicles since it provides the maximum longitudinal and lateral accelerations that can be extracted from the selected vehicle. The different points of the g-g diagram are usually computed independently from one another, e.g. the maximum longitudinal accelerations corresponding to given lateral accelerations are computed sequentially. In this work, the problem of computing the points of the g-g diagram is transformed into an optimal control problem, which allows to avoid one of the most annoying practical problems often encountered when deriving such diagrams, namely the ‘jumps’ between different solutions (i.e. large slip vs. small slip solutions at similar lateral acceleration) in adjacent points along the g-g envelope. In the proposed method, the objective is to maximise the area enclosed within the g-g diagram, which has a polar representation. The rate of change of the radial coordinate is the control input. Additional constraints are included to enforce the continuity between the states of the vehicle model in adjacent points along the envelope. These conditions can hardly be enforced using standard methods based on sequential and independent computation of the g-g points. An example of the application of the method is demonstrated on the classic double-track car model with nonlinear tyres.

A novel vehicle-track coupled dynamics model with disc brake systems: modelling and validation

Abstract: This study established a novel vehicle–track coupled dynamics model (VTCDM) considering the disc brake system of a high-speed train (HST). The structure parameters of each friction block are applied to compute the non-linear friction forces and torques. This more elaborate model enables detailed investigations on the coupled mechanical system excited by the brake sliding friction, wheel-rail rolling friction and track irregularity. Further, it is validated by comparing with the experimental results from the aspects of time domain, frequency domain, Poincaré map and phase plane. Results indicate that the brake system substantially influences the vehicle–track system (VTS) and causes strong non-linear characteristics. Furthermore, this model can be used for tribological and dynamics-related assessment, like braking squeal and friction-induced vibration.

Feasible trajectory planning for minimum time manoeuvring

Abstract: Path planning models are often only founded by geometric calculations and do not consider the vehicle's limitations. In critical situations, path following is crucial, as a departure from the trajectory can have significant consequences. It is therefore necessary to define trajectories which the vehicle has the capacity to follow, i.e. feasible trajectories. This paper presents a framework for feasible trajectory generation for use in minimum time manoeuvres (MTM). The feasibility of trajectories is evaluated against a Quasi-Steady-State (QSS) acceleration envelope and jerk constraints. The vehicle's dynamics feasibility is assessed through a new exact relation of vehicle trajectory curvature that is expressed relative to a track reference line. The physical restriction of these constraints, relative to the vehicle's transient capabilities, implies that QSS feasibility assessments also extend to the transient vehicle. Minimum curvature trajectories are also reviewed. Results are presented for four examples. First, a constant radius example highlights differences in the minimum curvature cost models. The second example compares minimum curvature trajectories against MTM solutions for the Tempelhof Airport Street Circuit (Berlin), resulting in a new minimum curvature objective. The last two examples, straight road and Adria International Raceway, show that the feasible trajectory model is a good predictor of the QSS handling limits, indicating its ability to define feasible trajectories. The maximum spread of results is 3.2%. A friction ellipse model is additionally presented for comparison against the Normal-Tangential-Acceleration (NTA) surface. Friction ellipse results showed to be comparable if the acceleration envelope alignment is sufficient.

Effect of suspension form on the vehicle-bridge coupled vibration of the maglev vehicle

Abstract: In order to find out the influence of suspension form on the medium and low-speed maglev system, first, the transfer functions of the heaving and pitching motions of the two kinds of levitation modules equipped with the two suspensions, respectively, were derived and compared. Second, the coupled-vibration equations of the levitation module, cabin and bridge were presented. At last, two kinds of dynamic models were built to analyse the dynamic performance of the two maglev vehicles. Results show that the effect of the suspension form on the levitation module response is significant, but that on the cabin and bridge is insignificant. The maximum air-gap fluctuation in MVES (maglev vehicle with end-mounted suspension) is about twice that in MVMS (maglev vehicle with mid-mounted suspension) at the speed of 160 km/h. Moreover, the maximum current in MVES is 7.4 A larger than that in MVMS, and the mean power consumption of the levitation system in MVES is 1.2 kW larger than that in MVMS. On the whole, according to the dynamic responses of the two maglev vehicles, the mid-mounted suspension is more conducive to reducing the air-gap fluctuation, current and power consumption of the levitation system.

Application of machine learning techniques to build digital twins for long train dynamics simulations

Abstract: The paper shows the feasibility of building closed-form and fast-to-evaluate surrogate models via supervised kernel-based machine learning regressions behaving as digital twins for computationally expensive multibody simulations. The aforementioned surrogate models are adopted to predict the railway vehicle dynamics safety indexes defined in the international standards, depending on the wheel-rail forces, directly from the results of longitudinal train dynamics simulations. The digital twin models are trained with the outputs of Simpack multibody simulations of a reference freight wagon, to which the in-train forces calculated by an in-house MATLAB longitudinal train dynamics simulator are applied. Two machine learning techniques are considered: the support vector machine and the least-squares support vector machine regressions. Both techniques ensure a good accuracy even with a limited number of training samples. The derivation of the surrogate models can strongly enhance the modelling capabilities of common longitudinal train dynamics simulators, that cannot evaluate the wheel-rail contact forces. At the same time, the method shown in the paper allows to strongly reduce the total computational times, as the evaluation of the closed-form surrogate models allows to effectively estimate the safety indexes with no need for computationally demanding multibody simulations.

Research on causes and countermeasures of wheel polygon wear based on Kik-Piotrowiski contact model

Abstract: In order to study the wheel polygon wear problems in high-speed trains, an iterative model of wheel wear was established based on 1) the train-track rigid-flexible coupling dynamics model, 2) Kik-Piotrowiski + Fastsim wheel-rail contact model, and 3) Archard wear model to predict the developing process of wheel polygon. Taking a certain type of high-speed train in China as an example, the developing process of the 20-order wheel polygon is simulated. Compared with the Hertz model, the results of the Kik-Piotrowiski model are more consistent with the actual situation, and the prediction of the wheel polygon is more accurate. The results show that with the increase of vehicle running speed, the dominant order of the final wheel polygon decreases gradually, while the excitation frequency always locates between 550 and 600 Hz, which verifies the ‘frequency fixed’ mechanism. By comparing the development of wheel polygon wear results under three working conditions 1) flexible wheelset + flexible rail, 2) rigid wheelset + flexible rail, and 3) flexible wheelset + rigid rail), and by analysing the harmonic response of rail, it is concluded that the third-order bending modal vibration of rail plays an important role in the forming of wheel polygon. .

Friction-adaptive stochastic nonlinear model predictive control for autonomous vehicles

Abstract: This paper addresses the trajectory-tracking problem under uncertain road-surface conditions for autonomous vehicles. We propose a stochastic nonlinear model predictive controller (SNMPC) that learns a tyre–road friction model online using standard automotive-grade sensors. Learning the entire tyre–road friction model in real time requires driving in the nonlinear, potentially unstable regime of the vehicle dynamics, using a prediction model that may not have fully converged. To handle this, we formulate the tyre-friction model learning in a Bayesian framework and propose two estimators that learn different aspects of the tyre–road friction. The estimators output the estimate of the tyre-friction model as well as the uncertainty of the estimate, which expresses the confidence in the model for different driving regimes. The SNMPC exploits the uncertainty estimate in its prediction model to take proper action when the uncertainty is large. We validate the approach in an extensive Monte Carlo study using real vehicle parameters and in CarSim. The results when comparing to various MPC approaches indicate a substantial reduction in constraint violations, as well as a reduction in closed-loop cost. We also demonstrate the real-time feasibility in automotive-grade processors using a dSPACE MicroAutoBox-II rapid prototyping unit, showing a worst-case computation time of roughly 40 ms.

An investigation of periodic degradation of axle box vibration spectrum for a high-speed rail vehicle based on Bayesian method

Abstract: Axle box vibration serves as the main source of excitations for rail vehicles. Due to the wear of wheel/rail contact and the re-profiling procedure, the axle box vibration usually degrades periodically with the increased mileage in the service. This could significantly impact the estimation of vibration fatigue when the component is subjected to the axle box vibration. This paper develop a method to describe the periodic evolution of axle box vibration spectrum to better characterise the vibration spectrum of axle box. In this study, a Wiener process incorporating with four random parameters was employed to model the non-linearity of the degradation process. The maximum likelihood estimation (MLE) algorithm is used to estimate the initial values of the random parameters, and a Bayesian approach is employed to update the parameters based on newly obtained data. Finally, the proposed methodology is tested using long-term field test data from a high-speed train, and the results demonstrate that it accurately estimates the evolution of the axle box acceleration spectral density (ASD) spectrum. This could aid in predicting the residual service life of structures subjected to axle box vibration and further contribute to the development of maintenance strategies and top-down design of the structure.

Identification of track irregularities with the multi-sensor acceleration measurements of vehicle dynamic responses

Abstract: Track irregularities induce potential risks to the safety and stability of railway track systems. This paper proposes a novel methodology to identify vertical and lateral track irregularities. The method involves measuring system-based attitude calculation and a model-based unknown input observer estimator, based on the dynamic responses of distributed multi-sensors on the vehicle and bogie. First, a mechanical model of wheel-rail contacts is built with dynamic methods. The model considers the different directions of motion for a railway vehicle and consists of two bogies and four wheelsets. Based on the multi-sensor acceleration measurement, the vertical and lateral acceleration signals of the vehicle and bogies are integrated into the displacement signal. Then a state-space description of the vehicle suspension model is established for inverse dynamical analysis to extract the input signals. A suitable unknown input observer is constructed to estimate the track irregularities by transforming the state space equations of the vehicle into an augmented system that can monitor the track irregularities in-service. This method provides an opportunity to reduce the costs of the monitoring infrastructure and provide quicker and more reliable information about the status of a track.

A study on the optimal spatial damping distribution in railway pantograph-catenary interaction

Abstract: Railway overhead contact lines are very low-damped structures with a high modal density in the low-frequency region. This has a significant impact on the interaction with the pantograph, especially in the high-speed case and in multiple pantographs operations. This paper studies the optimal spatial damping distribution in overhead contact lines obtained by introducing localised damping connections, resulting in a non-proportional damping distribution. To this end, the simulation software Cateway is presented and adopted in conjunction with evolutionary multi-objective optimisers to seek for the most efficient spatial damping distribution. The study is conducted on a high-speed reference model considering two different train speeds. The final goal of this optimisation is to obtain useful hints about the most and least sensitive regions to damping modifications. A dedicated study on the locus of the poles of the system is also proposed to corroborate the findings of the analysis. Results show that significant improvements on the current collection quality can be achieved by carefully designing the spatial damping distribution, especially for the rear (trailing) pantograph. On the other hand, wrong design choices can lead to a degradation of the contact forces.

Optimisation of turnout frog profile geometry using revenue service wheel profiles

Abstract: Railroad turnouts are an essential element of the track infrastructure that facilitates the movement of trains between adjacent or diverging tracks. Turnout frogs are subjected to high wheel impact forces due to the inherent need for a discontinuity in their geometry. To develop an optimised frog geometry to minimise wheel impacts, a parametric study was designed and executed that considered three critical design parameters: point (i.e. nose) slope, relative height difference between wing and point, and longitudinal wing slope. Four hundred wheel profiles were extracted from a dataset of one million revenue service wheel profiles based on a wheel classification methodology previously developed. Wheel impact was quantified for each frog geometry case based on wheel transfer distribution and vertical wheel trajectory which were analysed using a developed Python algorithm. A total of 30 unique geometries were evaluated, including the existing standard design geometry for a N.A. heavy point conformal frog. Results demonstrated that each parameter affects different locations along the frog and total impact is most affected by point slope. Lastly, an optimised frog geometry was selected that ensures well-distributed wheel transfer locations preventing the concentration of damage, and results in low total impact at the transfer point.

Vehicle-track coupled dynamics model for superconducting electrodynamic suspension train

Abstract: In the previous studies of superconducting EDS train, the magneto-electric coupling between superconducting magnets (SCMs) and null-flux coils (NFCs), was equivalent to a vibration system with constant stiffness. This premise has decoupled the magnetic/track interaction and is not able to study the dynamics issues in an accurate and comprehensive level. Therefore, the vehicle-track coupled dynamics model of superconducting EDS train, with magneto-electric-force coupling fully considered, was established to explore the vehicle-track interaction relationship in this paper. A mathematical model based on Newton’s laws and 3-D dynamic co-simulation model were built respectively by Simulink and MATLAB-SIMPACK to compare the operating performances with the time/frequency domain. Meanwhile, the dynamic electromagnetic forces were calculated by dynamic circuit theory rather than merely assuming the constant stiffness. The dynamic responses of suspension vehicle show that, the vibration of carbody and frame are mainly concentrated about 1 Hz and 5 Hz respectively. The use of equivalent model in the previous studies has overestimated the negotiation capacity of superconducting EDS train. Furthermore, the vertical vibration accelerations of frame in the coupled model are relatively larger, whereas the lateral vibration is comparatively smaller. Therefore, the electromagnetic calculation of superconducting EDS train with constant stiffness overestimates/underestimates the dynamic performances.

Influence of suspension schemes on medium-low speed maglev vehicle-guideway dynamic interaction

Abstract: A comparative study was conducted on Levitation Frame with Mid-set Air Spring (LFMAS) and Levitation Frame with End-set Air Spring (LFEAS). First of all, the work done by air spring force and by track excitation on two levitation frames were analysed, respectively, and the mechanism of the low dynamic interaction of LFMAS with guideway was explained theoretically; then, dynamics simulation and coupled vibration test on LFEAS and LFMAS were carried out using coupled vibration test bench of single levitation frame. Theoretical equations show that both the work done by the air spring forces and by track excitation on LFMAS are less than those on LFEAS under the same vibration condition, demonstrating that LFMAS has better levitation stability than LFEAS. Simulation and test results show that the fluctuation of levitation gap as well as the vibration acceleration of track beam platform, levitation frame and car-body of LFMAS are all smaller than those of LFEAS; with the increase of sine excitation frequency or vehicle speed, the superiority of LFMAS in dynamics performance is more obvious.

Real-time wheel–rail friction coefficient estimation and its application

Abstract: The friction coefficient at the wheel–rail interface is crucial for the traction, braking and guidance of the railway vehicle. Real-time knowledge of the friction coefficient could reduce wheel–rail damages as well as improve the vehicle running performance. The friction coefficient is very difficult to be directly measured; hence an indirect measurement method using an unscented Kalman filter was proposed in this paper. A re-adhesion controller was also developed. The method was assessed in a Simpack-Simulink co-simulation environment. The friction coefficient estimation method was found to be accurate, and the re-adhesion controller improved the vehicle braking performance as well as reduced the wheel–rail damage.

The mechanism of wheel polygonal wear based on rotor dynamics

Abstract: A rotor dynamic model of wheel-rail coupling system was established taking wheel eccentricity and initial polygon into consideration in order to investigate the mechanism of wheel polygonal wear. Considering the complex wheel-rail contact relationship, the equivalent yaw angle was proposed and the wheel-rail relative speed model was established. The law of wheel-rail self-excited vibration and its effect on polygonal wear were studied. The possibility of variable speed operation was investigated together with the sensitivity of the system parameters. The results show that the periodic longitudinal and lateral creep forces are essential for the wheel polygonal wear, which have the characteristics of supercritical Hopf bifurcation and ‘fixed wavelength’ and ‘fixed frequency’. While in some circumstances, longitudinal and lateral creep forces jointly cause polygonal wear, in other cases, longitudinal creep forces have almost no effect. By adjusting the longitudinal and lateral stiffness, primary suspension stiffness, and rail damping parameters, as well as by selecting an appropriate speed for variable speed operation, the wheel polygonal wear may be effectively suppressed. The findings offer a fresh viewpoint for the study of mechanisms and the prevention of wheel polygonal wear.

Control structures for rail vehicles using active steering technology

Abstract: In this study, an analytical method based on a linear single bogie model was used to investigate the mechanism of active steering for three control structures: wheelset yaw control (WYC), wheelset lateral control (WLC), and bogie yaw control (BYC). The results revealed that the WYC structure reduced both circumferential and axial wear, whereas the WLC and BYC structures mainly reduced circumferential wear, and BYC was ineffective when the primary lateral stiffness was low. Moreover, the impact of external forces on the control quantity was investigated by using a nonlinear full-vehicle model, with the wheelset unbalanced moment having the largest impact. Subsequently, the adaptation of the WYC and BYC structures to two control modes, namely, force and displacement control, was analysed. The results showed that for the WYC, the displacement control mode was favoured, whereas for the BYC, the force control mode was the sole alternative. Finally, the control efficiency was determined, with the WYC being recommended for low primary longitudinal stiffness and BYC for higher stiffness.

Suspension parameter optimal design to enhance stability and wheel wear in high-speed trains

Abstract: Ensuring running stability and minimising wheel tread wear are critical factors for enhancing the dynamic performance of high-speed trains. As an efficient method for improving vehicle performances, previous studies on suspension parameter optimisation have not fully considered these two factors. It is essential to pay attention to stability at extreme wheel-rail contact states, and the wheel wear evolution needs to be revealed instead of investigating the wear performance only through an index like wear number. This research aims to investigate the stability/wear Pareto optimisation of bogie suspension parameters for a high-speed passenger train. Stability-related indices are defined as the lateral ride comfort index at low equivalent conicity and the bogie frame acceleration at high conicity. To represent the long-term wheel wear performance, a contact spreading index is proposed and combined with the wear number index. The key suspension parameters are optimised through the genetic algorithm NSGA-II. The obtained Pareto front clearly reveals the relationship between the objective functions. To meet different performance requirements, four distinct matching rules of the suspension parameters are summarised by employing clustering analysis. Finally, the applicability of the parameter matching rules is examined by analysing stability at different equivalent conicities and wheel wear evolution.