Cette thèse porte sur le développement d'un ensemble d'outils numériques destinés à simuler différents aspects des interactions vagues-structure appliquées à l'exploitation des systèmes de récupération de l'énergie des vagues (SREV). Elle a été réalisée dans le cadre du projet ANR Monacorev (projet ANR11-MONU-018-01, 2012-2015).L'objectif est de pouvoir traiter la question des interactions à l'échelle d'une ferme de SREVs (≈ 1 km), et d'étudier l'impact d'une ou plusieurs fermes de SREVs à l'échelle régionale (≈ 10km) sur le champ de vague total. Des méthodes de modélisation et de simulation adaptées sont développées pour chacune de ces deux échelles. Jusqu'à présent, les interactions entre les SREVs étaient bien souvent étudiées en considérant que le fond était plat (l'influence d'un fond variable sur le champ de houle au niveau de la ferme étant alors jugé négligeable), ce qui permet de calculer facilement et rapidement le champ de vagues et les interactions grâce à l'utilisation de la théorie linéaire potentielle. Une application pratique de cette méthode est le calcul du rendement d'une ferme de SREVs, et l'optimisation de leurs positions relatives au sein d'un parc. Dans le cadre de la théorie linéaire, cette thèse propose une méthodologie de couplage originale entre un code de tenue à la mer (Aquaplus) et un code de propagation de la houle en zone côtière (Artemis), laquelle a été développée et qualifiée. Les simulations réalisées montrent que, pour une configuration de ferme de SREVs donnée, on ne peut pas toujours négliger les effets de la bathymétrie. Par exemple, la présence d'une plage de pente 10% au large d'une ferme de SREV peut modifier la hauteur des vagues de manière significative, et affecter ainsi le rendement de la ferme de manière significative par rapport au cas où le fond est uniformément plat. A l'échelle côtière régionale, il est aussi intéressant de simuler et prédire l'impact de fermes de SREVs sur le champ de vagues. Pour des raisons d'efficacité, une approche à phases moyennées de modélisation des vagues a été privilégiée, fondée sur le code spectral d'états de mer Tomawac. La représentation des effets d'un SREV à travers l'utilisation d'un terme puits (concept permettant de soustraire au spectre d'énergie d'état de mer local l'énergie correspondant à celle absorbée par le SREV), bien qu'incomplète du fait que les effets de radiation/diffraction ne sont pas pris en compte, a été étudiée et testée. Une nouvelle méthodologie prenant en compte ces effets dans un code spectral est présentée ici et testée, avec l'objectif de pallier à ces limitations. Les discussions sur la validité de deux approches permettent d'esquisser des pistes de développements ultérieurs pour la représentation des fermes de SREV à l'échelle régionale / This thesis focuses on the development of a set of numerical tools to simulate different aspects of the wave-body interactions applied to the exploitation of wave energy converters (WEC). It was conducted under the ANR Monacorev project (project-ANR11 MONU-018-01, 2012-2015).The objective is to address the issue of the interactions at the scale of a farm of WECs (≈ 1 km), and to study the impact of one or more WEC farms at the regional scale (≈ 10km ) on the total wave field. Modeling and simulation methods adapted for each of these two scales are developed. Until now, the interactions between WECs was often studied by considering that the bottom was flat (the influence of a variable bathymetry on the wave field at the farm site being considered to be negligible), allowing to easily and quickly calculate the wave field and interactions through the use of linear potential theory. A practical application of this method is the yield estimation for a WEC farm and the optimization of the WEC position within a park. In the framework of the linear theory, this thesis proposes an original coupling methodology between a seakeeping (Aquaplus) and a wave propagation code in coastal areas (Artemis), which was developed and qualified. Simulations show that, for a given WEC farm configuration, effects of the bathymetry cannot systematically ignored. For example, the presence of a 10% slope close to a WEC farm can significantly modify the wave height, and thus affect the performance of the farm by several percent compared to the case with a uniformly flat bottom. At the regional coastal scale, it is also interesting to simulate and predict the impact of WEC farms on the wave field. At this scale, for efficiency reasons, a phase-averaged simulation of waves was preferred, based on the sea state spectral code TOMAWAC. The representation of the effects of a WEC through the use of a sink-term (concept for subtracting the energy equivalent to that absorbed by the WEC to the sea state energy spectrum), though incomplete due to the fact that the scattering effects are not taken into account, has been studied and tested. A new methodology taking into account these effects in a spectral code is presented here and tested with the aim to overcome these limitations. Discussions on the validity of these approaches allow us to propose possible future developments for the modeling of WEC farm at the regional scale

Wave energy converter (WEC) harnesses energy from the ocean to produce electrical power. The electrical power produced by the WEC is fluctuating and is not maximized as well, due to the varying ocean conditions. As a consequence, without any intermediate power conversion stage, the output power from the WEC can not be fed into the grid. To feed WEC output power into the grid, a two-stage power conversion topology is used, where the WEC output power is first converted into DCpower through rectification, and then a DC-AC converter (inverter) is used to supply AC power into the grid. The main motive of this research is to extract maximum electrical power from the WEC by active rectification and smoothing the power fluctuation of the wave energy converter through a hybrid energy storage system consisting of battery and flywheel. This research also illustrates active and reactive power injection to the grid according to load demand through a voltage source inverter.

Grid connection of wave energy is one of the crucial remaining areas of development towards the commercialization of this renewable energy technology. One of the major challenges with the grid connection of the wave energy technology is power variability. The rapidly changing voltage and power production from very high peaks to lows, increases the complexity for the wave farm developers to reach an agreement with the grid owners to satisfy the grid compliance. Correspondingly, electrical network designs of the offshore wind sector also differ on some key features which includes the power variability, cable lengths, power ratings, connection layouts, sea depths and transmission distances. These differences present new challenges to engineers in adapting technology and knowhow from the wind industry wherever applicable; whereas in parts of the network where power ratings are <2 MW, new designs need to be derived. Hence, power system dynamic modelling of variable emerging wave energy puts a great field of research. CorPower Ocean AB is in the process of developing a 300-kW point absorber type Wave Energy Converter (WEC) that is a commercial fullscale prototype. In this regard, the thesis will discuss the topics of optimization of offshore wave energy electrical networks for farms primarily focused on a 10 MW rating. The modelling for RMS simulation, network efficiency, voltage profile and power quality analysis has been simulated on DIgSILENT PowerFactory. Grid connection compliance for voltage levels, voltage flicker and power factor has been evaluated against local site regulations and parameters for optimal efficiency and better power quality with respect to grid connection is discussed. The impact of grid impedance angle and the wave front incidence angle on the rating of wave farm being connected is also evaluated. The study leads to an optimized electrical layout of a wave farm which can tackle problems such as voltage flicker and varying power. The study also leads to the understanding of better layout for the point absorber with least transmission losses. This study can also be generalized for bigger wave farms in the future which will reduce the complexity and time for wave farms engineers while planning.

A small-scale wave energy converter was designed and built for teaching and academic purposes to be used at The Division for Electricity, in the Ångström Laboratory at Uppsala University. The design of the power take-off (PTO) makes use of magnets passing through a copper coil for electricity generation. The magnets are attached by a string to the floating buoy in the small-scale wave tank which leads to a joint oscillation. Design parameters are executed using COMSOL Multiphysics which illustrates the total voltage output generated as well as the total magnetic field. Simulations and calculations in MATLAB were performed to extract the expected damping coefficient and plots of the buoy position compared to the wave amplitude. Lastly, a PTO prototype were built and compared with the simulations. The PTO shows electricity generation with the aid of a voltmeter showcasing the voltage. Additional information on future improvements to further aid teaching and academic understanding of wave energy converter are mentioned in the final section of this study.