Xinbiao Xiao

Effect of curved track support failure on vehicle derailment

In order to investigate the effect of curved track support failure on railway vehicle derailment, a coupled vehicle–track dynamic model is put forward. In the model, the vehicle and the structure under rails are, respectively, modelled as a multi-body system, and the rail is modelled with a Timoshenko beam rested on the discrete sleepers. The lateral, vertical, and torsional deformations of the beam are taken into account. The model also considers the effect of the discrete support by sleepers on the coupling dynamics of the vehicle and track. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the calculation of the coupled vehicle and track dynamics, the normal forces of the wheels/rails are calculated using the Hertzian contact theory and their creep forces are determined with the nonlinear creep theory by Shen et al [Z.Y. Shen, J.K. Hedrick, and J.A. Elkins, A comparison of alternative creep-force models for rail vehicle dynamic analysis, Proceedings of the 8th IAVSD Symposium, Cambridge, MA, 1984, pp. 591–605]. The motion equations of the vehicle/track are solved by means of an explicit integration method. The failure of the components of the curved track is simulated by changing the track stiffness and damping along the track. The cases where zero to six supports of the curved rails fail are considered. The transient derailment coefficients are calculated. They are, respectively, the ratio of the wheel/rail lateral force to the vertical force and the wheel load reduction. The contact points of the wheels/rails are in detail analysed and used to evaluate the risk of the vehicle derailment. Also, the present work investigates the effect of friction coefficient, axle load and vehicle speed on the derailments under the condition of track failure. The numerical results obtained indicate that the failure of track supports has a great influence on the whole vehicle running safety.

Effect of Disabled Fastening Systems and Ballast on Vehicle Derailment

The effect of disabled fastening systems and ballast on railway vehicle derailment is investigated by developing a nonsymmetrical coupled vehicle/track model. In the model a half passenger car is considered, and modeled with a multi-body system with 18 degrees of freedom, which runs on a tangent track at a constant speed. The tangent track is modeled as two elastic beams by discrete nonsymmetrical supporters modeling fastening systems, sleepers, and ballasts. The normal contact forces between wheels and rails are described by Hertzian elastic contact theory, and the tangential forces by the nonlinear creep theory of Shen et al. (Proceedings of the 8th IAVSD Symposium, Cambridge, MA, pp. 591-605). In the numerical analysis, the disabled rail fastening, rail pad, and ballast, on one and two sides of the track are, respectively, considered. Through a detailed analysis, derailment coefficients and the track state variations are obtained. The derailment coefficients are defined as the ratio of the lateral force to the vertical force of the wheel and rail (indicated by L/V), duration of L/V, and rate of the wheel load reduction (indicated by AVIV), respectively. The variations of the contact points on the wheel treads, the track gauge, the track cross-level, and rail turnover angle are present in the paper. The numerical results obtained indicate that the failure of rail supports has a great influence on the vehicle running safety.

Study on safety boundary for high-speed train running in severe environments

This article reviews some important published papers regarding the discussions on the mechanism and the modelling of trains operating in severe environments which are originally defined. A few important derailment criteria are briefly discussed. A study strategy of the safety operation boundaries of high-speed trains operating in the severe environments is first put forward. In the strategy, the safety operation boundaries are defined as a number of separatrices which clearly indicate the safety operation area, warning area and derailment occurring area of a high-speed vehicle in operation. The defined separatrices are the limit surface functions of the key factors influencing the vehicle dynamic behaviour and its derailment. They are found through numerical simulation by using an advanced dynamics model for vehicle/track interaction and the derailment criteria. In order to fully understand the present strategy, a detailed numerical example of a high-speed vehicle passing over a buckled track is discussed. The given results clearly indicate the effects of the key factors on the wheel/rail normal forces, the derailment criteria limits and the vehicle derailment boundary.

A study of the derailment mechanism of a high speed train due to an earthquake

In order to investigate the mechanism of derailment of high-speed trains due to an earthquake, a coupled vehicle/track dynamic model considering the earthquake effect is developed. The vehicle is modelled as a multi-body system of 35 degrees of freedom and the nonlinear suspension characteristic is considered. The slab track model considers the deformable rails, the discrete support of fasteners and the deformable slabs. Rails are assumed to be Timoshenko beams supported by the rail fasteners discretely, and the slabs are modelled with solid finite elements. The coupling of the vehicle and the track considers the track moving with respect to the vehicle running at a constant speed, and such a coupling model can simulate the effect of the periodical discrete rail supports on the vehicle/track interaction. The least-square curve fitting (LSCF) approach is introduced to integrate the originally recorded earthquake acceleration to acquire the velocity and displacement-time series of the earthquake. The system motion equations are solved by means of an explicit integration method in the time domain. The present paper analyses in detail the effect of the earthquake characteristic on dynamical behaviour of the vehicle and the track and the transient derailment criteria. The considered derailment criteria include the ratio of the wheel/rail lateral force to the vertical force, the wheel loading reduction, and the wheel/rail contact point traces on the wheel tread and the wheel rise with respect to the rail top, respectively. The present investigation includes the effect of lateral earthquake motion, vertical earthquake motion, operation speed, and their combined effect on the existing derailment criteria, respectively.

Experimental and numerical investigation of the effect of rail corrugation on the behaviour of rail fastenings

This paper presents the results of a detailed investigation of the effects of rail corrugation on the dynamic behaviour of metro rail fastenings, obtained from extensive experiments conducted on site and from simulations of train–track dynamics. The results of tests conducted with a metro train operating on corrugated tracks are presented and discussed first. A three-dimensional (3D) model of the metro train and a slab track was developed using multi-body dynamics modelling and the finite element method to simulate the effect of rail corrugation on the dynamic behaviour of rail fastenings. In the model, the metro train is modelled as a multi-rigid body system, and the slab track is modelled as a discrete elastic support system consisting of two Timoshenko beams for the rails, a 3D solid finite element (FE) model for the slabs, periodic discrete viscoelastic elements for the rail fastenings that connect the rails to the slabs, and uniformly viscoelastic elements for the subgrade beneath the slabs. The proposed train–track model was used to investigate the effects of rail corrugation on the dynamic behaviour of the metro track system and fastenings. An FE model for the rail fastenings was also developed and was used to calculate the stresses in the clips, some of which rupture under the excitation of rail corrugation. The results of the field experiments and dynamics simulations provide an insight into the root causes of the fracture of the clips, and several remedies are suggested for mitigating strong vibrations and failure of metro rail fastening systems.

Dynamic behavior of an embedded rail track coupled with a tram vehicle

This paper presents an investigation into the dynamic behavior of an embedded rail track coupled with a tram vehicle in time domain. A new designed embedded rail track structure firstly introduced into the Chinese tramways is described and the results of vibration tests of the embedded rail track (ERT) and another fastened slab track (FST) are discussed. A three-dimensional (3D) dynamic model of a tram vehicle coupled with an embedded rail track was developed on the basis of the multi-body dynamics approach and the finite element method. In the model, the tram vehicle was modeled as a multi-body system. The embedded rail track was modeled as a two layer system consisting of two rails, filling material, slabs, and adjustment layer beneath slabs. The rails were treated as Timoshenko beams with continuous elastic supports, in which the modal superposition method was used to reduce the order of the partial differential equations of beams. Continuous viscoelastic elements were used to represent the filling material and rail pad that connecting the rails and the slabs. The concrete slabs were modelled using the 3D finite element method, while the modal superposition method was adopted to improve the computational efficiency. Uniformly viscoelastic elements were introduced to model the elastic layer beneath the concrete slabs. The proposed model was then applied to compare the dynamic response of the innovative embedded rail track with respect to a conventional fastened slab track. The numerical results indicate that the innovative embedded rail track has advantages over the fastened slab track for its potentialities to reduce the dynamic wheel/rail force, the vibration level and deformation of the track parts, and the track defects and damages.

Effects of Track Support Failures on Dynamic Response of High Speed Tracks

A model is proposed in this paper for investigating the effect of track support failures on the dynamic response of high speed tracks. In this model, the rails are modeled as two Timoshenko beams resting on discrete sleepers and interacting with a moving vehicle. The lateral, vertical and torsional deformations of the beams are all taken into account. Support failures are realized by changing the support stiffness and damping. To simulate the traveling of the vehicle along the track, the discrete supports to the rails are assumed to move backward at the train speed. Normal wheel/rail contact forces are calculated using the Hertzian contact theory and tangential (creep) wheel/rail forces are determined using Shen et al.s nonlinear creep theory. Differential equations of the vehicle/track system are solved by means of an explicit integration method. Effects of zero to six failed supports are simulated. Numerical results indicate that track support failures greatly affect the dynamic response of a tangent track. As the number of disabled supports increases, the normal wheel/rail forces, track displacement and track acceleration increase quickly, accelerating deterioration of the track.

Study on Abnormal Interior Noise of High-Speed Trains

Field experiments were carried out to investigate abnormal interior noise generation in a coach used as a dining car of a high-speed train, including field measurements to investigate the interior noise conditions of another passenger coach under the same operating conditions. Sound quality indexes at each interior noise measuring point were analyzed to determine the characteristics of the abnormal interior noise. The differences of vibration and noise in the two coaches were then compared to show the effect of the interior structure of the coach on the abnormal interior noise. In addition, the differences of vibration and noise in the dining coach before and after the wheel re-profiling were compared to examine the effect of the wheel roughness on the abnormal interior noise. The present work has identified mechanisms of abnormal interior noise generation in the dining car.

Experimental study on vibration and sound radiation reduction of the web-mounted noise shielding and vibration damping wheel

A railway wheel installed with the web-mounted noise shielding and vibration damping assemblies is introduced in this paper. The shielding and damping assemble is alternant constrained to the both ends connecting to the tyre and hub. This design can produce shear strain in periodical variation, and then vibration energy of the shielding plate and the wheel is dissipated effectively. Assembles can also reduce the noise radiation from the wheel web. In order to investigate the vibration and sound radiation reduction of this new type of wheel relevant tests are carried out in a semi-anechoic room. In the test, damping ratio, acceleration, sound energy, sound field and directivity of the damping wheel are given and analyzed. The same tests are conducted for a standard wheel as a comparison. The test results show that the damping ratio of the damping wheel increases significantly compared to the standard one, especially for the damping ratios at the prominent resonance frequencies. The increase of the damping ratio is as much as 44 times. The sound energy levels (SEL) of the damping wheel in the overall range and at a dominant resonance frequency are, respectively, 15 and 40 dB, much less than those of the standard one. By comparing the sound fields and directivities of the two wheels, the sound radiation of the damping wheel is lower in all directions.

The Effect of First-Order Bending Resonance of Wheelset at High Speed on Wheel-Rail Contact Behavior:

The first-order bending deformation of wheelset is considered in the modeling vehicle/track coupling dynamic system to investigate its effect on wheel/rail contact behavior. In considering the effect of the first-order bending resonance on the rolling contact of wheel/rail, a new wheel/rail contact model is derived in detail in the modeling vehicle/track coupling dynamic system, in which the many intermediate coordinate systems and complex coordinate system transformations are used. The bending mode shape and its corresponding frequency of the wheelset are obtained through the modal analysis by using commercial software ANSYS. The modal superposition method is used to solve the differential equations of wheelset motion considering its flexible deformation due to the first-order bending resonance. In order to verify the present model and clarify the influence of the first-order bending deformation of wheelset on wheel/track contact behavior, a harmonic track irregularity with a fixed wavelength and a white-noise roughness are, respectively used as the excitations in the two models of vehicle-rail coupling dynamic system, one considers the effect of wheelset bending deformation, and the other does not. The numerical results indicate that the wheelset first-order bending deformation has an influence on wheel/rail rolling contact behavior and is easily excited under wheel/rail roughness excitation.