Developing a formula for optimum power of an inverted piston-in-cylinder wave engine

Harvesting energy from the ocean waves has two significant advantages over other renewables: more attractive mean power density and integration into coastal structures. A commonly deployed device is the oscillating water column (OWC), which has so far been mounted on shore and proposed for floating plants. It is an inverted piston-in-cylinder which consists of an air chamber in contact with the sea so that the water column in the chamber oscillates with the waves and makes the air flow in and out of the chamber which turns a turbine. The objective of this study is to propose simple formulas for estimating the output power, efficiency and their maximum values of an inverted piston-in-cylinder converter based on the engine geometry and the most occurring sea state wavelength. Two mathematical models were developed for a floating inverted piston-in-cylinder wave engine based on the theoretical fluid dynamics and expressions were proposed for its output power and overall efficiency. The optimum values were found for both the power and efficiency. The relationship between two models is investigated and it is showed that however the second model is simpler than the first one but, it can be used when the wavelength is more than a specific value.