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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.
1

Optimization of an Ocean Current Turbine Design and Prediction of Wake Propagation in an Array

Unknown Date (has links)
This research focused on maximizing the power generated by an array of ocean current turbines. To achieve this objective, the produced shaft power of an ocean current turbine (OCT) has been quantified using CFD without adding a duct, as well as over a range of duct geometries. For an upstream duct, having a diameter 1.6 times the rotor diameter, the power increased by 8.35% for a duct that extends 1 diameter upstream. This research also focused on turbine array optimization, providing a mathematical basis for calculating the water velocity within an array of OCTs. After developing this wake model, it was validated using experimental data. As the downstream distance behind the turbine increases, the analytic results become closer to the experimental results, with a difference of 3% for TI = 3% and difference of 4% for TI = 15%, both at a downstream distance of 4 rotor diameters. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection
2

The performances of different comparative distances on water turbine

Chiu, Po-lin 06 September 2010 (has links)
This thesis aims to investigate the performance of a horizontal water turbine in ocean current. The design of the water turbine is based on the Blade Element Momentum theory to begin with. As the water current flows past a single turbine, the water inflow velocity and the rotational speed are the parameters to be investigated. Furthermore, the interaction of more than two turbines due to the relative distance is also discussed. The relative distance encompasses both the front and the back. The results show that the water inflow velocity and the turbine rotational speed influence the performance of the turbine. When two turbines function simultaneously, the flow field is different from the one of a single turbine and thus influences the performance of the other turbines in the vicinity. Lastly, the site arrangement of three turbines is discussed, and it is revealed that a proper arrangement can enhance the performance of the turbines.
3

Studies and design of horizontal-axis water turbines for electricity generation in an ocean current

Pan, Hsin-hua 02 September 2011 (has links)
In this thesis, the turbine blade design eligible for ocean current conditions is proposed using blade element momentum theory. in the beginning, the performance of water turbines is evaluated by CFD (computational fluid dynamics) package code, so as to design the suitable turbine under various conditions. The blade design encompasses parameters of the hydrofoil selection and blade shape which affect the turbine performance. Shortly following the investigation of the aforementioned parameters, the turbine¡¦s performance with radius of two meter is also studied. The current conditions include the yaw and the pitch angle of the turbine relative to the current flow direction, as well as the periodic flow conditions on the performance of the water turbine. Lastly, the electricity generation is estimated by the present device. The results show that hydrofoils with less changes in the angle of attack with respect to the lift-drag ratio help enhance the turbine¡¦s performance. The feedback mechanism is added to the blade design procedure to make sure that the turbine design caters to the best angle of attack. A turbine with two-meter radius can garner 34% of the sea current energy at most, living up to the project goal of exceeding the efficiency of 30%. The simulated test indicates that the adequate enlargement of the blade not only sustains the maximal efficiency, but it also lowers the stress imposed on the blade. Given the ocean current conditions, it is also shown that the turbine¡¦s efficiency is proportional to the cubic cosine incident angle of inflow velocity alongside with the enlargement of the turbine radius. When it comes to the current electricity generation, from the in-situ measurement data, the current maximal velocity near the sea region is around 1.3 m/s. If incorporated with the self excited induction generator with the efficiency of 55%, a one-meter-radius turbine is estimated to be able to generate 530W at most, while a two-meter-radius turbine is estimated to generate 2.5KW. However, the use of the permanent magnet generator can produce 45% more electricity than a self excited induction generator.
4

Intraseasonal Variability Of The Northeast Indian Ocean Circulation In An Ocean Model

Senan, Retish 07 1900 (has links) (PDF)
No description available.
5

Water Current Measurements using Oceanographic Bottom LanderLoTUS?

Kjelldorff, Maria January 2019 (has links)
oTUS is a Long Term Underwater Sensing, bottom landing, node for observations of ocean water temperatures. LoTUS measures temperature (moored to the seafloor) according to a spec-ified time schedule until, at the end of the mission, it surfaces to transmit the collected data to on shore recipients using an Iridium link. The paper presents an extension of the sensing capability to include water current velocity (speed and direction) using a robust, reliable and inexpensive Eulerian method. The method is based on the "tilting stick" principle where a combination of inertia measurement data and magnetic sensor data is used. The paper discusses the principal technique, the modeling of the system, practical considerations, and optimization of the setup for specific flow conditions along with verifying experimental data.
6

Effect of a diffuser on the power production of an ocean current turbine

Reinecke, Josh 03 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / Please refer to full text to view abstract.
7

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.
8

Distribuição e validade taxonômica do gênero Chrysaora (Cnidaria; Scyphozoa) na América do Sul / Distribution and taxonomic validity of the genus Chrysaora (Cnidaria; Scyphozoa) in South America

Rosa, Fernanda Creres [UNESP] 26 February 2016 (has links)
Submitted by FERNANDA CRERES ROSA null (fer_creres@hotmail.com) on 2016-04-04T19:15:40Z No. of bitstreams: 1 Fernanda Rosa - Dissertação Mestrado.pdf: 2522596 bytes, checksum: e6a718a620bc5e59e8744c6971a6c1c1 (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-04-06T14:43:55Z (GMT) No. of bitstreams: 1 rosa_fc_me_assis.pdf: 2522596 bytes, checksum: e6a718a620bc5e59e8744c6971a6c1c1 (MD5) / Made available in DSpace on 2016-04-06T14:43:55Z (GMT). No. of bitstreams: 1 rosa_fc_me_assis.pdf: 2522596 bytes, checksum: e6a718a620bc5e59e8744c6971a6c1c1 (MD5) Previous issue date: 2016-02-26 / Chrysaora é um dos gêneros mais ricos de espécies dentro da subclasse Discomedusae Haeckel, 1880. Na América do Sul existem duas espécies do gênero Chrysaora, Chrysaora lactea (Eschscholtz, 1829) e Chrysaora plocamia (Lesson 1830). A cifomedusa C. lactea é uma das mais comuns e amplamente distribuídas medusas de Scyphozoa na costa. A distribuição dessa espécie é contínua desde o Golfo do México até a costa norte da Argentina (Morandini e Marques 2010). Já a espécie C. plocamia apresenta um incomum padrão de distribuição, ocorrendo em ambos os lados do sul da América do Sul; região oriental do Pacífico Sul (Peru, Chile) e oeste do Atlântico Sul (Argentina), sofrendo forte influência das correntes oceânicas. Assim, o objetivo principal do projeto foi realizar um levantamento da distribuição do gênero Chrysaora na América do Sul. Adicionalmente buscou-se confirmar a ocorrência da espécie C. plocamia no litoral do Uruguai, analisar a estrutura morfológica e molecular das populaçõesde C. lactea distribuídas ao longo do Atlântico Sul Ocidental e comparar os indivíduos entre as diferentes regiões. Foram realizadas análises morfológicas e morfométricas, o estudo da composição dos nematocistos através das medidas e análises estatísticas, além de análises moleculares, através da avaliação do marcador molecular mitocondrial (16S) dos indivíduos da espécie C. lactea e C. plocamia, de diferentes localidades. Os resultados apontam que a distribuição da espécie C. lactea é continua desde o Uruguai até o norte do Brasil e que possivelmente não há incidência de espécies crípticas nessa região analisada. Já a espécie C. plocamia está associada às águas frias neríticas do Atlântico e Pacífico, notando-se a presença dessa espécie também na região do Uruguai. / Chrysaora is one of the richest genera within the subclass Discomedusae Haeckel, 1880. In South America, there are two species of the genus Chrysaora, Chrysaora lactea (Eschscholtz, 1829) and Chrysaora plocamia (Lesson 1830). The scyphomedusa C. lactea is one of the most common and widely distributed Scyphozoa jellyfish on the coast. The distribution of this species is continuous from the Gulf of Mexico to the north coast of Argentina (Morandini e Marques 2010). C. plocamia has an unusual distribution pattern, occurring on both sides of southern South America, eastern South Pacific (Peru, Chile) and western South Atlantic (Argentina). The objective of this study was to promote a survey of the distribution of the genus Chrysaora in South America. Additionally, we confirmed the occurrence of C. plocamia in Uruguay coast, analyzed the morphological and molecular structureof C. lactea distributed over Western South Atlantic comparing individuals between different regions, especially looking for the incidence of cryptic species. Morphological and morphometric analyzes were performed, as well as the study of the composition of nematocysts by measurements and statistical analysis, in addition to molecular analysis by evaluating the mitochondrial molecular markers 16S of individuals of C. lactea and C. plocamia from different locations. The results showed that the distribution of the species C. lactea is continuous from the Uruguay to the Northern Brasil and there was no incidence of cryptic species. Also, C. plocamia is associated with cold inshore waters of the Atlantic and Pacific, noting the presence of this species also in Uruguay.
9

Constrained Control for Helicopter Shipboard Operations and Moored Ocean Current Turbine Flight Control

Ngo, Tri Dinh 30 June 2016 (has links)
This dissertation focuses on constrained control of two applications: helicopter and ocean current turbines (OCT). A major contribution in the helicopter application is a novel model predictive control (MPC) framework for helicopter shipboard operations in high demanding sea-based conditions. A complex helicopter-ship dynamics interface has been developed as a system of implicit nonlinear ordinary differential equations to capture essential characteristics of the nonlinear helicopter dynamics, the ship dynamics, and the ship airwake interactions. Various airwake models such as Control Equivalent Turbulence Inputs (CETI) model and Computation Fluid Dynamics (CFD) data of the airwake are incorporated in the interface to describe a realistic model of the shipborne helicopter. The feasibility of the MPC design is investigated using two case studies: automatic deck landing during the ship quiescent period in sea state 5, and lateral reposition toward the ship in different wind-over-deck conditions. To improve the overall MPC performance, an updating scheme for the internal model of the MPC is proposed using linearization around operating points. A mixed-integer MPC algorithm is also developed for helicopter precision landing on moving decks. The performance of this control structure is evaluated via numerical simulations of the automatic deck landing in adverse conditions such as landing on up-stroke, and down-stroke moving decks with high energy indices. Kino-dynamic motion planning for coordinated maneuvers to satisfy the helicopter-ship rendezvous conditions is implemented via mixed integer quadratic programming. In the OCT application, the major contribution is that a new idea is leveraged from helicopter blade control by introducing cyclic blade pitch control in OCT. A minimum energy, constrained control method, namely Output Variance Constrained (OVC) control is studied for OCT flight control in the presence of external disturbances. The minimum achievable output variance bounds are also computed and a parametric study of design parameters is conducted to evaluate their influence on the OVC performance. The performance of the OVC control method is evaluated both on the linear and nonlinear OCT models. Furthermore, control design for the OCT with sensor failures is also examined. Lastly, the MPC strategy is also investigated to improve the OCT flight control performance in simultaneous satisfaction of multiple constraints and to avoid blade stall. / Ph. D.
10

Electromechanics of an Ocean Current Turbine

Tzelepis, Vasileios 18 December 2015 (has links)
The development of a numeric simulation for predicting the performance of an Ocean Current Energy Conversion System is presented in this thesis along with a control system development using a PID controller for the achievement of specified rotational velocity set-points. In the beginning, this numeric model is implemented in MATLAB/Simulink® and it is used to predict the performance of a three phase squirrel single-cage type induction motor/generator in two different cases. The first case is a small 3 meter rotor diameter, 20 kW ocean current turbine with fixed pitch blades, and the second case a 20 meter, 720 kW ocean current turbine with variable pitch blades. Furthermore, the second case is also used for the development of a Voltage Source Variable Frequency Drive for the induction motor/generator. Comparison among the Variable Frequency Drive and a simplified model is applied. Finally, the simulation is also used to estimate the average electric power generation from the 720 kW Ocean Current Energy Conversion System which consists of an induction generator and an ocean current turbine connected with a shaft which modeled as a mechanical vibration system.

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