3D Rigid-Flexible Coupling Dynamics Of High-Speed Train/Track System

After nearly 10 years of rapid development, China has built the world's largest high-speed railway network. As a result, how to ensure the running safety and high ride quality of high-speed trains in their long-term service would be a great challenge faced in high-speed railway operation. The running safety and high ride quality of high-speed trains mainly depend on the dynamic behavior of the train-tracks coupling system. Therefore, carrying out a wide and deep research on the high-speed train-track coupling dynamics is a basic condition for the continuous development of China's high-speed railway technology and maintain its leading position.High-speed train-track coupling dynamics research is a very complicated subject, its theoretical modeling and numerical simulation are related to Vehicle Engineering, Mechanics, Mathmatics, and many other disciplines. The current train-track coupling dynamics theory can't simulate and explain many dynamic phenomena and their mechanism faced in the operation of China's high-speed trains, such as the abnormal shaking of the carbody, the high-order polygonal wear of wheels and the fatigue damage of bogie suspension components, etc. Thus, high-speed train-track rigid-flexible coupling dynamics in complex operation environment is an urgent and basic research subject in China's railway research field.This thesis carried out a series of researches on the 3D rigid-flexible coupling dynamics of high-speed train-track system and some typical problems faced in the operation of high-speed trains. The research work includes the following aspects:(1) A detailed review of the studies on train/track coupling modeling methods and dynamic behavior was presented, in which the significance of the current work was cleared. Some problems existing in the high-speed train/track coupling dynamics modeling and their future development orientation were also discussed.(2) A detailed 3D rigid-flexible coupling dynamics model for high-speed train/track system was developed, and a corresponding numerical simulation program was also developed. This model considers four subsystems:train model, track model, wheel/rail rolling contact model, and boundary excitation model of train/track coupling. This model can simulate the rigid-flexible coupling dynamics behavior of high-speed train/track system at constant and variable operational speeds, which make it extend the analysis space of the traditional train/track coupling dynamics, and it also expands the analysis frequency range of the existing train/track coupling dynamics model.(3) A multi-rigid-body train model considering the longitudinal/lateral/vertical coupling behavior and a rigid-flexible coupling train model were respectively developed. In the multi-rigid-body model, each vehicle is simplified as a mass-spring-damping system with 42 degrees of freedom. And in the rigid-flexible coupling model, the car body and the bogie frame are modeling as flexible bodies, the flexible vibration responses of the car body and bogie frame are obtained with the aid of finite element modal analysis technology and modal superposition method. The carbody model considers the modal shapes under 50 Hz, and the bogie frame model includes the modal shapes under 1000 Hz. The train model also takes the time-frequency nonlinear characteristics of the suspension parts into account.(4) A detailed rigid-flexible coupling ballast track model and a flexible slab track model were developed. The ballasted track model is a three layers structure consisting of rails, sleepers, and ballast, while the slab track model is a two layers structure composed of rails and slabs. According to different dynamics research focus, two rail dynamic models were established. One is a finite Timoshenko beam model with discrete sleeper supporters. The other is a finite element model using the spatial beam elements. The vibration responses of the two kinds of rail models were obtained by using the modal superposition method. The sleeper was treated as an Euler beam with free-free boundaries, in which the vertical bending vibration, longitudinal and lateral translation and rolling movement were considered. The slab was modeled by using 3D solid finite elements, and its vibration response was also obtained by using the modal superposition method. The ballast bed was replaced with equivalent discrete mass bodies, only the vertical vibration was considered, the ballast bodies are connected by the shear spring-damping elements. The fastenings and the interconnecting piece between neighboring slabs were modeled as linear spring-damping elements. Uniformly viscoelastic elements were introduced to model the elastic layer beneath the concrete slabs and the ballast bed. The vibration behavior of the roadbed and bridge were neglect.(5) A spatial calculation model of wheel/rail rolling contact was improved, in which the wheel/rail contact points were determined based on the "tracing method" and the "minimum distance method". The normal forces were calculated by using the nonlinear spring model based on Hertzian contact theory. The wheel/rail tangent forces were determined by using Shen's model, and the calculation of wheel/rail creepage considered the effects of the wheel longitudinal vibration and the longitudinal, lateral, vertical and torsional movement.(6) Two new models, named "move rail modes model" and "track length adaptive model" were developed to simulate the dynamic behavior of a train running on an infinite track. In the "moving rail-modes model", two rails were modeled as Timoshenko beams, and their modal shapes were solved in the rail geometric coordinate, which moves along with the moving train coordinate, while the dynamic responses of rails were calculated in the global coordinate, and the calculation length of the track structures beneath the rails were automatic adjustment according to the location of the trains in the global coordinate,In the "track length adaptive model", the rails were modeled by finite element method, the calculation lengths of the track components were coordinated with each other, and they were also automatic adjustment according to the location of trains in the global coordinate.Based on the 3D rigid-flexible coupling dynamics model for high-speed train/track system, the numerical calculation carried out includes three aspects:? A detailed study on the dynamic response characteristics of high-speed train at variable operational speed was firstly carried out, then the wheel skid behavior under traction and low adhesion and the wheel lock behavior under heavy breaking were simulated. And the influence of the traction and breaking forces on the running stability, safety, and ride comfort was analyzed in detail. The dynamic behavior of the track system under the moving train with variable operational speed was also preliminary investigated.? A thorough investigation into the effect of flexible vibration of car body on the ride comfort and running safety of high-speed train was conducted, and the sensitive wavelengths of track irregularities for the ride comfort of high-speed train-were identified by using the rigid-flexible coupling model. A detailed analysis was also carried out on the influence of flexible vibration of bogie frame on its dynamic responses and the running safety and ride comfort of high-speed trains. A preliminary discussion on the correlation between the wheel high-order polygonal wear and the flexible vibration of the bogie frame was presented.? The effects of the modelling options of rail and track structures beneath rails on the high-speed train-track coupling dynamics was analyzed in detail. A comparison of the dynamic behavior between the ballast track and the slab track was conducted, and their differences were cleared. The rigid-flexible coupling model was finally used to analyze the sleeper passing impact and its key influence factors, and the relevant mitigation measures.