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 minutes. In addition, the anchor's yaw range during the descent is below 10°at the optimal conditions.
The aim of this paper is to present the initial results of feasibility studies aimed at optimising the towing configuration of a novel, complex shape (pyramid based) and thereby untested design of floating wind farm anchor during underwater towing. The study was carried out in the real physics Marine Simulator, at the National Decommissioning Centre. This enables us to study in detail, the drag/lift forces acting on the towed anchor/s, determine the optimal anchor installation arrangement (orientation, depth, position of towing cables, number of anchors towed together in an array) and establish the effects of the operational (towing velocity, drag) and environmental conditions (sea states, significant wave height, peak wave period) on the anchor's trajectory. The model developed is validated with computational fluid dynamics analysis to obtain representative drag and lift coefficients for the anchor during towing. Thus, this paper focuses on the calibration process to ensure robustness and relevance of the developed model in the simulator. Consistent results for the drag and lift coefficient were obtained for a range of towing speeds (0,25-3 m/s). The towing dynamics, forces acting on the anchor and the final configuration (e.g. water depth, offset angle) were obtained which in turn will allow the optimal conditions and requirements (e.g. equipment, vessel type etc.) to be recommend-ed in future studies.
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