An efficient frequency-domain based methodology for the preliminary design of FOWT substructures

Abstract An efficient frequency domain numerical tool for the preliminary design of the Floating Offshore Wind (FOW) substructures is developed, and validated against one of the leading state-of-the-art time domain based numerical tools: OpenFAST. It has been proven that the present tool enables to reach to similar conclusions as the state-of-the-art tools with a substantial reduction of the computational effort. This is achieved through two novel methods that obtain the hydrodynamic loads acting on the floating substructures. One estimates the linear hydrodynamic coefficients, and the other predicts the second-order wave loads. When combined with a simplified frequency domain response model, a quick assessment of the dynamics of numerous platform designs can be performed, accelerating the floater preliminary design process. The proposed method has been validated by carrying out a comparative analysis on a semi-submersible platform design space, characterised by the column diameter, the separation between the columns and the platform draft. The response motions have been compared against OpenFAST. Furthermore, the high efficiency of the proposed frequency domain tool makes it suitable to perform several sensitivity analyses that will allow for a better understanding of the dynamics and fine tune the foundations design accordingly from the early stages of design.