Development of a model for an offshore wind turbine supported by a moored semi-submersible platform
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Wind energy is one of the fastest growing sources of renewable energy in the world. There has been a lot of research, development, and investment in wind energy in recent years. Offshore sites offer stronger winds and low turbulence, along with fewer noise and visual impacts. Establishing large turbines at deepwater sites offers promising opportunities for generating high power output while utilizing the favorable environmental conditions. Researchers at Sandia National Laboratories (SNL) have developed a very large wind turbine model with a 13.2 MW rating that has 100-meter long blades; this turbine is designated as the SNL100 13.2 MW wind turbine. With a hub height of 146 meters and a rotor diameter of 205 meters, such a large turbine is best suited for offshore sites. Developing a wind turbine model for an offshore site requires that a platform model be developed first. Of the various kinds of floating platforms, a moored semi-submersible platform supporting the wind turbine, which offers stability by virtue of the intercepted water-plane area, is an appropriate choice. The goal of this study is to develop a semi-submersible platform model to support the 13.2 MW wind turbine, while keeping loads and deflections within safe limits. The platform is developed based on work completed as part of the Offshore Code Comparison Collaboration Continuation (OC4) Phase II project, which involved a 5 MW wind turbine supported by a semi-submersible platform. The present study focuses on three important topics: (i) development of the combined offshore wind turbine system model with the 13.2 MW wind turbine, a floating semi-submersible platform, and a mooring system; (ii) the entire procedure involved in modeling and analyzing first-order hydrodynamics using two codes, MultiSurf and WAMIT; and (iii) assembling of the integrated aero-hydro-servo-elastic model considering hydrodynamics in order to verify the steady-state and stochastic response of the integrated wind turbine system.