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

Abstract

a b s t r a c tA detailed description of adhesion is crucial in tribology, vehicle dynamics and railway systems, both theoretically and practically. However, an accurate adhesion model is quite hard to develop because of the complex and non-linear behaviour of the adhesion coefficient and the external unknown contaminants which are present between the contact surfaces. The problem becomes even more complicated when degraded adhesion and large sliding between the contact bodies (for instance wheel and rail) occur.In this paper the authors describe an innovative adhesion model aimed at increasing the accuracy in reproducing degraded adhesion conditions in vehicle dynamics and railway systems; the new approach turns out to be quite suitable also for multibody applications (fundamental in this research topic). The model studied in the work considers some of the main phenomena behind the degraded adhesion: the large sliding at the contact interface, the high energy dissipation, the consequent cleaning effect on the contact surfaces and, finally, the adhesion recovery due to the external unknown contaminant removal.The new adhesion model has been validated through experimental data provided by Trenitalia S.p.A. and coming from on-track tests carried out in Velim (Czech Republic) on a straight railway track characterised by degraded adhesion conditions. The tests have been performed with the railway vehicle UIC-Z1 equipped with a fully-working Wheel Slide Protection (WSP) system.The validation showed the good performances of the adhesion model both in terms of accuracy and in terms of numerical efficiency; high computational performances are required to implement the developed model directly online within more general and complex multibody models (e.g. in MatlabSimulink and Simpack environments). In conclusion, the adhesion model highlighted the capability of well reproducing the complex phenomena behind the degraded adhesion.

An innovative hardware in the loop architecture for the analysis of railway braking under degraded adhesion conditions through roller-rigs

“…This 2D multibody model simulates the longitudinal dynamics of the vehicle while an innovative 2D adhesion model especially developed [16,17] to accurately reproduce the real behaviour of the adhesion coefficient during braking phases under degraded adhesion conditions. The inputs are the estimated torques on the wheelsets and the outputs are the simulated wheelset angular velocities and the tangential contact forces on the wheelsets; the innovative controllers (software) reproduce on the roller-rig the same dynamical behaviour of the virtual train model (through the roller control torques) in terms of wheelset angular velocities, applied torques and, consequently, tangential forces [8].…”

“…The WSP device installed on the UIC-Z1 coach [12,17] allows the control of the torques applied to the wheelsets, to prevent macrosliding during the braking phase.…”

“…In Fig x w and accelerations _ x w ; the computation of the logical sliding state state WSP (equal to 1 if sliding occurs and 0 otherwise) and the consequent torque modulation, through a speed and an accelerometric criterion and by means of a suitable logical table [17]; the periodic braking release to bring back the perceived adhesion coefficient to the original value (often used when degraded adhesion conditions are very persistent and the WSP logic tends to drift).…”

“…The adhesion model has been especially developed to describe degraded adhesion conditions [17,[32][33][34] and calculates, for all the 4 wheelset-rail pair, the tangential contact forces T sim starting from the wheelset kinematic variables v ws ; x ws and the normal contact forces N cs (see Fig. 12).…”

“…The direct comparison between the experimental and simulated train velocities v sp ; v s is illustrated in Fig. 16 [17][18][19][20].…”