The radiation and vibratory response of a fluid-loaded structure with high internal complexity

Abstract

Recently, experiments were reported in which complex internal structure was shown to dramatically influence the scattering cross section of fluid-loaded shells [Photiadis et al., J. Acoust. Soc. Am. 101, 895–899 (1997)] and where spatially varying local admittances were proposed to explain the observed scattering details [Bucaro et al., J. Acoust. Soc. Am. 100, 2721 (1996)]. Here, measurements of the vibratory response of this same structure [a ribbed shell with a large number (∼1000) of internal oscillators] are shown. Comparisons are made to the response of an identical shell with no internal oscillators. For the complex structure, no distinct pass and stop bands for any of the circumferential orders is seen, and a high degree of localization at all circumferential orders and frequencies is observed. Generally speaking, the wave-number-frequency plots associated with the complex structure are significantly different than those for the simple framed cylinder at all but the highest azimuthal components (n>17). Moreover, the wave-number decompositions of these data reveal a strong dominance of local bending in the response of the complex structure and evidence that strong coupling between the circumferential orders contributes to the significantly enhanced radiation levels. [Work supported by the Office of Naval Research.]