Evaluation Method Study And Theory Analysis Of Lateral Running Stability And Dynamic Derailment Of High Speed Train

The lateral running stability and derailment of railway vehicle have always been the difficulties and hot research topics. In recent years, the rapid development of the world’s high-speed railway has brought huge economic benefits to the people’s livelihood, and also put forward new challenges and higher requirements of vehicle dynamics theory. Especially with the increasing of speed, the nonlinear characteristics of the wheel-rail contact geometry and creep force/creepage is more obvious at high speed than at the low speed condition, so the lateral running stability and derailment of high speed train needed to be studied deeply. On the one hand, the current on-line monitoring criterion of high speed vehicle lateral running stability is not completely the same at home and abroad. Due to the different vehicle design idea, structural characteristics and line conditions, the foreign evaluation criteria is not always suitable for evaluate the dynamic performance of high speed vehicle in China, therefor a reasonable evaluation criterion for high speed vehicle lateral running stability is desiderate to establish. On the other hand, the evaluation index of derailment coefficient and wheel unloading rate currently used in China have shown their limitations, and how to better evaluate the derailment of high speed train has not yet formed a clear and comprehensive understanding, so the high-speed train derailment mechanism is desiderate to be studied deeply and a more reasonable derailment assessment method is needed to be proposed.In view of this, in this paper, aiming at solving the lateral running stability and derailment problems of high speed train, by making wheel-rail interaction as the core content, combining the theoretical analysis and engineering applications, the key influence factors of lateral running stability of high-speed train, the high-speed trains lateral running stability evaluation method, the high-speed train derailment dynamic process and key factors, high-speed train derailment dynamic evaluation methods are deeply studied. The research works carried out and the innovative achievements made are summarized as follows:(1) Based on the characteristics of hunting instability and dynamic derailment of high speed train, the three-dimensional wheel-rail geometric contact model which is suitable for arbitrary wheel/rail profiles is established. The three-dimensional wheel-rail geometric contact numerical calculations algorithm is designed which can realize fast online solution, then the normal contact force, creep forces and creep torque in both the single point and multi-point contact situation are modeled. Verification and analysis show that the three-dimensional wheel-rail geometric contact model can accurately simulate the jump characteristics of the contact points when both the tread and flange contact with the rail, and it is suitable for analyzing running stability and dynamic derailment of high speed train, which can realize real-time online calculation of wheel-rail contact points, so it is convenience to achieve cooperative solving with kinetics equation.(2) By combining the three-dimensional wheel-rail geometric contact model, wheel-rail nonlinear contact force model and the vehicle dynamics equations, a nonlinear dynamic model which is more suitable for the analysis of dynamic performance of the high speed vehicle is established, and the corresponding computer calculation program is programed. By comparing with Adams/rail software calculation results, it is proved that the high-speed vehicle dynamic model built in this paper can effectively simulate the lateral stability of the vehicle when it running on straight track, it can accurately calculate the lateral displacement of the wheelset and non-linear characteristic of the wheel-rail contact force. Compared with Adams/rail commercial software, the vehicle dynamics numerical calculation method designed in this paper not only guarantee calculation precision, but also cost less computation time, and the controllability of the calculation process is improved. Moreover, it has advantages of capturing the dynamic response features in detail in the whole derailment process and analyzing the influence of angle of attack on the derailment. By comparing with the test data, it is proved that the vehicle nonlinear dynamic model built in this paper can well reflect the dynamic performance of the bogie in the time and frequency domain which change with speed.(3) Based on the high-speed vehicle nonlinear dynamic model built in this paper, the bifurcation characteristics of high speed vehicle hunting motion and its numerical analysis method is investigated. Aiming at studying on the key factors of high-speed train, the reasonable matching between wheel/rail nonlinear geometry parameters and high speed vehicle suspension parameters is investigated. How the wheel/rail and suspension nonlinear characteristics affect the critical speed and hunting limit cycles is investigated. The value ranges of primary longitudinal stiffness, stiffness and damping of yaw damper are given which can match well with the wheel/rail nonlinear geometry parameters. The results show that:the lateral running stability of the high-speed train is very sensitive to the wheel-rail contact geometry nonlinear characteristics. For different wheel-rail geometry matching case, the nonlinear characteristics of wheelset equivalent conicity is different, which will result in different critical speed of high-speed train and limit cycle bifurcation diagrams. The best value range of primary longitudinal stiffness of high-speed vehicle and wheel-rail profile matching is closely related. For the low wheelset equivalent conicity case when LMA wheel matching with CHN60rail, the hunting critical speed of high-speed train will increase when the value of primary longitudinal stiffness of high-speed vehicle is relatively low. But as for the high wheelset equivalent conicity case when S1002wheel matching with UIC60rail, the high-speed vehicle will have high lateral stability when the value of longitudinal positioning stiffness is large.(4) By combining the theory analysis and on-line monitoring of high-speed vehicle lateral running stability, applying computer simulation technology and comparing with the experimental data, three current methods to evaluate the stability of high speed trains are investigated, that is the linear stability analysis method, the nonlinear stability analysis method and the field testing criterion. The results show that:when the high speed vehicle system demonstrating a subcritical Hopf bifurcation, the vehicle vibration amplitude will significantly increase once the vehicle becomes unstable, in this case, there is a little difference between the nonlinear critical speed which is evaluated by the nonlinear stability theory analysis method and the hunting critical speed evaluated by the bogie lateral acceleration peak value(which is8m/s2) standard. However, when the high speed vehicle system demonstrating a supercritical Hopf bifurcation, the vehicle vibration amplitude will not suddenly become large once the vehicle becomes unstable, so the nonlinear critical speed evaluated by the nonlinear stability theory analysis method is much smaller than the hunting critical speed evaluated by the bogie lateral acceleration peak value(which is8m/s2) standard, in this case, bogie lateral acceleration peak value monitoring method is not suitable for early detection and early warning of high-speed trains instability.In order to solve the problem which the bogie lateral acceleration peak value monitoring method can’t effectively monitor the bogie small amplitude unstable oscillation in the case of a high speed vehicle system demonstrating a supercritical Hopf bifurcation, by combining the theoretical analysis with online monitoring method, a new method is first put forward for the lateral stability evaluation of high speed train based on the frequency distribution characteristics of bogie vibration energy, and the proposed method is verified to be valid with CRH3high-speed train examples. The results show that: the proposed method can well evaluate the lateral stability of high-speed train for two wheel-rail matching groups, which also can achieve the monitor role of the bogie small amplitude unstable oscillation for the supercritical bifurcation condition. (5) The determination method of the vehicle derailment critical state is established, the nonlinear characteristics of wheelset motion gesture and wheel/rail contact force in the derailment process for high speed trains is investigated. The results show that:the critical moment during the derailment process is the moment when the wheel-rail contact point near the position of maximum flange contact angle, when the wheel flange contact with the rail, the wheel vertical rise, the wheel-rail contact angle, wheel-rail contact force, wheelset lateral velocity and so on will increased sharply, and wheelset lateral movement limit cycle will appear "ears" shape back folding. The rail play the role of hindering the wheel flange climb on to it, if the wheel flange can completely break through the obstacle and cross the maximum flange contact angle, the derailment will occur under the effect of larger inertial force.The wheel jumping derailment model is established which is used to analysis the derailment behavior when the high-speed wheel impact with the rail and study on the key influence factors of wheel jumping derailment. The results show that:the main factors affecting the behavior of high-speed wheel derailment including the wheel lateral velocity, wheel-rail friction coefficient and wheel vertical load. The smaller the wheel-rail friction coefficient and the wheel vertical load, the greater the wheel jumping height, the more easily jumping derailment occurs.From the perspective of the nonlinear dynamics, the key factors which will greatly affect the dynamic derailment of high speed trains are studied. The results showed that:when the other parameters keep constant, the more severe the tread wear and the greater the distance between backs of wheel flanges, the more early the wheel flange will contact with the rail, the vehicle will more easily derailed for the same wheelset lateral displacement condition. As the angle of attack increases, the wheel-rail longitudinal creep force will reduce while the lateral creep force increase, the bigger the proportion of lateral creep force to the whole creep forces, the more likely vehicle derailment occur.The dynamic derailment mechanism is explained from the aspects of dynamic performance during derailment and mechanical mechanism and so on. The results show that:the essential reason of high-speed train derailment is because the high-speed vehicle system loses stability, the prerequisite of derailment is that the wheelset lateral displacement increase and exceed the wheel rail clearance, the mechanical mechanism of derailment is that the system damping cannot effectively weakening the wheelset lateral vibration and the wheel flange completely break through the obstacle of rail, so the derailment occur. The most unfavorable condition which will easily lead to derailment is that all the wheelset lateral displacement, wheel-rail lateral creep force and angle of attack are large.(6) The problems and reasons of the derailment coefficient indicator has limitations in evaluate the high speed train derailment are studied, the relationship between the main dynamic indexes and the wheel vertical rise is analyzed during the high-speed train derailment process. The results show that:the greater the inertia force and the kinetic energy of wheelset lateral vibration, the larger the energy of the vehicle lateral self-excited vibration, the greater the likelihood of derailment. Both the wheelset lateral velocity which reflecting the value of wheelset lateral vibration energy and the wheelset lateral acceleration which reflecting the value of wheelset inertia force can be chosen as the index which can reflect the value of wheel vertical rise.In order to solve the problems of which the derailment coefficient indicator has limitations in evaluate the high speed train derailment, a new comprehensive method for the evaluation of dynamic derailment for high speed train is first put forward which based on the RMS value of wheelset lateral acceleration, bogie lateral acceleration and derailment coefficient, the RMS limit value of wheelset lateral acceleration which is equal to1.50g is found by simulation methods under the condition for which the derailment does not occur. The proposed method is verified to be valid with high-speed train examples for two wheel-rail matching groups, the numerical simulation result shows that the RMS value of wheelset lateral acceleration and the value of wheel vertical rise show the same change law in time domain. The new method can reduce the misjudgment rate compared with the single derailment coefficient evaluation method, which can monitor the derailment more accurately for high speed trains and easy to implement engineering applications.