ABSTRACT

A finite element method is developed for the time domain analysis on the hydroelastic deformation of a pontoon-type very large floating structure with fully nonlinear free surface conditions. A three-dimensional free surface flow is formulated in the scope of potential flow theory with the nonlinear free surface conditions. To describe the motion of VLFS the Mindlin plate modeling is adopted. The equation of plate motion is discretized by finite elements using virtual work principle and integrated by Newmark method. To consider the fluid-structure interaction, the nonlinear free surface motion and the plate motion are numerically solved through an iterative method at each time step.

INTRODUCTION

To utilize the ocean space effectively, it is of great importance to investigate the dynamic response related to the safety and reliability of very large floating structure. In spite of much previous research (Watanabe et al.,2004, Kashiwagi,1998,1999) on hydroelastic response of a pontoon-type VLFS, there is still much work to be done. One thing is to consider the effect of nonlinear waves on hydroelastic response of VLFS. In case of extreme situations such as a large storm, the frequency domain analysis based on the linear theory is not appropriate. Therefore a time domain analysis is required to investigate the dynamic response of VLFS under such an extreme condition.

There are some previous researches on the time domain analysis of the hydroelastic response of VLFS. Endo & Yago(1999) have carried out a series of weight dropping test and also developed a time-domain analysis method based on FEM scheme. Their FEM scheme utilized the memory effect function for hydrodynamic effects. Watanabe et al.(1998) presented a transient response analysis of a VLFS due to impulsive landing of an airplane by finite element method. Ohmatsu(1998) has analyzed the transient response of VLFS by using an impulse response function.

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