Numerical investigations on nonlinear effects of catenary mooring systems for a 10-MW FOWT in shallow water.

This paper presents a detailed investigation on the influences of different water depths and mooring parameters on the nonlinear responses of mooring systems and motion behaviors of a 10 MW semi-submersible wind turbine. To reduce computational effort, a developed mooring design and analysis program MOOR_SAD is used for quasi-static analysis, which is validated through comparing with the simulation results in OrcaFlex. The fully coupled dynamic numerical analysis is performed using OrcaFlex-FAST and validated through the comparison of numerical and experimental results of the NREL OC5 DeepCwind. Then, thirty mooring cases with different water depths and mooring parameters are studied for analyzing the nonlinear responses of chain mooring lines and motion performances of the 10 MW FOWT in shallow water. The results show that when the chain properties and pretension of the mooring lines are kept the same, the shorter mooring line leads to a stronger nonlinearity in mooring restoring force and stiffness. Besides, the weight of the mooring line has little effect on the mooring shape. This study could be expected to provide an engineering approach for mooring analysis and design of FOWTs in shallow water. • The effects of water depths on the nonlinear responses of mooring systems and motion behaviors of a FOWT are investigated. • Sensitivity analysis for the nonlinear effects of mooring parameters is conducted. • The design recommendations for the catenary mooring system of a semi-submersible FOWT in shallow water are proposed. [ABSTRACT FROM AUTHOR]