Dynamics of high-speed train in crosswinds based on an air-train-track interaction model

Wanming Zhai,Jizhong Yang,Zhen Li,Haiyan Han 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.2

A numerical model for analyzing airtraintrack interaction is proposed to investigate thedynamic behavior of a high-speed train running on a track in crosswinds. The model is composed of atraintrack interaction model and a trainair interaction model. The traintrack interaction model is built onthe basis of the vehicletrack coupled dynamics theory. The trainair interaction model is developed basedon the train aerodynamics, in which the Arbitrary LagrangianEulerian (ALE) method is employed to dealwith the dynamic boundary between the train and the air. Based on the airtraintrack model, characteristicsof flow structure around a high-speed train are described and the dynamic behavior of the high-speed trainrunning on track in crosswinds is investigated. Results show that the dynamic indices of the head car arelarger than those of other cars in crosswinds. From the viewpoint of dynamic safety evaluation, the runningsafety of the train in crosswinds is basically controlled by the head car. Compared with the generally usedassessment indices of running safety such as the derailment coefficient and the wheel-load reduction ratio,the overturning coefficient will overestimate the running safety of a train on a track under crosswindcondition. It is suggested to use the wheel-load reduction ratio and the lateral wheelrail force as thedominant safety assessment indices when high-speed trains run in crosswinds.

Dynamics of high-speed train in crosswinds based on an air-train-track interaction model

Zhai, Wanming,Yang, Jizhong,Li, Zhen,Han, Haiyan Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.2

A numerical model for analyzing air-train-track interaction is proposed to investigate the dynamic behavior of a high-speed train running on a track in crosswinds. The model is composed of a train-track interaction model and a train-air interaction model. The train-track interaction model is built on the basis of the vehicle-track coupled dynamics theory. The train-air interaction model is developed based on the train aerodynamics, in which the Arbitrary Lagrangian-Eulerian (ALE) method is employed to deal with the dynamic boundary between the train and the air. Based on the air-train-track model, characteristics of flow structure around a high-speed train are described and the dynamic behavior of the high-speed train running on track in crosswinds is investigated. Results show that the dynamic indices of the head car are larger than those of other cars in crosswinds. From the viewpoint of dynamic safety evaluation, the running safety of the train in crosswinds is basically controlled by the head car. Compared with the generally used assessment indices of running safety such as the derailment coefficient and the wheel-load reduction ratio, the overturning coefficient will overestimate the running safety of a train on a track under crosswind condition. It is suggested to use the wheel-load reduction ratio and the lateral wheel-rail force as the dominant safety assessment indices when high-speed trains run in crosswinds.

A mechanical model of vehicle-slab track coupled system with differential subgrade settlement

Guo, Yu,Zhai, Wanming,Sun, Yu Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.1

Post-construction subgrade settlement especially differential settlement, has become a key issue in construction and operation of non-ballasted track on high-speed railway soil subgrade, which may also affect the dynamic performance of passing trains. To estimate the effect of differential subgrade settlement on the mechanical behaviors of the vehicle-slab track system, a detailed model considering nonlinear subgrade support and initial track state due to track self-weight is developed. Accordingly, analysis aiming at a typical high-speed vehicle coupled with a deteriorated slab track owing to differential subgrade settlement is carried out, in terms of two aspects: (i) determination of an initial mapping relationship between subgrade settlement and track deflections as well as contact state between track and subgrade based on a semi-analytical method; (ii) simulation of dynamic performance of the coupled system by employing a time integration approach. The investigation indicates that subgrade settlement results in additional track irregularity, and locally, the contact between the concrete track and the soil subgrade is prone to failure. Moreover, wheel-rail interaction is significantly exacerbated by the track degradation and abnormal responses occur as a result of the unsupported areas. Distributions of interlaminar contact forces in track system vary dramatically due to the combined effect of track deterioration and dynamic load. These may not only intensify the dynamic responses of the coupled system, but also have impacts on the long-term behavior of the track components.

A mechanical model of vehicle-slab track coupled system with differential subgrade settlement

Yu Guo,Wanming Zhai,Yu Sun 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.1

Post-construction subgrade settlement especially differential settlement, has become a key issue in construction and operation of non-ballasted track on high-speed railway soil subgrade, which may also affect the dynamic performance of passing trains. To estimate the effect of differential subgrade settlement on the mechanical behaviors of the vehicle-slab track system, a detailed model considering nonlinear subgrade support and initial track state due to track self-weight is developed. Accordingly, analysis aiming at a typical high-speed vehicle coupled with a deteriorated slab track owing to differential subgrade settlement is carried out, in terms of two aspects: (i) determination of an initial mapping relationship between subgrade settlement and track deflections as well as contact state between track and subgrade based on a semi-analytical method; (ii) simulation of dynamic performance of the coupled system by employing a time integration approach. The investigation indicates that subgrade settlement results in additional track irregularity, and locally, the contact between the concrete track and the soil subgrade is prone to failure. Moreover, wheel-rail interaction is significantly exacerbated by the track degradation and abnormal responses occur as a result of the unsupported areas. Distributions of interlaminar contact forces in track system vary dramatically due to the combined effect of track deterioration and dynamic load. These may not only intensify the dynamic responses of the coupled system, but also have impacts on the long-term behavior of the track components.

Effect of noise barrier on aerodynamic performance of high-speed train in crosswind

Zhao, Hai,Zhai, Wanming,Chen, Zaigang Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.4

A three-dimensional aerodynamic model and a vehicle dynamics model are established to investigate the effect of noise barrier on the dynamic performance of a high-speed train running on an embankment in crosswind in this paper. Based on the developed model, flow structures around the train with and without noise barrier are compared. Effect of the noise barrier height on the train dynamic performance is studied. Then, comparisons between the dynamic performance indexes of the train running on the windward track and on the leeward track are made. The calculated results show that the noise barrier has significant effects on the structure of the flow field around the train in crosswind and thus on the dynamic performance of the high-speed train. The dynamic performance of the train on the windward track is better than that on the leeward track. In addition, various heights of the noise barrier will have different effects on the train dynamic performance. The dynamic performance indexes keep decreasing with the increase of the noise barrier height before the height reaches a certain value, while these indexes have an inverse trend when the height is above this value. These results suggest that optimization on the noise barrier height is possible and demonstrate that the designed noise barrier height of the existing China Railway High-speed line analysed in this article is reasonable from the view point of the flow field structure and train dynamic performance although the noise barrier is always designed based on the noise-related standard.

Effect of noise barrier on aerodynamic performance of high-speed train in crosswind

Hai Zhao,Wanming Zhai,Zaigang Chen 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.4

A three-dimensional aerodynamic model and a vehicle dynamics model are established toinvestigate the effect of noise barrier on the dynamic performance of a high-speed train running on anembankment in crosswind in this paper. Based on the developed model, flow structures around the train withand without noise barrier are compared. Effect of the noise barrier height on the train dynamic performanceis studied. Then, comparisons between the dynamic performance indexes of the train running on thewindward track and on the leeward track are made. The calculated results show that the noise barrier hassignificant effects on the structure of the flow field around the train in crosswind and thus on the dynamicperformance of the high-speed train. The dynamic performance of the train on the windward track is betterthan that on the leeward track. In addition, various heights of the noise barrier will have different effects onthe train dynamic performance. The dynamic performance indexes keep decreasing with the increase of thenoise barrier height before the height reaches a certain value, while these indexes have an inverse trend whenthe height is above this value. These results suggest that optimization on the noise barrier height is possibleand demonstrate that the designed noise barrier height of the existing China Railway High-speed lineanalysed in this article is reasonable from the view point of the flow field structure and train dynamicperformance although the noise barrier is always designed based on the noise-related standard.

On effects of rail fastener failure on vehicle/track interactions

Lei Xu,Jianmin Gao,Wanming Zhai 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.5

Rail support failure is inevitably subjected to track geometric deformations. Due to the randomness and evolvements of track irregularities, it is naturally a hard work to grasp the trajectories of dynamic responses of railway systems. This work studies the influence of rail fastener failure on dynamic behaviours of wheel/rail interactions and the railway tracks by jointly considering the effects of track random irregularities. The failure of rail fastener is simulated by setting the stiffness and damping of rail fasteners to be zeroes in the compiled vehicle-track coupled model. While track random irregularities will be transformed from the PSD functions using a developed probabilistic method. The novelty of this work lays on providing a method to completely reveal the possible responses of railway systems under jointly excitation of track random irregularities and rail support failure. The numerical results show that rail fastener failure has a great influence on both the wheel/rail interactions and the track vibrations if the number of rail fastener failure is over three. Besides, the full views of time-dependent amplitudes and probabilities of dynamic indices can be clearly presented against different failing status.

On effects of rail fastener failure on vehicle/track interactions

Xu, Lei,Gao, Jianmin,Zhai, Wanming Techno-Press 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.5

Rail support failure is inevitably subjected to track geometric deformations. Due to the randomness and evolvements of track irregularities, it is naturally a hard work to grasp the trajectories of dynamic responses of railway systems. This work studies the influence of rail fastener failure on dynamic behaviours of wheel/rail interactions and the railway tracks by jointly considering the effects of track random irregularities. The failure of rail fastener is simulated by setting the stiffness and damping of rail fasteners to be zeroes in the compiled vehicle-track coupled model. While track random irregularities will be transformed from the PSD functions using a developed probabilistic method. The novelty of this work lays on providing a method to completely reveal the possible responses of railway systems under jointly excitation of track random irregularities and rail support failure. The numerical results show that rail fastener failure has a great influence on both the wheel/rail interactions and the track vibrations if the number of rail fastener failure is over three. Besides, the full views of time-dependent amplitudes and probabilities of dynamic indices can be clearly presented against different failing status.