| Summary: | 碩士 === 國立臺灣大學 === 造船及海洋工程學研究所 === 88 === Abstract
The hull whipping is the flexing motion of the whole hull structure. The pulsation of gas bubble can change the pressure field in its surrounding fluid, and induce the impact pressure on hull surface. In this paper, a mode superposition approach is used. The dynamic response for the significant mode is solved prior, the dynamic response of which structure is then approximated by linear superposition of these modes. The natural frequencies and mode shapes of structure in air are analyzed by 3-D FEM, the velocity potential of each vibration mode under bubble pulsation is solved by 3-D BEM.
First, a doubly asymptotic equation of motion (DA EOM) for bubble dynamics is adopted which is derived from the motion equation using the principle of energy conservation with the effect of fluid compressibility. A suitable initial condition for DA EOM is derived from the combination of DA EOM and empirical shock pressure function. We use LS/DYNA to simulate the motion of bubble to compare the results. The whipping response of ship structures caused by the bubble pulsation is then calculated by mode-superposition method. We build the 3-D FEM model for the modal analysis. The modal velocity potential function is calculated by 3-D BEM, in which the boundary condition on hull surface is adopted from mode shape analyzed by FEM. The pressure acting on hull surface is derived from velocity potential function, and transferred into two parts: an added modal mass and a bubble pulsation force.
A submerged cylindrical shell and a floating cylindrical shell are employed to illustrate the analysis procedure.
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