ASA 127th Meeting M.I.T. 1994 June 6-10

3pSAa1. Sound radiation from two semi-infinite dissimilar plates subject to a harmonic line force excitation in mean flow. Part I: Theory.

Sean F. Wu

Jinshuo Zhu

Dept. of Mech. Eng., Wayne State Univ., Detroit, MI 48202

Formulations are derived for predicting sound radiation from two semi-infinite dissimilar plates subject to a line force excitation at the joint in the presence of mean flow using the Wiener--Hopf technique and Fourier transformations. The acoustic pressure is solved in the wave-number domain first and expressed in terms of decomposition factors and eight parameters associated with displacements, slopes, bending moments, and shear forces at the joint of two plates. The decomposition factors are evaluated via contour integrations, and eight parameters are determined by a set of simultaneous equations derived from boundary conditions and the finiteness requirement imposed on the joint. It is shown that the set of equations reduces to a 2x2 matrix for a welded joint, a 3x3 matrix for a hinged joint, and a 4x4 matrix for a free--free joint, i.e., two plates being mechanically unconnected. The frequency-domain acoustic pressure is subsequently obtained by taking an inverse Fourier transformation, and expressed as a sum of residues enclosed by a deformed contour plus contributions from integrations along the branch cut. Asymptotic behaviors of the plate flexural displacement and acoustic pressure in the frequency-wave-number domain are obtained. Effects of mean flow on resulting sound radiation are examined. [Work supported by ONR.]