Computational Investigation of Irregular Wave Cancelation Using a Cycloidal Wave Energy Converter

Abstract

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.

Wave climate scatter performance of a cycloidal wave energy converter

“…This was achieved in simulations reported by Jeans et al [15], as well as experimentally validated by Siegel et al [16] in a small 2D wave flume. In a follup-up investigation to Jeans et al [15] which was reported by Fagley et al [17], an improved controller achieved cancelation of irregular waves with efficiencies almost identical to the earlier harmonic wave cancelation results reported by Siegel et al [13]. These findings justify the use of harmonic simulations, which are numerically less expensive, for parameter studies of the type reported here.…”

“…Consequently, if the power of a harmonic wave was to match the power of an ocean sea state for a matching wave period, H s = √ 2H Airy . Due to findings reported by Fagley et al [17], for the present parameter study harmonic wave cancelation simulations were used to estimate the efficiency for irregular wave buoy measured sea states, since it was found that the WEC could convert both types of waves with approximately equal efficiency if an appropriate feedback controller was employed. …”

Wave-to-wire Modelling of Wave Energy Converters

“…A vast case history -mostly based on numerical methods -describes the functionality of the different concepts (Chaplin et al, 2007;Hansen et al, 2012;Pecher et al, 2012b;Silva et al, 2013;Mackay et al, 2012;Seidel et al, 2012;Beatty et al, 2008; in operational conditions. Despite their importance, extreme events are rarely considered from a numerical point of view (Palm et al, 2013a) and more present in the literature concerned with physical modelling (Zanuttigh et al, 2013).…”

“…This type of problem can be solved using an observer of the excitation force state, in the form of an Extended Kalman Filter [38] or a Hilbert Transform [39].…”

“…The MEC is implemented using the velocity tracking logic where the velocity signal is generated in two steps: first, the actual wave frequency and amplitude are observed using the Hilbert transform [39] and, second, the observed frequency and amplitude are used in a look-up table to recover the reference velocity at the actual sample time. The general control layout traces out the implementation presented in [47].…”