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- Implementation of a non-Hertzian contact model for railway dynamic applicationPublication . Magalhães, Hugo; Marques, Filipe; Liu, Binbin; Antunes, Pedro; Pombo, João; Flores, Paulo; Ambrosio, Jorge; Piotrowski, Jerzy; Bruni, StefanoThe development of wheel–rail contact models is an active topic of railway research with the dual objective of improving the accuracy of multibody simulations and reducing its computational effort. This paper extends the online Hertzian contact model, proposed by Pombo et al. (Veh. Syst. Dyn. 45: 165–189, 2007) to propose a non-Hertzian contact model. The new methodology presented here includes the following steps: (i) search of the points of contact; (ii) identification of the undeformed distance function; (iii) evaluation of the contact patch; (iv) calculation of the normal and tangential contact forces; (v) application of the contact forces in the multibody vehicle model. Among several contact models available in the literature, this non-Hertzian contact approach uses the Kik–Piotrowski model for the normal contact force, while the tangential forces are obtained from the interpolation of the available Kalker Book of Tables for non-Hertzian (KBTNH) contact. With the purpose to demonstrate the proper implementation and selection of parameters that define this new model, several contact analysis and dynamic simulations are performed in which the wheel S1002 and the rail UIC50 are considered. First, the contact analyses that determine the contact condition of different wheel–rail interactions serve to assess the accuracy of the Hertzian and non-Hertzian models with respect to the software of reference CONTACT. Second, the Hertzian and non-Hertzian models are utilised to perform dynamic simulations of a wheelset, a bogie and a vehicle running in tangent and curved tracks. In short, this work provides, not only a complete description of the implementation of a non-Hertzian contact model in a multibody code, but also suggests for the proper selection of the parameters that promote better accuracy and optimal computational efficiency.
- 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.
- Implementation of a non-Hertzian Contact Model for Railway DynamicsPublication . Magalhães, Hugo; Marques, Filipe; Liu, Binbin; Pombo, João; Flores, Paulo; Ambrosio, Jorge; Bruni, StefanoThe development of wheel-rail contact models is an active topic of research, in which more accurate and reliable methodologies are required to improve the realism of multibody simulations while reducing the computational effort. However, their implementation in a multibody software consists of a challenging task for itself. This paper presents a generalized strategy for the implementation of non-Hertzian contact models. This new methodology is split into the following steps: determination of points of contact; identification of the undeformed distance function; determination of the contact patch; and calculation of the normal and tangential forces which are computed according to the contact conditions and the theories used. Here, the normal force is determined with the Kik-Piotrowski model, while the tangential forces are obtained from the interpolation of the Kalker Book of Tables for Non-Hertzian contact patches. To demonstrate the proper implementation of the new methodology, static and dynamic simulations have been performed. First, a static wheel-rail interaction at different slip conditions is simulated being observed a good agreement with respect to the results obtained from CONTACT. Secondly, a dynamic simulation of a bogie running in a tangent track is considered, in which the contact developed respect the Hertzian conditions. Thus, a comparison between the Hertzian approach and the proposed methodology is possible, being discussed the slight differences between the results obtained from both simulations. Besides the proposed implementation is 4.5 times slower than the Hertzian method considered in this work, for the case study presented in this work, the proposed methodology allows to deal with non-Hertzian contact.