Increasing energy demand and carbon emissions have driven the development of alternative energy solutions. One promising technology is wind energy. Wind energy technology developments has advanced substantially since the 1980s. Offshore wind turbines have become a major research focus, due to the promising offshore wind resource. However, challenges in offshore wind energy have arisen due to the additional wave loading and strong wind loads. Structural control systems have been implemented and researched in order to decrease dynamic response of these systems. The previous studies were successful at decreasing fatigue loads in the tower and support structure of offshore wind turbines. Giving these results, it is still unknown if the reduced loading enabled by structural control systems can allow for reduced material costs in the major structural components. This research examines on an offshore wind turbine's tower-monopile structure by adding several configurations of passive tuned mass dampers, while simultaneously reducing the thickness of the structure in order to reduce costs. A range of candidate tower-monopile systems are created, and simulated in FAST-SC with and without passive tuned mass dampers. Fatigue and ultimate loads are calculated and analyzed. A variety of design criteria are considered including fatigue and ultimate loads, as well as local and global buckling. The results demonstrate that the tower-monopile thickness may be reduced up to 6.2% and still satisfy all design criteria.

To enable the use of renewable energy throughout the system, the Dutch government aims to rely strongly on hydrogen gas as a green energy carrier. This thesis is dedicated to assessing the feasibility of meeting the future Dutch hydrogen demand with locally produced green hydrogen through offshore wind. The aim was realized by modelling the Dutch hydrogen demand in 2050 based on government plans and comparing this with the amount of green hydrogen the Netherlands can produce through offshore wind. Methods used include extensive literature reviews, energy system modelling, scenario analysis, and calculations. The results show that between 1,28 and 2,04 EJ of wind energy is necessary to meet the regular electricity demand and the electricity demand for hydrogen production through electrolysis. This needs to be compared to an offshore wind energy potential in the Dutch North Sea that ranges between 0,67 and 1,79 EJ. An analysis of the results shows that the offshore wind demand could be met, but it is more likely that the offshore wind energy potential is insufficient to meet the demand. The government envisions five applications for hydrogen, namely to be used as feedstock for the process industry, to generate high temperature heat, as energy storage for renewables (balancing the grid), as a transport fuel, and in the built environment. The results indicate that the demand of these five applications is unlikely to be met completely with offshore wind green hydrogen. However, the large majority of the hydrogen demand is dedicated to be used as a feedstock for the process industry. If this feedstock were to be from another source, meeting the demand of the remaining hydrogen applications with offshore wind is more realistic. Consequently, a main take-away is that the creation of a wind and solar based electricity grid with green hydrogen as a balancing agent is feasible. The results of this research gave rise to several recommendations. Firstly, renewable energy generation should be maximized using the full scope of different available techniques (not only focusing on offshore wind). Second, different decarbonization pathways other than offshore wind green hydrogen should be explored to account for process industry feedstocks. Third, the government should work closely together with other North Sea-bordering countries in order to make the best use of the available space. Fourth and final, efforts should be steered towards maximizing the wind energy potential of the Dutch North Sea, which is ideally suited for wind energy generation and should therefore be used in the best way possible.

Yes / The fast‐growing offshore wind energy sector brings opportunities to provide a sustainable energy resource but also challenges in offshore wind turbine (OWT) operation and maintenance management. Existing operational simulation models assume deterministic input reliability and failure cost data, whereas OWT reliability and failure costs vary depending on several factors, and it is often not possible to specify them with certainty. This paper focuses on modelling reliability and failure cost uncertainties and their impacts on OWT operational and economic performance. First, we present a probabilistic method for modelling reliability data uncertainty with a quantitative parameter estimation from available reliability data resources. Then, failure cost uncertainty is modelled using fuzzy logic that relates a component's failure cost to its capital cost and downtime. A time‐sequential Monte Carlo simulation is presented to simulate operational sequences of OWT components. This operation profile is later fed into a fuzzy cost assessment and coupled with a wind power curve model to evaluate OWT availability, energy production, operational expenditures and levelised cost of energy. A case study with different sets of reliability data is presented, and the results show that impacts of uncertainty on OWT performance are magnified in databases with low components' reliability. In addition, both reliability and cost uncertainties can contribute to more than 10% of the cost of energy variation. This research can provide practitioners with methods to handle data uncertainties in reliability and operational simulation of OWTs and help them to quantify the variability and dependence of wind power performance on data uncertainties. / Engineering and Physical Sciences Research Council. Grant Number: EP/P009743/1

This thesis presents an innovative approach to enhance the stability of floating offshore wind turbine (FOWT) platform through mooring actuation. First, an OC3- Hywind spar-buoy floating platform is modeled utilizing the Control-oriented, Reconfigurable, and Acausal Floating Turbine Simulator (CRAFTS) with a specific focus on predicting hydrodynamic and mooring line loads while intentionally excluding consideration of aerodynamic forces. The accuracy of this model is validated against the industry standard OpenFAST simulator through various test cases. The central objective of this study revolves around achieving robust stabilization of the spar buoy platform, primarily focusing on X-Z symmetric planar motions, including surge, pitch, and heave degrees of freedom (DOFs). To accomplish this, two linearization techniques are employed: one transforms the inherently complex nonlinear model from CRAFTS into a linear Mass-Spring-Damper (MSD) system, particularly targeting surge and pitch motions, while the other method involves the conversion of the nonlinear model from CRAFTS into the Functional Mockup Interface (FMI) within MATLAB/Simulink for linearization. The analysis utilizing Bode plots derived from these lin- earized models yields crucial insights into the system's response to mooring actuation. Notably, it emphasizes the inherent challenge in pitch control, characterized by lower gain compared to surge at relevant frequencies, necessitating substantial mooring actuation or cable length modifications for effective pitch stabilization. Then, a Linear Quadratic Regulator (LQR) controller is designed to mitigate surge and pitch motions. Numerical simulations conducted across diverse scenarios reveal the inherent challenge in simultaneously mitigating surge and pitch motions using the original platform configuration. To address this challenge, a control co-design strategy is proposed, leading to the development of an optimized mooring line configuration that effectively stabilizes both motions with minimal adjustments. In summary, this thesis introduces a control-oriented modeling approach and an innovative control strategy to enhance the stability of the floating wind turbine platform through mooring actuation. The results emphasize the potential for broader application of this approach to various floating platforms for FOWTs and the extension of stabilization efforts to address all six DOFs in future research, where aerodynamic loads are also incorporated.

The aim of this thesis is to evaluate different repowering alternatives from the viewpoint of increasing power production from existing offshore wind farms (OWF), as some of the first commissioned OWFs are approaching the end of their expected lifetime. The thesis presents a literature review of components and financial aspects that are of importance for repowering of OWFs. In the literature review, risks and uncertainties regarding repowering are also lifted and analysed. The thesis contains a case study on Horns Rev 1 OWF, where three different repowering scenarios are evaluated by technical and financial performance, aiming to compare the cost of repowering alternatives. The design of the case study is based around previous studies of offshore repowering having focused mainly on achieving the lowest possible levelized cost of energy (LCoE) and highest possible capacity factor, often resulting in suggested repowering utilizing smaller wind turbines than the existing ones. In order to evaluate the financial viability of repowering alternatives, the software RETScreen Expert was used to estimate the annual energy production (AEP) after losses and calculate the net present value (NPV) and LCoE for lifetime extension and full repowering utilizing different capacity wind turbines. Input values from the literature as well as real wind resource measurements from the site was utilized to achieve as accurate results as possible. The result of the case study shows that repowering of OWFs have the possibility of providing a very strong business case with all scenarios resulting in a positive NPV as well as lower LCoE than the benchmarked electricity production price. Although the initial investment cost of the different repowering alternatives presented in this thesis still are uncertain to some extent, due to the lack of reliable costs for repowering alternatives, this thesis provides a base for further research regarding the repowering of OWFs.

Submitted by Mateus Gomes (mateussg@msn.com) on 2018-05-25T17:01:45Z No. of bitstreams: 2 Dissertacao Mateus Gomes.pdf: 6830547 bytes, checksum: 47179b5d6a73fd8cdb299c49042f908c (MD5) Carta comprovante Mateus Gomes.jpg: 517376 bytes, checksum: 897b93ae582b7da42bf02be5122cf5a6 (MD5) / Approved for entry into archive by Milena Rubi ( ri.bso@ufscar.br) on 2018-06-04T13:13:11Z (GMT) No. of bitstreams: 2 Dissertacao Mateus Gomes.pdf: 6830547 bytes, checksum: 47179b5d6a73fd8cdb299c49042f908c (MD5) Carta comprovante Mateus Gomes.jpg: 517376 bytes, checksum: 897b93ae582b7da42bf02be5122cf5a6 (MD5) / Approved for entry into archive by Milena Rubi ( ri.bso@ufscar.br) on 2018-06-04T13:13:24Z (GMT) No. of bitstreams: 2 Dissertacao Mateus Gomes.pdf: 6830547 bytes, checksum: 47179b5d6a73fd8cdb299c49042f908c (MD5) Carta comprovante Mateus Gomes.jpg: 517376 bytes, checksum: 897b93ae582b7da42bf02be5122cf5a6 (MD5) / Made available in DSpace on 2018-06-04T13:13:34Z (GMT). No. of bitstreams: 2 Dissertacao Mateus Gomes.pdf: 6830547 bytes, checksum: 47179b5d6a73fd8cdb299c49042f908c (MD5) Carta comprovante Mateus Gomes.jpg: 517376 bytes, checksum: 897b93ae582b7da42bf02be5122cf5a6 (MD5) Previous issue date: 2018-02-26 / Não recebi financiamento / Electricity generation is a global challenge to be faced by several countries. This has led to the pursuit and development of new clean technologies to sustainable supply of the growing world demand for energy. Currently the main sources of renewable energy are: biomass, solar, geothermal, tidal, wind on and offshore (land and sea). Among these sources, wind energy presents worldwide growth and recently a significant increase in its use in the offshore segment. Brazil is among the ten largest onshore wind power producers in the world, however it does not have yet any offshore wind farms. The country has great potential for exploration of offshore wind power, since there are large population concentrations with increasing energy demands in coastal areas and an Exclusive Economic Zone (EEZ) of approximately 3.5 × 10^6 km^2. The objective of this work was to develop a methodology for the use of offshore wind energy through the proposal of an offshore wind farm on the Southeast coast of Brazil. The study was carried out for the Southeast region of Brazil in order to complement the energy matrix of the region, which today is mostly composed of hydroelectric power plants. The offshore wind farm proposal was carried out following the methodology developed in this work, which is based on two different types of data collection sources: ocean buoys and automatic meteorological stations. Weibull frequency distributions were calculated for each data collection source, power curve and capacity factor for the selected wind turbines in each locality, in order to identify the best location for the utilization of offshore wind energy in the Southeast region. The location of the collection point Cabo Frio 2 presented the best wind characteristics for offshore wind energy production, however its installation would require great complexity, so the selected collection point for the installation of an offshore wind farm in this work was the station A606 - Arraial do Cabo. The capacity factor calculated in the selected region was 0,51 for the wind turbine with lower power and 0,39 for the wind turbine with higher power, and the calculated wind speed at the reference height was 7,77 m/s, which is an adequate value for wind energy production. The wind farm proposed for this region is capable of supplying annually 604.461 MWh through 39 wind turbines, which are enough to supply the energy demand of approximately 115,870 residences during the whole year in a county located in the state of Rio de Janeiro. / A geração de energia elétrica é um desafio mundial a ser enfrentado por vários países. Isso tem levado a busca e desenvolvimento de novas tecnologias limpas para o abastecimento de forma sustentável da crescente demanda mundial por energia. As principais fontes de energia renováveis da atualidade são: biomassa, solar, geotérmica, maremotriz, eólica on e offshore (terra e mar). Dentre essas fontes, a energia eólica sinaliza crescimento mundial e recentemente um aumento significativo na sua utilização no segmento offshore. O Brasil está entre os dez maiores produtores mundiais de energia eólica onshore, entretanto ainda não possui empreendimentos eólicos offshore. O país possui grande potencial para exploração da fonte eólica offshore, visto que existem grandes concentrações populacionais com crescentes demandas energéticas em áreas costeiras e uma Zona Econômica Exclusiva (ZEE) de aproximadamente 3.5 × 10^6 km^2. O objetivo deste trabalho foi desenvolver uma metodologia para utilização da energia eólica offshore através da proposta de um parque eólico offshore no litoral Sudeste do Brasil. O estudo foi realizado para a região Sudeste do Brasil com intuito de complementar a matriz energética elétrica da região, que hoje é em sua maioria composta por hidroelétricas. A proposta do parque eólico offshore foi realizada seguindo a metodologia desenvolvida neste trabalho, que se baseia em dois diferentes tipos de fontes de coleta de dados: boias oceânicas e estações meteorológicas automáticas. Foram calculadas as distribuições de frequência de Weibull para cada fonte de coleta de dados, curva de potência e o fator de capacidade para os aerogeradores selecionados em cada localidade, com objetivo de identificar a melhor localização para utilização de energia eólica offshore na região sudeste. Os resultados mostram que, dentre os pontos de coleta de dados analisados, o local do ponto de coletas Cabo Frio 2 apresentou as melhoras características de ventos para exploração de energia eólica offshore, entretanto sua instalação demandaria grande complexidade, por isso o ponto de coleta selecionado para instalação de um parque eólico offshore neste trabalho foi a estação A606 - Arraial do Cabo. O fator de capacidade calculado na região selecionada foi de 0, 51 para o aerogerador com menor potência e 0,39 para o aerogerador com maior potência, e a velocidade no local calculada na altura de referência foi de 7,77 m/s, que é um valor adequado para produção de energia eólica. O parque proposto para esta região é capaz de fornecer anualmente 604.461 MWh, utilizando 39 aerogeradores, que são suficientes para abastecer cerca de 115.870 domicílios durante todo o ano para um município localizado no estado do Rio de Janeiro.

Electromagnetic fields (EMF) produced by high voltage (HV), submarine transmission cables leading from offshore wind energy generation facilities could affect foraging or migratory behaviors of electro-receptive fishes, including endangered Atlantic Sturgeon. However, no published studies have quantitatively evaluated the possible behavioral effects of EMF exposure on sturgeon during residence in coastal waters. This study evaluated behavioral responses by sub-adult Atlantic Sturgeon to electromagnetic and magnetic fields under controlled laboratory conditions. Fabricated EMF generators were used to emulate a range of field EMF conditions that migratory fishes could encounter in proximity to submarine HV sources. Sensor arrays and digital video recorders synoptically quantified EMF conditions and fish behaviors during experimental trials. This thesis will describe the unique, experimental EMF generator/sensor array, present results of the behavior study, and suggest implications of the findings for Atlantic Sturgeon management and conservation. 45 trials were conducted over the course of the study. Study fish were subjected to 3 different field strengths (5µT, 100 µT, 1000 µT), generated using both AC and DC current. Time spent in generated field area, number of passes through the field area, and swimming speed were used to quantify behavioral changes in test subjects. From the data collected and analyzed there was no evidence indicating a change in fish behavior due to the influence of field strengths, field orientations, or field types used during the study.

Dans le contexte actuel de transition énergétique, les acteurs de la production électrique (dont EDF) s'orientent de plus en plus vers les technologies "bas carbone", permettant de développer leur mix énergétique et d'assurer une production toujours plus respectueuse de l'environnement. Parmi l'ensemble des alternatives progressivement industrialisées au cours de ces dernières décennies, l'énergie éolienne voit son développement s'accélérer. De nouveaux projets voient le jour, notamment avec le développement de parcs éoliens posés en mer le long des côtes françaises.Afin de garantir une sécurité maximale des installations vis-à-vis des défaillances mécaniques, les ingénieurs doivent mettre en place un ensemble de vérifications ayant pour but d'assurer l'intégrité structurelle pendant une durée de vie donnée. Cette étape, nécessaire à la certification et donc à l'industrialisation du projet, exige un investissement numérique important. Dans le cas particulier de l'estimation de l'endommagement à durée de vie, un ensemble complet d'analyses doit être effectué afin de simuler les réactions structurelles en différents points de la conception et ce, pour l'ensemble des conditions environnementales de chargement possibles (cas de charge). Au total, quelques milliers de simulations correspondant à l'ensemble des situations probables sont à prévoir pour la seule estimation de l'endommagement à durée de vie. De plus, la prise en compte des différents phénomènes physiques du problème (aérodynamique, hydrodynamique, mécanique élastique), ainsi que la considération des non-linéarités des réponses liées à l'asservissement de la turbine, impliquent l'utilisation de codes de résolution temporels et multi-physiques coûteux pour chacune des situations de chargement à simuler.Afin de réduire l'investissement lié à l'estimation de cet endommagement, l'utilisation de méthodes numériques de substitution (également appelées métamodèles) est une alternative prometteuse. Ces méthodologies ont montré leur efficacité dans divers domaines de l'ingénierie permettant d'approcher, par diverses hypothèses statistiques, la réponse de modèles numériques en ne considérant qu'un nombre réduit de simulations.Ce travail de thèse s'est focalisé sur le développement d'outils numériques pour le dimensionnement efficace des structures éoliennes en mer et plus particulièrement sur l'utilisation des métamodèles de Krigeage (ou méthode de régression par processus gaussien) pour l'estimation de l'endommagement mécanique. Sous certaines hypothèses, cette méthode de substitution se prête particulièrement bien à l'approximation des réponses de modèles physiques, notamment grâce à la mise en place facilitée d'architectures itératives d'enrichissement ("active learning strategy"). Deux domaines ont principalement été étudiés : l'estimation rapide des quantités d'endommagement structurel par le développement de la méthode "Adaptive Kriging for Damage Assessment" (AK-DA) et les possibilités d'utilisation de cette dernière dans le cadre d'études de la fiabilité conceptuelle au regard de la tenue à l'endommagement. L'applicabilité de ces méthodes a été illustrée via l'utilisation d'exemples numériques inspirés du contexte industriel et de ses contraintes. / The mechanical certification of wind turbine structures is required for the funding of newoffshore projects on the French coasts. In order to ensure a maximal safety level of installations,a series of structural analyzes are required by the certification bodies. Amongst all, thedamage based computations represent an important numerical effort for EDF. The presentedworks focus on the applicability and the performances of Kriging metamodels for the estimationof the lifetime cumulated damage of offshore wind turbine structures (AK-DA approach)and the damage based reliability assessment of new designs (AK-MCS/AK-DA coupling).

The paper compares electricity production between the semi-submersible and the spar-buoy floating wind turbine systems under normal, stochastic and extreme wind conditions at Utsira Nord site located on the Norwegian continental shelf in the North Sea. The analysis of complex behavior of the floating wind turbine system and the fluid-structure interaction is performed in aero-servo-hydro-elastic code ASHES. The results indicate a slightly better energy performance of the semi-submersible than the spar in all load cases but one. The pitch and heave degrees of freedom are evaluated as the most relevant for the power output. It is shown that pitch and heave platform motions have smaller displacement in the semi-submersible floater than in the spar under average environmental conditions and at the rated wind speed operating range. The simulation also confirmed that the energy yield is very sensitive to the magnitude of the loads: the spar performed best under mild environmental conditions, while the semi-submersible was better under medium environmental conditions. Small difference in energy yield is attributed to the same baseline blade and external controller properties used for both floaters where generator torque was kept constant to limit the power excursions above the rated power. The method proposed under this paper has demonstrated that a good approximation of the energy performance of the floating wind turbine system can be performed in a fast and effective manner.

This thesis deals with the analysis of a permanent magnet synchronous generator suited for direct-drivenwind turbines inmegawatt class. The higher specific torque and power density of a transverse flux permanent magnet machine in comparison to conventional radial-flux machines make it a promising solution for direct-driven wind turbine generators. The novel transverse flux generator investigated in this work would allow a better utilization of the available nacelle space due to its more compact construction. The major part of the thesis deals with the finite element analysis and analytical calculations of transverse flux generators. The computations are performed for single units of the basic transverse flux topology (BTFM) and the one utilizing iron bridges (IBTFM). As the selection of the pole length in a transverse flux machine affects the pole-to-pole flux leakage and thus its performance, the topologies have been analyzed with respect to the varying dimensions in the direction of movement. The topologies utilizing IBTFM have been found to be superior to the BTFM with respect to the flux linkage (by 110%) and utilization of the magnets (by 84%). The machines with longest magnets gave the largest flux linkage, while machines with short magnets should be preferred for better magnet utilization. The four sets of dimensions have been selected for a dynamic finite element analysis. The power factor is evaluated for the topologies with the varying dimensions in the peripheral plane in static finite element analysis. The performance of the topologies with the best power factor in the studied range (0.62 in the BTFM and 0.57 in the IBTFM), as well as the topologies that give the highest power factor to magnet volume ratio, is compared with the dynamic simulations.The electromagnetic and cogging forces of the transverse-flux generator are estimated. The IBTFM is superior to the BTFM with respect to the force production, where the three-phase electromagnetic force is twice as large as in the BTFM. The force ripples of the three-phase electromagnetic force are found to be insignificant in both topologies. An analytical procedure based on the results from the finite element simulations is applied for evaluation of the transverse flux generators with different shapes and topologies. The effectiveness of each topology is investigated based on the estimation of the torque production in a certain nacelle volume. A toroidal generator with the iron-bridge topology is the most compact alternativefor a wind turbine as it has the highest torque-per-volume ratio. Furthermore, the analyticalmodel, including evaluation of the synchronous inductance, is developed and compared with the results obtained in the threedimensional finite element analysis. Themodel provides a good agreement for the studied set of dimensions. / QC 20101109