Design optimization and upscaling of a semi-submersible floating platform

This work examines the procedure of optimizing and upscaling a semi-submersible platform in order to support a predefined wind turbine. Particular challenges related to the design criteria for floating platforms and to technical changes in the turbine design are addressed. The designed floating systems are evaluated regarding their eigenfrequencies, nominal pitch, stability and global performance in selected sea states, using three different analysis methods (simplified spreadsheet calculations, linear frequency-domain analyses in DNVs software HydroD, and detailed time-domain equation-based models in Modelica). By means of the guideline for optimization and upscaling, presented here, support structures for 7.5 MW and 10 MW wind turbines are developed based on a 5 MW design. The procedur e allows for improved stability and dynamic performance compared to the baseline design, while also increasing the design efficiency. The optimization process yields a more than 10% lighter total system, which represents a more cost-effective floater solution for the 5 MW wind turbine. The natural periods are increased during optimization from original 17.3 s in heave and 27.0 s in pitch to 20.4 s and 34.7 s, respectively. This improved eigenfrequency performance of the floating system is maintained during upscaling.