Measurement and modeling of micro-perforated panels

Kang Hou, Purdue University

Abstract

As a promising noise control material, micro-perforated panel absorbers satisfy the trend towards a greener environment and energy efficiency. Any thin, planar material, when perforated with sub-millimeter pores of a certain depth and combined with a finite-depth air space, can be a good noise absorber. Compared with traditional porous (i.e., fibrous) materials, a micro-perforated structure is more friendly to the environment and more resistant to severe working conditions. The fundamental absorption mechanism of these systems is investigated here, including a discussion of pore end corrections. The Maa model has been successfully applied to the design of practical micro-perforated (MPP's) absorbers. However, recent studies have shown that a rigid perforated plate can be modeled as an equivalent fluid following the Johnson-Allard approach when an equivalent tortuosity is defined appropriately. In this thesis, a new finite element model of micro-perforated panels is proposed. By using existing finite element models of rigid porous materials, it has been shown that the acoustic properties of rigid micro-perforated panels can be successfully predicted. Furthermore, that approach can be extended to flexible micro-perforated panels, which can be modeled similarly by using poro-elastic finite elements. The finite element predictions were found to agree well with both measurements and analytical, planar models that allow for panel flexibility. Moreover, the finite element models are particularly useful when dealing with complex configurations and geometries, such as curved panels and segmented backing spaces. Accurate acoustical measurements of micro-perforated panels were implemented in the process of model validations. With the advance of standing wave tube measurements, the latest four-microphone measurements can provide more accurate estimates of material properties than could be obtained using the two-microphone method. Some concerns related to standing wave tube measurements are discussed, including correction for microphone mismatch, tube attenuation and the effect of circumferential boundary conditions. Several calibration methods for the standing wave tube are proposed to make this technique more reliable and accurate.

Degree

M.S.E.

Advisors

Bolton, Purdue University.

Subject Area

Mechanical engineering

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