Design loads for a large wind turbine supported by a semi-submersible floating platform

The dynamic response and reliability analysis of a 13.2 MW offshore wind turbine supported by a moored semi-submersible platform is the subject of this study. Loads data for the extreme response analysis involve time-domain simulations for a range of sea states representative of expected site-specific metocean conditions. To gain deeper insight into the dynamic behavior of this system and to obtain long-term loads efficiently and accurately, two studies are carried out sequentially. First, the short-term response of the integrated system is studied based on 1-h simulations for sea states identified using the Environmental Contour method for a 50-year return period. Response extremes for the integrated wind turbine system as well as system sensitivity to metocean conditions are studied. Next, the long-term response associated with the 50-year return period is estimated using statistical extrapolation based on loads derived from the 1-h simulations. Inverse First-Order Reliability Method procedures are employed to seek appropriate response quantile levels, e.g., the median response for 2D Inverse FORM. A more comprehensive 3D approach, which accounts for system response uncertainties, improves long-term response estimates. A proposed adaptive procedure in the 3D approach helps determine the number of simulations needed to guarantee accuracy in the long-term response estimation. (C) 2019 Elsevier Ltd. All rights reserved.