| Summary: | 碩士 === 淡江大學 === 機械與機電工程學系 === 92 === The influence of edge restraints on the sound absorption coefficient of porous materials is studied in this thesis. Instead of the use of air for actuating the porous materials, a uniformly distributed impulsive pressure is directly applied on the surface of the porous materials in the study. Through the Laplace domain finite element method, the surface acoustic impedance of porous materials is directly obtained and the sound absorption coefficient is calculated accordingly.
The sound absorption characteristics of porous plates with different thickness subjected to the influence of rolling as well as fixed boundary restraints are first studied. Two and three dimensional Laplace domain finite element methods are used for analyses, then one dimensional theoretical solutions and two microphones impedance tube experiments are used for verifications. Results show the increase of thickness or frequency will change the restraint of specimens gradually from rolling to fix. During the changing of restraint, the sound absorption coefficient is remarkably affected.
The Laplace domain finite element method is further applied for study the corrugated porous plates subjected to the influence of boundary restraints. Porous plate with symmetric and asymmetric wedge, elliptic, and pyramid surfaces are analyzed and optimal dimensions with the best sound absorption performance are also acquired. On the basis of same material and volume, it is found plates with wedge surface are superior to plates with pyramid surface in low frequency region, but on the contrary in mid- and high frequency regions. Moving the wedge tip of plates with asymmetric wedge could improve the sound absorption coefficient. The sound absorption frequency range of plates with elliptic surface is concentrated in a certain frequency band.
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