THE SEAREV WAVE ENERGY CONVERTER Alain Clément , Aurélien Babarit, Jean-Christophe Gilloteaux, Christophe Josset and Gaelle Duclos Laboratoire de Mécanique des Fluides, CNRS UMR6598 Ecole Centrale de Nantes 1, Rue de la Noe, 44300 Nantes - France. Alain.Clement@ec-nantes.fr ABSTRACT A new Wave Energy Converter, called SEAREV 1 , is presented. Mathematical models, both in frequency and time domains, have been used to optimize the shape and the mechanical parameters by using a genetic algorithm. A discrete real-time control of bang-bang type (latching control) permits to enhance the response of the system to the waves, and therefore the annual production of energy. INTRODUCTION The SEAREV wave energy converter is a floating device enclosing a heavy horizontal axis cylinder serving as an internal gravity reference (see Fig.2). The centre of gravity of the cylinder being off- centered, this component behaves mechanically like a pendulum. The rotational motion of this cylinder relative to the hull activates a hydraulic PTO which, in turn, set an electric generator into motion. Two major advantages of this arrangement are that, first: all the moving parts (mechanic, hydraulic, electric, components) are sheltered from the action of the sea inside a closed, waterproof shell; and secundly that the choice of a cylinder working as a pendulum involve neither endstop nor any security system limiting the stroke. This freely floating device is kept on site by a slack single line mooring which enable self alignment of the device in the dominant wave direction due to the general shape of the hull. This allows the device complying easily with tide The system being based on the strong coupling of two nonlinear mechanical oscillators, an analytical study of its behavior in regular and irregular waves has been performed. A complete mechanical model of the system has been written, including hydrodynamics of the wave device interaction and nonlinear mechanics of the internal Power Take Off. Only the linear version of the equations will be presented here. We 1 Système Électrique Autonome de Récupération d’Énergie des Vagues will show how the shape and all the mechanical parameters of the system have been optimized using a general purpose multi-parameter multi-criterion software, based on genetic algorithms. A specific real time control has been developed in order to enhance the production in low energetic sea states. Numerical time-domain simulations are presented to exemplify the benefit that latching control can bring to the system. Figure 1 The SEAREV device: external view MATHEMATICAL MODELLING The floating body is assumed to have two vertical planes of symmetry. We assume that the rotation axis of the internal cylinder is perpendicular to the main symmetry plane of the floating body. We suppose also the direction of wave propagation being parallel to this plane (self alignement). Under these assumptions, in a 2D incident wave train, the floating body will move only in surge, heave and pitch mode in the (xOz) plane (Fig.2). Let G x the surge motion, G z the heave motion of the centre of gravity G of the floating body, θ the pitch motion and α the relative motion between the floating body and the inner pendulum. The Power Take Off system (PTO) then works this relative motion α . Let b m the floating body mass, b I its 6 th European Wave and Tidal Energy Conference Glasgow, UK August 29 th - September 2 nd 2005 - 81 -