水中同心2重円筒の振動における内部流体による流体-構造カップリング

概要

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Vibrational characteristics of a point-driven "double shell"(two concentric submerged cylindrical shells coupled by the entrained fluid)are investigated. Strong- and weak- coupling theories are proposed to model the interaction of how the inner and outer shells are coupled by the entrained fluid. Each theory is based on Flugge's infinite-shell equation, the Helmhltz wave equation, and boundary conditions at the fluid-structure interfaces which depend on the coupling situation. Strong coupling forms a standing wavefield in the entrained fluid;weak coupling, a free wavefield. Experiments are carried out where generalized near-field acoustical holography(GENAH)is employed to provide the experimental vibration characteristics in wavenumber-frequency space of the finite double-shell. It is confirmed theoretically and experimentally that the outer shell of the double shell exhibits two separate dispersion curves:A higher-frequency curve bears in-phase vibrations with respect to the inner shell and suggests a forced response of the inner shell:the other lower-frequency curve, out-of-phase vibrations, and an induced response of the other shell. Fluid-structure coupling condition definitely affects the lower-frequency curve, but barely the higher-frequency one. Comparison between theoretical and experimental results demonstrates the validity of tha strong-coupling model.
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