Abstract:

A test facility has been set up to study the effect of structural modifications on membrane waves in cylindrical shells. Previous research on submerged shells has shown the importance of membrane waves in the mid-frequency, high aspect angle regimes. These shear and compressional waves are important because they are the principle determinants of the shell's radiation and scattering properties. Flexural waves serve mainly as modifiers of the membrane waves because they are poorly coupled to the acoustic medium. The current test structure is a thin plastic shell. The advantages of plastic include higher damping, a lower compressional wave speed, and easy machining. Single modes up to n=6 are generated using an axisymmetric source array and the resulting accelerations are measured with an axial line array. The measured accelerations are separated into flexural, compressional and shear waves. Data collected on the unmodified plastic shell show excellent agreement with theory. Membrane and flexural waves in both forward and backward propagation directions are clearly seen. The experimental dispersion curves closely match theoretical predictions. Recent modifications to the shell involve the addition of an axial rib. Data from the modified shell will be presented. [Work supported by ONR.]