An in depth experimental investigation into effects of incident wave characteristics front wall opening and PTO damping on the water column displacement and air differential pressure in an OWC chamber

Abstract

Abstract Efficiency of an OWC depends solely on the water column heave motion and air pressure differential in the chamber. In this study, an extensive experimental campaign is conducted to investigate the displacement of water column surface (WCS) and chamber air pressure under different incident waves, chamber underwater opening heights and applied PTO dampings. It is found that, transmitted wave height ( μ ) and transmitted wave pressure ( P w ) exponentially decay with the dimensionless wave frequency ( K h ) irrespective of the relative opening ( α ) and orifice ratio ( τ ) (PTO damping), however, the decay rate slows down as the orifice ratio decreases. Effects of orifice ratio on μ and P w heavily depend on the value of the K h such that as K h increases transmitted wave height, μ and pressure, P w become less sensitive to variations in the orifice ratio, τ . P w increase with the relative opening in a linear fashion but the upward trend declines for larger dimensionless wave frequencies. An almost perfect linear association is detected between transmitted wave height and pressure, and, captured wave length ( δ ) (incident wave length divided by chamber length). In the design stage, in order to prevent sloshing in the chamber δ smaller than approximately 4 should not be selected. Negative pressure peaks are always found to be larger than positive pressure peaks in magnitude. Further, a novel dimensionless pressure number N P R is proposed, which is found to be proportional to μ . Proportionality constant is also presented. Accordingly, prediction of μ or P w yields the value of the other in an accurate manner. Despite the complex wave-energy conversion processes the most important aspects and the related parameters can be described using very accurate simple analytical models.