Aerodynamic and hydrodynamic investigations on linear upscaling and optimization of floating offshore wind turbines

This study presents the procedure of upscaling Floating Offshore Wind Turbines (FOWTs) atop a semisubmersible platform using linear scaling. NREL 5 MW, IEA 10 MW, and IEA 15 MW reference wind turbines, together with OC4 DeepCwind semisubmersible platform, are used as baselines and upscaled up to 20 MW. Upscaled NREL 5 MW rotor blades are further optimized using HARP_Opt to obtain higher power and Co_Blade is used to obtain the best structural and composite material layup. Unsteady simulations of the turbines are performed using OpenFAST under different wave conditions and their performances are compared. It is found that upscaling FOWT is feasible and beneficial. Upscaling process increases the natural period and decreases the Response Amplitude Operator (RAO) of the FOWT. The power produced by optimized turbines with similar blade lengths as linearly scaled blades is conservative, although the power coefficient is higher. Further increasing the blade length more than linear scaling results in better performance with higher power production.