SEAREV : A FULLY INTEGRATED WAVE ENERGY CONVERTER

A new wave energy converter (WEC), called SEAREV , is presented. The mathematical models and numeric al simulators that have been developped, both in frequency and ti me domains, to assess the electricity production on a given test site are described. Genetic algorithm using these numerical models have then been implemented in order to optim ize the shape and the mechanical parameters of the device. A discrete r al-time control of bang-bang type (latching control) permits to enhance the response of the system to the waves, an d therefore the annual production of energy. INTRODUCTION The SEAREV wave energy converter is a floating device enclosing a heavy horizontal axis wheel serving as an internal gravity reference (see Fig.2). The centre of gravity of the wheel being off-centered, this component behaves mechanically like a pendulum. The rotational motion of this pendular wheel relative to the hull activates an hydraulic Power Take Off (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 wheel 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 alignme t of the device in the dominant wave direction due to the general shape of the hull. This allows the device complying easil y with tide The system being based on the strong coupling of tw nonlinear mechanical oscillators, an analytical s tudy of its behavior in regular and irregular waves has been performed. A c omplete mechanical model of the system has been wri tten, including hydrodynamics of wave device interaction and nonlin ear mechanics of the internal PTO. Only the linear version of the equations will be presented here. We will show how the shape and all the mechanical parameters of the syst m have been optimized using a general purpose multi-parameter m ulti-criterion software, based on genetic algorithm s. A specific real time control has been developed in order to enhance the production in low energetic se a states. Numerical time-domain simulations are presented to exemplify the benefit that latching control can bring to the system. MATHEMATICAL MODELLING The floating body is assumed to have two vertical p l nes of symmetry. We assume that the rotation axis of the internal cylinder is perpendicular to the main symmetry plan e of the floating body. We suppose also the directi on of wave propagation being parallel to this plane (self alig nement). Under these assumptions, in a 2D incident wave trai n, the floating body will move only in surge, heave and pitch mode in the (xOz) plane (Fig.2). 1 Système Électrique Autonome de Récupération d’Éner gie des Vagues Figure 1 The SEAREV device: external view 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 t he inner pendulum. The Power Take Off system (PTO) then works this relative motion α . Let b m the floating body mass, b I its inertia , p m the mass of the inner cylindrical pendulum, y I its moment of inertia. Let AP l = the distance between the center of rotation A of the inner pendulum and its own center of gravity P, GA d = the distance between the center of gravity of the floating body and the center of rota ti n of the pendulum. Wave amplitude and resulting body motion are assume d to be sufficiently small to justify working in the cla ssical linear potential flow theory. Let us define the four components position vector o f the system ( ) G G z x α θ , , , = Z , and the matrices M , B and K as: