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

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

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