An Experimental Study on Wave Forces and Pressures on an Oscillating Water Column Under Random Waves

A floating oscillating water column device (OWC) consists of a vertical cylinder, with a finite wall thickness, partly submerged as an open-bottom chamber in which air is trapped above the inner water free surface. The chamber is connected with the outer atmosphere by a duct housing an air turbine. Forced by incident waves from any direction, the water surface inside pushes the dry air above through a Wells turbine system to generate power. In the present contribution the volume flows, the wave forces, the added mass and damping coefficients and the mean second-order loads for various configurations of OWC devices are being presented. Finally, it is tested how differentiations in the device’s geometry (wall thickness, draught, shape of the chamber, turbine characterises) affect the inner pressure and as a result the absorbed power by the device.

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0513 Experimental Study on Efficiency Improvement of Fixed Oscillating Water Column Type Wave Energy Converter

The Proceedings of the Fluids engineering conference ◽

10.1299/jsmefed.2015._0513-1_ ◽

2015 ◽

Vol 2015 (0) ◽

pp. _0513-1_-_0513-3_

Author(s):

Tengen MURAKAMI ◽

Yasutaka IMAI ◽

Shuichi NAGATA ◽

Manabu TAKAO ◽

Toshiaki SETOGUCHI

Keyword(s):

Experimental Study ◽

Water Column ◽

Wave Energy ◽

Wave Energy Converter ◽

Efficiency Improvement ◽

Oscillating Water Column ◽

Energy Converter ◽

Type Wave ◽

Column Type

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Latching Control of a Floating Oscillating Water Column Wave Energy Converter in Irregular Waves

Volume 9A: Ocean Renewable Energy ◽

10.1115/omae2014-23260 ◽

2014 ◽

Cited By ~ 3

Author(s):

João C. C. Henriques ◽

Juan C. Chong ◽

António F. O. Falcão ◽

Rui P. F. Gomes

Keyword(s):

Water Column ◽

Wave Energy ◽

Rotational Speed ◽

Phase Control ◽

Wave Energy Converter ◽

Irregular Waves ◽

Oscillating Water Column ◽

Random Waves ◽

Energy Converter ◽

Excitation Force

The paper concerns the phase control by latching of a floating oscillating-water-column (OWC) wave energy converter of spar-buoy type in irregular random waves. The device is equipped with a two-position fast-acting valve in series with the turbine. The instantaneous rotational speed of the turbine is controlled through the power electronics according to a power law relating the electromagnetic torque on the generator rotor to the rotational speed, an algorithm whose adequacy had been numerically tested in earlier papers. Two alternative strategies (1 and 2) for the latching/unlatching timings are investigated. Strategy 1 is based on the knowledge of the zero-crossings of the excitation force on the floater-tube set. This is difficult to implement in practice, since the excitation force can neither be measured directly nor predicted. Strategy 2 uses as input easily measurable physical variables: air pressure in the chamber and turbine rotational speed. Both strategies are investigated by numerical simulation based on a time-domain analysis of a spar-buoy OWC equipped with a self-rectifying radial-flow air turbine of biradial type. Air compressibility in the chamber plays an important role and was modelled as isentropic in a fully non-linear way. Numerical results show that significant gains up to about 28% are achievable through strategy 1, as compared with no phase control. Strategy 2, while being much easier to implement in practice, was found to yield more modest gains (up to about 15%).

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