Enhancement of the energy capture performance of oscillating water column (OWC) devices using multi-chamber multi-turbine (MCMT) technology

The advancement of marine renewable energy technology has led to increased demands on current marine energy devices, particularly in relation to the energy capture capacity of wave energy converters (WECs). Among WECs, oscillating water column (OWC) devices are considered highly promising. This study examines the potential for enhancing the wave energy capture of OWC devices through the utilization of multi-chamber multi-turbine (MCMT) technology. Unlike traditional single-chamber OWCs, MCMT OWCs consist of multiple chamber modules that can operate in coordination during different wave phases to optimize the wave energy utilization. The interplay of water column movements within various chamber modules is closely interconnected. By considering these coupling effects, a reciprocal relationship between the air pressure and air-flow movement in different chamber modules is established, and a numerical model is developed to assess the functional performance of three-dimensional MCMT OWCs of arbitrary geometric shapes using a higher-order boundary element method (HOBEM). The study focuses on representative MCMT OWC designs with annular or rectangular cross-sections. Two specific scenarios are investigated: an annular MCMT OWC integrated into the monopile foundation of an offshore wind turbine, and a rectangular MCMT OWC integrated into a barge-type breakwater. Detailed numerical analyses are conducted, revealing that dividing the chamber into multiple modules can convert sloshing-mode free-surface movement into separate piston-mode movements, thereby enhancing the wave energy capture. By utilizing suitable turbine parameters and chamber dimensions, the peak hydrodynamic efficiency of MCMT OWCs has the potential to exceed unity, surpassing that of single-chamber OWCs by a factor of three. Additionally, employing a low rotational speed for the air turbine in MCMT OWCs can result in a doubled effective frequency bandwidth compared to single-chamber OWCs. This bandwidth can be extended even further with an increase in the rotational speed. This study also suggests that designing chamber modules with identical cross-sectional shapes may not always be the most advantageous approach for maximizing the wave energy capture.