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TECHNICAL PAPERS

An Investigation Into the Hydrodynamic Efficiency of an Oscillating Water Column

[+] Author and Article Information
Michael T. Morris-Thomas1

Department of Marine Technology,  Norwegian University of Science and Technology, Otto Nielsens vei 10, Trondheim No-7491, Norway

Rohan J. Irvin

 Woodside Energy Ltd., 240 St George’s Terrace, Perth WA 6000, Australia

Krish P. Thiagarajan

School of Oil and Gas Engineering,  The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia

1

Corresponding author. Electronic mail: mmthomas@ntnu.no

J. Offshore Mech. Arct. Eng. 129(4), 273-278 (Jul 19, 2006) (6 pages) doi:10.1115/1.2426992 History: Received November 02, 2005; Revised July 19, 2006

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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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

The energy contained within a linear progressive wave of unit amplitude as a function of water depth for a number of wave periods T=5s (—); T=10s (– – –); T=15s(−∙−); and T=20s(⋯)

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Figure 2

The oscillating water column wave energy device (1:12.5 scale model)

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Figure 3

Schematic of the experimental setup illustrating: the position of the oscillating water column relative to the wave maker; the wave probe positions; and the dimensions of the wave tank and model

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Figure 4

Schematic illustrating the geometry of each front wall configuration. These are denoted FW-A, FW-B, FW-C, and FW-D.

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Figure 5

The hydrodynamic efficiency ηmax versus Kh for b∕h=1 and a∕h=0.05 (—), a∕h=0.1 (– – –), a∕h=0.2(−∙−), and a∕h=0.4(⋯)

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Figure 6

Experimental results of ηmax versus Kh. The regression curves are denoted: FW-A, (– – –); FW-B, (—); FW-C, (−∙−); and FW-D, (⋯).

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Figure 7

Comparison of the measured and theoretical results for ηmax versus Kh for values of front wall submersion: a∕h=0.163, (—); a∕h=0.185, (– – –); and a∕h=0.250, (−∙−). The measured results are represented by their, respective, regression curves and appear as thicker lines in the figure.

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