Study On Dynamic Effects Of Flexible Bogie Frames On Vehicle System Dynamics For High Speed Train

Due to the lightweighting design of load-bearing structure and higher running speed,dynamic behavior of vehicle system caused by the vibration of load-bearing structure becomes one of the focuses to which more and more scholars pay attention. High frequency vibration excited by track spectrum between wheel and rail has weak effects on vehicle system while the train running in a high speed, however the vibration frequency of each structure can stay in a reasonable range through the ability of reducing vibration and absorbing energy of the suspension systems, especially the bogie frame which transmit and impair vibration, plays a significant role in two kinds of suspension device. So it is necessary that the elastic characteristic of bogie frame is considered while calculating the dynamic response of vehicle. The studies on considering the elastic characteristic of frame have important theoretical values and engineering application value for ensuring the safety,improving the ride comfort and the calculation of fatigue life.Firstly, a dynamic model of rigid-flexible coupled vehicle system and a dynamic model of multi-rigid-body vehicle system with 50 DOF are established with the multi-body dynamics software SIMPACK. The finite element model of bogie frame that has been simplified in structure is built and a flexible bogie frame model is established by the means of substructure analysis and component modal synthesis analysis, based on Lanzos method and Guyan method; then, a dynamic model of rigid-flexible coupled vehicle system, in which the flexibility of frame is considered, is built based on multibody system dynamics theory.Then, the developed dynamic model of rigid-flexible coupled vehicle system is used to calculate the dynamic responses of bogie frame with the wheel/rail forces excited by the German high speed low disturbance spectrum while the train is running at the different velocities and working conditions. Furtherly, the elastic vehicle critical speed, the vehicle running stability index, the reduction rate of wheel load and the derailment coefficient are deduced, compared with the results simulated by the multi-body vehicle system dynamics, so the conclusions are: when running at the same velocity, the vertical/lateral vibration acceleration in the end of side frame is obviously lager than that in the center of mass of frame. The model vibration accelerations of frame are mainly in the low frequency range of less than 100 Hz. the modal vibration that has large acceleration amplitude in the end of side frame happens when the vehicle is running at a relative small velocity like 100km/h, however the lateral modal vibration in the center of mass of frame hardly occurrs even under 350km/h of vehicle speed, so the external excitation has very little effect on the lateral modal vibration of that position. Considering the flexibility characteristic in the vehicle system model has hardly any influence on the vehicle running stability and ride comfort, has a little effect on thecurve negotiation performance. The reduction rate of wheel load of the leading wheelsets in the rigid vehicle system dynamic model is smaller than that in the rigid vehicle system dynamic model, and the trend of this performance in the second wheelsets is exactly opposite to the leading wheelsets. The derailment coefficient of the leading/second wheelsets is larger than that in the rigid-flexible coupled vehicle system dynamic model, compared with that in the rigid vehicle system dynamic model.Finally, original torsional stiffness and flexural stiffness of frame are calculated by using the static method, the physical properties of materials are modified to obtained the frame models that have the different distortion stiffness characteristic and flexural stiffness characteristic, and the effect whose two kinds of stiffness are given to the vehicle system dynamic behavior is researched. The result shows that, the flexural rigidity has hardly any influence on the running stability, and very little effect on the ride comfort, and the distribution of wheel/rail force in the same bogie becomes more and more asymmetrical with the flexural rigidity decreasing, which leads to the decreasing of the running safety on the warping line. The torsional stiffness has no influence on both running and ride comfort, As the torsional stiffness decreases, the vertical wheel/rail force is approaching to well-distribution, which improves the curve negotiation performance to a certain extent. so the bogie frame that has a relative high flexural stiffness and a relative small torsional stiffness is beneficial to improve the curve negotiation performance.