Station-keeping for floating offshore renewable energy: A physical modelling study of seabed – chain-anchor interactions.

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Offshore floating facilities are kept in place by mooring lines that are composed of chain, wire rope and/or novel synthetic fibre ropes that originate at the floater and terminate at an anchor located within the seabed. Current floating facilities mainly use chain mooring lines that form a catenary shape in the water column and arrive at the mudline in a horizontal orientation with a significant portion of the mooring line lying on the seabed. The final section of the mooring line is embedded in the seafloor and forms an inverse catenary between the mudline and the anchor padeye as the chain is tensioned from mooring-line loads. The formation of the inverse catenary within the seabed causes the embedded mooring line to absorb part of the mooring load, and influences the magnitude and inclination of the load transferred to the anchor.

This paper describes a small scale experimental set up for testing the inverse catenary of a mooring line at 1g, using model chain and polyester rope embedded in dry sand. These tests were performed to investigate the effect of chain and rope dimensions on seabed-mooring interactions . This study presents and compares results from these small-scale tests with centrifuge tests and theoretical chain models. Relationships between the measured inverse catenary profile that develop along the chain or rope as they are tensioned at the mudline, the displacement at the mudline and the magnitude and inclination of the load transferred to the anchor padeye are presented.

5th European Conference on Physical Modelling in Geotechnics (ECPMG2024)

Onshore and offshore foundation systems