Development of Advanced Multidisciplinary Methods for Railway Dynamics Applications

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A new simplified approach to deal with conformal contact in railway dynamics

Publication . Marques, Filipe; Magalhães, Hugo; Liu, Binbin; Pombo, João; Flores, Paulo; Ambrosio, Jorge; Bruni, Stefano

The 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.

2018-06Conference object

Open access

Implementation of a non-Hertzian Contact Model for Railway Dynamics

Publication . Magalhães, Hugo; Marques, Filipe; Liu, Binbin; Pombo, João; Flores, Paulo; Ambrosio, Jorge; Bruni, Stefano

The 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.

2018-06Conference object

Open access

Implementation of a non-Hertzian contact model for railway dynamic application

Publication . Magalhães, Hugo; Marques, Filipe; Liu, Binbin; Antunes, Pedro; Pombo, João; Flores, Paulo; Ambrosio, Jorge; Piotrowski, Jerzy; Bruni, Stefano

The 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.

2020-01Journal article

Restricted access

On the generation of enhanced lookup tables for wheel-rail contact models

Publication . Marques, Filipe; Magalhães, Hugo; Liu, Binbin; Pombo, João; Flores, Paulo; Ambrosio, Jorge; Piotrowski, Jerzy; Bruni, Stefano

In railway dynamics, the interpolation of lookup tables (LUTs) is a procedure utilized to reduce the computational effort when computing the wheel-rail contact forces. However, the generation of LUTs with multiple inputs and multiple outputs is a challenging task for which aspects such as their minimal size and uniform accuracy over the LUT domain have not been systematically addressed in the literature. Thus, this work presents a comprehensive methodology for a detailed analysis of general LUTs, and identifies ways to improve them. For that, an analysis of the variation of the input parameters is made and the interpolation error is assessed on the cells and edges of the original table, then, based on this analysis, two enhanced LUTs are proposed. The first one is approximately 5 times smaller than the original but holds similar accuracy. The second table exhibits half of the maximum interpolation error of the original LUT but holds an identical size. The methodology is demonstrated here using the recently published Kalker Book of Tables for Non-Hertzian contact (KBTNH) but it can be used by any other LUT approach in order to improve accuracy and/or to reduce size.

2019-09-15Journal article

Restricted access

Utilization of non-conformal wheel surfaces for railway dynamics

Publication . Marques, Filipe; Magalhães, Hugo; Pombo, João; Ambrosio, Jorge; Flores, Paulo

The 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.

2019-06-14Conference object

Restricted access