STRUCTURAL AND ACOUSTIC RESPONSE OF MASS-SPRING LOADED CYLINDRICAL-SHELLS - SPECTRAL FORMULATION AND RAY SYNTHESIS

Ray techniques resolve individual physical mechanisms in describing wa ve radiation and scattering, and have been successfully applied to rep arametrize the sound field of source excited elastic shells immersed i n fluid but without internal load. Motivated on the same grounds, this paper reexamines, in ray acoustic terms, a submerged thin cylindrical shell mounted with an interior mass-spring oscillator. The formulatio n is facilitated by spectral theory, just as for the empty shell case. As is well known now, internal loading is equivalent to inducing forc es, and moments in more general situations, at the internal-shell join ts that act on the shell as external forces. However, the strengths of such forces are determined by the dynamical balance of the composite system at these joints, and may be ultimately expressed in terms of th e empty shell displacements excited (by unit-amplitude forces) and obs erved at the joints. Both flexural and membrane waves contribute to th e latter, and hence their distinctive characteristics evince in the ov erall response via radiation of the coupling forces. With the modified ray acoustic algorithm developed recently for near-field scattering, all the ray fields are represented uniformly over the entire azimuthal domain, and they yield accurate numerical results compared to the nor mal mode series in the frequency range 1 less than or equal to ka less than or equal to 25 considered here. (C) 1996 Acoustical Society of A merica.