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

4pPAb12. Structural and acoustic responses of mass-spring loaded elastic cylindrical shells: Numerical implementation.

Jin-Meng Ho

SFA, Inc., 1401 McCormick Dr., Landover, MD 20785

Naval Res. Lab., Washington, DC 20375

An important step in dealing with the mass-spring loaded cylindrical shell is to evaluate the total shell displacements at the attachment points, which determine the strength of the equivalent forces. Through dynamical balance at such points, these displacements satisfy a system of linear equations whose coefficients involve the shell displacements generated by on-surface forces of unit strength, a Green's-function problem with both source and observer located on the shell surface. It is thus evident that flexural waves, though subsonic, must be accounted for in the ray acoustic solution to the latter problem. Numerical examples show that they produce high Q intense resonances because of their extremely small radiation damping, which would be dominated by structural damping for dissipative shell material, imprinting their signature in the far field through radiation of the induced forces and carrying much of the information on the internal load. By including the flexural as well as membrane waves, the ray model accurately predicts the induced forces, the shell displacements, and the surface and far-zone pressures in the frequency range of interest; 1(less than or equal to)ka(less than or equal to)25 (where k is the fluid acoustic wave number and (alpha) is the shell mean radius). [Work supported by ONR.]