Simplified load estimation and sizing of suction anchors for spar buoy type floating offshore wind turbines

Floating offshore wind turbines are complex dynamic structures, and detailed analysis of their loads require coupled aero-servo-hydro-elasto-dynamic simulations. However, time domain approach used for such analysis is slow, computationally expensive and requires detailed data about the wind turbine. Therefore, simplified approaches are necessary for feasibility studies, front-end engineering design (FEED) and the early phases of detailed design. This paper aims to provide a methodology with which the designer of the anchors can easily and quickly assess the expected ultimate loads on the foundations. For this purpose, a combination of a quasi-static wind load analysis and Morison's equation for wave load estimation using Airy waves is employed. Dynamic amplification is also considered and design load cases are established for ultimate limit state (ULS) design. A simple procedure is also presented for sizing suction caisson anchors. All steps are demonstrated through an example problem and the Hywind case study is considered for such purpose.