Rozprawy doktorskie na temat „Eddy currents”
Kliknij ten link, aby zobaczyć inne rodzaje publikacji na ten temat: Eddy currents.
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych rozpraw doktorskich naukowych na temat „Eddy currents”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj rozprawy doktorskie z różnych dziedzin i twórz odpowiednie bibliografie.
1
Belloufi, Messaoud. "Experimental studies of eddy currents". Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/12008.
Pełny tekst źródłaStreszczenie:
The thesis is mainly concerned with experimental studies of the heating effects of eddy currents. Sinusoidal and non-sinusoidal eddy current heating losses in non-magnetic conducting discs and spheres, subjected to a uniform field, are studied both theoretically and experimentally. The theory uses two different methods to calculate the power dissipation in the objects, and it employs Fourler series for the non-sinusoidal case. Some approximations for the losses at low frequency have been derived. The experimental study has three main sections. The first deals with the generation of uniform field for inducing eddy currents. Square Helmholtz coils have been designed, constructed and calibrated for this purpose. The second part is concerned with the measurement of the heat generated by eddy currents. A differential thermometer, using two matched therrnistors in a Blumlein bridge circuit, has been designed, built and calibrated. Operating close to balance, with a phase sensitive detector, the thermometer detects differences of 10-5 degrees C. In the third part, the experiment arranged for the eddy current heating measurements is described. The measured and the calculated results are compared, and the agreement was found to be about 2%. In foil wound inductors excited by alternating current, eddy currents together with proximity effect cause a redistribution of the current density across the width of the inductors. The current flow is increased along the edges of the foil and decreased along the centre portion. A thermal demonstration of this phenomenon, which is known as width effect, is described and studied by using the differential thermometer.
2
Giguere, Sylvain. "Pulsed eddy-currents for corrosion detection". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq44910.pdf.
Pełny tekst źródła
3
Ortiz, Gomez Natalia. "Eddy currents applied to space debris objects". Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/415734/.
Pełny tekst źródłaStreszczenie:
The increasing population of space debris in the near-Earth region poses a serious threat to operational satellites in-orbit. This situation has led to the development of numerous guidelines in order to mitigate the potential danger of in-orbit collisions, fragmentations and uncontrolled re-entries. Among the various recommendations, active debris removal is considered as a possible solution to help decrease the chance of the aforementioned risks. However, active debris removal has never been done in space and it still requires further development of various technologies and orbit testing before it can become a reality. One of the major challenges to overcome is how to capture rotating space debris objects. Some of these objects may have high rotational speeds which hampers their capture and subsequent controlled re-entry. This research focuses on the analysis of the eddy current phenomenon on space debris objects by the Earth magnetic field as well as its practical application to develop a de-tumbling method for active debris removal based on the generation of eddy currents. The first part of the project focuses on the development of a new mathematical approach which generalises the existing analytical models and simplifies the numerical methods typically employed to analyse the eddy current phenomenon. This mathematical approach, referred to as the magnetic tensor theory, is validated both numerically and experimentally. The theory is based on the discovery of a symmetric Cartesian tensor of second order with no negative eigenvalues, named the magnetic tensor. A method to evaluate this tensor based on a generic finite element method is provided as well as a particularization for a specific F.E.M. which leads to a direct formula to evaluate this tensor. This way, the eddy current torque solution may be found without the necessity to solve the classical Poisson equation with Neumann boundary conditions in each time step of the integration process of Euler’s equation. This breakthrough greatly reduces the complexity and computational time of the classical approach commonly adopted in the past. The second part of the project focuses on the design of a contactless de-tumbling method based on the generation of eddy currents named the eddy brake method. This design delves deeper into the idea first suggested by Kadaba and Naishadham in 1995 which consists in subjecting a space debris object to an enhanced magnetic field in order to damp its rotation. The advances in high temperature superconducting materials as well as spacecraft sensors and actuators has allowed for a compelling new design to be reached within this research which may serve as a stepping stone for future ADR missions. A thorough systems engineering design of the eddy brake is presented with special attention to the thermal and guidance, navigation and control subsystems. These subsystems have been identified as the two most relevant ones to support the operation of the eddy brake. The results show that the eddy brake is a promising solution to reduce the rotation of metallic space debris and allow for their subsequent capture.
4
Case, Russell. "REDUCING EDDY CURRENTS IN HIGH MAGNETIC FIELD ENVIRONMENTS". Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4305.
Pełny tekst źródłaStreszczenie:
When an electrical conducting volume is placed into the bore of an MRI undergoing an image scan, time varying magnetic gradients induce eddy currents in this conducting material. These eddy currents in turn produce a mechanical torque on this volume. It is the goal of this thesis to produce a computer simulation of eddy currents produced by placing conducting materials inside an MRI bore. The first part of the thesis establishes the physics and principles behind an MRI system along with several applications. Next, this thesis presents an analysis of eddy current effects produced on a conductor placed into an MRI bore. The design and construction of simulated MRI magnetic fields is then presented along with a study of simulated eddy currents in various test conducting volumes of selected materials. Finally, techniques are discussed for reducing eddy currents in these conducting volumes and materials, along with simulation results showing the reduction in the applied eddy current. The findings of this thesis are summarized in the conclusions and recommendations are made for modification and future applications of these techniques and simulations.M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE
5
Carstensen, Christian. "Eddy currents in windings of switched reluctance machines". Aachen Shaker, 2007. http://d-nb.info/989018482/04.
Pełny tekst źródła
6
Wilson, Thomas Lawler. "A multi-coil magnetostrictive actuator". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28243.
Pełny tekst źródłaStreszczenie:
Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Zinn, Ben T.; Committee Member: Book, Wayne; Committee Member: Glezer, Ari; Committee Member: Neumeier, Yedidia; Committee Member: Seitzman, Jerry.
7
Benhama, Abdelkrim. "Investigation of losses in foil windings of inverter fed transformers operating at medium frequencies". Thesis, University of Salford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386448.
Pełny tekst źródła
8
Oaten, Susan Rosemary. "Assessment of defects in ferromagnetic metals with eddy currents". Thesis, Brunel University, 1989. http://bura.brunel.ac.uk/handle/2438/5310.
Pełny tekst źródłaStreszczenie:
A study was made to identify and size surface breaking defects in ferromagnetic materials with eddy currents, whilst eliminating unwanted signals due to changes in magnetic permeability and probe lift-off. The former was overcome by the use of high frequencies and the latter by utilising the lift-off to characterise the defects. The lift- off or "touch" method was shown to be advantageous in that one could test steel objects having irregular surfaces, such as occurring with the presence of welds. In addition a theoretical investigation was undertaken to relate changes in the magnetic permeability, electrical conductivity and values of lift-off to the components of impedance of a detecting coil located above the plane surface of a ferromagnetic metal. The resultant theory was confirmed by experimental measurements.
9
FORTALEZA, LEONARDO GOUVEA E. SILVA. "NON-FERROMAGNETIC METALLIC FOREIGN BODY DETECTION BY EDDY CURRENTS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=28358@1.
Pełny tekst źródłaStreszczenie:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Projéteis de chumbo (não-ferromagnéticos) são corpos estranhos comuns na prática médica. Métodos convencionais de localização utilizam radiações ionizantes, impondo riscos à saúde e procedimentos que duram várias horas e tipicamente terminam malsucedidos. Mapas de campos magnéticos obtidos não-invasivamente e inocuamente com SQUIDs beneficiam a localização de agulhas metálicas ferromagnéticas, reduzindo o tempo de remoção bem-sucedida de 6 horas para 10 minutos. SQUIDs são os magnetômetros mais sensíveis, entretanto requerem temperaturas criogênicas, levando a altos custos e baixa portabilidade que impedem a difusão do uso clínico. O objetivo é desenvolver um dispositivo para localizar corpos estranhos metálicos não-ferromagnéticos visando remoção cirúrgica, respeitando requerimentos de projeto: alta sensibilidade, inocuidade, não-invasividade, baixo custo, segurança, portabilidade, facilidade de uso e operação em temperatura ambiente. Sensores GMR e GMI são considerados alternativas mais adequadas. Modelos teóricos de eletrodinâmica clássica aplicados às correntes parasitas servem como base. Dois sistemas eletrônicos são desenvolvidos em configuração gradiométrica para remover interferência ambiente, usando elementos sensores GMR e GMI disponíveis comercialmente. O desempenho é obtido com resultados de simulações, provando a capacidade de detecção de níveis esperados de densidade de fluxo magnético para certos raios de projéteis e distâncias. O Sistema GMI é mais qualificado, sua mais alta sensibilidade e melhor resolução favorecem maiores faixas de medição, inocuidade, segurança e facilidade de uso. Os resultados demonstram a viabilidade dos elementos sensores GMI nessa aplicação. Os benefícios de baixo custo, maior portabilidade e segurança facilitam a utilização clínica de técnicas de localização para corpos estranhos metálicos não-ferromagnéticos mais inócuas e efetivas.
Lead projectiles (non-ferromagnetic) are common foreign bodies in the medical practice. Conventional means of location use ionizing radiation, pose health risks and lead to procedures that last several hours, typically ending unsuccessfully. Magnetic field maps obtained non-invasively and innocuously with SQUIDs benefit the location of ferromagnetic metallic needles, reducing the time of successful removal from 6 hours to 10 minutes. SQUIDs are currently the most sensitive magnetometers, however require cryogenic temperatures, leading to high cost and low portability which prevent widespread clinical use. The objective is to design a device for locating non-ferromagnetic metallic foreign bodies for surgical removal, respecting project requirements of: high sensitivity, innocuousness, non-invasiveness, low cost, safety, portability, ease of use and room temperature operation. GMR and GMI sensors are considered as more suitable alternatives. Classical electrodynamics theoretical models applied to eddy currents induction serve as framework. Two electronic location systems are developed in gradiometric configuration to remove environmental interference, using commercially available GMR and GMI sensor elements. System performance is obtained from simulation results, demonstrating the capability of detecting the magnetic flux density levels expected under certain projectile radii and distances. The GMI system is more qualified, as its higher sensitivity and improved resolution favors larger measurement ranges, innocuousness, safety and ease of use. The results prove the viability of using GMI sensor elements in this application. The benefits of lower cost, higher portability and safety facilitate the clinical use of more innocuous and effective location techniques for non-ferromagnetic metallic foreign bodies.
10
Meuleners, Michael Joseph. "A numerical study of the mesoscale eddy dynamics of the Leeuwin Current system /". Connect to this title, 2005. http://theses.library.uwa.edu.au/adt-WU2007.0134.
Pełny tekst źródła
11
Prabhakaran, Pradeep. "Development of electronic instrument for defect measurements with eddy currents /". St. Lucia, Qld, 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17873.pdf.
Pełny tekst źródła
12
Ali, Raza. "Defect detection using eddy-currents and Hall effect sensor arrays". [Ames, Iowa : Iowa State University], 2007.
Znajdź pełny tekst źródła
13
Carstensen, Christian [Verfasser]. "Eddy Currents in Windings of Switched Reluctance Machines / Christian Carstensen". Aachen : Shaker, 2008. http://d-nb.info/1162790768/34.
Pełny tekst źródła
14
Smith, M. C. "Factors affecting the eddy currents response around installed aircraft fasteners". Thesis, Cranfield University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309685.
Pełny tekst źródła
15
Ati, Modafar K. "Calculation of electromagnetic field problems in large electrical machines using the finite element method". Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238937.
Pełny tekst źródła
16
Abbas, Al-Byati N. "The eddy-current damping of synchronous machines with solid cylindrical rotors". Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330125.
Pełny tekst źródła
17
Allen, Nancy. "Finite element modelling of eddy currents in nonlinear and moving media". Thesis, University of Bath, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362151.
Pełny tekst źródła
18
Chumbinho, Rogřio Paulo Antunes. "Kinematics and dynamics of a cyclonic eddy off Pt. Arena, California /". Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA298587.
Pełny tekst źródłaStreszczenie:
Dissertation (Ph. D. in Physical Oceanography) Naval Postgraduate School, December 1994."December 1994." Dissertation supervisor(s): R.L. Haney. Includes bibliographical references (p. 75-79). Also available online.
19
Gupta, D. K. "Transportation of ferromagnetic powder using linear motor devices". Thesis, Loughborough University, 1994. https://dspace.lboro.ac.uk/2134/9219.
Pełny tekst źródłaStreszczenie:
The travelling magnetic wave of a linear induction motor induces eddy currents in a secondary circuit (usually a sheet consisting at least partly of a non-magnetic metal, often aluminium), which cause the unrestrained member to move linearly in the direction of the travelling wave. A linear motor can also transport ferromagnetic powder, although this travels in the opposite direction to the travelling magnetic field. The motion is therefore due to a mechanism other than the eddy currents flowing in the sheet secondary. Expressions for the forces acting on an iron particle due to a travelling magnetic field are derived in the thesis. Preliminary experiments support the assumptions made in the derivations of the force expressions and lead to the formation of an hypothesis. This is shown to be capable of predicting both linear and rotational particle speeds and, with greater accuracy, the distance travelled and the rotation experienced by the particles. Experiments conducted on tubular and transverse flux motors have enabled different linear motors to be identified as suitable for a number of powder transportation applications. The results obtained show also the importance of large flux density values, the tangential to normal flux density ratio and large pole-pitch winding arrangements, with the latter lending support to the original hypothesis. The results of a finite element investigation of the tubular motor did not closely agree with the results from the experimental motor although similar trends were evident. Flux density values within particles were found to be considerably greater than those outside, as assumed in the hypothesis.
20
Тиркусова, Надія Володимирівна, Надежда Владимировна Тыркусова, Nadiia Volodymyrivna Tyrkusova i Д. О. Варакин. "Разработка алгоритма и программного обеспечения для расчета параметров гидродинамики вихревых потоков". Thesis, Видавництво СумДУ, 2010. http://essuir.sumdu.edu.ua/handle/123456789/4423.
Pełny tekst źródła
21
Meuleners, Michael Joseph. "A numerical study of the mesoscale eddy dynamics of the Leeuwin Current system". University of Western Australia. School of Environmental Systems Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0134.
Pełny tekst źródłaStreszczenie:
[Truncated abstract] The study of eastern ocean boundary currents has been principally restricted to the Pacific and Atlantic ocean regions. The traditional view of the circulation near eastern ocean boundaries is that upwelling-favourable winds force surface waters offshore, leading to upwelling of cold, nutrient-rich subsurface water at the coast, the formation and offshore advection of a coastal front, and the generation of alongshore currents, generally having an equatorward surface flow and a poleward undercurrent. The eastern ocean boundary system of the southern Indian Ocean, off the west coast of Australia, is unique compared with these regions because a warm, poleward surface flow, known as the Leeuwin Current, dominates the dynamics over the continental shelf. Satellite imagery has shown the Leeuwin Current consists of a complex system of meanders, jet-like streams, and eddies, and has a seasonal and interannual variability. The oceanic circulation of the region between Carnarvon (latitude 25°S) and Jurien Bay (latitude 31°S) was examined using observational and remotely sensed data in conjunction with a detailed numerical modelling study. The model was validated using in situ ADCP and CTD data, and the horizontal eddy viscosity parameterization was tested against field observations. ... The resulting offshore meander grew laterally, shallowed, and closed to form an anticlockwise eddy to the original clockwise eddy’s south, forming a characteristic LC eddy pair (dipole). The model demonstrated the LC and Leeuwin Undercurrent (LUC) coupling played an important role in the onset of eddies at both sites. When an energy diagnostic scheme was used, the dominant instability process linked to the anticlockwise eddy’s development at site 1 was a mixed mode barotropic and baroclinic instability. The baroclinic instability’s source was the available potential energy stored within the mean lateral density gradient. The LC’s meandering southerly flow interacting with the LUC’s northerly subsurface flow generated the horizontal shear that sourced the barotropic instability. The dominant instability process at site 2 was baroclinic in origin. Possible links between the eddy field dynamics and the shelfslope region’s alongshore topographic variability were considered. The results of a suite of five model runs, differing only in the specification of bottom topography, were contrasted to investigate the effects. Except for the expected alongshore variability, delay in the onset of instabilities, varying growth rates, and some differences in the dominant wavebands’ mesoscale patterns, the overall impression was the response was similar.
22
Nalladega, Vijayaraghava. "Design and Development of Scanning Eddy Current Force Microscopy for Characterization of Electrical, Magnetic and Ferroelectric Properties with Nanometer Resolution". University of Dayton / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1249514169.
Pełny tekst źródła
23
Lippi, Silvio. "Analysis of rotor eddy-current losses in synchronous motors". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.
Znajdź pełny tekst źródłaStreszczenie:
La stima delle perdite rotoriche per correnti parassite (Eddy currents) è cruciale nella progettazione dei moderni motori SPM. Poichè le loro prestazioni dipendono fortemente da esse. I motori devo essere progettati in modo da prevenire eccessive perdite rotoriche, le quali possono portare alla demagnetizzazione dei magneti e ad un deterioramento delle performance generali della macchina. Nel capitolo 1 sono illustati i principi fisici che descrivono il comportamento dei motori elettrici e delle perdite rotoriche per correnti parassite. Sono poi discusse le proprietà dei materiali impiegati nell'ambito della costruzione di macchine elettriche ed infine sono presentate le tecniche al momento più diffuse per la stima delle correnti parassite. Dopo di che nel capitolo 2 è analizzato un modello semplificato di un SPM, in cui il rotore è sostituito con un cilindro solido. In particolare è stata investigata la dipendenza dalla resistività del materiale impiegato per il rotore. Una tecnica basata sul current sheet per la stima delle perdite rotoriche è presentata in dettaglio e implementata. Infine è riportata la validazione della procedura basata sul current sheet. Nel capitolo 3 l'analisi è estesa a un reale motore SPM, in particolare sono investigate le perdite nei magneti. Sono quindi illustrate le criticità di tale analisi e i limiti del modello. Per finire nel capitolo 4 sono riportati i risultati dei test effettuati, e sono discussi possibili futuri sviluppi del metodo illustrato.
24
KYROUSI, FOTEINI. "Large eddy simulations of gravity currents over an erodible bed with suspended sediment transport". Doctoral thesis, Università degli Studi di Trieste, 2018. http://hdl.handle.net/11368/2922531.
Pełny tekst źródłaStreszczenie:
Le correnti di gravità sono flussi prevalentemente orizzontali causati da variazioni di densità rispetto al fluido circostante. Tali flussi, possono scatenare il trasporto di notevoli volumi di sedimenti provocando così rapide deformazioni del letto dei corsi d’acqua, dei bacini causando importanti problemi di natura ambientale. Nonostante la rilevanza di tale fenomeno, non è ancora ben compreso il meccanismo che causa la ri-sospensione dei sedimenti.
Un nuovo modello idro-morfodinamico viene presentato nel presente lavoro di Tesi al fine di simulare i processi di trasporto dei sedimenti indotti dalla propagazione delle correnti di gravità su fondo mobile. L’idrodinamica del flusso è risolta mediante il modello LES-COAST, che utilizza il metodo Large-eddy mentre i cambiamenti morfologici causati dall’erosione e dalla deposizione sono simulati mediante il modello level-set. L’accoppiamento dei due strumenti modellistici è realizzato attraverso la strategia dei confini immersi. Il modello numerico accoppiato è stato sviluppato in ambiente parallelo, condizione che consente di simulare problemi a scala reale. Il modello è stato applicato alla simulazione della migrazione delle forme di fondo al fine di valutarne le capacità. I risultati ottenuti sono stati confrontati con i dati esito di un analogo studio numerico ed è emersa la capacità del modello di catturare correttamente l’idrodinamica dei flussi acqua-sedimento e i connessi mutamenti morfologici del fondo.
La sospensione dei sedimenti indotta dalle correnti di gravità è inizialmente simulata assumendo condizioni al contorno stazionarie e i risultati numerici sono validati con dati sperimentali. Le impostazioni numeriche adottate in questo caso permettono di indentificare la regione del flusso con maggiore capacità erosiva e determinare le condizioni del flusso che dominano la dinamica della sospensione dei sedimenti. Inoltre, è stato approfondito l’effetto dei sedimenti sospesi sulla condizione di stabilità della corrente di gravità nonché l’influenza di tale condizione sulla distribuzione dei sedimenti sospesi.
Infine, il modello accoppiato idro-morfodinamico è utilizzato per simulare le forme di fondo generate da tale tipologia di correnti. È importante notare che la propagazione di correnti di gravità con elevato potere erosivo su fondi mobili può causare notevoli deformazioni del letto che possono avere un effetto non trascurabile sulla dinamica del flusso. Per la prima volta sono state realizzate delle simulazioni numeriche 3D delle correnti di gravità che interessano letti deformabili. L’evoluzione istantanea dei pattern di erosione e deposizione sono quindi presentati, contribuendo così a una conoscenza più dettagliata dell’interazione flusso- sedimenti e flusso-fondo in correnti di gravità.Gravity currents are essentially horizontal flows driven by a density difference with respect to the ambient fluid. Such flows, can trigger the transport of large amounts of sediment resulting in rapid deformations on the bed of rivers and reservoirs, and causing important environmental issues. Despite the importance of such phenomena, the main mechanisms that lead to sediment entrainment in such flows are still poorly understood. In this thesis a coupled hydro-morphodynamic model is presented in order to simulate sediment transport processes induced by the propagation of gravity currents over erodible-beds. The hydrodynamics of the flow is resolved using the LES-COAST model, that employs the large eddy simulation method, and the topological changes due to erosion and deposition are tracked by the level-set method. The coupling between the two models is achieved through the immersed boundary methodology. The resulting hydro-moprhodynamic tool works in parallel environment that makes the simulation of real systems possible. This model is applied to the simulation of the ripple migration problem in order to test its capabilities. The obtained results are compared with data provided by a similar numerical study and indicate that the model is able to capture correctly the hydrodynamics of the sediment-laden flow and the related topological changes. The sediment pick-up induced by gravity currents is initially simulated assuming stationary flow boundaries and the numerical results are validated by experimental data. The numerical setting considered in this case allows to identify the region of the flow with higher erosive capacity and determine the flow features which play a dominant role on the sediment entrainment. Moreover, the effect of the suspended sediment on the stability condition of the gravity current is examined, along with the influence of the latest on the suspended sediment distribution. Finally, the developed hydro-morphodynamic model is used to simulate the bed forms generated by such flows. It is worth-noting that the propagation of highly erosive gravity currents over loose beds can lead to considerable bed deformation that significantly influence the flow dynamics. For the first time, 3D numerical simulations of gravity currents flowing over a deformable beds are performed. The instantaneous evolution of the generated scour and deposition patterns is presented providing a better insight on the flow-sediment and flow-bed interaction in buoyancy driven flows.
25
Gromov, Andrey. "Impedance of Soft Magnetic Multilayers : Application to GHz Thin Film Inductors". Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3135.
Pełny tekst źródła
26
Skutt, Glenn R. "High-Frequency Dimensional Effects in Ferrite-Core Magnetic Devices". Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30596.
Pełny tekst źródłaStreszczenie:
MnZn ferrites are widely used in power electronics applications where the switching frequency is in the range of several tens of kilohertz to a megahertz. In this range of frequencies the combination of relatively high permeability and relatively low conductivity found in MnZn ferrite helps to minimize the size of magnetic devices while maintaining high efficiency. The continuing improvement in semiconductor switches and circuit topologies has led to use of high-frequency switching circuits at ever increasing power levels. The magnetic devices for these high-power, high-frequency circuits require magnetic CORES that are significantly larger than standard ferrite-core devices used at lower power levels. Often such large ferrite cores must be custom designed, and at present this custom design is based on available material information without regard for the physical size of the structure.
This thesis examines the issues encountered in the use of larger MnZn ferrite cores for high-frequency, high-power applications. The two main issues of concern are the increased power dissipation due to induced currents in the structure and the change in inductance that results as the flux within the core is redistributed at higher frequencies. In order to model these problems using either numerical or analytical methods requires a reliable and complete set of material information. A significant portion of this work is devoted to methods for acquiring such material information since such information is not generally available from the manufacturers. Once the material constants required for the analysis are determined, they are used in both closed-form and numerical model to illustrate that large ferrite cores suffer significant increases in loss and significant decreases in inductance for frequencies as low as several hundred kilohertz. The separate impacts of the electrical and magnetic losses in the core are illustrated through the use of linear finite element analyses of several example core structures. The device impedances calculated using the FEA tools show fair agreement with measurement. An analysis of gapped structures and segmented cross-sections shows that these design options can reduce the severity of the dimensional problems for some designs.Ph. D.
27
Heger, Walter. "Using the finite difference and the finite element method to solve an electric current diffusion problem". Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66150.
Pełny tekst źródła
28
Sorger, Luís Gonçalo Lourenço. "Characterization of processed materials by electrical currents: development of equipment and applications". Master's thesis, Faculdade de Ciências e Tecnologia, 2014. http://hdl.handle.net/10362/12180.
Pełny tekst źródłaStreszczenie:
Dissertação para obtenção do Grau de Mestre em
Engenharia MecânicaStructural characterization of welded or processed materials is critical for a correct assessment of their properties. Microstructural analysis by optical microscopy provides information to identify the distinctive zones, their extent and the major transformations induced. For structural analysis, hardness is the simplest property to measure, providing information on the existence of ductile or brittle zones in the material. Furthermore, it can be qualitatively correlated to yield strength. However, these techniques are time consuming and destructive and, therefore, there is need for new, dedicated, preferably non-destructive, characterization methods. The same changes in properties and structure, due to welding and processing, also alter the electrical conductivity of materials. In fact, studies have demonstrated a relation between microstructure and conductivity of friction stir processed Al alloys, relating decreases in this property to the increase in the barriers to electron mobility due to the refined grain of the dynamically recrystallized zone, while the opposite occurs in heat affected zones were grain growth exists. The aim of this thesis was to apply eddy currents electrical conductivity characterization techniques to a wider range of materials, and develop equipment for an alternative electrical current evaluation method, namely, four-point probe potential drop measurements. A prototype for an automated four-point probe electrical conductivity characterization equipment was designed, built and successfully tested. Electrical conductivity characterization techniques, by eddy currents, have been applied to different metallic materials(AISI 1020, AISI 304, AZ31, Ti Grade 5, Ti Grade 2, Lead and Copper) processed by solid-state (Friction Stir Processing (FSP)) and fusion (Metal Active Gas (MAG) and Tungsten Inhert Gas (TIG)) to evaluate the effects on their electrical conductivity profiles and compare them with the hardness profiles and the microstructural features. Results show that the electrical conductivity variations that occur due to welding and processing can be related to the hardness and the microstructure of materials and, depending on the material, this relation can be direct or inverse.
29
OLIVO, MATTEO. "Efficient Methods for the Study of Eddy-Currents Effects in Medium-Voltage Rotating Electrical Machines". Doctoral thesis, Università degli Studi di Trieste, 2020. http://hdl.handle.net/11368/2960316.
Pełny tekst źródłaStreszczenie:
Lo scopo di questa tesi è presentare alcuni metodi efficienti (dal punto di vista computazionale) per il calcolo degli effetti dovuti alle correnti parassite (eddy currents) in macchine elettriche rotanti in media tensione. Due applicazioni in particolare sono state considerate nel dettaglio.
Inizialmente viene analizzato il fenomeno delle correnti parassite indotte nell'albero di motori asincroni a due poli e il conseguente effetto sulle prestazioni della macchina, focalizzandosi in particolare sul fattore di potenza. La seconda parte della tesi concentra la sua attenzione sullo studio dell'avviamento da rete di motori sincroni con rotore massiccio.
Per ciascuna applicazione vengono introdotte alcune procedure di calcolo, facenti uso di opportuni modelli numerici basati sul metodo degli elementi finiti, per mezzo delle quali vengono adeguatamente calcolati i parametri dei circuiti equivalenti di macchina, tenendo conto degli effetti legati alle correnti parassite. I modelli numerici sono opportunamente definiti, in modo tale da ridurre al massimo la complessità delle geometrie e il conseguente onere computazionale.
I risultati delle procedure innovative qui proposte sono confrontati con i dati provenienti da prove sperimentali sulle macchine oggetto di studio e con analoghi risultati di calcolo dedotti tramite le procedure comunemente utilizzate. Il confronto fra questi dati ha dimostrato che gli approcci di calcolo introdotti in questa tesi permettono di ottenere risultati con un elevato livello di accuratezza e una netta riduzione dell'onere computazionale.The efficient computation of eddy-current effects in medium voltage electric machines is discussed in this dissertation. Two particular cases are considered. Firstly, the effects of shaft eddy-currents on two-pole induction motor performance is addressed, with special focus on the power factor. In the second part of the thesis the start-up calculation of a large synchronous motor with solid rotor is analyzed. For each application a special calculation procedure is introduced. These procedures adopt a set of suitable finite-element models to properly compute the machine equivalent circuit parameters that are mainly influenced by eddy-current-related phenomena. By suitably choosing finite-element models boundary conditions and excitations their geometry is simplified to the maximum possible extent, in order to reduce the computational burden. The results of the new calculation methods are compared with experimental data and with analogous results obtained from commonly-adopted calculation procedures. The comparison proves that the proposed approaches can lead to high accuracy levels with very remarkable computational savings.
30
Jones, Travis Hamilton. "Analysis and Optimization of Eddy Current Detection in Animal Tissue". The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1398919426.
Pełny tekst źródła
31
Chen, Chen. "Simulation, design and experimental validation of a passive magnetic damper for ultra-fast actuators". Thesis, KTH, Elektroteknisk teori och konstruktion, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-153639.
Pełny tekst źródłaStreszczenie:
A contact system driven by a high energetic Thomson actuator requires to be decelerated from full speed down to zero. The forces originated from the interaction between a stationary copper tube and a moving array of magnets combined with plastic or ferromagnetic material are used to generate eddy-current damping. Five different configurations of small but strong (N52) neodymium magnets and spacers were benchmarked for simple free-fall damping. A comparison between experimental results and simulations (using COMSOL) has shown that the most effective damping is reached by two consecutive permanent magnets with opposite magnetization directions ,separated by low-carbon content steel concentrators(SN - Fe concentrator- NS). The proposed damper design is the result of the balance between various parameters such as magnet orientation topology in the array, spacer material and its dimensions, copper tube thickness and the air gap between copper tube and array. Furthermore, the design was scaled up and an actuator-drive system was added to perform more realistic tests, which demonstrated the damping effectiveness on a fast moving armature actuated by a Thomson coil energized by a capacitor bank. All models in the simulation predicted the damping effect in advance. Investigations were conducted with two cases: (1) A solid copper rod was supposed to pass through the magnet array; (2) A plastic shaft was applied to support the magnet array. Finally a damping prototype with a plastic shaft was built for completing damping tests. The results of these tests validated the numerical model with a high degree of accuracy.
32
Денисов, Станіслав Іванович, Станислав Иванович Денисов, Stanislav Ivanovych Denysov, Ганна Валеріївна Бабич, Анна Валерьевна Бабич, Hanna Valeriivna Babych, Людмила Анатоліївна Денисова, Людмила Анатольевна Денисова, Liudmyla Anatoliivna Denysova i Ye A. Peredriy. "Effective Landau-Lifshitz-Gilbert Equation for a Conducting Nanoparticle". Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35362.
Pełny tekst źródłaStreszczenie:
We study the role of conductivity in the magnetization dynamics of single-domain ferromagnetic particles.
Our approach is based on the coupled system of Maxwell’s and Landau-Lifshitz-Gilbert (LLG) equations
that describes both the induced electromagnetic field and the magnetization dynamics. We show that
the effective LLG equation for a conducting particle contains two additional terms compared to the ordinary
LLG equation. One of these terms accounts for the magnetic field of eddy currents induced by an external
magnetic field, and the other is magnetization dependent and is responsible for the conductivity
contribution to the damping parameter. By analytically solving Maxwell’s equations, we determine this
contribution and demonstrate the importance of conduction effects for large nanoparticles.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35362
33
Foley, Brian M. "A System for Detecting the Position of a Molten Aluminum Metal-Front within a Precision Sand Mold". Digital WPI, 2009. https://digitalcommons.wpi.edu/etd-theses/50.
Pełny tekst źródłaStreszczenie:
Manufacturers of cast metal parts are interested in the development of a feedback control system for use with the Precision Sand-Casting (PSC) process. As industry demands the ability to cast more complex geometries, there are a variety of challenges that engineers have to address. Certain characteristics of the mold, such as thick-to-thin transitions, extensive horizontal or flat surfaces, and sharp corners increase the likelihood of generating defective casts due to the turbulent metal-flow during fills. Consequently, it is critical that turbulent flow behavior within the mold be minimized as much as possible. One way to enhance the quality of the fill process is to adjust the flow rate of the molten metal as it fills these critical regions of the mold. Existing systems attempt to predict the position of the metal level based on elapsed time from the beginning of the fill stage. Unfortunately, variability in several aspects of the fill process makes it very difficult to consistently predict the position of the metal front. A better approach would be to embed a sensor that can detect the melt through a lift-off distance and determine the position of the metal-front. The information from this sensor can then be used to adjust the flow rate of the aluminum as the mold is filled. This thesis presents the design of a novel non-invasive sensor monitoring system. When deployed on the factory floor, the sensing system will provide all necessary information to allow process engineers to adjust the metal flow-rate within the mold and thereby reduce the amount of scrap being produced. Moreover, the system will exhibit additional value in the research and development of future mold designs.
34
Ribbenfjärd, David. "A lumped element transformer model including core losses and winding impedances". Licentiate thesis, KTH, School of Electrical Engineering (EES), 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4307.
Pełny tekst źródłaStreszczenie:
In order to design a power transformer it is important to understand its internal electromagnetic behaviour. That can be obtained by measurements on physical transformers, analytical expressions and computer simulations. One benefit with simulations is that the transformer can be studied before it is built physically and that the consequences of changing dimensions and parameters easily can be tested.
In this thesis a time-domain transformer model is presented. The model includes core losses as magnetic static hysteresis, eddy current and excess eddy current losses. Moreover, the model comprises winding losses including eddy currents, capacitive effects and leakage flux. The core and windings are first modelled separately and then connected together in a total transformer model. This results in a detailed transformer model.
One important result of the thesis is the possibility to simulate dynamic hysteresis including the eddy current shielding in the magnetic core material. This is achieved by using Cauer circuit combined with analytical expression for static and dynamic hysteresis. Thereby, all magnetic loss components in the material can be simulated accurately. This dynamic hysteresis model is verified through experiments showing very good agreement.
35
Almelah, Rema Bashir. "Ekman currents caused by variable wind in models of upper ocean with depth and time dependent eddy viscosity". Thesis, Keele University, 2018. http://eprints.keele.ac.uk/5601/.
Pełny tekst źródłaStreszczenie:
The work examines response of the upper ocean to time-varying winds. In the Ekman paradigm the effect of wind is considered as time-varying horizontally uniform tangential wind stress applied to the ocean surface and the turbulent diffusion of momentum is described employing the Boussinesq closure hypothesis via a single scalar eddy viscosity. In contrast to all previous studies we take into account both its depth and time dependence and examine effects of density strati�cation. We found exact general solution to the full Navier-Stokes equations which describes dynamics of the Ekman boundary layer in terms of the Green's function. Several cases of varying eddy viscosity have been examined: (a) According to the Zikanov et al. [2003] parameterization (justified by LES) the eddy viscosity in non-strati�ed fluid increases linearly with depth in the upper part of the fluid, reaching the maximum value at some depth specifi�ed by the wind speed, and then decreases linearly with depth in the lower layer. For this model the explicit analytic solution describing Ekman response to arbitrary wind has been obtained and thoroughly compared with the available models employing more simple eddy viscosity pro�les lacking the LES validation. The range of situations where much simpler models can be used with acceptable accuracy has been identi�fied. (b) We considered the simplest model of the upper ocean with mixed layer at the top and strati�fied fluid below, which in terms of the Ekman model reduces to a two-layer model: the top (turbulent) layer is characterized by a high constant value of eddy viscosity, while the bottom layer has a much smaller viscosity also assumed to be constant. Basic scenarios such as sharp increase of wind and switch o� of the wind have been analysed from the viewpoint of fi�nding how and when the vertical profi�le of strati�cation affects the surface current caused by wind varying in time. It has been found under what conditions the surface velocity vector is noticeably affected by the presence of strati�cation. The parameter controlling whether the presence of strati�cation will manifest itself on the surface is shown to be the non-dimensional depth of the pycnocline: the surface velocity �field is quite sensitive to the depth of the mixed layer, but is much less sensitive to the strength of strati�cation. From the perspective of remote sensing of the characteristics of strati�fication the using HF radars, it has been concluded that these fi�ndings open new possibilities. (c) When the eddy viscosity is assumed to be both time and depth dependent, three basic scenarios have been thoroughly examined: (i) An increase of wind ending up with a plateau; (ii) Switch-off of the wind; (iii) Periodic wind. Their analysis shows that accounting for time dependence of eddy viscosity substantially changes the response, compared to the predictions of the models with constant in time viscosity. We also report a severe limitation of the Ekman type models employed in modelling of the oceanic surface boundary layer. The Ekman current caused by a growing wind quickly becomes unstable with respect to inviscid inflectional instability. These instabilities are fast, which suggests spikes of dramatically enhanced mixing in the corresponding parts of the water column. The instabilities also break down a fundamental element of the Ekman-type models the assumed spatial uniformity. The results require a radical revision of the existing paradigm.
36
Koivula, A. (Antero). "Magnetic resonance image distortions due to artificial macroscopic objects:an example: correction of image distortion caused by an artificial hip prosthesis". Doctoral thesis, University of Oulu, 2002. http://urn.fi/urn:isbn:951426827X.
Pełny tekst źródłaStreszczenie:
Abstract
Eddy currents and susceptibility differences are the most important
sources that interfere with the quality of MR images in the presence of an
artificial macroscopic object in the volume to be imaged. In this study,
both of these factors have been examined.
The findings show that the RF field is the most important cause of
induced eddy currents when gradients with relatively slow slew rates are
used. The induced eddy currents amplify or dampen the RF field with the
result that the flip angle changes. At the proximal end in the vicinity of
the hip prosthesis surface, there have been areas where the flip angle is
nearly threefold compared to the reference flip angle. Areas with
decreased flip angles have also been found near the surface of the
prosthesis top. The incompleteness of the image due to eddy currents
manifests as signal loss areas.
Two different methods based on MRI were developed to estimate the
susceptibility of a cylindrical object. One of them is based on
geometrical distortions in SE magnitude images, while the other takes
advantage of phase differences in GRE phase images. The estimate value of
the Profile™ test hip prosthesis is χ = (170 ± 13)
10-6.
A remapping method was selected to correct susceptibility image
distortions. Correction was accomplished with pixel shifts in the
frequency domain. The magnetic field distortions were measured using GRE
phase images. The method was tested by simulations and by imaging a hip
prosthesis in a water tank and in a human pelvis. The main limitations of
the method described here are the loss of a single-valued correction map
with higher susceptibility differences and the problems with phase
unwrapping in phase images. Modulation transfer functions (MTF) were
exploited to assess the effect of correction procedure. The corrected
image of a prosthesis in a human hip after total hip arthroplasty appears
to be equally sharp or slightly sharper than the corresponding original
images.
The computer programs written for this study are presented in an
appendix.
37
Pinchuk, Amy Ruth. "Spectrally correct finite element analysis of electromagnetic fields". Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75780.
Pełny tekst źródłaStreszczenie:
Direct solution for three dimensional electric or magnetic field vectors throughout the frequency spectrum is accomplished by a finite element formulation which includes displacement and conduction currents, and requires no special treatment for material interfaces. Analysis of bus bar and Bath cube eddy current problems demonstrate the capabilities of the method.Spurious components in solutions to vector field problems are shown to corrupt deterministic solutions. These corruptions are identifiable with spurious modes familiar to high frequency modal analysis. Spectrally correct mixed order finite elements are demonstrated to retrieve accuracy in deterministic analyses.
The formulation may be limited by computer round-off at matrix assembly which affects the solenoidality of vector fields. Furthermore, extreme values encountered in low frequency eddy current analysis lead to ill conditioning and unreliable solutions. These numerical instabilities are overcome by parametric adjustment of permittivities. Error estimates are established to monitor inaccuracies introduced by permittivity adjustment.
38
Girardon, Hugo. "Shape reconstruction of deposits inside a steam generator using eddy current measurements". Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX086.
Pełny tekst źródłaStreszczenie:
Le contrôle non destructif est un outil essentiel pour évaluer la sûreté des infrastructures dans les centrales nucléaires. En particulier, la présence de dépôts conducteurs dans les tubes en U des générateurs de vapeur constitue un enjeu de la sûreté en bloquant le circuit d'eau secondaire. Pour détecter ces dépôts, des sondes à courants de Foucault sont insérées dans les tubes en U pour générer des courants et mesurer en retour un signal d'impédance. Pour inverser ces mesures et reconstruire la forme du dépôt, nous développons une méthode d'optimisation de forme avec descente de gradient régularisée. Du fait du caractère inconnu et possiblement complexe de la géométrie et de la topologie du dépôt, nous nous proposons de le modéliser par le biais d'une fonction level-set. La méthodologie est validée dans un premier temps sur des configurations axisymétriques artificielles et une rapide convergence est assurée par un choix réfléchi des paramètres de régularisation ainsi qu'une adaptation fine des pas de descente. En nous appuyant sur la configuration réelle dans laquelle sont réalisées les mesures expérimentales, nous considérons ensuite une modélisation plus réaliste incorporant la plaque entretoise ainsi que la présence d'imperfections sur la paroi intérieure du tube. Plus précisément, nous utilisons un modèle asymptotique pour prendre en compte ces imperfections et nous les traitons comme de nouvelles inconnues dans notre problème inverse. Une stratégie d'optimisation multi-critères se basant sur l'utilisation de différentes fréquences est ensuite développée pour résoudre le problème. Nous présentons différents résultats numériques sur des tests artificiels ou réels pour montrer la validité de note approche. Nous nous focalisons ensuite sur la transposition du modèle 2D-axisymétrique à des configurations 3D plus génériques. La résolution des équations de Maxwell en présence de courants de Foucault en 3D pose plusieurs problèmes de modélisation de part le choix de la formulation du problème ainsi que des coûts de calculs conséquents à réduire avant de pouvoir élaborer l'algorithme de reconstruction. Avec l'expérience acquise dans la reconstruction en 2D-axisymétrique, nous proposons ensuite une stratégie d'inversion efficace que nous mettons en œuvre sur des données artificielles 3D. La validation des exemples numériques prouve ainsi la faisabilité de l'inversion pour des problèmes de taille conséquente pour des coûts modérés et avec une bonne précision et robustesse par rapport au bruit et aux erreurs de modélisationNon-destructive testing is an essential tool to assess the safety of the facilities within nuclear power plants. In particular, conductive deposits on U-tubes in steam generators constitute a safety issue as they may block the cooling loop. To detect these deposits, eddy-current probes are introduced inside the U-tubes to generate currents and measuring back an impedance signal. We develop a shape optimization technique with regularized gradient descent to invert these measurements and recover the deposit shape. To deal with the unknown geometry, and its possibly complex topological nature, we propose to model it using a level set function.The methodology is first validated on synthetic axisymmetric configurations and fast convergence is ensured by careful adaptation of the gradient steps and regularization parameters. Using the actual domain, from which the acquisitions are made, we then consider a more realistic modeling that incorporates the support plate and the presence of imperfections on the tube interior section. We employ in particular an asymptotic model to take into account these imperfections and treat them as additional unknowns in our inverse problem. A multi-objective optimization strategy, based on the use of different operating frequencies, is then developed to solve this problem. We present various numerical examples with synthetic and experimental data showing the viability of our approach.The focus is then placed on the transposition of the 2D-axisymmetric work to more generic 3D configurations. Solving Maxwell eddy-current equations in 3D raises modeling issues related to the choice of the problem formulation as well as high computational costs that need to be reduced before discussing the reconstruction algorithm. Using the knowledge acquired with 2D-axisymmetric reconstruction, an efficient inversion strategy is then proposed and implemented on 3D synthetic data. Validating numerical examples demonstrate the feasibility of the inversion even for large data at a relatively moderate cost and with good accuracy and robustness with respect to noise and modeling errors
39
Marcusson, Birger. "Magnetic Leakage Fields and End Region Eddy Current Power Losses in Synchronous Generators". Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-331182.
Pełny tekst źródłaStreszczenie:
The conversion of mechanical energy to electrical energy is done mainly with synchronous generators. They are used in hydropower generators and nuclear plants that presently account for about 80% of the electric energy production in Sweden. Because of the dominating role of the synchronous generators, it is important to minimize the power losses for efficient use of natural resources and for the economies of the electric power companies and their customers. For a synchronous machine, power loss means undesired heat production. In electric machines, there are power losses due to windage, friction in bearings, resistance in windings, remagnetization of ferromagnetic materials, and induced voltages in windings, shields and parts that are conductive but ideally should be non-conductive. The subject of this thesis is prediction of end region magnetic leakage fields in synchronous generators and the eddy current power losses they cause. The leakage fields also increase the hysteresis losses in the end regions. Magnetic flux that takes paths such that eddy current power losses increase in end regions of synchronous generators is considered to be leakage flux. Although only a small fraction of the total magnetic flux is end region leakage flux, it can cause hot spots, discoloration and reduce the service life of the insulation on the core laminations. If unattended, damaged insulation could lead to electric contact and eddy currents induced by the main flux between the outermost laminations. That gives further heating and deterioration of the insulation of laminations deeper into the core. In a severe case, the core can melt locally, cause a cavity, buckling and a short circuit of the main conductors. The whole stator may have to be replaced. However, the end region leakage flux primarily causes heating close to the main stator conductors which makes the damage possible to discover by visual inspection before it has become irrepairable.
40
Kruse, Denise M. "Large eddy simulation of interactions between free convection, wind driven currents, and baroclinicity in Labrador Sea deep mixed layers". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA380272.
Pełny tekst źródłaStreszczenie:
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, June 2000.Thesis advisor(s): Guest, Peter ; Harcourt, Ramsey. "June 2000." Includes bibliographical references (p. 91-92). Also available online.
41
Mouton, Zac. "Modelling and design of an eddy current coupling for slip-synchronous permanent magnet wind generators". Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80114.
Pełny tekst źródłaStreszczenie:
Thesis (MScEng)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Slip-synchronous permanent magnet generators (SS-PMG) is a recently proposed direct-grid connected direct-drive generator topology for wind power applications. It combines a permanent magnet synchronous generator and a slip permanent magnet generator through a common permanent magnet rotor. In this study the possibility of using an eddy current coupling as the slip permanent magnet generator is investigated. The eddy current coupling has the attractive advantage of completely removing cogging and load torque ripple, which are known problems in the SS-PMG. However, the analytical modelling of the eddy current coupling is complex. Three different topologies are considered for the eddy current coupling. A finite element model is presented for the eddy current coupling. It is shown that 2D finite element methods are inaccurate compared to 3D finite element methods when solving eddy currents in eddy current couplings. In order to test the accuracy of the finite element modelling of a large eddy current coupling a prototype slip rotor is designed to operate with an existing permanent magnet rotor. Two topologies are optimally designed and compared for the slip rotor, using 3D finite element transient simulations. One of the designed topologies is used for the construction of the prototype slip rotor. The manufactured eddy current coupling allows for comparison between the 3D finite element simulations and measured results, which shows an excellent correlation. Based on observations of the 3D finite element simulations an analytical approximation of the eddy current coupling is proposed for low slip frequencies. It is shown that the analytical model is very dependent on the accurate modelling of the eddy current paths in the slip rotor, something that is difficult to determine accurately. An approximation is made, again based on 3D finite element simulations, which allows the accurate modelling of the current paths for different axial lengths. The analytical model is used for rapid design optimisation of both the slip rotor and permanent magnet rotor of the eddy current coupling, for two different eddy current coupling topologies. The optimised eddy current coupling design with the best results is compared to existing slip permanent magnet generator technologies. The eddy current coupling is shown to have the potential to be a feasible alternative to existing slip permanent magnet generator topologies for application in slip-synchronous permanent magnet generators. It has excellent torque versus slip behaviour, and no cogging or load torque ripple. However, the manufacturing and assembly process of the proposed slip rotor has to be improved for the eddy current coupling to be a realistic competitor to the existing slip permanent magnet generator technologies.
AFRIKAANSE OPSOMMING: Die glip-sinkroon permanente magneet generator is ʼn direk-aangedrewe wind generator wat direk aan die krag netwerk gekoppel kan word. Dit kombineer ʼn permanente magneet sinkroon generator en ʼn permanente magneet glip generator deur middel van ʼn gemeenskaplike permanente magneet rotor. In hierdie studie word die moontlike gebruik van ʼn werwelstroom skakel as plaasvervanger vir die permanente magneet glip generator ondersoek. Die werwelstroom skakel het geen vertandings of las draaimoment rimpeling nie, wat bekende probleme vir die glip-sinkroon permanente magneet generator is. Die analitiese modellering van die werwelstroom skakel is egter nie eenvoudig nie. Daar word drie verskillende topologieë oorweeg vir die werwelstroom skakel. ʼn Eindige element model word ontwikkel vir die werwelstroom skakel. Dit word bevind dat 2D eindige element analise onvoldoende is vir die berekening van werwelstrome in die werwelstroom skakel, en gevolglik word 3D eindige element modelle gebruik in hierdie studie. Om die akkuraatheid van die eindige element model te beproef word ʼn prototipe glip rotor optimaal ontwerp deur middel van eindige element analise. Die glip rotor vorm saam met ʼn bestaande permanente magneet rotor ʼn werwelstroom skakel. Vir hierdie ontwerp word twee werwelstroom skakel topologieë gebruik, en met mekaar vergelyk. Die topologie wat beter presteer word gebruik vir die vervaardiging van die glip rotor. ʼn Vergelyking van die gemete waardes van die vervaardigde werwelstroom skakel en die resultate van die 3D eindige element simulasies dui daarop dat die 3D eindige element modellering ʼn baie goeie voorspelling van die werklikheid is. ʼn Analitiese model vir die werwelstroom skakel onder lae glip toestande is ontwikkel deur gebruik te maak van observasies uit die 3D eindige element simulasies. Die analitiese model is baie afhangklik van die modellering van die werwelstrome se stroompaaie, iets wat moeilik is om akkuraat te bepaal. ʼn Benadering word gemaak wat die akkurate modulering van die stroompaaie moontlik maak vir verskillende aksiale lengtes. Die analitiese model word dan gebruik vir vinnige optimering van die werwelstroom skakel se ontwerp vir twee verskillende werwelstroom skakel topologieë. Die geoptimeerde ontwerp wat die beste resultate toon word vergelyk met bestaande permanente magneet glip generators. Dit word gewys dat die werwelstroom skakel die potensiaal het om ʼn uitvoerbare alternatief tot die permanente magneet glip generator te wees, vir gebruik in glip-sinkroon permanente magneet generators. Die werwelstroom skakel toon baie goeie draaimoment teenoor glip gedrag, en het geen vertandings of las draaimoment rimpeling nie. Voordat die werwelstroom generator ʼn realistiese kompeteerder teenoor die bestaande glip-sinkroon tegnologie is, moet daar verbeterde vervaardigings maniere gevind word vir die voorgestelde glip rotor.
42
McFerran, Jennifer. "An Electromagnetic Method for Cancer Detection". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1253558341.
Pełny tekst źródła
43
Pipis, Konstantinos. "Eddy-current testing modeling of axisymmetric pieces with discontinuities along the axis by means of an integral equation approach". Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS176/document.
Pełny tekst źródłaStreszczenie:
Le contrôle non destructif (CND) de pièces pour des applications dans l'industrie a mené au besoin de modèles rapides et précises. Tels modèles servent au développement des méthodes d'inspection, à l'optimisation des capteurs utilisés aux essais, à l'évaluation des courbes de Probabilité de Detection (POD) ainsi qu'à la caractérisation de défauts. Cette thèse se focalise au CND par Courants de Foucault (CF) de pièces cylindriques avec des discontinuités selon z et contenant un défaut fin. Un modèle pour l'inspection de telles pièces a été développé afin de traiter des applications comme l'inspection des pièces alésées trouvées en aéronautique et des tubes des générateurs de vapeur utilisés dans l'industrie nucléaire. Ce modèle est basé sur une formulation d'équation intégrale. Plus précisément, la variation de l'impédance du capteur, dit signal CF, est calculée à partir d'une équation intégrale sur la surface du défaut. La formulation suivie est basée sur la méthode d'intégration surfacique (SIM). Cette formulation nécessite, d'un côté, le calcul du champ électrique en absence du défaut et, de l'autre côté, l'expression d'une fonction de Green qui correspond à la géométrie de la pièce sans défaut. Les deux problèmes électromagnétiques sont résolus en utilisant la méthode Truncation Region Eigenfunction Expansion (TREE). La méthode TREE est un outil performant pour la résolution des problèmes électromagnétiques qui prend en compte la décroissance rapide de l'intensité du champ afin de tronquer le domaine d'intérêt à une distance, où le champ est négligeable.Le modèle est validé en comparant le signal CF calculé avec des résultats obtenues par une approche combinant la méthode d'intégration volumique (VIM) et SIM, dite l'approche VIM-SIM (implémentée dans la plateforme CIVA) ainsi qu'avec le modèle d'éléments finis (FEM). Nous avons traité trois configurations différentes : un demi-espace conducteur alésé avec un défaut fin, une plaque conductrice avec un alésage et un défaut, et un tube semi-infini avec un défaut fin à la proximité de son bord. La comparaison des résultats montre un très bon accord entre les trois modèles. Le temps de calcul avec le modèle SIM est considérablement inférieur aux temps de calcul des autres modèles. En outre, le modèle SIM donne la possibilité d'effectuer le balayage du capteur dans le tube ou l'alésage dans le cas des pièces aléséesNondestructive Testing (NDT) of parts for industrial applications such as in nuclear and aeronautical industry has led to the need for fast and precise models. Such models are useful for the development of the inspection methods, the optimisation of probes, the evaluation of the Probability of Detection (POD) curves or for the flaw characterisation.This PhD thesis focuses on the eddy-current NDT of layered cylindrical pieces with discontinuities in the z direction and containing a narrow crack. A model for the inspection of such pieces is developed in order to be applied on the inspection of fastener holes met in aeronautics and of steam generator tubes in nuclear sector.The model is based on an integral equation formalism. More precisely, for the calculation of the impedance change one needs to solve an integral equation over the surface of the narrow crack, which is represented by a surface electric dipole distribution. This is the method known as surface integration method (SIM). This formulation requires, on the one hand, the calculation of the electric field in the absence of the flaw, the so-called primary field, and, on the other hand, the Green's function expression corresponding to the geometry of the flawless piece. Both electromagnetic problems are solved by means of the Truncation Region Eigenfunction Expansion (TREE) method. The TREE method is a powerful tool for the solution of electromagnetic problems which uses the rapid decrease of the field in order to truncate the region of interest at a distance where the field is negligible.The model is validated by comparing the results of the coil impedance variation with those obtained by an approach that combines the volume integral method (VIM) with SIM, known as VIM-SIM method, implemented in the commercial software CIVA and the finite element method (FEM) implementation in COMSOL software. Three different configurations have treated. The more general geometry of a conducting half-space with a borehole, a conducting plate with a borehole and a crack and a conducting semi-infinite tube with a crack near the edge. The results of the three models show good agreement between them. The computational time of the SIM model is significantly lower compared to previous models. Furthermore, another advantage of the SIM model is that it provides the possibility of a scan inside the borehole
44
Båvall, Lennart. "A measurement approach to determination of coating thickness with eddy currents and to a capacitive person detector for robot safety /". Linköping : Univ, 2004. http://www.bibl.liu.se/liupubl/disp/disp2004/tek843s.pdf.
Pełny tekst źródła
45
Walker, Rachel. "Large-eddy Simulation of the Inner Continental Shelf Under the Combined Effects of Surface Temperature Fluxes, Tidal Currents and Langmuir Circulation". Scholar Commons, 2015. https://scholarcommons.usf.edu/etd/5590.
Pełny tekst źródłaStreszczenie:
In a shallow shelf region, turbulent motion can have a major effect on coastal processes including ecosystem functioning, surface gas exchange and sediment resuspension. Many factors contribute to such turbulence; wind and wave forcing, buoyancy induced by surface heat fluxes and tidal forcing all play a key role in generating vertical mixing in this shallow region. Alongside these independent sources of turbulence, combinations thereof can lead to full-depth turbulent structures acting secondary to the mean flow and leading to enhanced vertical mixing throughout the entire water column.
Field and laboratory experiments can often prove to be costly and time consuming, and reproducing or maintaining the complex flow dynamics of real world ocean flows is a constant challenge to these methods of research. As such, those interested in developing realistic and useful models of the marine environment to further understand its behavior often rely on 3-dimensional mathematical modeling and simulation. In this dissertation, simulations will be presented of turbulent flow and associated vertical mixing in a domain representative of the shallow coastal ocean, sufficiently far off shore that the land-ocean boundary does not significantly affect the flow behavior. This will be done using a large-eddy simulation (LES) method; solving the governing Navier-Stokes equations over a finite grid designed to capture the large, energy containing turbulent scales, and modeling the smaller, sub-grid scales.
The simulations to be presented feature combinations of coastal forcing mechanisms which are either presently unexplored or the analysis of which has been hindered by the complexity of field measurements and the challenge of isolating independent causes of turbulent motion. This will include surface heat fluxes, tidal forcing and Langmuir (or wave) forcing, acting both in isolation and in conjunction with each other, in order to bridge existing gaps in knowledge and provide a more complete understanding of the generation of full-depth turbulent structures in this shallow coastal water column.
46
Combes, Vincent. "Upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34814.
Pełny tekst źródłaStreszczenie:
The upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary is explored using a high resolution ocean model for the last 60 years. Three ocean circulations have been modeled. From North to South, we investigate the dynamics of the Gulf of Alaska (GOA), the California Current System (CCS) and the Humboldt Current System (HCS, also known as the Peru-Chile Current System). The statistics of coastal waters transport are computed using a model passive tracer, which is continuously released at the coast. By looking at the passive tracer concentration distribution, we find that the Pacific Decadal Oscillation modulates the coastal variability of the GOA, the North Pacific Gyre Oscillation controls the upwelling of the CCS, while the El-Niño Southern Oscillation affects the upwelling of Peru and Chile mainly through coastally trapped Kelvin waves. Results also emphasize the key role of the mesoscale eddies in the offshore transport of coastal waters masses. The passive tracer experiments, performed in this study in the GOA, CCS, and HCS, therefore could provide a dynamical framework to understand the dynamics of the upwelling/downwelling and offshore transport of nutrient rich coastal water and to interpret how it responds to atmospheric forcing. This also could reinforce our interpretation (and therefore predictions) in the changes in vertical and offshore advection of other important biogeochemical quantities, essential in understanding ecosystem variability.
47
Oscarsson, Mattias. "Modelling and design approaches of magnetostrictive actuators". Licentiate thesis, Stockholm : Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4435.
Pełny tekst źródła
48
Akuetevi, Cataria Quam Cyrille. "Dynamics of turbulent western boundary currents at low latitudes, a numerical study". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU002/document.
Pełny tekst źródłaStreszczenie:
Les courants turbulents de bord ouest sont l'un des phénomènes les plus dominants des océans, il en existe aux faibles latitudes aussi. Ils sont caractérisés par une dynamique très turbulente avec une forte production d'énergie cinétique, et une forte variabilité interne. Plusieurs régions existent où les courants de bord ouest se rétrofléchissent (décollage de la côte) pour former des structures cohérentes: des anticyclones, des bursts (arrachements) et des dipoles. Circulant le long de la côte, les courants de bord ouest interagissent très fortement avec le bord ouest et la bathymétrie et sont donc un problème de couche limite. Cependant aucune étude du point de vue de la théorie de couche limite n'a été jamais été faite. Cette thèse aborde le problème d'un point de vue de couche limite par l'utilisation d'un modèle idéalisé "shallow water" à très haute résolution (2.5km) afin d'isoler et de comprendre les processus. Les résultats sont ensuite appliqués à des sorties de modèle réaliste Drakkar (~10km) basé sur le code NEMO. Le courant de Somali est ensuite pris pour cette applicationStrong western boundary currents are one of dominant features of the world oceans, also at low latitudes. They exhibit a turbulent dynamics and their region is a source of strong kinetic energy production and internal variability of the worlds oceans. Several places exists where the western boundary currents retrofect (i.e separation from the coast) and generate coherent structures as anticyclonic eddies, bursts and dipoles. The dynamics of turbulent western boundary currents has so far not been extensively studied in the viewpoint of turbulent boundary-layer theory. The approach followed in this thesis is to use a fine resolution (2.5km) reduced-gravity shallow water model to understand the turbulent boundary-layer processes and then apply these findings to the Ocean General Circulation Model NEMO in the Drakkar configuration (~10km). The case of the Somali Currentis considered for this application
49
Sun, Xin. "Flow characteristics in compound channels with and without vegetation". Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/7992.
Pełny tekst źródłaStreszczenie:
The flow characteristics in compound channels with and without vegetation on the floodplain were investigated experimentally and numerically in this thesis. Detailed measurements of velocity and boundary shear stress, using a Pitot tube and an acoustic Doppler velocimeter together with a Preston tube, were undertaken to understand the flow characteristics in compound channels. Eight no-rod cases, two emergent-rod cases and two submerged-rod cases were tested. Unsteady large eddies that occur in the shear layer were explored numerically with Large Eddy Simulation (LES) to identify its generation and its effects on the flow behaviors. Mean flow parameters were predicted using the quasi-2D model by considering the shear effect. Usirgg the data of depth-averaged velocity and boundary shear stress, the contributions of shear-generated turbulence and bed-generated turbulence to the Reynolds shear stress were identified, the apparent shear stress was calculated using the modified method of Shiono and Knight (1991) and the depth-averaged secondary current force was then obtained. Large eddies were important to the lateral momentum exchange in shallow non-vegetated compound channels and even in deep vegetated compound channels. In the compound channel with one-line rods at the floodplain edge, the secondary current forces were of opposite signs in the main channel and on the floodplain and the bed shear stress was smaller than the standard two-dimensional value of yHSo due to the vegetation effect, where y,H,So are the specific weight of water, water depth and bed slope respectively. In vegetated compound channels, the velocity patterns were different to those and the discharges were smaller than those in non-vegetated compound channels under similar relative water depth conditions. The anisotropy of turbulence was the main contribution to the generation of secondary currents in non-vegetated and vegetated compound channels, but the Reynolds stress term was more important in the vegetated compound channels. Results of cross spectra showed the mechanisms of the turbulent shear generation near the main channel-floodplain junction are due to large eddies in the non-vegetated compound channel and owing to wakes in the vegetated compound channel. LES results indicated that large eddies caused significant spatial and temporal fluctuations of velocity and water level in the compound channel and the instantaneousv alues of these flow parameters were significantly higher than the mean values. In vegetated compound channels, the flow moved from the main channel to the floodplain and from the floodplain to the main channel alternately. The characteristic frequencies of the large eddy were less than 1Hz which was consistent with the experimental data. The capability of the quasi-2D model to predict the 2D mean flow parameters in compound channels were assessed under different flow conditions and also improved by using the mean wall velocity as the boundary condition and appropriate values of the lateral gradient of the secondary current force. In the vegetated compound channels, new approaches were proposed to treat the drag force in the cases of oneline emergent rods at the floodplain edge and submerged rods on the floodplain.
50
Wills, Dominic. "Methods to quantify and reduce rotor losses in a solid rotor yoke permanent magnet machine". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4014.
Pełny tekst źródłaStreszczenie:
Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Certain types of electric machines are particularly susceptible to the proliferation of eddy currents flowing within the solid conducting regions in the rotor. Single-layer, non-overlapping windings within uneven open slots are some stator properties that can produce damaging, asynchronous magnetic field harmonics which manifest in the rotor as eddy currents. The ohmic losses caused by these eddy currents are a source of inefficiency and can cause a marked increase in the temperature of the rotor. This temperature rise can be dangerous for the magnets, which have to be kept within temperature limits to avoid partial or full demagnetization. The research work presented here is concerned with reducing the effect of eddy currents in the rotor magnets and solid rotor yoke of an electric machine. The work presents analytical methods to calculate the magnetic fields, eddy currents and solid loss in an electric machine due to current in the winding and due to the interaction of the permeance variation in the stator with the magnets in the rotor. A method is also suggested where the analytical theory can be used with a magnetostatic finite element solution to produce a transient solid loss result. The research work also investigates a method for optimal segmentation in both level and penetration, and provides some design suggestions. The work presents the method of partial magnet segmentation, which is a technique whereby thin incisions are made into the magnet material from one or both sides. Another method of partial rotor segmentation is also presented where the incisions are made into a portion of the magnet-facing solid yoke. These methods attempt to interrupt the flow of eddy currents and increase the resistance ‘seen’ by the eddy currents, while also keeping construction difficulty and cost to a minimum. The methods are verified using finite element calculations which are compared to measured results. The result is that partial magnet segmentation is a very useful, effective and practical method of segmenting magnets. The loss reduction profile can be similar to that of traditional full segmentation. The method of partial rotor segmentation also shows a large reduction in rotor power loss. With implementation of these methods on a test machine, one can expect an efficiency increase of more than 4 %
AFRIKAANSE OPSOMMING: Sekere tipes van elektriese masjiene is veral sensitief vir die vloei van werwelstrome in solied geleidende gebiede in die rotor. Enkellaag, nie-oorvleuelende wikkelings in oneweredige oop gleuwe is enkele stator eienskappe wat skadelike, asinchrone magneetveld harmonieke tot gevolg kan hê, wat as werwelstrome in die rotor manifesteer. Die ohmiese verliese wat deur hierdie werwelstrome teweeg gebring word is 'n bron van ondoeltreffendheid en kan lei tot 'n merkbare toename in die temperatuur van die rotor. Hierdie temperatuur styging hou gevaar in vir die magnete en moet binne temperatuur limiete gehou word om gedeeltlike of self volle demagnetisering te vermy. Die navorsing vervat in hierdie document is gemoeid met die vermindering van die effek van werwelstrome in die rotor magnete en in die soliede rotor juk van 'n elektriese masjien. Die werk bied analitiese metodes aan vir die berekening van die magneetvelde, werwelstrome en soliede verliese in ’n elektriese masjien as gevolg van strome in die wikkelings en die interaksie van die permeansie variasie van die stator met die magnete in die rotor. ’n Metode word ook voorgestel waar die analitiese teorie saam met ’n magnetostatiese eindige element oplossing gebruik word om ’n resultaat vir die oorgang soliede verliese te verkry. Die navorsingswerk ondersoek ook ’n metode vir die optimale segmentering in beide vlak sowel as penetrasie, en verskaf sekere ontwerp voorstelle. Die werk bied die metode aan van gedeeltelike magneet segmentering, wat 'n tegniek is waarvolgens dun insnydings gemaak word aan een of beide kante van die magneet materiaal. Nog ’n metode van gedeeltelike rotor segmentering word beskou waar die insnydings in in ’n gedeelte aan die magneetkant van die soliede rotor juk gemaak word. Hierdie metodes poog om die vloei van werwelstrome te onderbreek en die weerstand soos "gesien" deur die werwelstrome te verhoog, terwyl konstruksie kompleksiteit en koste tot ’n minimum beperk word. Die metodes word bevestig deur eindige element berekeninge wat met gemete resultate vergelyk word. Die gevolg is dat gedeeltelike magneet segmentering 'n baie nuttige, doeltreffende en praktiese metode van die segmentering van magnete is. Die verliesverminderingsprofiel van gedeeltelike segmentering kan soortgelyk wees aan dit van tradisionele volle segmentering. Die metode van gedeeltelike rotor segmentering toon ook 'n groot afname in rotor drywingsverlies. Met die implementering van hierdie metodes op ’n toetsmasjien, kan ’n mens ’n verhoging in benuttingsgraad verwag van meer as 4 %