On the Directivity of Railway Noise Sources
This dissertation deals with the directivity of railway noise. The directivity of railway noise is of particular importance when we have high-rise buildings close to the track, tunnel openings, partial barriers, or when we calculate the maximum sound pressure level during a pass-by based on the sound power level of the different sub-sources of a train. On the other hand, directivity is a part of source description.
The directivity of the different sub-sources of a train has been studied systematically by carrying out new measurements, collecting relevant information from the literature and modelling the physical processes. The focus has been on railway rolling noise from wheels and track but both railway traction noise and aerodynamic noise are also dealt with. First the individual sub-sources are studied and then the sound pressure level contributions from each of these sources are combined to yield the directivity of a whole train.
In general, the directivity of a whole train is both distance and speed dependent. Moreover, high speed source motion can affect the directivity dramatically. All these results are summarized into equations practical to use for engineering applications.
railway traction noise
railway rolling noise
railway aerodynamic noise
equivalent source line
sound emission time
sound immission time
the Doppler factor