Simulation of Diffractions and Reflections of arbitrary order with the Sound Particle Diffraction Model based on the Uncertainty Relation

Regular paper

Stefan Weigand

HafenCity University

Monday 1 june, 2015, 16:20 - 16:40

0.9 Athens (118)

In room and city acoustics, beside reflections, screening effects become important, often even of higher order. There are even cases where sound reaches immision points solely by diffraction. For these applications, ray tracing methods are appropriate and well established.These, however, are unable to simulate diffraction effects in a generally correct way. Standards for noise control engineering (as the VDI 2720) still propose the old detour model (Maekawa) which however is only valid for single diffraction, not at arbitrarily shaped obstacles and not in cascade. For reflections, still the combination with the mirror image source method is proposed which is highly inefficient for higher orders. Stephenson’s energetic sound particle diffraction model is based on the uncertainty relation ('the closer the by-pass distance to an edge the wider the distribution of the diffracted secondary sound particles’). It has been well validated meanwhile by comparison with Svensson´s exact wave-theoretical secondary edge source model. In principle, it is capable to be efficiently applied for general cases of arbitrary reflection and diffraction orders. Meanwhile it has also been extended to 3D diffraction at edges of arbitrarily shaped apertures. In this paper, some more realistic cases of single and double diffraction are presented combined with geometric and diffuse reflections. The results of some numerical experiments are discussed. The new algorithm extends the spectrum of feasible cases of numerical noise immission prediction considerably.

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