Application of Direct Boundary Element Method to Three Dimensional Hydrodynamic Analysis of Interaction Between Waves and Floating Offshore Structures

Abstract

A three-dimensional hydrodynamic analysis of interaction between a floating offshore structure and sea waves has been carried out using a novel approach which is based on the weighted residual technique and the direct boundary element method. The main advantage of the direct boundary element method is the fact that one can determine the total velocity potential directly. Direct BEM is more versatile and computationally more efficient than indirect BEM. Besides, the BEM can easily be coupled with other numerical methods, e.g. finite element method (FEM) in order to carry out structural analysis of deck of the platform due to impact. Firstly, the boundary value problem of three-dimensional interaction between regular sea waves and a semi-submersible will be described. Secondly, the direct boundary element method has been applied to predict hydrodynamic behaviour of Khazar Semi-Submersible Drilling Unit (KSSDU), which is the largest semi-submersible drilling platform under construction for a location in the Caspian Sea, North of Iran. The rigid body motion responses in six degrees of freedom of KHAZAR semi-submersible in response to encountering waves have been calculated by using the direct boundary element method. The results obtained from the direct BEM will be compared with those obtained by the results based on the conventional boundary element method (indirect BEM) which were obtained by the designers of KHAZAR semi-submersible.