Instability phenomenon associated with two typical high speed railway vehicles

From the numerous field and roller rig tests, we observe one type of high speed railway vehicle has a small amplitude periodical oscillation and another one has a large amplitude periodical oscillation at loss of stability. The lateral dynamic models of the high speed bogies are established with the nonlinearity of wheel rail contact and the non-smoothness of yaw damper taken into consideration. Following the bifurcation approach, simulation results of the two bogies are extensively computed with use of the path-following method. They demonstrate the supercritical and subcritical bifurcations exist in the different types of the considered vehicle systems. The application of Hopf normal theory makes a weak way to mathematically prove the bifurcation types for the two types of high speed railway vehicles Therefore the influence of parameters variation on the deduced function in normal form is further studied and the numerical method is also used for verification. The bifurcation analysis demonstrates that the yaw damper is one of the key parameters that can change the Hopf bifurcation type.