ASA 126th Meeting Denver 1993 October 4-8

4aSA3. An efficient method for designing quiet composite structures via material tailoring.

Jung Bae Oh Gary H. Koopmann

Ctr. for Acoust. and Vib., Penn State Univ., University Park, PA 16802

An efficient design method is successfully developed for achieving structures that radiate minimum acoustic power based on a material tailoring. First, the far-field acoustic power of a planar radiator is written as a quadratic expression in terms of the Rayleigh--Ritz formulation. Second, a complete acoustic power design sensitivity is developed analytically that is needed to find a search direction for the improved design. This analytical sensitivity significantly reduces computation time as compared to the finite difference scheme and provides an exact design sensitivity information. The formulations for acoustic power and design sensitivity are coupled together within the numerical optimization code, CONMIN, to minimize acoustic power radiated from a planar surface subject to various excitation conditions via local thickness tailoring. The design of quiet structures for general conditions---harmonic point excitation, uniformly distributed harmonic acoustic loading, and random acoustic loading---in the given frequency band is achieved successfully. Results on various test cases show that the hybrid composite structure is the most promising material for minimizing radiated acoustic power. The optimum hybrid composite plate shows that the radiated acoustic power can be reduced up to 10 dB on various test cases.