Deployment feasibility studies of variable buoyancy anchors for floating wind applications

To study the feasibility of deploying a novel type of anchor with variable buoyancy for mooring floating offshore wind turbines, a set of detailed modelling studies was performed in the state-of-the-art, Marine Simulator at the National Decommissioning Centre (NDC). The aim of the multi-physics simulations is to fully assess the proposed deployment method using a small tugboat fitted with a simple winch, thereby simplifying the process and reducing installation costs. The anchor has a 10 m square base, 4.5 m height and weight of 163 tonnes. The anchor is subjected to irregular waves with a JONSWAP spectrum with a significant wave height up to 5 m and peak period of 10 s. The analysis is divided in three sections: characterisation of the anchor buoyancy, positioning the anchor under the stern of the vessel and the controlled descent of the anchor to the seabed. An ideal winch speed of 0.35 m/s is identified, at which working load range on the winch cable decreases from 80 kN at the lowest winch speeds to about 30 kN. The sinking trajectory is similar at all winch speeds, however, the slower the descent, the further the anchor drifts. At this winch velocity, the descent from the resting position under the stern to the seabed takes roughly 5 min. In addition, the anchor’s yaw range during the descent is below 10∘ at the optimal conditions.