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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.
21

Performance Analysis and Tank Test Validation of a Hybrid Wave-Current Energy Converter with a Single Power Takeoff

Jiang, Boxi 01 July 2020 (has links)
Marine and hydrokinetic (MHK) energy, including ocean waves, tidal current, ocean current and river current, has been recognized as a promising power source due to its full-day availability and high energy potential. At this stage, ocean current energy, tidal energy and ocean wave energy are currently the most competitive sourves among all the categories of MHK. The state of art MHK energy harvesting technology mainly focus on harvesting either ocean wave energy or current energy, but not both. However, a significant amount of ocean waves and tidal/ ocean current coexist in many sites and traditional devices that harvest from a single form of MHK energy, cannot make full use of the coexisting ocean energy. Furthermore, MHK energy harvesting devices need to advance to be cost-effective and competitive with other energy sources. This is difficult to achieve. Ocean wave excitation is irregular, which means that ocean wave height and wave periods are unpredictable and excitation forces on energy harvesting devices can have large variance in amplitude and frequency. Such problems/ restrictions can be possibly addressed by the concept of a hybrid energy converter. In this sense, a hybrid wave-current ocean energy conveter (HWCEC) that simutaneously harvests energy from current and wave with one single power takeoff (PTO) is designed.The wave energy is extracted through relative heaving motion between a floating buoy and a submerged second body, while the current energy is extracted using a marine current turbine (MCT). Energy from both sources are integrated by a hybrid PTO whose concept is based on a mechanical motion rectifier (MMR). In this study, different working modes are investigated together with switching criteria.Simulations were conducted with hydrodynamic coefficients obtained from computational fluid dynamics analysis and boundary element method. Tank tests were conducted for a HWCEC under co-existing wave and current inputs. For comparison, separate baseline tests of a turbine and a two-body point absorber, each acting in isolation, are conducted. Experimental results validate the dynamic modeling and show that a HWCEC can increase the output power with a range between 29-87 percent over either current turbine and wave energy converter acting individually, and it can reduce by up to 70 percent the peak-to-average power ratio compared with the wave energy converter on the tested conditions.Such results demonstrate the potential of the HWCEC as an efficient and cost-effective design. / Master of Science / Ocean energy has been recognized as a promising power source due to its full-day availability and high energy potential. At this stage, ocean current energy, tidal energy and ocean wave energy are currently the most competitive sources among all the categories of ocean energy. The state of art ocean energy harvesting technology mainly focus on harvesting either ocean wave energy or current energy, but not both. However, a significant amount of ocean waves and tidal/ ocean current coexist in many sites and traditional devices that harvest from a single form of ocean energy, cannot make full use of the coexisting energy resource. Furthermore, MHK energy harvesting devices need to advance to be cost-effective and competitive with other energy sources. This is difficult to achieve. Ocean wave height and wave periods are unpredictable and excitation forces on energy harvesting devices can have large variance in amplitude and frequency. Such restrictions can be possibly addressed by the concept of a hybrid energy converter. In this sense, a hybrid wave-current ocean energy converter (HWCEC) that simultaneously harvests energy from current and wave with one single power takeoff (PTO), which consists of ball screw, gearbox, and generator, is designed.The wave energy is extracted through relative heaving motion between a floating buoy and a submerged second body, while the current energy is extracted using a marine current turbine (MCT). Energy from both sources are integrated by a hybrid PTO whose concept is based on a mechanical motion rectifier (MMR). In this study, different working modes are investigated together with switching criteria.Simulations were conducted with hydrodynamic coefficients obtained from computational fluid dynamics analysis and boundary element method. Tank tests were conducted for a HWCEC under co-existing wave and current inputs. For comparison, separate baseline tests of a turbine and a two-body, wave-energy-harvesting structure, each acting in isolation, are conducted. Experimental results validate the dynamic modeling and show that a HWCEC can increase the output power with a range between 29-87 percent over either current turbine and wave energy converter acting individually, and it can reduce by up to 70 percent the peak-to-average power ratio compared with the wave energy converter on the tested conditions.Such results demonstrate the potential of the HWCEC as an efficient and cost-effective design.
22

Modelling and verification of the dynamics of an ocean current energy converter

Graaff, Simon 12 1900 (has links)
Thesis (MScEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: South Africa has a signi cant potential resource for electrical power generation in the Agulhas Current on the southeast coast. The Ocean Current Energy Convertor studied in this project was designed to generate power from this current. The feasibility of this device was investigated by analysing the dynamic stability and controllability of the convertor, when acted upon by hydrodynamic forces while harvesting energy from the current. A simulation model was developed to predict the dynamic behaviour using the Simulink software suite. A scale model of the prototype was built and tested in the Towing Tank at Stellenbosch University, and the experimental results were compared against the simulation results. A control algorithm was designed, using the mathematical model, to control the roll angle and deployment depth. The control algorithm was tested in simulation. The results indicated that the simulation model accurately predicted the behaviour of the prototype in testing, and results showed that the device is both stable and controllable. It was concluded that this OCEC design concept warrants further investigation. The recommendations are that the experimental model be improved to ensure reliable experimental results, that further complexity be added to the simulation model, and that the control algorithm be tested on the improved prototype in the towing tank. / AFRIKAANSE OPSOMMING: Die Agulhas-seestroom aan die suidooskus van Suid-Afrika bied 'n aansienlike potensiële hulpbron vir elektriese kragopwekking. Die seestroomenergieomsetter (SEO) wat in hierdie projek bestudeer is was ontwikkel om krag uit hierdie seestroom te genereer. Die doenlikheid van hierdie toestel is ondersoek deur die dinamiese stabiliteit en beheerbaarheid van die omsetter onder die invloed van hidrodinamiese kragte te analiseer terwyl dit energie van die stroom inwin. 'n Simulasiemodel is met behulp van Simulink-sagteware ontwikkel om die dinamiese gedrag te voorspel. 'n Skaalmodel van die prototipe was gebou en in die sleeptenk by Universiteit Stellenbosch getoets en die eksperimentele resultate met die simulasie se resultate vergelyk. 'n Beheer-algoritme is daarna ontwerp, deur middel van die wiskundige model, om die rolhoek en diepte van ontplooiing te beheer.Hierdie algoritme is tydens simulasie getoets. Die resultate het aangedui dat die simulasiemodel akkuraat die gedrag van die prototipe tydens toetse voorspel het, en die resultate het gewys dat die toestel beide stabiel en beheerbaar is. Die gevolgtrekking is gemaak dat die SEO se ontwerpkonsep verdere studie regverdig. Die aanbevelings is dat die eksperimentele model verbeter word om betroubare eksperimentele resultate te verseker, dat verdere kompleksiteit by die simulasiemodel gevoeg word, en dat die beheer-algoritme op die verbeterde model in die sleeptenk getoets word.
23

A hydrokinetic resource assessment of the Florida Current

Unknown Date (has links)
The Straits of Florida has been noted as a potential location for extraction of the kydrokinetic energy of the Florida Current, in view of the strength of the current and its proximity to the shore. ... This research explores the Florida Current as a potential renewable energy source. By utilizing historical data, in situ observations of the Florida Current, and computer model data, the hydrokinetic resource of the Florida Current is characterized both spatially and temporally. Subsequently, based on the geographic variability of the hydrokinetic power and other factors that impact the economy of a hydrokinetic turbine array installation, the ideal locations for turbine array installation within the Florida Current are identified.... Additionally, an interactive tool has been developed in which array parameters are input - including installation location, turbine diameter, turbine cut-in speed, etc. - and array extraction estimates, ideal installation position, and water depth at the installation points are output. As ocean model data is prominently used in this research, a discussion about the limitations of the ocean model data and a method for overcoming these limitations are described. Globally, the distribution of hydrokinetic power intensity is evaluated to identify other currents that have a high hydrokinetic resource. / by Alana E. Smentek-Duerr. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.
24

Numerical simulation of the flow through an aqxial tidal-current turbine employing an elastic-free-surface approach. / Simulação numérica do escoamento através de uma turbina axial de corrente de maré utilizando uma metodologia de parede elástica para a modelagem da superfície livre.

Almeida, Fernando Mattavo de 15 June 2018 (has links)
Together with the world economic growth is the increasing of energy generation demand. However, the upgrade of world power production capability could affect the environment negatively. Even the clean and renewable sources, such as hydroelectricity and wind powers have socio-economic and environmental disadvantages. For example, the required flooded area for a hydro power plant construction could devastate entire forests, and the installation of a wind farm power plant could affect migratory rotes of birds and generate high levels of noise. Hence, for the balancing of advantages and disadvantages of each power generation source, it is necessary to diversify, which requires investments in new power sources. In this context, the energy generation in the ocean is highlighted. The first point concerning the ocean energy is that there is no need of population removal from the installation area, such as the onshore based methods and the second point is that most of the population is concentrated in coastal areas. Therefore the production occurs near to the demand, decreasing the costs with energy distribution. The two main methodologies for harassing energy from oceans are based on gravity waves and in tides. And since the tidal cycles are governed mainly by the gravitational interaction between oceans, Moon and Sun, they are easily predictable, which increases the reliability of such systems. These works explores methodologies to analyse the power generation from a single axial tidal current turbine through a Steady State RANS methodology. Are discussed the effects of flow directionality, inlet velocity profile and turbulence levels and the results are compared with an experimental scheme. It is proposed an alternative methodology for free surface modelling in the CFD analysis. The usual methodology, VOF, it is based on a homogeneous, biphasic approach which requires an additional mesh refinement and is computationally expensive. This new methodology introduces an elastic wall approach in the free surface region in which the stiffness is calculated to provide the same restoring effect as gravity. In general, the results for open domain matched with the experimental results, validating the numerical model and the confined domain has shown a higher power and thrust coefficients if compared with the open domain, which is in accordance with the actuator disk theory approach. The elastic free surface presented convergence problems related to high Froude numbers and therefore to high deformations. However, a simulation with 10% of the original inlet velocity was performed, achieving reasonable results for both power and thrust coefficients evaluation. / O crescimento econômico mundial e o aumento na demanda pela geração de energia andam juntos. No entanto, uma maior capacidade de produção de energia poderia afetar negativamente o meio ambiente. Mesmo as fontes limpas e renováveis, como a hidrelétrica e a eólica acarretam em impactos socioeconômicos e ambientais. Por exemplo, a construção de uma usina hidrelétrica demanda uma imensa área alagada que pode devastar florestas inteiras e a instalação de uma usina eólica pode afetar a migração de certas espécies de pássaros e produzir altos níveis de barulho. Portanto, para equilibrar as vantagens e desvantagens devidas a cada meio de produção de energia, é necessária a diversificação, que demanda de investimentos em novas fontes. Neste contexto, a geração de energia nos oceanos é destacada. O primeiro ponto a respeito desta fonte é de que não há a necessidade de remoção da população na área de instalação, tal como os métodos de geração dentro do continente. O segundo principal ponto é a respeito da distribuição de energia. A maior parte da população mundial vive em regiões costeiras, diminuindo, portanto, a distância entre a produção e demanda, reduzindo assim, seus custos. As duas principais metodologias para se explorar a energia proveniente dos oceanos são: Energia de Ondas e Energia de Marés. E considerando que os ciclos de mare são governados principalmente pela interação gravitacional entre os oceanos, lua e sol, eles são facilmente previsíveis, o que aumenta a confiabilidade dos sistemas de geração de energia baseados em marés. Este trabalho explora as metodologias para analisar a geração de energia a partir de uma única turbina axial de corrente de maré através de uma metodologia baseada nas equações de Navier-Stokes com a média de Reynolds, analisadas em regime permanente. São discutidos efeitos da direção do escoamento, perfil de velocidades na entrada e nos níveis de turbulência. Os resultados são comparados com experimentos. É proposta uma metodologia alternativa para a modelagem da superfície livre com CFD uma vez que a metodologia atual é baseada em um escoamento bifásico que demanda de um refinamento adicional da malha e é computacionalmente caro. A nova metodologia usa uma parede elástica na região da superfície livre com a rigidez ajustada para se obter o mesmo efeito de restauração que a gravidade. De maneira geral, os resultados para o domínio aberto se aproximaram dos resultados experimentais, validando o modelo numérico e além disso, o modelo considerando confinamento da turbine mostrou maiores valores para os coeficientes de potência e empuxo, estando portanto, de acordo com a teoria do disco atuador. O modelo com a superfície livre elástica apresentou problemas de convergência, relacionados com números de Froude elevados, uma vez que isto se relaciona com maiores deformações na região da superfície livre. Uma simulação com 10% da velocidade original foi realizada, obtendo-se resultados coerentes para ambos coeficientes de potência e empuxo.
25

Geração de energia elétrica por ondas marinhas gerenciadas por microcontroladores. / Electricity generation by marine waves managed by microcontrollers.

Kawano, Mario 12 March 2015 (has links)
O objetivo desse trabalho é a construção de um sistema de geração de energia elétrica, para uso em locais remotos, tendo como fonte primária a energia proveniente de ondas marinhas. Numa primeira etapa foram realizados estudos e análises dos principais parâmetros significativos para a geração da energia elétrica e os dados de consumo de eletroeletrônicos. Este sistema serviu para coletar e armazenar dados que orientam o desenvolvimento de bombas e turbinas para a geração de energia elétrica. Foram também usados para avaliar o seu rendimento em diversas aplicações que necessitavam de energia elétrica. O uso da energia elétrica gerada também foi estudado para melhorar o seu rendimento diante dos vários equipamentos que foram utilizados desde notebooks até geladeiras convencionais. Foram empregados um microcontrolador, da família \"arduino\", vários sensores colocados em pontos estratégicos no local e os dados armazenados em memória durante o período do desenvolvimento. Sensores de pressão, vazão, amplitude das ondas, sentido do vento, temperatura e vários medidores (de tensão e corrente em AC e DC) foram usados para obter valores numéricos para análises de rendimentos de conversão em energia elétrica, vazão e outros parâmetros importantes para uma posterior melhoria no projeto inicial. Os dados foram armazenados em memórias do tipo cartão SD de 16 G bytes. Foi confeccionada uma bomba de água movida pelas ondas marinhas. Sua implantação ocorreu na Ilha do Arvoredo, em Guarujá, SP, onde a energia elétrica era gerada através do uso de motores a diesel. A água é bombeada a uma altura de 30 metros e armazenada em um tanque com capacidade de 20.000 litros. A água armazenada vai diretamente para uma turbina geradora de eletricidade por um sistema controlador de pressão e, pode gerar uma potência elétrica de até 200 W. O excedente de água poderá ser também usado para os viveiros de animais marinhos. A maior parte dos materiais que foram utilizados na fabricação dos equipamentos foi de materiais recicláveis reduzindo o custo do projeto. Esse projeto estará disponível para comunidades carentes que necessitam de energia elétrica em locais remotos, normalmente ilhas, mas podem ser adaptadas em terra desde que possuam quedas de água. O projeto de geração de energia usando ondas marinhas é inovador e com fins sociais para pessoas de baixa renda como os pescadores. Normalmente o pescado conseguido nas proximidades de ilhas isoladas são salgados para serem conservados devido à falta de refrigeração. / The aim of this work is the constructions of an electrical power generation system for use in remote locations, having primary source of energy from sea waves. At a first step were carried out studies and analyzes of the main important parameters for the generation of electricity and electronics power consumption data. This system was used to collect and store data that guide the development of pumps and turbines for generating electricity. Various electronics applications were also used to evaluate the total electricity was required and were studied to improve their performance like notebooks or conventional refrigerators. A microcontroller was employed and several sensors placed at strategic points in the power generation energy system and the data stored in the memory card during the development period. Pressure sensors, flow, amplitude of waves, wind direction, temperature and various electrical sensors (voltage and current in AC and DC) that were used to obtain numerical values for analysis of conversion into electrical energy, water flow and other important parameters for further improvement the initial project. The data were stored on SD memory card of 16 G bytes. A water pump driven by ocean sea waves was made. This work has taken place in Ilha do Arvoredo, in Guarujá, SP, where the electricity was generated using diesel engines. The water is pumped until 30 meters high and stored in a tank with 20.000 liters. This stored water goes directly to the turbine by a pressure system control and generate an electrical power output up to 200 W. When not require, the exceeding water can also be used for marine animals nurseries. Most materials that were used in manufacturing of the equipment is recyclable materials reducing the cost of the project. The final project will be available to poor communities that need electricity in remote locations. Usually the fish achieved near isolated islands are salted to be maintained for lack of refrigeration.
26

Energias oceânicas: arcabouço legal e entraves a serem superados para o desenvolvimento no Brasil / Oceanic energies: legal framework and obstacles to be overcome for development in Brazil

Oliveira, Rafael Mendonça 24 June 2016 (has links)
Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-01T19:01:21Z No. of bitstreams: 1 RafaelMendoncaOliveira.pdf: 2075889 bytes, checksum: 9a87800d10facd20512342f1e6275efe (MD5) / Made available in DSpace on 2017-06-01T19:01:21Z (GMT). No. of bitstreams: 1 RafaelMendoncaOliveira.pdf: 2075889 bytes, checksum: 9a87800d10facd20512342f1e6275efe (MD5) Previous issue date: 2016-06-24 / This study aims to investigate the regulatory, political and legal challenges to the development of renewable energy from ocean sources in Brazil, identifying barriers to introducing this type of generation, taking into account the current legal framework, making a parallel with countries at a more advanced stage of maturity both in terms of technology as well as industrial development policies and to encourage oceanic resources. This research explores the records of the potential of marine energy on Brazilian coast for generation of electricity, considering environmental, regulatory, infrastructure and financial constraints. It also highlights the progress and technological challenges relevant to the economic feasibility for the development of an industry-based and long-term sustainability. From the compilation and analysis of data and experience from various countries in the world and the concatenation of the most successful models, it presents a projection on a timeline which establishes a relationship between the development of the market of oceanic generation and the inclusion of new public policies. / Este trabalho tem como objetivo investigar os desafios regulatórios, políticos e jurídicos para o desenvolvimento da energia renovável de fontes oceânicas no Brasil, identificando os entraves para a introdução deste tipo de geração, levando em consideração o arcabouço jurídico atual, fazendo um paralelo com países que se encontram num estágio mais avançado de maturidade, tanto em termos tecnológicos bem como em políticas de desenvolvimento industrial e de incentivo a fontes oceânicas. Esta investigação explora os registros das potencialidades das energias marinhas na costa brasileira para geração de energia elétrica, considerando as restrições ambientais, regulatórias, de infraestrutura e financeiras. Também se destacará a evolução e os desafios tecnológicos pertinentes à viabilidade econômica para o desenvolvimento de uma indústria de base e sustentabilidade em longo prazo. A partir da compilação e análise de dados e experiências obtidas em diversos países no mundo e da concatenação dos modelos mais exitosos, apresenta-se uma projeção em uma linha de tempo em que se estabelece uma relação entre o desenvolvimento do mercado da geração oceânica e a inserção de novas políticas públicas.
27

Development of a procedure for power generated from a tidal current turbine farm

Li, Ye 11 1900 (has links)
A tidal current turbine is a device functioning in a manner similar to wind turbine for harnessing energy from tidal currents, a group of which is called a farm. The existing approaches used to predict power from tidal current turbine farms oversimplify the hydrodynamic interactions between turbines, which significantly affects the results. The major focus of this dissertation is to study the relationship between turbine distribution (the relative position of the turbines) and the hydrodynamic interactions between turbines, and its impact on the power from a farm. A new formulation of the discrete vortex method (DVM-UBC) is proposed to describe the behavior of turbines and unsteady flow mathematically, and a numerical model is developed to predict the performance, the unsteady wake and acoustic emission of a stand-alone turbine using DVM-UBC. Good agreement is obtained between the results obtained with DVM-UBC and published numerical and experimental results. Then, another numerical model is developed to predict the performance, wake and acoustic emission of a two-turbine system using DVM-UBC. The results show that the power of a two-turbine system with optimal relative position is about 25% more than two times that of a stand-alone turbine under the same conditions. The torque such a system may fluctuate 50% less than that of a stand-alone turbine. The acoustic emission of such a system may be 35% less than that of a stand-alone turbine. As an extension, a numerical procedure is developed to estimate the efficiency of an N-turbine system by using a linear theory together with the two-turbine system model. By integrating above hydrodynamic models for predicting power and a newly-developed Operation and Maintenance (O&M) model for predicting the cost, a system model is framed to estimate the energy cost using a scenario-based cost-effectiveness analysis. This model can estimate the energy cost more accurately than the previous models because it breaks down turbine’s components and O&M strategies in much greater detail when studying the hydrodynamics and reliability of the turbine. This dissertation provides a design tool for farm planners, and shed light on other disciplines such as environmental sciences and oceanography.
28

Assessment of tidal stream energy potential for Marine Corps Recruit Depot Parris Island

Gay, Thomas Joseph 24 August 2010 (has links)
The energy of the tides represents one globally existent source of renewable energy, and has the potential to play a major role in a sustainable future. An assessment of the potential for tidal energy extraction using marine current turbines at a particular location in the Beaufort River near Parris Island, South Carolina is presented. The Marine Corps Recruit Depot located on Parris Island is situated between the confluence of the Broad and Beaufort Rivers. These rivers are tidally dominated, and experience some of the largest tidal ranges in the southeastern United States, between 2.5 and 3 meters during spring tide periods. Because Parris Island already has much of the necessary land-based infrastructure in place, there is logical potential for the extraction of kinetic energy from the nearby tidal streams using underwater turbines for power production. In order to evaluate the potential of a particular location to produce significant amounts of energy using these types of devices, extensive investigations must be conducted to determine important site characteristics such as water depth, current velocity, and water level fluctuations over time. This potential was investigated using in-situ measurements in the vicinity of the pump station on Parris Island, and by developing a numerical model of the region using the Regional Ocean Modeling System (ROMS). This model was calibrated using the results from the in-situ measurements, and was then used to determine the impacts of tidal energy extraction on the local flow field. Results from in-situ measurements indicate that tidal currents along the portion of the Beaufort River analyzed in this study are driven primarily by the semi-diurnal M2 tidal constituent. The tidal range at the study site is approximately 2 meters on average, with a mean depth-averaged current velocity magnitude of 0.57 m/s predicted for a period of one year. A mean depth-averaged current velocity magnitude of 0.59 m/s was observed over the course of the longer-term ADCP deployment from November 12 to December 17, 2009. The maximum current speed at the site is approximately 1.2 m/s at the water surface. The ROMS model applied to the coastal areas surrounding Parris Island, SC produces results that closely resemble in-situ measurements collected previously during both the boat-based survey and the longer-term ADCP deployment. In the analysis of the effects of energy extraction from the system, four separate cases were considered in which 10, 20, 30, and 60% of the total kinetic energy contained in the flow was dissipated near the location of the longer-term ADCP deployment. Minimal impacts on the local hydrodynamics were observed across the four cases considered.
29

Development of a procedure for power generated from a tidal current turbine farm

Li, Ye 11 1900 (has links)
A tidal current turbine is a device functioning in a manner similar to wind turbine for harnessing energy from tidal currents, a group of which is called a farm. The existing approaches used to predict power from tidal current turbine farms oversimplify the hydrodynamic interactions between turbines, which significantly affects the results. The major focus of this dissertation is to study the relationship between turbine distribution (the relative position of the turbines) and the hydrodynamic interactions between turbines, and its impact on the power from a farm. A new formulation of the discrete vortex method (DVM-UBC) is proposed to describe the behavior of turbines and unsteady flow mathematically, and a numerical model is developed to predict the performance, the unsteady wake and acoustic emission of a stand-alone turbine using DVM-UBC. Good agreement is obtained between the results obtained with DVM-UBC and published numerical and experimental results. Then, another numerical model is developed to predict the performance, wake and acoustic emission of a two-turbine system using DVM-UBC. The results show that the power of a two-turbine system with optimal relative position is about 25% more than two times that of a stand-alone turbine under the same conditions. The torque such a system may fluctuate 50% less than that of a stand-alone turbine. The acoustic emission of such a system may be 35% less than that of a stand-alone turbine. As an extension, a numerical procedure is developed to estimate the efficiency of an N-turbine system by using a linear theory together with the two-turbine system model. By integrating above hydrodynamic models for predicting power and a newly-developed Operation and Maintenance (O&M) model for predicting the cost, a system model is framed to estimate the energy cost using a scenario-based cost-effectiveness analysis. This model can estimate the energy cost more accurately than the previous models because it breaks down turbine’s components and O&M strategies in much greater detail when studying the hydrodynamics and reliability of the turbine. This dissertation provides a design tool for farm planners, and shed light on other disciplines such as environmental sciences and oceanography.
30

Ocean current energy resource assessment for the United States

Yang, Xiufeng 13 January 2014 (has links)
Ocean currents are an attractive source of clean energy due to their inherent reliability, persistence and sustainability. The Gulf Stream system is of particular interest as a potential energy resource to the United States with significant currents and proximity to the large population on the U.S. east coast. To assess the energy potential from ocean currents for the United States, the characterization of ocean currents along the U.S. coastline is performed in this dissertation. A GIS database that maps the ocean current energy resource distribution for the entire U.S. coastline and also provides joint velocity magnitude and direction probability histograms is developed. Having a geographical constraint by Florida and the Bahamas, the Florida Current has the largest ocean current resource which is fairly stable with prevalent seasonal variability in the upper layer of the water column (~200m). The core of the Florida Current features higher stability than the edges as a result of the meandering and seasonal broadening of the current flow. The variability of the Gulf Stream significantly increases as it flows past the Cape Hatteras. The theoretical energy balance in the Gulf Stream system is examined using the two-dimensional ocean circulation equations based on the assumptions of the Stommel model for quasi-geostrophic subtropical gyres. Additional turbine drag is formulated and incorporated in the model to represent power extraction by turbines. Parameters in the model are calibrated against ocean observational data such that the model can reproduce the volume and kinetic energy fluxes in the Gulf Stream. The results show that considering extraction over a region comprised of the entire Florida Current portion of the Gulf Stream system, the theoretical upper bound of averaged power dissipation is around 5.1 GW, or 45 TWh/yr. If the extraction area comprises the entire portion of the Gulf Stream within 200 miles of the U.S. coastline, the theoretical upper bound of averaged power dissipation becomes approximately 18.6 GW or 163 TWh/yr. The impact of the power extraction is primarily constrained in the vicinity of the turbine region, and includes a significant reduction of flow strength and water level drop in the power extraction site. The turbines also significantly reduce residual energy fluxes in the flow, and cause redirection of the Gulf Stream. A full numerical simulation of the ocean circulation in the Atlantic Ocean is performed using Hybrid Coordinate Ocean Model (HYCOM) and power extraction from the Florida Current is modeled as additional momentum sink. Effects of power extraction are shown to include flow rerouting from the Florida Strait channel to the east side of the Bahamas. Flow redirection is stronger during peak summer flow resulting in less seasonal variability in both power extraction and residual fluxes in the Florida Current. A significant water level drop is shown at the power extraction site, and so is a slight water level rise along the coasts of Florida and the Gulf. The sum of extracted power and the residual energy flux in the Florida Current is lower than the original energy flux in the baseline case, indicating a net loss of energy reserve in the Florida Current channel due to flow redirection. The impact from power extraction on the mean flow field is concentrated in the near field of the power extraction site, while shifts in the far flow field in time and space have little impact on the overall flow statistics.

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