Nonlinear mooring system for a ‘Sharp-Eagle’ wave energy converter

Abstract

This numerical study investigated the effects caused by the UoE Tether shock absorber (in the following named UoE tether) on the motion and load characteristics of the 500 KW sharp-eagle WEC. Both 3-leg and 4-leg mooring configurations with different line combinations were selected in the share-eagle WEC project. The line combinations include a chain line and two hybrid mooring lines, i) a UoE Tether and ii) a nylon rope section. The UoE tether is a passive damper that has been proven in recent field demonstrations to reduce peak tensions in mooring lines during extreme environmental conditions. This paper discusses the line tension and motion characteristics of the WEC and compares the variations of mooring configurations and line combinations with respect to its capability to stabilise the device and reduce tension. Compared with the other two line combinations, the UoE tether could significantly reduce the peak tensions under the extreme wave conditions. Under the same mooring configuration, the UoE tether can reduce up to 31% and 67% peak tension. On the other hand, the UoE could allow a shorter mooring line design with a similar safety factor. Compared to the single Chain design, the length of the mooring line could be reduced by around 25%. It was also found that the UoE tether would not significantly influence the motion characteristics of the WEC, which means it would not affect the device installation characteristics. This work will be helpful for practitioners and researchers working in the wave energy industry, particularly decision-makers in mooring system design.