The radiation from railway wheel modes and their effect on loudness, sharpness, and equivalent pressure level

Abstract

The noise of railway wheels is one of the main contributors to railway rolling noise. Auralization, the rendering of sound fields from virtual sources, is a promising tool for studying rolling noise, as it enables the study of perceptual qualities of noise. Generating such sound fields based on physical models requires knowledge of the structural vibrations and radiation characteristics of the wheels. The vibration and radiation of a railway wheel are typically dominated by highly undamped modes. The amplitudes of the various modes depend on the roughness excitation and the contact position of the wheel on the rail. For auralization, it is relevant to investigate which modes are significant in reproducing the equivalent sound pressure level (SPL), as well as psychoacoustic quantities. Identifying significant modes can also help simplify the physical model. This article explores the influence of lateral contact positions on wheel radiation and analyzes the modal contributions to pass-by SPLs. Using a timedomain prediction model for the sound pressure produced by one wheel as it passes a stationary track side position, the psychoacoustic quantities loudness and sharpness were investigated. The smallest number of modes required to reproduce equivalent pressure levels and psychoacoustic quantities is identified for two contact positions. For simplicity, the discussion is limited to one wheel, surface roughness, and vehicle speed. The results show possible simplifications in auralization models and can enable noise mitigation with a focus on psychoacoustic parameters.