A comprehensive set of experimental and numerical comparisons of the performance of two self-reacting point absorber wave energy converter (WEC) designs is undertaken in typical operating conditions. The designs are either currently, or have recently been, under development for commercialization. The experiments consist of a series of 1:25 scale model tests to quantify hydrodynamic parameters, motion dynamics, and power conversion. Each WEC is given a uniquely optimized power take off damping level. For hydrodynamic parameter identification, an optimization based method to simultaneously extract Morison drag and Coulomb friction coefficients from decay tests of under-damped, floating bodies is developed. The physical model features a re-configurable reacting body shape, a feedback controlled power take-off, a heave motion constraint system, and a mooring apparatus. A theoretical upper bound on power conversion for single body WECs, called Budal's upper bound, is extended to two body WECs. The numerical analyses are done in three phases. In the first phase, the WECs are constrained to heave motion and subjected to monochromatic waves. Quantitative comparisons are made of the WEC designs in terms of heave motion dynamics and power conversion with reference to theoretical upper bounds. Design implications of a reactive power take-off control scheme and relative motion constraints on the wave energy converters are investigated using an experimentally validated, frequency domain, numerical dynamics model. In the second phase, the WECs are constrained to heave motion and subjected to panchromatic waves. A time domain numerical model, validated by the experimental results, is used to compare the WECs in terms of power matrices, capture width matrices, and mean annual energy production. Results indicate that the second WEC design can convert 30% more energy, on average, than the first design given the conditions at a representative location near the West coast of Vancouver Island, British Columbia, Canada. In the last phase, the WECs are held with three legged, horizontal, moorings and subjected to monochromatic waves. Numerical simulations using panelized body geometries for calculations of Froude-Krylov, Morison drag, and hydrostatic loads are developed in ProteusDS. The simulation results---mechanical power, mooring forces, and dynamic motions---are compared to model test results. The moored WEC designs exhibit power conversion consistent with heave motion constrained results in some wave conditions. However, large pitch and roll motions severely degrade the power conversion of each WEC at wave frequencies equal to twice the pitch natural frequency. Using simulations, vertical stabilizing strakes, attached to the reacting bodies of the WECs are shown to increase the average power conversion up to 190% compared to the average power conversion of the WECs without strakes. / Graduate / scottb@uvic.ca

Cette thèse s’inscrit dans le cadre du 12ème appel à projet du Fonds Unique Interministériel (FUI) lancé par l’Etat au premier semestre 2011. Le projet « EM BILBOQUET » a été colabellisé par les pôles de compétitivité Mer Bretagne, Mer PACA et Tenerrdis. Il consiste en la réalisation d’un nouveau système de génération d’électricité issue du mouvement relatif entre deux corps flottants, mus par la houle. Dans cette thèse, nous nous sommes intéressés au contrôle optimal à appliquer sur la génératrice via les convertisseurs statiques, afin d’extraire le maximum d’énergie de la houle incidente. Dans un premier temps, nous avons établi les équations dynamiques régissant le comportement de la structure dans la houle en adoptant les hypothèses de la théorie potentielle. Pour ce faire, nous avons développé un code de calcul spécifique, basé sur une résolution du problème linéaire de tenue à la mer, par des méthodes dites semi-analytiques. Ce code de calcul permet de déterminer les coefficients hydrodynamiques nécessaires à l’écriture de l’équation dynamique dans le domaine fréquentiel, mais aussi dans le domaine temporel via une modification de la formulation de Cummins. Cette dernière nous permet ainsi, dans un second temps, de formuler le problème de maximisation de l’énergie récupérée comme un problème d’optimisation où la variable à optimiser est le couple résistant de la génératrice. Le problème est résolu en temps réel en adoptant une résolution par algorithme dit à horizon fuyant. / In this thesis, we perform a study on a self-reacting point absorber, project FUI 12 “EM BILBOQUET”, in order to optimise energy extraction from incoming waves. Main researches use seabed for providing reference to a floating body, called buoy. However, as it is well-known that ocean energy is greater far away from the shore, sea-depth becomes a constraint. In this thesis a damping plate attached to a spar keel is proposed to allow the floating body to react against it. Energy resulting from the relative motion between the two concentric bodies i.e. the buoy and the spar is harnessed by a rack-and-pinion, which drive a permanent magnet synchronous generator through a gearbox. In the first part of the thesis we have developed a wave-to-wire model i.e. a model of the whole electro-mechanical chain from sea to grid. To this purpose we have developed our own hydrodynamic code, based on linear potential theory and on a semianalytical approach, solving the seakeeping problem. The hydrodynamic coefficients obtained such as added mass, radiation damping, and wave excitation forces are required for solving the dynamic equation based on Cummins formulation. The second part of the thesis focuses on the self-reacting point-absorber optimal control strategy and the Model Predictive Control (MPC) formulation is proposed. Objective function attempting to optimise the power generation is directly formulated as an absorbed power maximisation problem and thus no optimal references, such as buoy and/or spar velocity, are required. However, rather than using the full-order WEC model in the optimisation problem, that can be time-consuming due to its high order, and also because of the linear assumptions, we propose the use of a “phenomenologically" one-body equivalent model derived from the Thévenin’s theorem.

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