Simplification of mooring line number for model testing based on equivalent of vessel/mooring coupled dynamics

To decrease the complexity of experimental setup that often results in low reliability of the experimental results for typical offshore floating structures with increasingly excessive mooring lines, a mooring line number simplification methodology is proposed based on equivalent of the vessel/mooring coupled dynamics for vessel with original and simplified mooring systems. The Non-dominated Sorting Genetic Algorithms-II (NSGA-II) is adopted to achieve the static restoring forces equivalent, where the line length, axial stiffness and submerged mass of the simplified mooring system are obtained. The line diameter is then determined based on dynamic restoring forces equivalent when the mooring system is exerted by forced oscillations. Using correlation coefficients, the vessel/mooring coupled dynamics of vessel with original and simplified mooring systems are compared to determine the optimal simplified mooring system. The feasibility of the proposed methodology is demonstrated by an application for a VLFS’s mooring system comprising 20 mooring lines. Two simplified mooring systems are obtained with the correlation coefficients of coupled vessel/mooring dynamics lager than 0.97. It can be concluded that the proposed method can be used as a useful tool to guide mooring line number simplification for model testing.