From physical sources to equivalent noise sources

The aim of the Harmonoise work package concerning railway-noise sources is to provide sources to be included in propagation calculations. A main step to reach this aim is to determine equivalent noise sources from physical noise sources. But in terms of model complexity and calculation times, a too precise description would not be adapted to the purpose of the Harmonoise project. Therefore the number of equivalent sources has to be significant lower than the number of physical sources. The equivalent noise sources have to be defined in terms of strength, directivity, and height. Because one of the project requirements is to use the same source heights for all train categories, reasonable source heights have to be determined by sensitivity studies. The MAT2S program which describes trains by its point sources to calculate pass-by levels (taking into account propagation in a simple way) is used to test different train descriptions: a description using physical sources and a less detailed description using equivalent sources. The comparison of the calculated pass-by levels allows to determine the accuracy of the equivalent-source description. MAT2S allows also sensitivity studies. This method has been applied to the TGV-R and will be used for further types of trains.