Hydrodynamics of restrained buoy with an approach to wave energy absorption enhancement

In single-body converters of ocean wave energy, oscillations of a floating body (buoy) serve as the main driving force for electricity generation. Buoy geometry optimization is known as an approach to enhance the efficiency of these converters. In the present research, the process of wave energy absorption in point absorber converter is modeled as a spring-damper system. Two geometries are considered for the buoy of the converter (conical and spherical-cap). The effects of buoy geometry on its dynamics in the nonlinear wave are investigated and comparison of these effects on dynamic performances of the modeled converter are reported. Equalization of environmental conditions and modeling of the two models were discussed, and a new equalization method was proposed. Effective wave energy on each model was calculated based on geometrical characteristics of the corresponding buoy. Then, the models were hydrodynamically analyzed via boundary element method by taking the diffraction theory as the governing theory. The incident wave was assumed to be a second-order Stokes wave.
Results were obtained in both time and frequency domains and validated against the results of available research. Maximum dynamic responses of the restrained buoy with spherical-cap geometry in heave and surge (vertical and horizontal directions, respectively) were found about 4.4% and 11.3% higher than the conical buoy, respectively. The average percentage of absorbed wave energy by the modeled converter with spherical-cap buoy was about 2.2-2.5% higher than that of the other model. The average percentage of absorbed energy by the models were predicted to range within 20-24%.