Modelling and testing of a pressure-differential wave energy converter with flexible membranes. (May 2023)

• Record Type: Journal Article
• Authors: Milani, Lydia; Thorniley, Sam; Kurniawan, Adi; Wolgamot, Hugh
• Is Part Of: Applied ocean research. Volume 134(2023)
• Publication Date: 2023-05
• Subjects: Wave energy -- Numerical modelling -- Model testing -- Pressure differential -- Flexible membranes; Ocean engineering -- Periodicals; 620.416205
• DOI: 10.1016/j.apor.2023.103516
• Languages: English
• ISSNs: 0141-1187

Abstract

Abstract: We investigate a wave energy converter composed of two submerged, bottom-fixed air-filled cylindrical chambers, separated by a distance of ideally half a wavelength, and closed on top by flexible membranes. A passing wave creates a pressure differential between the two chambers which drives the membranes and causes air to flow through a turbine. Using linear analysis and physical model testing, we show that the device exhibits broad-banded power absorption. Our linear model successfully predicts the pressure differential and absorbed power measured in the tests, except at low frequencies, where the differences are attributed to unstable membrane conditions due to a negative total stiffness. Using a simple model, we show that the flat-membrane equilibrium, in the absence of additional stiffness, is unstable. By introducing an additional stiffness to the membrane, this instability can be avoided and the natural period of the device can theoretically be tuned to any value. With a matching flow resistance, it is possible to attain absorbed power values close to the theoretical limit. Highlights: A pressure-differential WEC with flexible membranes is modelled and tested. The deformation of the membranes is modelled using the generalised-mode approach. The power take-off is represented at model scale by an assembly of capillary tubes. The device is unstable at low frequencies due to its inherent negative stiffness. Adding stiffness yields broad-banded power absorption near the theoretical limit.