Offshore Wind Turbine and Substructure Modelling for a Float Over Installation Design

Abstract

We can learn from the offshore oil and gas experience for the future offshore wind turbine installation. For the offshore ‘wind farm’ developments, the installation of wind turbines onto preinstalled foundations using the heavy lift vessel method or stabilized vessel is now well established, though, for large units, this requires multiple lifts and hence extensive offshore assembling. As demand for lift vessels increases, their availability to match a future large specific project’s schedule cannot be guaranteed. Consequently, an alternative wind turbine installation vessel design has been developed for not only installing simultaneously two wind turbines in a single piece, but also with a high air gap (up to 70 ft). This paper presents this new design. The new vessel design consists of a catamaran shaped vessel with dimensions that permit it to go around variety of substructures (piles foundation, tripod, concrete foundation or floating substructure) for float-over installation of wind turbines. For the float-over operation, a thorough understanding of dynamic behavior and environmental conditions are necessary to allow the design load to be assessed, with the objective to minimize the risk and maximize the operating sea states. This paper gives a description of how the substructure / Wind turbine / transition piece / floating unit can be modeled. This new vessel design greatly extends the geographical range for offshore wind turbine installation using the float-over method and offers a cost effective alternative to relying on crane vessels.