Coupled dynamic response analysis of floating offshore wind turbine considering chain-soil interaction

• A chain-soil interaction model was developed using the AQWA dynamic link library and validated against analytical solutions. • An integrated chain-soil-aero-hydrodynamic framework was established by coupling the model with FAST for FOWT dynamic response analysis. • The coupled system was applied to investigate FOWT dynamic responses considering the effect of chain-soil interaction, wind speed, and soil strength. The chain–soil interaction plays a critical role in the dynamic response of floating offshore wind turbines (FOWTs) due to the load transfer nature of mooring chains. However, it is often neglected in conventional analyses because of the complexity of modeling seabed interaction. This study developed a chain–soil interaction model using the dynamic link library of AQWA and validated its accuracy. By integrating this model with the aero-servo-elastic tool OpenFAST, a fully coupled chain–soil–aero–hydrodynamic system was established to investigate the dynamic response of FOWTs. The 10 MW OC4-DeepCwind semi-submersible with a chain–polyester–chain mooring system was analyzed under different wind speeds and soil strengths. Results show that considering chain–soil interaction significantly increases surge motion at rated wind speed, with the mean surge amplitude rising by about 45.2%. The interaction reduces the dynamic surge stiffness of the mooring system, enhancing sensitivity to low-frequency excitation, while wave-frequency peaks remain unchanged. Moreover, the maximum mooring tension decreases due to the greater suspended chain length in water. Among the three operating conditions studied (lower rated, rated, and cut-out wind speed), the maximum surge, pitch, and mooring tensions occur at the rated wind speed of 11.4 m/s. Increasing soil strength enhances mooring system stiffness, thereby reducing floater surge and pitch motions but increasing maximum tensions at the fairlead and anchor. These results indicate that neglecting chain–soil interaction leads to underestimation of surge response, reduced positioning capability of the mooring system, and potentially unsafe FOWT motions.