International Journal of Applied Engineering Research

Nonlinear mathematical model of a railway single wheelset moving on curved tracks is constructed in which single-point and two-point wheel-rail contact has taken into consideration. The considered system is modeled by 6 degrees of freedom which govern lateral displacement, vertical displacement, roll angle and yaw angle of single wheelset and lateral displacement of each left and right rails. Longitudinal, lateral and vertical primary suspensions with linear suspension characteristics are provided to the system. Combination of linear Kalker's theory and nonlinear Heuristic model has been adopted to calculate the creep forces introduced on wheel and rail contact due to friction properties of the wheel-rail contact geometry. A numerical simulation is constructed to solve the associated differential governing equations of motion of the model using fourth order Runge-Kutta method. Principles of limit cycle and phase plane approach is applied to realize the stability and to evaluate the concerning hunting critical velocity of the system in which subjected to different parameters of wheel conicity and primary suspension characteristics. Dynamic responses of lateral, yaw, roll and vertical motions of single wheelset moving on curved tracks of constant radius R and constant super-elevation angle φ_se are presented. The single wheelset simulation model is utilized to evaluate the critical velocity of the system in which the hunting phenomenon occurs under different values of wheel conicity. The results obtained shows that hunting critical velocity is proportional inversely to wheel conicity. Comparison between these results and the results obtained by same model moving on tangent tracks and with other previous 4 DOF is presented. The comparison shows the same dynamic behavior of the three models with low hunting critical velocity rates in the case of the system on curved tracks. Influence of super-elevation angle of the curved tracks on hunting critical velocity of the system is investigated to different values of wheel conicity. It has shown that small amounts of super-elevation angle increase the hunting critical velocity and elminate hunting unstability while simulation model shows that high amounts of super-elevation angle make the flanges touch rails and cause hunting unstability. As a result, the super-elevation angle has compromise values must be chosen according to the different prameters used on the system.