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

1pUW5. Modeling and analysis of three-dimensional scattering from Arctic Ice features.

Tarun K. Kapoor

Henrik Schmidt

Dept. of Ocean Eng., MIT, Cambridge, MA 02139

Interpretation of low-frequency acoustic scattering data from Arctic Ice is facilitated with realistic models of the large-scale features observed under the ice sheet. Previous analyses have modeled these, for example, as a hemispherical protuberance on an an infinite plane. Here, the under-ice feature is modeled as a solid elastic sphere attached in the center of a thin elastic plate. The sphere is assumed to be completely submerged in water while the plate is assumed to be floating on water. The interaction between the plate and sphere is characterized in terms of equivalent coupling forces and bending moments at the attachment ring which are determined by matching the kinematics of the sphere and the plate at the junction. At our frequencies of interest [ka~O(1)], the model demonstrates scattering of the sphere modes into the in-plane and out-of-plane motions of the plate. A comparison will be made between the scattered fields from the free and coupled spheres. The analytical results will also be compared with those obtained from the CEAREX89 scattering experiments conducted in the Central Arctic region with 1.8-lb SUS charges detonated at nominal depths of 800 ft. [Work supported by ONR, High Latitude Program.]