Preliminary Study On Flexible Wheelsets

With the operation speed increase of trains, the wheel/rail contact impacts become more serious, which leads to the evident problems such as operation safety issue, seating comfort, wheel/rail abnormal wear, and wheel/rail noise. The conventional rigid multi-body dynamics model for vehicle/track is limited to analyze low-frequency dynamic phenomenon, unable to describe the medium to high frequency dynamic phenomenon. The medium to high frequency dynamic behavior is very much concerned with the wheel/rail contact impact and wheel set elastic deformation. So it is significant to consider the wheelset flexibility in modeling the high-speed train/track to analyze the medium to high frequency dynamic behavior of the train and the track.A flexible wheelset model is developed using numerical method. It considers the wheelset axle bending and neglects the crossing-influence of the wheelset axle bending deformations in the different planes of the rigid axle of the wheelset. For simplicity the wheels are modeled as rigid bodies, based on this model the differential equations for the deformed wheelset are formulated to get the translational and angular displacements of the axle centerline. The elastic deformation of the axle leads to the change of the left and right wheels poses. Caused by the wheelset axle deformation the spatial configures of the wheelsets could not be confirmed by the movement of the wheelset centroid which leads some big difficulties such as the wheel/rail contact points’locations, the creepages and creep-forces, and the normal pressure between the wheel and the rail. The below is my work in wheel-rail contact model.In the confirmation of contact points, firstly the poses of the left and right wheels at any moment caused by the elastic deformation of the axle are determined. Then using "the tracing method" describes the traces of the spatial contact points on the wheel treads. Thirdly search for the real the wheels/rail contact points by using the method that is called as "minimum gap seeking method". As described above, the gradual derivation based on the wheelset elastic deformation figures out the wheelrail contact geometrical relation.In the normal force calculation of wheel/rail, due to the different poses of the two wheels under the deformation of the axle, firstly, the vertical compressing between the wheel and the rail is calculated by using the vertical displacements of the wheel and rail. Then, the normal compressing is calculated based on the spatial geometry relation of the normal compressing and the known vertical compressing. Then apple the Hertz theory to the calculation of the normal wheel/rail contact force.The calculation of the creep forces of the wheel/rail needs to consider the effect of the axle deformation on the relative slip velocity between the wheel and the rail since the relative slip velocity is dominant in the creepage forming. In the calculation the coordinate systems fixed on the nominal rolling circles of the wheels, with the origins at the centers of the nominal rolling circles, are regarded as the transform coordinate systems. Then describe the creepage in the wheel rail contact local ordination. At last make out the creep forces based on Kalker linear creep theory.Finally, dynamic model for the vehicle and track, considering the flexible wheelset, is verified. In the verification, firstly, the validity of the new wheel/rail contact model is verified by making the comparison of the results calculated with both the rigid multi-body model and the present model only considering the rigid modals. Then, in order to verify the effect of the elastic modal of the axle, each mode is coupled into the dynamic system to analyze the deformation of the wheel axle in single modal vibration. Thirdly, in order to calculate the effect of the bending modes on the system behavior, the white noise and sine irregularity of the track are used as excitations generated between the wheel and the rail, the wheel/rail normal forces, the yaw angular displacements and their spectra are calculated.