Errors when assuming locally reacting boundary condition in the estimation of the surface acoustic impedance

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• 作者：Raffaele Dragonetti ; ^{dragonet@unina.it" class="auth_mail" title="E-mail the corresponding author} ; Rosario A. Romano
• 关键词：Surface acoustic impedance ; Porous material ; Non-locally reactive behaviour ; Locally reactive behaviour
• 刊名：Applied Acoustics
• 出版年：2017
• 出版时间：1 January 2017
• 年：2017
• 卷：115
• 期：Complete
• 页码：121-130
• 全文大小：953 K

文摘

Numerical simulations usually require boundary conditions in terms of surface acoustic impedance. The surface acoustic impedance depends on the porous material acoustic properties (e.g., characteristic impedance and wave number) and its thickness as well as the type of wave front impinging on its surface. The locally reactive behaviour hypothesis is often assumed to simplify the choice of proper boundary conditions assigning a constant acoustic impedance value on the porous material surface at a given frequency and for each angle of sound incidence. This hypothesis is also used in measurement procedures or for the estimation of the edge effects.

In this paper, it is shown that, in general, a porous material behaves partly as a locally reactive and partly as a non-locally reactive material depending on the ratio between the sound velocities in the free air and in the porous material. By using numerical FEM simulations it is shown that, given a porous material, the acoustic impedance may change or not along the material surface depending on the type of wave front that impinges on its surface.

The error when assuming the locally reactive behaviour for porous materials backed by a hard surface and planar incident wave front to compute surface acoustic impedance values has been investigated comparing results yielded by theoretical models available in the literature and the one proposed for non-locally reactive behaviour materials. The last one is validated by means of FEM simulations and experimental results.