Multiline anchor force dynamics in floating offshore wind turbines

Abstract

AbstractFloating offshore wind energy has seen significant progress, evidenced by multiple demonstration projects and the first floating wind farm (Hywind Scotland). However, the high capital cost associated with floating wind development remains one of the primary hurdles in the industry's growth. In efforts to lower this cost, this paper investigates a novel shared anchor concept to reduce the total number of anchors and installations. Two different multiline geometries are studied—a 3‐line anchor system and a 6‐line anchor system. Simulations of the anchor forces are generated using National Renewable Energy Laboratory's OC4‐DeepCwind semisubmersible floating system and 5‐MW wind turbine, and the anchor forces of the 2 different multiline geometries are compared to those of a conventional single‐line anchor geometry. Multiline anchor net force is calculated by vector summing the contributing tensions of the lines connected to the anchor. Results show that the behavior of the multiline anchor net force is governed by the connected line contributing the largest tension. Mean and maximum anchor forces are decreased in the 3‐line anchor system and increased in the 6‐line anchor system, relative to the single‐line system. The average direction of multiline anchor net force is aligned with environmental load direction, and a wider range of multiline anchor net force directions are exhibited for wave‐dominated load cases. Direction reversal of the multiline anchor net force under constant wind, wave, and current direction is small and infrequent. These force direction results reveal that a multiline anchor must have axisymmetric strength.