Bifurcation Analysis of a High-Speed Railway Wheelset with Nonlinear Wheel-Rail Contact on the Switch Rails

With the continuous increase in the operating speed of high-speed vehicles, abnormal vibrations and carbody swaying during turnout passage have become increasingly pronounced. The hunting instability of vehicle systems in the turnout zone has consequently emerged as one of the major challenges restricting safe and smooth vehicle operation. To enhance the critical speed of vehicles passing through turnouts and to mitigate the lateral instability induced by speed increase, this study takes the No. 18 ballastless high-speed turnout as the research object. Based on nonlinear dynamics theory and incorporating the nonlinear wheel-rail contact relationships corresponding to different characteristic switch rail profiles, a single wheelset dynamic model is established, and the bifurcation behaviors of the system under various rail profiles are analyzed. The main findings are as follows: Under different lateral displacements, when the wheel-rail contact points are simultaneously distributed on both the switch rail and the stock rail with the minimum switch rail head width (15 mm), or when the contact points are solely distributed on the switch rail with the minimum head width (35 mm), the equivalent conicity reaches relatively small values. In these cases, the Hopf bifurcation speed is relatively low, exhibiting subcritical bifurcation characteristics and resulting in poor hunting stability of the system. For vehicle system parameter optimization, particular reference should be made to the Bautin bifurcation diagrams of wheelset systems under the 15 mm and 35 mm switch rail head width profiles, since the system is more sensitive to parameter variations under these conditions and more prone to hunting motion. To improve operational stability, it is necessary to ensure higher critical speeds under these profiles and to conduct coordinated optimization of vehicle system parameters with respect to the corresponding bifurcation critical lines.