ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

2aSA11. Acoustics wave diffraction on a cylindrical shell with two local masses.

Rostislav A. Dudnik

Andrei B. Kolpakov

Dept. of Phys., Inst. Arch. & Civil Eng., 65 Il'inskaya St., 603600 N.-Novgorod, Russia

The diffraction of a plane sound wave on a thin cylindrical shell having inhomogeneity presented by two identical inertia masses fastened symmetrically on its surface is considered. It is shown that the field scattered by such a shell presents a superposition of the fields radiated by both the symmetrical and antisymmetrical low-frequency azimuth modes excited depending on the direction of initial wave propagation toward the vertical plane of the shell symmetry ((Phi)=0; (Phi)=180). In support of the existence of corresponding nonsingular normal velocity distributions, a specialized experimental investigation was carried out for the force-excited shell models. The experimental investigation of near as well as far acoustical fields of these shell was executed also. The calculation results of frequency responses and directionality diagrams of the field scattered by the shell with two masses fastened diametrically opposed at the initial only symmetrical oscillations are presented. These results are compared with analogous results for the shell having one inertia mass (at (Phi)=180). It was found that the radiation level control is possible for the investigated oscillation structure by such division of a unit inhomogeneity in certain frequency diapasons.