An Investigation Into the Hydrodynamic Efficiency of an Oscillating Water Column

Abstract

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%.

Assessment of primary energy conversions of oscillating water columns. I. Hydrodynamic analysis

“…As a result of this, a longer horizontal duct may be desirable for tuning the BBDB to the wave states of longer wave periods. Morris-Thomas et al 16 have experimentally studied the hydrodynamic efficiency on fixed OWCs with different front shapes. From the comparison, it can be seen that the front shapes have some but limited influence on the wave energy conversion efficiencies of the fixed OWC.…”

Comparison of 2d and 3d Simulations of an Owc Device in Different Configurations

“…Sarmento (1992) also carried out wave flume experiments on an OWC device and studied both linear and quadratic power take off mechanisms using filters and an orifice plate respectively. Morris- Thomas et al (2007) carried out experiments to determine the hydrodynamic efficiency of an OWC device with varying wall thickness, draught of the front wall for various wave parameters. Thiruvenkatasamy and Neelamani (1997) studied the effect of nozzle area on the efficiency of an OWC device through wave flume experiments.…”

Numerical Simulation of a Dual-Chamber Oscillating Water Column Wave Energy Converter

“…Generally, when investigating the performance of an OWC device with a single chamber, the motion of the free surface inside the chamber is represented by that at the chamber-center [13,17]. To check whether the method is also suitable for the dual-chamber device, two different methods were adopted to calculate oscillating water column volumes in the chambers.…”

“…This internal pressure fluctuation runs the air above the internal free surface inside the enclosed chamber through the turbine, which eventually drives the electrical generator to produce electricity. A great volume of researches has been carried out to investigate the efficiency of OWCs analytically [4][5][6][7], numerically [8][9][10][11][12] and experimentally [13][14][15][16][17][18][19], most of which focus on the single chamber device. Generally, for a single chamber OWC, it has been recognized that if the device is to be an efficient absorber, it should operate at near-resonance conditions [20][21][22][23].…”