Investigation of Wave Power Conversion Efficiency and Hydrodynamic Characteristics of a Floating Twin-Hybrid Wave-Energy Device in Random Waves

The potential advantages of wave-energy converters can be extended beyond their capability to produce clean and safe energy, including wave attenuation using hybrid devices. This study presents an experimental investigation of the power production and wave attenuation capabilities of a floating twin-raft hybrid device. Model tests were performed using different random waves and damping values for a simulated power take-off (PTO) system. The coefficients of wave transmission (Kt), reflection (Kr), dissipation (Kl), and mechanical power conversion efficiencies for the seaside raft (η1) and rear side raft (η2) were estimated. It was observed that varying the peak wave period considerably affects the hydrodynamic characteristics, whereas wave height has a lesser influence. The PTO simulation is an area of uncertainty in wave-energy converters. Moreover, the study of the influence of PTO damping on device performance is new. Varying the PTO damping marginally influenced the Kt, Kr, and Kl, whereas the power conversion efficiencies of both seaside and rear-side rafts varied significantly. η1 and η2 were maximized at low-input wave height conditions. As the wave height increased, η1 and η2 decreased. This occurred due to the significant wave-energy dissipation. Liberal (Kt < 0.5 and η1 or η2 > 0.2) and stringent (Kt < 0.2 and η1 or η2 > 0.4) hydrodynamic performance conditions were used to discuss the effective range of available wave frequencies under different PTO damping conditions. This would help identify the areas where this type of device can be applied. This study validated the concept of a floating twin-body hybrid wave-energy converter. This study belongs to the concept development stage of wave-energy conversion technologies, and the conclusions can help further develop and improve this concept.