Multiline anchor force dynamics in floating offshore wind turbines

Abstract

Floating 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 wavedominated 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.

Floating offshore wind turbines: Installation, operation, maintenance and decommissioning challenges and opportunities

“…The cost of geo-technical investigations is a function of water depth, site conditions, preexisting survey data and method of investigation. The geo-technical site investigation costs are also dependent on the number of anchors (Fontana (2019)). In a wind farm with shared anchors, there is a significant reduction in the number of anchors.…”

Study on Array Floating Platform for Wind Energy and Marine Space Optimization

“…It is also vital that cost reduction of mooring system builds on reasonable distance between floating offshore wind turbines. In Casey's research [8,9], the NREL 5MW wind turbine on OC4 semi-submersible…”

Comment on wes-2021-120

“…This would help to bring down geo-technical site investigation costs. (Fontana (2019)) compared the costs of installation and geo-technical site investigation for different farm sizes. It was found that a multi-line configuration reduces the installation cost for wind farms with 36 or more wind turbines.…”