• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 265
  • 61
  • 34
  • 22
  • 13
  • 10
  • 10
  • 9
  • 7
  • 4
  • 4
  • 4
  • 1
  • 1
  • 1
  • Tagged with
  • 524
  • 524
  • 174
  • 151
  • 84
  • 64
  • 64
  • 54
  • 49
  • 48
  • 46
  • 44
  • 41
  • 39
  • 38
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
341

SIlver Tower - A New Paradigm for Tall Building Design

Vann, Michael Preston 01 June 2016 (has links)
The events of September 11, 2001, seemed to many to presage the end of the skyscraper as an urban form. Some 15 years later, the skyscraper is more prevalent than ever before, owing to its unique advantages over other building forms in an urban, environmental, and sociological context. Skyscrapers are rising ever higher, pushing the limits of architecture and engineering. In 2001 there were 23 buildings over 1,000 feet in height. As of this writing there are 173 buildings over 1,000 feet completed or under construction, with 300 more in various phases of proposal. Despite their enormous initial cost in both capital and energy, the skyscraper maximizes the use of constricted urban space and provides enormous opportunities for technological and sociological innovation which, despite more that 100 years of skyscraper construction, are only just beginning to be realized. This thesis will explore a number of as-yet unrealized possibilities for skyscraper development to prognosticate and articulate future typologies designed to address increasing problems of energy efficiency, population density and disaster preparedness. As the human population grows, and more people move to the cities, larger and larger buildings will be necessary to house them at densities sufficient to ensure energy efficiency and minimize sprawl. The skyscraper is uniquely suited to meet these demands. / Master of Architecture
342

Digital control algorithms : low power wind turbine energy maximizer for charging lead acid batteries

Hamilton, Christopher 01 January 2009 (has links)
Fossil fuel consumption throughout the world is drawing attention to the need for alternative energy sources to provide for the large demand for energy. It is becoming more apparent everyday that fossil fuels are unreliable sources of energy due to the volatile pricing of such commodities as well as the toll that these energy sources take on the environment. Fossil fuels are non-renewable sources of energy that when burned to create energy produce bi-products that are extremely harmful to the global environment. Today, renewable energy sources such as wind and solar energy are playing larger roles as sources of electricity and are providing new jobs as well as research opportunities both in academia and in industry. It is for this reason that wind turbine energy harvesting is the topic of this thesis and how the efficiency of wind turbine power conversion systems can be improved to become a more viable source of energy. Large wind turbines, along with their power conversion electronics, exist today for the sole purpose of serving a large population of consumers with "green" electricity. Unfortunately, systems designed for low power wind turbines do not utilize advanced methods of maximizing energy draw from wind turbines both from hardware and software point of views. This theses is presents a method of efficient energy extraction and conversion from low power wind turbines to charge lead ac id batteries.
343

Möjligheter och utmaningar med återanvändning av vindturbinblad : Analys och fallstudie i nya tillämpningsområden

Back, Lovisa, Mikaelsdotter, Ida January 2024 (has links)
En ökad energianvändning, tillsammans med utbyggnaden av vindkraft, förväntas leda till ökade avfallsmängder från uttjänta vindturbinblad och krav på en hållbar hantering över hela värdekedjan. Komplexiteten i materialen som används i vindturbinbladen försvårar återvinningen, vilket leder till att majoriteten av bladen hamnar på deponi med både miljöföroreningar och resursförluster som resultat. Studien syftar till att undersöka möjligheterna och utmaningarna med återanvändning av vindturbinblad till olika tillämpningsområden genom att utvärdera befintlig forskning samt genomförda och potentiella projekt, med fokus på miljömässiga, tekniska och ekonomiska aspekter. Data samlades in genom både kvantitativa och kvalitativa metoder, vilket omfattar litteraturstudier och semistrukturerade intervjuer med relevanta aktörer inom vindkrafts- och återvinningsindustrin. Metoden innefattar även en SWOT-analys och en fallstudie som undersöker återanvändning av vindturbinblad i Umeå kommun, inklusive en undersökning av kommunens marknadsbehov samt vilka möjligheter och utmaningar potentiella aktörer ser kring återanvändningsprocessen. De sammanlagda resultaten från litteraturstudie, intervjuer och SWOT-analys visar på flera tekniska, ekonomiska och miljömässiga möjligheter med återanvändning av vindturbinblad, inklusive möjligheten att potentiellt minska både materialkostnader och växthusgasutsläpp jämfört med alternativen förbränning eller deponering. Flertalet utmaningar identifierades, inklusive utmaningar kring nedmontering, transport, testning av materialets styrka samt brist på information kring materialets innehåll. Även ekonomiska och logistiska hinder kring ansvar hos tillverkare och verksamhetsutövare samt bristen på samarbete för att skapa en effektiv värdekedja konstaterades. Resultatet lyfter betydelsen av samarbete mellan aktörer, tillverkare och avfallshanterare som avgörande för att skapa effektiva lösningar och möjliggöra återanvändning av vindturbinblad. Fallstudien av Umeå kommuns marknadsbehov visar att återanvändning av vindturbinblad skulle kunna täcka en betydande del av kommunens behov för lekplatser, gångbroar och stadsmöbler och samtidigt bidra till en besparing av koldioxidutsläpp. Trots ekonomiska, tekniska och logistiska utmaningar kring nedmontering, bearbetning och transport, ser potentiella aktörer skapande av hållbara affärsmodeller och teknisk kapacitet som positiva möjligheter. Studien bidrar till ökad förståelse och kunskap kring möjligheter och utmaningar med återanvändning av vindturbinblad, vilket är avgörande för att effektivisera processen för nuvarande och framtida aktörer inom branschen. Det är särskilt relevant utifrån de förväntade avfallsmängderna i framtiden och behovet av en effektiv värdekedja. / An increased use of energy, coupled with the expansion of wind power, is expected to lead to increased amounts of waste from end-of-life wind turbine blades and demands for sustainable management across the entire value chain. The complexity of the materials used in wind turbine blades makes recycling difficult, which leads to the majority of blades ending up in landfills with both environmental pollution and resource losses as a result. The study aims to investigate the opportunities and challenges of repurposing wind turbine blades for various application areas by evaluating existing research as well as completed and potential projects, with a focus on environmental, technical and economic aspects. Data was collected through both quantitative and qualitative methods, including literature studies and semi-structured interviews with relevant stakeholders in the wind power and recycling industry. The method also includes a SWOT analysis and a case study that investigates repurposing of wind turbine blades in the municipality of Umeå, including an investigation of the municipality's market needs as well as what opportunities and challenges potential stakeholders see in the repurposing process. The combined results from literature studies, interviews and SWOT analysis shows several technical, economic and environmental opportunities with repurposing of wind turbine blades, including the possibility of potentially reducing both material costs and greenhouse gas emissions compared to the alternatives of incineration or landfilling. Several challenges were identified, including challenges around disassembly, transport, testing the material's strength and lack of information about the material's content. Financial and logistical obstacles regarding the responsibility of manufacturers and operators as well as the lack of cooperation to create an efficient value chain were also found. The result highlights the importance of cooperation between stakeholders, manufacturers and waste handlers as crucial to creating effective solutions and enabling the reuse of wind turbine blades. The case study of Umeå municipality's market needs shows that reuse of wind turbine blades could cover a significant part of the municipality's needs for playgrounds, pedestrian bridges and urban furniture and at the same time contribute to saving carbon dioxide emissions. Despite financial, technical and logistical challenges surrounding dismantling, processing and transport, potential stakeholders see the creation of sustainable business models and technical capabilities as positive opportunities. The study contributes to increased understanding and knowledge about opportunities and challenges with the reuse of wind turbine blades, which is crucial for streamlining the process for current and future stakeholders in the industry. It is particularly relevant based on the expected amounts of waste in the future and the need for an efficient value chain.
344

Experimental substructuring of an A600 wind turbine blade  : A study of the influence of interface loading

Santos, Judas, Al-Mahdi, Nidaa January 2016 (has links)
Dynamic Substructuring is a powerful tool for simplification of the analysis of complex structures and it has been well established along the years in analytical calculations by means of the Craig-Bampton technique. Recently, a new branch of substructuring, the Experimental Dynamic Substrucuring, appeared as a promising field of research for the engineering community. This area presents several intrinsic difficulties, evincing a need to develop the traditional substructuring methods towards obtaining better results using the experimental approach. In this scenery, the Transmission Simulator technique emerges as an instrument for potential improvement of the achieved results. This work represents a study on the use of the Transmission Simulator technique in the analysis of an Ampair A600 wind turbine blade subjected to loads at the interface to the hub, and it is a part of the benchmarking studies of SEM (Society of Experimental Mechanics). The work consisted of collecting experimental data via vibration tests of a single blade connected to different sizes of transmission simulators. After that, a mathematical representation of the blade was obtained via subtraction of the effect of the transmission simulators via substructuring technique. The computed model was subsequently coupled to a model of the remainder of the wind turbine (the hub plus two blades), and the results were compared to data acquired in tests of the whole assembly. The final findings did not reflect the theory prospects and further investigation is necessary to evaluate the effectiveness of the used methodology.
345

Modellierung des Oberschwingungsverhaltens von Windparks mit probabilistischen Ansätzen / Harmonic Behavior Modeling of Wind Farms Using Probabilistic Approaches

Malekian Boroujeni, Kaveh 19 July 2016 (has links) (PDF)
Oberschwingungen als ein Merkmal der Elektroenergiequalität gewinnen durch die starke Netzintegration leistungselektronisch geregelter Anlagen wie Windenergieanlagen und nichtlineare Lasten zunehmend an Bedeutung. Bestehende Normen entsprechen nicht den zukünftigen Erfordernissen des Elektroenergiesystems und bedürfen diesbezüglich einer Überarbeitung. In der Arbeit werden wesentliche Einflussfaktoren auf das Oberschwingungsverhalten von Windparks identifiziert, beschrieben und modelliert. Dabei wird der stochastische Charakter der Oberschwingungen mithilfe von probabilistischen Ansätzen erfasst. Des Weiteren wird ein neuer Ansatz zur Untersuchung der Wechselwirkung zwischen dem Windpark und dem vorgelagerten Netz entwickelt. Der Ansatz ermöglicht, die vom Windpark verursachte Änderung der Oberschwingungsspannung am Netzanschlusspunkt zu ermitteln. Diese Arbeit liefert einen Beitrag zur Verbesserung bestehender Normen für die Anbindung von Windparks. / Harmonics, as one of the power quality criteria, are increasingly gaining attention due to the progressive contribution of renewable energy resources and the application of the nonlinear load in the power system. Current standards do not conform to the future requirements of the power system, thus requiring a revision. In this work, main influence factors on the harmonic behavior of wind farms are identified, explained, and modelled. Thereby, the stochastic nature of harmonics is taken into account using probabilistic approaches. Moreover, a novel approach is developed to investigate the interaction between the wind farm and the upstream grid. With the aid of this approach, it is possible to determine the voltage change caused by the wind farm at the point of connection. This work contributes to improve the existing standards for the connection of wind farms.
346

An integrated energy storage scheme for a dispatchable wind and solar powered energy system

Garrison, Jared Brett 23 August 2010 (has links)
Wind and solar technologies have experienced rapid market growth recently as a result of the growing interest for implementation of renewable energy. However, the intermittency of wind and solar power is a major obstacle to their broader use. The additional risks of unexpected interruptions and mismatch with demand have hindered the expansion of these two primary renewable resources. The goal of this research is to analyze an integrated energy system that includes a novel configuration of wind and solar coupled with two storage methods to make both wind and solar sources dispatchable during peak demand, thereby enabling their broader use. Named DSWiSS for Dispatchable Solar Wind Storage System, the proposed system utilizes compressed air energy storage (CAES) that is driven from wind energy and thermal storage supplied by concentrating solar thermal power in order to achieve this desired dispatchability. Although DSWiSS mimics the operation of a typical CAES facility, the replacement of energy derived from fossil fuels with energy generated from renewable resources makes this system unique. While current CAES facilities use off peak electricity to power their compressors, this system uses power from wind turbines. Also, rather than using natural gas for heating of the compressed air before its expansion through a turbine, DSWiSS uses solar thermal energy and thermal storage. For this research, two models were created; the first is a dynamic model of a 1.5 MW variable speed wind turbine, programmed in PSCAD/EMTDC, that utilizes rotor resistive control to maintain rated power output. This model simulates the dynamic response of the wind turbine to changing wind conditions as well as the nominal performance parameters at all wind speeds. The second model is a steady state thermodynamic simulation of the turbomachinery power unit in the DSWiSS facility. By assuming conditions similar to those of a currently operating CAES facility in McIntosh, Alabama, the model calculates the performance parameters of DSWiSS and estimates the relative energy input requirements. By combining these models with a levelized lifetime cost analysis estimates of the power system performance and the cost of energy for the DSWiSS facility were estimated. The combination of these components yielded an efficiency greater than 46% for the main power block and a nearly equal utilization of both renewable resources. It was also estimated that the overall system is only slightly more expensive per unit of electricity generated than the current technologies employed today, namely coal, nuclear, and natural gas, but is comparable to a stand-alone solar thermal facility. However, this economic analysis, though accurate with regard to the technologies chosen, will not be complete until cost values can be placed on some of the externalities associated with power generation such as fuel cost volatility, national security, and emissions. / text
347

Energy Storage System for Wind-Diesel Power System in Remote Locations

Cordeiro, Roberto January 2016 (has links)
The aim of this thesis is to show how much fuel can be saved in a power system based in diesel generators with integrated wind turbine (WDPS – Wind Diesel Power System) when a storage system is integrated. Diesel generator is still the most used power system for remote locations where the conventional grid doesn’t reach and its integration with wind turbine is seen as a natural combination to reduce diesel consumption. However, the wind intermittency brings some challenges that might prevent the necessary diesel savings to the level that justifies the integration with wind turbine. The introduction of a storage system can leverage the wind energy that would otherwise be wasted and use it during periods of high demand.The thesis starts by describing the characteristics of energy storage systems (ESS) and introducing the major ESS technologies: Flywheel, Pumped Hydro, Compressed Air and the four main battery technologies, Lead Acid, Nickel-Based, Lithium-ion and Sodium-Sulphur. The aim of this step it to obtain and compile major ESS parameters to frame then into a chart that will be used as a comparison tool.In the next step, wind-diesel power systems are described and the concept of Wind Penetration is introduced. The ratio between the wind capacity and diesel capacity determines if the wind penetration is low, medium and high and this level has a direct relation to the WDPS complexity. This step also introduces important concepts pertaining to grid load and how they are affected by the wind penetration.Next step shows the development of models for low, medium and high penetration WDPS with and without integrated ESS. Simulations are executed based on these models in order to determine the diesel consumption for each of them. The simulations are done by using reMIND tool.The final step is a comparative study where the most appropriated ESS technology is chosen based on adequacy to the system, system size and location. Once the technology is chosen, the ESS economic viability is determine based on the diesel savings obtained in the previous step.Since this is a general demonstration, no specific data about wind variation and consumer demand was used. The wind variation, which is used as the input for the wind turbine (WT), was obtained from a typical Weibull Distribution which is the kind of distribution that most approximate a wind pattern for long term data collection. The wind variation over time was then randomly generated from this distribution. The consumer load variation is based on a typical residential load curves. Although the load curve was generated randomly, its shape was maintained in conformity with the typical curves.This thesis has demonstrated that ESS integrated to WDPS can actually bring a reasonable reduction in diesel utilization. Even with a wind pattern with a low mean speed (5.31 m/s), the savings obtained was around of 17%.Among all ESS technologies studied, only Battery Energy Storage System (BESS) showed to be a viable technology for a small capacity WDPS. Among the four BESS technologies studied, Lead-Acid presents the highest diesel savings with the lower initial investment and shorter payback time. / O objetivo dessa tese é determinar quanto combustível pode ser economizado quando se integra um sistema de armazenamento de energia (ESS na sigla em Inglês) a um sistema gerador baseado em gerador diesel integrado com turbina eólica (WDPS na sigla em Inglês). Geradores à diesel são largamente utilizados em áreas remotas onde a rede de distribuição de eletricidade não chega, e a integração de geradores à diesel com turbinas eólicas se tornou a combinação usual visando a economia de combustível. No entanto, a intermitência do vento cria alguns desafios que podem inclusive tornar essa integração inviável economicamente. A introdução de ESS à esse sistema visa o aproveitamento da energia que seria desperdiçada para usá-la em periodos de alta demanda.A tese começa descrevendo as características de ESS e suas principais tecnologias: Flyweel, hidroelétrica de bombeamento, ar-comprimido e as quatro principais tecnologias de bateria, Chumbo-Ácido, Níquel, Íon de Lítio e Sódio-Sulfúrico. O objetivo dessa etapa é obter os principais parâmetros de ESS e apresentá-los numa planilha para referência futura.Na etapa seguinte, geradores à diesel são descritos e é introduzido o conceito de Penetração do Vento. A razão entre a capacidade eólica e a capacidade do gerador diesel determina se a penetração é baixa, média ou alta, e esse nível tem uma relação direta com a complexidade do WDPS. Nessa etapa também são introduzidos importantes conceitos sobre demanda numa rede de distribuição de eletricidade e como esta é afetada pela penetração do vento.A etapa seguinte apresenta a modelagem de WDPS com baixa, média e alta penetração, incluindo a integração com ESS. Sobre esses modelos são então executadas simulações buscando determinar o consumo de diesel de cada um. As simulações são feitas usando a ferramenta reMIND.A última etapa é um estudo comparativo para determinar qual tecnologia de ESS é a mais apropriada para WDPS, levando-se em conta sua localização geográfica e capacidade. Uma vez que a escolha tenha sido feita, a viabilidade econômica do ESS é calculada baseado na ecomonia de combustível obtida na etepa anterior.Como esta tese apresenta uma demonstração, não foram utilizados dados reais de variação do vento nem de consumo. A variação do vento foi obtida de uma distribuição Weibull típica, que é a distribuição que mais se aproxima da característica do vento coletada em logo prazo. A variação do vento no tempo foi gerada aleatoriamente baseada nessa distribuição. A curva de consumo é baseada em curvas de consumo residenciais típicas. Embora a curva de consumo tenha sido gerada aleatoriamente, o seu formato foi mantido em conformidade com as curvas típicas.Essa tese demonstrou que ESS integrado à WDPS pode trazer uma economia razoável. Mesmo usando uma distribuição de vento com baixo valor médio (5.3 m/s), a economia obtida foi de 17%.Dentre as tecnologias de ESS pesquisadas, apenas o sistema de armazenamento com bateria (BESS na sigla em Inglês) se mostrou viável para um WDPS com pequena capacidade. Dentre as quatro tecnologias de BESS pesquisadas, Chumbo-Ácido foi a que apresentou a maior economia de diesel com o menor investimento inicial e com o menor tempo de retorno do investimento.
348

Multiplicative robust and stochastic MPC with application to wind turbine control

Evans, Martin A. January 2014 (has links)
A robust model predictive control algorithm is presented that explicitly handles multiplicative, or parametric, uncertainty in linear discrete models over a finite horizon. The uncertainty in the predicted future states and inputs is bounded by polytopes. The computational cost of running the controller is reduced by calculating matrices offline that provide a means to construct outer approximations to robust constraints to be applied online. The robust algorithm is extended to problems of uncertain models with an allowed probability of violation of constraints. The probabilistic degrees of satisfaction are approximated by one-step ahead sampling, with a greedy solution to the resulting mixed integer problem. An algorithm is given to enlarge a robustly invariant terminal set to exploit the probabilistic constraints. Exponential basis functions are used to create a Robust MPC algorithm for which the predictions are defined over the infinite horizon. The control degrees of freedom are weights that define the bounds on the state and input uncertainty when multiplied by the basis functions. The controller handles multiplicative and additive uncertainty. Robust MPC is applied to the problem of wind turbine control. Rotor speed and tower oscillations are controlled by a low sample rate robust predictive controller. The prediction model has multiplicative and additive uncertainty due to the uncertainty in short-term future wind speeds and in model linearisation. Robust MPC is compared to nominal MPC by means of a high-fidelity numerical simulation of a wind turbine under the two controllers in a wide range of simulated wind conditions.
349

Etude des effets des charges aérodynamiques sur le comportement dynamique non linéaire des éoliennes à axe vertical / Study of the aerodynamic loads effects on the nonlinear dynamic behavior of a vertical axis wind turbine

Bel Mabrouk, Imen 15 December 2017 (has links)
Ce sujet de thèse s'intéresse à l'étude des effets des charges aérodynamiques sur le comportement dynamique non linéaire d'une éolienne à axe vertical de type Darrieus. Cette dernière présente, comparativement aux autres éoliennes, des profits très importants à exploiter, notamment dans les milieux urbains. Il s'agit d'une technologie fiable caractérisée surtout par son fonctionnement omnidirectionnel ainsi que son adaptation à tout type de vent. Généralement, ces éoliennes, ayant des phénomènes aérodynamiques complexes, sont affectées par des vibrations au niveau de leur système de transmission de puissance. En fait, ces vibrations commencent à se manifester à partir des pales du rotor jusqu'au génératrice. L'écoulement autour de ses pales présente également un fort caractère instationnaire. Cette caractéristique augmente d'avantage les vibrations aérodynamiques, qui sont automatiquement transmise au système d'engrenage d'éolienne. À ce niveau, nous avons développé un code de calcul numérique permettant de simuler la complexité des aspects aérodynamiques instationnaires tout en gardant un compromis entre la fiabilité des prédictions et la rapidité de calcul. Les simulations sont réalisées suivant une méthode de mécanique des fluides numérique (CFD) instationnaire bidimensionnel. Les résultats de simulation comparés avec ceux disponibles dans la littérature sont en bonne concordance, le rendement aérodynamique étant optimisé, qui présente un apport scientifique notable. Cette étude numérique a été l'objectif de l'analyse de l'impact des charges aérodynamiques vis-à-vis le comportement dynamique du système d'engrenage de l'éolienne en régime non-stationnaire. Dans ce contexte, une étude paramétrique a été développée afin d'établir le fonctionnement optimal de l'éolienne, caractérisé par un couple aérodynamique plus performant associé à des niveaux de vibrations dynamiques acceptables. En général, il est difficile d'identifier précisément la réponse dynamique des éoliennes à cause du caractère turbulent et stochastique des charges aérodynamiques. Par conséquent, il est indispensable de tenir en compte la variabilité des paramètres d'entrée pour assurer la robustesse du système étudié. Adoptons l'objectif de dimensionnement robuste. Une méthode d'évaluation basée sur des approches stochastiques, particulièrement la méthode du Chaos Polynomial, est utilisée pour simuler le comportement dynamique non-linéaire du système d'engrenage d'éolienne, en tenant compte des incertitudes. Ces dernières sont au niveau des charges aérodynamiques, inhérentes au calcul des niveaux vibratoires du système d'engrenage. Ce qui implique un apport scientifique important. Les résultats obtenus par l'approximation par Chaos Polynomial démontrent une forte dispersion des charges aérodynamiques aléatoires dans la réponse dynamique du système d'engrenage, contrairement aux études déterministes. Ce qui prouve l'insuffisance de telles études pour une analyse de robustesse. Les résultats mettent également en évidence la forte corrélation entre les phénomènes aérodynamiques complexes et les vibrations dynamiques. Le couplage établi constitue l'originalité de notre travail. / This thesis focuses on the study of the aerodynamic loads effects on the nonlinear dynamic behavior of Darrieus--type vertical axis wind turbine. The latter has received more attention due to its efficiency in urban regions compared to other wind turbines. In fact, the wind flow speed in urban regions continuously changes direction and is extremely turbulent. The inherent characteristics of its omni-directionality make it more suitable to harnessing this kind of flow. It is known that Darrieus wind turbine is characterized by an inherently unsteady aerodynamic behavior and a complex flow around rotor blades. The non-stationary behavior of the mentioned turbine increases vibration. These aerodynamic vibrations are transmitted to the gearing mechanism. We have, firstly, developed a numerical simulation, allowing to simulate the complexity of the unsteady aerodynamic phenomena keeping a compromise between the reliability of prediction and the rapidity of calculation. This numerical simulation has been carried out using a two-dimensional unsteady Computational Fluid Dynamics (CFD) method. Simulation results compared to those available in the literature are in good agreement. The Darrieus turbine efficiency is also optimized; thus introducing a significant scientific contribution. The latter is the objective of analyzing the aerodynamic load impact in the dynamic behavior of the Darrieus turbine in non-stationary regime. In this context, a parametric study has been developed in order to find optimal functioning of the studied turbine, which is characterized by the most performing aerodynamic torque associated with acceptable levels of dynamic vibration. In general, it is difficult to predict the dynamic response of the wind turbine with a good level of accuracy due to the aerodynamic loads turbulence and uncertain characteristics. It becomes necessary to take into account the uncertainty in the input parameters to ensure the robustness of the Darrieus turbine geared system. In a robustness study objective, the Polynomial Chaos method is adopted to predict the nonlinear dynamic behavior of the gearing system taking into account uncertainties which are associated to the performance coefficient of the input aerodynamic torque. This leads to an important scientific research contribution. The results have shown a large dispersion of the random parameter in the dynamic response of the gearing system compared to the deterministic study. That proves the insufficiency of that study for a robustness analyses. They have also proved that the Polynomial Chaos method is an efficient probabilistic tool for uncertainty propagation. Finally, the new proposed robust mechanical analysis indicates a good capacity to investigate the dynamic behavior of the Darrieus turbine thanks to its superior predictive capabilities in coupling complex aerodynamic phenomena with a mechanical gearing system vibration. Where the originality of such correlation in our work.
350

Conception, modélisation et contrôle d'un tube anti-roulis multidirectionnel pour une barge offshore portant une éolienne / Design, modelling and control of a multidirectional anti-roll tank for an offshore barge offshore carrying a wind-turbine

Coudurier, Christophe 01 December 2017 (has links)
Suite à la mise en place de politiques publiques favorisant les énergies renouvelables, la construction de fermes éoliennes offshore est en plein essor aux quatre coins du monde. Or, la technique de l'éolienne offshore posée, la seule utilisée actuellement, n'est pas viable économiquement dans des eaux trop profondes. Ceci représente un sérieux frein au développement de l'énergie éolienne. Pour cette raison, la communauté scientifique s'intéresse depuis plusieurs années aux éoliennes sur plates-formes flottantes. En eau profonde, cette technologie est intéressante. Mais le fait que l'éolienne ne soit pas encastrée au fond de la mer augmente très significativement les sollicitations mécaniques induites par les vagues.Pour réduire ces sollicitations qui ont de nombreux effets néfastes, différentes approches sont possibles. Essayer de compenser les oscillations « avant-arrière » du mât de l'éolienne en pilotant la force de poussée exercée au niveau du rotor a déjà été écarté dans la littérature. Nous nous sommes concentrés sur l'ajout d'un dispositif de stabilisation interne à la plate-forme, de type Tuned Liquid Column Damper (un tube en U contenant un liquide, TLCD, encore appelé tube anti-roulis), utilisé dans d'autres contextes. Le dispositif que nous proposons est un dispositif actif où les paramètres du TLCD sont ajustés en temps réel, au cours du mouvement induit par les vagues. La mise à jour des paramètres suit une stratégie reposant sur une analyse des interactions entre le TLCD et la plate-forme (appelée ici barge) sur laquelle est installée l'éolienne. Nous avons modélisé le mouvement de la barge seul et son couplage avec le TLCD dans le plan grâce à une approche Lagrangienne. Nous avons étudié les effets des interactions du TLCD avec la barge dans le cas où le coefficient de perte de charge dans le tube était constant. Les limites de cette approche ont été détaillées grâce aux résultats classiques de la littérature sur les oscillateurs mécaniques couplés. Nous nous sommes ensuite concentrés sur une approche active consistant à modifier les caractéristiques du système en temps réel. Nous avons proposé des stratégies de type Linear Quadratic Regulator et de type Model Predictive Control agissant sur le coefficient de perte de charge. Dans un deuxième temps, les simulations nous ont ensuite permis d'écarter la commande MPC dont le rapport performance / complexité n'est pas favorable par rapport à la commande LQR dans ce cas précis.Une étude plus générale du système, en trois dimensions, nous a permis de vérifier que le TLCD classique dans sa version passive ou dans la version active que nous proposions n'est pas du tout robuste à l'incidence de la houle. Nous avons donc imaginé et modélisé des dispositifs inspirés du TLCD mais permettant d'amortir les oscillations de la houle de manière efficace, indépendamment de l'incidence de la houle. Nous avons nommé ces dispositifs TLMCD, pour Tuned Liquid Multiple Columns Damper.Les dispositif que nous proposons sont des systèmes TLMCD actifs. Ils sont conçus d'après les modélisations 3D que nous avons développées et une étude des coûts. Pour ces dispositifs, nous avons aussi détaillé les spécificités de la synthèse des stratégies LQR pour amortir les oscillations de la barge indépendamment de l'incidence de la houle.La performance de ces solutions d'amortissement a finalement été évaluée par simulation pour un large éventail de conditions de houle, couvrant les spécifications d'un “ cahier des charges ” que nous présentons. On observe une réduction des oscillations en roulis de la barge qui peut atteindre un facteur 4 par rapport à l'éolienne flottante sans TLCD. Ces résultats nous montrent que le dispositif TLMCD que nous proposons est un dispositif intéressant pour amortir de manière significative, robuste et économiquement abordable notre système. / Thanks to the recent policies of subsidizing renewables energies, constructions of offshore wind farms are booming all over the world. Yet, fixed-bottom wind turbine technology, the only one currently deployed, are too costly for deep waters. This hinders the development of wind power. This is why the scientific community has an interest in floating wind turbines (FWT). The cost of these wind turbines does not depend much on water depth. But since the wind turbine is not fixed into the seabed, the mechanical stress caused by the waves significatively raises.To reduce these detrimental loads, different approaches can be used. The litterature already discarded the control of the wind thrust applied on the rotor to compensate the "fore-aft" oscillations of the tower. We focused on stabilizing floating wind turbine by means of an attached damping system placed inside the float, it is a Tuned Liquid Column Damper (a U-tube containing a liquid, TLCD, also known as anti-roll tank), used in other areas. The damper we propose is an active system where TLCD parameters are continuously modified. Parameters are updated according to a strategy defined thanks to an analysis of the interactions between TLCD and the float (referred to as barge) supporting the wind turbine. We modelled the coupled dynamics of the barge and the TLCD in the vertical plan using a Lagrangian approach. We studied the motions of the damped system for a constant head-loss coefficient in the TLCD. The limits of this approach were detailed thanks to the classic results in double oscillators literature. Then, we focused on an active approach involving a time varying of the head-loss coefficient. We proposed Linear Quadratic Regulator and Model Predictive Control strategies to determine the head-loss coefficient. At a later stage, simulations enabled us to discard the MPC strategy as its complexity/performance ratio is rather bad compared to the LQR strategy in this particular case.A more general study of the system, in three dimensions, showed us that the TLCD is not robust against wave incidence. Therefore, we imagined and modeled new dampers inspired by the TLCD, which can damp the float effectively, regardless of the wave incidence. We named those dampers Tuned Liquid Multiple Column Damper (TLMCD).The dampers we propose are active TLMCD. Their designs are based on their dynamic properties and a cost study. We also detailed the specificities of LQR design to ensure the best possible robustness against wave incidence.The performance of the proposed TLMCD dampers was assessed through numerical simulations for a wide range of sea conditions. We observe that barge roll can be reduced by a factor of four compared to the undamped FWT. These results show us that the TLMCD we propose is interesting to damp significantly, robustly and economically our FWT.

Page generated in 0.0569 seconds