### ASA 127th Meeting M.I.T. 1994 June 6-10

## 5aUW6. Relation between the landing-launching coefficient and the
attenuation of surface waves propagating around an elastic cylindrical object.

**Jean-Marc Conoir
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*Lab. d'Acoust. Ultrason. et d'Electron. LAUE) URA 1373, Univ. du Havre,
Place R. Schuman, 76610 Le Havre, France
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**P. Millerat
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A. Derem
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*LCTAR, Velizy, France
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One approach for developing a physical understanding of the scattering of
sound from elastic objects in water is to use the Sommerfeld--Watson
transformation (SWT). Following the works of Uberall et al., it is known that
elastic objects resonances are due to a phase matching of the surface waves
propagating around the scatterer. What is more, resonance widths are related to
surface waves attenuation, thereby showing the close link between resonance and
surface waves propagation phenomena. According to the geometrical theory of
diffraction, surface waves are also characterized by a landing coefficient and
a launching one, both identical in the present case. This landing--launching
coefficient calculated from the SWT gives an indication, as resonance widths
and surface waves attenuation, on the coupling between the object and the
surrounding fluid. The purpose of this work is to determine an analytical
relation between the landing--launching coefficient and the attenuation of
surface waves. This relation comes from an identification between the
Breit--Wigner approximation of resonances and the Mittag--Leffler expansions
related to surface waves contribution. Thereafter, a method of identification
of the background introduced by Flax et al. in the acoustic scattering theory
has been developed.