Study On Dynamic Response Of D₃₂ Flat Car Rigid-flexible System And Fatigue Strength Of Depressed Center Flat Frame

With the country's rapid economic development and the requirements of rail transport, the applications of long and heavy freight car represented by depressed center flat car are more and more frequent. With the high-speed and light trend demand taken into account, and due to its heavy load and large size, the structural elastic vibration and fatigue problem of long and heavy freight car becomes very prominent. So the rigid-flexible coupling phenomenon emerges and has significant effect on the dynamic response of vehicle system in operation. And violent vibration may emerge to violate clearance, and dynamic stress increases to cause fatigue damage of structure. Based on finite element method and rigid-flexible coupling multi-body dynamics theories, the dynamic response of 320t depressed center flat car system and the fatigue life of its depressed center flat frame in operation have been studied by ANSYS and SIMPACK in this thesis, which provides some meaningful guidances and basis for the design and improvement of the car.The primary work and remarks of the thesis are as follows:1. The kinematic equation of the rigid multi-body system for vehicle has been analyzed. Based on Kane equation the dynamic equation of vehicle system has been set up after all kinds of force elements and constraints were introduced. Hereon, based on d' Alembert law and Jourdain's principle of virtual power, the deformation of elastic body in rigid-flexible coupling vehicle system has been expressed by Rayleigh-Ritz method. And the kinematic and dynamic equations of the elastic body have been set up, which laid a theoretical foundation for obtaining the dynamic response and analyzing the dynamic characteristics of the system. At the same time, the SID-FEM and its calculation of the elastic body in multi-body system procedure have been analyzed in order to realize data exchange between FE and multi-body system procedures.2. The wheel-rail contact relation, the wheel-rail quasi-elastic contact model, and the formula of wheel-rail creeping force have been described. All nonlinear factors have been correctly simulated by piecewise linear method. Also the description way of track random excitation has been discussed. And the track irregularity power spectrum expression has been derived. Simultaneously based on IFFT, the track spectrum has been processed with numerical simulation to obtain its simulation sample in time domain in order to be fit for modeling and dynamically simulating vehicle system. 3. The dynamic equation of depressed center flat frame has been derived. And its dynamic equation on modal coordinates, which can be transformed to physical coordinates, has also been established after superelement introduced. Based on modal analysis theory the needed modal shapes and parameters of the frame could be solved. According to the structural features, position and connection status of the depressed center flat frame, its FE model has been set up, and its inherent dynamic characteristics been calculated. After the FE model of the depressed center flat frame been reduced by substructure method, its elastic model including dynamic characteristics has been established. This method has greatly reduced the total number of DOF of the depressed center flat frame to be fit for correctly and effectively analyzing the vibration response of vehicle system. By studying the effect of modal number selection of elastic body on the dynamic response of the vehicle system, the modal number should be selected enough, which the number was the former eight orders in this thesis.4. The multi-body system dynamic models (including rigid multi-body system dynamic and rigid-flexible coupling multi-body system dynamic model) of 320t depressed center flat car have been set up to simulate to obtain their dynamic responses. Then the results have been comprehensively compared with the experimental data to show that the rigid-flexible coupling model was more reasonable. Also the effect of sampling frequency in simulation on the dynamic response of the vehicle system has been studied.5. The effects of running speed and suspension parameter of axlebox on the dynamic response of vehicle system, especially the elastic vibration of depressed center flat frame, have been studied in depth to obtain some useful conclusions based on 320t depressed center flat car rigid-flexible coupling multi-body system dynamic model, which provides the basis for selecting suspension parameter, determining running speed, evaluating dynamic clearance and improving design.6. The load history applied on depressed center flat frame, which obtained in simulation based on 320t depressed center flat car rigid-flexible coupling multi-body system dynamic model, has been transformed into ANSYS . Then the dynamic stress history and stress spectrum on concerned position of its depressed center flat frame has been calculated after analyzing. Thereafter the fatigue life prediction model has been set up. And by the fatigue cumulative damage theory the fatigue life of the frame has been predicted. At the same time the effects of running speed, suspension stiffness and damping of axle box have been studied.