I dagsläget finns det en mängd olika storlekar på vindkraftverk, allt från små landbaserade vindkraftverk på några hundra kilowatt till havsbaserade kraftverk på upp till 14 MW. Bland de största vindkraftverken ute till havs, är direktdrivna vindkraftverk dominerande på grund av en högre driftssäkerhet och livslängd på komponenterna. En stor nackdel med dessa direktdrivna vindkraftverk är att för att få ut en hög effekt ur en relativt låg rotationshastighet, behöver generatorerna vara väldigt stora och blir då väldigt tunga. Syftet med det här arbetet var att titta närmare på vilka fördelar som potentiellt finns med att halvera vikten på nacellen som innehåller drivlinan och generatorn. De delarna som utreds i den här rapporten är viktens inverkan på vindkraftverkets torn och fundament men även kostnader för att transportera och montera vindkraftverk. Då allting som rör vindkraftverk är väldigt komplext, har en hel del förenklingar fått göras. För det första förenklades vindkraftverks torn till en fast inspänd balk med en punktmassa på toppen, vilket motsvarar massan för nacellen, hubben och bladen. När det kommer till transporter och montering har det inte gått att få fram exakt vad det kostar att transportera och montera en nacell, men utifrån en del data kunde uppskattningar göras för att skapa en bild av vad kostnaderna låg på och vilka kostnadsfördelar som skulle kunna finnas av att minska vikten.För att få bra data på olika vindkraftverk användes data för olika referenskraftverk som finns tillgängliga för forskningssyfte. De som användes var NREL 5 MW, LW 8 MW, DTU 10 MW och IAE 15 MW. Efter beräkningar på dessa vindkraftverk kan det konstateras att en minskning av krafterna som verkar på fundamenten är den stora fördelen men en halverad vikt på nacellen. I de beräkningar som gjordes låg minskningarna på mellan 13 – 17%. När det kommer till viktens inverkan på tornet är det svårare att dra några klara slutsatser. Enligt beräkningarna minskade de maximala tryckspänningarna med ungefär 1.5 – 2.5%, medan dragspänningarna istället ökade med 0.6 – 2.1 %. Tryckspänningarna i tornet var de största och därav minskar de största spänningarna i tornet, men då till exempel vissa vindkraftverks torn är gjorda i betong, som är sämre på att ta upp dragspänningar, kan ökande dragspänningar vara något som vill undvikas. När beräkningar gjordes för egenfrekvenserna på tornet visade de att egenfrekvensen ökar med ungefär 20 % vid en halverad vikt, vilket både kan vara en fördel och en nackdel. När det kommer till kostnader för transporter och montering är det svårt att ge en exakt siffra eller procentsats över hur mycket billigare det blir. Det kan vara allt från några tiotusentals kronor per nacell i vissa delar, upp till miljontals kronor för ett helt projekt i andra delar. / Today there is a large amount of different wind turbines, from small onshore turbines with an effect of only a few kilowatts to huge offshore turbines with an effect of 14 MW. The largest offshore turbines are dominated by turbines with a direct drive drivetrain due to a higher operational reliability and longer life span of the components. A major disadvantage of these direct-drive wind turbines is that in order to have a high power output from a relatively low rotational speed, the generators become very large and heavy.For this project, the purpose is to analyze the potential benefits of lowering the weight of the nacelle, which contains the drivetrain and the generator. The parts discussed in this report are the nacelle’s weight’s impact on the wind turbine’s tower and its foundation and the costs for transporting and assembling wind turbines. Since everything that concerns wind turbines is very complex, a lot of simplifications had to be made. First of all, the wind turbine’s tower was simplified as a cantilever beam with a mass at the top corresponding to the mass of the nacelle, hub and blades. When it comes to transportations and installations, it has not been possible to find out the exact costs to transport and install a nacelle, but based on some data, estimations could be made of what the costs are and what benefits there could be of reducing the weight. To get reliable data on different wind turbines, reference turbines were used. These are turbines used for research and almost all information is accessible online. The reference turbines that were used were the NREL 5 MW, the LW 8 MW, the DTU 10 MW and the IAE 15 MW. After calculations on these wind turbines, it became clear that the forces affecting the foundations are the biggest advantages (regarding forces) with a reduced weight on the nacelle. In the calculations that were made, the forces were reduced by between 13 - 17% if the nacelle weighs 50% less. When it came to the impact of weight of the nacelle had on the tower, it was more difficult to come to any clear conclusions. The calculations shows that the maximum compressive stresses decreased by approximately 1.5 – 2.5% while the tensile stresses increased by 0.6 – 2.1 %. The compressive stresses in the tower were the largest and hence, the largest forces on the tower decrease. But since some wind turbines are made of concrete, which isn’t as good on taking tensile forces, therefor increasing tensile stresses may be undesirable. When analyzing the natural frequencies of the different towers, calculations showed that the natural frequency were raised by approximately 20%.When it comes to costs of transportations and installations, it is difficult to give an exact figure or percentage of how much cheaper it will be. It could range from a couple of thousand US dollars per nacell in some instances, up to a several hundred thousand US dollar for an entire project in other instances.

Cascade Drives develops electromechanical linear actuators based on multiple pinions interacting with a gear rack. With a patented load sharing mechanism, that uses flexible torsional elements, the torque is equally distributed among the pinions. The same technology was used to develop an innovative wind turbine gearbox design for a Vestas V52 wind turbine, which is more compact and consists of less parts than the current solutions. In this thesis project, this gearbox design was analyzed through software tools, in order to verify its feasibility and refine its design for improvement. In the first part of this thesis, the gearbox was analyzed using Romax, a drivetrain analysis software. From this analysis, the gearbox’s gears, bearings, shafts and housing were assessed and some design refinements were done based on the results to improve the gearbox’s safety factors and life time. In the second part of this thesis, multibody dynamic (MBD) simulations were performed for the gearbox using MSC ADAMS, to study the dynamic response of the gearbox for three load cases of interest. An MBD model was created, which included the tooth contact flexibility and the flexibility of the torsional elements. Through these simulations, the flexible torsional elements’ stiffness was tuned in order to achieve an equal torque distribution among the gears for this application. Thus, the gearbox design was verified as a feasible solution for a Vestas V52 wind turbine. / Cascade Drives utvecklar elektromekaniska linjära ställdon baserade på flera pinjonger som interagerar med ett kuggrack. Med en patenterad lastdelningsmekanism som tillåter torsion, är vridmomentet lika fördelat mellan alla pinjonger. Samma teknik har använts för att utveckla en innovativ vindkraftväxellåda för ett Vestas V52 vindkraftverk, som är mer kompakt och består av färre delar än de nuvarande lösningarna. I denna avhandling analyserades denna växellådsdesign genom mjukvaruverktyg för att verifiera dess genomförbarhet och förfina dess design. I den första delen analyserades växellådan med Romax, en mjukvara för analys av drivlinor. Från denna analys utvärderades växellådans växlar, lager, axlar och hus och vissa konstruktionsförbättringar gjordes baserat på resultaten för att förbättra växellådans säkerhetsfaktorer och livslängd. I den andra delen utfördes multikroppsdynamiska (MBD) simuleringar för växellådan med MSC ADAMS, för att studera växellådans dynamiska svar för tre belastningsfall av intresse. En MBD -modell skapades, som inkluderade kuggkontaktflexibiliteten och lastfördelningselementens flexibilitet. Genom dessa simuleringar justerades styvheten för att uppnå en jämn vridmomentsfördelning mellan växlarna för applikationen. Växellådskonstruktionen verifierades således som en genomförbar lösning för ett Vestas V52 vindkraftverk.

The development of aerodynamic boundary layers on wind turbine blades is an important consideration in their performance. It can be quite challenging to replicate full scale conditions in laboratory experiments, and advanced diagnostics become valuable in providing data not available from traditional means. A new variant of Doppler global velocimetry (DGV) known as cross-correlation DGV is developed to measure boundary layer profiles on a wind turbine blade airfoil in the large scale Virginia Tech Stability Wind Tunnel. The instrument provides mean velocity vectors with reduced sensitivity to external conditions, a velocity measurement range from 0ms^-1 to over 3000ms^-1, and an absolute uncertainty. Monte Carlo simulations with synthetic signals reveal that the processing routine approaches the Cramér-Rao lower bound in optimized conditions. A custom probe-beam technique is implanted to eliminate laser flare for measuring boundary layer profiles on a DU96-W-180 wind turbine airfoil model. Agreement is seen with laser Doppler velocimetry data within the uncertainty estimated for the DGV profile. Lessons learned from the near-wall flow diagnostics development were applied to a novel benchmark model problem incorporating the relevant physical mechanisms of the high amplitude periodic turbulent flow experienced by turbine blades in the field. The model problem is developed for experimentally motivated computational model development. A circular cylinder generates a periodic turbulent wake, in which a NACA 63215b airfoil with a chord Reynolds number Re_c = 170, 000 is embedded for a reduced frequency k = (pi)fc/V = 1.53. Measurements are performed with particle image velocimetry on the airfoil suction side and in highly magnified planes within the boundary layer. Outside of the viscous region, the Reynolds stress profile is consistent with the prediction of Rapid Distortion Theory (RDT), confirming that the redistribution of normal stresses is an inviscid effect. The fluctuating component of the phase- averaged turbulent boundary layer profiles is described using the exact solution to laminar Stokes flow. A phase lag similar to that in laminar flow is observed with an additional constant phase layer in the buffer region. The phase lag is relevant for modeling the intermittent transition and separation expected at full scale. / Ph. D.

Transition is an important phenomenon in large scale, commercial, wind tunnel testing at low speeds because it is an excellent indicator of an airfoil performance. It is difficult to estimate transition through numerical techniques because of the complex nature of viscous flow. Therefore experimental techniques can be essential. Over the transition region the rate of heat transfer shows significant increases which can be detected using infrared thermography. This technique has been used predominantly at high speeds, on small models made of insulated materials, and for short test runs. Large scale testing has not been widely undertaken because the high sensitivity of transition to external factors makes it difficult to detect. The present study records the process undertaken to develop, implement and validate a transition detection system for continual use in the Virginia Tech Stability Wind Tunnel: a low speed, commercial wind tunnel where large, aluminium models are tested. The final system developed comprises of two high resolution FLIR A655sc infrared cameras; four 63.5-mm diameter circular windows; aluminium models covered in 0.8-mm silicone rubber insulation and a top layer of ConTact© paper; and a series of 25.4-mm wide rubber silicone fiberglass insulated heaters mounted inside the model and controlled externally by experimenters. This system produces images or videos of the model and the associated transition location, which is later extracted through image processing methods to give a final transition location in percentage chord. The system was validated using two DU96-W-180 airfoils of different chord lengths in the Virginia Tech Stability Wind Tunnel, each tested two months apart. The system proved to be robust and efficient, while not affecting the airfoil performance or any other system in use in the wind tunnel. Transition results produced by the system were compared to measurements obtained from pressure data and stethoscope tests as well as the numerical predictions of XFOIL. The transition results from all four methods showed excellent agreement with each other for the two models, for at least two Reynolds numbers and for several angles of attack on both suction and pressure side of the model. The agreement of data obtained under such different conditions and at different times suggests that the infrared thermography system efficiently and accurately detects transition for large aluminium models at low speeds. / Master of Science

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.

<p>The 21st century would be a nightmare for Don Quijote: thousands of windmills are installed all over the globe and the number will increase tremendously over the next years. If climate change was an issue in the early 17th century, Don Quijote might have specialized in fighting nuclear or fossil fuel power plants.</p><p>The change in power production is clearly pronounced, and it inspires the market to respond immediately. Numerous wind turbine manufacturers emerge, developing one technological innovation after another. The trend clearly goes in one direction: horizontal axis wind turbines in all possible variations. However, there are a few companies that do not follow the mainstream – they swim against the current and introduce new concepts, with the potential to set new standards in the industry.</p><p>Nevertheless, the question whether these companies can establish operations and survive in an industry dominated by large multinational corporations arises. If these companies want to become recognized, they need to compete on an international scale from the outset – they become born globals.</p><p>This master’s thesis investigates the preconditions under which an innovative start-up company can become born global in the wind turbine industry. For that, distinctive resources and capabilities of such companies, as well as key success factors for the industry are defined. Furthermore, enhancing or restricting parameters lying within company’s environment – in particular, within its networks – are discovered. These findings are based on and supported by the case study of an innovative vertical axis wind turbine manufacturer. In addition, the influence of this company’s university spin-off origin is investigated.</p>

Wind energy technologies are considered to be among the most promising types of renewable energy sources, which have since attracted broad considerations through recent years due to the soaring oil prices and the growing concerns over climate change and energy security. In Kuwait, rapid industrialisation, population growth and increasing water desalination are resulting in high energy demand growth, increasing the concern of oil diminishing as a main source of energy and the climate change caused by CO2 emissions from fossil fuel based energy. These demands and challenges compelled governments to embark on a diversification strategy to meet growing energy demand and support continued economic growth. Kuwait looked for alternative forms of energy by assessing potential renewable energy resources, including wind and sun. Kuwait is attempting to use and invest in renewable energy due to the fluctuating price of oil, diminishing reserves, the rapid increase in population, the high consumption of electricity and the environment protection. In this research, wind energy will be investigated as an attractive source of energy in Kuwait.

The 21st century would be a nightmare for Don Quijote: thousands of windmills are installed all over the globe and the number will increase tremendously over the next years. If climate change was an issue in the early 17th century, Don Quijote might have specialized in fighting nuclear or fossil fuel power plants. The change in power production is clearly pronounced, and it inspires the market to respond immediately. Numerous wind turbine manufacturers emerge, developing one technological innovation after another. The trend clearly goes in one direction: horizontal axis wind turbines in all possible variations. However, there are a few companies that do not follow the mainstream – they swim against the current and introduce new concepts, with the potential to set new standards in the industry. Nevertheless, the question whether these companies can establish operations and survive in an industry dominated by large multinational corporations arises. If these companies want to become recognized, they need to compete on an international scale from the outset – they become born globals. This master’s thesis investigates the preconditions under which an innovative start-up company can become born global in the wind turbine industry. For that, distinctive resources and capabilities of such companies, as well as key success factors for the industry are defined. Furthermore, enhancing or restricting parameters lying within company’s environment – in particular, within its networks – are discovered. These findings are based on and supported by the case study of an innovative vertical axis wind turbine manufacturer. In addition, the influence of this company’s university spin-off origin is investigated.

Thesis (MEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Support tower structures of Wind Energy Conversion Systems (WECS) are major cost items and by means of integrated design and optimization, the Life-Cycle Cost (LCC) can be reduced substantially. In this thesis, Horizontal Axis Wind Turbine (HAWTs) tower structures are investigated by means of a technique or tool that can bene t in decision making related situations to reduce the LCC of such WECS support towers from inception to disposal. Often, during the conceptual design phase a certain level of uncertainty or fuzziness exists and plays a role. The central focus in this project is on lattice type towers; however an account on tapered, tubular monopole towers is given as well. The problem is identi ed to be of a multi-objective nature, where a variety of criteria or objectives that are identi ed play a role in the possible reduction of the total LCC of the structure. The study also entails the delineation and discussion of the factors and components that a ect the LCC of a steel structure. The decision maker has control over only a few of these factors and components as identi ed, and these can be formulated by means of an objective to be minimized (or maximized in several other cases). Some of the objectives are incommensurable and others are commensurable with each other. In other words, several of these objectives either `compete' or don't `compete' against each other, respectively. The investigation resulted in the development of a multi-objective LCC optimization using the λ-formulation (or min-max formulation) as the objective aggregating approach for the four objectives identi ed (varied during analysis for sensitivity checks). The objectives are user-de ned in terms of membership functions that grade the degree of membership from total acceptance to total rejection by means of boundary values. This formulation is Non-Pareto based and the decision maker obtains the best trade-o or best compromise solution. The detailed discussion around these objectives is included in the literature study. The objectives in the multi-objective study are weight, cost, perimeter and nodal deflections, and a weighting of the objectives is possible but this is excluded from this study. A Genetic Algorithm (GA), coded in MATLAB, is implemented as the optimization tool or technique. The algorithm uses a quadratic penalty function approach and a natively written Finite Element Analysis (FEA) tool is used for the response model in the tness evaluation process, where the performance for stability, capacity and overall deflections of an individual in the population is quanti ed. A GA has the advantage that it operates on an entire population of individuals using basic principles such as genetics, crossover, mutation, selection and survival of the ttest from biology and Darwinian principles. GAs are very robust and e ective global search methods that can be applied to most elds of study. GAs have previously been e ectively applied in structural, single objective optimization (structural weight) problems. The GA is adopted and modi ed and veri ed with results on academic problems obtained from literature. Satisfactory performance was observed, although room for improvement is identi ed. A case study on a full scale model is performed, using circular hollow sections and equal leg angle sections. These are commonly used steel profi les for lattice type towers. The results obtained are as expected. The structural mass was used as a measure to compare the results. A heavier structure is obtained using the equal leg angle sections compared to the CHS structure with a di fference of up to 20% in weight. The best compromise solutions are feasible and near optimal, given the conditions of the equally weighted objectives in this study. The membership function defi nition and boundary value determination still remains a key issue when using fuzzy logic to incorporate the preference information of the decision maker. / AFRIKAANSE OPSOMMING: Toringstrukture van windturbines is belangrike kostekomponente van `n windkragopwekking stelsel. Deur middel van geï ntegreerde ontwerp en optimalisering kan die lewensikluskoste aansienlik verminder word. In hierdie tesis word horisontale-as windturbinetoringstrukture ondersoek. Deur middel van `n tegniek of hulpmiddel wat kan baat vind by besluitneming situasies, word die lewensiklus-koste van sodanige windturbine ondersteuning torings vanaf voorgebruik-fase tot lewenseinde-fase verminder. Dikwels, tydens die konseptuele ontwerp-fase, speel `n sekere vlak van onsekerheid of verwarring ook `n rol. Die sentrale fokus in hierdie projek is op staal vakwerk tipe torings gelê. `n Vereenvoudigde ontleeding van buisvormige torings is ook benader. Die probleem is van multikriteria aard, waar `n verskeidenheid van kriterie of doelwitte ge denti seer was. Hulle speel `n rol in die moontlike vermindering van die totale lewensiklus-koste van die struktuur. Die studie behels ook die bespreking en afbakening van die faktore en komponente wat die lewensiklus-koste van 'n staal struktuur bepaal. Die besluitnemer het slegs beheer oor sekere van hierdie faktore en komponente, en hierdie word deur middel van `n saamgevoegde doel-funksie gede neer wat dan geminimeer word. Sommige van die doelfunksies kompeteer met mekaar en sommige kompeteer nie met mekaar nie. Die ondersoek het gelei tot die ontwikkeling van `n multikriteria lewensiklus-koste optimalisering met behulp van die λ-formulering (of min-max formulering). Hierdie is `n tegniek wat die kriterie in vorm van `n verteenwoordigende doel-funksie saamvoeg. Daar is vier doelwitte wat geï denti seer was. Die gebruiker de nieer spesiale, lineêre doel-funksies wat van totale aanvaarding tot totale verwerping streek. Dit word deur middel van randwaardes gedoen. Hierdie formulering is nie Pareto gebaseer nie, en die besluitnemer verkry die `best trade-off ' of die beste kompromis oplossing. Die detailleerde bespreking rondom hierdie doelwitte is in die literatuurstudie ingesluit. Die doelwitte wat in die multikriteria studie gebruik word is gewig, koste, omtrek van die snitpro el en strukturêle defleksie. `n Gewig kan aan elke kriterium toegeken word, maar dit word van hierdie studie uitgesluit. `n Genetiese algoritme (GA), geï mplementeer in MATLAB, word as die optimalisering instrument en tegniek gebruik. Die algoritme gebruik `n kwadratiese `straf-funksie' en `n MATLAB Eindige Element Analise (EEA) word gebruik vir die gedragsmodel in die `fi ksheid' evalueringsproses. Die prestasie vir stabiliteit, kapasiteit en algehele verlegging van `n individu in die GA bevolking word daardeur gekwanti seer. `n GA het die voordeel, dat dit met `n hele bevolking van individue werk. Dit is gebaseer op beginsels van genetika en Darwin se beginsels. GAs is baie stabiel en ook e ektiewe globale soek metodes wat van toepassing in verskillende studierigtings is. GAs is al e ektief toegepas in strukturêle optimalisering (veral strukturêle gewig optimalisiering). Die GA in hierdie studie was aangepas en die gedrag en prestasie is bevestig met resultate van akademiese probleme uit die literatuur. Bevredigende prestasie is waargeneem, maar ruimte vir verbetering is ook geï denti seer. `n Gevallestudie oor `n grootskaal model is uitgevoer, en die gebruik van ronde holpro ele en gelykbenige hoekpro ele is uitgevoer. Dit is algemeen gebruikte staalpro ele vir vakwerk tipe torings. Die resultate wat verkry is, is soos verwag. Die strukturêle massa is gebruik as `n maatstaf om die resultate te vergelyk. `n Swaarder struktuur is die resultaat wanneer gelykbenige hoekpro ele gebruik word in vergelyking met die ronde holpro el struktuur. `n Verskil tot 20% in gewig is waargeneem. Die beste kompromis oplossing is haalbaar en naby-optimaal, gegewe die omstandighede van die gelyk geweegde doelfunksies in hierdie studie. Die doel-funksie de nisie, die voorkeur van die besluitnemer en die bepaling van die randwaardes bly steeds `n belangrike kwessie by die gebruik van hierdie benadering.

A framework for evaluating different wind turbine foundations has been proposed and applied in six hypothetical case studies located in three sites in different locations throughout Sweden.The framework is based on decision making method PROMETHEE II and consists of nine criteria covering financial, environmental and technical aspects of wind turbine foundations. The foundation has been evaluated from two different stakeholder perspectives – civil designers and financial advisors. Application of this framework has shown that an existing commonly used wind turbine foundation type is not the most favourable alternative, whilst a new market entrant – prefabricated foundation – shows promising results. Using PROMETHEE II it became evident that in any given case, a prefabricated foundation is ranked as the most or a close second to most suitable type of foundation. Gravity caissons ranked as the least favourable option in almost all, except one, case. Comparing these three alternatives prefabricated foundation showed greater economic feasibility, lower impact on environment and technologically more applicable than other alternatives with very few existing drawbacks.