ABSTRACT

The Green's function method has been frequently used for wave force evaluation acting on three dimensional large offshore structures_ However, the numerical calculation of the method is not an easy task because of the complex nature of the Green's function. This paper provides an effective calculation method of the Green's function in the integral form which includes some singular points and the infinite integral. The program based on the proposed method has been developed for calculating wave forces acting on threedimensional floating (or fixed) body, and some numerical examples are presented.

INTRODUCTION

Recently, various types of offshore structures such as concrete gravity platform, floating airport, or floating bridge have been constructed or proposed. The evaluation of wave forces acting on them has been a critical problem for the design of such large offshore structures. For a large three-dimensional body having arbitrary shape, the Green's function method (or the source distribution method), which is based on the potential theory, may be the most frequently used one among the existing methods (Garnson. 1972. 1978. Clauss, 1992). However, there are several difficulties in the numerical calculation of the method because of the complex nature of the Green's function. The first difficulty is ill the calculation of the Green's function itself. and the second one is in the calculation of ß -matrix which is defined as an integral of the Green's function over a surface element of the structure. In order to apply the Green's function method to the practical problems, it has been desired to find more effective calculation method of the Green's function and the ß -matrix. In this paper, both the singularity of the integrand and the infinite interval, which are included in the Green's function of the integral form are avoided. An analytical solution of the ß -matrix under some special conditions is also deduced. Numerical examples for the wave forces acting on vertical circular cylinder. hemisphere. and horizontal cylinder as a semi-submerged floating foundation are also presented.

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