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Doctoral Dissertation Announcement
Candidate: Nabeel T. Alshabtat
Doctor of Philosophy
Department: Mechanical and Aeronautical Engineering
Title: Beading and Dimpling Techniques to Improve the Vibration and Acoustic Characteristics of Plate Structures
Dr. Koorosh Naghshineh, Chair
Dr. Judah Ari-Gur
Dr. Tarun Gupta
Dr. Peter Gustafson
Date: Monday, June 13, 2011 2:00 p.m. to 4:00 p.m.
Parkview Campus, Room D-210
A method of improving the vibration and acoustic characteristics of beams and plates based on creating surface dimples or beads is presented in this study. This method couples the finite-element method with an optimization technique based on the genetic algorithm (GA). The improvement of the vibration and acoustic characteristics of beams and plates is achieved by two separate strategies: the first strategy is optimizing the natural frequencies of beams and plates, and the second one is minimizing the sound radiation from such vibrating structures.
The simulation results indicate 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. When using beads, this change depends on bead location, size, and orientation. The optimal designs of dimpled and beaded beams and plates are presented separately.
The reduction of the sound radiation from vibrating beams and plates by creating dimples and beads is also explored. 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 one of its natural frequencies, and the second one is the minimization of the sound power of a vibrating plate at a fixed frequency. The optimization examples prove the efficiency of beading and dimpling techniques in designing quiet plates at a specific frequency.