ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

3aSA6. High-frequency threshold processes for leaky waves on cylinders of variable thickness: Fluid shell case.

S. F. Morse

Z. W. Feng

P. L. Marston

Dept. of Phys., Washington State Univ., Pullman, WA 99164-2814

To develop an understanding of high-frequency scattering processes by complicated elastic objects, it is helpful to identify benchmark problems which exhibit new kinds of leaky wave scattering contributions. It is found that scattering by a nonconcentric circular cylinder exhibits scattering processes not present in the simple case of uniform thickness. By application of a cylindrical harmonic addition theorem, the scattering was computed for a right circular fluid cylinder with a circular off-set vacuum core. The speed of sound in the fluid corresponded to the longitudinal velocity for steel and exceeded the speed for the outer fluid (water). For a uniform-thickness cylinder of sphere, previous calculations show a backscattering signature as the frequency was raised above the propagation threshold for the leaky waveguide mode analogous to the s[inf 1] Lamb wave [P. L. Marston, Phys. Acoust. 21, 1--234 (1992), Sec. 4.11]. When the thin part of a variable thickness shell is on the shadow side, the vicinity of the s[inf 1] mode threshold exhibits a new backscattering process due to mode cut off in the thin region and reversal of the associated ray. The local decrease in backscattering due to the thickness resonance is also affected. [Work supported by ONR.]