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  • 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.
161

MEASUREMENT DRIVEN FATIGUE ASSESSMENT OF OFFSHORE WIND TURBINE FOUNDATIONS

Wilberts, Frauke January 2017 (has links)
The installed capacity of offshore wind turbines in Europe is increasing with the monopile being the most common type of foundation. During its lifetime an offshore wind turbine is exposed to high dynamic loads which eventually can result in the fatigue of the substructure. This thesis will show how the linear damage accumulation approach based on the Miner’s rule can be used to estimate the damage induced on the substructure of an offshore wind turbine using measurements from strain gauges. Furthermore, the most important environmental influences will be illustrated and the different stress concentration factors and the size effect introduced in the industry guideline DNVGL-RP-C203 will be analysed towards their effect on the calculated lifetime.
162

Etude expérimentale et numérique du couplage des phénomènes aérodynamiques et hydrodynamiques sur une éolienne offshore flottante / Experimental and numerical study of hydrodynamic and aerodynamic coupled effects on a floating wind turbine

Lacaze, Jean-Baptiste 14 September 2015 (has links)
Le présent travail est une étude sur la modélisation des éoliennes flottantes alliant à la fois des chargements hydrodynamiques et aérodynamiques. L’approche expérimentale a tiré profit de la grande soufflerie de Luminy opérée par le MIO (Institut Océanologique de Méditerranée), unissant une soufflerie de très bonne qualité avec un bassin équipé de systèmes de génération de houle et de courant. Les dimensions de cette installation imposent un travail à échelle très réduite introduisant ainsi les interrogations sur les similitudes à respecter (Reynolds, Froude) et les complexités de maquettage. Ces travaux ont permis de développer des outils numériques avec d’un côté une approche fréquentielle basé sur un code utilisant les éléments finis développé par l’IFP au début des années 70, et de l’autre, une approche temporelle basé sur les formulations de Morison ou de Rainey permettant l’introduction de méthodes avancées de calculs des efforts aérodynamiques. / The present work focuses on the modeling of the hydrodynamic and aerodynamic loads on a floating wind turbine. The experimental approach took advantage of the wind and wave flume in Luminy operated by the MIO (Mediterranean Institute for Oceanography) comprising a wind tunnel with a very high flow quality blowing over a wave tank. The dimensions of the installation impose working at very small scales for which the similitudes (Reynolds, Froude) introduce high modeling complexities. This work allowed the development of numerical tools using one the one hand a frequency domain approach based on a finite element code developped by IFP¨in the early seventies, and in the other hand a time-domain approach based on Morison or Rainey formulation for hydrodynamic loads allowing the introduction of advanced methods for aerodynamic loads computation.
163

Ansatz für die Modellierung und Simulation von Hybridgleitlagern für Wellen mit großen Durchmessern und geringen Drehzahlen am Beispiel einer Windkraftanlage

Jonuschies, Ingo, Brökel, Klaus 26 September 2017 (has links) (PDF)
Motivation "Am stetig steigenden Anteil der erneuerbaren Energien, der auf der einen Seite durch die ehrgeizigen Ziele der Politik forciert und auf der anderen Seite durch wirtschaftliche Interessen beflügelt wird, stellt die Windenergie den größten und aussichtsreichsten Bestandteil dar (BMU 2012). Setzt sich der gegenwärtige Trend fort, so ist in den nächsten Jahren mit Multimegawattanlagen im mehrstelligen Megawattbereich zu rechnen."
164

Système multi physique de simulation pour l'étude de la production de l'énergie basée sur le couplage éolien offshore-hydrolien / Multi-physical system of simulation for the study of energy production based on offshore wind and tidal power hybrid system

Tekobon, Jerry 12 December 2016 (has links)
Les travaux de thèse concernent le développement d’une plateforme d’émulation temps réel destinée aux études théoriques et expérimentales des systèmes hybrides éolien- hydrolien. Diverses architectures de couplages énergétiques sont traitées sur la base des similitudes fonctionnelles des deux systèmes et par des concepts d’émulation à la fois numériques et expérimentaux. La notion de simulation en temps « accéléré » a été développée. Le concept a été validé sur la plateforme expérimentale en utilisant l’évolution de la puissance moyenne délivrée par une turbine éolienne de petite puissance. Cette approche pourra permettre de réduire les temps d’observation des campagnes de mesure, d’accélérer les études sur le potentiel éolien des sites en développement. Nous avons développé également deux types de couplage du système hybride éolien-hydolien. Un couplage électrique basé sur la connexion en parallèle sur un bus continu des deux turbines. Nous avons développé un concept innovant d’un couplage électromécanique basé sur l’utilisation d’une seule génératrice asynchrone sur laquelle sont simultanément couplés les arbres de la turbine éolienne et de la turbine hydrolienne. Pour cela, un servomoteur à commande vectorielle nous a servi à émuler la turbine éolienne pendant qu’un moteur synchrone nous a servi d'émulateur de turbine hydrolienne. L’arbre de la génératrice sert de couplage mécanique entre les deux systèmes. Nous avons mis en évidence dans les expérimentations effectuées, la complémentarité des productions électriques des deux systèmes, et également le besoin de leur adjoindre un système de stockage pour palier à une baisse simultanée de deux productions d’énergie. / The thesis work concerns the development of a real-time emulation platform for theoretical and experimental studies of offshore wind and tidal power hybrid systems. Various energy coupling architectures are processed on the basis of the functional similarities of two systems and by both numerical and experimental emulation concepts. The notion of accelerated time used for real time simulation has been developed. The concept was validated on the experimental platform using the evolution of the mean power delivered by a small wind turbine. This approach can reduce the observation times of the measurement campaigns and could accelerate the studies for the wind potential of developing sites. We have also developed two types of coupling of the wind-tidal hybrid system. An electrical coupling based on the connection in parallel on a continuous bus of two turbines. We have developed an innovative concept of an electromechanical coupling based on the use of a single asynchronous generator on which the wind turbine and tidal turbine are simultaneously coupled. For this purpose, a vector-controlled servomotor was used to emulate the wind turbine while a synchronous motor was used as a tidal turbine emulator. The generator shaft is used as a mechanical coupling between the two systems. We have demonstrated in the experiments that we have developed the complementarity of the electrical productions of the two systems; we highlighted the need to add a storage system to compensate the simultaneous decrease of the two energy productions. The real time simulations results allow us to validate the feasibility of such a coupling.
165

Extending the fatigue life of a T-joint in a composite wind turbine blade

Hajdaei, Amirhossein January 2014 (has links)
Wind turbines are classic examples of structures where their operating lifetime is controlled by the fatigue properties of the material. This is exacerbated by the 2D nature of the composite materials used in blade construction which are typically fabrics in a variety of formats (e.g. non crimp fabrics, uniweave, woven). The formation of internal detailed shapes within the blade, allowing features such as spars, shear webs and other connections, inevitably requires these 2D material configurations to be formed into 3D shapes. This introduces positions within the structure where load transfer occurs across regions with no fibre reinforcement. These weak areas become natural positions for the initiation of damage that can occur well before fatigue damage would be expected in the basic material subject to simple in-plane loading. The aim of this study is to modify and improve the blade structure in order to extend its working life and minimize geometry related fatigue issues. To achieve this goal T-sections have been manufactured as representative element of the blade's spar. T-sections have been made of carbon or glass fabric infused with epoxy resin using a vacuum-assisted resin-transfer moulding technique. The structure has been modified with different toughening techniques to increase its interlaminar fracture resistance (toughness) and hence delay or stop crack propagation. Methods such as the use of veil layers, tufting and 3D weaving techniques have been employed to improve the interlaminar fracture toughness of the T-joint. The changing parameters in samples are, the addition of the veil layer to the composite structure, veil material, tufting stitches and use of different 3D fibre weaving architectures in the fabrication of the composite T-joint. For T-joint testing, there was no standardised specimen shapes and no standard for specimen dimensions; as well as no test fixture designs or test procedures. Consequently, it was required to design a test rig and develop a test procedure for tensile and fatigue tests of T-joints. An additional investigation was performed to establish test specimen geometry suitable for testing in available Instron machines. Manufactured specimens were quasi-static and fatigue tested. Test results were compared and showed that 3D woven and polyester veil T-joints had the best performance among modified structures. However, it has been found that these structural modifications are performing differently in quasi-static and fatigue loading. The 3D woven four layer to layer inter wave sample that showed the best result in a quasi-static test was not the one with the best fatigue results but it was amongst the ones with the highest performance. SEM and optical microscopy were used to investigate fractured specimens in an attempt to establish the mechanisms involved in the fracture process of the T-joint. Finally, based on test and investigations results it has been concluded that the 3D weaving was the most effective modification to improve the static and fatigue properties of the T-joint. The T-joint modified with polyester veil showed the second best performance in both static and fatigue tests but the addition of the polyamide caused had negative effects on these properties.
166

Desenvolvimento de uma máquina síncrona trifásica com núcleo do rotor produzido a partir da metalurgia do pó e ímãsde neodímio-ferro-boro para aplicação em aerogeradores

Borba, Monir Goethel January 2016 (has links)
Este trabalho tem como objetivo o projeto, construção e análise do funcionamento de uma máquina elétrica síncrona trifásica com núcleo do rotor produzido a partir da metalurgia do pó e ímãs de neodímio-ferro-boro para aplicação em aerogeradores. Tomando como base a máquina elétrica modelo VTOP da fabricante Grupo Voges, foram realizadas mudanças na forma construtiva dos núcleos do estator e do rotor. O pacote chapas que compõem o núcleo do estator foi montado de maneira que as ranhuras apresentem um ângulo de inclinação de 10º ao longo de toda a extensão da máquina. Para o rotor, foi projetado e construído um núcleo através do processo de metalurgia do pó utilizando como matéria-prima pó de ferro puro. A esse novo núcleo foram acrescentados ímãs de neodímio-ferro-boro. Após a montagem dos componentes, a máquina elétrica foi ensaiada em uma bancada de testes. Paralelamente com a confecção do núcleo foi efetuada a simulação computacional da máquina com três tipos diferentes materiais no núcleo do rotor. Os resultados encontrados indicaram que a metalurgia do pó é uma alternativa viável para produção do núcleo de máquinas elétricas. Entretanto alterações na topologia e na forma de fixação dos ímãs são necessárias para um melhor desempenho. / This work aims at the design, construction and performance analysis of a three-phase synchronous electric machine with a rotor core produced by powder metallurgy and neodymium-iron-boron magnets for application in wind turbines. Based on the electric machine VTOP model of the manufacturer Grupo Voges, changes were carried out in the constructive form of the stator and rotor cores. The bundle of plates that make the role of stator core were mounted with a 10º slope along the entire length of the machine. For the rotor, a core was designed and built by employing powder metallurgy process using pure iron powder as raw material. The neodymium-iron-boron magnets were added to this new core. After assembling the components, the electric machine was tested on a test bench. Simultaneously with the core fabrication, the machine was simulated with three different materials in the rotor core. The results indicated that powder metallurgy is a viable alternative to produce the core of electric machines. However, changes in the topology and shape of the magnets are necessary for better assembly, improving the performance.
167

Practical application of topology optimization to the design of large wind turbine towers

Warshawsky, Brandon Lee 01 July 2015 (has links)
Structural topology optimization is a mathematical approach developed to perform design optimization with the purpose of reducing the material usage, while maximizing structural performance, in accordance to specific design constraints. The principles behind this technique have been around for many decades, but recent advancements in the processing power of computers have allowed for the solving of complex problems, such as the optimization of tall wind turbine towers, bridges, and the bracing systems in skyscrapers. There are two approaches commonly used in structural topology optimization: discrete and continuum. This thesis uses continuum topology optimization, which involves adjusting the distribution of a porous elastic solid material to extremize the design objective(s) and to satisfy constraints. The material porosity is the design variable that is adjusted during the optimization process. The design domain is broken down into a system of continuum degenerated finite elements, which are used for both structural analysis and to create a mesh representation of the structural system, just as pixels make up a picture. Solid elements are modeled as having no porosity, while void spaces have total porosity. As the optimization process occurs, the shape of the boundaries, and the number and size of internal holes are altered in order to best meet the design objective(s) and constraint(s). The purpose of performing continuum structural topology optimization of structural elements is to obtain promising concepts which provide a basis upon which to begin the design process. The steps taken in this thesis to optimize the wind turbine tower are: 1. Create a solid model of the tower domain 2. Define the material properties 3. Determine the equivalent static design wind forces using the extreme loading conditions outlined in IEC 61400 4. Formulate the optimization problem by specifying the objective and constraint functions. 5. Solve the optimization problem and interpret the results. This study on continuum topology optimization on the tower shell, indicates even with a significant reduction in material from the original design space, the structure is capable of meeting the design criteria. The results indicate that opening void spaces in the shell of the tower and creating an open lattice shape may be an effective method to reduce the volume of wind turbine towers, as it has in other applications. This concurs with the stated goal of my research, which is to show that topology optimization has the potential to be used in a multitude of practical applications in order to increase efficiency, and reduce cost of the production of wind power.
168

Aerodynamika axiálních větrných turbín / Aerodynamics of axial wind turbines

Dubnický, Ladislav January 2019 (has links)
Nowadays, the climate change issue is becoming more and more actual in our society. Increase of the average temperature on Earth in a couple of degrees could have catastrophic consequences. One of the possible solutions seems to be renewable energy sources as photovoltaics, biomass of water and wind energy. This thesis deals with the aerodynamics problems of wind energy source. Wind turbines transform kinetic energy of wind to mechanical power. The efficiency is physically limited to 59,26 %, but in reality, it is getting around 45 %. This is caused by three biggest losses inducted in wind turbines as wake losses, losses due to finite number of blades and drag losses. Based on analytical relationships and including these three losses the aerodynamics blade design is conducted. Later, the numerical simulations show higher values of drag and lower values of lift force on airfoil compared to analytical calculation. In fact, percentage deviations are acceptable and to conclude, the numerical analysis was able to relatively accurately simulate force action of free stream velocity on the blade.
169

ANALYTICAL AND NUMERICAL MODELING OF FOUNDATIONS FOR TALL WIND TURBINE IN VARIOUS SOILS

Gaihre, Nirajan 01 May 2020 (has links)
Wind farm construction is increasing progressively, to cope-up with the current global energy scenario. The advantage of clean energy and sustainability helps wind turbine construction to flourish rapidly. Location of wind turbines is independent of foundation soil condition but depends on the wind speeds and socio-environment issues. Hence, a construction sites may not be favorable in terms of geotechnical demands. The taller wind towers facilitate the generation of high energy production, which will increase loads on the foundation, and eventually increase the dimension of the foundation. Hence, the choice of a suitable foundation system is necessary for geotechnical engineer to design tall wind towers. This study aims to analyze different foundation types e.g., raft/mat foundation, pile group foundation, and piled raft/mat foundation using analytical calculation verified with numerical models using PLAXIS 3D software. The foundation for steel wind turbine towers 100 m high was designed for different types of soils e.g., soft clayey soil, medium-stiff clayey soil, stiff clayey soil, and sandy soil. The design wind speed was taken from the ASCE 7-10 (2010) standard for Occupancy Category III and IV Buildings and Other Structures, as the Illinois region falls in that category. The parametric study was performed by varying the diameter of raft/mat, wind speed, number of piles, and soil types to evaluate the settlement in any type of foundation with load sharing proportion in piled raft/mat foundation. First, the raft/mat foundation design was carried out manually by changing the diameter of 15 m, 20 m, 25 m, 30 m, and 35 m, and changing load by considering different wind speed. Then the foundation was modeled using PLAXIS 3D software with a raft/mat diameter of 25 m, 30 m, and 35 m only, by considering the eccentricity and factor of safety criteria. With the increase in wind speed, the differential settlement on the raft/mat foundation was found to be increased. However, the increase in diameter of raft/mat caused the reduction in differential settlement. Soft clayey soil was found to be more sensitive than other soils used in the present study. For the same diameter of raft/mat, applied the same wind load, the differential settlement of foundation in soft clayey soil was found to be 6-10 times higher than the sandy soil.The position of piles was fixed based on the spacing criteria in the pile group foundation. The number of piles used in this study were 23, 32, and 46. Settlement was found to be varied with the number of piles in all soils used in this study. The lateral deflection for soft clayey soil decreased to half, when number of piles increased from 23 to 46. The differential settlement was found to be increased with the increase in wind speed in pile group foundation. Raft/mat foundation settlement was found to be 4 to 6 times higher than the settlement in pile group foundation in any soils, used in this study, for a given wind speed.The result of piled raft/mat foundation showed that the majority of the total load is shared by the piles (i.e., 60% to 94%) and remaining load is shared by the raft/mat (i.e., 6% to 40%), based on the stiffness of raft/mat and piles as well as pile-soil-pile interaction. The increase in wind speed in the wind turbines increased the differential settlement of piled raft/mat foundation in all soils. Similarly, the lateral deflection also increased with the increase in wind speed in pile raft/mat foundation in all soils. The PLAXIS 3D analysis revealed that the differential settlement in soft clayey soil was 1.5 to 2.0 times higher than the settlement in sandy soil.The validation of numerical modeling was carried out by the raft/mat foundation using Boussinesq’s theory and calculating settlement for single pile and group pile foundation. The current study showed that the soft clayey soil and medium-stiff clayey soil favor deep foundation, like pile group and piled raft/mat rather than shallow foundation, like raft/mat foundation. The results obtained from both analytical calculation and numerical modeling was found to be approximately matching. This study will help local construction company and geotechnical engineer to guide a proper foundation design of tall onshore wind turbine.
170

Renewables Based Power generation for Kenya Pipeline Company

Washika, Tony January 2011 (has links)
This study presents a Techno-economic assessment of a renewables based power generation project for PS 21, a Pumping Station for Kenya Pipeline Company located in Nairobi, Kenya. The load for the pumping station is 1135 kW Continuous. The assessment criteria used was levelized cost of energy. The hybrid renewable energy system software HOMER was used for assessment, and modeling was done using hourly TMY data for solar irradiance and wind.  According to the results, Hybrid Solar PV-Wind- Battery renewable energy systems can supply adequate power for pumping station purposes. Optimization modeling at 2010 prices gave a levelized cost of energy of $0.2 per kWh for the most optimal solution which consisted of 2 No. 1650 kW Vestas V 82 Wind Turbines and 4070 kW of PV modules. This cost of energy just matches the purchase price from the National grid which varies between $0.14 and $0.2 per kWh, and therefore, the project is economically feasible. Mainly due to concerns of global warming, the view in the Kenyan government and society towards renewable energy is very favorable and  the project is also politically and socially feasible.   Sensitivity analysis demonstrated that wind energy is more viable than solar PV energy in areas of high wind speeds, with about 7.5 m/s annual average wind speeds.   The results show that the levelised cost of energy may be significantly decreased in future due to the fact that the cost of PV modules is progressively reducing. Payments for CERs under CDM mechanism of the Kyoto Protocol would lower the levelised cost of energy further. The Project was found to be feasible. / <p>I was a distance student and did the presentation online via centra.</p>

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