Model-based acoustic substitution source methods for assessing shielding measures applied to trains

Abstract

A promising means of reducing the rolling noise from trains is local shielding in the form of vehicle-mounted shrouds combined with low trackside barriers. This is much less visually intrusive than classic lineside noise barriers. Various experimental methods have been proposed that allow the performance to be assessed under static conditions, enabling rapid comparisons of different configurations. This paper focuses on acoustic substitution source methods and their application to the noise radiated from the wheel. The vibrating wheel can be represented by a set of acoustic point sources at its surface. Modal behaviour of the wheel is simulated by applying appropriate phase relations between the acoustic point sources. Transfer functions between the point sources and microphone positions at the trackside are measured reciprocally. By comparing measurements of these transfer functions with and without the shielding devices installed, an insertion loss spectrum can be obtained. To calculate the reduction of the total pass-by noise, the acoustic point source contributions need to be weighted appropriately for which the TWINS calculation model for railway rolling noise is used. The performance of the method has been investigated for a closely mounted wheel skirt.