ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

5aSA4. Minimization of the sound power radiated by a cubic structure using velocity constraints.

Daniel H. Kruger

J. Adin Mann, III

Ted Weigandt

2019 Black Eng. Bldg., Iowa State Univ., Ames, IA 50011

Sound power radiated by a cubic structure as a function of normal surface velocity was written using the boundary element method [K. A. Cunefare and G. H. Koopman, J. Vib. Acoust. 113, 387--394 (1991)]. This function was minimized by a gradient method with linear and second-order velocity constraints. The constraints were formulated to reflect physical limitations in the ability of constrained layer damping material to modify structural velocity. Complex velocity phase was held constant while amplitude was allowed only to decrease. Initially, simulated velocity patterns were used to test the method and software created. Sound power reductions of 3 dB were achieved while modifying the normal velocity amplitude over only 0.46% of the surface area of the cube at a single frequency. Later, velocity of a real structure was measured using a laser vibrometer. Minimum sound power and corresponding velocity distributions were calculated for nondimensional ka ranging from 0.5 to 3.0. [Work supported by NSF, Contract No. MSS-9103377.]