Responses of offshore wind turbines with different power capacities on tetrapod jacket systems under dynamic loads in layered clay

Abstract

Tetrapod piled jacket (TPJ) foundations have been widely employed to support offshore wind turbines (OWTs). The dynamic response of TPJs in layered soil under combined environmental and seismic loads remains insufficiently understood—especially regarding the kinematic and inertial effects across varying rated powers and water depths. Thus, this study employs advanced three-dimensional finite element simulation to comprehensively analyze the seismic responses of three semi-rigid-piled TPJ systems in layered clay deposit. The results indicate that when environmental and seismic loads act simultaneously, their effects on the TPJ's deformation tend to counterbalance each other. The peak acceleration of the TPJ structure locates at the height of z/L_T = 0.5–0.6, whose response is governed by the its third-order fore-aft mode. In addition, the lower-capacity TPJ-supported OWTs shows greater sensitivity to dominant seismic excitation frequencies and the variations in the stiff clay layer thickness than higher-capacity systems. Also, it exhibits minimal pile-soil response differences due to stronger pile-group effects. For all three TPJ systems, the peak values of the acceleration envelope consistently occur near the depth of soil layer interface, where a distinct accumulation of soil shear strain is observed. These findings offer valuable insights into TPJ system dynamic response in complex marine environments.