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

5aUW7. Scattering by an elastic shell with nonconcentric cylindrical surfaces: Generalized Debye series expansion.

E. Danila

J.-M. Conoir

J.-L. Izbicki

Lab. d'Acoust. Ultrason. et d'Electron. LAUE), URA CNRS 1373, Univ. du Havre, Place R. Schuman, 76610 Le Havre, France

The scattered pressure by a solid elastic shell defined by two nonconcentric cylindrical surfaces is considered; the cylinder axes are parallel. The shell is immersed in a fluid and is excited by a monochromatic plane wave impinging on it normally to the axis. The generalized Debye expansion (GDE) formalism is used to physically analyze all the local interactions involving in the scattering process. Two cylindrical coordinate systems, each associated with one cylindrical surface, are introduced. With this choice, all the needed cylindrical wave functions can be written either in one system or the other thanks to the Graf addition theorem and the boundary conditions can be simply expressed; the scattered pressure can be calculated. It is also possible to relate the elements of the S matrix to the local interaction coefficients, i.e., reflexion and transmission modal coefficients coming from the GDE. In next future, it allows to obtain an expression of the background which is useful to calculate the target resonances.