The Importance of Dynamic Mooring Analysis for Reliable Prediction of Suction Anchor Dynamic Response in Floating Offshore Wind Turbines

Accurate prediction of the dynamic load-bearing characteristics of suction anchors is critical for the safety and reliability of floating offshore wind turbines. This study bridges the gap between mooring approaches and anchor foundation response assessment by systematically quantifying how the choice of mooring analysis method (dynamic or quasi-static) affects the predicted displacement response of suction anchors. Using OpenFAST coupled with a validated suction anchor dynamic response model (SADR), the motion responses of the suction anchor foundation for the OC4 semi-submersible platform are computed under regular waves of varying heights and periods, as well as irregular sea states representing operational and extreme conditions. The results reveal that the ratio of the anchor displacement predicted by dynamic mooring analysis to that predicted by quasi-static mooring analysis grows nonlinearly with increasing wave height and rises substantially as wave period lengthens, indicating that mooring dynamic effects become progressively more pronounced under large wave heights and long-period swell conditions. Statistical analysis under irregular waves further reveals that under moderate operational conditions, the response variability predicted by the two methods remains comparable; however, under extreme sea states, dynamic analysis yields not only larger peak displacements but also substantially greater response variability, with standard deviations significantly exceeding those obtained from quasi-static predictions. These findings provide quantitative evidence that the application of quasi-static mooring analysis to anchor foundation design carries a substantial risk of underestimating true responses, and that this underestimation becomes increasingly severe under high wave heights, long periods, and extreme conditions. The work establishes that dynamic mooring analysis is essential for reliable suction anchor foundations design and long-term serviceability assessment.