Optimization of Heave Motions for a Four Column Semi-Submersible Based on Genetic Algorithm

Semi-submersible is designed with low heave motions compared with conventional ships by utilizing the cancelation effects between pontoons and columns. During the past years, continuous efforts have been devoted to reducing the heave amplitudes considering utilizing dry-tree system. Different concepts of semi-submersible have been proposed with favorable heave response. Deep draft semi-submersibles have been proved to be efficient in reducing the heave motions, and the damper structures under the pontoon may also reduce the heave responses significantly. Those concepts are beyond the conventional semi-submersible design, which may bring high costs for fabrication and installations. During computer-aided design and analysis, optimization algorithms are used to search for the optimal hull configuration. However, due to the restrictions of computer capacities, the global optimization algorithm, in some cases, have difficulties in finding out the optimal solutions without the aid from engineering experience. In this paper, the geometry of a ring-pontoon four-column semi-submersible is generated by parametric modelling. The heave transfer functions at center of gravity are calculated using WADAM. Genetic algorithm is used to find the most favorable heave responses. In the end, the parameters that influence the heave motions are summarized and discussed.