Multibody modeling of railway vehicles: Innovative algorithms for the detection of wheel–rail contact points

Abstract

a b s t r a c tThe multibody simulation of railway dynamics needs a reliable and efficient method to properly describe the contact between wheel and rail.In this work innovative methods to evaluate the position of contact points are presented. The aim is to develop a method which can be implemented on-line, assuring a calculation time consistent with real-time calculations of multibody dynamics. At the same time it has to be very accurate, to properly predict the local forces at contact in order to describe even the wear of contact surfaces.In this work the authors present two different approaches to find stationary points during a multibody simulation. In the former the conditions to define a local minima are wrote in an analytical way. This makes possible to combine the conditions in order to reduce the analytic problem's dimension and then to solve numerically the problem with a low computational burden. The latter approach calculates the location of local minima using a method based on neural networks. The paper will cover the details of the proposed methods and the performances, in terms of computation time and accuracy, will be compared with those of the conventional algorithms used by commercial softwares, showing their reliability and low computational burden. Moreover, an implementation of the proposed models in a multibody simulator will be presented, in order to show their suitability for this application.

Development of an innovative wheel–rail contact model for the analysis of degraded adhesion in railway systems

“…The complete 3D model of the vehicle dynamics is equipped with a 3D, multi-contact wheel-rail contact model (see the bibliographic references [2,7,8]). In that case, the vehicle model and the adhesion model create a dynamic loop (unlike the initial case described in Section 2): the vehicle model calculates the inputs of the adhesion model while its outputs are passed back to the vehicle model to carry on the dynamical simulation.…”

“…The wheel-rail contact model (multiple contact) includes three different steps: the detection of the contact points P c (some innovative procedures have been recently developed by the authors in previous works [2,7,8]), the solution of the normal contact problem through the global Hertz theory [9] to evaluate the normal contact forces N c and the solution of the tangential contact problem by means of the global Kalker-Polach theory [9,1,6] to compute the tangential contact forces T c and the adhesion coefficient f (see the diagram in Fig. 14).…”

“…This kind of models necessarily represents a trade-off between accuracy and numerical efficiency and consists of three fundamental logical steps: the detection of the contact point positions [2,7,8,[3][4][5], the calculation of the normal contact forces (based on the improvements of the Hertz theory [9,3,4,5]) and the evaluation of the tangential contact forces (mainly based on the Kalker theory [9] and the Polach one [1,6]). …”

An innovative degraded adhesion model for railway vehicles: development and experimental validation

“…2). The detection of the contact points P c is based on some innovative procedures recently developed by the authors in previous works [10,22,34]. The normal contact problem is then solved through the global Hertz theory [6,11,29] to evaluate the normal contact forces N c .…”

“…The main approaches employ either constraint equations [42,43] or exact analytical methods aimed at the reduction of the algebraic problem dimension [9,10,15,22,23,34]. Generally, the normal problem solution is based on the Lagrange multipliers [42,43] and on improvements of Hertz theory [6,11,29].…”