Global sensitivity study on the semisubmersible substructure of a floating wind turbine: Manufacturing cost, structural properties and hydrodynamics

Abstract

Trading off the capital expenditure and dynamic performance of the substructure through optimization techniques is the key to wide application of floating wind turbines (FWT) in the energy industry. The optimization of floating substructure is a high-dimensional problem. Sensitivity analysis can help reducing the dimensions of design space by highlighting the most relevant design parameters to potential objective functions or to constraints, and increasing the understanding in the interrelationship of various parameters throughout the design space. This paper evaluates the influence of the hull main dimensions and mooring system parameters on the manufacturing cost, structural properties and hydrodynamics of a four-column semi-submersible FWT. Two widely-used global sensitivity analysis methods, the variance-based method and the density-based method, are employed to measure the sensitivity contributions of 10 design parameters. The column radius is found to be one of the most influential factors for substructure manufacturing cost and surge natural frequency, while the platform pitch and tower fore-aft natural frequency are more sensitive to column spacing. Regarding the hydrodynamics, column spacing, column radius and platform draft are the three of the most critical factors for the wave-frequency response in surge, pitch and tower top acceleration. The impact of draft is less significant in the case of low-frequency (second-order) hydrodynamic response, column spacing and radius are much more dominant. These results are confirmed by the visual inspection of the input-output samples. This information provides a new perspective to the FWT substructure design space and serves as a basis for the further sensitivity investigation on the long-term dynamic performance such as the peak platform tilting angle, nacelle acceleration, fatigue damage at tower base and fairlead.