Wheel–rail contact simulation with lookup tables and KEC profiles: a comparative study

Abstract

This paper describes and compares the use and limitations of two constraint-based formulations for the wheel-rail contact simulation in multibody dynamics; (1) the use of contact lookup tables and (2) the Knife-edge Equivalent Contact constraint method (KEC-method). Both formulations are presented and an accurate procedure to interpolate within the data in the lookup table is also described. Since the wheel-rail constraint contact approach finds difficulties at simultaneous tread and flange contact scenarios, the lookup table method is implemented with a penetration-based elastic contact model for the flange, turning the method into a hybrid (constant in the tread and elastic in the flange) approach. To deal with the 2-point contact scenario in the KEC-method, a regularisation of the tread-flange transition allows the use of the constraint approach in the tread and also in the flange. To show the applicability and limitations of both methods, they are studied and compared with special emphasis in the calculation of normal and tangential contact forces. Numerical results are based on the simulation of a two-wheeled bogie vehicle in different case studies that consider irregular tracks and two wheel-rail profiles combination: profiles that do not show two-point wheel-rail contacts and profiles that do show two-point wheel-rail contacts. Although results show a good agreement between both approaches, the use of the KEC-method is more extensive since it allows to reproduce the wheel-climbing scenario that cannot be simulated with the lookup table method with the hybrid contact approach. It is concluded that simulations with this later method may not be in the safe side.

Comparison of numerical and computational aspects between two constraint-based contact methods in the description of wheel/rail contacts

“…Therefore, the reaction forces for the wheelset Q nor,wi cannot be obtained using the KEC constraint Jacobian matrix Q nor,wi = −C wi,KEC q λ in Eq. ( 19) [17,24]. As shown in the left and right of Fig.…”

“…To this end, track kinematics vehicle kinematics and wheel/rail contact will be discussed. More insight into the kinematics and contact mechanism can be found in [12,16,24].…”

“…As will be shown in the following section, it is a convenient frame to define contact point position vectors, because they are not influenced by the wheelset pitch rotation, which is particularly high in these bodies. More details about body and wheelset kinematics can be found in [12,16,24]. The position vector of contact points on the surface of the left and right wheel profile in Fig.…”

“…When the two-point contact scenario occurs, the wheel-flange contact event suddenly appears and is treated as an impact. Therefore, the elastic flange contact event may require small time step size for the time integration [28] and the flange contact stiffness controls numerical simulation performance [24].…”

“…The authors of [16] state that the area of allowable motion for the wheel with null irregularity cannot be guaranteed to be the same as for wheels with irregularities. Later, in [24], the KEC-equivalent wheel profiles were proved to be acceptable for use in irregular tracks with accuracy.…”