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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.
421

Application of the New IEC International Design Standard for Offshore Wind Turbines to a Reference Site in the Massachusetts Offshore Wind Energy Area

Roach, Samuel C 21 March 2022 (has links)
This thesis summarizes the simulation and analysis performed for the MassCEC project described herein. The intent was to perform a “dry run” of the new IEC offshore wind turbine design standard, IEC 61400-3-1 and to illustrate the use of that standard in the Massachusetts Offshore Wind Energy Area. IEC 61400-3-1 is a design standard used to ensure wind turbine structural performance over the design life of the machine. Each installed wind turbine must be certified by a Certified Verification Agent using this standard before installation. The certification process typically uses a structural dynamics model to predict a turbine’s structural response in the presence of a range of operational conditions and meteorological oceanographic conditions, which are codified into Design Load Cases. The area in question is located approximately 24 km of south of Martha’s Vineyard with an assumed water depth of 40 m. The National Renewable Energy Laboratory’s FAST software (V8.12) was used to perform simulations of a large subset of the DLCs. Wind data files were generated using NREL’s TurbSim and IECWind. This thesis discusses the instructions of the standard, preparation for simulation of Design Load Cases, and analysis of results. Results from simulations show the application of the standard in detail as applied to a reference turbine. Limitations and ambiguities of the standard in the simulation of control failure cases are analyzed. The application of the standard to hurricane loading is also analyzed alongside an example case for a Category 5 hurricane. The standard is found to be fundamentally reasonable in application to a reference turbine in the Massachusetts Offshore Wind Energy Area.
422

Hydrodynamic behavior of packed-bed reactors on a floating platform : liquid distribution and drainage dynamics

Zhang, Jian 01 April 2021 (has links)
Pour combler l'écart entre l'augmentation de la demande énergétique et l'épuisement de la production d'hydrocarbures onshore, l'exploitation des hydrocarbures offshore est de plus en plus envisagée, en particulier les gisements de gaz / pétrole dans les eaux plus profondes. En attendant, un grand nombre d'unités de traitement déployées pour la production d'hydrocarbures doivent respecter les contraintes environnementales conçues pour la protection maritime. Les systèmes tels que les réacteurs et les épurateurs à lit fixe embarqués deviennent inévitablement l'une des options les plus prometteuses pour atteindre ces deux objectifs. De nombreux efforts dans la littérature pour dévoiler l'hydrodynamique de l'écoulement multiphasé dans les lits garnis révèlent que des défis persistent soit dans leur conception / mise à l'échelle, soit dans leurs opérations. De plus, exposer ces réacteurs à des conditions marines difficiles telles que la convolution de la dynamique des navires et de l'hydrodynamique à l'intérieur des réacteurs à lit fixe conduit à des situations encore plus compliquées pour maintenir des performances de fonctionnement acceptables dans les conditions flottantes. Un grand nombre de preuves issues de la littérature a jusqu'à présent mis en évidence l'échec des colonnes garnies avec des garnissages aléatoires, des garnissages structurés ou des mousses à alvéoles ouvertes, pour empêcher la maldistribution des liquides dans les lits fixes destinés à fonctionner à bord de navires ou de platesformes flottantes. Les efforts de recherche doivent donc se poursuivre dans le but de trouver des composants internes robustes et capables de résilience contre la maldistribution des liquides dans les réacteurs / unités de séparation gaz-liquide. Ce projet de doctorat s’est proposé des recherches visant dans un premier temps de tester des internes disponibles commercialement pouvant préserver des performances similaires à celles des unités terrestres classiques. Au meilleur de notre connaissance, la sensibilité et la susceptibilité des réacteurs monolithes à une mauvaise distribution soumis à des conditions offshore n'ont pas encore été étudiées. Plutôt que de se concentrer uniquement sur une étude des lits monolithiques, le chapitre 1 opte pour une campagne expérimentale plus large comprenant un garnissage aléatoire et un garnissage en mousse à cellules ouvertes pour des comparaisons systématiques de la distribution des liquides en conditions flottantes. La distribution liquide des colonnes embarquées garnies de divers garnissages et pour une large plage de débit gaz / liquide est systématiquement comparée à l'aide d'un capteur à treillis métallique (WMS) et d'un émulateur hexapode à six degrés de liberté. La vraisemblance de conditions météorologiques extracôtières rudes pourrait menacer la sureté de l'exploitation des lits fixes, en particulier dans des situations extrêmes telles que des cyclones, des épisodes d'icebergs, etc. Pour assurer la sécurité du personnel et des installations, l’opération des colonnes garnies à bord doit être immédiatement interrompue pour éviter des problèmes de sécurité critiques sous de telles circonstances. Par conséquent, la base de connaissances sur la dynamique de drainage des liquides dans les lits flottants est iv essentielle pour assurer une vidange rapide du liquide. Néanmoins, l'étude de la dynamique du drainage liquide des lits fixes en conditions flottantes est à tout le moins rare. Par conséquent, le chapitre 2 se propose de comparer expérimentalement le drainage du liquide dans des colonnes garnies dans les conditions marines à celui observé dans une colonne statique verticale à l’instar des applications terrestres. En dehors de cela, l'influence des mouvements du navire (par exemple, cavalement, embardée, pilonnement, roulis, tangage, et lacet) à différentes amplitudes et périodes d'oscillation sur la dynamique de drainage des liquides est étudiée pour approfondir nos connaissances. Parallèlement à l'étude expérimentale, un modèle numérique Euler-Euler transitoire et en trois dimensions est utilisé en complément pour tenter de prédire la dynamique du drainage des liquides dans les lits flottants. D'autres facteurs susceptibles d'affecter la dynamique de drainage sont analysés par la simulation numérique. Ainsi, le chapitre 3 met en évidence l'influence globale des propriétés des liquides, de la structure du lit et des types de mouvement associé à la sollicitation marine. Par ailleurs, la campagne expérimentale en fournissant des données mesurables a permis de valider le modèle dans les conditions de roulis et de tangage testées au laboratoire. / To fill the gap between increasing energy demand and depletion of onshore hydrocarbon production, offshore hydrocarbon exploitation is increasingly contemplated especially the gas/oil fields in the deeper water. Meantime, large amount of deployed processing units for hydrocarbon productions must comply with the environmental codes designated for maritime protection. Systems such as embarked packed-bed reactors and scrubbers inevitably become one of the most promising options to achieve both purposes. Numerous efforts in literature to unveil the hydrodynamics of multiphase flow in packed beds reveal that challenges persist either in their design/scale-up or during the operations. Moreover, exposing these reactors to harsh marine conditions such as the convolution of ship dynamics and hydrodynamics inside packed-bed reactors leads to even more complex situations to maintain the proper operation performance of packed-bed reactors under floating conditions. A lot of evidence from literature has pointed out the failure of random and structured packings and open-cell foams, to prevent liquid maldistribution in packed beds destined to operate on-board sailing ships and floating platforms. Research efforts must therefore continue in the quest for robust internals capable of resilience against liquid maldistribution in gas-liquid reactors/separation units. The proposed Ph.D. research aims at firstly following a sound path to adapt commercially existing internals being capable of preserving performance similar to landbased packed beds. To the best of literature exploring, the sensitivity and susceptibility of monolith reactors to maldistribution subjected to offshore conditions have yet to be investigated. Rather than focusing on a study of monolith beds alone, Chapter 1 opts for a broader experimental campaign including a random packing and an open-cell foam packing for the sake of systematic comparisons of the liquid distribution under floating conditions. Liquid distribution of embarked columns packed with various internals under wide gas/liquid flow range is systematically compared with the assistance of wire mesh sensor (WMS) and six-degree-of-freedom emulator hexapod. Severe offshore weather conditions threaten the operation safety of floating packed beds especially encountering extreme situations such as cyclone, iceberg episodes and so forth. To ensure the safety of staff and facilities, the onboard packed columns must be immediately shutdown to avoid critical safety concerns under such circumstances. Therefore, knowledgebase of liquid draining dynamics in floating packed beds is the essence to ensure timely discharge of liquid. Nevertheless, the study regarding liquid drainage dynamics of packed beds under floating conditions is scarce to say the least. Then, Chapter 2 compares liquid draining of packed columns embarking on floating platforms with static land-based one experimentally. Other than that, the influence of ship motions (e.g., roll, roll & pitch, heave etc.) with different oscillation amplitudes and periods on liquid draining dynamics is investigated to deepen the insights. vi In parallel with the experimental study, a 3D transient Euler-Euler CFD model is employed as a supplementary analysis to further deepen the understanding of liquid drainage dynamics in floating packed beds. More factors possibly affecting the draining dynamics are exploited by numerical simulation. Consequently, Chapter 3 highlights the comprehensive influence of liquid properties, bed structure and moving types instead of focusing on impact of movements alone. Meanwhile, with sufficient body of experimental campaign, the validity and accuracy of model are strongly endorsed.
423

Docagem ou afretamento de UMS: a escolha ótima para a extensão da vida útil das plataformas de petróleo de campos marítimos maduros sob o enfoque das opções reais

Silveira, Thiago Martins 28 May 2015 (has links)
Submitted by thiago martins silveira (t.silveira2003@ig.com.br) on 2015-12-11T19:37:29Z No. of bitstreams: 1 Dissertação THIAGO envio vitor 11.12.pdf: 1008243 bytes, checksum: 0a7a2e57fa290ee5228d81e283f0d348 (MD5) / Approved for entry into archive by Marcia Bacha (marcia.bacha@fgv.br) on 2015-12-21T18:14:36Z (GMT) No. of bitstreams: 1 Dissertação THIAGO envio vitor 11.12.pdf: 1008243 bytes, checksum: 0a7a2e57fa290ee5228d81e283f0d348 (MD5) / Approved for entry into archive by Marcia Bacha (marcia.bacha@fgv.br) on 2015-12-21T18:14:53Z (GMT) No. of bitstreams: 1 Dissertação THIAGO envio vitor 11.12.pdf: 1008243 bytes, checksum: 0a7a2e57fa290ee5228d81e283f0d348 (MD5) / Made available in DSpace on 2015-12-21T18:15:06Z (GMT). No. of bitstreams: 1 Dissertação THIAGO envio vitor 11.12.pdf: 1008243 bytes, checksum: 0a7a2e57fa290ee5228d81e283f0d348 (MD5) Previous issue date: 205-05-28 / O objetivo deste trabalho é propor a utilização do arcabouço teórico das opções reais e a posterior aplicação do modelo binomial na avaliação de projetos relacionados à exploração e produção de petróleo, tendo em vista a flexibilidade gerencial, os riscos e as incertezas técnicas e de mercado que norteiam o setor petrolífero upstream. Ademais, a aplicação do modelo proposto capta o papel crucial da volatilidade do preço do petróleo na avaliação da decisão de investimento e revela a existência dos custos irrecuperáveis extremos decorrentes do ativo real, neste caso, a unidade marítima de petróleo. Assim, com o intuito de prolongar o ciclo de produção de unidade marítima de petróleo com características preestabelecidas, propõe-se a avaliação econômica de duas alternativas tecnológicas para a extensão de vida útil da plataforma marítima objeto de estudo, sendo estas alternativas tratadas como opções de expansão. As alternativas propostas são duas: o afretamento da UMS (Unidade de Manutenção e Segurança) acoplada à plataforma e a docagem da plataforma a partir da desmobilização, isto é, o descomissionamento, e envio da plataforma ao estaleiro. Na aplicação da primeira opção, a UMS se configura em uma embarcação equipada com toda a estrutura necessária para a realização de serviço de manutenção e revitalização, sem que ocorra interrupção da produção de petróleo. Por outro lado, a opção de descomissionamento é desprovida de receita até o retorno da plataforma do estaleiro. No que tange à metodologia do presente trabalho, o modelo binomial com probabilidades de risco neutro é aplicado considerando a receita proveniente da produção de petróleo de uma plataforma marítima com sistema de produção flutuante com 14 poços, sendo 10 produtores e 4 injetores e sustentada por 8 linhas de ancoragem. Também é definida a volatilidade do projeto como sendo a volatilidade do preço do petróleo. Por fim, as opções de expansão podem ser exercidas a qualquer momento antes da data de expiração das opções, data esta coincidente para ambas as opções e referente ao término de contrato de afretamento da UMS, que corresponde ao período de cinco anos. Neste período de cinco anos, as duas alternativas são exercidas a partir do primeiro ano, com receitas e custos distintos em virtude das especificidades decorrentes das alternativas tecnológicas propostas. A partir da aplicação do modelo binomial com probabilidades de risco neutro sob o enfoque das opções reais, as duas alternativas tecnológicas são tratadas como opções americanas na avaliação econômica da revitalização e manutenção da plataforma marítima. Também realiza-se a análise tradicional do VPL para as duas alternativas. As duas análises apontam para a escolha da UMS como alternativa ótima de expansão da vida útil da plataforma. Ademais, a análise sob o enfoque das opções reais capta um valor adicional em ambas as alternativas tecnológicas, fruto das características inerentes à indústria petrolífera. Quanto à estrutura do trabalho em questão se divide em cinco capítulos: introdução, referencial teórico, metodologia, apresentação dos resultados e as considerações finais. / This paper purposes the use of theoretical framework of real options and posterior employment of binomial model in project evaluation concerning the exploration and production of oil, in view of manager flexibility, risks, techniques and market uncertainties that guide the upstream oil sector. Furthermore, the apliccation of the proposed model captures the crucial role of the volatility of oil price in the evaluation of investment decision and brings out the presence of high sunk costs resulting from real asset, in this case, offshore oil platform. Thus, in order to prolong the maritime unit of production cycle oil with predetermined characteristics, it is proposed economic evaluation of two alternative technologies for the lifetime extension of offshore studied, and these alternatives treated as options to expansion. The alternatives proposals are: the chartering of MSU (Maintenance and Safety Unit) coupled to platform and the send of offshore platform in the dock after its decommissioning and its send to shipyard. In the implementation of the first option, MSU configures a equipped vessel with all the necessary structure to perform maintenance and revitalization without interruption of oil production. On the other hand, the option of decommissioning is devoid of revenue until the regress of the offshore platform from the shipyard. Concerning the methodology of this study, the binomial model with risk-neutral probabilities is applied regarding the revenue arising from the oil production of offshore platform with floating production system that accept 14 oil wells, including 10 production well and 4 injection well and supported by 8 anchor line. The volatility of project is also defined as the volatility of oil price. Lastly, the options to expand may be exercised anytime before its expiration date that coincides for both options and concerning the end of contract of MSU that correspond to the period of five years. In this period, both alternatives are exercised from the first year, with differents revenue and costs by virtue of specificities resulting from the technological alternatives proposals. From the application of binomial model with risk-neutral probabilities from the standpoint of real options, these two alternatives are treated as american options in the evaluation of revitalization and maintenance of offshore platform. Also takes place the traditional analysis of NPV for both alternatives. These two analysis point at choice of MSU as the best alternative for prolonging the useful life of offshore platform. Moreover, the analysis from the standpoint of real options capture additional value in both technological alternatives, the result of characteristics inherent in the oil industry. As for the structure of the work in question is divided into five chapters: introduction, theoretical framework, methodology, presentation of results and final considerations.
424

Gerenciamento de portfólio de projetos: uma proposta de modelo de gestão para projetos de engenharia offshore pautada na integração contratada/cliente

Alves, Plínio de Melo January 2016 (has links)
Submitted by Marcia Silva (marcia@latec.uff.br) on 2017-04-04T19:41:31Z No. of bitstreams: 1 Dissert Plinio de Melo Alves.pdf: 5439128 bytes, checksum: ed523a38de8977df17e89facf367e578 (MD5) / Approved for entry into archive by Biblioteca da Escola de Engenharia (bee@ndc.uff.br) on 2017-05-15T12:34:10Z (GMT) No. of bitstreams: 1 Dissert Plinio de Melo Alves.pdf: 5439128 bytes, checksum: ed523a38de8977df17e89facf367e578 (MD5) / Made available in DSpace on 2017-05-15T12:34:10Z (GMT). No. of bitstreams: 1 Dissert Plinio de Melo Alves.pdf: 5439128 bytes, checksum: ed523a38de8977df17e89facf367e578 (MD5) Previous issue date: 2016 / O Gerenciamento de Portfólio tem sido aplicado há mais de 60 anos em alguns setores focados em investimentos financeiros. A utilização da metodologia expandiu anos depois para otimização do uso de recursos na implementação e Gestão do Produto e de Projetos. Dentro deste conceito, este trabalho de pesquisa tem por objetivo contribuir com a literatura atual e incluir o Gerenciamento de Portfólio de Projetos (GPP) na agenda empresarial, propondo um método de gestão para integração e gerenciamento de um portfólio de projetos de engenharia offshore na indústria de óleo e gás, numa multinacional brasileira contratada por uma multinacional norueguesa (o cliente). A metodologia utilizada é a pesquisa-ação. Adicionalmente, a pesquisa visa caracterizar as particularidades do GPP no contexto offshore como fatores que influenciam a forma de gerenciar o portfólio. Para tanto, foi necessário identificar na bibliografia de GPP os possíveis componentes a serem utilizados no contexto offshore. Para atingir o objetivo da pesquisa, foi implementado um modelo de gestão para avaliar suas potencialidades e limitações de aplicação, representando contribuições para o ambiente acadêmico, pela proposição de mais uma opção de modelo de GPP e empresarial, pela demonstração da implementação do método em um caso prático / Portfolio Management has been applied for about 60 years in some sectors focused on financial investments. The methodology application has increased some years later for resource usage optimizing on Implementing and Management for Products and Projects. Within this concept, the research focuses on contribution to the current bibliography and add in Project Portfolio Management (PPM) in entrepreneurial agenda, proposing a method for an Offshore Engineering Project Portfolio integration and management at oil and gas industry in a Brazilian multinational company, contracted by a Norwegian multinational company (the customer). The methodology used was action-research. In addition, the research aims to describe the particularities of Engineering PPM into offshore context, like factors that affect the way to manage the portfolio. For this purpose it was necessary identify in PPM theoretical framework the possible components to be used in offshore context. To achieve the research target, it was implemented the management system to evaluate their potentialities and application limitations, which contributes to academic environment, by presenting another option of PPM template and corporate, by showing a practice implementation
425

Multi-Criterion Macro-Siting Analysis of Offshore Wind Farm Potential in Sweden. / Multikriterie- och makroplaceringsanalys av havsbaserad vindkraftspotential i Sverige.

Sundström, Oskar January 2021 (has links)
Sweden has a great potential for offshore wind energy production. As technology develops and policies change, construction of offshore wind farms in the country is likely to increase. The presented methodology is to apply MCDM and AHP methods in a GIS to produce an evaluation map of potential sites for offshore wind energy production.  The aim of this thesis was to determine what data is relevant and needed to translate Swedish and international standards and regulations regarding offshore wind farm siting into one or more layers of GIS data within the exclusive economic zone of Sweden. Furthermore the locations of the existing Areas of National Interests for offshore wind energy production have been evaluated using the evaluation map. The evaluation map has been obtained using several exclusionary criteria and buffer distances as well as four evaluation criteria. In addition, the results of this study have been used to calculate a potential net annual energy production for offshore wind energy in Sweden. The analysis considers some of the social, technical and environmental constraints present in offshore wind farm siting. The exclusion, buffer and evaluation criteria were determined in the initial literature review of previous studies on the topic. Datasets were collected from several different open online resources and Swedish government agencies, the analysis was performed using the QGIS software. To assess the results, the resulting evaluation map has been classified into four different categories: poor, average, good and excellent. The analysis shows that it is possible to translate Swedish and international standards into one layer of GIS data. Furthermore the results of this study show that 52% of the defined Areas of National Interest for offshore wind energy production should not be considered for wind farm siting according to the exclusion constraints, additionally only 19% of the Areas of National Interest for offshore wind energy production are classified as good or excellent. In contrast, 20.3% of the entire study area is deemed to be suitable for offshore wind farm siting, out of which 62.7% is classified as good or excellent. The potential net annual energy production has been estimated to be 56.1 TWh annually within the Areas of National Interest for offshore wind energy production and 915.3 TWh annually within the entire study area. / Sverige har en stor potential för produktion av havsbaserad vindkraft. När teknologin utvecklas och de politiska förutsättningar förändras, kommer konstruktionen av havsbaserad vindkraft i landet troligtvis öka. Den presenterade metodologin går ut på att använda MCDM och AHP metoder i ett GIS för att producera en utvärderingskarta för potentiella platser att producera havsbaserad vindenergi.  Målet med den här studien har varit att ta reda på vilken data som krävs och är relevant för att överföra svensk samt internationell standard och regler kring placeringen av havsbaserad vindkraft till ett eller flera lager av GIS data inom Sveriges exklusiva ekonomiska zon. Vidare har de existerande riksintressena för havsbaserad vindkraft utvärderats med hjälp av utvärderingskartan. Denna karta har blivit framtagen med hjälp av flertalet buffertzoner samt exkluderings- och fyra stycken utvärderingskriterier. Slutligen har studiens resultat används för att beräkna en potentiell årlig energiproduktion för offshore vindkraft i Sverige. Studien beaktar några av de sociala, tekniska och miljömässiga begränsningar som finns för havsbaserad vindenergi. Buffertzonerna samt exkluderings- och utvärderingskriterierna har bestämts med hjälp av en inledande litteraturstudie av tidigare forskning på ämnet. Den datan som använts i analysen har inhämtats från flera olika öppna onlineresurser samt från svenska myndigheter. Den efterföljande analysen har genomförts med hjälp av programmet QGIS. För att möjliggöra en kvantifiering av resultaten har utvärderings kartan omklassificerats till fyra olika kategorier: “poor”, “average”, “good” samt “excellent”. Studien visar att det är möjligt att överföra svensk samt internationell standard och regler till ett lager av GIS data. Resultatet visar att att enbart 48% av arean inom de definierade riksintressena för havsbaserad vindkraft bör beaktas vid allokering av havsbaserad vindenergi, enligt de begränsningar som definierats i denna studie. Vidare påvisar resultatet att enbart 19% av arean inom de utpekade riksintressena för vindkraft kan klassificeras som “good” eller “excellent”. Samtidigt påvisar studien att 20.3% av studieområdet bedöms som lämpligt för allokering av havsbaserad vindkraft, av dessa lämpliga områden klassificeras 62.7% som “good” och “excellent”. Den potentiella årliga energiproduktionen uppskattas till 56.1 TWh inom riksintressena för havsbaserad vindkraft samt till 915.3 TWh inom hela studieområdet.
426

Analysis of Grain Size Distribution and Hydraulic Conductivity for a Variety of Sediment Types with Application to Wadi Sediments

Rosas Aguilar, Jorge 05 1900 (has links)
Grain size distribution, porosity, and hydraulic conductivity from over 400 unlithified sediment samples were analized. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations commonly used to estimate hydraulic conductivity from grain size analyses. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values. Modifications of the empirical equations, including changes to special coefficients and statistical off sets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, off shore marine, and wadi sediments. Expected hydraulic conductivity estimation errors were reduced. Correction factors were proposed for wadi sediments, taking mud percentage and the standard deviation (in phi units) into account.
427

Numerical modelling and control of an oscillating water column wave energy converter

Freeman, Kate January 2015 (has links)
An oscillating water column (OWC) wave energy converter (WEC) is a device designed to extract energy from waves at sea by using the water to move trapped air and thus drive an air turbine. Because the incident waves and the force caused by the power take-off (PTO) interact, control of the power take off (PTO) system can increase the total energy converted. A numerical model was developed to study the interaction of an OWC with the water and other structures around it. ANSYS AQWA is used here to find the effects on the water surface in and around the central column of a five-column, breakwater-mounted OWC. For open OWC structures, coupled modes were seen which lead to sensitivity to incident wave period and direction. The frequency-domain displacements of the internal water surface of the central column were turned into a force-displacement, time-domain model in MATLAB Simulink using a state space approximation. The model of the hydrodynamics was then combined with the thermodynamic and turbine equations for a Wells turbine. A baseline situation was tested for fixed turbine speed operation using a wave climate for a region off the north coast of Devon. A linear feedforward controller and a controller based on maximising turbine efficiency were tested for the system. The linear controller was optimised to find the combination of turbine speed offset and proportional constant that gave maximum energy in the most energy abundant sea state. This increased the converted energy by 31% in comparison to the fixed speed case. For the turbine efficiency control method, the increase was 36%. Energy conversion increases are therefore clearly possible using simple controllers. If increased converted energy is the only criterion for controller choice, then the turbine efficiency control is the best method, however the control action involves using very slow turbine speeds which may not be physically desirable.
428

Performance of drag embedment anchors dragged through remolded clay and loaded at various horizontal orientations

Lynk, John Michael 24 September 2010 (has links)
Drag embedment anchors (DEAs, or anchors) are used as foundations to secure mobile offshore drilling units (MODUs) in soft clay soils on the sea floor. In 2004 and 2005, Hurricanes Ivan, Katrina, and Rita caused the mooring failures of 17 mobile offshore drilling units moored with anchors. Since then, a great deal of research has been conducted regarding anchor performance and reliability. This report provides an overview of anchor research and industry practice to date, and discusses the results of two research experiments to assess anchor performance. One experiment investigated the effect that embedding anchors in the same soil path several times had on bearing force. The second experiment investigated what effect changing the direction of the horizontal load vector relative to the anchor shank had on embedded anchor bearing force. The results of these experiments suggest that remolding clay may have an effect on anchor bearing force capacity, and that repeatable results are obtainable when testing the effect of changing the direction of applied horizontal load. / text
429

Design Considerations for Monopile Founded Offshore Wind Turbines Subject to Breaking Waves

Owens, Garrett Reese 1987- 14 March 2013 (has links)
The majority of offshore wind farms utilize monopile substructures. As these wind farms are typically located in water depths less than 30 meters, the effect of breaking waves on these structures is of great concern to design engineers. This research investigation examines many of the practical considerations and alternative ways of estimating breaking wave forces. A survey of existing European wind farms is used to establish a realistic range of basic design parameters. Based upon this information a parametric study was pursued and a series of realistic design scenarios were evaluated. Comparisons include the sensitivity to the wave force model as well as to analytical and numerical wave theories used to evaluate the wave kinematics. In addition, the effect of different kinematics stretching techniques for linear waves is addressed. Establishing whether the bathymetry will induce spilling or plunging wave breaking is critical. Spilling wave breaking can be addressed using existing wave and wave force theories; however for plunging wave breaking an additional impact force must be introduced. Dimensionless design curves are used to display pertinent trends across the full range of design cases considered. This research study provides insight into the evaluation of the maximum breaking wave forces and overturning moment for both spilling and plunging breaking waves as a function of bottom slope.
430

Modelling Waves and Currents in Northeastern Lake Ontario to Assess the Impacts of a Proposed Offshore Wind Farm

McCombs, Matthew 02 October 2013 (has links)
A spectral wave model (SWAN) coupled with a depth averaged hydrodynamic model (Delft3D) was used to understand the wave and flow dynamics of the Kingston Basin of Lake Ontario during large winter storm events. This model was then used to assess the impact of an offshore wind farm in the Kingston Basin. Results over different model domains with various forcing methods were compared to achieve the highest correlation with wave, current and water level observations from several locations. Storm events were modelled over the complex bathymetry of the basin and results were verified using wave and current profiler data collected during the winters of 2009-10 and 2011-12. Waves were composed of both locally generated wind sea and swell from the main basin of Lake Ontario, while flows throughout the Kingston Basin showed a complex circulation pattern. This circulation is composed of several wind-driven gyres, which are magnified during storm events. The impact of waves on the circulation patterns within the basin is highest in shallow areas where wave breaking drives circulation. To simulate a wind farm, a transmission coefficient was used in the wave model to represent the effects on waves, and an energy loss term was added to the hydrodynamic momentum equations to represent the added drag of the piles on the circulation. The results indicate that the coastal areas in eastern Lake Ontario will be minimally affected. The headlands of Big Sandy Bay, Wolfe Island, could see the largest coastal effects with changes in significant wave height predicted to be < 2%. The majority of impacts to circulation occur in the near-field, with changes in current magnitude of < 0.08 m s-1 (up to 50%). Areas near Wolfe Island exhibit changes of ~ 0.05 m s-1 (30 %), although overall circulation patterns throughout the basin are not affected. The majority of changes to surface waves and wind-driven currents are due to wind farm position with respect to wind direction and the re-direction of flows and waves as they pass through the wind farm. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-30 09:30:01.042

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