Date of Award

1-2011

Degree Name

Doctor of Philosophy

Department

Mechanical and Aeronautical Engineering

First Advisor

Dr. Koofosh Naghshineh

Second Advisor

Dr. Judah Ari-Gur

Third Advisor

Dr. Peter Gustafson

Fourth Advisor

Dr. Tarurt Gupta

Abstract

A method of improving the vibroacoustic characteristics of beams and plates is presented. This method is based on creating dimples or beads on the surface of the structures. The proposed method couples the finite element method with an optimization technique based on the genetic algorithm (GA). The improvement of the vibroacoustic characteristics of beams and plates is achieved by two separate strategies. The first strategy is optimizing the natural frequencies of beams and plates. The second strategy is minimizing the sound radiation from such vibrating structures. Optimizing the natural frequencies of some types of beams and simply supported plates by creating dimples and beads on their surfaces is investigated. The simulation results indicated that creating cylindrical dimples on simply-supported, free-free, and cantilever beams decreases their fundamental frequencies, while creating dimples on a clamped beam may increase its fundamental frequency. Furthermore, creating spherical dimples or cylindrical beads on the surface of a simply-supported plate increases its fundamental frequency. The change in plate fundamental frequency depends on dimple location and size, as well as on bead location, size, and orientation. The optimal designs of dimpled and beaded beams and plates are presented. The reduction of the sound radiation from vibrating beams and plates by creating dimples and beads is also investigated. The main effect of creating beads or dimples is the significant change in the beam or plate mode shapes (especially the higher order mode shapes). The change of the mode shape plays a significant role in the mechanism of volume velocity cancellation, which causes a reduction in the sound power. Two cases of optimization problems are considered: the first case is the minimization of the sound power of a vibrating plate at a natural frequency, and the second is the minimization of the sound power of a vibrating plate at a fixed frequency. The optimization examples proved the efficiency of beading and dimpling techniques in designing quiet plates at a specific frequency.

Access Setting

Dissertation-Open Access

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