Дисертації: "Magnetic field simulator"

1

Gieschen, Brian D. (Brian David) Carleton University Dissertation Engineering Electronics. "A two-dimensional steady-state finite difference simulator for semiconductor magnetic field sensors." Ottawa, 1995.

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2

Cui, Han. "Modeling, Implementation, and Simulation of Two-Winding Plate Inductor." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78301.

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Design of magnetic component is a key factor in achieving high frequency, high power-density converters. Planar magnetics are widely used in bias power supplies for the benefits of low profile and their compatibility with printed-circuit boards (PCB). The coupled inductors with winding layers sandwiched between two core plates are studied in this dissertation in order to model the self-inductance, winding loss, and core loss. The most challenging task for the plate-core inductor is to model the magnetic field with finite core dimensions, very non-uniform flux pattern, and large fringing flux. The winding is placed near the edge of the core to maximize the energy within the limited footprint and the amount of energy stored outside the core volume is not negligible. The proportional-reluctance, equal-flux (PREF) model is developed to build the contours with equal amount of flux by governing the reluctance of the flux path. The shapes of the flux lines are modeled by different functions that guided by the finite-element simulation (FES). The field from the flux lines enables calculation of inductance, winding loss, and core loss, etc. The inductance matrix including self-inductance and mutual inductance of a coupled inductor is important for circuit simulation and evaluation. The derivation of the inductance matrix of inductors with plate-core structure is described in Chapter 2. Two conditions are defined as common-mode (CM) field and differential-mode (DM) field in order to compute the matrix parameters. The proportional-reluctance, equal-flux (PREF) model introduced is employed to find the CM field distribution, and the DM field distribution is found from functions analogous to that of a solenoid's field. The inductance calculated are verified by flex-circuit prototypes with various dimensions, and the application of the inductance model is presented at the last with normalized parameters to cover structures within a wide-range. In circuit where coupled inductors are used instead of transformers, the phase shift between the primary and secondary side is not always 180 degrees. Therefore, it is important to model the winding loss for a coupled inductor accurately. The winding loss can be calculated from the resistance matrix, which is independent of excitations but only relates to the frequency and geometry. The methodology to derive the resistance matrix from winding losses of coupled inductors is discussed. Winding loss model with 2D magnetic field is improved by including the additional eddy current loss for better accuracy for the plate-core structures. The resistance matrix calculated from the model is verified by both measurement results and finite-element simulation (FES) of coupled-inductor prototypes. Accurate core loss model is required for designing magnetic components in power converters. Most existing core loss models are based on frequency domain calculation and they cannot be implemented in SPICE simulations. The core loss model in the time domain is discussed in Chapter 5 for arbitrary current excitations. An effective ac flux density is derived to simplify the core loss calculation with non-uniform field distribution. A sub-circuit for core loss simulation is established in LTSPICE that is capable of being integrated to the power stage simulation. Transient behavior and accurate simulation results from the LTSPICE matches very well with the FES results. An equivalent circuit for coupled windings is developed for inductors with significant fringing effect. The equivalent circuit is derived from a physical model that captures the flux paths by having a leakage inductor and two mutual inductors on the primary and secondary side. A mutual resistor is added to each side in parallel with one mutual inductor to model the winding loss with open circuit and phase-shift impact. Two time-varying resistors are employed to represent the core loss in the time-domain. The equivalent circuit is verified by both finite-element simulation (FES) and prototypes fabricated with flexible circuit.
Ph. D.

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3

Сергєєв, Дмитро Віталійович. "Імітатор магнітного поля для наносупутників". Bachelor's thesis, КПІ ім. Ігоря Сікорського, 2021. https://ela.kpi.ua/handle/123456789/44626.

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У даній роботі описано процес створення системи керування імітатором магнітного поля, який буде використовуватися для випробування підсистеми орієнтації та стабілізації наносупутників КПІ ім. Ігоря Сікорського. Розглянуто конструкцію та принцип роботи магнітних імітаторів. Проведений аналіз існуючих аналогів системи керування. За результатами аналізу прийнято рішення використовувати імпульсний метод регулювання та мостову схему регулятора. Розроблено структурну та принципову схему пристрою. Підібрані необхідні компоненти та створено експериментальний макет системи, для якого написано програмне забезпечення. Проведено випробування, під час якого виявлені значні пульсації струму у котушках імітатора. Для зменшення пульсацій розраховано та створено вихідний фільтр для драйвера котушки. Результати розрахунку підтверджені експериментальними даними.
This paper describes the process of creating a control system for a magnetic field simulator, which will be used to test the orientation and stabilization subsystem of nanosatellites of Igor Sikorsky Kyiv Polytechnic Institute. The design and principle of operation of magnetic simulators are considered. The analysis of existing analogues of the control system was carried out. Based on the results of the analysis, it was decided to use the pulse regulation method and the bridge circuit of the regulator. The structural and schematic diagrams of the device were developed. The necessary components were selected and an experimental system layout was created, for which software was written. A test was performed, during which significant current ripple in the simulator coils was detected. To reduce ripple, the output filter for the coil driver was calculated and created. The calculation results are confirmed by experimental data.

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4

Ueda, Hiroyuki. "Studies on low-field functional MRI to detect tiny neural magnetic fields." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263666.

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付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」
京都大学
新制・課程博士
博士(工学)
甲第23205号
工博第4849号
京都大学大学院工学研究科電気工学専攻
(主査)教授小林哲生, 教授松尾哲司, 特定教授中村武恒
学位規則第4条第1項該当
Doctor of Philosophy (Engineering)
Kyoto University
DFAM

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5

Schumacher, Kristopher Ray. "Direct numerical simulation of ferrofluid turbulence in magnetic fields /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9892.

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6

Wagner, Timothy A. (Timothy Andrew) 1974. "Field distributions within the human cortex induced by transcranial magnetic simulation." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86789.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.
Includes bibliographical references (leaves 120-125).
by Timothy A. Wagner.
S.M.

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7

Ozcan, Sinan. "Simulation of field controllable fluids with suspended ferrous particles in micro tubes." abstract and full text PDF (free order & download UNR users only), 2005. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1433348.

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8

Al, Kanale Ahmed. "Investigation of recovery of stellar magnetic field geometries from simulated spectropolarimetric data." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-316290.

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Powerful remote sensing techniques can covert time variability of polarization profiles of stellar spectral lines into vector magnetic fields maps of stellar surfaces. These techniques are widely applied to interpret observations but have been tested using only simplistic tests. It would be of interest to test magnetic inversion methods using polarization spectra simulated for realistic and physical models of stellar magnetic fields provided by recent 3D numerical simulations. Doppler Imaging is a method to reconstruct vector magnetic field maps of stellar surfaces from variation of polarization profiles. The work in this thesis presents numerical experiments to evaluate the performance of Magnetic Doppler Imaging (MDI) code INVERS10. The numerical experiments showed that in given high-resolution observations in four Stokes parameters, the code is capable of reconstructing magnetic field vector distributions, over the stellar surface, simultaneously and without any prior assumptions about the magnetic field geometry. Input data consists of polarization measurements in the line profiles and the reconstruction is performed by solving the regularized inverse problem. Right results were obtained by testing different type of models covering simple, complex and unusual complex magnetic field distribution. Whilst using incomplete Stokes parameter datasets containing only Stokes I and V profiles, the INVERS10 code was able to reconstruct a global stellar magnetic fields of only simple models and give accurate and reliable results. Testing the code with different inclination and azimuth angle successfully gave the lowest deviation when same values are used from the true map.

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9

Dadzis, Kaspars. "Modeling of directional solidification of multicrystalline silicon in a traveling magnetic field." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-117492.

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Melt flow plays an important role in directional solidification of multicrystalline silicon influencing the temperature field and the crystallization interface as well as the transport of impurities. This work investigates the potential of a traveling magnetic field (TMF) for an active control of the melt flow. A system of 3D numerical models was developed and adapted based on open-source software for calculations of Lorentz force, melt flow, and related phenomena. Isothermal and non-isothermal model experiments with a square GaInSn melt were used to validate the numerical models by direct velocity measurements. Several new 3D flow structures of turbulent TMF flows were observed for different melt heights. Further numerical parameter studies carried out for silicon melts showed that already a weak TMF-induced Lorentz force can stir impurities near to the complete mixing limit. Simultaneously, the deformed temperature field leads to an increase of the deflection of crystallization interface, which may exhibit a distinct asymmetry. The numerical results of this work were implemented in a research-scale silicon crystallization furnace. Scaling laws for various phenomena were derived allowing a limited transfer of the results to the industrial scale.

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10

Andreu, Segura Jordi. "Statistical Mechanics of Superparamagnetic Colloidal Dispersions Under Magnetic Fields." Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/113485.

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Les dispersions col·loïdals, un terme encunyat pel científic escocès Thomas Graham el 1861, han estat objecte d’interès en diferents àrees científiques durant més d'un segle. Una dispersió col·loïdal es caracteritza per l’existència d'una fase dispersa uniformement distribuïda dins un medi dispersiu. Diferents compostos entren dins aquesta categoria, com els aerosols (fum, boira, núvols o pols), les escumes, les emulsions (maionesa o llet) o els gels (mantega o melmelada). Les millores recents en la síntesi de partícules i l'estabilitat col·loïdal han impulsat la millora en el disseny de nous col·loides, conferint-los les propietats requerides en cada aplicació. Entre la gran varietat de dispersions col·loïdals (existents en la naturalesa o dissenyades per l'home), hem estudiat un tipus singular de dispersions on les partícules col·loïdals mostren un comportament superparamagnetic anomenades dispersions col·loïdals superparamagnètiques. En aquestes dispersions, sorgeixen característiques sorprenents quan un camp magnètic extern és aplicat, com a conseqüència del balanç entre les interaccions característiques entre col·loides i la interacció magnètica anisotròpica dipol-dipol entre les partícules col·loïdals constituents. Al llarg d'aquesta tesi s'ha utilitzat diferents models teòrics i de simulació per tractar diferents fenòmens que apareixen en aquestes dispersions col·loïdals superparamagnètiques. Per una banda, hem mostrat com l’aplicació de camps magnètics uniformes a aquestes dispersions indueix l’agregació reversible de les partícules superparamagnètiques. A la vista dels models teòrics i simulacions, hem proposat un nou criteri basat en les propietats físiques de les dispersions col·loïdals per predir la formació d'agregats, i la seva validesa s'ha discutit comparant el comportament predit amb resultats experimentals. Hem aportat evidencies de la existència d'un estat d'equilibri on els agregats assoleixen una distribució de mides estable, un fet ja suggerit amb anterioritat però establert sense prou claredat. També ens hem centrat en la descripció de la cinètica de creixement d'aquests agregats i en la seva implicació en diferents fenòmens observats experimentalment. La necessitat d'assolir escales de temps grans, com en certes situacions experimentals, ha motivat el desenvolupament de nous models i estratègies de simulació per reduir els temps de càlcul requerits en simulacions estàndard. Hem presentat un nou model de simulació que proporciona un mètode fiable i més ràpid per descriure la formació d'estructures en forma de cadena que apareixen en dispersions superparamagnètiques. El model ha estat validat comparant-ne els resultats obtinguts amb altres resultats de simulacions estàndard de Dinàmica de Langevin i s'ha aplicat a situacions experimentals, com ara el temps de relaxació T2 dels protons en solucions aquoses de nanopartícules superparamagnètiques. Mencionar també que aquest model de simulació ha estat implementat i el corresponent programari s’ha posat a disposició de la comunitat científica de forma gratuïta, concebut com una eina de simulació que pot ser ampliada fàcilment per resoldre altres problemes d’interès. Per altra banda, també hem discutit diferents efectes que sorgeixen com a conseqüència de l’aplicació de camps magnètics inhomogenis a aquestes dispersions superparamagnètiques. En concret, hem estudiat el moviment de les partícules magnètiques disperses en fluids a través de camps magnètics inhomogenis, el que es coneix com magnetoforesi. Per a tal efecte, hem centrat els esforços en la descripció de la separació magnètica de col·loides mitjançant l’aplicació de gradients de camp magnètic uniformes, des de dispersions superparamagnètiques a mescles de col·loides amb diferent resposta magnètica. Hem validat aquests models teòrics comparant-los amb simulacions per ordinador i n’hem discutit la seva utilitat comparant-ne les prediccions amb resultats experimentals. L’anàlisi racional d'aquests resultats proporciona un marc idoni per a millorar el disseny i el rendiment de diferents separadors magnètics, així com plantejar noves estratègies de separació, com per exemple la separació cooperativa en dispersions superparamagnètiques. Existeixen, encara, problemes oberts que esperem que aquest treball ajudi a afrontar com, per exemple, entendre la interconnexió entre les estructures induïdes en dispersions superparamagnètiques i la seva dinàmica d’agregació. Aquest és un aspecte important en una gran varietat d'aplicacions industrials i de laboratori com són els processos de separació magnètica, tractament d’aigües residuals i eliminació de contaminants, immunoassaigs en aplicacions clíniques o la creació de nous materials supramoleculars. Tanmateix, esperem que els resultats que es presenten al llarg d'aquest document encoratgin nous estudis dins el camp de col·loides magnètics, ja sigui perfeccionant els resultats i mètodes aquí presentats o contribuint al desenvolupament de noves estratègies per afrontar problemes encara per resoldre.
Colloidal dispersions, a term coined by the Scottish scientist Thomas Graham in 1861, have been the subject of interest in different scientific areas during more than a century. A colloidal dispersion is characterized by the existence of a dispersed phase uniformly distributed throughout a dispersion medium. Many different compounds fall in this category like aerosols (smog, fog, clouds or dust), foams, emulsions (mayonnaise or milk) or gels (butter or jelly). Recent improvements in particle synthesis and colloidal stability have boosted the controlled design of new colloids on demand, targeting the required properties for each application. Among the large variety of different colloidal dispersions (either found in nature or man-made), we have studied a singular type of such dispersions where the colloids have a superparamagnetic behavior called superparamagnetic colloidal dispersions. In these dispersions, surprising features arise under the application of an external magnetic field, as a consequence of the interplay between characteristic colloidal interactions and the anisotropic magnetic dipole-dipole interaction between their constituent colloidal particles. Along this thesis we have used different theoretical and simulation methods to discuss a number of phenomena appearing in superparamagnetic colloidal dispersions. On the one hand, we have shown that the application of a uniform magnetic field to such dispersions may induce the reversible aggregation of superparamagnetic particles. In view of theoretical models and computer simulations, a new criterion based on the physical properties of the colloidal dispersion has been proposed to predict the formation of aggregates, and its validity has been discussed by comparing the predicted behavior with experimental results. We have provided evidences of the existence of an equilibrium state, where aggregate sizes acquire a steady distribution, an issue previously suggested but unclear up to now. We have also focused our attention on the growth kinetics of the aggregates and its implications in different phenomena observed in experiments. The need to reach the large time scales of some experiments has motivated the development of new models and simulation strategies to overcome the large time consuming calculations required in standard simulations. We have presented a new simulation model that provides a faster and reliable approach to address the formation of chain-like structures in superparamagnetic dispersions. The model has been validated by direct comparison with standard Langevin Dynamics simulations and has been applied to experimental situations like the T2 relaxation time of protons in aqueous solutions of superparamagnetic nanoparticles. Let us mention that the simulation model has been implemented and the corresponding computer code is free and available to the scientific community, envisaged as a new modeling tool readily extensible to other problems of interest. On the other hand, we have analyzed different effects arising as a consequence of the application of inhomogeneous magnetic fields to such superparamagnetic dispersions. Specifically, we have studied the controlled motion of magnetic particles dispersed in a liquid medium by using inhomogeneous magnetic fields, what is known as magnetophoresis. To do so, we have focused the efforts on the description of the magnetic separation of colloids by the application of uniform magnetic field gradients, from superparamagnetic dispersions to mixtures of colloids with different magnetic response. We have validated the theoretical models adopted against computer simulations and we have discussed their usefulness by comparing the predictions obtained with experimental results. The rational analysis of these results provides a proper starting framework to enhance the design and performance of different magnetic separators, as well as to shape new separation strategies, like the cooperative magnetophoretic separation in superparamagnetic dispersions. There exists, of course, open problems that we hope this work will help to deal with. For instance, a better understanding of the interplay between the induced structures in superparamagnetic dispersions and their aggregation kinetics. This is an important issue in a vast variety of industrial and lab applications as, for example, in magnetic separation-based processes, waste-water treatment and pollutant removal, immunoassays in clinical applications or in the assisted assembly of new supramolecular materials. Nevertheless, we hope that the results presented along this document could encourage further studies in magnetic colloids science, either refining the results and approaches provided here or developing new strategies to face unsolved problems.

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11

Jiang, Yuxiang. "A Unipolar Pulse Electromagnetic Field Apparatus for Magnetic Therapy: Design, Simulation and Development." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37854.

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As a magnetic therapy apparatus with medical benefits, the Unipolar Pulse Electromagnetic Field (UPEMF) apparatus is presented to produce unipolar pulsed magnetic waveforms with an intensity, shape, and frequency that meet medical requirements. The unipolar pulse is the most significant advantage, as the implemented apparatus is considered to be the first improvement in Pulse Electromagnetic Fields (PEMFs). The magnetic field is generated by a specially designed electromagnetic unit. In this unit, an electromagnet is concentrated by a designed concentrator to strengthen the magnetic field at the north pole and weaken the field on the opposite end. An electromagnetic shield is adopted to eliminate the effects of the south pole but allow the output from the north pole. Excited by a designed pulsed waveform generator, the electromagnetic unit generates a strong alternating-current magnetic field. In my work, the detailed design and development of the electromagnetic unit for UPEMF are introduced, therein being modeled and tested using Finite Element Method simulations. The model is characterized mathematically in three parts: the concentrator, the electromagnetic shield, and the overall unit. The testing and performance measurements of the actual Unipolar Pulse Electromagnetic Field apparatus are achieved using a Gauss meter and oscilloscope.

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12

Mitma, Pillaca Elver Juan de Dios [UNESP]. "Estudo do comportamento magnético de plasma durante o processo de implantação iônica por imersão em plasma." Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/91826.

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Made available in DSpace on 2014-06-11T19:25:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-05Bitstream added on 2014-06-13T19:53:18Z : No. of bitstreams: 1 mitmapillaca_ejd_me_guara.pdf: 802438 bytes, checksum: be2c83ec017ba3f36efb9e9da538c9e6 (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Universidade Estadual Paulista (UNESP)
O estudo do efeito do campo magnético sobre o processo de implantação iônica por imersão em plasma (3IP) é de grande interesse para o tratamento de materiais. Sendo 3IP uma técnica relativamente nova e de grande relevância para diversas aplicações tecnológicas é importante que ela seja pesquisada e analisada detalhadamente. A aplicação de um campo magnético estático, transversal em relação ao campo elétrico formado durante este processo produz um sistema de campos cruzados ExB. Este sistema de campos cruzados gera um aumento significativo da densidade de plasma na vizinhança do alvo, resultando num maior corrente de implantação, e conseqüentemente um tratamento mais rápido e uma dose retida mais alta em relação ao processo 3IP convencional. Neste trabalho, analisamos mediante simulação numérica, o efeito da distribuição do campo magnético axial no processo 3IP. O campo magnético é produzido por um par de bobinas instaladas fora da câmara de vácuo cujos raios e distância de separação são variadas. Encontramos que a densidade de corrente de implantação depende essencialmente da configuração do campo magnético. Assim, com uma adequada configuração das bobinas (10,0 cm de raio e 42,0 cm de separação) obtivemos uma densidade de corrente quase uniforme de aproximadamente 1,5 mA/cm2 que é 1.5 vezes maior em relação ao caso do sistema 3IP sem campo magnético. O efeito da tensão aplicada assim como da pressão do gás sobre o plasma no processo 3IP é também investigado. O sistema 3IP com campos ExB cruzados é estudado utilizando a técnica de simulação numérica em duas dimensões. Esta simulação é realizada com o código computacional KARAT que emprega o algoritmo “particle-in-cell” (PIC) para simular o movimento de partículas carregadas no campo eletromagnético.
Detailed investigation of the effect of magnetic field on the process of plasma immersion ion implantation (PIII) is of great interest for the material treatment. Being a relatively novel and of great relevance for technological applications technique, the PIII demands further research and careful analysis. The application of static magnetic field, transversal in respect to the electric field established during this process, produces a system of crossed fields ExB. This system of crossed fields promotes an increase of the plasma density, resulting in higher implantation current, and consequently in a shorter treatment time and a higher retained dose in comparison to the conventional PIII process. In this work we have analyzed by means of numerical simulation the effect of magnetic field distribution on the PIII processing. The magnetic field is produced by a pair of external coils, whose radii and separation distance were varied. We found that the density of the implantation current essentially depends on the magnetic field configuration. Thus, with an appropriate configuration of the coils (10,0 cm radius and separation of 42,0 cm) we have obtained an almost uniform current density of approximately 1,5 mA/cm2 that is 1,5 times bigger in relation to the case PIII without magnetic field. The effect of the target bias as well as the gas pressure on the ion current incident on the target is also investigated. The PIII system with crossed ExB fields has been studied using two-dimensional numerical simulation. The simulation is accomplished by the computer code KARAT which employs the particle-in-cell (PIC) algorithm for simulating the movement of charged particles in the electromagnetic field.

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13

Zelda, Jan. "Generátor pro leteckou aplikaci HUMS." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254451.

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Presented diploma thesis deals with development of the autonomous electric energy source for Health and Usage Monitoring Systems placed at the rear part of a helicopter. Firstly, the HUMS systems were described briefly and the research of available energy sources was made after that. After that, the magnetic properties of the materials were described with the special focus on the permanent magnets. The draft also includes the creation of model of the magnetic field using the final element method. Prototype was assembled and the other design solutions were evaluated. The evaluation of various designs passed in the use of SOMA optimization algorithms. The generator is followed by the draft of the electronics, which streamlines and regulates a voltage supplied by the generator. At the end of the thesis, the complete source prototype was assembled and tested with two different regulators

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14

Yigitler, Huseyin. "Permanent Magnet Design And Image Reconstruction Algorithm For Magnetic Resonance Imaging In Inhomogeneous Magnetic Fields." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607627/index.pdf.

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Recently, the use of permanent magnets as magnetic field sources in biomedical applications has become widespread. However, usage of permanent magnets in magnetic resonance imaging (MRI) is limited due to their inhomogeneous magnetic field distributions. In this thesis, shape and geometry optimization of a magnet is performed. Moreover, placement of more than one magnet is optimized to obtain desired magnetic field distribution in specific region of space. However, obtained magnetic field distribution can not be used in the conventional MRI image reconstruction techniques. Consequently, an image reconstruction technique for MRI in inhomogeneous magnetic fields is developed. Apart from these, since any reconstruction technique requires signal data, an MRI simulator in inhomogeneous magnetic fields is constructed as a part of this thesis. Obtained results show that the theory developed in this thesis is valid. Consequently, new MRI devices that have permanent magnets as magnetic field sources can be constructed in the future.

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15

Hurtig, Tomas. "Plasma cloud penetration across magnetic boundaries." Doctoral thesis, KTH, Alfvén Laboratory, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3804.

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16

Boulware, Jeffrey C. "Experiment and Simulation on the Dynamics of a Slug of Liquid Oxygen Displaced by a Pulsed Magnetic Field." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/690.

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A magnetic fluid system could potentially replace mechanically moving parts in a satellite as a means of increasing system reliability and mission lifetime, but rather than a standard ferrofluid with magnetic particles, liquid oxygen (LOX) may be a more adequate working fluid. As a pure paramagnetic cryogen, LOX is already heavily used in space, but still requires basic research before being integrated into system development. The objectives of the research conducted were to verify LOX as a magnetic working fluid through experiment and establish a theoretical model to describe its behavior. This dissertation presents the theoretical, experimental, and numerical results of a slug of LOX being pulsed by a 1.1 T solenoid in a quartz tube with an inner diameter of 1.9 mm. The slug oscillated about the solenoid at 6-8 Hz, producing a pressure change of up to 1.2 kPa. System efficiency based on the Mason number was also studied for various geometric setups, and, using a one-dimensional, finite-differenced model in Matlab 2008a, the numerical analyses confirmed the theoretical model. The research provides groundwork for future applied studies with complex designs.

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17

Yarimpabuc, Durmus. "Numerical Simulation Of Thermal Convection Under The Influence Of A Magnetic Field By Using Solenoidal Bases." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613393/index.pdf.

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The effect of an imposed magnetic field on the thermal convection between rigid plates heated from below under the influence of gravity is numerically simulated in a computational domain with periodic horizontal extent. The numerical technique is based on solenoidal basis functions satisfying the boundary conditions for both velocity and induced magnetic field. The expansion bases for the thermal field are also constructed to satisfy the boundary conditions. The governing partial differential equations are reduced to a system of ordinary differential equations governing the time evolution of the expansion coefficients under Galerkin projection onto the subspace spanned by the dual bases. In the process, the pressure term in the momentum equation is eliminated. The system validated in the linear regime is then used for some numerical experiments in the nonlinear regime.

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18

Weeber, Rudolf [Verfasser], and Christian [Akademischer Betreuer] Holm. "Simulation of novel magnetic materials in the field of soft matter / Rudolf Weeber. Betreuer: Christian Holm." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2015. http://d-nb.info/106664585X/34.

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19

Mitma, Pillaca Elver Juan de Dios. "Estudo do comportamento magnético de plasma durante o processo de implantação iônica por imersão em plasma /." Guaratinguetá : [s.n.], 2007. http://hdl.handle.net/11449/91826.

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Orientador: Konstantin Georgiev Kostov
Banca: Joaquim José Barroso de Castro
Banca: Mario Ueda
Resumo: O estudo do efeito do campo magnético sobre o processo de implantação iônica por imersão em plasma (3IP) é de grande interesse para o tratamento de materiais. Sendo 3IP uma técnica relativamente nova e de grande relevância para diversas aplicações tecnológicas é importante que ela seja pesquisada e analisada detalhadamente. A aplicação de um campo magnético estático, transversal em relação ao campo elétrico formado durante este processo produz um sistema de campos cruzados ExB. Este sistema de campos cruzados gera um aumento significativo da densidade de plasma na vizinhança do alvo, resultando num maior corrente de implantação, e conseqüentemente um tratamento mais rápido e uma dose retida mais alta em relação ao processo 3IP convencional. Neste trabalho, analisamos mediante simulação numérica, o efeito da distribuição do campo magnético axial no processo 3IP. O campo magnético é produzido por um par de bobinas instaladas fora da câmara de vácuo cujos raios e distância de separação são variadas. Encontramos que a densidade de corrente de implantação depende essencialmente da configuração do campo magnético. Assim, com uma adequada configuração das bobinas (10,0 cm de raio e 42,0 cm de separação) obtivemos uma densidade de corrente quase uniforme de aproximadamente 1,5 mA/cm2 que é 1.5 vezes maior em relação ao caso do sistema 3IP sem campo magnético. O efeito da tensão aplicada assim como da pressão do gás sobre o plasma no processo 3IP é também investigado. O sistema 3IP com campos ExB cruzados é estudado utilizando a técnica de simulação numérica em duas dimensões. Esta simulação é realizada com o código computacional KARAT que emprega o algoritmo "particle-in-cell" (PIC) para simular o movimento de partículas carregadas no campo eletromagnético.
Abstract: Detailed investigation of the effect of magnetic field on the process of plasma immersion ion implantation (PIII) is of great interest for the material treatment. Being a relatively novel and of great relevance for technological applications technique, the PIII demands further research and careful analysis. The application of static magnetic field, transversal in respect to the electric field established during this process, produces a system of crossed fields ExB. This system of crossed fields promotes an increase of the plasma density, resulting in higher implantation current, and consequently in a shorter treatment time and a higher retained dose in comparison to the conventional PIII process. In this work we have analyzed by means of numerical simulation the effect of magnetic field distribution on the PIII processing. The magnetic field is produced by a pair of external coils, whose radii and separation distance were varied. We found that the density of the implantation current essentially depends on the magnetic field configuration. Thus, with an appropriate configuration of the coils (10,0 cm radius and separation of 42,0 cm) we have obtained an almost uniform current density of approximately 1,5 mA/cm2 that is 1,5 times bigger in relation to the case PIII without magnetic field. The effect of the target bias as well as the gas pressure on the ion current incident on the target is also investigated. The PIII system with crossed ExB fields has been studied using two-dimensional numerical simulation. The simulation is accomplished by the computer code KARAT which employs the particle-in-cell (PIC) algorithm for simulating the movement of charged particles in the electromagnetic field.
Mestre

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20

Flaux, Pierrick. "Measurement of the neutron electric dipole moment at the Paul Scherrer Institute : production of magnetic fields." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMC222/document.

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Le travail réalisé au cours de cette thèse concerne le développement du système de bobines de l'expérience n2EDM à l'Institut Paul Sherrer (PSI). Le but de cette expérience est de mettre en évidence de nouvelles sources de violation CP à travers la mesure du moment dipolaire électrique du neutron. L'actuelle limite supérieure sur la mesure de nEDM, $2.9 \cross 10^{-26}$ e.cm (90\% C.L.) à été obtenue par la collaboration RAL-Sussex-ILL en 2006.L'expérience n2EDM vise à améliorer d'un ordre de grandeur la sensibilité statistique en gardant sous contrôle les effets systématiques. Cela requiert la production d'un champ magnétique très uniforme. Les non-uniformités de ce dernier sont en effet responsable de la dépolarisation des neutrons et impliqués dans plusieurs effets systématiques.Dans le premier chapitre, les motivations physiques sont discutées.Le second chapitre décrit le principe de mesure de l'expérience n2EDM, ainsi que l'importance de l'uniformité du champ magnétique. Le chapitre s'achève par une présentation globale du dispositif expérimental.Le troisième chapitre présente le logiciel COMSOL et discute du design et des performances de la bobine B$_{0}$, en charge de la production du champ magnétique principal.Dans le quatrième chapitre, le système de bobines correctrices chargées de corriger les non-uniformités du champ magnétique et celles devant produire des gradients spécifiques sont présentées.Finalement, le cinquième et dernier chapitre présente l'étude des dipôles magnétiques localisés et de leur influence sur l'expérience
This work presents the design of the coils system developed for the n2EDM experiment at the Paul Sherrer Institute (PSI). The goal of this experiment is to reveal new sources of CP violation through the measurement of the neutron electric dipole moment. The current upper limit of the nEDM measurement, $2.9 \cross 10^{-26}$ e.cm (90\% C.L.) was achieved by the RAL-Sussex-ILL collaboration in 2006.The n2EDM experiment aims at improving by one order of magnitude the statistical sensitivity while keeping under control the systematics effects. It requires to produce a very uniform field, its non-uniformities being responsible of the neutron's depolarization and of severals systematic effects.In the first chapter, the theoretical motivation are discussed.The second chapter describes the measurement principle of the n2EDM experiment, as well as the importance of the magnetic field uniformity. This chapter ends by an overview of the apparatus.The third chapter introduces the COMSOL software and discuss the design and the performances of the B0 coil, in charge of the production of the main magnetic field.In the fourth chapter, the correcting coils used to suppress the non-uniformities of the magnetic field and the ones which produce specific gradients are presented.Finally, the fifth and last chapter talks about the study of localised magnetic dipoles and their influence on the experiment

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21

Gupta, Aditya. "SIGNAL PROCESSING OF AN ECG SIGNAL IN THE PRESENCE OF A STRONG STATIC MAGNETIC FIELD." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2206.

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This dissertation addresses the problem of elevation of the T wave of an electrocardiogram (ECG) signal in the magnetic resonance imaging (MRI). In the MRI, due to the strong static magnetic field the interaction of the blood flow with this strong magnetic field induces a voltage in the body. This voltage appears as a superimposition at the locus of the T wave of the ECG signal. This looses important information required by the doctors to interpret the ST segment of the ECG and detect diseases such as myocardial infarction. This dissertation aims at finding a solution to the problem of elevation of the T wave of an ECG signal in the MRI. The first step is to simulate the entire situation and obtain the magnetic field dependent T wave elevation. This is achieved by building a model of the aorta and simulating the blood flow in it. This model is then subjected to a static magnetic field and the surface potential on the thorax is measured to observe the T wave elevation. The various parameters on which the T wave elevation is dependent are then analyzed. Different approaches are used to reduce this T wave elevation problem. The direct approach aims at computing the magnitude of T wave elevation using magneto-hydro-dynamic equations. The indirect approach uses digital signal processing tools like the least mean square adaptive filter to remove the T wave elevation and obtain artifact free ECG signal in the MRI. Excellent results are obtained from the simulation model. The model perfectly simulates the ECG signal in the MRI at all the 12 leads of the ECG. These results are compared with ECG signals measured in the MRI. A simulation package is developed in MATLAB based on the simulation model. This package is a graphical user interface allowing the user to change the strength of magnetic field, the radius of the aorta and the orientation of the aorta with respect to the heart and observe the ECG signals with the elevation at the 12 leads of the ECG. Also the artifacts introduced due to the magnetic field can be removed by the least mean square adaptive filter. The filter adapts the ECG signal in the MRI to the ECG signal of the patient outside the MRI. Before the adaptation, the heart rate of the ECG outside the MRI is matched to the ECG in the MRI by interpolation or decimation. The adaptive filter works excellently to remove the T wave artifacts. When the cardiac output of the patient changes, the simulation model is used along with the adaptive filter to obtain the artifact free ECG signal.
Ph.D.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering PhD

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22

Vilppola, J. H. (Jari Heikki). "Solar wind:detection methods and long-term fluctuations." Doctoral thesis, Oulun yliopisto, 2003. http://urn.fi/urn:isbn:9514271955.

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Abstract The Cassini/Huygens mission is a collaborative mission of NASA and ESA to study the Saturnian system. Cassini Plasma Spectrometer (CAPS)is one of the scientific investigations onboard the Cassini orbiter. It consists of three separate spectrometers: Electron Spectrometer (ELS), Ion Mass Spectrometer (IMS) and Ion Beam Spectrometer (IBS). The University of Oulu has a co-investigator status in the CAPS project, and been mainly involved in simulating the structure and scientific performance of the IBS instrument. IBS is a high resolution hemispherical electrostatic analyser aimed to study the solar wind ions. This thesis contains an Introduction and five original papers. Papers I–III contain a detailed description of the simulation process of the IBS instrument and related results. In Paper I the manufacturing tolerances were calculated in order to verify that the high resolution requirements can be achieved using available manufacturing processes. In Paper II the simulations have been further developed and the instrument properties have been studied in more detail. In Paper III the simulation model is used to help the analysis and interpretation of the laboratory calibrations of the IBS flight model. Papers IV and V study the long-term fluctuations in solar wind and interplanetary magnetic field in the period range of 1–2 years (so called mid-term quasi periodicities, MTQP), using the wavelet transformation method to produce dynamic power spectra. In paper IV the MTQP structure in solar wind speed at 1 AU was studied using the longest available series of geomagnetic activity. It was shown that the long-term occurrence MTQP fluctuations roughly follows the long-term solar activity, suggesting that MTQP fluctuations are closely connected with the solar dynamo activity. Moreover, it was also noted that MTQP activity may offer a possibility for a precursory signal which could be used to predict significant changes in long-term solar activity. While Paper IV presents the temporally longest study of MTQP fluctuations, Paper V gives the spatially widest treatment of the same phenomenon. Paper V studies MTQP fluctuations in solar wind and interplanetary magnetic field measured by four probes in the outer heliosphere. It is shown that two MTQP fluctuations of different periods (1.3 and 1.7 years)co existed during solar cycle 22, while during solar cycle 21 only the 1.7-year band existed. This suggests that the solar dynamo acts differently during even and odd cycles. It is also shown that the two MTQP fluctuations during solar cycle 22 are organized latitudinally. While the 1.3-year periodicity originates from equatorial regions, the 1.7-year fluctuations arise at mid-latitudes
Original papers Original papers are not included in the electronic version of the dissertation. Vilppola, J. H., Keisala, J. T., Tanskanen, P. J., & Huomo, H. (1993). Optimization of hemispherical electrostatic analyzer manufacturing with respect to resolution requirements. Review of Scientific Instruments, 64(8), 2190–2194. https://doi.org/10.1063/1.1143958 Vilppola, J. H., Tanskanen, P. J., Huomo, H., & Barraclough, B. L. (1996). Simulations of the response function of a plasma ion beam spectrometer for the Cassini mission to Saturn. Review of Scientific Instruments, 67(4), 1494–1501. https://doi.org/10.1063/1.1146881 Vilppola, J. H., Tanskanen, P. J., Barraclough, B. L., & McComas, D. J. (2001). Comparison between simulations and calibrations of a high resolution electrostatic analyzer. Review of Scientific Instruments, 72(9), 3662–3669. https://doi.org/10.1063/1.1392337 Mursula, K., Zieger, B., & Vilppola, J. H. (2003). Mid-term quasi-periodicities in geomagnetic activity during last 15 solar cycles: Connection to solar dynamo strength. Solar Physics, 212(1), 201–207. https://doi.org/10.1023/a:1022980029618 Mursula, K., & Vilppola, J. H. (2004). Fluctuations of the Solar Dynamo Observed in the Solar Wind and Interplanetary Magnetic Field at 1 AU and in the Outer Heliosphere. Solar Physics, 221(2), 337–349. https://doi.org/10.1023/b:sola.0000035053.17913.26

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23

Favrot, Gervais F. (Gervais Freret) 1948. "Magnetic field reversal effect in inter-Landau level absorption and simulated spin-flip Raman scattering in n-type InSb." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/47697.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1998.
Includes bibliographical references (p. 187-193).
This thesis is a theoretical and experimental study of inter-Landau level transitions in n-type InSb. Three main topics are considered: (i) The first observation was made of a magnetic field reversal effect in a spin-conserving inter-Landau level absorption transition. (ii) Advancements were made in the theory of intraband absorption and scattering processes. (iii) Experiments were carried out on the spin-flip Raman laser to examine crystal anisotropy. An important feature of this research is the prediction and observation of a striking magnetic field reversal effect in the inter-Landau level magnetoabsorption in n-InSb. The magnitude of the absorption associated with two transitions is observed to change by a factor of nearly 3 upon reversal of magnetic field direction. The effect results from the inversion asymmetry of the tetrahedral zincblende structure. The transitions which show the effect are the double cyclotron resonance and the double cyclotron resonance combined with spin-flip. The reversal effect involves the interference between two matrix elements which contribute to the absorption, one having tetrahedral symmetry, and the other spherical symmetry. The tetrahedral matrix element results from the inversion-asymmetry mechanism. The isotropic matrix element is associated with the wave vector-dependent electric quadrupole EQ and magnetic dipole MD absorption. The isotropic matrix element changes sign on reversal of q, and the one for inversion asymmetry changes sign on reversal of B, so the interference term changes sign on reversal of either q or B. Stimulated spin-flip Raman (SFR) scattering has been studied in applied magnetic fields up to 18 T. For 10-[mu]m pumping, the SFR laser output is dominated by structure associated with linear intraband absorption and shows significant anisotropy with regard to crystal orientation in the applied field. Calculations have been made for the transition matrix elements and absorption coefficients for the anisotropic intra-conduction-band magneto-optical transitions. The theory includes warping-induced transitions and the effects of band nonparabolicity in the Pidgeon and Brown model. Reasonable agreement between theory and experiment is obtained.
by Gervais F. Favrot, Jr.
Ph.D.

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24

Kubrak, Volker. "Transport of two-dimensional electrons through magnetic barriers." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364636.

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25

Jocher, Agnès. "Control of soot formation in laminar flames by magnetic fields and acoustic waves." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066043.

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Cette thèse consiste en l'étude expérimentale et numérique des processus de formation des particules de suie au sein des flammes laminaires non-pré-mélangées et partiellement prémélangées sous l'influence d'un champ magnétique ou d'une stimulation acoustique. Dans une premiére étape, la capacité du code CIAO à prédire la fraction volumique de suie dans une flamme axisymétrique est étudiée. Par la suite, deux flammes subissant une stimulation acoustique ont été étudiées. Les résultats peuvent être utilisés pour améliorer les modèles de suie futurs, en particulier concernant les différentes échelles temporelles de la chimie en phase gazeuse, et la formation d'hydrocarbures polyaromatiques (PAH) et de suie couplée avec des flux transitoires. Pour étudier la formation des particules de suie sous l'influence de gradients de champ magnétique, un brûleur de type Santoro est utilisé. Les techniques de mesure utilisées dans le cadre de cette thèse sont l'imagerie directe à haute cadence, la technique Background Oriented Schlieren (BOS) et la méthode d'Absorption/Emission Modulée (MAE). Une augmentation de la fraction volumique de suie intégrée a été mise en évidence lorsque le gradient de champ magnétique est ascendant. Une analyse de stabilité linéaire locale appliquée à l'écoulement non-visqueux est présentée pour une flamme sous l'influence de la perturbation magnétique envisagée. Le gradient de champ magnétique provoque alors une réduction du taux d'amplification. De fait, l'étude est complété par l'identification d'un domaine où les flammes qui oscillent naturellement peuvent être stabilisées et contrôlées par des gradients de champ magnétique
In this thesis light is shed on the soot formation processes in laminar coflow flames influenced by magnetic field gradients and acoustic forcing. Both influences have been assessed experimentally and numerically. First, the CIAO in-house code's ability to predict soot volume fraction fields in a steady coflow flame is studied. Then, two acoustically forced cases were studied. These findings are used to improve future soot models, especially, concerning the different time scales of gas phase chemistry and the formation of polycyclic aromatic hydrocarbons (PAH) and soot coupled with unsteady flows. To investigate soot formation under magnetic field gradients, a Santoro type burner is used. The measurement techniques applied in the course of this thesis are high-speed luminosity measurements, Background Oriented Schlieren (BOS) and one- and two-color Modulated Absorption/Emission (MAE) techniques. The magnetic field impact on soot formation was first studied experimentally in steady laminar flames. A scaling of soot production similar to the increased integrated soot volume fraction with increased oxygen content in the coflow was documented. A local inviscid stability analysis is presented for an ethylene coflow flame to investigate the flame's response to small perturbations of the mean velocity, temperature, fuel, and oxygen massfraction under magnetic field exposure. The magnetic field is found to reduce the perturbations' growth rate. The magnetic field study is completed by identifying a domain where naturally oscillating flames can be stabilized and controlled by magnetic field gradients

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26

Murray, Michelle J. "Solar flux emergence : a three-dimensional numerical study." Thesis, University of St Andrews, 2008. http://hdl.handle.net/10023/441.

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Flux is continually emerging on the Sun, making its way from the solar interior up into the atmosphere. Emergence occurs on small-scales in the quiet Sun where magnetic fragments emerge, interact and cancel and on large-scales in active regions where magnetic fields emerge and concentrate to form sunspots. This thesis has been concerned with the large-scale emergence process and in particular the results from previous solar flux emergence modelling endeavours. Modelling uses numerical methods to evolve a domain representing simplified layers of the Sun’s atmosphere, within which the subsurface layer contains magnetic flux. The flux is initialised such that it will rises towards the surface at the start of the simulation. Once the flux reaches the solar surface, it can only emerge into the atmosphere if a magnetic buoyancy instability occurs, after which it expands rapidly both vertically and horizontally. The aim of this thesis is to test the robustness of these general findings from simulations to date upon the seed magnetic field. More explicitly, we have used three-dimensional numerical simulations to investigate how variations in the subsurface magnetic field modify the emergence process and the resulting atmospheric field. We initially consider a simple constant twist flux tube for the seed field and vary the tube’s magnetic field strength and degree of twist. Additionally, we have examined the effects of using non-constant twist flux tubes as the seed field by choosing two different profiles for the twist that are functions of the tube’s radius. Finally, we have investigated the effects of increasing the complexity of the seed field by positioning two flux tubes below the solar surface and testing two different configurations for the tubes. In both cases, the magnetic fields of the two tubes are such that, once the tubes come into contact with each other, reconnection occurs and a combined flux system is formed. From our investigations, we conclude that the general emergence results given by previous simulations are robust. However, for constant twist tubes with low field strength and twist, the buoyancy instability fails to be launched when the tubes reach the photosphere and they remain trapped in the low atmosphere. Similarly, when the non-constant twist profile results in a low tension force throughout the tube, we find that the buoyancy instability is not initialised.

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27

PERIGO, ELIO A. "Desenvolvimento de um focalizador magnético utilizando um arranjo periódico de ímãs permanentes para aplicaçãao em dispositivos de microondas de potência." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11338.

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Made available in DSpace on 2014-10-09T12:50:50Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T13:58:24Z (GMT). No. of bitstreams: 1 11097.pdf: 8468953 bytes, checksum: 884442a7a2e945eacad452d3697f2149 (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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28

Huo, Suguo. "Micromagnetic simulation and MFM study of micromagnetic structures in ferromagnetic materials." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287631.

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29

Lamb, Christopher John. "Computer simulation of the action of a mechanical prosthetic heart valve and investigation of aortic flow field characteristics by magnetic resonance velocimetry." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312718.

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30

Harapát, Jan. "Komplexní simulační model vibračního generátoru." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-230987.

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This work is focusing on analysis of current development in energy harvesting projects in aerospace industry field, and on analysis of current development in vibration generator field. It is also concentrating on establishment of a complex simulation model of vibration generator. It deals with modeling of magnetic field of generator and its cross connection with a mechanic and an electronic model.

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31

Massire, Aurélien. "Non-selective Refocusing Pulse Design in Parallel Transmission for Magnetic Resonance Imaging of the Human Brain at Ultra High Field." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112180/document.

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En Imagerie par Résonance Magnétique (IRM), l’augmentation du champ magnétique statique permet en théorie de fournir un rapport signal sur bruit accru, améliorant la qualité des images. L’objectif de l’IRM à ultra haut champ est d’atteindre une résolution spatiale suffisamment haute pour pouvoir distinguer des structures si fines qu’elles sont actuellement impossibles à visualiser de façon non-invasive. Cependant, à de telles valeurs de champs magnétiques, la longueur d’onde du rayonnement électromagnétique envoyé pour basculer les spins des protons de l’eau est du même ordre de grandeur que l’objet dont on souhaite faire l’image. Des phénomènes d’interférences sont observés, ce qui se traduit par l’inhomogénéité de ce champ radiofréquence (RF) au sein de l’objet. Ces interférences engendrent des artefacts de signal et/ou de contraste dans les images IRM, et rendent ainsi leur exploitation délicate. Il est donc crucial de fournir des solutions pour atténuer la non-uniformité de l’excitation des spins, à défaut de quoi de tels systèmes ne pourront atteindre leurs pleins potentiels. Pour obtenir des diagnostics pertinents à très haut champ, il est donc nécessaire de créer des impulsions RF homogénéisant l'excitation de l'ensemble des spins (ici du cerveau humain), optimisées pour chaque individu. Pour cela, un système de transmission parallèle (pTX) à 8 canaux a été installé au sein de notre imageur à 7 Tesla. Alors que la plupart des systèmes IRM cliniques n’utilisent qu’un seul canal d’émission, l’extension pTX permet de jouer différentes formes d’impulsions RF de concert. La somme résultante de ces interférences doit alors être optimisée pour atténuer la non-uniformité observée classiquement. L’objectif de cette thèse est donc de synthétiser ce type d’impulsions, en utilisant la pTX. Ces impulsions auront pour contrainte supplémentaire le respect des limitations internationales concernant l'exposition à des champs radiofréquence, qui induit une hausse de température dans les tissus. En ce sens, de nombreuses simulations électromagnétiques et de températures ont été réalisées en introduction de cette thèse, afin d’évaluer la relation entre les seuils recommandés d’exposition RF et l’élévation de température prédite dans les tissus. Cette thèse porte plus spécifiquement sur la conception de l’ensemble des impulsions RF refocalisantes utilisées dans des séquences IRM non-sélectives, basées sur l’écho de spin. Dans un premier temps, seule une impulsion RF a été générée, pour une application simple : l’inversion du déphasage des spins dans le plan transverse. Dans un deuxième temps, sont considérées les séquences à long train d’échos de refocalisation appliquées à l’in vivo. Ici, l’opérateur mathématique agissant sur la magnétisation, et non pas son état final comme il est fait classiquement, est optimisé. Le gain en imagerie à très haut champ est clairement visible puisque les opérations mathématiques (la rotation des spins) voulues sont réalisées avec plus de fidélité que dans le cadre des méthodes de l’état de l’art. Pour cela, la génération de ces impulsions RF combine une méthode d’excitation des spins avec navigation dans l’espace de Fourier, les kT-points, et un algorithme d’optimisation, appelé Gradient Ascent Pulse Engineering (GRAPE), utilisant le contrôle optimal. Cette conception est rapide grâce à des calculs analytiques plus directs que des méthodes de différences finies. La prise en compte d’un grand nombre de paramètres nécessite l’usage de GPUs (Graphics Processing Units) pour atteindre des temps de calcul compatibles avec un examen clinique. Cette méthode de conception d’impulsions RF a été validée expérimentalement sur l’imageur 7 Tesla de NeuroSpin, sur une cohorte de volontaires sains
In Magnetic Resonance Imaging (MRI), the increase of the static magnetic field strength is used to provide in theory a higher signal-to-noise ratio, thereby improving the overall image quality. The purpose of ultra-high-field MRI is to achieve a spatial image resolution sufficiently high to be able to distinguish structures so fine that they are currently impossible to view in a non-invasive manner. However, at such static magnetic fields strengths, the wavelength of the electromagnetic waves sent to flip the water proton spins is of the same order of magnitude than the scanned object. Interference wave phenomena are then observed, which are caused by the radiofrequency (RF) field inhomogeneity within the object. These generate signal and/or contrast artifacts in MR images, making their exploitation difficult, if not impossible, in certain areas of the body. It is therefore crucial to provide solutions to mitigate the non-uniformity of the spins excitation. Failing this, these imaging systems with very high fields will not reach their full potential.For relevant high field clinical diagnosis, it is therefore necessary to create RF pulses homogenizing the excitation of all spins (here of the human brain), and optimized for each individual to be imaged. For this, an 8-channel parallel transmission system (pTX) was installed in our 7 Tesla scanner. While most clinical MRI systems only use a single transmission channel, the pTX extension allows to simultaneously playing various forms of RF pulses on all channels. The resulting sum of the interference must be optimized in order to reduce the non-uniformity typically seen.The objective of this thesis is to synthesize this type of tailored RF pulses, using parallel transmission. These pulses will have as an additional constraint the compliance with the international exposure limits for radiofrequency exposure, which induces a temperature rise in the tissue. In this sense, many electromagnetic and temperature simulations were carried out as an introduction of this thesis, in order to assess the relationship between the recommended RF exposure limits and the temperature rise actually predicted in tissues.This thesis focuses specifically on the design of all RF refocusing pulses used in non-selective MRI sequences based on the spin-echo. Initially, only one RF pulse was generated for a simple application: the reversal of spin dephasing in the transverse plane, as part of a classic spin echo sequence. In a second time, sequences with very long refocusing echo train applied to in vivo imaging are considered. In all cases, the mathematical operator acting on the magnetization, and not its final state as is done conventionally, is optimized. The gain in high field imaging is clearly visible, as the necessary mathematical operations (that is to say, the rotation of the spins) are performed with a much greater fidelity than with the methods of the state of the art. For this, the generation of RF pulses is combining a k-space-based spin excitation method, the kT-points, and an optimization algorithm, called Gradient Ascent Pulse Engineering (GRAPE), using optimal control.This design is relatively fast thanks to analytical calculations rather than finite difference methods. The inclusion of a large number of parameters requires the use of GPUs (Graphics Processing Units) to achieve computation times compatible with clinical examinations. This method of designing RF pulses has been experimentally validated successfully on the NeuroSpin 7 Tesla scanner, with a cohort of healthy volunteers. An imaging protocol was developed to assess the image quality improvement using these RF pulses compared to typically used non-optimized RF pulses. All methodological developments made during this thesis have contributed to improve the performance of ultra-high-field MRI in NeuroSpin, while increasing the number of MRI sequences compatible with parallel transmission

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Parreiras, Sofia de Oliveira. "Vórtices magnéticos em materiais nanoestruturados: experimento e simulação." CNEN - Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, 2012. http://www.bdtd.cdtn.br//tde_busca/arquivo.php?codArquivo=209.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
O estudo de discos magnéticos com a configuração de vórtices magnéticos tem atraído grande interesse científico recentemente. Nessa estrutura os spins formam circuitos fechados no plano e, próximo ao centro do disco, se alinham perpendicularmente ao plano de forma a reduzir a densidade de energia de troca. O grande potencial de aplicação de vórtices magnéticos como, por exemplo, em memórias magnéticas e nanopartículas para o tratamento de câncer, chama a atenção para a investigação das condições de estabilidade e o controle de suas propriedades. Neste trabalho, estudamos a alteração que dois tipos diferentes de anisotropia provocam nas propriedades de vórtices através de medidas de Microscopia de Força Magnética (MFM) e simulações micromagnéticas utilizando o código OOMMF (NIST) que aplica a equação de Landau-Lifshitz-Gilbert para simular a configuração de spin e calcular a energia e a magnetização de microestruturas. A primeira parte do trabalho envolveu o estudo da influência da anisotropia magnetocristalina planar na estabilidade de vórtices magnéticos em discos de Co60Fe40 em relação a discos de permalloy, que possui anisotropia magnetocristalina nula. Os resultados de simulação micromagnética para discos com diâmetros entre 0,5 e 8 m mostraram que a anisotropia favorece o alinhamento dos spins e a divisão da estrutura em domínios, reduzindo a estabilidade do vórtice. Os resultados foram comprovados experimentalmente em medidas de MFM de discos de Co60Fe40 com diâmetros entre 2 e 8 m. Na segunda parte do trabalho foi estudada a influência do fenômeno de exchange bias na dinâmica de vórtices magnéticos. Para isso foram realizadas simulações de discos de Permalloy/Fe50Mn50 com diâmetro de 0,5 m variando o acoplamento magnético entre as camadas. As simulações de curvas de histerese mostraram que o acoplamento aumenta a estabilidade dos vórtices. Nas simulações de relaxação foi observado que devido ao exchange bias o movimento girotrópico do núcleo apresenta uma frequência variável que aumenta com o tempo, o que não acontece na ausência de exchange bias. Já nas simulações em que os discos estão sujeitos a um campo magnético girante foi observado que a velocidade crítica em que a polaridade do vórtice é invertida aumenta com o aumento do acoplamento e com o aumento da frequência do campo. Essa velocidade pode ser escolhida em uma ampla faixa escolhendo os valores do acoplamento magnético e da frequência de oscilação. Portanto é possível controlar a velocidade crítica de inversão da polaridade de vórtices magnéticos através do fenômeno de exchange bias.
The study of magnetic dots with magnetic vortex spin configuration has recently attracted great scientific interest. In this structure, the spins form closed circuits in the plane of the magnetic dot and, near the center, align perpendicularly to the plane in order to reduce exchange energy density. The great potential of applications of magnetic vortices (as for example magnetic memories and nanoparticles for cancer treatment) draws attention for the investigation of the stability conditions for the vortex configuration. In the case of soft ferromagnetic materials in micron and submicron scales, small changes in shape, size and materials anisotropy can modify the energy equilibrium. In this work, we studied the change of vortex proprieties in microsized dots due to two different types of anisotropy using the code OOMMF (NIST) that applies the Landau-Lifshitz-Gilbert equation to simulate the spin configuration and compute the energy and magnetization of microstructures. These results were compared to Magnetic Force Microscopy (MFM) investigations of the magnetic configuration in microsized dots prepared by lithographic process. In the first part, we studied by numerical simulation the influence of planar magnetocrystaline anisotropy in Co60Fe40 disks and compare to permalloy disks, material that shows zero magnetocrystalline anisotropy. The results for disks with diameters between 0.5 and 8 m showed that the anisotropy favors spins alignment and domains division, reducing vortex stability. The results for Co60Fe40 disks with diameters between 2 and 8 m were verify experimentally by MFM measurements. In the second part, we studied the influence of exchange bias in the magnetic vortex dynamics. A series of micromagnetic simulations for Permalloy/Fe50Mn50 disks with 0.5 m of diameter was done varying the magnetic coupling constant between the layers. The hysteresis simulations showed that the vortex stability increases with the coupling constant. In relaxation simulations we observed that the gyrotropic movement has a variable frequency that increases with time, which is not observed when exchange bias is absent. Under a rotating magnetic field, the critical velocity for vortex polarity reversion increases with the coupling constant and frequency. Our results show that the critical velocity can be adjusted in a wide range by selecting the magnetic coupling constant and the oscillating frequency, i.e., it is possible to control the critical velocity for vortex polarity inversion through the exchange bias coupling.

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Penkal, Bryan James. "Steps in the Development of a Full Particle-in-Cell, Monte Carlo Simulation of the Plasma in the Discharge Chamber of an Ion Engine." Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1367586856.

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Schwarm, Fritz-Walter Verfasser], Jörn [Gutachter] [Wilms, and Peter A. [Gutachter] Becker. "Monte Carlo Simulation of Cyclotron Lines in Strong Magnetic Fields - Theory and Application / Fritz-Walter Schwarm ; Gutachter: Jörn Wilms, Peter A. Becker." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017. http://d-nb.info/1134953453/34.

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Schwarm, Fritz-Walter [Verfasser], Jörn [Gutachter] Wilms, and Peter A. [Gutachter] Becker. "Monte Carlo Simulation of Cyclotron Lines in Strong Magnetic Fields - Theory and Application / Fritz-Walter Schwarm ; Gutachter: Jörn Wilms, Peter A. Becker." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017. http://d-nb.info/1134953453/34.

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Schoe, Annika [Verfasser]. "The influence of the earth's magnetic field and the topography on pigeon's homing routes : a comparison of measured tracks with a novel simulation algorithm / Annika Schoe." Konstanz : Bibliothek der Universität Konstanz, 2018. http://d-nb.info/1166053873/34.

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Barnes, Gary James. "Computational modelling for type-II superconductivity and the investigation of high temperature superconducting electrical machines." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365887.

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Imbs, Julien. "Modélisation numérique de débitmètre électromagnétique." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE047.

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Cette thèse a pour objet la modélisation et l’étude de débitmètres électromagnétiques produits par la société Siemens. Ces appareils permettent de mesurer le débit volumique d’un fluide conducteur en mouvement sous un champ magnétique par le biais d’électrodes mesurant le potentiel induit. L’objectif principal des travaux présentés est de modéliser un débitmètre électromagnétique, afin de disposer d’un modèle fiable et réaliste d’un point de vue magnétique, et de l’optimiser par la suite. La premier chapitre de cette thèse est consacrée à l’historique et au fondement de la théorie des débitmètres électromagnétiques de l’époque de Faraday à nos jours. Le chapitre II présente et décrit les débitmètres industriels conçus par Siemens à Haguenau en posant les bases, les termes et les notions nécessaires à la compréhension des travaux réalisés durant cette thèse. Le chapitre III vise à établir l’équation qui régit le fonctionnement des débitmètres électromagnétiques reliant le potentiel induit, la vitesse du fluide et le champ magnétique. On discutera également des principales hypothèses retenues dans le cadre de la théorie pour la modélisation numérique. Le chapitre IV introduit dans un premier temps la théorie sur le magnétisme et les principaux matériaux magnétiques. Dans un second temps, c’est la caractérisation magnétique des principaux composants utilisés pour la conception des débitmètres électromagnétiques qui est réalisée. Dans le chapitre V, une introduction à la modélisation numérique est effectuée, afin de justifier l’importance de la méthode des éléments finis pour la simulation électromagnétique des débitmètres sur le logiciel NX. La deuxième partie du chapitre se concentre sur le développement et la simulation du modèle numérique d’un débitmètre électromagnétique. Ensuite, la troisième partie est consacrée à la méthode expérimentale mise en place afin de mesurer le champ magnétique et comparer les résultats obtenus avec ceux issus de la simulation. La simulation numérique du champ magnétique ayant été validée par les mesures, le chapitre VI est consacré à la dynamique moléculaire des particules chargées contenues dans le fluide afin d’en déterminer la différence de potentiel. Enfin, le chapitre VII est consacré à l’étalonnage des débitmètres électromagnétiques, où l’on confrontera un modèle théorique aux valeurs expérimentales mesurées en production sur le site de Haguenau
This work concerns numerical modelling and study of electromagnetics flowmeters developed by Siemens. These devices are able to measure the flowrate of a conductive fluid in motion subject to a magnetic field. An induced potential is created and measured by two electrodes. The main purpose of this thesis is to modelize an electromagnetic flowmeter in order to get a realistic and reliable model to optimize the sensor in the futur. The first part of the work is to introduce the development theory of elec-tromagnetic flowmeter since the discovery of the induction law of Farady until today. The chapter II describes the industrial electromagnetics flowmeters manufactured by Siemens and provides the necessary knowledges for a better understanding of this work. In the chapter III, the electromagnetic flowmeter equation is derived and solved for the case of a homogenous magnetic field and point electrodes. This equation allows to get a relation between the induced potential, the velocity of the fluid and the magnetic field. We will discuss about the assumptions choose for this theory and used for the numerical model. In a first time the chapter IV focus on the theory of the magnetism and magnetics materials. In a second time, we present the magnetic characterization of the materials used in the electromagnetics flowmeters. In the chapter V, an introduction to the numerical modelling is done in order to justify the using of the finite element method for the magnetic simulation on the software NX Nastran. The second part of this chapter concerns the development and the numerical simulation of an electromagnetic flowmeter. At last, the third part is about the installation of a test bed to measure the magnetic field produced inside the electromagnetic flowmeter and to compare the results with the simulation. Numerical simulation of the magnetic field being checked by the measurements, the next chapter introduces molecular dynamics of the charged particles inside the measuring pipe in order to compute electrical potential. Finally, the last part introduces the calibration of electromagnetics flowmeters where a theoretical model was developed in order to compare them with experimentals values measured in production on Haguenau Siemens site

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Harrison, Michael George. "Equilibrium and dynamics of collisionless current sheets." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/705.

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Konšel, Ladislav. "Simulace dynamického chování vybavovače jističe." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219754.

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This work includes the theory of circuit breaker construction and is focused mainly on overload function. It mainly deals with electronic circuit breakers, i.e. equipped with an electronic trip unit. The work is focused on the part of trip unit - maglatch of trip unit. For the purposes of simulation, the geometric model is created. Maxwell program is used for the simulation. The work describes the options for conditions input which are necessary for simulation. Using the distribution of magnetic field intensity and magnetic flux density in the section of trip unit maglatch is determined by the simulation. Furthermore, the force effects acting on the armature of the maglatch are calculated. Force values and the directions acting on the armature are determined by changing the simulation parameters - shift of the armature and coil current. Simulations are performed both for steady-state and for dynamic simulation – movement of armature is taken into account. The supply source for the maglatch is created by an external circuit.

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Nam, Moon-Sun. "Magnetotransport in BEDT-TTF salts." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342589.

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Přikryl, Matěj. "Hydrodynamické tlumiče na principu magnetické kapaliny." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318383.

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This diploma thesis covers the topic of magnetic fluids and their utilisation in hydrodynamic dampers. The first part of the work consists of research on the current state of technology in hydraulic dampers with the focus on dampers using magnetorhelogical fluid. This chapter is followed by research on magnetic fluids with regard to their physical properties and mathematical description, which is used for CFD simulation of flow. The second part deals with the computational simulation of the flow of MR liquid in real MR damper in order to determine the damping characteristic and it's comparison with the experimental data.

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Sadauskas, Tomas. "Tiesiaeigio asinchroninio variklio magnetinio lauko imitacija." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2006. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2006~D_20060623_095632-82775.

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In this thesis is investigated how magnetic field varies at different instants of time in the air gap of linear induction motor and outside of it. The are given results of simulation, which show the change of magnetic flux at different instants of time of linear induction motor in the air gap, outside the inductors, also magnetic flux dependencies on air gap width. Two models of linear induction motor with secondary element and without it are compared.

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Сабокар, Олег Сергійович. "Удосконалення магнітно-імпульсного обладнання для технологій ремонту транспортних засобів". Thesis, Харківський національний автомобільно-дорожній університет, 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/39634.

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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.13 – техніка сильних електричних та магнітних полів. Національний технічний університет "Харківський політехнічний інститут", Харків 2019. Дисертація присвячена вирішенню завдання поліпшення технічних показників обладнання магнітно-імпульсної обробки металів (міоми) для використання в технологіях металообробки і технологіях ремонту транспортних засобів. У роботі представлена розробка альтернативної конструкції вузла заряду ємнісних накопичувачів енергії та розробка системи індукційного нагріву. Дано числові показники нагріву при варіації часових параметрів збуджуючого струму і конструктивних параметрів інструменту індуктора. Розглянута модель системи збудження струму індуктора доповнена експериментальними дослідженнями системи в режимі резонансу напруги. Запропоновано використання модифікованої часової форми біполярного меандру сигналу збудження для зменшення кількості спектральних складових. Сконструйована система індукційного нагріву, що працює в режимі резонансу напруги, показала свою працездатність і ефективність. Було запропоновано виконувати збудження коливань струму імпульсами напруги модифікованої форми з частотою нижче на 20% від резонансної частоти, що забезпечує прийнятний ККД в режимі роботи системи без навантаження. Розробка система індукційного нагріву пройшла апробацію і випробування на підприємствах "Веда Авто Сервіс" (м. Київ) і АТ "Елеватормлинмаш" (м. Харків). Результати дисертаційної роботи використовують при підготовці бакалаврів та магістрів на кафедрі автомобільної електроніки Харківського національного автомобільно-дорожнього університету.
Thesis for the degree of Candidate of Technical Sciences for specialty 05.09.13 "Equipment of strong electric and magnetic fields" – National Technical University "Kharkiv Polytechnic Institute". Kharkiv, 2019. The thesis is dedicated to the solution of the problem of the technical performance of magnetic-impulse metal processing equipment improving for use in metal-working technologies and vehicle repair technologies. The paper presents the development of an alternative design for the capacitive energy storage charge system and the development of an induction heating system. The numerical heating indicators was given with a variation of the time parameters of the exciting current and the design parameters of the inductor tool. The system model of inductor current excitation in the mode of current resonance was considered and supplemented by experimental studies of the system in voltage resonance mode. The use of a modified time form of the bipolar meander of the excitation signal to reduce the number of spectral components was proposed. The induction heating system designed that operates in the voltage resonance mode has shown its efficiency. It was proposed to perform the excitation of current oscillations by voltage pulses of the modified form with a frequency lower than 20% of the resonant frequency, which ensures acceptable efficiency in the system operation without load. The development of the induction heating system has been tested and implicated at the enterprises of "Veda Auto Service" (Kyiv) and "Elevatormlinmash" (Kharkiv). The results of the thesis are used in the preparation of bachelors and masters degree at the department of automobile electronics of the Kharkiv National Automobile and Highway University.

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Pillin, Béatrice. "Utilisation des champs magnétiques intenses pour la séparation d'inclusions : application aux particules solides immergées dans les métaux liquides." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0017.

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La separation de particules solides immergees dans un liquide en ecoulement au travers d'un champ magnetique statique intense a ete etudiee. Des forces magnetiques, liees aux susceptibilites magnetiques et au gradient spatial de champ magnetique, ou bien des forces electromagnetiques, liees aux conductivites electriques et au mouvement relatif de l'element conducteur par rapport au champ magnetique, peuvent etre mises en oeuvre. La separation est effective lorsque ces forces agissent sur la trajectoire des particules perpendiculairement a la direction de l'ecoulement. Ce sont les forces precedemment citees agissant soit directement sur la particule, soit via le liquide par l'intermediaire de forces de pression. A partir de la distribution du champ magnetique delivre par un bobinage supraconducteur axisymetrique vertical, deux principes de separation sont proposes. Un exploite les zones de gradient de champ ou un ecoulement de liquide conducteur et/ou magnetique, de type cylindrique parallele a l'axe du bobinage permet d'obtenir des forces electromagnetiques et magnetiques. L'autre exploite la zone centrale de champ homogene ou un ecoulement de type conique convergent ou divergent, incline par rapport a l'axe du bobinage, permet d'obtenir des forces electromagnetiques. Les effets des forces electromagnetiques et magnetiques sur la deviation de particules sont demontres experimentalement grace a la conception et l'exploitation de dispositifs creant des ecoulements cylindrique ou conique dans les differentes zones de champ de bobinages supraconducteurs. Des solutions aqueuses a proprietes conductrices et/ou magnetiques chargees en particules de plexiglas sont testees. Une simulation numerique des aspects electromagnetiques induits dans le procede est developpee et validee a partir des ordres de grandeur deduits de l'approche theorique ou obtenus experimentalement.

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46

Сабокар, Олег Сергійович. "Удосконалення магнітно-імпульсного обладнання для технологій ремонту транспортних засобів". Thesis, Національний технічний університет "Харківський політехнічний інститут", 2019. http://repository.kpi.kharkov.ua/handle/KhPI-Press/39631.

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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.13 – техніка сильних електричних та магнітних полів. Національний технічний університет "Харківський політехнічний інститут", Харків 2019. Дисертація присвячена вирішенню завдання поліпшення технічних показників обладнання магнітно-імпульсної обробки металів (міоми) для використання в технологіях металообробки і технологіях ремонту транспортних засобів. У роботі представлена розробка альтернативної конструкції вузла заряду ємнісних накопичувачів енергії та розробка системи індукційного нагріву. Дано числові показники нагріву при варіації часових параметрів збуджуючого струму і конструктивних параметрів інструменту індуктора. Розглянута модель системи збудження струму індуктора доповнена експериментальними дослідженнями системи в режимі резонансу напруги. Запропоновано використання модифікованої часової форми біполярного меандру сигналу збудження для зменшення кількості спектральних складових. Сконструйована система індукційного нагріву, що працює в режимі резонансу напруги, показала свою працездатність і ефективність. Було запропоновано виконувати збудження коливань струму імпульсами напруги модифікованої форми з частотою нижче на 20% від резонансної частоти, що забезпечує прийнятний ККД в режимі роботи системи без навантаження. Розробка система індукційного нагріву пройшла апробацію і випробування на підприємствах "Веда Авто Сервіс" (м. Київ) і АТ "Елеватормлинмаш" (м. Харків). Результати дисертаційної роботи використовують при підготовці бакалаврів та магістрів на кафедрі автомобільної електроніки Харківського національного автомобільно-дорожнього університету.
Thesis for the degree of Candidate of Technical Sciences for specialty 05.09.13 "Equipment of strong electric and magnetic fields" – National Technical University "Kharkiv Polytechnic Institute". Kharkiv, 2019. The thesis is dedicated to the solution of the problem of the technical performance of magnetic-impulse metal processing equipment improving for use in metal-working technologies and vehicle repair technologies. The paper presents the development of an alternative design for the capacitive energy storage charge system and the development of an induction heating system. The numerical heating indicators was given with a variation of the time parameters of the exciting current and the design parameters of the inductor tool. The system model of inductor current excitation in the mode of current resonance was considered and supplemented by experimental studies of the system in voltage resonance mode. The use of a modified time form of the bipolar meander of the excitation signal to reduce the number of spectral components was proposed. The induction heating system designed that operates in the voltage resonance mode has shown its efficiency. It was proposed to perform the excitation of current oscillations by voltage pulses of the modified form with a frequency lower than 20% of the resonant frequency, which ensures acceptable efficiency in the system operation without load. The development of the induction heating system has been tested and implicated at the enterprises of "Veda Auto Service" (Kyiv) and "Elevatormlinmash" (Kharkiv). The results of the thesis are used in the preparation of bachelors and masters degree at the department of automobile electronics of the Kharkiv National Automobile and Highway University.

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47

Langlois, Yilin. "Modélisation de l’arc électrique dans un disjoncteur à vide." Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL062N/document.

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Un modèle numérique d’un arc électrique diffus dans un disjoncteur à vide à champ magnétique axial (AMF) a été développé dans le but de mieux comprendre à terme la transition d’un mode de fonctionnement diffus de l’arc vers un mode plus concentré. Le comportement du plasma d’arc a été simulé depuis la sortie de la zone de mélange cathodique jusqu’à l’entrée de la gaine anodique. Le modèle bidimensionnel est basé sur un système d’équations hydrodynamiques à deux fluides non magnétisés (ions et électrons), incluant les équations de conservation d’énergie ionique et électronique. Il est démontré que les processus d’ionisation et de recombinaison et les effets visqueux sont négligeables. Les transferts radiatifs ne sont pas considérés en première approximation. Outre les forces dues au champ AMF, le modèle inclut les forces dues aux trois composantes du champ magnétique induit par l’arc. Deux régimes d’écoulement des ions, supersonique (aux faibles densités de courant) et subsonique (aux fortes densités de courant), sont considérés. Près de la cathode, les conditions aux limites sont spécifiées à partir de résultats de la littérature. A proximité de l’anode, elles sont basées sur une description simplifiée de la gaine anodique. Les résultats de simulation présentés mettent en évidence une constriction du courant et un comportement différent des ions aux faibles et aux fortes densités de courant, et renseignent sur l’influence de divers paramètres (intensité du courant, distance interélectrode). Ce travail présente également une étude expérimentale, basée sur des visualisations par vidéo rapide de l’arc et des mesures pyrométriques de la température de la surface de l’anode
A model of a diffuse arc in a vacuum circuit breaker with an axial magnetic field (AMF) has been developed with the ultimate aim to better understand the transition of the arc from a diffuse mode to a more confined mode. The interelectrode plasma is simulated from the exit of the mixing region on the cathode side to the entrance of the anode sheath. The two-dimensional model is based on the solution of a system of two-fluid (ions and electrons) hydrodynamic equations, including in particular the energy balance equations relative to both the ions and the electrons, which are treated as non-magnetized particles. It is demonstrated that ionisation and recombination processes, as well as viscous effects, can be neglected. Radiation losses are not taken into account in a first approximation. In addition to the forces due to the AMF, the model considers the forces created by the three components of the magnetic field induced by the arc current. The possibility of both supersonic (at low current density) and subsonic (at high current density) ionic flow regimes is considered. On the cathode side, the boundary conditions are specified using results from the literature. On the anode side, they are based on a simplified description of the anode sheath. The simulation results presented show a constriction of the current lines, emphasize the differences in the behaviour of the ions at low and high current densities, and provide some insight on the influence of various operating parameters (arc current, gap length). The present work comprises also an experimental study, based on high-speed camera visualisations of the arc and measurements of the temperature at the anode surface

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48

Heyrendt, Laurent. "Études des actions des forces magnétiques volumiques créées par un champ magnétique intense sur des fluides à seuil - possibilités de transition solide-gel." Phd thesis, Université de Lorraine, 2012. http://tel.archives-ouvertes.fr/tel-00799586.

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Les fluides à seuil ont des propriétés mécaniques étonnantes : en dessous d'une certaine contrainte, appelée contrainte seuil, le fluide se comporte comme un solide. Au-delà de la contrainte seuil, ils s'écoulent comme un gel. Ce mémoire porte sur l'étude des actions des forces magnétiques volumiques sur ces fluides. Nous étudions la possibilité de réaliser la transition solide--gel à partir des forces magnétiques volumiques créées par différents dispositifs magnétiques. Ces fluides n'ont pas de propriétés magnétiques particulières. Il est donc nécessaire de créer des champs magnétiques intenses pour agir sans contact sur ces fluides. Nous étudions différentes configurations magnétiques capables de dépasser la contrainte seuil au sein du fluide. L'influence des différents paramètres des configurations magnétiques est explorée, notamment à l'aide d'études paramétriques. Notre travail mêle des équations de magnétostatique et de mécanique des fluides non-newtoniens. Les calculs de magnétostatique sont menés de façon analytique alors que la partie mécanique et le couplage magnéto-mécanique sont traités par un logiciel de simulation numérique par la méthode des éléments finis. Les conditions magnétiques et mécaniques nécessaires à la transition solide--gel et à la modification d'écoulements de fluides à seuil sont discutées, notamment à l'aide de simulations numériques et de nombres adimensionnels.

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49

Cebron, David. "L'instabilité elliptique dans les enveloppes fluides des planètes et des étoiles." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10089/document.

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L’instabilité elliptique peut apparaître dès qu’un écoulement présente des lignes de courant elliptiques, ce qui en fait une instabilité générique des fluides tournants. Si sa pertinence en aéronautique ne laisse plus de doute, sa prise en compte dans l’étude des écoulements géo- et astrophysiques pose de nombreuses questions qui constituent la motivation principale de ce travail théorique, numérique et expérimental. Après une introduction aux écoulements tournants, le chapitre 1 présente les trois forçages mécaniques présents aux échelles planétaires qui seront considérés dans ce travail : les marées, la précession et la libration. Un état de l’art sur les écoulements et les instabilités associés à ces forçages est alors décrit, formant le cadre de cette étude. Le chapitre 2 présente les premières simulations numériques de l’instabilité elliptique en géométrie ellipsoïdale. Ces simulations nous permettent de quantifier l’influence de différentes complexités géophysiques et d’obtenir des lois d’échelles caractérisant l’instabilité. L’interaction de l’instabilité elliptique avec les deux autres forçages mécaniques est ensuite considérée. La section 2.4 montre que la présence simultanée de marées et de libration est susceptible d’exciter une instabilité elliptique au sein des astres synchronisés. La section 2.5 développe et valide une théorie analytique sur l’interaction des marées et de la précession. Enfin, la section 2.6 démontre que l’instabilité elliptique peut se développer à partir d’écoulements convectifs ou stratifiés. Le chapitre 3 s’intéresse à la magnétohydrodynamique (MHD) de l’instabilité elliptique. De nouveaux résultats sur l’aspect inductif de l’instabilité sont obtenus et validés numériquement. La génération d’un effet dynamo associé à l’instabilité elliptique est également abordé. Une partie expérimentale liée à ce travail est ensuite décrite, basée sur un dispositif MHD. Après une étude de la dynamique non-linéaire de l’instabilité sous champ, le dispositif est modifié afin de mettre en place une dynamo synthétique. L’amplitude du champ magnétique imposé pouvant être assez assez grande pour restabiliser l’écoulement, ce dispositif permet d’étudier la saturation par l’écoulement d’une telle dynamo. Des premiers résultats en ce sens sont présentés. Le chapitre 4 utilise les résultats obtenus pour étudier la présence de l’instabilité elliptique au sein de planètes, lunes et étoiles connues. Le cas particulier de la Lune est d’abord considéré et un scénario, basé sur l’instabilité elliptique, est proposé puis évalué pour expliquer la dynamo lunaire primitive. Les astres telluriques sont ensuite considérés dans un cadre plus général, et une étude de stabilité adaptée à ce contexte montre que l’instabilité est possible sur la Terre primitive, Europe et trois exoplanètes (55CnCe, CoRoT-7b et GJ1214b). Enfin, la possible existence de l’instabilité au sein de certains systèmes extra-solaires à Jupiter chauds est considérée, montrant sa pertinence pour certains d’entre eux tel que celui de Tau-boo
The elliptical instability is a generic instability which takes place in any rotating fluid whose streamlines are (even slightly) elliptically deformed. Its presence in an aeronautical context is well established, but its existence in geo- or astrophysical large scale flows raises many issues. This is the starting point of this theoretical, numerical and experimental work.After introducing basics of the rotating flows, chapter 1 presents the three natural planetary mechanical forcings considered in this work : tides, precession and libration. A state-of-the-art of the flows and instabilities associated with these forcings is then given, which constitutes the framework of this study.Chapter 2 presents the first numerical simulations of the elliptical instability in an ellipsoidal geometry, relevant for planets. These simulations allow to quantify the influence of different natural geophysical complexities, and to derive the scaling laws needed to bridge the gap between numerics and planetary applications. The interaction of the elliptical instability with the two other forcings is then considered. Section 2.4 shows that the simultaneous presence of tides and libration can excite an elliptical instability inside fluid layers of synchronized celestial bodies. In section 2.5, a theoretical analysis of the interaction between tides and precession is developed and validated. Finally, in section 2.6, we prove that the elliptical instability can still develop over convective or stratified flows.Chapter 3 focuses on the magnetohydrodynamics (MHD) of the elliptical instability. New results on the magnetic induction by the elliptical instability are obtained and validated numerically. The possible dynamo capability of the instability is also tackled. The experimental part of this work, based on a MHD setup, is then described. Our measurements allow to study the non-linear dynamics of the instability under an external imposed magnetic field. The experimental setup is then modified in order to obtain a synthetic dynamo. The amplitude of the imposed magnetic field being large enough to restabilize the flow, this setup allows to study the saturation by the flow of such a dynamo. First results on this point are presented. Chapter 4 uses the obtained results to study the presence of the elliptical instability in known planets, moons, and stars. The particular case of the Moon is first considered and a scenario, based on the elliptical instability, is proposed and evaluated to explain the primitive lunar dynamo. Telluric bodies are then considered in a more general context, and a stability analysis adapted to this context shows that the instability can be expected in the Early Earth, Europa and three exoplanets (55CnCe, CoRoT-7b et GJ1214b). Finally, the possible development of the instability in extra-solar Hot-Jupiters systems is considered, showing its relevance for some of them, such as the system of Tau-boo

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50

Kessler, Philippe. "Simulation des grandes échelles d’écoulements compressibles en géométrie complexe." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0201.

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La transition a la turbulence d'ecoulements en geometrie complexe est etudiee par simulation numerique compressible bidimensionnelle et tridimensionnelle. On presente une simulation des grandes echelles d'un jet rond d'air, comparee a une experience en laboratoire et a une autre simulation numerique incompressible. Cette comparaison nous a permis de valider notre outil numerique. Nous montrons un bon accord entre les resultats experimentaux et notre simulation numerique en zone transitionnelle. On applique notre outil numerique a une geometrie complexe et industrielle: l'entree d'air en incidence. Cette etude est effectuee avec un code a gestion multi-domaine des transferts d'informations par methode aux caracteristiques. Les resultats sont compares a ceux d'une experience faite au ceat de poitiers. Nous avons mis en evidence les tourbillons de kelvin-helmholtz, ainsi que les tourbillons longitudinaux, responsables des fluctuations de pression au niveau du premier etage du compresseur. Enfin, on a reproduit une experience magnetohydrodynamique faite au laboratoire madylam, en geometrie bidimensionnelle ronde. L'influence du champ magnetique sur un ecoulement de mercure soumis aux forces de laplace cree un cisaillement au niveau de l'electrode. On presente une evolution temporelle de la vorticite et de la pression, ainsi que les statistiques obtenues en regime permanent. Nous montrons des resultats qualitatifs satisfaisants, mais par contre sur les statistiques, nous surestimons les valeurs moyennes et fluctuantes. Nous montrons que les caracteristiques de l'ecoulement ne sont pas bidimensionnelles, mais doivent etre tridimensionnelles

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