Hydrodynamic mechanisms of energy-focusing and multi-body interference in composite bucket foundation-based wind–wave hybrid systems

The composite bucket foundation (CBF), characterized by its large arc transition section, can reconstruct the local wave field, providing a new mechanism for wave energy regulation in wind–wave hybrid systems (WWHSs). This study investigates the novel CBF-based WWHSs. Dimensionless coefficients describing the energy-focusing effect, interference, and dual-interference mechanisms are introduced to evaluate the CBF energy-focusing and multi-body interference characteristics under various wave conditions, damping parameters, and system configurations. A harmonic energy decomposition method is further employed to reveal the evolution of the buoy motion response spectrum. The results show that the CBF reshapes the wave field and forms an energy convergence zone on the wave-ward side, thereby enhancing buoy energy capture. Under optimal conditions, the energy-focusing coefficient of the CBF-OB hybrid system reaches 5.679. Meanwhile, multi-body interference exhibits pronounced spatial selectivity. The wave-ward side buoy is almost unaffected, whereas the lateral buoys in the microarray experience energy suppression, with their RAO decreasing to 0.807 times that of a single buoy. The dual-interference mechanism in COBRA further amplifies the motion of the wave-ward side buoy to 2.672 times that of a single buoy, increasing energy capture by up to 5.770 times. Meanwhile, the lateral buoys show increased motion but not necessarily higher power output. In addition, the presence of the CBF induces energy transfer among harmonics, producing small secondary peaks near the dominant frequency and enhancing higher-order harmonic energy. These findings provide valuable insights for the coordinated exploitation of wind and wave energy in coastal regions such as Xiaomai Island.