Train-track System Research Articles

Dynamic Analysis of Metro Train-Monolithic Bed Track System under Tunnel Differential Settlement

The metro tunnel lines built in a soft soil area may suffer from tunnel differential settlement due to the high compressibility of soft soil, the engineering constructions nearby tunnel lines, and the cyclic load of metro trains. In this paper, a dynamic coupling model for a metro train-monolithic bed track system under tunnel differential settlement is established. A cosine function is introduced to simulate a real settlement curve measured from a metro tunnel in southern China, and the vibration performance of the train-track system under tunnel settlements is investigated in both the time domain and frequency domain. Based on the standards for the train safety and passengers’ comfort, the speed limit for the metro train traveling on a monolithic bed track with different settlement distributions are concluded. The present research could be useful for the operation and maintenance of metro tunnels in soft soil areas.

An influence of track stiffness discontinuity on pantograph base vibrations and catenary–pantograph dynamic interaction

Abstract In this article, the computational methodology of the catenary–train–track system vibration analysis is presented and used to estimate the influence of vehicle body vibrations on the pantograph–catenary dynamic interaction. This issue is rarely referred in the literature, although any perturbations appearing at the pantograph–catenary interface are of great importance for high-speed railways. Vehicle body vibrations considered in this article are induced by the passage of train through the track stiffness discontinuity, being a frequent cause of significant dynamic effects. First, the most important assumptions of the computational model are presented, including the general idea of decomposing catenary–train–track dynamic system into two main subsystems and the concept of one-way coupling between them. Then, the pantograph base vibrations calculated for two train speeds (60 m/s, 100 m/s) and two cases of track discontinuity (a sudden increase and a sudden decrease in the stiffness of track substrate) are analyzed. Two cases of the railway vehicle suspension are considered – a typical two-stage suspension and a primary suspension alone. To evaluate catenary–pantograph dynamic interaction, the dynamic uplift of the contact wire at steady arm and the pantograph contact force is computed. It is demonstrated that an efficiency of the two-stage suspension grows with the train speed; hence, such vehicle suspension effectively suppresses strong sudden shocks of vehicle body, appearing while the train passes through the track stiffness discontinuity at a high speed. In a hypothetical case when the one-stage vehicle suspension is used, the pantograph base vibrations may increase the number of contact loss events at the catenary–pantograph interface.

Experimental investigation for wheel polygonisation of high-speed trains

The wheel polygonisation is the harmonic wave along the wheel circumference, which has been widely reported in high-speed railway vehicles in China in recent years. The polygonization mechanism has not been fully understood yet, and this work discusses one possible mechanism through several experiments. Firstly, a field test for the CRH3 high-speed train with polygonal wheels is carried out. It is found that the vibration in vertical takes major responsibility, and there are several resonance bands for the train-track system. Another field test shows that the rail is sensitive to the polygonisation characteristic frequency, but the wheel axle is not. Then the rail local vibration modes are analyzed by the operational deflection shape (ODS) test in the laboratory. A loaded bogie is fixed on the tested track to simulate the real working conditions. The result shows that the frequency of one local mode is 591 Hz, which is a typical wheel polygonisation frequency. Besides, the wheel-rail contact point is not on the vibration node of this local mode. Thus, the resonance of this local rail mode can be one possible mechanism for the high-order wheel polygonisation.

A near-fault vertical scenario earthquakes-based generic simulation framework for elastoplastic seismic analysis of light rail vehicle-viaduct system

This paper focuses on the rapid elastoplastic analyses of light rail vehicle (LRV)- benchmark viaduct system to different seismic scenarios considering the dynamic substructuring method (DSM). Combining the energy-variational principle with the vehicle-bridge interaction (VBI) system, a new framework of train-track system space dynamics is constructed. The present study has established the train-track-bridge coupled system (TTBCS) model, calculated the elastic-plastic seismic responses of the light rail transit bridge (LRTB) subjected to the combined effect of vertical and horizontal earthquakes. Considering three ground motion ensembles, i.e. pulse-like near-fault ground motions (NFGMs), non-pulse-like NFGMs, and far-field ground motions (FFGMs). Results indicate that the large vertical ground motions (VGMs) type NFGMs greatly impact the seismic response of the running safety of the LRV in the low-frequency band compared to the non-pulse-like NFGMs and FFGMs. The results underscore the significance of distinguishing velocity pulses of different types when selecting NFGMs for assessing the nonlinear dynamic response of the VBI system.

Intelligent computing hardware for collision avoidance and warning in high speed rail networks

One of the very important issue is safety of transport vehicle, particularly in increasing number of trains on the same tracks and collision avoidance warning system. We have successfully developed Linux based hardware, modules and software code for IoT enabled Train Tracking and Collision avoidance warning system. A strong tracking of the vehicle an entire system and their updates of data in database and analysis of the database from multi-angles may reduce the occurrence of an accident even in the critical failure situation. In view of this we have made two types of train tracking system using Linux based robust hardware, which simultaneously monitors the movement of train by two different mechanism and the data collected are instantaneously stored in cloud server. Based on the live data analysis, the signalling of trains to different tracks or halt can be estimated. The estimated computational results will be highly useful in providing collision avoidance alerts. Also, we have developed user interactive GUI screen for onboard train module as well as on various analytics utilizing server module data. This paper strongly recommends a secure & safety process purely depend on tracking of any device simultaneously by two different mechanism. The system developed in the present work is cost effective, hence this system can be added as an additional safety layer to the existing safety systems in the train.

Study on Dynamic Behaviour of Metro Train and Embedded Track System I: Theoretical Modeling, Experimental Analysis and Verification

Study on Dynamic Behaviour of Metro Train and Embedded Track System I: Theoretical Modeling, Experimental Analysis and Verification

Dynamic Behaviour of Metro Train and Embedded Track System II: Effect of Track Parameters on Dynamic Behaviour

Dynamic Behaviour of Metro Train and Embedded Track System II: Effect of Track Parameters on Dynamic Behaviour

Two-way Hertzian spring in numerical analysis of coupled train-track system vibrations

The paper presents and compares two methods for simulation the train-track system vibrations, differing in the wheel-rail contact model used. In the first method, two-way Hertzian spring is used, in the second – a non-deformable constraint. In both methods, a flat computational model is assumed, consisting of an Euler-Bernoulli beam resting on a Winkler-type elastic foundation with damping and a set of rail vehicles modeled by dynamic systems with ten degrees of freedom. The results of numerical analysis are presented, in order to determine an influence of the contact constraints’ deformability on the vibration simulations. It is found that the replacement of non-deformable contact constraints by two-way Hertzian springs has no significant effect on track vibration simulations and has a little effect on vibration simulations of vehicle body and bogie. The developed simulation method can be used for numerical studies of the phenomenon of instantaneous detachments of wheels from rails, after minor modifications directed to introduce one-way Hertzian springs (i.e. not carrying tensile forces) being a more accurate contact model.

Effects of steel spring floating slab on vibration and noise of a rail transit box-girder

In order to study the effects of a steel spring floating slab track (SSFST) on the vibration and noise of rail transit overhead box-girders, a train–track system coupling model in the frequency domain was established. Two numerical models – a finite-element model to analyse the vibration and a boundary-element model for predicting structure-borne noise – were then built. Based on a field test of one 30 m long simply supported box-girder paved with ordinary slab track (OST) in an urban rail transit system, the models were verified to be effective at predicting the vibration and noise of the box-girder. Meanwhile, both the vibration- and noise-reduction effects of SSFST were assessed in comparison with OST. After substituting SSFST for OST, the maximum reductions of the overall vibration acceleration level and overall sound pressure level of the box-girder were 34·7 dB and 25 dB, respectively. Finally, the effects of the SSFST's parameters on the noise of the box-girder were investigated. The results showed that the isolator stiffness is the primary factor that affects the noise characteristics of the box-girder, followed by the floating slab thickness. However, the floating slab length and fastener stiffness were found to have little influence on the noise radiation.

Moving element analysis of partially filled freight trains subject to abrupt braking

This paper is concerned with a computationally efficient numerical study on the dynamic response of a partially filled freight train subject to abrupt braking using the moving element method. The motion of liquid inside the freight container is modelled based on the potential flow theory. A trigonometric function is employed to represent the free surface elevation of the liquid cargo. The vehicle components are represented by interconnected rigid multi-bodies and the track is modelled by a Euler beam resting on a viscously damped Pasternak-type foundation. The accuracy of the liquid sloshing model is examined by comparison with available results in the literature. This paper also investigates the effect of the liquid cargo filling level, the initial train speed and the braking torque on the dynamic response of the coupled liquid freight train-track system.

Dynamic Response of High-Speed Train-Track System Due to Unsupported Sleepers

This paper is concerned with a numerical study on the dynamic response of a high-speed rail (HSR) system subjected to unsupported sleepers using the moving element method (MEM). A three-phase computational scheme in conjunction with the MEM is proposed to account for the motion of the unsupported sleepers in relation to the truncated rail segment in the moving coordinate system. The accuracy of the proposed computational scheme is examined by comparison with available analytical results in the literature and against the finite element method using commercial software. A parametric study is conducted using a computational model consisting of a 10-degree of freedom train model and a three-layer ballasted track model to investigate the effect of unsupported sleepers on the dynamic response of the HSR system. Various factors affecting the response of the HSR system, including the speed of the train, the number of unsupported sleepers and the distance between the unsupported sleepers, are examined and discussed.

Influence of slab arch imperfection of double-block ballastless track system on vibration response of high-speed train

According to the structural damage characteristics of ballastless track of high-speed railway by investigation, a novel method for evaluating the influence of ballastless track of high-speed railway is presented. The dynamic model of ballastless track with damage property is established based on train-track spatial vibration system. The calculated and in situ tested results were compared to certify the model and computation program. Taking the track slab imperfections occurred in a tunnel along the real high-speed railway as an example, the influence of vibration responses of the train-track system with slab imperfections under different conditions is calculated and analyzed in comparison with normal slab. In addition, the maintenance effect on the repaired track structure is evaluated by considering the operate safety and comfort of high-speed train. It is concluded that large amplitude of slab arch imperfection results in higher acceleration of slab and car body. Therefore, train operation speed should be controlled in accordance with the safety standard such as wheel load reduction rate and derailment coefficient. In the case of low amplitude of slab arch imperfection, train operation speed should be controlled in accordance with the comfort standard such as Sperling index. The specific operation velocities were given correspondingly. Therefore, the mechanism and conclusions above can forecast intuitively in the field of track maintenance. The paper proposes a practical and valuable method for evaluating double-block ballastless track of high-speed railway.

Moving element analysis of high-speed rail system accounting for hanging sleepers

It is very common in the ballasted track system that sleepers are not well supported by the ballast materials due to the uneven settlement of the ballast under repeated train passage. These unsupported track elements are often termed as hanging sleepers and they can lead to undesirable effects due to increased dynamic response of the train-track system, especially when the speed of the train is high. In this paper, we present a computation scheme in conjunction with the moving element method for the analysis of high-speed train-track dynamics accounting for hanging sleepers. The proposed computational scheme will be first verified by comparison with available analytical results. The dynamic response of a high-speed train traveling on a ballasted track considering unsupported sleepers is next investigated. Various factors affecting the response of the high-speed rail system including the speed of the train, the number of hanging sleepers and the pattern of the hanging sleepers will be examined and discussed.

On the sloshing effect in half-filled freight trains during braking

This paper is concerned with a computationally efficient numerical study on the dynamic responses of a half-filled freight train during braking phase using the moving element method. The motion of liquid inside the freight tank is modelled based on potential flow theory. The vehicle components are represented by interconnected rigid multi-bodies and the track is modelled by an Euler beam resting on a Pasternak-type foundation. The accuracy of the proposed computational model is examined by comparison with available results in the literature. This paper also investigates the effect of the initial train speed and the braking torque on the dynamic response of the train-track system.

An efficient method for predicting train-induced vibrations from a tunnel in a poroelastic half-space

This paper presents an efficient method for the prediction of vibrations induced by underground railways in a poroelastic half-space. The proposed method accounts for both the saturated porous characteristic of the soil and the free surface effect. An analytical tunnel model, which is coupled with a train-track system, is firstly developed to calculate the dynamic response of the tunnel–soil interface in a poroelastic full-space. By assuming that the near field response of the tunnel is not affected by the existence of the free surface, vibrations of the poroelastic half-space is then calculated by the two-and-a-half-dimensional (2.5-D) boundary integral equation for saturated porous media along with the Green's function for a poroelastic half-space. Soil vibrations generated by the quasi-static and dynamic train load are presented. It is found that an increase of the soil permeability leads to a decrease of the soil displacement. A saturated soil model may be more suitable for calculating the train-induced vibration in water-rich region. Isolation effectiveness of a float slab is also investigated. The simulation results show that floating the track slab can moderately induces the ground vibration, but also causes more transmission of vibration under certain conditions.

Calibration and experimental validation of a dynamic model of the train-track system at a culvert transition zone

This article describes the calibration and experimental validation of the dynamic model of the train-track system at a culvert transition zone. The dynamic analyses were performed explicitly using a 3D model in LS-DYNA software and implicitly using a 2D model on ANSYS software. In both programmes, contact algorithms were employed to take the wheel-rail interaction into account. The parameters for the 3D model were calibrated based on the track receptance test. The 3D model was used for the static and dynamic calibration of the 2D model. The damping adopted in the 2D model was significantly amplified to compensate for the radiation damping in the transverse direction of the track, which cannot be incorporated in a plane model. An excellent agreement was obtained between the vertical displacements of the rail, the vertical accelerations of the sleepers and the wheel-rail interaction forces computed by the two models. The computation time of the 2D model is about 25 times lower than the computation time of the 3D model. The 2D model was used to simulate the passage of the Alfa Pendular train at 220 km/h at the transition zone and a very good match between measured and computed responses has been obtained.

Numerical simulation of floor vibrations of a metro depot under moving subway trains

With the development of subway lines in urban areas, building structures are sometimes subjected to train-induced vibrations, and there is a need to develop prediction models to evaluate the vibration serviceability. In this paper, a new type of subway-depot system is investigated, where subway trains run through the top story of a 3-story metro depot, while the first two stories were developed for offices and shops to avoid the waste of large city areas. Considering the increasing use of such a structural system and the possible serviceability problems, the floor vibrations of a metro depot under moving subway trains were numerically simulated, where the train-track system was treated as the vibration source and studied separately, and the influence of train speed and fastener configuration on the vibration response was discussed. The metro depot was modeled taking the stiffness of the partition walls into account, and vibration responses of the building at different locations were compared and validated through field tests. Besides, vibration level of the second floor was evaluated using an acceleration index that considers frequency weighting. Finally, parameter analysis was carried out so as to provide some references to the vibration control.

A study on the dynamic train-track interaction over cut-fill transitions on buried culverts

Sudden changes in the structural and geotechnical properties of railway tracks along its course are normally associated with subgrade stiffness transitions, differential settlements and, ultimately, hanging sleepers that reduce the performance of the railway system. This paper aims at analysing and quantifying the impact of such situations, particularly cut-fill transitions combined with the presence of culverts, on the train-track system response. A cut-fill transition on a buried culvert is used as case study for which track geometry and stiffness evaluation data were available. A numerical model, considering the coupled train-track interaction, was developed using a 3D FEM dynamic analysis tool that was further improved here with a mixed implicit-explicit time integration scheme. The results suggest that the faster degradation rates typically found at similar locations are mostly related to the development of early permanent deformations in the subgrade layers, rather than to sudden stiffness transitions, which then aggravate the problem by causing important dynamic amplifications in the train-track interaction. Therefore, numerical approaches similar to the one presented herein can be valuable tools for designers and railway infrastructure managers in order to anticipate and mitigate such negative effects at these locations.

Experimental assessment of the dynamic behaviour of the train-track system at a culvert transition zone

This article describes the experimental assessment of the dynamic behaviour of the train-track system at a culvert transition zone located at the Northern line of the Portuguese railway network. Based on receptance tests, the dynamic flexibility of the track along the transition was characterised. From the full track resonance frequency, a reduction of 60% was observed on the dynamic flexibility of the track on the structure in relation to the track on the embankment; The dynamic response of the track was also monitored in different sections for the passage of the Alfa Pendular trains at a speed of 220km/h. Based on these tests, it was concluded that the displacements of the track on the structure and on the transition wedge were, respectively, 45% and 30% lower than those of the track on the embankment. Despite the significant variations of the dynamic stiffness of the track, the accelerations of the sleepers, after the application of a low-pass filter for eliminating contributions from irregularities of the track and of vehicle wheels, did not exhibit relevant variations along the transition zone. Likewise, no substantial variations were registered in terms of the dynamic loads applied by the train at the monitored track sections. Finally, synchronized measurements of the dynamic response of the track and of the inspection vehicle EM 120 were made at a speed of 100km/h, where no significant amplifications induced by the transition were recorded for the accelerations on the axles, on the bogies and on the vehicle box.

Moving element analysis of discretely supported high-speed rail systems

In this paper, a computational scheme in conjunction with the moving element method has been proposed to investigate the dynamic response of a high-speed rail system in which the discrete sleepers on the subgrade support the railway track. The track foundation is modeled as a beam supported by uniformly spaced discrete spring-damper units. The high-speed train is modeled as a moving sprung-mass system that travels over the track. The effect of the stiffness of the discrete supports, train speed, and railhead roughness on the dynamic behavior of the train–track system has been investigated. As a comparison, the response of a continuously supported high-speed rail system that uses a foundation stiffness equivalent to that of a discretely supported track has been obtained. The difference in results between the “equivalent” continuously supported and the discretely supported high-speed rails has been compared and discussed. In general, the study found that a high-speed train that travels over a discretely supported track produces more severe vibrations than that travels over a continuously supported track of equivalent foundation stiffness.