A Numerical Investigation of the Energy Efficiency Enhancement of Oscillating Water Column Wave Energy Converter Systems

Abstract

This work focuses on the geometry effects over the performance of oscillating water column (OWC)-type wave energy converter (WEC) systems and searches for the OWC geometries that enhance the energy efficiencies under the same wave conditions. To analyze the hydrodynamic performances of the WEC systems, an in-house smoothed particle hydrodynamics (SPH) code based on weakly compressible fluid approach is utilized. The energy efficiency enhancement studies of the determined OWC device are carried out with a two-step geometry modification procedure. The first step starts with the validation of the free-surface elevation and orbital velocity time histories. Then, a three-by-three simulation matrix that depends on the geometrical design parameters of chamber length and front wall draft is run at three different wave conditions, and the OWC geometry that produces the maximum energy efficiency is determined. In the second step, the corner regions of the obtained optimal geometry are chamfered, and another simulation matrix is tested at the wave condition that yields maximum wave energy. It is observed in this step that the energy efficiency index can still be improved by 4.3% by only chamfering the back face of the OWC chamber. To scrutinize the physical grounds of this increase, the correlation between the time-averaged vorticity and energy efficiency is presented. Finally, the performance of the best configuration is also examined in three different wave periods, where the suggested geometry shows better performance with respect to base geometry results in all wave conditions.

Keywords

• wave energy
• free-surface hydrodynamics
• wave energy converters
• energy efficiency
• SPH method