Optimal Design And Analysis Of Mooring Lines For Shallow Water Floating Wind Turbine

The mooring line is an integral part of the floating turbine mooring system and plays a vital role in the stability of the floating turbine platform.When the floating turbine is moored in shallow water,there will be problems such as excessive platform response and insufficient response force.The research object of the paper is the Longyuan floating wind turbine and its mooring system undertaken by CIMC Raffles,which is installed in shallow water at a depth of35 meters.In view of its shallow water mooring response force is insufficient,the platform response is too large and so on,the optimization research of the floating wind turbine mooring system scheme is carried out.The main research contents are as follows:Based on the Morison equation and the finite element method,a time domain coupled numerical simulation model of the Longyuan floating wind turbine and its mooring system was established to calculate and analyze the hydrodynamic results such as amplitude response operator,radiation damping and additional mass,and to analyze the effect of water depth change due to high and low tide on the response of the floating wind turbine platform and the mooring tension to understand the motion law of the Longyuan floating wind turbine.A static optimization algorithm is prepared using NSGA-II genetic algorithm to narrow down the initial parameter range with limiting the maximum tension of the floating wind turbine platform and mooring line as the objective function.Then the dynamic optimization is performed in the reduced parameter range,with the cost minimization as the objective function and the constraints of limiting the turbine platform motion and the maximum mooring line tension,and the OC4-Deep Cwind semi-submersible platform and NREL offshore 5MW wind turbine are used to verify that the program is optimality seeking.The validated optimization procedure was applied to the Longyuan floating wind turbine mooring line to optimize the design parameters such as mooring chain length,axial stiffness and wet weight of Longyuan floating wind turbine mooring line,to carry out static optimization and dynamic optimization,and to compare the optimized mooring system with the original mooring system motion data,and found that the optimized floating wind turbine platform response and mooring tension meet the specification requirements and are better than the original mooring system,proving that the optimized mooring solution has better performance.Finally,the platform response and mooring tension of the Longyuan floating wind turbine with the optimized mooring system were calculated under the broken cable condition to ensure the safety of the Longyuan floating wind turbine under the broken cable condition and to provide a reference for the subsequent mooring system optimization design of the CIMC Raffles.