Influence of steady aerodynamic loads on hunting stability of high-speed trains

The influence of environmental steady aerodynamic loads on the both carbody hunting motion and bogie hunting motion stability of high-speed trains (HSTs) is presented in this paper. A lateral HST dynamics model with 17 degrees of freedom (DOFs) is established to reflect the dynamic characteristics of carbody hunting and bogie hunting motions. The nonlinear creep force saturation and variable friction coefficient nonlinear characteristics are considered in the model. Then the continuous modal tracking method and numerical simulation method are used to evaluate the hunting stability and acquire the bifurcation diagram, respectively. The linear hunting stability and bifurcation behavior, subject to different wheel/rail match equivalent conicity and friction coefficient conditions, are investigated in detail for both the carbody and bogie hunting motions. The results show that crosswind aerodynamic loads will change the normal wheel/rail force and quasi-static contact position. Additionally, the creep coefficient and creep force saturation modified coefficient, which are closely related to hunting stability, will also be affected. The crosswind aerodynamic loads can significantly impact the hunting stability and bifurcation characteristics, especially under condition of small friction coefficient. The double grazing phenomenon with occurrence of carbody hunting motion will change to single grazing phenomenon when the crosswind aerodynamics loads are large enough.