Nearfield acoustic radiation from stiffened cylindrical shells

Abstract

Sound radiation from plates and shells has usually been studied in the farfield. As far as nearfield radiation is concerned, only a few results are known. A modal method is presented, which allows the computation of nearfield components. The movement of the shell is expanded on the basis of the in?vacuoeigenmodes. The nearfield pressure is calculated for every vibration mode [this implies a difficult integration over the axial wavenumber). Summation over the modes leads to the whole pressure radiated. It will be shown that pressure magnitude does not steadily decrease with radius r, but minima and maxima pressure occur. Particular attention is paid to the efficiency of different circumferential modes and their contributions to the nearfield pressure. Furthermore, the distance from the shell, at which it is not absolutely necessary to take into account the reactive field, can be evaluated. Results are presented that show that nearfield acoustic radiation is directly connected to surface vibrations. [Work supported by Thomson Sintra, Valbonne, France.]