Multiscale Problems in Multibody System Contacts – An International

New developments on the wheel-rail contact problem for railway dynamics João Pombo, Jorge Ambrósio IDMEC – Instituto Superior Técnico Av. Rovisco Pais, 1049-001, Lisboa, Portugal e-mail: [jpombo, jorge]@dem.ist. utl.pt The dynamic analysis of complex, three-dimensional, railway vehicles involves the construction of three independent models: the vehicle model; the track model; and the wheel-rail contact model. In this work, a multibody formulation with Cartesian coordinates is used to describe the kinematic structure of the rigid bodies and joints that constitute the vehicle model. A parameterization methodology is applied for the accurate description of the three-dimensional track model, including its irregularities. The guidance of the railway vehicles along the track is determined by the complex interaction between the wheels and rails, which requires a detailed characterization of this contact mechanism. The kinematics of guidance of a wheelset is based on the wheels and rails geometries while the dynamics of guidance depends on the wheel-rail contact forces. The accurate prediction of the location of the contact points between wheel and rail surfaces is fundamental for the calculation of the contact forces. A generic wheel-rail contact detection formulation is presented here in order to determine, during the dynamic simulation, the contact points even for the most general three-dimensional motion of the wheelset. This formulation also allows the study of lead and lag flange contact scenarios where the contact point in the wheel flange does not have to be located in the same plane as the contact point in the tread. Such scenarios are fundamental to evaluate the risk of potential derailments, to study the dynamic behavior in the presence of switches or to investigate the curving performance when dealing with high angles of attack. The parametric description adopted for the representation of the wheel and rail surfaces allows performing the dynamic analysis of railway vehicles using profiles obtained from direct measurements or by design requirements. This methodology also allows changing the rail profile during the dynamic analysis in order to account for the wear variation along the track or to study switch transitions. The numerical implementation of this wheel-rail contact model leads to a fast and efficient algorithm where the coordinates of the contact points are obtained online during dynamic analysis and, therefore, not requiring the use of pre-calculated lookup tables. An elastic force model that allows computing the normal contact forces in the wheel-rail interface, accounting for the energy loss during contact, is implemented. The tangential wheel-rail contact forces are calculated using distinct creep force models described in the literature. The methodologies proposed here are demonstrated by their application to the dynamic analysis of the ML95 vehicle, which is operated by the Lisbon metro company. The advantages and drawbacks of the formulation are discussed with emphasis on the dynamic behavior of the ML95 trailer vehicle when negotiating a small radius curved track, as depicted in figure 1. Special emphasis is put on the calculation of the wheel-rail contact forces taking into account both tread and flange. Fig. 1: Views of the ML95 trailer vehicle negotiating a small radius curved track