José Martínez-Casas

Rail corrugation growth accounting for the flexibility and rotation of the wheel set and the non-Hertzian and non-steady-state effects at contact patch

In this work, a simulation tool is developed to analyse the growth of rail corrugation consisting of several models connected in a feedback loop in order to account for both the short-term dynamic vehicle–track interaction and the long-term damage. The time-domain vehicle–track interaction model comprises a flexible rotating wheel set model, a cyclic track model based on a substructuring technique and a non-Hertzian and non-steady-state three-dimensional wheel–rail contact model, based on the variational theory by Kalker. Wear calculation is performed with Archards wear model by using the contact parameters obtained with the non-Hertzian and non-steady-state three-dimensional contact model. The aim of this paper is to analyse the influence of the excitation of two coinciding resonances of the flexible rotating wheel set on the rail corrugation growth in the frequency range from 20 to 1500 Hz, when contact conditions similar to those that can arise while a wheel set is negotiating a gentle curve are simulated. Numerical results show that rail corrugation grows only on the low rail for two cases in which two different modes of the rotating wheel set coincide in frequency. In the first case, identified by using the Campbell diagram, the excitation of both the backward wheel mode and the forward third bending mode of the wheel set model (B-F modes) promotes the growth of rail corrugation with a wavelength of 110 mm for a vehicle velocity of 142 km/h. In the second case, the excitation of both the backward wheel mode and the backward third bending mode (B-B modes) gives rise to rail corrugation growth at a wavelength of 156 mm when the vehicle velocity is 198 km/h.

3D Acoustic Modelling of Dissipative Silencers with Nonhomogeneous Properties and Mean Flow

A finite element approach is proposed for the acoustic analysis of automotive silencers including a perforated duct with uniform axial mean flow and an outer chamber with heterogeneous absorbent material. This material can be characterized by means of its equivalent acoustic properties, considered coordinate-dependent via the introduction of a heterogeneous bulk density, and the corresponding material airflow resistivity variations. An approach has been implemented to solve the pressure wave equation for a nonmoving heterogeneous medium, associated with the problem of sound propagation in the outer chamber. On the other hand, the governing equation in the central duct has been solved in terms of the acoustic velocity potential considering the presence of a moving medium. The coupling between both regions and the corresponding acoustic fields has been carried out by means of a perforated duct and its acoustic impedance, adapted here to include absorbent material heterogeneities and mean flow effects simultaneously. It has been found that bulk density heterogeneities have a considerable influence on the silencer transmission loss.

Mitigation of Railway Wheel Rolling Noise by Using Advanced Optimization Techniques

Rolling noise emitted by railway wheels is a problem that affects human health and limits the expansion of the railway network. This problem is caused by the wheel-rail contact, and it is predominant over the rest of noise sources from the vehicle/track system for the usual speed conditions in urban areas. The minimization of rolling noise through changes on the wheel shape by means of the finite element method is discussed in this work, which focuses on potential shape modifications in existing wheels in the form of an optimal wheel web perforation distribution. Such a modification is a cost-effective solution that can be performed in a relatively short term in already manufactured and operating railway wheels. To this end, two objective functions with different computational costs are studied and analysed with several configurations of a genetic algorithm-based optimizer. Both approaches focus on minimizing rolling noise. Approach 1 is based on the minimization of the area below the sound power vs. frequency curve of the wheel, and thus requires solving the system dynamics. On the other hand, Approach 2 is based on the maximization of the natural frequencies of the wheel in order to shift its resonances out of the excitation range, and therefore it only requires a modal analysis. The acoustic radiation analysis is performed through the computation of the normal surface velocities, using a time-domain approach and including a contact filter applied in the track roughness, considered as excitation. Moreover, the structural requirements for fatigue strength in wheels proposed by the optimizer are ensured according to actual standards. Results using Approach 1 reflect that an optimized distribution of perforations on the web of a railway wheel, can reduce significantly the sound power level in the entire studied frequency domain (0–5 kHz). This is related to the high sensitivity of the acoustic radiation response with the perforation pattern. Such a phenomenon appears to have a higher impact on noise minimization than that associated with the reduction of the radiating surface due to perforations. The high reduction of the radiated sound power is primarily due to the fact that certain wheel vibration modes with high acoustic contribution are shifted out of the excitation range corresponding to the contact force, this effect being observed in the best solution of Approach 1. Less significant sound power reduction is obtained with Approach 2, although its associated computational cost is considerably lower.