Wave diffraction and radiation from a semi-submersible floating foundation for wind turbines: a semi-analytical study

Many marine structures are composed of vertical axisymmetric floats. In this paper, a semi-analytical model based on the linear potential flow theory and an eigenfunction expansion method is developed to study wave diffraction and radiation by an array of cylindrical structures. Each structure can be formed by three coaxial cylinders of different dimensions. Based on the semi-analytical model, a constrained matrix equation of motion is presented and solved to evaluate the performance of multiple interconnected cylindrical structures. In order to verify the accuracy of the semi-analytical model, a typical OC4-DeepCwind floating offshore wind turbine (FOWT) is selected for validation. The validated model is, then, applied to study the effect of base column submergence depth, radius, and thickness on the motion response of a semi-submersible platform. Although the results of this study are of significance for the selection of the optimum semi-submersible FOWT for specific locations (with specific prevailing wave directions), the focus of this work was placed on the semi-analytical model itself, which is efficient in modeling the interaction of the wave field and can be used in future FOWT projects.