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

3pSA5. Dispersion of longitudinal waves in periodic septate liquid--elastic waveguides.

L. Sheiba

EG&G WASC, Inc., 1396 Piccard Dr., Rockville, MD 20850

The propagation of longitudinal waves in a composite liquid--elastic waveguide is analyzed. The waveguide is a periodic structure consisting of alternating liquid--elastic cylinders joined by rigid septa. The elastic material (Lame constants: (mu)<<(lambda), Poisson relation (sigma)(implies)0.5) and the liquid material ((mu)=0, (sigma)=0.5) are assumed to have low compressibility, and the septa are rigid and weightless. Consequently, the boundary between the cylinder and the septum's radial displacement is absent, and the axial displacements are planar. The admittance matrix Y of the unit cylinder is initially constructed within a framework of the hypothesis of plane cross sections, neglecting strains induced by hydrostatic stress. Hydrostatic stress waves are approximately included by adding to the unit cylinder admittance matrix correction (Delta)Y associated with the strains of hydrostatic stress in the cylinder. Transfer matrix of the liquid--elastic waveguide and its elements, expressed through the waveguide sections elastic parameters, have been obtained. It has been shown that damping in a waveguide with a periodic structure is much greater in comparison with a regular waveguide, even when the latter is made with a high-loss material.