Hopf Bifurcation Characteristics Of The Cooperrider Bogie

Railway vehicles run along a straight line. The lateral stability of the system will change essentially when the running speed is improved. When the speed increases to a critical value, there will be a stable lateral vibration of the vehicle and then the hunting motion will appear. Therefore, the running quality of vehicles will descend. Moreover, it can cause serious wheel/rail wear and even major accidents as derailment. Compared to the bogies of railway passenger cars, the bogies of railway freight cars have strong nonlinear suspension characteristics. In order to prevent hunting instability, running speed of the vehicle must be below the critical speed. Suspension parameter should be chosen correctly to increase critical speed. Hence, it is necessary to study the nonlinear flutter of railway freight car system.The Cooperrider Bogie is considered as research object, the Hopf bifurcation nonlinear dynamics of the system is studied in this thesis. The effect of active and semi-active control on the response of the system is discussed. Specific works are as follows:1) The model of Cooperrider Bogie with7degrees of freedom which runs along a straight line is built. Based on the stability theory and Hopf bifurcation theory, hunting instability of the Bogie is studied. The nonlinear critical speed, linear critical speed and the amplitude of hunting flutter is determined.2) The secondary suspension torsional spring of Cooperrider Bogie is considered as a nonlinear spring. The effect of system parameter on the Hopf bifurcation is analyzed by changing the coefficients of nonlinear spring. The process of the system changing from subcritical Hopf bifurcation to supercritical Hopf bifurcation is also studied.3) Based on the semi-active control technology, a magneto-rheological damper added on the secondary suspension of the bogie on the lateral direction. The response of the system with control is compared to that without control so that the influence of semi-control on the Hopf bifurcation of the system is analyzed.4) The optimal control force is calculated based on the active control technology. A further analysis of effects of active control on the Hopf bifurcation of the system is made by acting the optimal control force on the system by an actuator.The nonlinear flutter characteristics of Cooperrider Bogie are investigated by the research on nonlinear flutter of the four aspects as above. The research provided a theoretical basis to a further improvement of lateral stability of the railway freight car system.