Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 80-85).

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Ο ηλεκτρομαγνητισμός είναι το θέμα που πραγματεύεται η παρούσα εργασία. Αναγνωρίζοντας το σημαντικό ρόλο που παίζουν, κατά τη διαδικασία της μάθησης οι βιωματικές νοητικές παραστάσεις σχεδιάστηκαν και πραγματοποιήθηκαν δύο πειραματικές καταστάσεις που συνδέουν τον ηλεκτρισμό με το μαγνητισμό ώστε να οδηγηθούμε στην ανίχνευση των νοητικών παραστάσεων των μαθητών της ΣΤ΄τάξης του Δημοτικού σχολείου για τον ηλεκτρομαγνητισμό. Στο πρώτο μέρος παρουσιάζεται τόσο η επιστημονική όσο και η σχολική γνώση, όπως αναφέρεται στο ΑΠΣ του Δημοτικού Σχολείου, για τον ηλεκτρισμό, το μαγνητισμό και τον ηλεκτρομαγνητισμό, καθώς και η θεωρητική παρουσίαση του όρου "νοητικες παραστάσεις" και αναφορά σε σχετικές με το θέμα της εργασίας έρευνες από τη διεθνή και ελληνική βιβλιογραφία. Στο δεύτερο μέρος παρουσιάζεται το μεθοδολογικό πλαίσιο της εργασίας και το αντικείμενο της έρευνας.Στο τρίτο μέρος παρουσιάζονται τα αποτελέσματα, ο τρόπος επεξεργασίας των δεδομένων και η ανάλυσή τους. Τέλος στο τέταρτο μέρος επιχειρείται μια σύνοψη των αποτελεσμάτων και μια αναφορά στα συμπεράσματα που προέκυψαν από την ερευνητική διαδικασία. / -

The aim of this thesis is to investigate surface waves supported on a variety of metallic metasurfaces at microwave frequencies. The goal is to characterise the propagation of these surface waves in the plane of the structure and in some cases study how their presence gives rise to features in the scattering parameters of radiation incident on the metasurface.

The Finite-Difference Time-Domain (FDTD) method has been used extensively in electromagnetic field modeling because of its ability to robustly handle interactions of fields with complex heterogeneous structures. In particular, the total/scattered field formulation has allowed for efficient implementation of arbitrarily directed uniform plane waves, consequently facilitating efficient modeling of far-field scattering problems. The total/scattered approach is not restricted to plane waves and can be expanded to any waveforms that can be described in analytical or semi-analytical form. While existing formulations of FDTD have been immensely successful, they are not well suited to problems that involve near field scattering/interaction problems, where both the source and object are in the same domain but at a substantial distance from each other. This is due to the exceedingly high demands for computational resources that may result from the domain size, and/or dramatically different requirements for the mesh density in the source and object areas. One solution to this problem is to separate the domain into source and scatterer regions coupled by surface boundary radiation conditions. However, this method can incur large storage requirements for calculation of the radiation conditions. A specific near-field situation of interest to the utility industry is the case of workers near high voltage powerlines. In this instance, the field pattern takes on a cylindrical, transverse electromagnetic character. More general radiating sources can be accurately represented in the near-field by using spherical wave expansions, which are often used to represent antennas measured on test ranges. Successful implementation of these analytic solutions is feasible within the FDTD framework, and would allow for the illumination of the scatterer modeled at a considerably lower cost than in the standard approach. This thesis presents a method where these non-uniform, near-field, sources can be implemented implicitly as source conditions in an existing FDTD method. The specific case of powerline fields is described first, followed by the more general case of spherical waves. The analytic solution for powerline fields is implemented to show that near-field source configuration can be successfully modeled implicitly with accurate and efficient results. The method is validated by comparing with known analytic solutions, with very good accuracy being achieved. Then, a specific example of a human under a powerline close by is modeled to examine predictions made earlier under the assumption of a plane wave source condition. For a similar powerline source configuration, results of organ dosimetry predict that induced fields are from ten to sixty percent greater than predicted with the plane wave source. This same approach is applied to model a more general and difficult problem, namely spherical waves as sources in the total/scattered FDTD, called the SW-FDTD. Since transverse properties of spherical modes are known, the behavior of a mode can be represented on a one-dimensional radial grid. Thus, much like the plane wave sources in the FDTD method, the spherical wave modes are time-stepped on one-dimensional staggered electric/magnetic field source grids in the radial direction, representing mode propagation in free space. Spherical wave modes can then be interpolated and summed on the Huygens’ surface to represent the total field of the source, thus providing the coupling between the complex source and a scatterer using one-dimensional grids. It is assumed that the object of interest is beyond the reactive near-field of the source, and therefore there is no significant coupling between source and object. The SW-FDTD method is validated by comparing simulations with several analytic solutions that increase in complexity, demonstrating very good accuracy. Issues relating to the numerical implementation are discussed, including the effects of numerical dispersion, stability, and simple Mur first order boundary conditions. Incorporation of the method as a source condition in an existing FDTD program, and validation of this synthesis, show that the SW-FDTD method can implictly model sources as accurately as explicit models do. The efficiency, and the reduction of errors remain issues for further research to improve the overall utility of the SW-FDTD method. / Graduate

[pt] É analisado o problema de difração de uma onda eletromagnética cilíndrica pela borda de um semi-cilindro parabólico. O problema é formulado em termos das funções de Weber do cilindro parabólico que são soluções da equação de onda em coordenadas cilindro-parabólicas. A solução é obtida com o auxílio da técnica de Wiener-Hopf que fornece, para os campos espalhados, um resultado em termos de uma equação integral. Obtém-se, então, as aproximações assintóticas destes resultados. Estas aproximações fornecem para regiões afastadas da fronteira de sombra uma solução em termos de ponto de sela isolado, e nas regiões próximas desta fronteira, uma solução em termos de ponto de sela próximo a um pólo. / [en] The work consider the analysis of the diffraction of a eletromagnetic cylindrical wave by the edge of a parabolic semi-cylinder. Weber functions are used to formulate the problem. The solution of this formulation is then obtained by the use of the Wiener-Hopf téchnique leading to an integral equation which is solved by assymptotic approximations.

M.Ing. (Electrical And Electronic Engineering) / The metals manufacturing industry is the link between the mining industry, where the ore is mined, and the manufacturing industries, where metals are utilized to create a wide range of products. Melting processes.are used in the manufacturing of metals from the ore, of which induction melting is one of the possible melting processes. In this study the improvement of induction melting of metals is investigated. A new topology for an induction melting furnace is proposed, and this topology is thoroughly investigated. The induction melting process is influenced by certain user-controlled variables as well as the electromagnetic layout of the furnace. In this study, the influence of these variables on the performance of the furnace are investigated through finite element simulations and insight is also gained into the influence of the electromagnetic layout of the system. An experimental induction melting furnace is described in this study, investigated and compared to the predictions from the simulations. Improvements from structural, thermal and measuring viewpoints are also investigated and implemented.

<div>A numerical simulation was developed to capture the phenomena of electromagnetic stirring in a metallurgical ladle. Electromagnetic stirring requires an external magnetic field to be imposed on the molten steel bath, which is governed by the principles of magnetohydrodynamics. Electromagnetic stirring benefits over traditional stirring methods by offering non-invasive stirring, melt homogeneity, and ease of configuration alterations. Insight to the electromagnetic stirring phenomena is limited experimentally due to the high temperatures of the molten-steel bath. This investigation will include two numerical simulations, the first of which is to generate a magnetic field to properly stir the steel bath. The second incorporates the generated magnetic field and solves the fluid flow due to the magnetohydrodynamics interactions. The results of these numerical simulations will help to provide further understanding of the electromagnetic stirring method. This simulation was used to analyze the molten-steel bulk velocity, vortex formation, flow development time, slag-eye size, and wall shear stress in a metallurgical ladle.</div><div><br></div><div><div>The transient development of the bulk velocity in an EMS ladle was compared with the literature study completed by Sand et al. 2009. The comparison of the developed bulk velocity resulted in a percentage difference of 0.98% and an absolute difference of 0.007 [m/s]. Both numerical models, in the current work and the literature study, obtained a developed flow within 25 seconds of stirring. For the parametric studies, it was found that the addition of a circumferential taper angle to the geometry reduced the bulk velocity and slag-eye size formed compared to a cylindrical ladle. The electric current amperage of the external magnetic field coil system was determined to precisely adjust the bulk velocity. A 150 [A] reduction in amperage results in a ~20% loss in the bulk velocity magnitude. The locations of the high shear stress regions were determined which remained near the stirring unit.</div><div><br></div><div>From this study, it is recommended to use a magnetohydrodynamics package offered within a multiphysics numerical solver since the FLUENT® MHD module inherently under-predicts the velocity as well as the issue of the numerical instabilities of the Lorentz force calculations.</div></div><div><br></div>

A dynamic momentum compaction factor, also referred to as a dynamic $\Delta\gamma\sb{t}$, lattice for the FNAL Antiproton Source Debuncher Storage Ring is studied, both theoretically and experimentally, for the purpose of improving stochastic precooling, and hence, improving the global antiproton production and stacking performance. A dynamic $\Delta\gamma\sb{t}$ lattice is proposed due to the competing requirements inherent within the Debuncher storage ring upon $\gamma\sb{t}$. Specifically, the Debuncher storage ring performs two disparate functions, (i) accepting and debunching a large number of ps/pulse at the outset of the production cycle, which would perform ideally with a large value of $\gamma\sb{t}$, and (ii) subsequently employing stochastic cooling throughout the remainder of the p production cycle for improved transfer and stacking efficiency into the Accumulator, for which a small value $\gamma\sb{t}$ is ideal in order to reduce the diffusive heating caused by the mixing factor. In the initial design of the Debuncher optical lattice, an intermediate value of $\gamma\sb{t}$ was chosen as a compromise between the two functional requirements. The goal of the thesis is to improve stochastic precooling by changing $\gamma\sb{t}$ between two desired values during each p production cycle. In particular, the dynamic $\Delta\gamma\sb{t}$ lattice accomplishes a reduction in $\gamma\sb{t}$, and hence the mixing factor, through an uniform increase to the dispersion throughout the arc sections of the storage ring. Experimental measurements of cooling rates and system performance parameters, with the implementation of the dynamic $\Delta\gamma\sb{t}$ lattice, are in agreement with theoretical predictions based upon a detailed integration of the stochastic cooling Fokker Planck equations. Based upon the consistency between theory and experiment, predictions of cooling rates are presented for future operational parameters of the Antiproton Source with the dynamic $\Delta\gamma\sb{t}$.

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