SOUND RADIATION FROM FINITE CYLINDRICAL-SHELLS, PARTIALLY COVERED WITH LONGITUDINAL STRIPS OF COMPLIANT LAYER

A vibro-acoustic model of a finite cylindrical shell partially covered with a compliant material layer is presented. The finite shell is ter minated by a cylindrical rigid baffle and is covered by strips of comp liant material lying parallel to the shell axis. The support shell mot ion is obtained by using Flugge's operator and the layer is taken to b e a locally reacting material having dissipative properties but withou t thickness. The whole system is excited by mean of a harmonic driving force applied to the supporting shell. In the infinite exterior mediu m, the acoustic pressure satisfies the Helmholtz equation. The acousti c pressure and the shell displacement are expanded in the eigenfunctio ns of the finite, non-covered, in vacuo, cylindrical shell. This leads to the construction of linear systems whose unknowns are the modal am plitudes of the pressure and of the shell displacement. If the cross-s ection of the partially covered shell has a plane of symmetry, the lin ear system splits into two independent, symmetric and antisymmetric pa rts. Nevertheless, each system displays coupling of circumferential or der, meaning that the problem is no longer axisymmetric, as the totall y covered problem was. Numerical results concerning acoustic radiation in water (radiated power) and shell vibration (radial quadratic veloc ity of the shell) are presented. They exhibit a surprising influence o f the partial covering of a shell by a compliant layer: namely, that p artially covering a shell in water can considerably increase the radia tion compared to that from the bare cylinder, in a frequency range loc ated well below the coincidence frequency. (C) 1995 Academic Press Lim ited