Effect of various motion modes on the performance of a floating pneumatic wave energy converter with a backward bent duct

Abstract

A floating pneumatic wave energy conversion device with a backward bent duct has six degrees of freedom (DOF) motion, each of which may have different effects on wave energy conversion efficiency. To understand the contribution of each DOF motion to the capture width ratio (CWR), this study explored the impact of nine distinct motion modes on the CWR, including fixed mode; 1-DOF motion modes of surge, heave, and pitch; pairwise combinations of these 1-DOF motion modes; 3-DOF mode (surge, heave, and pitch), and 6-DOF mode (surge, heave, pitch, sway, roll, and yaw), based on Reynolds Averaged Navier-Stokes (RANS) equations. The results revealed the following: (1) The CWRs were essentially equal in both the 3-DOF and 6-DOF modes, suggesting that the influence of yaw, roll, and sway on the CWRs is very small and can be ignored. (2) As the wave period increases from a short period of 4 s to a long period of 9 s, the main contributor to energy conversion gradually shifts from surge motion to heave motion. (3) Different motions can also affect the motion characteristics of other degrees of freedom. This study provides an understanding of the contribution and influence mechanism of different single degrees of freedom and different combinations of single degrees of freedom on the energy conversion and motion characteristics of a floating pneumatic wave energy converter, laying a foundation for further optimization of the converter.