Mating Control of a Wind Turbine Tower-Nacelle-Rotor Assembly for a Catamaran Installation Vessel

Abstract

The assembly and installation costs of an offshore wind farm can approach 20% of the capital expenditures; therefore, time efficient installation methods are needed for installing offshore wind turbines. This study investigates the feasibility of a novel wind turbine installation concept using a catamaran. The catamaran is designed to carry wind turbine assemblies on board and to perform installation using lifting grippers. The installation of a rotor-tower-assembly onto a spar foundation is considered with a focus on the mating process of a tower-nacelle-rotor assembly. The spar foundation has been pre-installed at a representative site in the North Sea, and the catamaran has thrusters regulated by a dynamic positioning system. Numerical modelling of various components of the concept are introduced. Time-domain simulations of the system are performed in irregular waves, and the relative motion and velocity between the tower bottom and the spar top are analysed during the mating process. It was found that the active heave compensator can effectively reduce the relative heave velocity and the risks of structural damage during the mating process.