In this paper, the forces acting on a large offshore structure in the presence of current have been investigated numerically. The velocity potential in a wave-current coexisting field can be separated into a steady current potential and an unsteady wave potential.
The unsteady wave potential with effects of both a uniform current and a large structure is calculated by using wavelet boundary element method. Non-orthogonal wavelets are used as shape functions in boundary integral equations. These kinds of wavelets have compact supports and closed-formed expression that have been proposed by authors. Besides one can choose the vanishing moments of the wavelets Independently of the order of B-splines. With use of non-orthogonal wavelets as shape function, many entries of matrix coefficients which contain kernel functions and the shape functions on the boundaries have small values and can be neglected without any effect on accuracy of solution. Sparse coefficient matrixes are obtained by truncating the small elements a priori. The Schneider’s level-dependent truncation schemes are used for this purpose which selects the truncated entries by comparing the predetermined threshold with the distance between the supports of two basis function.Comparison of the present results with those of Hsiao et al. (1999) are made. The agreement is satisfactory. The numerical model proposed here has its adaptability to the problem of waves, current and a large structure interaction.