Design and analysis of the bulbous-bottomed oscillating resonant buoys for an optimal point absorber wave energy converter

This study proposes innovative bulbous-bottomed buoy designs for an optimal oscillating-body wave energy converter (WEC). The effects of buoy shapes and the shape-influenced hydrodynamic coefficients on the motion and power absorption efficiency of a single-body heaving WEC are investigated. The frequency-domain analyses and spectral modeling were performed in ANSYS AQWA considering regular and irregular waves for optimal and sub-optimal power take-off (PTO). The wave climate data was obtained for ShiDao station China, and the middle frequency of the wave range with the highest probability of occurrence was selected as standard natural frequency, which was achieved by equalizing the diameter, mass, and volume of all the buoys. The bulbous-bottomed buoys could achieve 28.1% higher absorption efficiencies than the non-bulbous shapes. The buoy with the most expansive bulbous bottom of 1.6m height (SB-3) is the most optimal buoy with the highest power absorption and efficiency in both optimal and suboptimal PTO modes, with a maximum of 16.8% and 21.5% increase in response amplitude operator (RAO) and power absorption, correspondingly, relative to non-bulbous cylindrical-hemispherical (C-HS) buoy. The experimental validation of the simulated RAO and power of the 1:12.5 scale model of the SB-3 revealed 28% and 27.18% greater values, respectively, compared to C-HS, justifying that the SB-3 buoy could be a better choice for designing an oscillating-body WEC in all waves. By increasing the bulbous bottom width by 90% and fillet height by 100%, the performance of the bulbous buoys was enhanced by 12.2%. • The bulbous-bottomed oscillating buoys were designed for an optimal WEC. • Hydrodynamic response was evaluated via simulations, compared against test results. • Adding bulbous shapes in buoy can significantly enhance the WEC performance. • Bulbous buoy (SB-3) was the optimal design with a 28.1% increase in absorbed power. • The experimental verification justified the simulated power with a 4.25% error.