A hybrid numerical method for analysing multi-mode sound propagation in ventilation ductwork

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Conference Proceeding
23rd International Conference on Noise and Vibration Engineering 2008, ISMA 2008, 2008, 1 pp. 497 - 511
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The control of noise in a ventilation system requires a detailed knowledge of the acoustic characteristics of components within the system, as well as knowledge of how each component interacts with one another. Mathematically modelling such systems presents a considerable challenge not least because these systems are relatively large and often consist of complex geometries separated by relatively long duct runs. Accordingly, this article examines a hybrid numerical approach that utilises a multi-modal eigenvalue approach for long uniform duct runs, but then uses mode matching to map this solution onto a finite element based model of a complex component. Results are presented here for two cylinders placed within a rectangular duct and a dissipative splitter silencer. Transmission loss predictions are presented for plane wave and multi-modal excitation and it is noted that multi-modal excitation has a significant effect on the acoustic behaviour of the components. Furthermore, multiple cylinders are capable of generating high transmission loss values over narrow frequency bands, which makes them potentially useful for attenuating narrow band noise from ventilation fans. © 2008 by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved.
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