A Problem of Long Period Yaw Motion of an Ultra-Large Floating Offshore Wind Turbine and its Reduction Countermeasure

Abstract

Abstract In June 2022, the New Energy and Industrial Technology Development Organization (NEDO) of Japan created a 2 trillion yen “Green Innovation Fund” in June 2022. The fund will “develop technologies for wind turbines and floating structures that are suited to Asian weather and ocean conditions for floating wind turbines, which are expected to expand in the medium to long term, and demonstrate the integrated design of wind turbines, floating structures, cables, and other components with a cost level that can compete globally, leading to their social implementation”. The demonstration of floating wind turbines in actual sea areas in Japan has been conducted off coast of Fukushima Prefecture, off coast of Goto in Nagasaki Prefecture, and in the Hibikinada Sea in Fukuoka Prefecture, where technological accumulation and investigation toward commercialization are being conducted. While the rated power generation capacity of these demonstration wind turbines is 2–7 MW, the rated power generation capacity envisioned in the above-mentioned fund is 15 MW, and the specifications for the design of floating structures to accommodate ultra-large wind turbines have become more stringent. As a new issue, it is a relative yaw motion between a nacelle and a tower. The characteristic of such yaw motion has a long period yaw motion, and it is relatively slower than pitch or heave motion but relatively faster as its nacelle tracking motion for catching the wind direction. The effects of reduction of yaw motion and yaw motion speed by a virtual propulsion system attached to the floating structure were qualitatively and quantitatively investigated as countermeasures against the yaw motion problem.