Hybrid Contact Search Algorithm for Wheel/Rail Contact Problems

In this investigation, the on-line and off-line hybrid contact algorithm for modeling wheel/rail contact problems is developed based on the elastic contact formulation. In the tabular contact search used in existing specialized railroad vehicle dynamics codes, contact points are predicted using an assumption of rigid contacts. For this reason, the contact points can be different from those predicted by the on-line based contact search used in general elastic contact formulations. The difference in the contact point becomes significant when flange contacts that have large contact angles are considered. In the hybrid algorithm developed in this investigation, the off-line tabular search is used for treating tread contacts, while the on-line iterative search is used for treating flange contacts. By so doing, a computationally efficient procedure is achieved while keeping accurate predictions of contact points on the wheel flange. Furthermore, the use of the proposed hybrid algorithm can eliminate the use of time-consuming on-line search procedures for the second points of contact as well. Since the location of second points of contact is pre-computed in the contact geometry analysis, the occurrence of two-point contact can be predicted using the look-up table in a straightforward manner. For the two-point contact scenarios encountered in curve negotiations, the online search is used for flange contacts, while the off-line search is used for tread contacts simultaneously. The on-line one-point contact search is also important for flange climb scenarios. It is demonstrated by several numerical examples that the proposed hybrid contact search algorithm can be effectively used for modeling wheel/rail contacts in the analysis of general multibody railroad vehicle systems.