Optimization of a Four-Column Semi-Submersible Platform for a 16 MW Wind Turbine

Abstract The study aims to establish a sound basis for platform optimization of semi-submersible floating wind platforms for large-capacity wind turbines by systematically assessing the key structural and dynamic performance drivers. A four-column semi-submersible platform with a centrally located turbine (w.semi-c) is investigated under metocean conditions representative of the Celtic Sea, and benchmarked against a geometrically comparable three-column semi-submersible platform (w.semi) designed for the same 16 MW turbine. Within a constrained benchmarking scope, column spacing is adopted as a representative geometric parameter, while other principal dimensions are kept constant for consistency and comparability. The evaluation focuses on structural eigenfrequencies, hydrostatic stability, frequency-domain responses in free-floating conditions, and time-domain responses under operational and survival conditions. The results indicate that the w.semi-c achieves a stiff-stiff structural design without diagonal braces and provides significantly greater separation between the structural natural eigenfrequency and the turbine 3P excitation, demonstrating a clear structural advantage for large-capacity turbines. Hydrostatic analyses indicate slightly better initial stability for w.semi-c, while w.semi exhibits superior large-angle stability. Frequency- and time-domain analyses further demonstrate that w.semi-c provides better yaw and offset performance, whereas w.semi generally exhibits small tilt responses, reduced nacelle accelerations, and lower mooring tensions under survival conditions. Directional time-domain analyses further show that w.semi-c maintains more robust responses across different environmental headings, without altering the overall performance trends. Both concepts demonstrate good dynamic responses under operational conditions. These findings provide insights into potential trade-offs among structural dynamics, stability behavior, and coupled motion responses associated with different semi-submersible configurations, and provide guidance to support the concept selection and optimization of semi platforms for next-generation large floating wind turbines.