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- A three-dimensional approach for contact detection between realistic wheel and rail surfaces for improved railway dynamic analysisPublication . Marques, Filipe; Magalhães, Hugo; Pombo, João; Ambrosio, Jorge; Flores, PauloThe wheel-rail contact modeling problem assumes a preponderant role on the dynamic analysis of railway systems using multibody systems formulations. The accurate and efficient evaluation of both location and magnitude of the wheel-rail contact forces is fundamental for the development of reliable computational tools. The wheel concave zone might be a source of numerical difficulties when searching the contact points, which has been neglected in several works. Here, it is demonstrated that the minimum distance method does not always converge when the wheel surface is not fully convex, being an alternative methodology proposed to perform the contact detection. This approach examines independently the contact between each wheel strip and the rail, where the maximum virtual penetration is determined and associated with the location of the contact point. Then, an Hertzian-based force model is considered for both normal and tangential forces. The results obtained from dynamic simulations show that the minimum distance method and the proposed methodology provide a similar response for simplified wheel profiles. However, the new approach described here is reliable in the identification of the contact point when realistic wheel profiles are considered, which is not the case with the minimum distance method.
- A new simplified approach to deal with conformal contact in railway dynamicsPublication . Marques, Filipe; Magalhães, Hugo; Liu, Binbin; Pombo, João; Flores, Paulo; Ambrosio, Jorge; Bruni, StefanoThe contact between a wheel and a rail in the context of railway dynamics is mostly the result of the interaction of two convex surfaces. However, when negotiating sharp curves and due to worn profiles, the conformal contact tends to occur. In this type of interaction, the contact zone cannot be contained in a single plane as opposed to the non-conformal case. Hence, a new methodology to deal with conformal contact in the framework of railway dynamics is proposed in this work. A curved axis in the lateral direction is considered, and it is used to measure the separation between profiles. Moreover, the contact patch is divided into strips in which it is locally planar, and the pressure distribution is estimated based on Kik-Piotrowski model. The interaction between a wheel and rail has been tested for four static cases. The preliminary results show that this methodology can be a reliable alternative to the use of more computationally intensive approaches as the boundary or finite element methods.
- Utilization of non-conformal wheel surfaces for railway dynamicsPublication . Marques, Filipe; Magalhães, Hugo; Pombo, João; Ambrosio, Jorge; Flores, PauloThe dynamic analysis of railway systems using multibody systems formulation is nowadays a reliable tool for several studies, in which the wheelrail contact interaction has significant importance. The definition of contacting geometries affects directly the dynamic response of the system. For sake of simplicity and computational efficiency, some authors simplify the wheel profile to avoid its concave part. This work intends to study the impact of utilizing a simplified non-conformal profile instead of a real wheel profile. For this purpose, an Hertzian-based contact force model is used to compute either the normal and creep forces. A wheelset rolling over a straight track is used as demonstration case. The results show that although the location of the contact points is similar, the use of simplified wheel profile may have an extensive impact on the dynamic response of the system.