Experimental investigation of a land-based dual-chamber OWC wave energy converter

Highlights: • Hydrodynamics of a dual-chamber OWC device is investigated experimentally. • Higher efficiency is achieved by applying a dual-chamber design. • A wider effective frequency bandwidth is achieved by a dual-chamber OWC device. • The sub-chamber breadth has little effect on the overall efficiency of the system. • The hydrodynamic efficiency decreases with increasing barrier wall draft. -- Abstract: Extensive investigation on wave energy converters (WEC) that convert wave power into electricity is required to improve competitiveness of wave energy, one of the most promising renewable energy resources. Better hydrodynamic performance should enable wave devices to compete favorably with conventional power plants in the near future. In this study the hydrodynamic performance of a land-based dual-chamber Oscillating Water Column (OWC) device is investigated experimentally, with emphasis on its overall performance and respective performance of the two sub-chambers of the system. The effects of the chamber breadth and the barrier wall draft on the hydrodynamic efficiency, the free surface elevation and the air pressure inside the chambers are investigated over a wide range of wave periods with a constant wave amplitude. Numerical simulations using fully nonlinear numerical wave tanks (NWTs) within the framework of potential flow theory are also carried out to cross-check the results, and help to further understand the experimental observations. It is found that both the maximum efficiency and the range of wave frequencies that leads to a higher rate of wave energy absorption, i.e. the effective frequency bandwidth, increase in the dual-chamber OWC system when compared to an equivalent typical single-chamber OWC device. The overall efficiency of the system is found to be insensitive to the variation of the sub-chamber breadth, while the efficiency of the two sub-chamber increases with its breadth when the total chamber breadth is kept the same. Additionally, the hydrodynamic efficiency is found to decrease with increasing barrier wall draft. The rear chamber (i.e., on the landward side) outperforms the front chamber (i.e., on the seaward side) for most of the wave frequencies investigated in this study, especially for the wave frequency that is at or close to the resonance frequency of the system.