Broadband 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 range 0.8<ω/ωr<12 (where ωr is the ring frequency for the shell). The ribs are arranged in a near periodic array with small random deviations in the rib locations of magnitude da/a=0.05. The physical processes that give rise to peaks in the scattering cross section are discussed and the ability of various theoretical models to predict the locations of the highlights is examined. The measurements provide further confirmation that the principle sources of scattering for typical ribbed shells in this frequency range are specular reflection, phase matching to fast membrane waves, phase matching to flexural Bloch waves, and Bragg scattering from the ribs. They also reveal that the scattered spectrum of the flexural Bloch waves can be more complicated than originally thought.