Analysis of oscillating-water-column wave energy converter configurations for integration into caisson breakwaters

Energy production from ocean waves remains in the research and development phase, due in part to the lack of maturity of the technology, as well as the economical unfeasibility of large-scale projects. Integration of wave energy converters into breakwaters is a strategy to improve the economic viability of the energy conversion system. The cost of electricity is reduced through the sharing of construction, installation, maintenance and operation activities. This work focuses on the design of an oscillating-water-column device to be integrated into a caisson used for breakwaters. A numerical model based on linear potential flow theory was developed. The viscous flow effects in the duct and the nonlinear turbine damping characteristic were linearized for the application of a frequency domain analysis. Furthermore, the device performance was estimated under irregular wave conditions using stochastic modelling for three wave climates and the influence of tidal variability is studied. The design and performance optimization of the submerged duct, air chamber and turbine are considered for the following oscillating-water-column duct configurations: conventional; U-shape; and L-shape. The results show all devices have better power conversion performance for the lower wave periods observed in the Mediterranean Sea than for the studied North Atlantic Ocean wave climates. The U-shaped converter outperforms the other configurations in all three locations, with a maximum theoretical annual pneumatic power of 46.8kW/m when compared with 39.4kW/m and 38.0kW/m for the L-shape and conventional device, respectively. The tidal level variation does have some influence on the device performance, but the impact is minor. •An OWC is optimized, considering structural constraints from a typical caisson.•Analysis made of three OWC shapes integrated into a conventional caisson breakwater.•The performance of each device was assessed for three wave climates.•The U-shaped OWC provides highest power capture potential for the studied wave climates.•Devices have a higher hydrodynamic efficiency in wave climates with low wave periods.