Com a busca pela sustentabilidade no abastecimento de energia elétrica, a fonte eólica tem ganhado grande destaque na matriz energética global por possuir modelo de negócio consolidado, pois conta com aerogeradores modernos, naceles instalados em alturas cada vez maiores, geradores elétricos mais potentes e com sistemas de controle altamente tecnológicos. No Brasil, a energia eólica vem sendo a grande vencedora dos leilões de energia, aumentando de forma significativa seu portfólio pela viabilidade na construção de grandes complexos que devido à elevada potência instalada, realiza seu acesso ao Sistema Interligado Nacional (SIN) em níveis de tensão cada vez maiores, ou seja, em pontos mais sensíveis do sistema de transmissão. Motivado por esse crescimento e pela representatividade dos novos parques em pontos vitais do SIN, o objetivo desta dissertação é avaliar as diferentes metodologias e conceitos adotados como premissa no projeto do sistema de proteção aplicado a uma Central de Geração Eólica (CGE), apresentando como conclusão, além dos diagramas de sequência a serem utilizados no cálculo das correntes de curto-circuito, uma metodologia completa de definição dos ajustes de proteção para atender as especificidades construtivas dessas instalações. / Through the search for sustainability in electric power supply, the Eolic source has gained distinction in the global energetic matrix, as it has a consolidated business framework, which counts on modern wind turbines, nacelles installed at higher and higher altitudes, more powerful electric generators with high-technology control systems. In Brazil, Eolic energy has been the great winner in energy auctions, which has increased significantly its portfolio, due to its viability in the construction of large complexes. Having a high installed power capacity, these large projects enable access to the Sistema Interligado Nacional - SIN (National Interconnected System) at higher and higher voltage levels, that is, at more sensitive points of the transmission system. Motivated by all this development and by the representativeness of the new wind farms, installed at vital points of the SIN, the objective of this dissertation is to assess the different methodologies and concepts adopted as premise in the protection system project applied to a Central de Geração Eólica CGE (Eolic Generation Center). The conclusion presented herein, besides the sequence diagrams for the short circuit calculations, provides a complete methodology of definition of the protection adjustments required to comply with the building specificities of these installations.

Submitted by Cátia Araújo (catia.araujo@unipampa.edu.br) on 2017-01-25T13:05:54Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Resposta e controle das vibrações de uma torre eólica usando MR-TLCD (magneto reológico-amortecedor de coluna liquida sintonizada).pdf: 11585143 bytes, checksum: 5e1cc7e29c5d0f247a939325b0a384fe (MD5) / Approved for entry into archive by Cátia Araújo (catia.araujo@unipampa.edu.br) on 2017-01-25T13:06:32Z (GMT) No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Resposta e controle das vibrações de uma torre eólica usando MR-TLCD (magneto reológico-amortecedor de coluna liquida sintonizada).pdf: 11585143 bytes, checksum: 5e1cc7e29c5d0f247a939325b0a384fe (MD5) / Made available in DSpace on 2017-01-25T13:06:32Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Resposta e controle das vibrações de uma torre eólica usando MR-TLCD (magneto reológico-amortecedor de coluna liquida sintonizada).pdf: 11585143 bytes, checksum: 5e1cc7e29c5d0f247a939325b0a384fe (MD5) Previous issue date: 2014-08-25 / As torres eólicas são estruturas esbeltas projetadas para resistir a efeitos dinâmicos da ação do vento. Uma vez excitada, a torre pode entrar em ressonância ocasionando ruptura e falhas em sua estrutura, pás e rotores. Além de evitar possíveis falhas catastróficas, o sistema de amortecimento pode prevenir fadiga prematura de componentes estruturais da torre, entre eles, o gerador e as pás. A presença de amortecimento limita a amplitude de vibração quando o sistema, que sofre vibração forçada, aproxima-se da ressonância. Dentro desse contexto, foi elaborado um modelo numérico de uma torre eólica que determina a resposta da mesma sob uma excitação forçada. A excitação se deu por meio de um motor de corrente contínua desbalanceado, localizado no topo da torre. A estrutura analisada é composta por uma coluna metálica com um motor elétrico de corrente contínua desbalanceado e acoplado a um amortecedor do tipo MR-TLCD (Tuned Liquid Column Dampers with magnetorheological). Neste trabalho, foi utilizado um amortecedor semiativo, no qual consiste de um tubo em formato de ‘U’ e utiliza o fluido magneto-reológico, onde este impede o movimento de grandes amplitudes sujeito à ação de forças externas. No MR-TLCD é possível diminuir a energia cinética do fluido através da válvula de controle. O Magneto Reológico, quando submetido a um campo magnético, aumenta significativamente a sua viscosidade aparente. A equação de movimento do sistema acoplado entre a torre, motor elétrico e MRTLCD foi formulado através das equações de Lagrange. Nesta dissertação, apresentam-se as respostas dinâmicas regulares e caóticas de uma torre eólica com um amortecedor do tipo MR-TLCD através do método numérico da dinâmica não linear, utilizando-se da série temporal, do retrato de fase, do espectro de Fourier (FFT) e das curvas de ressonância. Com ensaios experimentais foram obtidos os valores dos parâmetros das configurações físicas e geométricas da estrutura a serem utilizados nas experiências numéricas. / The wind towers are slender structures designed to handle the dynamic effects of wind action. A once excited, the tower can resonate causing rupture and failures in structure, blades and rotors. Besides preventing possible catastrophic failure the damping system could prevent premature fatigue in structural components of the tower between them the rotor and blades. The presence of damping vibration is limited when the system suffer forced vibration approaches of the resonance. In this context was developed a numerical model of a wind tower which determines the response of the structure under a forced excitation. The excitation was done by a dc motor unbalanced situated on the top of the tower. The structure consists of a metallic column with an electric unbalanced dc motor attached to a MR-TLCD damper. This dissertation was presented a Semi-active damper in which consists in U-tube format using magneto rheological fluid (Tuned Liquid Column Dampers with magneto rheological, MR-TLCD). The fluid existing inside the U-tube prevents the movement of large amplitude subject to the actions of external loads. In MR-TLCD is possible to reduce the kinetic energy of the fluid through the control valve. The fluid used in this work, when exposed in a magnetic field significantly increases its apparent viscosity. The motion equation of coupled system between the tower, electric motor and MRTLCD was formulated using the Lagrange equations. This dissertation was presented the regular and chaotic dynamic of a tower using a MR-TLCD damper through the numerical method of nonlinear dynamics, utilizing a time series, phase portrait, Fourier spectrum (FFT) and resonance curves. The characteristic of experimental model was used for developed the numerical model. Also the free vibration tests were utilized for determine the structural parameters of the system.

In this thesis, the reliability of small wind turbines is studied. Both conventional reliability analysis methods and the novel Bayesian models (Bayesian Hierarchical Modelling (BHM)) are used to analyse the reliability performance of the Gaia-Wind turbines / assemblies and components of the Gaia-Wind turbine. In Chapter 2, a simple failure mode and effect analysis (FMEA) is conducted. An approximated risk priority number (RPN) is calculated for each failure mode and assembly. The assembly that is identified to have the highest RPN is the "Rotor and Blade Assembly". As for the failure modes, "Blade Split" and "Generator Failure" failure modes are identified to have the highest RPNs. In Chapter 3, the conventional methods including the Kaplan-Meier Analysis, Weibull Plot Analysis, Homogeneous Poisson Process (HPP) Analysis, and Crow-AMSAA (Non-Homogeneous Poisson Process (NHPP)) Analysis are used to study the reliability performance of the generic turbine and the critical assemblies based on the approximated RPNs. By using these conventional methods, the L10 life can be approximated (Kaplan-Meier), the main failure modes of an assembly can be identified (Weibull Plot Analysis), the annual failure rate can be estimated (HPP), and the number of future failures can be predicted (NHPP). These methods have been implemented in a novel on-line interactive platform, named ReliaOS (Chapter 7), which effectively facilitates the process of converting the information in the warranty record to the meaningful reliability information. Three novel BHM models are proposed and implemented in WinBUGS (an open source software), namely the repair model, the environmental model, and the informative prior framework, (Chapter 5 and Chapter 6). The repair model is used to quantify the repair effectiveness of a generic repair action. The model is applied on both the turbine level as well as the component level. At the turbine level, the annual failure rate of the generic turbine is predicted to be 0:159 per turbine per year at the first year. Individual turbines can be categorised into different quality levels ("Good", "Good- Normal", "Normal", "Normal-Bad", and "Bad") based on the predicted annual failure rate values. At the component level, "Blade split", "Cracked Frame", and "Generator Failure" failure modes are studied. These are the most critical failure modes for "Rotor and Blade Assembly", "Tower, Foundation, and Nacelle", and "Generator" assemblies respectively. "Cracked Frame" failure mode is predicted to have the lowest characteristic life and a slightly increasing failure rate trend. The repair effectiveness of the "Cracked Frame" failure mode is identified to be slightly ineffective. The environmental model quantifies the influence of three environmental covariates, i.e. AverageWind Speed (AWS), Turbulence Intensity (TI), and Terrain Slope (TS). These environmental covariates are all identified to have negative impact to the reliability of the generic turbine, where TI and AWS have more pronounced impact than TS. The informative prior BHM framework offers a way of quantifying the reliability of the drivetrain frame (which corresponds to the "Cracked Frame" failure mode) in a situation where zero failure instance is recorded for the new drivetrain frame design. This is achieved by jointly considering the simulation results from SOLIDWORKS as the prior information into the BHM model. This thesis strives to understand the reliability performance of the Gaia-Wind small wind turbine from different perspectives, i.e. the generic turbine, individual turbines, and the components, by the use of conventional methods and the proposed BHM models. The novel on-line reliability platform, ReliaOS, mitigates the difficulties in converting the information in the data to the reliability information for the end users. It is believed that the proposed BHM models and the ReliaOS on-line reliability analysis platform will improve the reliability analysis of small-wind turbines.

Aerogeradores, ou turbinas eólicas, são máquinas instaladas em grandes parques eólicos que convertem a energia cinética do vento em energia elétrica. A definição da separação e da interação entre máquinas é um fator fundamental de análise durante a fase de projeto, pois os chamados efeitos de esteira podem inviabilizar o desenvolvimento de um parque eólico. Em geral, a esteira de um aerogerador está caracterizada por um significativo déficit de velocidade e uma intensificação dos níveis de turbulência, o que ocasiona a diminuição da eficiência aerodinâmica e a redução da vida útil das máquinas localizadas a sotavento. Embora existam diferentes pesquisas destinadas à compreensão e previsão dos efeitos de esteira, o problema permanece como uma questão desafiadora que exige a adoção de ferramentas de alta precisão para sua identificação. Este trabalho apresenta uma metodologia experimental em túnel de vento, para a caracterização e avaliação do campo de escoamento na esteira aerodinâmica de um modelo reduzido, sob diferentes condições de escoamento incidente. Especificamente, investiga-se a influência da turbulência atmosférica para quatro perfis de escoamento: i) uniforme-suave; ii) uniforme-turbulento; iii) lei potencial com expoente α = 0,11; iv) lei potencial com expoente α = 0,23. Todos os casos foram conduzidos sob condições de estratificação neutra, e foi utilizado anemômetro de fio-quente para efetivar as medições dos perfis de velocidade média e intensidade da turbulência, em diferentes posições da esteira. Os resultados mostraram diferenças substanciais no comportamento dos perfis de esteira, em função dos níveis de turbulência incidente. Particularmente, observou-se que o incremento da turbulência atmosférica reduz o déficit de velocidade e promove uma maior mistura turbulenta, o que acelera a dissipação dos efeitos de esteira. Assim, a metodologia experimental em túnel de vento evidencia-se como uma importante ferramenta de análise que possibilita amplo espectro para a investigação, precisão e confiabilidade de projetos eólicos. / Wind turbines are machines installed in large wind farms to convert the wind's kinetic energy into electrical power. For an optimal wind farm siting, it is necessary to take into account the interaction between wind turbine wakes. In general, wake effects are associated with velocity deficit and enhanced turbulence intensity. This may reduce the aerodynamic efficiency and lifetime of downwind turbines, making the project unfeasible. Several experimental and numerical studies have been conducted to unravel the behavior of wind turbine wakes under different inflow conditions. However, current wind farm siting tools are incapable of accurately predicting and assessing its effects. This document presents an experimental methodology in the wind tunnel to survey the influence of the atmospheric turbulence on the wake flow field of a wind turbine model. Specifically, four different flow conditions were investigated: i) uniform-laminar; ii) uniform-turbulent; iii) power law exponent α = 0.11; iv) power law exponent α = 0.23. All cases were developed under neutrally stratified conditions. Hot-wire anemometry was used to obtain high-resolution measurements of the mean velocity and turbulence intensity profiles at different downwind positions. Results show that different turbulence intensity levels of the incoming flow lead to substantial differences in the spatial distribution of the wakes. Particularly, higher ambient turbulence promotes a faster wake recovery and lower velocity deficit. In conclusion, the use of wind tunnel experiments is a trustworthy alternative that brings precision and reliability to wind projects.

A high fidelity approach coupling the computational fluid dynamics method (CFD) and multi-body dynamics method (MBD) is presented for aero-servo-elastic wind turbine simulations. The approach uses the incompressible CFD dynamic overset code CFDShip-Iowa v4.5 to compute the aerodynamics, coupled with the MBD code Virtual.Lab Motion to predict the motion responses to the aerodynamic loads. The IEC 61400-1 ed. 3 recommended Mann wind turbulence model was implemented in this thesis into the code CFDShip-Iowa v4.5 as boundary and initial conditions, and used as the explicit wind turbulence for CFD simulations. A drivetrain model with control systems was implemented in the CFD/MBD framework for investigation of drivetrain dynamics. The tool and methodology developed in this thesis are unique, being the first time with complete wind turbine simulations including CFD of the rotor/tower aerodynamics, elastic blades, gearbox dynamics and feedback control systems in turbulent winds. Dynamic overset CFD simulations were performed with the benchmark experiment UAE phase VI to demonstrate capabilities of the code for wind turbine aerodynamics. The complete turbine geometry was modeled, including blades and approximate geometries for hub, nacelle and tower. Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Detached Eddy Simulation (DES) turbulence models were used in the simulations. Results for both variable wind speed at constant blade pitch angle and variable blade pitch angle at fixed wind speed show that the CFD predictions match the experimental data consistently well, including the general trends for power and thrust, sectional normal force coefficients and pressure coefficients at different sections along the blade. The implemented Mann wind turbulence model was validated both theoretically and statistically by comparing the generated stationary wind turbulent field with the theoretical one-point spectrum for the three components of the velocity fluctuations, and by comparing the expected statistics from the simulated turbulent field by CFD with the explicit wind turbulence inlet boundary from the Mann model. The proposed coupled CFD/MBD approach was applied to the conceptual NREL 5MW offshore wind turbine. Extensive simulations were performed in an increasing level of complexity to investigate the aerodynamic predictions, turbine performance, elastic blades, wind shear and atmospheric wind turbulence. Comparisons against the publicly available OC3 simulation results show good agreements between the CFD/MBD approach and the OC3 participants in time and frequency domains. Wind turbulence/turbine interaction was examined for the wake flow to analyze the influence of turbulent wind on wake diffusion. The Gearbox Reliability Collaborative project gearbox was up-scaled in size and added to the NREL 5MW turbine with the purpose of demonstrating drivetrain dynamics. Generator torque and blade pitch controllers were implemented to simulate realistic operational conditions of commercial wind turbines. Interactions between wind turbulence, rotor aerodynamics, elastic blades, drivetrain dynamics at the gear-level and servo-control dynamics were studied, showing the potential of the methodology to study complex aerodynamic/mechanic systems.

The objective of this study is to develop an integrated multibody dynamics computational framework for the deterministic and reliability-based design optimization of wind turbine drivetrains to obtain an optimal wind turbine gear design that ensures a target reliability under wind load and gear manufacturing uncertainties. Gears in wind turbine drivetrains are subjected to severe cyclic loading due to variable wind loads that are stochastic in nature. Thus, the failure rate of drivetrain systems is reported to be relatively higher than the other wind turbine components. It is known in wind energy industry that improving reliability of drivetrain designs is one of the key issues to make wind energy competitive as compared to fossil fuels. Furthermore, a wind turbine is a multi-physics system involving random wind loads, rotor blade aerodynamics, gear dynamics, electromagnetic generator and control systems. This makes an accurate prediction of product life of drivetrains challenging and very limited studies have been carried out regarding design optimization including the reliability-based design optimization (RBDO) of geared systems considering wind load and manufacturing uncertainties. In order to address these essential and challenging issues on design optimization of wind turbine drivetrains under wind load and gear manufacturing uncertainties, the following issues are discussed in this study: (1) development of an efficient numerical procedure for gear dynamics simulation of complex multibody geared systems based on the multi-variable tabular contact search algorithm to account for detailed gear tooth contact geometry with profile modifications or surface imperfections; (2) development of an integrated multibody dynamics computational framework for deterministic and reliability-based design optimization of wind turbine drivetrains using the gear dynamics simulation software developed in (1) and RAMDO software by incorporating wide spatiotemporal wind load uncertainty model, pitting gear tooth contact fatigue model, and rotor blade aerodynamics model using NREL AeroDyn/FAST; and (3) deterministic and reliability-based design optimization of wind turbine drivetrain to minimize total weight of a drivetrain system while ensuring 20-year reliable service life with wind load and gear manufacturing uncertainties using the numerical procedure developed in this study. To account for the wind load uncertainty, the joint probability density function (PDF) of 10-minute mean wind speed (V₁₀) and 10-minute turbulence intensity (I₁₀) is introduced for wind turbine drivetrain dynamics simulation. To consider wide spatiotemporal wind uncertainty (i.e., wind load uncertainty for different locations and in different years), uncertainties of all the joint PDF parameters of V₁₀, I₁₀ and copula are considered, and PDF for each parameter is identified using 249 sets of wind data. This wind uncertainty model allows for the consideration of a wide range of probabilistic wind loads in the contact fatigue life prediction. For a given V₁₀ and I₁₀ obtained from the stochastic wind model, the random time-domain wind speed data is generated using NREL TurbSim, and then inputted into NREL FAST to perform the aerodynamic simulation of rotor blades to predict the transmitted torque and speed of the main shaft of the drivetrain that are sent to the multibody gear dynamics simulation as an input. In order to predict gear contact fatigue life, a high-fidelity gear dynamics simulation model that considers the detailed gear contact geometry as well as the mesh stiffness variation needs to be developed to find the variability of maximum contact stresses under wind load uncertainty. This, however, leads to a computationally intensive procedure. To eliminate the computationally intensive iterative online collision detection algorithm, a numerical procedure for the multibody gear dynamics simulation based on the tabular contact search algorithm is proposed. Look-up contact tables are generated for a pair of gear tooth profiles by the contact geometry analysis prior to the dynamics simulation and the contact points that fulfill the non-conformal contact condition and mesh stiffness at each contact point are calculated for all pairs of gears in the drivetrain model. This procedure allows for the detection of gear tooth contact in an efficient manner while retaining the precise contact geometry and mesh stiffness variation in the evaluation of mesh forces, thereby leading to a computationally efficient gear dynamics simulation suited for the design optimization procedure considering wind load uncertainty. Furthermore, the accuracy of mesh stiffness model introduced in this study and transmission error of gear tooth with tip relief are discussed, and a wind turbine drivetrain model developed using this approach is validated against test data provided in the literature. The gear contact fatigue life is predicted based on the gear tooth pitting fatigue criteria and is defined by the sum of the number of stress cycles required for the fatigue crack initiation and the number required for the crack to propagate from the initial to the critical crack length based on Paris-Erdogan equation for Mode II fracture. All the above procedures are integrated into the reliability-based design optimization software RAMDO for design optimization and reliability analysis of wind turbine drivetrains under wind load and manufacturing uncertainties. A 750kW GRC wind turbine gearbox model is used to perform the design optimization and the reliability analysis. A deterministic design optimization (DDO) is performed first using an averaged joint PDF of wind load to ensure a 20-year service life. To this end, gear face width and tip relief (profile modification) are selected as design variables and optimized such that 20-year fatigue life is ensured while minimizing the total weight of drivetrains. It is important to notice here that an increase in face width leads to a decrease in the fatigue damage, but an increase in total weight. On the other hand, the tip relief has almost no effect on the total weight, but it has a major impact on the fatigue damage. It is shown in this study that the optimum tip relief allows for lowering the greatest maximum shear stresses on the tooth surface without relying heavily on face width widening to meet the 20-year fatigue life constraint and it leads to reduction of total drivetrain weight by 8.4%. However, if only face width is considered as design variable, total weight needs to be increased by 4.7% to meet the 20-year fatigue life constraint. Furthermore, the reliability analysis at the DDO optimum design is carried out considering the large spatiotemporal wind load uncertainty and gear manufacturing uncertainty. Local surrogate models at DDO optimum design are generated using Dynamic Kriging method in RAMDO software to evaluate the gear contact fatigue damage. 49.5% reliability is obtained at the DDO optimum design, indicating that the probability of failure is 50.5%, which is as expected for the DDO design. RBDO is, therefore, necessary to further improve the reliability of the wind turbine drivetrain. To this end, the sampling-based reliability analysis is carried out to evaluate the probability of failure for each design using the Monte Carlo Simulation (MCS) method. However, the use of a large number of MCS sample points leads to a large number of contact fatigue damage evaluation time using the 10-minute multibody drivetrain dynamics simulation, resulting in the RBDO calculation process being computational very intensive. In order to overcome the computational difficulty resulting from the use of high-fidelity wind turbine drivetrain dynamics simulation, intermediate surrogate models are created prior to the RBDO process using the Dynamic Kriging method in RAMDO and used throughout the entire RBDO iteration process. It is demonstrated that the RBDO optimum obtained ensures the target 97.725 % reliability (two sigma quality level) with only 1.4 % increase in the total weight from the baseline design with 8.3 % reliability. This result clearly indicates the importance of incorporating the tip relief as a design variable that prevents larger increase in the face width causing an increase in weight. This, however, does not mean that a larger tip relief is always preferred since an optimum tip relief amount depends on stochastic wind loads and an optimum tip relief cannot be found deterministically. Furthermore, accuracy of the RBDO optimum obtained using the intermediate surrogate models is verified by the reliability analysis at the RBDO optimum using the local surrogate models. It is demonstrated that the integrated design optimization procedure developed in this study enables the cost effective and reliable design of wind turbine drivetrains.

The objectives of this study are (1) to develop an accurate and efficient fatigue analysis procedure that can be used in reliability analysis and reliability-based design optimization (RBDO) of composite wind turbine blades; (2) to develop a wind load uncertainty model that provides realistic uncertain wind load for the reliability analysis and the RBDO process; and (3) to obtain an optimal composite wind turbine blade that satisfies target reliability for durability under the uncertain wind load. The current research effort involves: (1) developing an aerodynamic analysis method that can effectively calculate detailed wind pressure on the blade surface for stress analysis; (2) developing a fatigue failure criterion that can cope with non-proportional multi-axial stress states in composite wind turbine blades; (3) developing a wind load uncertainty model that represents realistic uncertain wind load for fatigue reliability of wind turbine systems; (4) applying the wind load uncertainty model into a composite wind turbine blade and obtaining an RBDO optimum design that satisfies a target probability of failure for a lifespan of 20 years under wind load uncertainty. In blade fatigue analysis, resultant aerodynamic forces are usually applied at the aerodynamic centers of the airfoils of a blade to calculate stress/strain. However, in reality the wind pressures are applied on the blade surface. A wind turbine blade is often treated as a typical beam-like structure for which fatigue life calculations are limited in the edge-wise and/or flap-wise direction(s). Using the beam-like structure, existing fatigue analysis methods for composite wind turbine blades cannot cope with the non-proportional multi-axial stress states that are endured by wind turbine blades during operation. Therefore, it is desirable to develop a fatigue analysis procedure that utilizes detailed wind pressures as wind loads and considers non-proportional multi-axial stress states in fatigue damage calculation. In this study, a 10-minute wind field realization, determined by a 10-minute mean wind speed V10 and a 10-minute turbulence intensity I10, is first simulated using Veers’ method. The simulated wind field is used for aerodynamic analysis. An aerodynamic analysis method, which could efficiently generate detailed quasi-physical blade surface pressures, has been developed. The generated pressures are then applied on a high-fidelity 3-D finite element blade model for stress and fatigue analysis. The fatigue damage calculation considers the non-proportional multi-axial complex stress states. A detailed fatigue damage contour, which indicates the fatigue failure locally, can be obtained using the developed fatigue analysis procedure. As the 10-minute fatigue analysis procedure is deterministic in this study, the calculated 10-minute fatigue damage is determined by V10 and I10. It is necessary to clarify that the rotational speed of the wind turbine blade is assumed to be constant (12.1 rpm) and the pitch angle is fixed to be 0 degree for different wind conditions, since the rotational speed control and pitch angle control have not been considered in this study. For predicting the fatigue life of a wind turbine, a fixed Weibull distribution is widely used to determine the percentage of time the wind turbine experiences different mean wind speeds during its life-cycle. Meanwhile, fixed turbulence intensities are often used based on the designed wind turbine types. These simplifications, i.e., fixed Weibull distribution and fixed turbulence intensities, ignore the realistic uncertain wind load when designing a reliable wind turbine system. In the real world, both the mean wind speed and turbulence intensity vary constantly over one year, and their annual distributions are different at different locations and in different years. Thus, it is necessary to develop a wind load uncertainty model that can provide a realistic uncertain wind load for designing reliable wind turbine systems. In this study, 249 groups of measured wind data, collected at different locations and in different years, are used to develop a dynamic wind load uncertainty model. The dynamic wind load uncertainty model consists of annual wind load variation and wind load variation in a large spatiotemporal range, i.e., at different locations and in different years. The annual wind load variation is represented by the joint probability density function of V10 and I10. The wind load variation in a large spatiotemporal range is represented by the probability density functions of five parameters, C, k, a, b, and τ, which determine the joint probability density function of V10 and I10. In order to obtain the RBDO optimum design efficiently, a deterministic design optimization (DDO) procedure of a composite wind turbine blade has been first carried out using averaged percentage of time (probability) for each wind condition. A wind condition is specified by two terms: 10-minute mean wind speed and 10-minute turbulence intensity. In this research, a probability table, which consists of averaged probabilities corresponding to different wind conditions, is referred as a mean wind load. The mean wind load is generated using the dynamic wind load uncertainty model. During the DDO process, the laminate thickness design variables are tailored to minimize the total cost of composite materials while satisfying the target fatigue lifespan of 20 years. It is found that, under the mean wind load condition, the fatigue life of the initial design is only 0.0004 year. After the DDO process, even though the cost at the DDO optimum design is increased by 31.5% compared to that at the initial design, the predicted fatigue life at the DDO optimum design is significantly increased to 19.9995 years. Reliability analyses of the initial design and the DDO optimum design have been carried out using the wind load uncertainty model and Monte Carlo simulation. The reliability analysis results show that the DDO procedure reduces the probability of failure from 100% at the initial design to 49.9% at the DDO optimum design considering only wind load uncertainty. In order to satisfy the target 2.275% probability of failure, it is necessary to further improve the fatigue reliability of the composite wind turbine blade by RBDO. Reliability-based design optimization of the composite wind turbine blade has been carried out starting at the DDO optimum design. Fatigue hotspots for RBDO are identified among the laminate section points, which are selected from the DDO optimum design. Local surrogate models for 10-minute fatigue damage have been created at the selected hotspots. Using the local surrogate models, both the wind load uncertainty and manufacturing variability has been included in the RBDO process. It is found that the probability of failure is 50.06% at the RBDO initial design (DDO optimum design) considering both wind load uncertainty and manufacturing variability. During the RBDO process, the normalized laminate thickness design variables are tailored to minimize the total cost of composite materials while satisfying the target 2.275% probability of failure. The obtained RBDO optimum design reduces the probability of failure from 50.06% at the DDO optimum design to 2.28%, while increasing the cost by 3.01%.

The work in this thesis deals with the development of an aeroelastic simulation tool for horizontal axis wind turbine applications. Horizontal axis wind turbines can experience significant time varying aerodynamic loads, potentially causing adverse effects on structures, mechanical components, and power production. The needs for computational and experimental procedures for investigating aeroelastic stability and dynamic response have increased as wind turbines become lighter and more flexible. A finite element model for simulation of the dynamic response of horizontal axis wind turbines has been developed. The developed model uses the commercial finite element system MSC.Marc, focused on nonlinear design and analysis, to predict the structural response. The aerodynamic model, used to transform the wind flow field to loads on the blades, is a Blade-Element/Momentum model. The aerodynamic code is developed by The Swedish Defence Research Agency (FOI, previously named FFA) and is a state-of-the-art code incorporating a number of extensions to the Blade-Element/Momentum formulation. The software SOSIS-W, developed by Teknikgruppen AB was used to generate wind time series for modelling different wind conditions. The method is general, and different configurations of the structural model and various type of wind conditions can be simulated. The model is primarily intended for use as a research tool when influences of specific dynamic effects are investigated. Verification results are presented and discussed for an extensively tested Danwin 180 kW stall-controlled wind turbine. Code predictions of mechanical loads, fatigue and spectral properties, obtained at different conditions, have been compared with measurements. A comparison is also made between measured and calculated loads for the Tjæreborg 2 MW wind turbine during emergency braking of the rotor. The simulated results correspond well to measured data. / QC 20100826

Wind power is a renewable energy source that is increasingly used all over the world. Most wind turbines have a horizontal axis of rotation but a few have a vertical axis of rotation. The concept presented in this thesis is a straight-bladed vertical axis wind turbine with a direct driven cable-wound permanent magnet synchronous generator. A comparison of the two different types of wind turbines, vertical axis wind turbines and horizontal axis wind turbines, have been performed considering several different aspects. However, the main focus in this thesis is on the generator. Several generators have been modelled with a combined field and circuit model, which has been solved by using the finite element method. A 12 kW generator has been designed, which has a high overall efficiency and a high overload capability. The generator has been constructed at the department and was tested in the laboratory before being mounted in a vertical axis wind turbine. Results from experiments correspond well with results from simulations. The generator has been tested for different loading conditions and the harmonic content of the voltage has been analysed. A 12 kW vertical axis wind turbine was completed and tests have been performed. The results are encouraging and further studies on the prototype will be performed in the future. The simulation method has been used to study electromagnetic losses in several generators. The comparison showed that the average losses should be considered when a variable speed generator for wind power is designed and it concluded that the design optimization process becomes a compromise between lowering the electromagnetic losses and having high overload capability. When constructing a wind turbine, it is important to consider vibrations in the structure. Torsional vibrations in the drive shaft connecting the turbine to the rotor of the generator have been studied. It is shown that a direct driven generator is to prefer over an induction generator with a gearbox when torsional vibrations are concerned. This thesis is based on eight papers all concerning vertical axis wind turbines with three of them focusing on the generator.

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