Scattering of a cylinder covered with an arbitrary distribution of admittance and application to the design of a tramway noise abatement system
Résumé
An urban low-height barrier meant to attenuate tramway noise emission for nearby walking pedestrians or cyclists is studied. A semi-analytical solution for the two-dimensional scattering of a line source by a cylinder covered by an arbitrary distribution of impedance and its image with respect to a vertical baffle is derived. This description is used to model the shadowing due to a semi-cylindrical noise barrier close to a tramway. This solution is used in a gradient-based optimization approach of the admittance distribution to maximize the broadband insertion loss in a given receiver zone. A feasible optimized surface treatment made of a porous layer and a micro-perforated resonant panel is proposed, with an improvement of 14 dB(A) with respect to an entirely rigid barrier. The optimization gain with respect to a uniform absorbent admittance is about 8 dB(A). Extra tests with the boundary element method show that this gain is reduced but still significant if more realistic conditions are considered.
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