On Wheel-Rail Profile Optimization For Railway Vehicle

Matching relationship of the wheel/rail profiles is always the main focus of high-speed railway home and abroad, as it has direct influence on the performance, the cost and the safety when railway vehicle running. With the high-speed railways large-scalely built and operation, the problems in the wheel and rail are outburst. Currently, the prevalent methods to duel with the wheel/rail failure and crack are rail grinding and wheel re-profiling. These methods can efficiently improve the contact status of the wheel/rail and extend their life time. But if wheels and rails mismatch in their profiles, they present the bad behavior from their beginning use, and hence the maintenance cost for them will soar. It is easy to see that the good dynamic performance and the low maintenance costs can be obtained through designing new wheel/rail profiles which have a friendly interaction in their rolling contact. Therefore, from the practical and cognitive points of view, studies on wheel/rail profile optimization are very important. In this thesis, based on the nonlinear programing theory, the vehicle-track coupling dynamics theory, wheel-rail rolling contact theory, the numerical optimization for wheel profile are investigated as follows.1. A new numerical method optimization method is put forward. The wheel/rail normal gap is taken as the target function in this method. Compared to those inverse methods, the method put forward in this paper is based on forward solution strategy and the optimized profile can be obtained without massive practice experiences. To improve the computing speed of the new method, the sequential quadratic programming(SQP) combined with lagrange formula , quasi-newton method, and BFGS method is used to calculate the approximate matrix of quasi-Newton, and this matrix is taken as the hessian matrix of the lagrangian function. The new method is also coded into computational program to solve the optimization problem.2. The wheel-rail profiles matching design isdeveloped considering the rail cant and track gauge by applying the new numerical method optimization method. The dynamics behaviours and contact geometry property of the the original wheel profile (LMa) and the optimized profile arecompared, and the suitable parameters of the rail cant and track gauge for home railway system are found.3. Based on the vehicle-track coupling dynamics model, a optimization method considering the weights of the wheel/rail normal gap is proposed. In this method, the different field in wheel tread is taken with different wight when optimizing, when given the parameters of the railway vehicle and the track. The vehicle-track coupling dynamics model and Kallker's theory of three-dimensional elastic bodies in rolling contact with non-Hertzian are utilized to analyze the dynamics behaviours ,the shape of the contact patch and the distributation of the stress in the contact patch for the optimized profile. And the result shows that the contact stress is reduced significantly and the distribution of wheel rail contact point is improved remarkabley, which imply that the rolling contact figure and damage in the wheel and rail will be decreased significantly and the cost of operation will be greatly reduced.