Development of a CFD-based numerical wave tank model for the Inertial Sea Wave Energy Converter (ISWEC)

The Inertial Sea Wave Energy Converter device (ISWEC) is a Wave Energy Converter (WEC) that exploit the pitch motion of the hull, due to the presence of the waves, to produce energy. This motion combined by the rotational speed of a flywhell, due to the gyroscopic effect, induce a rotation around the power take-off’s axis (PTO’s axis), allowing in this way the production of energy. The whole device consists of an hermetically sealed hull, in which there are the flywhell and the PTO. This device is also provided by suitable mooring systems for the seabed. The advantage of this technology, is to use a device whose moving parts are not in direct contact with the marine environment, thus allowing reduced operational and maintenance costs. In this thesis, in the first part there will be carried out a general overview of the marine renewable energies, with particular attention to the ocean wave energy. Then there will be a focus on the ISWEC device, not going into too much detail as to complex mathematical formulations, instead focusing on the physics that constitutes the basis of the operation’s principle of this technology, patented at the Polytechnic of Turin in 2007 and implemented at the Island of Pantelleria in the Mediterranean Sea in 2015. A description of the hydrodynamics of the WECs will be presented, with a theoretical deepening on the waves and their mathematical characterization. With the collaboration of the Centre for Ocean Energy Research (C.O.E.R.) at the University of Maynooth, a numerical model was developed, based on the Computational fluid dynamics (CFD) approach in order to validate the numerical model against experimental wave tank tests, conducted at the Ecole Central Nantes (France), by using the CFD open-source software OpenFoam. This model validation will be focused on the empty tank model, free response, and moored response after a preliminary convergence study and wave maker assessment. A simplified mooring version was created and implemented, by designing it as an appropriate spring with an equivalent stiffness. In this way, it was possible to compare the interaction with the structure between the numerical and experimental signals.