Applicable Directivity Description of Railway Noise Sources
THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Applicable Directivity Description of Railway Noise Sources XUETAO ZHANG Department of Civil and Environmental Engineering Division of Applied Acoustics, Vibroacoustic Group CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden 2010 Applicable Directivity Description of Railway Noise Sources XUETAO ZHANG ISBN 978-91-7385-416-0 © Xuetao Zhang, 2010 Doktorsavhandlingar vid Chalmers tekniska högskola Ny serie nr 3097 ISSN 0346-718X Department of Civil and Environmental Engineering Division of Applied Acoustics Chalmers University of Technology SE – 412 96 Göteborg Sweden Tel: +46 (0) 31-772 2200 Fax: +46 (0) 31-772 2212 Cover: 3D directivity pattern of a perpendicular dipole pair, viewed along the axis of the red dipole component which is 4 dB weaker than the blue one. Printed by Chalmers Reproservice Göteborg, Sweden, 2010 ii Applicable Directivity Description of Railway Noise Sources XUETAO ZHANG Department of Civil and Environmental Engineering Division of Applied Acoustics Chalmers University of Technology Abstract For a sound source, directivity is an important parameter to specify. This parameter also reflects the physical feature of the sound generation mechanism. For example, turbulence sound is of quadrupole directivity while fluid-structure interaction often produces a sound of dipole characteristic. Therefore, to reach a proper directivity description is in fact a process of understanding the sound source in a better way. However, in practice, this is often not a simple procedure. As for railway noise engineering, several noise types of different directivity characters are often mixed together, such as wheel and rail radiation, engine and cooling fan noise, scattered fluid sound around bogies and turbulent boundary layer noise along train side surfaces.
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