An oscillating water column device enables the conversion of wave energy into electrical energy via wave interaction with a semi-submerged chamber coupled with a turbine for power take off. This present work concentrates on the wave interaction with the semi-submerged chamber, whereby a shore based oscillating water column (OWC) is studied experimentally to examine energy efficiencies for power take-off. The wave environment considered comprises plane progressive waves of steepnesses ranging from kA=0.01 to 0.22 and water depth ratios varying from kh=0.30 to 3.72, where k, A, and h denote the wave number, wave amplitude, and water depth, respectively. The key feature of this experimental campaign is a focus on the influence of front wall geometry on the OWC’s performance. More specifically, this focus includes: front wall draught, thickness, and aperture shape of the submerged front wall. We make use of a two-dimensional inviscid theory for an OWC for comparative purposes and to explain trends noted in the experimental measurements. The work undertaken here has revealed a broad banded efficiency centered about the natural frequency of the OWC. The magnitude and shape of the efficiency curves are influenced by the geometry of the front wall. Typical peak magnitude resonant efficiencies are in the order of 70%.

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A flexible sheet in uniform parallel flow is studied in order to quantify its fluid dynamic drag and fluid-elastic stability characteristics. An experimental campaign is undertaken that involves a cantilevered sheet in air flow characterised by Reynolds numbers of order R ¼ 10 4 210 6 . The properties of the sheet include: constant mass per unit area; small but finite flexural rigidity; varying aspect ratios from within the range 0:43ol=Lo1, where L and l denote the length and width, respectively; and tension applied at the trailing edge. The unique aspect of the present work is an investigation into the influence of in-plane tension on both the fluid drag and fluid-elastic stability of the sheet. In the absence of tension, the configuration resembles a flag and the drag coefficient is observed to decrease with increasing aspect ratio and Reynolds number. In the presence of tension, the fluid drag is significantly reduced in the region below the critical flow velocity at which convected wave instabilities appear. This critical flow velocity can be increased through the moderate application of in-plane tension. Under lateral tension, the drag of the sheet is given to good approximation by the turbulent boundary layer drag law for a flat plate. Once stability is lost, however, the drag coefficient increases rapidly with Reynolds number due to convected waves travelling over the sheet's surface. r

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Model tests were conducted on two 1:100 scaled models of a typical concrete gravity substructure at the University of Western Australia. The two models had dimensions 0.5m length × 0.5m width with the first model being a sealed closed bottom box of height 0.1m and the second model being an open bottom box with skirt length of 0.1m. The open bottom model had the capacity to hold an air cushion with dimensions 0.49m width × 0.49m length × 0.08m height. Each model was floated at a constant draft of 0.1m and tested in water depths ranging between 0.03m (shallow) and 0.8m (deep). The environment comprised of regular waves with periods ranging between 0.6s and 3.5s and amplitude of 0.08m–0.02m. To quantify the dynamic response the heave and pitch motion of each model were measured. The model test results were compared with a theoretical solution based on long wavelength, linear wave assumptions applied to a box shaped floating vessel without an internal free surface. Results show that experimental trends compare reasonably well with analytical solution. Added mass values were predicted from heave and pitch decay tests. The results show that introducing air cushion support into a CGS increases the pitch response, while having little effect of the heave motion. The theory is also used to delineate regions of safe and unsafe tow-out operations of the air cushion structure.