Phase-averaged analysis of an oscillating water column wave energy converter


A. Fleming – Doctoral Dissertation, Australian Maritime College, September, 2012

Abstract

The work described in this thesis is concerned with the application of phase-averaging to experimental data obtained for a forward-facing bent-duct oscillating water column (OWC) wave energy converter. Experiments were performed on a three-dimensional model of the OWC in monochromatic waves. The research includes the development of new curve-fitting and ensemble-averaging phase-averaging algorithms designed to phase-average two-dimensional particle-imaging velocimetry (PIV) data. The phase-averaged PIV velocity fields were then used for qualitative and quantitative analysis. Qualitatively – visualisation of the velocity fields as vectors over a wave cycle shows the average flow field phenomena including bulk flow, water column slosh, front wall swash and downwash, vortices and an outflow jet. Quantitatively – two-dimensional kinetic energy and vorticity was calculated from the phase-averaged velocity fields and used in an energy balance analysis.

Experimental and theoretical data were combined in an energy balance analysis of the OWC to map the flow of energy from the incoming waves to intermediate stores and finally to sinks, which importantly permits the inclusion of non-linear phenomena. Using the energy model it was found that for the OWC model tested that the phase-averaged energy dissipated by the power-take-off was greater during water outflow than during water inflow. Phase-averaged experimental analysis of OWCs is an additional tool suitable for the design of underwater geometry of OWCs with potential application to other wave energy converters.

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