Preliminary investigation of a shared mooring arrangement for a floating offshore wind turbine farm in deep water

In recent years, floating wind has been attracting increasing attention due to its ability to be deployed in greater water depths, which are usually associated with higher wind energy. At present, floating wind technology is more expensive than fixed offshore wind, with higher cost being driven by challenges such as the extended length of mooring lines, installation of anchors in deep water etc. For floating wind to become more competitive it will be necessary to devise methods that are able to bring down the overall cost by addressing areas such as these.

This paper presents a relatively novel concept that may help reduce the capital cost by using an arrangement of ‘shared mooring lines’. This arrangement is able to significantly reduce the number of anchors used in a windfarm, compared to the current common industry practice of using 3 mooring lines to moor each individual turbine, by connecting some of the turbines to their neighbours, rather than the seabed. Furthermore, this study aims to address a scenario in which shared mooring lines are expected to be more favourable, i.e. deep water (1000 m) and large (10 MW) turbines.

This numerical study provides some insights to a cost-saving mooring concept for a FOWT wind farm, by investigating loads in mooring lines and anchors, as well as relative displacement of the FOWTs in the windfarm. The cost saving is roughly estimated in terms of number of anchors and length of mooring line saved — serving as preliminary guidance for shared mooring line arrangements to be applied on larger windfarms or other geometric layouts (e.g. staggered rectangular array or hexagonally shared mooring connection).