Le présent travail est une étude sur la modélisation des éoliennes flottantes alliant à la fois des chargements hydrodynamiques et aérodynamiques. L’approche expérimentale a tiré profit de la grande soufflerie de Luminy opérée par le MIO (Institut Océanologique de Méditerranée), unissant une soufflerie de très bonne qualité avec un bassin équipé de systèmes de génération de houle et de courant. Les dimensions de cette installation imposent un travail à échelle très réduite introduisant ainsi les interrogations sur les similitudes à respecter (Reynolds, Froude) et les complexités de maquettage. Ces travaux ont permis de développer des outils numériques avec d’un côté une approche fréquentielle basé sur un code utilisant les éléments finis développé par l’IFP au début des années 70, et de l’autre, une approche temporelle basé sur les formulations de Morison ou de Rainey permettant l’introduction de méthodes avancées de calculs des efforts aérodynamiques. / The present work focuses on the modeling of the hydrodynamic and aerodynamic loads on a floating wind turbine. The experimental approach took advantage of the wind and wave flume in Luminy operated by the MIO (Mediterranean Institute for Oceanography) comprising a wind tunnel with a very high flow quality blowing over a wave tank. The dimensions of the installation impose working at very small scales for which the similitudes (Reynolds, Froude) introduce high modeling complexities. This work allowed the development of numerical tools using one the one hand a frequency domain approach based on a finite element code developped by IFP¨in the early seventies, and in the other hand a time-domain approach based on Morison or Rainey formulation for hydrodynamic loads allowing the introduction of advanced methods for aerodynamic loads computation.

Marine and hydrokinetic (MHK) energy, including ocean waves, tidal current, ocean current and river current, has been recognized as a promising power source due to its full-day availability and high energy potential. At this stage, ocean current energy, tidal energy and ocean wave energy are currently the most competitive sourves among all the categories of MHK. The state of art MHK energy harvesting technology mainly focus on harvesting either ocean wave energy or current energy, but not both. However, a significant amount of ocean waves and tidal/ ocean current coexist in many sites and traditional devices that harvest from a single form of MHK energy, cannot make full use of the coexisting ocean energy. Furthermore, MHK energy harvesting devices need to advance to be cost-effective and competitive with other energy sources. This is difficult to achieve. Ocean wave excitation is irregular, which means that ocean wave height and wave periods are unpredictable and excitation forces on energy harvesting devices can have large variance in amplitude and frequency. Such problems/ restrictions can be possibly addressed by the concept of a hybrid energy converter. In this sense, a hybrid wave-current ocean energy conveter (HWCEC) that simutaneously harvests energy from current and wave with one single power takeoff (PTO) is designed.The wave energy is extracted through relative heaving motion between a floating buoy and a submerged second body, while the current energy is extracted using a marine current turbine (MCT). Energy from both sources are integrated by a hybrid PTO whose concept is based on a mechanical motion rectifier (MMR). In this study, different working modes are investigated together with switching criteria.Simulations were conducted with hydrodynamic coefficients obtained from computational fluid dynamics analysis and boundary element method. Tank tests were conducted for a HWCEC under co-existing wave and current inputs. For comparison, separate baseline tests of a turbine and a two-body point absorber, each acting in isolation, are conducted. Experimental results validate the dynamic modeling and show that a HWCEC can increase the output power with a range between 29-87 percent over either current turbine and wave energy converter acting individually, and it can reduce by up to 70 percent the peak-to-average power ratio compared with the wave energy converter on the tested conditions.Such results demonstrate the potential of the HWCEC as an efficient and cost-effective design. / Master of Science / Ocean energy has been recognized as a promising power source due to its full-day availability and high energy potential. At this stage, ocean current energy, tidal energy and ocean wave energy are currently the most competitive sources among all the categories of ocean energy. The state of art ocean energy harvesting technology mainly focus on harvesting either ocean wave energy or current energy, but not both. However, a significant amount of ocean waves and tidal/ ocean current coexist in many sites and traditional devices that harvest from a single form of ocean energy, cannot make full use of the coexisting energy resource. Furthermore, MHK energy harvesting devices need to advance to be cost-effective and competitive with other energy sources. This is difficult to achieve. Ocean wave height and wave periods are unpredictable and excitation forces on energy harvesting devices can have large variance in amplitude and frequency. Such restrictions can be possibly addressed by the concept of a hybrid energy converter. In this sense, a hybrid wave-current ocean energy converter (HWCEC) that simultaneously harvests energy from current and wave with one single power takeoff (PTO), which consists of ball screw, gearbox, and generator, is designed.The wave energy is extracted through relative heaving motion between a floating buoy and a submerged second body, while the current energy is extracted using a marine current turbine (MCT). Energy from both sources are integrated by a hybrid PTO whose concept is based on a mechanical motion rectifier (MMR). In this study, different working modes are investigated together with switching criteria.Simulations were conducted with hydrodynamic coefficients obtained from computational fluid dynamics analysis and boundary element method. Tank tests were conducted for a HWCEC under co-existing wave and current inputs. For comparison, separate baseline tests of a turbine and a two-body, wave-energy-harvesting structure, each acting in isolation, are conducted. Experimental results validate the dynamic modeling and show that a HWCEC can increase the output power with a range between 29-87 percent over either current turbine and wave energy converter acting individually, and it can reduce by up to 70 percent the peak-to-average power ratio compared with the wave energy converter on the tested conditions.Such results demonstrate the potential of the HWCEC as an efficient and cost-effective design.

Ocean wave as a renewable energy source possesses great potential for solving the world energy crisis and benefit human beings. The total theoretical potential wave power on the ocean-facing coastlines of the world is around 30,000 TWh, although cannot all be adopted for generating electricity, the amount of the power can be absorbed still can occupy a large portion of the world's total energy consumption. However, multiple reasons have stopped the ocean wave energy from being widely adopted, and among those reasons, the most important one is immature of the Power Take-off (PTO) technology. In this dissertation, a self-reactive two-body wave energy point absorber that is embedded with a novel PTO using the unique mechanism of Mechanical Motion Rectifier (MMR) is investigated through design, analysis and testing to improve the energy harvesting efficiency and the reliability of the PTO. The MMR mechanism can transfer the reciprocated bi-directional movement of the ocean wave into unidirectional rotation of the generator. As a result, this mechanism brings in two advantages towards the PTO. The first advantage it possess is that the alternating stress of the PTO is changed into normal stress, hence the reliability of the components are expected to be improved significantly. The other advantage it brings in is a unique phenomenon of engagement and disengagement during the operation, which lead to a piecewise nonlinear dynamic property of the PTO. This nonlinearity of the PTO can contribute to an expanded frequency domain bandwidth and better efficiency, which are verified through both numerical simulation and in-lab experiment. During the in-lab test, the prototyped PTO achieved energy transfer efficiency as high as 81.2%, and over 40% of efficiency improvement compared with the traditional non-MMR PTO under low-speed condition, proving the previously proposed advantage. Through a more comprehensive study, the MMR PTO is further characterized and a refined dynamic model. The refined model can accurately predict the dynamic response of the PTO. The major factors that can influence the performance of the MMR PTO, which are the inertia of the PTO, the damping coefficient, and the excitation frequency, are explored through analysis and experiment comprehensively. The results show that the increase on the inertia of the PTO and excitation frequency, and decrease on the damping coefficient can lead to a longer disengagement of the PTO and can be expressed analytically. Besides the research on the PTO, the body structure of the point absorber is analyzed. Due to the low-frequency of the ocean wave excitation, usually a very large body dimension for the floating buoy of the point absorber is desired to match with that frequency. To solve this issue, a self-reactive two-body structure is designed where an additional frequency between the two interactive bodies are added to match the ocean wave frequency by adopting an additional reactive submerged body. The self-reactive two-body structure is tested in a wave to compare with the single body design. The results show that the two-body structure can successfully achieve the frequency matching function, and it can improve more than 50% of total power absorption compared with the single body design. / Doctor of Philosophy / Ocean wave as a renewable energy source possesses great potential for solving the world energy crisis and benefit human beings. The total theoretical potential wave power on the ocean-facing coastlines of the world is around 30,000 TWh, although impossible to be all transferred into electricity, the amount of the power can be absorbed still can cover a large portion of the world's total energy consumption. However, multiple reasons have stopped the ocean wave energy from being widely adopted, and among those reasons, the most important one is immature of the Power Take-off (PTO) technology. In this dissertation, a novel two body wave energy converter with a PTO using the unique mechanism of Mechanical Motion Rectifier (MMR) is investigated through design, analysis, and testing. To improve the energy harvesting efficiency and the reliability of the PTO, the dissertation induced a mechanical PTO that uses MMR mechanism which can transfer the reciprocated bi-directional movement of the ocean wave into unidirectional rotation of the generator. This mechanism brings in a unique phenomenon of engagement and disengagement and a piecewise nonlinear dynamic property into the PTO. Through a comprehensive study, the MMR PTO is further characterized and a refined dynamic model that can accurately predict the dynamic response of the PTO is established. The major factors that can influence the performance of the MMR PTO are explored and discussed both analytically and experimentally. Moreover, as it has been theoretically hypothesis that using a two-body structure for designing the point absorbers can help it to achieve a frequency tuning effect for it to better match with the excitation frequency of the ocean wave, it lacks experimental verification. In this dissertation, a scaled two-body point absorber prototype is developed and put into a wave tank to compare with the single body structure. The test results show that through the use of two-body structure and by designing the mass ratio between the two bodies properly, the point absorber can successfully match the excitation frequency of the wave. The highest power capture width ratio (CWR) achieved during the test is 58.7%, which exceeds the results of similar prototypes, proving the advantage of the proposed design.

Recent events regarding energy policies throughout the globe and advances in technology are making offshore wind farms become a reality. Most offshore wind farms are still, however, built close to land masses, and need to be rigidly attached to the seabed in one way or another. In many countries, both public and private entities are developing new concepts of floating platforms to overcome the thirty to thirty-five-metre depth limit. Some of these new platforms use and adapt previous Oil and Gas platform concepts, while others are built up from scratch. This Master Thesis covers a hydrodynamic and structural analysis of a new concrete floating platform concept developed for medium to deep waters. This work is based on data from experimental model-scale tests performed in a wave tank and from numerical models using linear potential theory, limited here only to regular wave trains. The study focused on the behavior of the heave plates attached to the platform: test data was analyzed in order to find indicators of the largest dynamic pressures on the plates when only motion data was available, and the structural behavior of the plates was studied under different static pressure distributions using a commercial Finite Element Method software. The results from these analyses show that the normal accelerations of the plates -assumed rigid- strongly correlate with the dynamic pressures measured; and that the general structural behavior of the plate, in terms of deformations and bending moments, is well captured when the hydrodynamic load distribution is simplified into a uniformly distributed load of the same magnitude. The results obtained will help reduce the computational effort currently needed in the design of these floating structures, especially at some stages, when numerous scenarios, load cases and combinations need to be studied.

Early in the ship design process, naval architects must often evaluate and compare multiple hull forms for a specific set of requirements. Analytical tools are useful for quick comparisons, but they usually specialize in a specific hull type and are therefore not adequate for comparing dissimilar hull types. Scale model hydrodynamic testing is the traditional evaluation method, and is applicable to most hull forms. Scale model tests are usually performed on the largest model possible in order to achieve the most accurate performance predictions. However, such testing is very resource intensive, and is therefore not a cost effective method of evaluating multiple hull forms. This thesis explores the testing of small scale models. It is hypothesized that although the data acquired by these tests will not be accurate enough for performance predictions, they will be accurate enough to rank the performance of the multiple hull forms being evaluated.