Large-scale testing of a hydraulic non-linear mooring system for floating offshore wind turbines

Abstract

The mooring system has been recognised as a key area of expense that needs to be addressed to improve the cost competitiveness of floating offshore wind turbines. Recent interest in the usage of lighter and more compliant mooring materials has shown that they have the potential to reduce peak line loads, which would in-turn reduce costs. However, the lack of operational experience with such materials has limited their adoption in a risk averse industry. This paper reports on the large-scale physical testing of a hydraulic-based mooring component with non-linear stiffness characteristics. The performance of the device is measured before it is subject to conditions representative of an offshore deployment via a combined physical and numerical modelling approach. The results show that the dynamic stiffness of the component is a function of load history and hydraulic pre-charge pressure, while the inclusion of the device as part of the OC4 semi-submersible floating wind platform can reduce the peak mooring line loads by up to 9%. The modelling also suggests that a 40% reduction in peak loading is possible if the device can be scaled further. The paper supports the adoption of innovative mooring systems through dedicated component and performance testing.