Many analytical methods have been proposed to calculate hydroelastic responses of a very large pontoon type structure in waves. In relation to the elastic response of such pontoon type structure in waves, Isshiki and Nagata proposed four kinds of variational principles related to motions of the elastic floating plate on a water surface and clarified the mutual relationship of these variational principles. "Modified Hamilton-Dirichlet's Principle 2", which is expressed only using the velocity potential, is one of four kinds of variational principles for the motions of fluid and plate. In this paper, in order to calculate the wave-induced responses of an elastic floating plate in waves, a new method is proposed which uses the "Modified Hamilton-Dirichlet's Principle 2" and the eigenfunction expansion method for fluid motion. The velocity potentials in fluid regions with and without the plate are expanded by eigenfunctions in vertical mode which satisfy the governing equations and free-surface conditions, taking into account the presence of the plate in the same manner as Kim and Ertekin. This "Modified Hamilton-Dirichlet's Principle 2" is finally reduced to a variational equation which corresponds to boundary conditions on the plate's edge. The formulation of proposed method is applicable for the floating plate of arbitrary plan geometry. However, in this paper, as a 1st step of this study, calculated results for two kinds of floating plate of rectangular plan geometry in an open sea are compared with experimental results.

INTRODUCTION

Pontoon-type VLFS is one of the typical structural types of very large floating structures (VLFS). Various numerical methods have been proposed to predict the hydroelastic response of this structure in waves (Watanabe (2004), Chen (2006)). These methods are classified into the modal expansion method and the direct method. These analyses are carried out in the frequency domain or in the time domain.

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