Posters

Abstract

In order to study the feasibility of deploying a new type of anchor with variable buoyancy for mooring floating offshore wind turbines, a set of detailed modelling studies were performed in the state-of-the-art, Marine Simulator of the National Decommissioning Centre. Using the multi-physics simulation allows for a more economical proof-of-concept approach that will allow to fully assess the proposed deployment method and de-risk future offshore deployment. By using the proposed floating anchor, the use of heavy-lifting cranes and vessels can be avoided. Hence, reducing operational costs and complexity. Once the anchor has been towed to the deployment site, the anchor can be deployed using a simple winch from a smaller vessel. The 163 tonnes anchor has a 10m-by-10m square base and is 4.5m tall. Firstly, a careful characterisation of the anchor’s buoyancy, is carried out. Results indicate that the anchor needs approximately 4 tonnes of ballast to ensure negative buoyancy and start sinking. The deployment is divided in two main sections: positioning the anchor under the vessel’s stern and its controlled descent to the seabed. A range of winch velocities and associated forces acting on the winch cable, along with three-dimensional anchor descent trajectory and orientation, are analysed. The ocean conditions consist of irregular waves with a JONSWAP spectrum with significant wave height of 3m and peak period of 10s. In the presence of passive heave compensation, the working load range on the winch cable decreases from 80kN at the lowest winch velocities to about 30kN for winch velocities above 0.35m/s. The faster the descent, the further the anchor drifts from its initial position. At winch velocities over 3.5m/s, the descent to the seabed takes roughly 5 minutes. In the considered range of winch velocities, the anchor rotates about its vertical axis within a range of ±20°.