ASA 126th Meeting Denver 1993 October 4-8

4pSA4. Diffraction effects from the joining of two curved plates.

Douglas Rebinsky Andrew Norris

Dept. of Mech. & Aerosp. Eng., Rutgers Univ., P.O. Box 909, Piscataway, NJ 08855-0909

Acoustic scattering from a fluid-loaded shell consisting of two joined curved plates is considered. Asymptotic approximations are made based upon the assumption that the fluid wavelength is much shorter than the smaller radius of curvature. A plane wave in the fluid incident upon a line weld at which the shell properties and curvature are discontinuous, but the tangent is continuous, is considered. The problem simplifies by first assuming that the angle of incidence with respect to the tangent plane at the weld is not near the critical angle for supersonic membrane waves on either side of the weld. The discontinuity then generates a diffracted wave field in the fluid which is determined by solving a Wiener--Hopf problem. This background wave field in turn forces the ordinary differential equations describing the membrane waves. From their solution, diffraction coefficients are obtained for the membrane waves generated on each curved plate by the incident acoustic field. When the incident wave is close to one of the critical angles it couples directly to the shell waves via curvature, and the interaction of this launched membrane wave with the discontinuity results in scattered membrane wave fields with diffraction coefficients determined in a manner similar to the previous case. [Work supported by ONR.]