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SUMMARYThe performance of oscillating water column (OWC) systems depends on a number of factors in a complex manner. The objective of this work is to analyse the influence of the wave conditions, the damping caused by the turbine and the tidal level on the efficiency of the conversion from wave to pneumatic energy that occurs in the OWC chamber. To achieve this, a comprehensive experimental campaign is carried out, involving in total 387 tests of a model OWC under varying wave conditions (both with regular and irregular waves), damping coefficients and tidal levels. It is found that the damping exerted by the turbine is the factor that most affects the chamber efficiency-even more than the wave conditions. It follows that a proper selection of the turbine is crucial not only to the performance of the turbine itself but also to that of the chamber, which reflects the importance of the turbine-chamber coupling in OWC systems. The next factor in order of importance is the wave period. Finally, we find that the influence of the tidal level, which is examined in this work for the first time, is significant under certain conditions.

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a b s t r a c tAlthough oscillating water column (OWC) systems are one of the most studied types of wave energy converter, developing a method for selecting the optimum turbine for an OWC at a given sitedi.e., subjected to a particular wave climatedremains a current research topic. The objective of this work is to develop and apply a methodology for determining the optimum turbine-induced damping, i.e., that which maximises the performance of the conversion from wave to pneumatic energy, in an OWC equipped with a self-rectifying impulse turbine. The turbine can then be dimensioned to achieve this damping level. Illustrated through a case study, this method adopts a holistic approach encompassing the site-specific wave climate variability. A validated RANS-VOF model is implemented to compute the performance of the OWC for a range of damping coefficients (corresponding to different turbines) and wave conditions, selected based on their energy content and weighted by their occurrence at the site. In this manner, the pneumatic power matrices corresponding to different values of turbine-induced damping are computed, and the optimum damping accounting for the wave climate variability is determined. We find that this methodology may lead to a significant improvement in the annual energy output of the OWC chamber.