Analysis of mooring system for floating wind turbine based on macro-model of chain-seabed interaction

Traditional fully integrated analyses of floating wind turbines (FTWs) assume a fixed mooring point on the seabed, overlooking the effects of the embedded mooring line within the seabed. This simplification introduces inconsistency and uncertainty in mooring system design. In this study, a macro-model was proposed to simulate the interaction between the mooring line and seabed soil, and it was implemented into SIMA (a fully coupled aero-hydro-servo-elastic engineering tool). The macro-model captures the coupled non-linear relationship between incremental displacement and resultant soil reaction force in three-dimensional space. After verifying the model, effects of seabed friction and embedded chain on the mooring line were evaluated. Subsequently, mooring analyses of the VolturnUS-S floater supporting the IEA 15MW floating wind turbine were performed using the macro-model to assess key parameters in mooring line design. Then, three representative cases under dynamic conditions are designed to investigate the influence of the embedded line on mooring system response. The study demonstrated that the macro-model of chain-seabed interaction effectively captures the response of the mooring chain considering gradual mobilization of soil reaction forces and effective width parameters due to the chain geometry. Without modelling the embedded line, mooring lines have larger tension due to smaller displacement near the padeye on the seabed, emphasizing the importance of embedded line on seabed friction mobilization under both static and dynamic conditions. The seabed friction shares the load transferred from the floater, and significantly affects the anchor load. This study develops a crucial tool for mooring design of floating wind turbines considering the embedded chain.