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Siegel S.G.,Atargis Energy Corporation
Applied Ocean Research | Year: 2015

Numerical results from a three-dimensional radiation model are presented where a cycloidal wave energy converter (WEC) is interacting with an incoming straight crested airy wave. The radiation model was developed in response to experimental observations from 1:10 scale experiments which were conducted in the Texas A&M Offshore Technology Research center wave basin. These experiments were the first investigations involving a WEC where three dimensional wave radiation effects were present due to the fact that the span of the WEC was much smaller than the width of the basin. The radiation model predicted the observed surface wave patterns in the experiment well, and showed that radiation induced wave focusing increased the recoverable wave power beyond the two-dimensional predictions for small WEC spans, while approaching the two-dimensional limit for very large spans. The numerical model was subsequently used to investigate the sensitivity of the WEC to misalignment between the incoming waves and the WEC shaft as well as the impact of a gap in the blade setup of a double WEC. For misalignment, the loss in efficiency was found to be strongly dependent on the ratio between WEC span and incoming wavelength, where short spans (on the order of one wavelength or less) which are realistic for actual ocean deployment showed only minor reductions in efficiency, while very long spans were found to be more sensitive to misalignment. The blade gap in a double WEC setup was found to have a relatively minor effect (up to 30%) on efficiency. Efficiency was found to either increase or decrease depending on the size of the gap. © 2014 Elsevier Ltd.

Siegel S.G.,Atargis Energy Corporation
Applied Ocean Research | Year: 2014

A lift based cycloidal wave energy converter (WEC) was investigated using potential flow numerical simulations in combination with viscous loss estimates based on published hydrofoil data. This type of wave energy converter consists of a shaft with one or more hydrofoils attached eccentrically at a radius. The main shaft is aligned parallel to the wave crests and submerged at a fixed depth. The operation of the WEC as a wave-to-shaft energy converter interacting with straight crested waves was estimated for an actual ocean wave climate. The climate chosen was the climate recorded by a buoy off the north-east shore of Oahu/Hawaii, which was a typical moderate wave climate featuring an average annual wave power PW=17kWh/m of wave crest. The impact of the design variables radius, chord, span and maximum generator power on the average annual shaft energy yield, capacity factor and power production time fraction were explored. In the selected wave climate, a radius R=5m, chord C=5m and span of S=60m along with a maximum generator power of PG=1.25MW were found to be optimal in terms of annual shaft energy yield. At the design point, the CycWEC achieved a wave-to-shaft power efficiency of 70%. In the annual average, 40% of the incoming wave energy was converted to shaft energy, and a capacity factor of 42% was achieved. These numbers exceeded the typical performance of competing renewables like wind power, and demonstrated that the WEC was able to convert wave energy to shaft energy efficiently for a range of wave periods and wave heights as encountered in a typical wave climate. © 2014 Elsevier Ltd.

Jeans T.L.,University of New Brunswick | Fagley C.,Atargis Energy Corporation | Siegel S.G.,Atargis Energy Corporation | Seidel J.,Atargis Energy Corporation
International Journal of Marine Energy | Year: 2013

The performance of a lift based wave energy converter in unidirectional irregular deep ocean waves is investigated. The energy converter consists of two hydrofoils attached parallel to a horizontal main shaft at a radius. The main shaft is aligned parallel to the wave crests and submerged at a fixed depth. The local flow field induced by the incident wave will cause the hydrofoils to rotate about the main shaft. The orientation of each hydrofoil is adjusted to produce the desired level of bound circulation. The energy converter and incident wave field are modeled using potential flow theory. The wave field is assumed to be long-crested and the hydrofoil span infinitely long, thereby the resulting flow field is two-dimensional. Each hydrofoil is modeled as a point vortex moving under a free surface. The irregular ocean wave is modeled by linear superposition of a finite number of regular wave components. The amplitude and frequency of each component is determined based on a Bretschneider spectrum. The hydrofoil position and bound circulation are controlled using a sensor located up-wave of the device and wave state estimator. The results demonstrate the converter's ability to effectively extract energy from multiple wave components simultaneously. Inviscid hydrodynamic efficiencies for incident wave fields consisting of 7 and 10 regular wave components were 85% and 77%, respectively. © 2013 Elsevier Ltd. All rights reserved.

Fagley C.P.,Atargis Energy Corporation | Seidel J.J.,Atargis Energy Corporation | Siegel S.G.,Atargis Energy Corporation
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2012

The ability of a Cycloidal Wave Energy Converter (CycWEC) to cancel irregular deep ocean waves is investigated in a time integrated, inviscid potential flow simulation. A CycWEC consists of one or more hydrofoils attached eccentrically to a shaft that is aligned parallel to the incoming waves. The entire device is fully submerged in operation. A Bretschneider spectrum with 40 discrete components is used to model an irregular wave environment in the simulations. A sensor placed up-wave of the CycWEC measures the incoming wave height and provides a signal for the wave state estimator, a non-causal Hilbert transformation, to estimate the instantaneous frequency, phase and amplitude of the irregular wave pattern. A linear control scheme which proportionally controls hydrofoil pitch and compensates for phase delays is adopted. Efficiency for the design Bretschneider spectrum shows more than 99% efficiency, while non-optimum, off design operating conditions still maintain more than 85% efficiency. These results are in agreement with concurrent experimental results obtained at a 1:300 scale. Copyright © 2012 by ASME.

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