A pressure-differential wave energy converter (WEC) is a unique design, compared to conventional kinematic WECs. It contains two flexible, air-filled bags that turn pressure fluctuations caused by ocean waves and swells into alternating expansion and compression cycles. The two bags are strategically oriented based on the dominant wave environment and exchange air back and forth with each passing wave. A turbine is located between the two bags and used to extract power from the internal airflow.
A fixed-bottom pressure-differential design can be directly analyzed in the frequency domain by modeling the bag motion as a generalized body mode. However, for a floating system, the device motion influences its power output and a coupled analysis approach is required. As a result, the authors developed a time-domain numerical model to analyze the floating pressure differential WEC system.
The equations of motion describing the bag and rigid body motion of the device are solved in a coupled fashion. The hydrodynamic diffraction and radiation coefficients for all relevant system motions have been computed via WAMIT. The bag motion was introduced within WAMIT as an additional generalized body mode. The hydrodynamic performance of the system is validated against 1:50-scale wave tank measurements and the influence of motion coupling on the power performance is characterized.