An engineering model for the prediction of the sound radiation from a railway track

Abstract

Models for predicting railway rolling noise such as TWINS are well-established and have been validated against field measurements. However, there are still some areas where improvements are required. In particular, the radiation from the rail is based on a model of a rail in free space whereas in reality the rail is located close to the ground; there are also limitations in the existing model for the sound radiation from the sleepers. Besides, the influence of the ballast absorption on the sound power radiated by the track is neglected. This paper draws on recent research into the effects of the proximity of the rail and sleeper to an absorptive ground on their sound radiation, based on the boundary element method. In reality, the rail is located above the ballast over part of its length, and attached periodically to the concrete sleepers elsewhere. The sound radiation of the rail for those two situations can be predicted using the 2D boundary element method. In order to obtain a realistic rail radiation model for engineering applications, a method to combine those two results is proposed and the resulting average rail radiation is verified by using a 3D boundary element model. An improved sleeper radiation model is also proposed and verified using the 3D boundary element model. These new engineering models for the rail and sleeper radiation have been used together with TWINS to predict the sound radiation from operational tracks and the results have been compared with field measurements. Compared with the TWINS model, the rail radiation is found to be increased below 300 Hz, but decreased above 1 kHz; the sound radiation from the sleeper is reduced compared with the TWINS model below 600 Hz.