Chengbiao Cai

Fundamentals of vehicle–track coupled dynamics

This paper presents a framework to investigate the dynamics of overall vehicle–track systems with emphasis on theoretical modelling, numerical simulation and experimental validation. A three-dimensional vehicle–track coupled dynamics model is developed in which a typical railway passenger vehicle is modelled as a 35-degree-of-freedom multi-body system. A traditional ballasted track is modelled as two parallel continuous beams supported by a discrete-elastic foundation of three layers with sleepers and ballasts included. The non-ballasted slab track is modelled as two parallel continuous beams supported by a series of elastic rectangle plates on a viscoelastic foundation. The vehicle subsystem and the track subsystem are coupled through a wheel–rail spatial coupling model that considers rail vibrations in vertical, lateral and torsional directions. Random track irregularities expressed by track spectra are considered as system excitations by means of a time–frequency transformation technique. A fast explicit integration method is applied to solve the large nonlinear equations of motion of the system in the time domain. A computer program named TTISIM is developed to predict the vertical and lateral dynamic responses of the vehicle–track coupled system. The theoretical model is validated by full-scale field experiments, including the speed-up test on the Beijing–Qinhuangdao line and the high-speed running test on the Qinhuangdao–Shenyang line. Differences in the dynamic responses analysed by the vehicle–track coupled dynamics and by the classical vehicle dynamics are ascertained in the case of vehicles passing through curved tracks.

High-speed train-track-bridge dynamic interactions - Part I: theoretical model and numerical simulation

This paper presents a framework to systematically investigate the high-speed train–track–bridge dynamic interactions, aiming to provide a method for analysing and assessing the running safety and the ride comfort of trains passing through bridges, which are critically important for the design of new high-speed railway bridges. Train–track–bridge interactive mechanism is illustrated. A fundamental model is established for analysing the train–track–bridge dynamic interactions, in which the vehicle subsystem is coupled with the track subsystem through a spatially interacted wheel–rail model; and the track subsystem is coupled with the bridge subsystem by a track–bridge dynamic interaction model. Modelling of each subsystem and each interactive relationship between subsystems are presented. An explicit–implicit integration scheme is adopted to numerically solve the equations of motion of the large non-linear dynamic system in the time domain. Computer simulation software named the train–track–bridge interaction simulation software (TTBSIM) is developed to predict the vertical and lateral dynamic responses of the train–track–bridge coupled system.

Coupling Model of Vertical and Lateral Vehicle/Track Interactions

SUMMARY A new dynamic model of vehicle/track interaction is presented. The model considers the vehicle and the track as a whole system and couples the vertical interaction with the lateral interaction. The vehicle subsystem is modeled as a multi-body system with 37 degrees of freedom, which runs on the track with a constant velocity. The track substructure is modeled as a discretely supported system of elastic beams representing the rails, sleepers and ballasts. The normal contact forces between wheels and rails are described by Hertzian nonlinear elastic contact theory and the tangential wheel/ rail forces are decided by the creep theory. Numerical results are compared with those of conventional dynamic models of railway vehicles. Applications of the coupling model to the investigation of safety limits against derailment due to the track twist and the combined alignment and cross-level irregularities are reported at the end of the paper.

High-speed train-track-bridge dynamic interactions - Part II: experimental validation and engineering application

Experimental validation is a precondition for dynamic simulation of high-speed train–track–bridge interaction system to be applied to railway engineering in the field. The paper first presents an onsite experiment of the train–track–bridge interaction dynamics carried out on the Beijing–Tianjin high-speed railway, and then the experimental results are used to validate the train–track–bridge interaction simulation software (TTBSIM). There is a good correlation between the calculated results and the measured data. As a case study, the Yellow River Bridge in the Beijing–Shanghai high-speed railway is studied, from modelling of the bridge structure to evaluating the dynamic performance of the train–track–bridge interaction system under the CRH3 EMU passing through at speeds of 250–375 km/h. The calculated and measured results are also compared in the case of such a large steel bridge under high-speed moving train, demonstrating the effectiveness of the TTBSIM simulation for dynamic evaluation of complex bridge structures in high-speed railways.

TRAIN/TRACK/BRIDGE DYNAMIC INTERACTIONS: SIMULATION AND APPLICATIONS

SUMMARY This paper describes a numerical simulation technique that is used to investigate the dynamic train/track/bridge interaction. Two dynamic models are established to simulate the dynamic responses of a train running on the bridges with the ballasted track and the non-ballasted slab track, respectively. Effect of the track structure and the wheel/rail interaction on the system dynamics is considered in the models. The influence of track random irregularities on train/track/bridge dynamic interactions is investigated. The proposed simulation technique is applied to practical construction engineering in the Chinese first special railway line for passenger transport. The structural design of three extraordinary large bridges with non-ballasted tracks in this line is evaluated through a detailed simulation in the design stage and results show that these bridges are able to satisfy the demand of dynamic performance for the high-speed transport.

Effect of Locomotive Vibrations on Pantograph-Catenary System Dynamics

Abstract An interactive model is developed to simulate dynamic behavior of pantograph-catenary systems. Vibrating responses of locomotive roof are directly inputted as excitations to the pantograph, which are obtained with the locomotive-track coupling dynamic model. Effect of locomotive vibrations on pantograph-catenary interactions is investigated for various cases. It is shown that the influence of locomotive vibrations upon the pantograph-catenary system dynamics is not negligible if the track geometric condition is not good, especially in high speed operation.

Low-frequency vibration control of floating slab tracks using dynamic vibration absorbers

This study aims to effectively and robustly suppress the low-frequency vibrations of floating slab tracks (FSTs) using dynamic vibration absorbers (DVAs). First, the optimal locations where the DVAs are attached are determined by modal analysis with a finite element model of the FST. Further, by identifying the equivalent mass of the concerned modes, the optimal stiffness and damping coefficient of each DVA are obtained to minimise the resonant vibration amplitudes based on fixed-point theory. Finally, a three-dimensional coupled dynamic model of a metro vehicle and the FST with the DVAs is developed based on the nonlinear Hertzian contact theory and the modified Kalker linear creep theory. The track irregularities are included and generated by means of a time–frequency transformation technique. The effect of the DVAs on the vibration absorption of the FST subjected to the vehicle dynamic loads is evaluated with the help of the insertion loss in one-third octave frequency bands. The sensitivities of the mass ratio of DVAs and the damping ratio of steel-springs under the floating slab are discussed as well, which provided engineers with the DVAs adjustable room for vibration mitigation. The numerical results show that the proposed DVAs could effectively suppress low-frequency vibrations of the FST when tuned correctly and attached properly. The insertion loss due to the attachment of DVAs increases as the mass ratio increases, whereas it decreases with the increase in the damping ratio of steel-springs.

Interface Damage Assessment of Railway Slab Track Based on Reliability Techniques and Vehicle-Track Interactions

AbstractThe interface damage as one of the most critical damage issues in railway slab tracks is evaluated in this work on the basis of reliability techniques and vehicle-track interactions. First, a coupled dynamics model of a vehicle and the slab track is developed involving nonlinear spring-damper elements for simulation of the interface damage. Furthermore, considering the random nature of the damage length, the damage height, the rail pad stiffness, and the elastic modulus of cement asphalt (CA) mortar layer, explicit mathematical expressions between the input stochastic variables and output dynamic responses are obtained on the basis of the combination of the response surface method (RSM) and the dynamic simulations of vehicle-track system. Subsequently, Monte Carlo (MC) simulations are performed for the probability analysis by directly using the response surface functions. Finally, by adopting the amplification factor (AF) of the dynamic response as the control indices, the damage assessment criter...

Development of a Vibration Attenuation Track at Low Frequencies for Urban Rail Transit

Railway-induced vibrations at low frequencies have become an important environmental issue with the rapid development of urban rail transit. In this study, a new vibration attenuation track (VAT) capable of passively mitigating vibrations at low frequencies is developed based on an integrated theoretical and experimental study. The full-scale VAT is built which incorporates a floating slab track (FST) and the attached dynamic vibration absorbers (DVAs) with key parameters determined by the fixed-point theory and modal analysis technique. The vibration attenuation performance of the VAT is investigated under train dynamic loads by establishing a three-dimensional coupled dynamic model of a metro vehicle-VAT-subgrade system, and is further elucidated and validated by carrying out full-scale dynamic tests under different harmonic loadings. Computational and experimental results both show that vibrations of the track are effectively absorbed by the attached DVAs leading to a significant reduction of the subgrade vibrations at the low frequency of 9–16 Hz.

Application of dynamic vibration absorbers in designing a vibration isolation track at low-frequency domain

This paper aims to develop a low-frequency vibration isolation track based on passive vibration isolation theory and vehicle–track interaction analysis. First, a preliminary low-frequency vibration isolation track is proposed by attaching multiple dynamic vibration absorbers to a discontinuous floating slab track, and the optimal design parameters of the multidynamic vibration absorber are determined by searching the minimum values of two assessment functions. Further, a three-dimensional coupled dynamic model of a metro vehicle and the low-frequency vibration isolation track is established by using Ansys Parametric Design Language, where the equations of motion of the vehicle subsystem and the wheel–rail contact calculations are incorporated in the software Ansys using the Ansys Parametric Design Language, and the low-frequency vibration isolation track subsystem is directly created by using common elements in Ansys. The vibration isolation performance of the preliminary low-frequency vibration isolation track with multidynamic vibration absorber is investigated under harmonic load and vehicle dynamic load, respectively. Results show that the slab acceleration and supporting force are significantly reduced at low frequencies of 10–20 Hz compared with those of the traditional floating slab tracks. Finally, an improved low-frequency vibration isolation track is developed for actual manufacturing and practical application, and simulations show that the improved low-frequency vibration isolation track exhibits a more robust vibration isolation performance even if optimal design parameters have variations due to manufacturing errors or material deterioration.