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CASE STUDY

Durability Assessment of Mooring Chains and Design Optimisation of Mooring Systems for FOWT

Client(s): Scottish Enterprise and Nippon Foundation

Consortium: TODA Corporation, Kyushu University, Bridon-Bekaert and TTI-MR Ltd

Dates: 2019 - 2023

AIMS

To demonstrate the feasibility of a nylon taut mooring system for two 2MW FWTs, situated off the west coast of Japan (Goto Island), through analysis and field testing. Carry out feasibility design studies on a larger-scale system (10MW+).

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Approach

TTI-MR’s role in this project focused on the following activities:

  • Further development of a multi-objective mooring system design tool which has been used to design and analyse efficient mooring systems based on Toda’s ballasted spar FWT platform. Based on the design work, two systems were deployed off Goto Island during the project, with inspections carried out to determine system condition.

  • Benchmarking of nylon and alternative rope based mooring systems against conventional chain-based systems.

  • Carry out detailed comparison of synthetic rope analysis techniques and further develop nylon models.

  • Concept design of TTI-MR’s novel top end tensioning and fairlead system for FWTs

Key Outcomes and Impact

This project provided evidence for developers and Classification Societies on the feasibility of using synthetic ropes for FWT mooring systems through detailed modelling and analysis, laboratory testing and field deployments at two sites (benign and exposed). Systems for mooring line on-boarding (e.g. fairleads) and tensioning were investigated and developed.

Industry Relevance

Significant progress was made in this ongoing project that will contribute to gathering evidence for the qualification of nylon ropes for FWT mooring systems. Two scales of system were considered in the project (turbine ratings: 2MW and 10MW+). In addition to the design and analysis of the systems, TTI-MR are led a review of the qualification status of synthetic ropes for FWT mooring systems. The development of taut mooring systems for spar-type FWT substructures gives direct experience of a configuration to be studied in this proposal.