Vehicle Track Interaction Research Articles

Prediction of long-term differential track settlement in a transition zone using an iterative approach

A methodology for the simulation of long-term differential track settlement, the development of voided sleepers leading to a redistribution of rail seat loads, and the evolving irregularity in vertical track geometry at a transition between two track forms, is presented. For a prescribed traffic load, the accumulated settlement is predicted using an iterative approach. It is based on a time-domain model of vertical dynamic vehicle–track interaction to calculate the contact forces between sleepers and ballast in the short-term. These are used in an empirical model to determine the long-term settlement of the ballast/subgrade below each sleeper. Gravity loads and state-dependent track conditions are accounted for, including a prescribed variation of non-linear stiffness of the supporting foundation along the track model. In parallel, a two-dimensional (2D) non-linear finite element model of layered soil is verified versus field measurements and used to determine the support stiffness of each sleeper in the track model. The methodology is applied to a transition zone between a ballasted track and a slab track that is subjected to heavy haul traffic. Analyses of the influence of higher axle loads and the implementation of under sleeper pads on sleeper settlement are demonstrated.

Optimal design of rail level crossings and associated transition zones using adaptive surrogate-assisted optimization

Transition zones such as level crossing and bridge approaches are critical links in railway networks due to higher degradation rates and maintenance needs. In this context, parametric optimization has been applied to improve the design in transition zones; however, it requires a more computationally efficient tool to support repetitive function evaluations, since the involved vehicle–track dynamic simulations are becoming more expensive to evaluate. For this purpose, a surrogate-based simulation methodology is proposed to search for an optimal combination of parameters relevant to the geometry and elasticity of track structures. Specifically, the presented methodology integrates finite element (FE)-based modeling with surrogate-assisted optimization: (1) the FE model is developed to characterize the dynamic behavior of a level crossing under a moving vehicle; (2) the optimization problem is formulated upon this mechanical model by extending the expensive FE simulations to an adaptive surrogate modeling scheme. This integration facilitates efficient exploration of the track design space (thereby reducing the computational cost), and a reasonable balance can be achieved between solution quality and computational effort. The methodology is applied to a Dutch railway case. Results show that compared to a reference design, the optimized design significantly improves performance indicators relevant to wheel–rail contact forces and energy dissipation in the ballast layer. The solution brings great potential in achieving a more desirable vehicle–track interaction and improving the connecting performance between level crossings and transitions. The methodology is applicable to other railway structures and may also contribute to improvements in current track design practices.

Insulated rail joint (IRJ) contact characterisation-an ultrasonic reflectometry approach for a cross-material interface

Vehicle–track interaction at insulated rail joints (IRJs) plays a significant role in the wear evolvement and damage of the IRJ components. It is, however, challenging to characterise the contact conditions within the region non-destructively and accurately using experimental tools, especially when the IRJ contact involves both wheel–rail and wheel–endpost contact pairs. This study presents an ultrasonic technique to monitor and characterise static IRJ contacts in a non-invasive manner. The proposed ultrasonic reflectometry technique can realise high-resolution visualisation of contact patch and contact pressure distribution for both wheel–rail contact and wheel–endpost contact, by striking a beam of focused ultrasonic signals at the contact interface. Different data post-processing strategies are applied for the two types of contacts and a deconvolution algorithm is applied to rectify the measurements near the rail–endpost boundary. The ultrasonic measurements are verified through finite element simulations and the results show good agreement with each other in terms of both contact area and contact pressure level. It is expected that the proposed ultrasonic approach can be a reliable tool to assist in revealing the contact behaviour of IRJs more profoundly.

A numerical study on tread wear and fatigue damage of railway wheels subjected to anti-slip control

Tread wear and rolling contact fatigue (RCF) damage propagated on railway wheels are the two extremely important focal points as they can tremendously deteriorate wheel/rail interactions and hunting stability and destroy wheel surface materials, and subsequently, cut down the lifetime of the wheels. The on-board anti-slip controllers are of essence aiming to hold back the striking slipping of the powered wheelsets under low-adhesion wheel/rail conditions. This paper intends to investigate the impact of anti-slip control on wheel tread wear and fatigue damage under diverse wheel/rail friction conditions. To this end, a prediction model for wheel wear and fatigue damage evolution on account of a comprehensive vehicle-track interaction model is extended, where the wheel/rail non-Hertzian contact algorithm is used. Furthermore, the effect of frictional wear on the fatigue damage at wheel surface is considered. The simulation results indicate that the wheel/rail contact is full-slip under the low-adhesion conditions with braking effort. The wear amount under the low-adhesion conditions is observably higher than that under the dry condition. It is further suggested that the wheel tread is prone to suffering more serious wear and fatigue damage issues with a higher anti-slip control threshold compared to that with a lower one.

Vehicle Dynamics and Train-Induced Ground Vibration—Theoretical Analyses and Simultaneous Vehicle, Track, and Soil Measurements

Ground vibrations near railway lines are generated by the forces that are acting between wheel and rail. It seems to be a straight forward assumption that the vehicle dynamics are important for the level and the frequencies of the excitation forces. Different vehicle dynamics phenomena are analysed for their role in the excitation of ground vibrations: rigid body modes of the bogies, elastic (bending) modes of the car body, and elastic modes of the wheelset. The theoretical analyses use rigid body models, simplified elastic models, and detailed elastic models. Some of these problems are vehicle–track interaction problems where 3D finite-element boundary-element models have been used for the track and soil. It is shown that the rigid or flexible vehicle modes are well in the frequency range of ground vibrations (4 to 100 Hz). They have an influence on the excitation force but the additional forces are rather small and can be neglected in ground vibration prediction. The theoretical results are checked by experimental results of a simultaneous measurement of vehicle, track, and ground vibrations.

Study on railway curve squeal using a rigid-flexible coupling model of vehicle and track

Squeal noise occurring in narrow curves is one of the most annoying noise issues for people living by the railway track. When vehicles pass through those curves, squeal noise is mainly generated due to the large, high-frequency, lateral sliding friction force. To investigate generation mechanism of curve squeal, a three-dimensional (3D) vehicle-track interaction model with a flexible wheelset and a flexible curved track is built in a multi-body simulation tool in this paper. Compared to conventional rigid models, this model allows to obtain the high frequency friction force between wheel and rail. This calculated friction force in the frequency domain is analyzed to identify the major modes. Those modes are compared with the modal properties of the wheelsets and rails in order to determine which of their modes have the main contribution to the friction force and the squeal noise. In addition, a parametric study is performed to study the influence of vehicle speed, curve radius, wheel/rail friction coefficient and further parameters on the dominant modes of friction forces.

Vehicle-track coupled dynamics model for superconducting electrodynamic suspension train

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.

Multi-objective optimisation methodology for stiffness combination design of bridge-embankment transition zones in high-speed railways

Bridge-embankment transition zones, in which unexpected amplifications of vehicle-track interactions and infrastructure degradation are concentrated, are critical areas of high-speed railways. To mitigate the dynamic issues induced by uncertain filler stiffness, an available stiffness combination of transition zone components is required. Combining with robust designs, a multi-objective optimisation methodology is proposed to determine the compromise design of transition zones, which considers trade-offs among dynamic stress, dynamic displacement and system robustness. An optimal stiffness combination of subgrade bed surface layer (E1) and graded broken stone area (E2) in a typical bridge-embankment transition zone is presented by employing this methodology. The results indicate that the Pareto fronts visually show the dynamic response contradiction. Based on the conflicting evaluation criteria, i.e., minimizing the displacement and stress of the subgrade and maximizing the system robustness, the knee points objectively render the best compromise design with E1 and E2 values of 1200 and 1000 MPa, respectively. Not only the dynamic response of the vehicle-track-subgrade system but also the negative effect brought by filler uncertainties are well controlled. Such a methodology is available for configuration design of projects in which uncertainties exist and design criteria are hard to weigh.

Modern Tendencies in Vehicle-Based Condition Monitoring of the Railway Track

Condition Monitoring (CM) describes the continuous observation of a dynamical system or process in order to track the evolution of its state and to detect signs of faults in an early stage. It constitutes the core block for performing fault diagnosis and prognosis, allowing a condition-based assessment of the system and supporting the implementation of an intelligent, cost-effective maintenance policy. This study focuses on the vehicle-based monitoring of railway infrastructure. First, the main concepts related to intelligent maintenance systems and strategies are depicted in a general framework. Later on, the specific application, the railway track-vehicle interaction system, is introduced. Railway vehicle instrumentation for track condition monitoring is analysed, with a special focus on the inertial measurement systems. A review of the processing algorithms used for railway monitoring is done and a taxonomy is proposed, based on the methodology approach: model-based, data-driven or hybrid. An analysis on the monitoring algorithms according to the geographical region is also made. It has been found that the railway vocation of each individual region determines the monitoring objectives pursued, as well as the methodological approach and the specific algorithms used. Finally, current trends and research gaps in railway monitoring are identified and outlined.

Short pitch corrugation mitigation by rail constraint design

Short pitch corrugation is a quasi-periodic rail defect that induces a high level of noise and accelerates track degradation. This paper proposes a methodology to mitigate short pitch corrugation by rail constraint design, including four steps. In Step 1, corrugation is numerically reproduced by employing a three-dimensional (3D) finite element (FE) vehicle-track model with degraded fastenings. In Step 2, the corrugation initiation mechanism is identified by the operating deflection shapes (ODSs) approach. In Step 3, different types of rail constraints are designed and their effects on rail vibration modes are analysed. Then FE models of these rail constraints are built up and validated. In Step 4, rail constraint models from Step 3 are applied to the 3D FE vehicle-track interaction model and their effectiveness on corrugation mitigation is evaluated. The results indicate rail longitudinal compression modes and the induced longitudinal dynamic contact force dominate the initial differential wear and corrugation initiation. Based on this mechanism, a new rail constraint is designed in this work that can completely suppress longitudinal compression modes and significantly reduce the fluctuation amplitude of the longitudinal contact force so that corrugation can hardly initiate. This paper first points out a direction for field corrugation mitigation by strengthening the rail longitudinal constraint.

Dynamic response of vehicle-track interaction at the bolted rail joint in the presence of the polygonal wheel

Rail joints are the weakest link in the railway track structure due to the presence of discontinuities in the track stiffness and wheel-rail contact geometry. This paper presents the dynamic response of vehicle-track interaction at the bolted rail joint (BRJ) in the presence of polygonal wheel wear. A three-dimensional coupled vehicle-track dynamic model was established using the finite element method (FEM) and the multi-body system (MBS) approach, in which the flexibilities of the wheelset and track are taken into account. The proposed dynamic model is validated by the comparisons of field measurement and calculated vertical axle-box acceleration in time and frequency domains. The effects of the flexible wheelset in the presence of polygonal wear on the vehicle-track dynamic interaction at the BRJs are illustrated through comparisons with those obtained using without polygonal wheel model. The results show that the polygonal wheel wear and the rail joint irregularities can induce high-magnitude vertical wheel-rail contact force, and exacerbate the vibration responses of the axle box, the wheelset, and the rails. The simulation results also indicate that the wheelset bending modes, the P2 resonance due to rail joint excitation, and the track vibration modes have significant effects on the vertical vehicle-track dynamic interaction at the supported and suspended BRJs.

Development of a model for stochastic analysis of vehicle–track interaction considering spatial variability of track parameters

In this work, a model for achieving stochastic analysis of vehicle–track interaction systems is proposed based on random field realization of track parameters and the finite element coupling of rigid-elastic bodies. Aiming at the clarification of the spatial variability and correlation of track parameters on the influence of vehicle–track dynamic performance, a general scheme based on Karhunen–Loève Expansion and cyclic calculation method is developed to realize a multi-dimensional random field that holds an arbitrary marginal distribution function and correlation structure, and to consider the inhomogeneity of system parameters along the longitudinal direction efficiently. Furthermore, the validation of the random field expansion against the vehicle–track system is implemented, and the dynamic effects of random track parameters are investigated through two special issues. Numerical results show that the spatial correlation of fastener stiffness affects the extreme response, especially the low-frequency component of rail displacement. The spatial dependence of the filling layer has little influence on the dynamic behavior of the vehicle subsystem, but it obviously changes the extreme stress and strain of the filling layer. Ignoring the spatial correlation of random variables might underestimate the performance of the track system.

Mechanism of Derailment at the Guardrail Position of Turnout and a Reasonable Guardrail Interval Limit

Recently, derailments have been occurring frequently at the guardrail position of double-slip turnouts. In order to provide a theoretical basis for effectively avoiding derailment at the guardrail position of turnouts, this study presented a derailment mechanism, discussed the rationality of the current guardrail interval limit and its calculation method, and proposed a method for calculating the guardrail interval limit based on the vehicle running attitude and wheelset angle of attack. Based on the established calculation model, this paper calculated the guardrail interval limit for the main types of single turnouts and double-slip turnouts in China, and studied the main factors influencing the interval limit and corresponding patterns. The following conclusions were drawn. (1) In actual maintenance, it suggested to set the guardrail interval limit at 1365 mm, which can meet the requirements of the most turnouts and avoid wear incurred by vehicle–track interactions at the opening section of guardrails and derailment. (2) For single turnouts, the required guardrail interval limit becomes smaller with the decrease of the frog number, radius of the lead curve, and the increase in gage width. Further, the interval limit decreases when the endpoints of the lead curve and gage widening become closer to the buffer segment at the toe end of the guardrail. Adopting straight-track design at the restoring segment of gage widening is more likely to cause a larger twisting angle of the bogie than a curved-track design, and larger twisting angle means requiring a smaller guardrail interval limit. (3) For double-slip turnouts, the required guardrail interval limit is reduced with the decrease in the frog number and increase in gage width. The broken rail comprising the switch rail and stock rail in front of the guardrail can also enable the bogie to approach or reach the inscribing state, resulting in a negative impact not smaller than that produced by a curved rail. The larger the attack angle at the tip of the switch rail and the closer the tip of the switch rail and the end of gage widening to the buffer segment of the guardrail, the smaller the guardrail interval limit.

Comparison of the dynamic response and environmental impact between traditional and innovative railway track systems

ABSTRACT Railways employ a range of different railway track forms. Here, a ballasted track design is compared to three different slab track solutions. The track designs are compared using both a life cycle analysis (LCA) and a methodology for simulation of three-dimensional vertical dynamic vehicle–track interaction, which has been verified versus field measurements. The interaction between vehicle and track is simulated in the time domain using an extended state-space vector approach. For the investigated load cases involving representative wheel and track irregularities, it is concluded that the maximum stress in the concrete parts is, for all designs, below the maximum flexural tensile strength. From the LCA, it is concluded that the production of steel and concrete cause most CO2 emissions, while the CO2 emissions due to maintenance activities such as tamping and rail grinding are only a small part of the overall emissions.

Development of vehicle-track coupled dynamics theory and engineering practice

<p indent="0mm">Railway vehicles running on track structures constitute an interactive and inseparable large-scale dynamics system. For a long time, studies on railway vehicle dynamics and on track structure vibration were carried out separately due to the complexity of wheel-rail nonlinear systems and the classification of disciplines, which consequently results in the classical theory system of separate vehicle dynamics and track dynamics. However, the dramatic increase of operating speed and hauling mass of modern railway transportation intensifies dynamic interactions between vehicles and tracks, and such complicated vehicle-track interaction problems fail to be handled by the classical subsystem dynamics theory. Therefore, it is necessary to break through the subsystem research framework and comprehensively investigate the vehicle-track interaction mechanism, so as to achieve the optimal dynamic performance design of the whole system. For this purpose, the vehicle-track coupled dynamics theory system is developed on the basis of absorbing the theoretical achievements of vehicle dynamics and track dynamics, which treats the vehicle subsystem and the track subsystem as a large integrated system by establishing a wheel-rail spatial dynamic coupling model. The vehicle-track coupled dynamics problems can be divided into three aspects: The vertical, lateral and longitudinal coupled dynamics. Generally, the vehicle-track vertical coupled dynamics mainly studies the train-track vertical interaction problem. The vehicle-track lateral coupled dynamics focuses on the stability and safety of vehicle lateral movement on the elastic-damping track structure. In recent years, with the development of long marshalling heavy-haul trains, especially running in the complex environment of long ramps in mountainous areas, the longitudinal impulse of vehicles in a train and its influence on the track system are aggravated, bringing prominent safety problems of the train and track system, which is exactly the mission of longitudinal coupled dynamics research. In view of these three aspects, the vehicle-track coupled dynamics model has undergone the development process from simple to complex, including the unified vertical coupled model, the vertical-lateral spatial coupled model, and the vertical-lateral-longitudinal three-dimensional coupled model. In this paper, the theory system of vehicle-track coupled dynamics will be briefly introduced, including the academic rationale and its formation process. Most of the emphasis is laid on the construction of the unified model of vehicle-track vertical coupled dynamics (namely the fundamental model), and the vehicle-track spatial coupled dynamics model and its recent development. Based on the theory and its simulation platform, an optimal matching design principle of the vehicle and track dynamic performance is proposed, providing a scientific solution for high safety and high stability design of the modern rail transportation system. The vehicle-track coupled dynamics theory ends the long history of separate investigations on vehicle dynamics and track dynamics, and opens up a new research field of railway large-scale system dynamics. As a new theory system, it is recognized worldwide that the vehicle-track coupled dynamics has become the fundamental method for research on railway engineering dynamics after nearly <sc>30 years</sc> of development. This theory has been widely applied to railway engineering practice and has successfully solved a series of key dynamics problems in tremendous railway engineering projects. For this, some practical engineering projects are selected to illustrate the application of the theory, including the investigations on the selection of the plane and vertical profiles design scheme for a Chinese high-speed railway line, the key parameters design for a high-speed railway with a design speed of <sc>400 km/h,</sc> the design of rail asymmetrical grinding profiles for a heavy-haul railway curved line, the safety control of a long heavy-haul train under crush conditions, and the vibration reduction and optimization design of floating slab tracks for metro railways. It is demonstrated that the vehicle-track coupled dynamics theory and its applications strongly support the remarkable development of Chinese railways.

Random simulation method of track irregularities and its application in vehicle-track dynamic analysis

ABSTRACT Track irregularity holds strong randomicity, evolvability, and large data sets during the long-term operation of a rail line, possessing a significant influence on the dynamic performance of vehicle-track systems. In this work, methods for simulating track random irregularities are developed by combining the track irregularity probability model (TIPM) and the number theory method and by the Karhunen-Loève expansion (KLE). Furthermore, the vehicle-track interaction model considering the interaction between the vehicle, track, and wheel-rail interaction is constructed at a 3-D space, where the multi-rigid-body dynamics, finite method, and wheel-rail contacts are applied to construct matrix-coupled vehicle-track interaction equations. Finally, a unified random vibration analysis framework for the vehicle-track system is presented. From perspectives of the amplitude, power spectral density, and probabilistic distribution, the accuracy and efficiency of TIPM and KLE models in simulating track random irregularities and revealing system dynamics performance are compared and analysed in detail.

Modelling ballast via a non-linear lattice to assess its compaction behaviour at railway transition zones

Locations in railway tracks where significant variations of the track properties occur are subject to increased track deterioration. To successfully mitigate this, the mechanisms leading to the increased deterioration need to be understood. To this end, this work presents a non-linear constitutive law for a lattice model able to describe the compaction behaviour of railway ballast. The parameters of the non-linear connections are tuned against lab experiments of cyclic loading tests and direct shear tests. The tuned lattice can be used with different foundation properties provided that the ballast in the track is equivalent to that of the tests. The non-linear lattice model is applied to the case of railway transitions, for which ballast compaction under train loading is studied as a cause of geometry degradation. It is observed that for the studied cases of a culvert crossing and of a ballast-slab transition, the operation-induced compaction converges monotonously to a stable situation, without leading to significant changes in the vehicle-track interaction. Ballast compaction is therefore insufficient as a stand-alone mechanism to explain a process of progressive degradation of the track geometry. Other mechanisms like autonomous differential settlement at the foundation level must be taken into account in such cases.

A new hydraulic damper dynamics model and the availability on high speed vehicle dynamics investigation

The function of the hydraulic damper of the high-speed Multi-Electric-Units (EMUs) is to offer viscous damping to reduce the vibrations and to keep the stability of the vehicle. It is the key component and it has great effects on the high-speed EMU dynamics. A new hydraulic damper dynamics model including two clamping points stiffness, a viscous damping and two centralised masses, is presented in this paper. A high-speed vehicle–track interaction dynamics model is developed, in which the new hydraulic damper dynamics model is introduced in it to investigate the damper and vehicle dynamics. With numerical simulation, the clamping point loads and damping forces of four types of dampers of the vehicle are obtained. The reliability of the new damper dynamics model is validated with comparison between the simulation results and the field test results. The availability of the new damper dynamics model is confirmed with the comparison of the results between a simplified damper dynamics model and the new damper dynamics model for two types of high-speed EMUs in China. With the help of the new damper dynamics model, the optimised clamping point stiffness of the dampers and the effect of the damper mass on the vehicle system dynamics are discussed. The investigation results show that the vibration difference between the damper and the connected components of the vehicle could be obtained.

Charakterystyka wybranych rodzajów zużycia koła i ich wpływ na współpracę pojazdu szynowego z torem

The aim of this paper is to present the selected types of rail wheel wear and their influence on vehicle-track interaction. The first part discusses the wheel-rail interface and presents the essential information about the wear of rail vehicle wheels. Differences in the nature of the wear of rail and tram wheels are pointed out. Then, characteristics of typical forms of wheel wear are presented, together with the description of the mechanisms of their occurrence and the existing technical measures leading to their reduction. In the last part of the text, the impact of the previously described forms of wheel wear on the vehicle-track interaction is discussed.

Different Types of Continuous Track Irregularities as Sources of Train-Induced Ground Vibration and the Importance of the Random Variation of the Track Support

Irregularities of the track are a main cause of train-induced ground vibration, and track maintenance is of great importance. Although geometric irregularities at the wheel-rail contact are widely used, other types of irregularities, such as stiffness irregularities, irregularities from different track positions and irregularities in the wave propagation, were analysed in the present study. The track behaviour was investigated by a multi-beam-on-soil model. This track model is coupled with a vehicle model to calculate the vehicle–track interaction. The track model was also used for the track filtering, which transfers a track support error to the equivalent rail irregularity or, conversely, the sharp axle pulse on the rail to a smoother pulse on the soil. In the case in which this filtering varies randomly along the track, the pulses of the moving static load induce a certain ground vibration component (“the scatter of axle pulses”). This effect was calculated by the superposition of axle pulses in the frequency domain and by a stochastic simulation. Simultaneous vehicle, track and soil measurements at a certain site were used to evaluate the different excitation and ground vibration components. The agreement between calculations and axle-box and soil measurements is good. The ground vibrations calculated from rail irregularities and corresponding dynamic loads, however, clearly underestimate the measured ground vibration amplitudes. Only the static load that is moving over a varying track support stiffness can produce the important mid-frequency ground vibration component by the scatter of axle pulses.