On the Singularity Theory Applied in Rail Vehicle Bifurcation Problem

The application of Hopf bifurcation is essential to rail vehicle dynamics because it corresponds to the linear critical speed. In engineering, researchers always wonder which vehicle parameters are sensitive to it. With the nonlinear singularity theory's development, it has been widely applied in many other engineering areas. This paper mainly studies the singularity theory applied in nonlinear rail vehicle dynamics. First, the bifurcation norm forms of wheelset and bogie system are, respectively, deduced. Then the universal unfolding is obtained and the influences of perturbation on bifurcation are investigated. By the analysis of a simple bar-spring system, the relationship between the unfolding and original perturbation parameters can be found. But this may be difficult to calculate for the case in vehicle system because of higher degrees-of-freedom (DOFs) and indicate that can explain the influence of all possible parameters perturbations on vehicle bifurcation.

Improved Curving Performance for Two-Axle Rail Vehicles With Actuated Solid Wheelsets Using H∞ Control

Application of active suspension on passenger vehicles has engaged many vehicle dynamics specialists in recent years. The technology can be used for different purposes including improving comfort, stability or wear behavior. Despite these benefits, industries do not yet find these technologies attractive enough. One reason is that the achieved benefits do not pay back for itself since the vehicle will become more expensive. Therefore, more steps should be taken to make active suspension attractive. One such a step can be using active suspension for resolving classical limitations in rail vehicle dynamics. An example of this is a non-bogie rail vehicle with two axles. One of the problems associated with these vehicles is their short axle distance limiting the length of the vehicle. The short axle distance is partly for limiting wheel-rail wear. This paper describes how to reduce wheel wear through achieving better wheelset steering in curves so that longer axle distances can be allowed. Wheelset steering is performed by H∞ control strategy.