Numerical and experimental analysis of the efficiency of an Oscillating Water Column

The WaveSax is an Oscillating Water Column with an immersed Wells turbine. It is thought to be installed on harbours or other marine structures as offshore platforms or multi-purpose floating units. The aim of this work is to investigate its efficiency when it is deployed in the Mediterranean sea. Two different and complementary approaches are used to investigate the response of the device to the incoming waves. First a numerical algorithm WaveFoam [1] is used to simulate the interaction between the WaveSax and a regular wave with a period in the range of those characteristics of the coasts in central Italy [2]. The presence of the turbine is modeled with a porous sect whose porosity parameter is set so to obtain a pressure jump across it similar to that produced by the chosen turbine. Experimental analysis performed in the wave tank focused on the control parameters (torque and angular velocity), which are varied to maximize the efficiency. The experimental results show that the control strategy acting on the angular velocity are the most efficient. Furthermore the numerical simulations show that the presence of a wall behind the device increases the captured power because of partial reflections on it.