A VFIFE-based non-contact monitoring approach for mooring line tension in floating offshore wind turbines

The safety of mooring systems is critical for Floating Offshore Wind Turbines (FOWTs), yet contact-based tension monitoring suffers from difficult installation, susceptibility to damage and limited long-term reliability. This study proposes a non-contact monitoring method based on the Vector Form Intrinsic Finite Element (VFIFE), which determines mooring tension from the measured motion of the floating platform. The principles of applying VFIFE to mooring dynamics are presented and a numerical model established. Using the IEA 15 MW turbine and the VolturnUS-S semi-submersible platform, three mooring configurations—chain-only, chain-nylon and chain-polyester—are designed. Platform motions simulated in OrcaFlex under various sea states are converted to fairlead motions and as input to the VFIFE model, which returns the monitored tension; the results are compared with the OrcaFlex benchmark and validated against wave-basin tests of a 1:80 scaled FOWT model, where the inferred tensions are compared with load-cell measurements. The monitored tensions agree well with both references in the mean and slowly varying components, whereas the wave-frequency component, and hence the standard deviation, is reproduced with lower accuracy. The approach offers a cost-effective, mechanics-based solution for long-term FOWT mooring safety monitoring.