BROAD-BAND ACOUSTIC SCATTERING FROM A RIBBED SHELL

Monostatic acoustic scattering measurements have been made on a large aspect ratio (L/D = 6.2) ribbed cylindrical shell over the frequency r ange 0.8<omega/omega(r)<12 (where omega(r) is the ring frequency for t he shell). The ribs are arranged in a near periodic array with small r andom deviations in the rib locations of magnitude d alpha/alpha = 0.0 5. The physical processes that give rise to peaks in the scattering cr oss section are discussed and the ability of various theoretical model s to predict the locations of the highlights is examined. The measurem ents provide further confirmation that the principle sources of scatte ring for typical ribbed shells in this frequency range are specular re flection, phase matching to fast membrane waves, phase matching to fle xural Bloch waves, and Bragg scattering from the ribs. They also revea l that the scattered spectrum of the flexural Bloch waves can be more complicated than originally thought. (C) 1995 Acoustical Society of Am erica.