The scattering of sound by objects buried in underwater sediments is studied in the context of an exactly soluble model. The model consists of two fluid half-spaces separated by a planar, fluid, transition layer of arbitrary thickness. Attenuation is included in any of these regions by using complex wave numbers. A directional source field, generated in the upper half-space by a continuous line array, insonifies an object placed in the lower half-space. The scattered field detected by another line array placed anywhere in the system may be calculated. The solution is determined from the T matrix for the bounded scattering system and is exact (in linear acoustics) to all orders of multiple scattering among the interfaces and object. Numerical results are presented to investigate the effect of the local acoustic environment on the free-field, in-water scattering resonances of thin spherical shells. The field scattered by a shallowly buried object is discussed with emphasis on the importance of evanescent wave scattering in detection from above the sediment over an extended range. An initial set of experiments meant to verify the model are described. Results are presented and discussed for the measured scattering response of buried, spherical, evacuated, steel shells, that are 2.25% and 11% of the outer radius in thickness.
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In a previous paper [R. H. Hackman, J. Acoust. Soc. Am. 75, 35–45 (1984)] a spheroidal-coordinate-based transition matrix formalism was established for acoustic and elastic wave scattering. In this paper, we consider the acoustic scattering by a solid elastic cylinder with hemispherical endcaps and a length-to-diameter ratio of 10. Numerical results are presented for the backscattered form function as a function of frequency for various angles of incidence. These results are compared with experimental measurements taken at the Naval Coastal Systems Center and given a physical interpretation.
In a previous paper [Roger H. Hackman, J. Acoust. Soc. Am. 75, 35–45 (1984)], a spheroidal-coordinate-based transition matrix formalism was established for acoustic and elastic wave scattering. In this paper, the acoustic scattering by a solid elastic cylinder with hemispherical endcaps and a length-to-diameter ratio of 10 is considered. Numerical results are presented for the backscattered form function as a function of frequency for various angles of incidence. These results are compared with experimental measurements taken at the Naval Coastal Systems Center and given a physical interpretation.
of the radial motion from the other two (which remain coupled) is the result of an intermediate perturbation expansion of the shell equations in terms of two parameters. The structurally diffracted field of the radial motion, delivered analytically by the new structural Kirchhoff scattering theory, becomes an extended source of sound that is now likewise available analytically. The predictions to be presented of the target strength of an internal partial frame in a cylindrical shell generalize those made by Rumerman for a full end frame [J. Acoust. Soc. Am. 93, 55-65 (1993)].
11:155aUW12. High-frequency scattering from a spherical shell: Thickness quasiresonance. Gary Steven Sammelmann (Code 130B, Coastal Systems Sta.,
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