Dissertations / Theses on the topic 'Transient electromagnetic fields'

From past experiments conducted with high intensity lasers, it has been known for some time that laser matter interactions result in the emission of short, transient electromagnetic pulses. Previous investigations into laser generated electromagnetic pulses provide basic information regarding frequencies where such pulses may be present, along with the time duration of the pulses. Such investigations have also demonstrated a number of measurement techniques in which basic information on the pulses may be obtained. The purpose of this current investigation is to obtain a more thorough description and understands of electromagnetic pulses generated for laser matter interaction. To this end, spatial radiation patterns emanating from various laser excited matter sources was predicted using antenna theory for far field radiators. Experimentally, it is the intention of this investigation to gather comprehensive time and frequency domain data on laser matter generated electromagnetic pulses using a number of specific laser targets. Radiation detection techniques using broadband, calibrated EMC horn antennas were devised. A unique measurement system known as an inverse superhetereodyne receiver was designed, tested and demonstrated. An experimental setup using such instrumentation was established. Using the above instrumentation and experimental setup should yield comprehensive time and frequency domain data over a spectra range of 1-40 GHz and with a time resolution of 50 ps. Because the experimental system employed is calibrated, measurements can be corresponded to incident electromagnetic fields. Several tests were conducted to ensure the proper operation of experimental apparatus. A modulation test was conducted on the inverse superhetereodyne receiver to ensure that the experimentally observed signals appeared when and where predicted within the receiver's bandwidth. The experimental setup was used to measure radiation emitted from an electrostatic discharge source of known distance and discharge voltage. Frequency domain data from the discharges were collected and compiled using a Matlab application ultimately intended to measure laser matter interaction generated electromagnetic pulses, resulting in a compiled frequency domain description comprising 1-17 GHz. The inverse Fourier transform was used to retrieve the time domain response from the compiled data. The discharge gaps characteristics where systematically altered as to allow a parametric study of the compiled data. The discharge measurements demonstrate the measurement system's ability to analyze unknown, short duration; broadband microwave signals.
M.S.
Department of Physics
Arts and Sciences
Physics

Die dreidimensionale Positionsbestimmung unter Tage ist eine in der bergbautechnischen Praxis häufig gestellte Aufgabe. Die derzeit gebräuchlichen Verfahren basieren überwiegend auf zahlreichen relativen Messungen zwischen Festpunkten an der Erdoberfläche und dem zu bestimmenden Punkt unter Tage. Das hier vorgestellte Verfahren ist ein im geodätischen Sinn absolutes Verfahren. Die Punktbestimmung erfolgt direkt mit Hilfe der Festpunkte über Tage und dem unbekannten Punkt unter Tage. Relative Messungen zu benachbarten Punkten sind nicht notwendig. Die Grundlage des Verfahrens bildet die zeitliche Erfassung transienter elektromagnetischer Felder an einem zu bestimmenden Punkt unter Tage. Die Quellen dieser Felder sind gleichstromdurchflossene Drahtschleifen an der Erdoberfläche, die näherungsweise magnetische Dipole darstellen. Nach Abschalten des Stromes zerfällt das statische Magnetfeld und induziert elektrische Ströme in der leitfähigen Erde. Das transiente Magnetfeld wird unter Tage an einem Punkt für verschiedene Senderpositionen aufgezeichnet. Mit Hilfe eines Inversionsalgorithmus werden letztlich die dreidimensionalen Koordinaten des Messpunktes bestimmt
Three-dimensional positioning in mines and caves is a common challenge. The methods currently used are based on numerous relative measurements. The method presented here is an absolute procedure in a geodesic sense. The coordinates of the unknown point are directly calculated using the surface points and the point underground. Relative measurements to neighboring points are not necessary. The localization procedure is based on recording transient electromagnetic fields under-ground. They are generated at the surface using direct-current carrying wire loops, which approximately represent magnetic dipoles. After shutoff the static magnetic field decays and induces electric currents in the conductive Earth. The transient electromagnetic field is recorded at an unknown point in the subsurface for different source positions. Finally, the three-dimensional coordinates of this point are reconstructed using an inversion algorithm

Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 12 Dec 2003.
Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2048" Stavroula Foteinopoulou. 12/12/2003. Report is also available in paper and microfiche from NTIS.

La première partie de la thèse étudie le balayage des gradients de conductivité électrique avec la force de Lorentz induite par ultrasons (SECG-UILF). Pour réduire la puissance de stimulation instantanée du transducteur émetteur et en même temps la pression acoustique maximale du transducteur, cette thèse propose d'appliquer l'excitation de l'impulsion ultrasonore à la modulation de fréquence linéaire ou l'excitation de l'impulsion ultrasonore à fréquence sinusoïdale dans SECG-UILF. Pour les gradients de conductivité électrique à balayage avec la force de Lorentz induite par l’ultrasons à la modulation de fréquence linéaire (SECG-LFM-UILF), un signal électrique de puissance instantanée maximale de 39,54 dBm est utilisé pour exciter le transducteur de transmission, ce qui est inférieur de 25,5 dB à la puissance instantanée maximale de l'impulsion étroite haute tension négative (65,05 dBm) adopté dans le SECG-UILF traditionnel. Et en temps, la pression acoustique d'émission maximale dans le SECG-LFM-UILF est inférieure de 0,44 MPa à celle du SECG-UILF traditionnel. Des expériences de SECG-LFM-UILF sont effectuées en utilisant des fantômes de conductivité à la gélose saline à plusieurs formes de conductivité allant de 0,2 S/m à 0,5 S/m, ce qui montre que: (1) le SECG-LFM-UILF peut détecter avec précision la distance longitudinale des gradients de conductivité électrique; (2) le rapport signal sur bruit des images de balayage B reconstituées de la distribution de gradient de conductivité électrique par le SECG-LFM-UILF est comparable à celui obtenu par le biais du SECG-UILF traditionnel; et (3) en utilisant une largeur de bande de fréquence de modulation de 2 MHz et une durée de modulation de 500 μs, une résolution longitudinale de 1 mm est obtenue. Pour balayer des gradients de conductivité électrique avec une force de Lorentz induite par ultrasons à fréquence fréquentielle (SECG-SF-UILF), le schéma de démodulation en phase présente une implémentation matérielle plus simple que le schéma de démodulation IQ, mais ne peut détecter que la moitié de la plage longitudinale. Des expériences de SECG-SF-UILF sont effectuées sur un échantillon de feuille de cuivre à deux couches, qui démontrent qu’en utilisant une largeur de bande de fréquences de 2 MHz et 64 fréquences discrètes, la plage longitudinale de l’échantillon peut être détectée avec précision. La deuxième partie de la thèse étudie l'élastographie à base d'approche de corrélation croisée. Pour élargir la largeur de bande de fréquence du champ de déplacement de l’onde de cisaillement afin d’améliorer la qualité de la carte de vitesse de l’onde de cisaillement, cette partie étudie l’application de la force de Lorentz pour la génération de champs d’onde de cisaillement. Tout d'abord, la génération des sources des ondes de cisaillement sur la surface du support souple à travers le mécanisme de la force de Lorentz est étudiée en stimulant un anneau ou un patch conducteur non ferromagnétique avec un champ magnétique transitoire. La mesure de déplacement à l'aide d'une sonde laser interférométrique confirme les caractéristiques d'origine, de fréquence et d'amplitude de la force de Lorentz. Sous un champ magnétique transitoire dont la vitesse de changement est de 10,44 kTs-1, le patch génère une source de champ des ondes de cisaillement d'amplitude de 100 µm à la surface de l'échantillon de fantôme d'alcool polyvinylique (PVA). Ensuite, le potentiel des champs d'ondes de cisaillement générés pour la reconstruction de la vitesse des ondes de cisaillement basée sur la corrélation croisée est exploré. Sur la base de l’approche de corrélation croisée, les cartes qualitatives de la vitesse des ondes de cisaillement sont reconstruites à partir de 100 cadres des champs de déplacement, à partir desquels les interfaces ou les limites entre des régions de rigidité différente peuvent être clairement reconnues, lesquelles sont complètement dissimulées dans les images ultrasonores
The first part of the thesis studies the scanning electric conductivity gradients with ultrasonically induced Lorentz force (SECG-UILF). To reduce the instantaneous stimulation power to the transmitting transducer and at the same time the peak acoustic pressure from the transducer, this thesis proposes to apply the linearly frequency-modulated ultrasound pulse excitation or the sinusoidal step-frequency ultrasound pulse excitation in SECG-UILF. For the scanning electric conductivity gradients with linearly frequency-modulated ultrasound-induced Lorentz force (SECG-LFM-UILF), electrical signal of peak instantaneous power of 39.54 dBm is used to excite the transmitting transducer, which is 25.5 dB lower than the peak instantaneous power of the negative high-voltage narrow pulse (65.05 dBm) adopted in traditional SECG-UILF; and at the same time, the peak transmitting acoustic pressure in SECG-LFM-UILF is 0.44 MPa lower than that in traditional SECG-UILF. Experiments of SECG-LFM-UILF are done using multi-shaped saline agar phantoms of conductivity ranging from 0.2 S/m to 0.5 S/m, which show that: (1) the SECG-LFM-UILF can detect precisely the longitudinal distance of the electric conductivity gradients; (2) the signal-to-noise ratio of the reconstructed B-scan images of the electrical conductivity gradient distribution by the SECG-LFM-UILF are comparable to that obtained through the traditional SECG-UILF; and (3) using modulation frequency bandwidth of 2 MHz and modulation duration of 500 μs, a longitudinal resolution of 1 mm is achieved. For the scanning electric conductivity gradients with step-frequency ultrasound induced Lorentz force (SECG-SF-UILF), the in-phase demodulation scheme is simpler in hardware implementation than the IQ demodulation scheme but can only detect half of the longitudinal range. Experiments of SECG-SF-UILF are done on a sample of two-layer copper foil, which demonstrate that, using a frequency bandwidth of 2 MHz and 64 discrete frequencies, the longitudinal range of the sample can be detected precisely. The second part of the thesis studies the cross-correlation approach based elastography. To expand the frequency bandwidth of the shear wave displacement field so as to improve the quality of the shear wave velocity map, this part studies application of the Lorentz force for generation of shear wave fields. First, generation of shear wave sources on the soft medium surface through the mechanism of the Lorentz force is investigated by stimulating a non-ferromagnetic conductive ring or patch with a transient magnetic field. The origin and the frequency and amplitude characteristics of the Lorentz force acting on the conductive ring are confirmed by the displacement measurement using an interferometric laser probe. Under a transient magnetic field of changing rate of 10.44 kTs-1, the patch generates a shear wave field source of amplitude of 100 μm at the surface of the sample of polyvinyl alcohol (PVA) phantom. The shear wave fields created and propagating in the PVA phantom by experiments agree qualitatively well with the theoretical shear wave fields calculated through the analytical Green function solution. Then, the potential of the generated shear wave fields for the cross-correlation based shear wave velocity reconstruction is explored. Based on the cross-correlation approach, the qualitative shear wave velocity maps are reconstructed from 100 frames of the displacement fields, from which the interfaces or boundaries between regions of different stiffness can be clearly recognized, which are completely concealed in the ultrasound images

Orientador: Maria Cristina Dias Tavares
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: Esta tese tem como objetivo o desenvolvimento de modelos mais precisos para o cálculo de parâmetros elétricos de linhas aéreas de transmissão para estudos de transitórios na faixa de frequência 0 a 2 MHz. Esta faixa de frequência cobre a maioria das perturbações eletromagnéticas nos sistemas elétricos: energização, faltas simétricas e assimétricas, rejeições de carga, descargas atmosféricas, perturbações harmônicas, etc. Na faixa de frequência citada, em consequência da dependência dos parâmetros do solo com a frequência, a condutividade elétrica do solo (sg) tem a mesma ordem de grandeza que o produto entre a frequência angular do sinal incidente no solo (w) e a permissividade elétrica do solo (eg). Portanto, as suposições de baixa frequência tradicionalmente adotadas - sg constante e weg desprezível (sg >> weg) - podem levar a modelos que não representam de forma adequada a resposta da linha no caso de transitórios rápidos (com espectro de frequência acima de 1 kHz). O objetivo central desta tese é verificar a influência da dependência dos parâmetros do solo no cálculo da impedância longitudinal e admitância transversal por unidade de comprimento em comparação com os modelos tradicionais de cálculo. As análises são feitas inicialmente para o caso de um único condutor acima do solo e posteriormente através de um estudo para uma linha de transmissão trifásica, 440 kV, em operação no sistema elétrico brasileiro. As impedâncias longitudinais e as admitâncias transversais de retorno pelo solo são avaliadas através de métodos tradicionais de cálculo e através de integração numérica das formulações de Carson modificadas para inclusão do modelo de solo que considera a depêndencia de sg e weg em função da frequência
Abstract: This thesis aims to propose more accurate models for calculating the electrical parameters of overhead power transmission lines. The influence of earth's conductivity and permittivity frequency dependence is evaluated when calculating transversal and longitudinal transmission lines' parameters in the frequency range 0 to 2 MHz. This frequency range covers the majority of the electromagnetic transients in electrical systems (switching transients, faults' transients, load rejections, harmonic disturbances, etc). Between 1 kHz to 2 MHz, the product of the signal angular frequency (w) by the dielectric constant (eg) of the soil may have the same order of magnitude as the conductivity (sg), due to the variation of these parameters with frequency. Therefore, the assumptions of low frequency traditionally used - the soil conductivity (sg) considered as constant and weg that can be negligible (sg >> weg) - can lead to incorrect models that do not adequately represent the transmission line's response, in cases of fast transients phenomena (with frequency spectrum above 1 kHz). The importance of properly considering the frequency dependent soil model is presented for the one-conductor case and for a single three-phase transmission line (440 kV, considered ideally transposed). The aim is to compare the transmission line parameters calculated considering the conductivity and weg frequency dependence ground model in relation to the common ground representation, with constant conductivity and weg that may be neglected. It is also compared the results obtained from the complex plane method with those obtained from the Carson's modified expressions for longitudinal parameters and between Carson's modified potential-coefficient correction factors and from the most common approximated methods for transversal admittance parameters
Doutorado
Energia Eletrica
Doutor em Engenharia Elétrica

As descargas atmosféricas são reconhecidamente responsáveis por uma parcela expressiva das interrupções não programadas de fornecimento de energia em sistemas elétricos, contribuindo de forma significativa para a composição dos índices de qualidade de energia mesmo no caso de regiões com níveis ceráunicos moderados. No caso de sistemas de distribuição, grande parte dos problemas está relacionada às sobretensões induzidas por descargas próximas às linhas, as quais decorrem dos campos elétrico e magnético, associados à corrente que se propaga ao longo do canal da descarga. O conhecimento das características de tais campos é, portanto, fundamental para a determinação das sobretensões induzidas nas linhas aéreas de energia. Embora a importância do tema tenha propiciado nos últimos anos o desenvolvimento de um grande número de pesquisas a respeito dos campos eletromagnéticos e das tensões induzidas por descargas atmosféricas, na grande maioria dos trabalhos o solo é representado através de um plano condutor perfeito, portanto com condutividade infinita. Embora tal simplificação possa, em geral, ser considerada válida para a indução magnética e para o campo elétrico vertical, ela não é aplicável ao campo elétrico horizontal, em especial no caso de solos com alta resistividade. Este estudo visa avaliar o comportamento dos campos elétrico (vertical e horizontal) e indução magnética gerados por descargas atmosféricas nuvem-terra, levando em consideração os parâmetros da descarga (amplitude, forma de onda e velocidade de propagação da corrente) e os diferentes modelos para representação do canal da descarga. Além do caso de solo perfeitamente condutor, são consideradas situações mais realistas, isto é, verificando-se a influência, nos campos, de parâmetros como a resistividade e permissividade do solo.
The occurrence of lightning discharges causes a significant amount of unscheduled supply interruptions in overhead lines of electricity systems, contributing to decrease quality indicators of these systems, even in the case of regions with moderated ground flash density. Focusing on the distribution systems, great part of the problems are related to the induced voltages due to lightning discharges in the vicinity of overhead lines, which results from the electric and magnetic fields associated with the current propagation along the return stroke channel. The knowledge of the characteristics of lightning electromagnetic fields is, therefore, crutial for determining induced voltages on overhead lines. Although the importance of the assumption has propitiated in the last years the development of a great number of research concerning the lightning electromagnetic fields and induced voltages on overhead lines, in most of the studies the hypothesis of a perfect conducting ground is assumed. While such assumption can be considered valid for magnetic induction field and for the vertical component of the electric field, it doesn’t apply to the horizontal electric field, especially in the case of ground with high resistivity. The aim of this work is to present and to discuss the characteristics of the electric field (vertical and horizontal components) and magnetic induction generated by the cloud-to-ground lightning discharge, taking into account the lightning parameters (amplitude, waveform and propagation speed of the return stroke current) and the different return stroke models. Besides the case of perfect conducting ground, the influences of the ground permittivity and finite conductivity in the calculation of the electromagnetic fields are so considered.

The master thesis is focused on the simulation of the toroid coils in Ansoft Maxwell 3D software, which uses finite element method for electromagnetic field simulation. Firstly the process creation of the geometric model toroid coil with seventy-five threaded is presented. It is necessary to debug this model and prepare it for the mesh generation. Physical properties are assign to this model and it gives rise to the physical model. We will set boundaries, excitation current, core material, winding material and the parameters for the mesh generations. New material Kashke K4000 will be created in the materials library and subsequently we will define its BH curve on the basis of datasheet. Analysis is made in two modes. Direct currents (7,5A; 10A; 15A; 20A; 25A) and (non)linear materials are used in magnetostatic solution. Toroid coil is excited by current pulse in transient solution. In Ansoft Maxwell Circuit editor a source which generates current pulse will be created. This excitation will be assigned to the toroid coil as an extern source through a terminal. Core material is linear in the case of transient analysis, because Ansoft Maxwell 3D doesn´t allow to use nonlinear material in this solution. Settings are different in transient and in magnetostatic analysis. End time and time step are entered to solve this task in transient analysis. Time points are entered too. Flux density and electromagnetic field strength are calculated in these time points and later it will be possible to view the results. Calculated fields are shown as the pictures in this thesis. The procedure how to use a field calculator in the postprocessing is given as well. The achievements are summarized in the conclusion.

Une molécule soumise à un champ laser infra-rouge intense (dans la gamme des 10 14 W.cm−2) peut être ionisée par effet tunnel. Le paquet d’ondes électroniques (POE) ainsi libéré est alors accéléré par le champ laser et, lorsqu’il repasse à proximité de l’ion parent, il a une certaine probabilité de se recombiner dans son état fondamental. Lors de cette recombinaison, le POE libère son énergie sous la forme d’un flash attoseconde (1as=10 −18s) de rayons XUV. Cette émission cohérente est produite à chaque demi-cycle laser résultant en un train d’impulsions attosecondes. Dans le domaine spectral, ce train correspond à un spectre discret d’harmoniques de la fréquence lasers. L’étape de recombinaison de l’électron avec l’ion parent peut être considérée comme une sonde de la structure des orbitales de valence moléculaires participant à la génération d’harmoniques et de la dynamique ayant lieu dans l’ion pendant l’excursion de l’électron dans le continuum. En caractérisant en amplitude, phase et polarisation, l’émission harmonique associée à cette recombinaison, il est possible de remonter à ces informations structurales et dynamiques avec une précision de l’ordre de l’Ångström et une résolution attoseconde. En particulier, la phase de l’émission harmonique qui est difficile à caractériser, encode des informations indispensables à la bonne compréhension des processus ayant lieu dans le milieu de génération. Nous présentons les principes et testons de nouvelles techniques permet tant de caractériser la phase de l’émission attoseconde suivant plusieurs dimensions à la fois et dans un laps de temps optimisé. Dans une première partie, nous présentons une méthode permettant de caractériser rapidement la phase spectrale de l’émission harmonique, fondée sur un modèle en champ fort de la photoionisation à deux couleurs (RABBIT). Nous introduisons ensuite une nouveau dispositif interférométrique à deux sources, permettant de mesurer les variations de phase de l’émission attoseconde induites par l’excitation d’un paquet d’ondes rotationnelles ou vibrationnelles. Ce dispositif très stable, compact et sobre énergétiquement repose sur l’utilisation d’un élément optique de diffraction (DOE) binaire. Après avoir qualifié notre dispositif par des simulations numériques et des expériences préliminaires, nous montrons qu’il est si sensible qu’il permet de mesurer les variations de phase en fonction du paramètre d’excitation pour différentes trajectoires électroniques dans le continuum. Pour l’azote et le dioxyde de carbone, les mesures expérimentales montrent des variations de phase très différentes pour les deux premières trajectoires électroniques. Ce DOE est ensuite utilisé pour mesurer la phase de l’émission harmonique dans les molécules alignées dans les mêmes conditions expérimentales que le RABBIT. Les deux expériences menées successivement donnent des résultats compatibles que nous combinons par deux méthodes différentes : le CHASSEUR et le MAMMOTH. Enfin, nous proposons de combiner le DOE avec un réseau transitoire pour caractériser simultanément la phase de l'émission attoseconde moléculaire suivant deux axes de polarisation différents. Ces différentes techniques de mesure de phase nous ont permis d’étudier précisément l’émission harmonique suivant différentes dimensions (angle d’alignement, intensité de génération, trajectoire électronique) et d’en tirer de nouvelles informations sur le mécanisme de génération dans les molécules
When a low-frequency laser pulse is focused to a high intensity into a gas, the electric field of the laser light may become of comparable strength to that felt by the electrons bound in an atom or molecule. A valence electron can then be 'freed' by tunnel ionization, accelerated by the strong oscillating laser field and can eventually recollide and recombine with the ion. The gained kinetic energy is then released as a burst of coherent XUV light which is spectrally organized as harmonics of the fundamental driving field frequency.In high-harmonic molecular spectroscopy, the recombining electron wave-packet probes the structure of the molecule and the dynamics occurring in the ion left after tunnel ionization. The XUV burst is imprinted with this information which can be retrieved through an accurate characterization of the amplitude, phase and polarization of the harmonics. In the case of small molecules as nitrogen and carbon dioxide, impulsive alignment allows to change the direction of recombination of the electron wave-packet with respect to the molecular axis. The XUV burst from the molecular sample should then be characterized both along the spectral dimension and the alignment angle one, and this for the two polarization components. In this report, we present a new experimental scheme to perform two-source interferometry to measure the phase of the emission in aligned molecules along the alignment angle dimension. We how a refined spatio-spectral analysis of the fringe patterns obtained with this very stable interferometer allows one to extend high-harmonic spectroscopy from short to long trajectories. We then show how the combination of this setup together with RABBIT gives access to a bidimensionnal (spectrum and alignment angle) phase map with no arbitrary constant. Finally comparing two-source interferometry with transient grating spectroscopy leads to inconsistent results that can be interpreted taking into consideration polarization effects

In this thesis, the problem of calculating power transmission line induced or radiated electromagnetic fíelds is studied by decomposing the line into a large number of snall segments, k¡own as Hertzian dipoles. Since the presence of lossy ground makes the electromagnetic fìeld distribution very different from that of the same dipole over perfectly conducting ground, different approaches should be followed for the lossy and lossless ground assumptions. The contribution of each dipole on the total electric and magnetic field is calculated using three analytical techniques. Two of these methods are frequency-domain solutions for the problem of dipole radiation above lossy ground, while the third method is a time-domain exact solution for the same problem based on the assumption of perfectly conducting ground. The theoretical background and extent of validity of each technique are reviewed in this thesis. Tlie results derived by applying each method are compared with those obtained using a commercial software package. The time-domain solution for the problem of power transmission line electromagnetic fields is obtained using Fourier and inverse Fourier transforms, rvhich enables us to obtain the electromagnetic waveforms associated with power system transients. The effect of different parameters such as conductivity and relative permittivity of the ground, the line{o-observation point distance, height, and sag of the transmission line is studied. Further, the impact of downscaling of transmission line on different electromagnetic parameters is analyzed, and the appropriate scale factor for each parameter is derived.

Στην παρούσα διπλωματική εργασία μελετήθηκε και προσομοιώθηκε η επίδραση των μεταβατικών φαινομένων σε μεταλλικές κατασκευές. Συγκεκριμένα μελετήθηκαν οι επιπτώσεις της πτώσης ενός κεραυνού σε ένα πλοίο. Για την πραγματοποίηση αυτής της μελέτης χρησιμοποιήθηκε το πρόγραμμα προσομοίωσης emp3 , το οποίο έχει κατασκευασθεί από την εταιρία field precision και είναι κατάλληλο για τη μελέτη τέτοιων φαινομένων. Το emp3 στηρίζεται στη μέθοδο των πεπερασμένων στοιχείων στο πεδίο του χρόνου (FETD-FINITE-ELEMENT-TIME-DOMAIN) και καταλήγει σε συμπεράσματα με πλήρη επίλυση των εξισώσεων του Maxwell χρησιμοποιώντας μια ψευδογλώσσα επιπέδου assembly .Στο υποπρόγραμμα mesh.exe σχεδιάστηκε ένα πλοίο και το περιβάλλον του και στη συνέχεια δημιουργήθηκε το αρχείο .ein στο οποίο χωρίστηκε η διάταξη σε διάφορες περιοχές ανάλογα με τις ηλεκτρομαγνητικές ιδιότητες της καθεμίας, με σκοπό να παρατηρήσουμε τα ηλεκτρομαγνητικά πεδία που δημιουργεί το μεταβατικό φαινόμενο (κεραυνικό πλήγμα) στις τρείς διαστάσεις. Τέλος, τρέξαμε το αρχείο .ein στο emp3.exe και παραθέσαμε τα αποτελέσματα της προσομοίωσης που προέκυψαν τόσο από το υποπρόγραμμα vemp3.exe όσο από το υποπρόγραμμα probe.exe και εξαγάγαμε κάποια συνολικά συμπεράσματα. Στο πρώτο Κεφάλαιο θα γίνει αναφορά στο φυσικό φαινόμενο του κεραυνού και συγκεκριμένα στους τρόπους δημιουργίας του,στις παραμέτρους του καθώς και στους παράγοντες που τον επηρεάζουν. Στο δεύτερο Κεφάλαιο θα γίνει ανάλυση των διεργασιών που ακολουθούν την πτώση ενός κεραυνού σε ένα πλοίο και συγκεκριμένα στις επαγόμενες τάσεις και στα παραγόμενα ηλεκτρομαγνητικά πεδία καθώς και στις βλάβες που προκαλούνται τόσο στο πλοίο όσο και στα εξαρτήματα του. Στο τρίτο Κεφάλαιο θα γίνει ανάλυση του προγράμματος προσομοίωσης emp3 ,της μεθόδου στην οποία στηρίζεται ,της ψευδογλώσσας που χρησιμοποιεί και του έτοιμου παραδείγματος bdeflect με σκοπό την κατανόηση της διαδικασίας προσομοίωσης και των αποτελεσμάτων. Στο τέταρτο Κεφάλαιο θα γίνει η παρουσίαση της διαδικασίας προσομοίωσης και των αποτελεσμάτων. Συγκεκριμένα παρατείθεται η κατασκευή της γεωμετρίας του πλοίου και του περιβάλλοντος του,ο χωρισμός της συνολικής διάταξης σε περιοχές με διαφορετικά ηλεκτρομαγνητικά χαρακτηριστικά, η εισαγωγή του κώδικα στο emp3.exe τα αποτελέσματα που εξήχθησαν στα vemp3.exe και probe.exe καθώς και ορισμένα συμπεράσματα που προέκυψαν από τη διεξαγωγή της παρούσας διπλωματικής εργασίας.
In this dissertation the effect of the transient phenomena in metallic structures was studied and simulated.Specifically. were studied the effects of a lighting stroke on a ship. In order to carry out this study,was used the simulation program emp3, which is manufactured by the company field precision and is suitable for the study of such phenomena. The emp3 program is based on the method FETD-FINITE-ELEMENT-TIME-DOMAIN and concludes with complete resolution of Maxwell's equations using a pseudocode level assembly.In the subprogram mesh.exe was designed the ship and its environment and then was created the .ein file, in which the construction was divided in different regions depending on the electromagnetic characteristics of each area, in order to observe the fields that were created by the transient phenomenon (lighting stroke), in three dimensions. Finally, we ran the file .ein in emp3.exe and presented the simulation results, which were obtained from both the subprogram vemp3.exe and the subprogram probe.exe and drew some overall conclusions. In the first chapter there will be a reference to the natural phenomenon of lightning strike and specifically to the ways of it's creation, its parameters and the factors that influence it.Ιn the second chapter there is the analysis of the processes, which follow the fall of a lightning stroke on a ship and specifically the induced voltages generated electromagnetic fields and also the harms caused both to the ship and it's components. In the third chapter there is the analysis of the simulation program emp3, the method which it is based on, the pseudocode which is used and the already existed example bdeflect in order to understande the process simulation and results.In the fourth chapter the simulation process and the results are given. Specifically, the construction of the geometry of the ship and its environment, the separation of the total provision in areas with different magnetic characteristics, the insertion of the code in emp3.exe,the results exported to vemp3.exe and probe.exe and some conclusions drawn during this thesis are presented.

碩士
國立中山大學
機械與機電工程學系研究所
101
This study investigated the temperature field variation on material surface cause by the generation of Joule heat when transient electromagnetic wave hit at the surface of the material and the relationship between the temperature field variation and the electromagnetic field variation. Surface Plasmon wave is the collective shock behavior of free electrons within the metal that was affected by external electromagnetic field. The electron waves would not penetrate the metals because the shielding effect since high electron density of metal, but generate the confined longitudinal wave on surface. This wave is called non-radiative surface plasmon waves. Electromagnetic waves will be obtained by the finite difference time domain method for solving Maxwell''s equations. The relationship between the electromagnetic wave and the material surface thermal field can be analysis by two methods, to change the wavelength of electromagnetic or to change the materials

The indirect effects of a nearby lightning strike on an airborne vehicle with its long trailing conducting plume is not well understood. Since airborne vehicles and its payload are expensive, their loss as a result of either a direct strike or due to the induced current and voltage of a nearby lightning strike is not desirable. The electromagnetic field generated due to the induced current on the skin of the vehicle may get coupled with the internal circuitry through the apertures on the vehicle body. If the coupled electromagnetic energy is more than the damage threshold level of the sensitive devices of the control circuit, they may fail which may lead to aborting the mission or a possible degradation in the vehicle performance. It has been reported that lightning induced phenomena was the cause of malfunctioning as well as aborting of some of the lunar missions. So in the present work, the computation of induced current and voltage on the skin of the vehicle body in the presence of an ionized long trailing exhaust plume has been attempted. The lightning channel is assumed to be vertical to the ground plane and extends up to a height of 7.5 km. The radiated electric and magnetic fields from the lightning channel at different heights from 10 m to 10 km and for lateral distances varying from 20 m to 10 km from the lightning channel are computed and the field waveforms are presented. For the computation of the radiated electric and magnetic fields from the lightning channel, modified transmission line with exponential current decay (MTLE) model for representing the lightning channel and the Heidler’s expression for the lightning channel base current are used. The peak amplitude of the lightning current used is 12 kA with a maximum current derivative of 40 kA/µs. It is seen that the vertical electric field in general, is bipolar in nature and that the height at which the change in polarity reversal takes place increases with increase of lateral distance from the lightning channel. The vertical electric field just above the ground is unipolar for all lateral distances from the channel and this is because the contribution due to the image of the lightning channel dominates the vertical electric field. The horizontal electric field is always unipolar for all heights and all lateral distances from the lightning channel studied. The effect of variation in the rate of rise of lightning current (di/dt) and the velocity of lightning current on the radiated electric and magnetic fields for the above heights and distances have also been studied. It is seen that the variation in maximum current derivative does not have a significant influence on the electric field when ground is assumed as a perfect conductor but it influences significantly the horizontal electric field when ground has finite conductivity. The velocity of propagation of lightning current on the other hand has a significant influence for both perfectly as well as finitely conducting ground conditions. For the computation of the induced current and voltage on the body of the airborne vehicle due to the coupling of the above mentioned electromagnetic fields radiated from a near by lightning discharge, the vehicle and its exhaust plume have been modeled as a transmission line and Finite Difference Time Domain (FDTD) numerical technique has been used for the computation. Regardless of the vehicle size, the structure can be modeled as a nonuniform transmission line consisting of a series of sections consisting of capacitive and inductive components. These components of the vehicle and its exhaust plume are computed using the Method of Moment (MoM) technique. The interaction of the electromagnetic wave with the plume depends on the electrical conductivity as well as the gas dynamic characteristics of the plume. Hence, in this research work an attempt has also been made to study the electrical conductivity (σe) and permittivity (εe) as well as the gas dynamic properties of the exhaust plume taking into consideration its turbulent nature. In general, the airborne vehicle can be considered as perfectly conducting (conductivity 3x107 S/m) where as the plume has finite conductivity. The electrical properties of an airborne vehicle exhaust plume such as electrical conductivity and the permittivity and their distribution along axial and radial directions depend on several factors. They are (i) propellant composition, (ii) impurity content in the propellants which generate ionic charge particles in the exhaust and (iii) the characteristics of the exhaust plume intensive parameters such as temperature, pressure, velocity and the presence of shock waves. These properties of the exhaust plume are computed in the two separate regions of interest as discussed next. The first region is inside the combustion chamber and up to the nozzle throat of the vehicle and the second region is from the throat to the exterior i.e., the ambient atmosphere or the downstream of the plume. In the first region where chemical reaction kinetics have to be considered, NASA Chemical Equilibrium with Application (CEA) software package has been used to compute the intensive parameters of the fluid at the throat of the nozzle. The pressure in the combustion chamber is taken as 4410 kPa and the back pressure at the exit plane is taken as 101.325 kPa. In the second region, FLUENT software package have been used for the fluid dynamic study of the exhaust plume from the vehicle nozzle throat to the exterior domain. The data obtained from the first region using CEA provides the parameters at the nozzle throat that are used as input parameters for the second region. In the study, a conical nozzle configuration of throat radius (rt) of 0.0185 m (nozzle exit plane radius is 0.05 m), half cone angle of 18º and nozzle expansion ratio (Ae/At) of 7.011 are used. The contour plot of the intensive parameters of the exhaust plume and the mass fraction of the charged particles are presented. The vehicle exhaust flow passes through different types of expansion and compression waves. In the present work, simulation is done for a slightly under expanded nozzle i.e. nozzle exit static pressure is slightly more than the ambient static pressure. Since the exit pressure is more than the ambient pressure, the exhaust gases expand to reach the ambient pressure. As the expansion waves reach the contact discontinuity (i.e. the boundary where the outer edge of the gas flow meets the free stream air), they again reflect back inward to create compression waves. These compression waves force the flow to turn back inward and increase its pressure. If the compression waves are strong enough, they will merge into an oblique shock wave. In the present work, more than eight such barrel shocks are captured. When the shock waves are generated, Mach number reduces sharply and static temperature and static pressure increases where as the total temperature of the exhaust remains constant in the shock wave formations. The characteristics of the plume such as pressure, temperature, velocity and concentration of the charged particles (i.e., e¯, Na+ and Cl¯) and neutral species such as CO, CO2 , Cl, H, HCl, H2O, H2 , N2, Na, NaCl, O, OH and O2 along axial and radial directions in the external domain have been studied. The above parameters are used to compute the collision frequencies and plasma frequencies of the charged particles as well as the number density of the species along axial and radial directions of the exhaust plume. These parameters are used to compute the effective conductivity distribution in the axial and radial directions for an incident electromagnetic field of frequency 1 MHz. The peak value of the conductivity computed is 0.12 S/m near the exit plane and it reduces to 0.02 S/m at an axial distance of 7.5 m from the exit plane which is well within the range suggested in the published literature. It has been observed that the oscillation in the conductivity along axial direction is a reflection of the shock wave formation in the exhaust plume. The electrical conductivity and the relative permittivity of the exhaust plume have been computed for three different radii of the nozzle at the exit plane i.e., 0.025 m, 0.05 m and 0.075 m. It is seen that the distribution of the conductivity and relative permittivity along the axial direction of the exhaust are independent of the nozzle exit plane radius. To study the coupling of lightning electromagnetic field with the vehicle and its exhaust plume two cases have been considered. These are (i) when the vehicle and its exhaust plume are at certain height above the ground and (ii) when the exhaust plume is touching the ground. The dimensions of the vehicle used in the study are as follows: length of the vehicle is 20 m and the length of its exhaust plume is 75 m. The radius of the vehicle is taken as 0.5 m. The vehicle and its exhaust plume are assumed to be at a lateral distance of 250 m from the lightning channel. In case one, when the vehicle and its inhomogeneous exhaust plume tip is at a height of 10 m above the ground, both the ends are open. So the reflection coefficients of the current wave and voltage wave at the end points are -1 and +1 respectively irrespective of the characteristic impedances of the vehicle and its exhaust plume. So when the reflected current propagates it will tend to reduce along the length of the object. Hence, the induced current at the end points are zero and the currents in the end segments are less than those in the intermediate segments. The spatial distribution of the peak magnitude of the time varying induced current, |Imax|, in each segment along the length of the vehicle without and with the exhaust plume are presented. In case of vehicle without plume, the maximum value of the induced current is at the middle segment of the vehicle and its value is 4.8 A. The presence of the inhomogeneous plume enhances the maximum value of the induced current to 33 A and its position is shifted to the exhaust plume side. When the voltage wave propagates, it will enhance the induced voltage in the vehicle body. The time varying potential difference between the end points of the vehicle without plume and the vehicle with its exhaust plume which drives the induced current are computed and it is seen that the potential difference for the vehicle without plume is unipolar whereas it is bipolar for the vehicle with exhaust plume. The lightning induced current on the skin of the vehicle will generate an electromagnetic field which may couple with the internal electronic devices and circuits through the apertures. The amount of electromagnetic energy that will be transmitted through an aperture on the vehicle skin and coupled with the internal electronic equipments depends on the characteristics of the induced current on the skin of the vehicle, the electrical size, shape, orientation and location of the aperture and the location of the internal electronic devices with respect to the aperture. So the time varying induced current and its di/dt at three different locations on the vehicle body i.e., tail of the vehicle, middle of the vehicle and vehicle nose are computed. It is seen that the induced current on the vehicle and its di/dt in the absence of the plume are oscillating in nature but they are critically damped in the presence of the trailing inhomogeneous exhaust plume. It also shows that the enhancement of induced current and its di/dt at the tail are much more than at the middle or at the nose of the vehicle which is true for an electrically short vehicle i.e., lv/λmin ≈ 0.067 as cited in the literature. So the presence of an aperture on the skin of the vehicle near to tail will transmit maximum electromagnetic energy into the inside of the vehicle. Therefore during design of the electrically short airborne vehicles, any aperture should be avoided near the tail of the vehicle or internal electronic devices should be placed away from the tail of the vehicle. In case 2, when the plume is touching the ground, the transient induced current in the plume will propagate into the soil. The effective impedance for smaller currents will be quite high (the inductance and capacitance effect are not taken into consideration for calculating the impedance. So the impedance of the soil is dominated by only the resistance). However, as soon as the current exceeds a certain value, the resulting soil gradient can reach the breakdown gradient of the soil i.e., 200-500 kV/m as cited in literature resulting in soil ionization. This will effectively lower the soil impedance. These dynamic characteristics of the soil resistance with induced current are incorporated by considering the expression for the soil resistance. To study the effect of soil resistivity on the time varying induced current and the voltage, computations have been done for various resistivities of the soil i.e., 0 Ωm, 100 Ωm and 200 Ωm. For soil resistivity of 0 Ωm, the reflection coefficients at the ground and at the open ends for the current wave are +1 and -1 respectively. So at the ground end, the reflected current wave will enhance and at the open end it will diminish as it propagates along the length of the vehicle and its exhaust. As the resistivity of the soil increases, the reflection coefficient of the current at the ground end decreases from +1, so the peak magnitude of the current reduces along the length till the length is half of the total length of the plume and the vehicle. Therefore, the peak magnitude of the induced current in the ground segment is much more than the peak magnitude of the current in the segment at the open end. For a finitely conducting plume, the peak value of the potential difference between the two ends of the vehicle and its exhaust plume are 92 kV, 91 kV and 90 kV for soil resistivities of 0 Ωm 100 Ωm and 200 Ωm respectively. Therefore the influence of the soil resistivity on the induced current is found to be not much significant. The spatial distribution of the peak magnitude of the time varying induced current in each segment along the length of the vehicle with inhomogeneous exhaust plume for the above three different soil resistivities are presented at a lateral distance of 250 m from the lightning channel. It is seen that when the plume is touching the ground, the induced current on the vehicle at the tail, middle and nose sections are marginally more than when the vehicle and its exhaust are at a height of 10 m above the ground. The effects of different parameters such as peak value and maximum di/dt of lightning current, velocity of lightning current, lateral distance of the vehicle from lightning channel and the height of the tip of the exhaust plume above the ground on the induced current and voltage on the airborne vehicle have also been studied. The peak amplitude of the lightning current used are 30 kA and 100 kA in addition to 12 kA mentioned earlier for the field computation. Also maximum di/dt values of 40 kA/µs and 120 kA/µs for the lightning current have been used for the computation. It is observed that the induced current increases with increase of the peak value, maximum di/dt as well as the velocity of propagation of the lightning current where as the induced current will reduce with increase of lateral distance and height of the tip of the exhaust plume above the ground. As an offshoot of the present work, the axial and radial distribution of the parameter, σe/ωεe (loss tangent of the exhaust plume) for an incident electromagnetic wave (lightning electromagnetic field) frequency of 1 MHz have been computed to study the conducting properties of the exhaust plume. σe/ωεe of the exhaust plume at 1 MHz frequency varies from 2324 to 365. Since σe/ωεe >>1, the plume behaves as a good conductor and the displacement currents can be neglected. In addition to this, the variation of parameter σe/ωεe for frequency ranges of 0.1 MHz to 5 GHz are also studied where σe and εe are the maximum effective conductivity and permittivity of the exhaust plume at the chosen frequency of an incident EM wave. It shows that the parameter σe/ωεe is 1.8x104 at 0.1 MHz and reduces to 0.45 for 5 GHz and its value is 1 at a frequency of 2.285 GHz. Therefore at lower EM wave frequency, the exhaust plume behaves as a good conductor and that conductivity reduces with increase of the frequency. The exhaust plume in the present study behaves as a good conductor below or at the EM wave frequency of 2.285 GHz. The microwave attenuation of electromagnetic wave through the ionized plume (the angle of incidence of microwave is 90o and transmission of microwave is always transverse to the exhaust plume) has also been studied using the above electrical characteristics computed and it is seen that the attenuation follows the axial variation in the conductivity of each cross section of the plume. In the present work, a theoretical model has also been developed to compute the microwave attenuation through the vehicle exhaust plume using the electrical conductivity computed earlier for any angle of incidence of the microwave. The thesis also lists some additional topics for further studies.

In the recent years, there has been a trend to run metallic pipelines carrying petroleum products and high voltage AC power lines parallel to each other in a relatively narrow strip of land. The case of electromagnetic interference between high voltage transmission lines and metallic pipelines has been a topic of major concern since the early 60’s. The main reasons for that are: • The ever increasing cost of right-of-ways, suitable for power lines and pipelines, along with recent environmental regulations, aiming to protect nature and wildlife, has forced various utilities to share common corridors for both high voltage power lines and pipelines. Therefore, situations where a pipeline is laid at close distance from a transmission line for several kilometers have become very frequent. • The rapid increase in energy consumption, which has led to the adoption of higher load and short circuit current levels, thus making the problem more acute. Due to this sharing of the right-of-way, overhead AC power line field may induce voltages on the metallic pipelines running in close vicinity leading to serious adverse effects. This electromagnetic interference is present both during normal operating conditions as well as during faults. The coupling of the field with the pipeline takes place either through the capacitive path or through the inductive or conductive paths. In the present work, the induced voltages due to capacitive and inductive coupling on metallic pipelines running in close vicinity of high voltage power transmission lines have been computed.The conductor surface field gradients calculated for the various phaseconfigurations have been presented in the thesis. Also the electric fields under transmission lines, for both single circuit and double circuit (various phase arrangements) have been analysed. Based on the above results, an optimum configuration giving the lowest field under the power line as well as the lowest conductor surface gradient has been arrived at and for this configuration induced voltage on the pipeline has been computed using the Charge Simulation Method (CSM). For comparison, induced voltages on the pipeline have been computed for the various other phase configurations also. A very interesting result is that the induced voltage on the pipeline becomes almost negligible at a critical lateral distance from the center of the powerline and beyond which the induced voltage again increases.This critical distance depends on the conductor configuration. Hence it is suggested that the pipeline be located close to the critical distance so that the induced voltage would be close to zero. For calculating the induced voltage due to the inductive coupling, electromotive force (EMF),induced along the pipeline due to the magnetic field created by the transmission line has been calculated. The potential difference between the pipeline and the earth, due to the above induced EMFs, is then calculated. As the zones of influence are generally formed by parallelism, approaches, crossings as well as removals, the computation involves subdividing the zone into several sections corresponding to these zones. The calculation of voltages is carried out at both the ends of the sections. Each section is represented by an equivalent π electrical network, which is influenced by the induced EMF. The induced EMF is calculated during faulted conditions as well as during steady state conditions. Inductive coupling calculations have been carried out for the following cases: •Perfect parallelism between powerline and pipeline. •zone of influences formed by parallelism, approaches, crossings and removals. It has been observed that when the pipeline is approaching the HV transmission line at an angle, then running parallel for certain distance and finally deviating away, the induced voltage is maximum at the point of approach or removal of the pipeline from the transmission line corridor.The induced voltage is almost negligible near to the midpoint of the zone of influence. The profile of the induced voltage also depend on whether the pipeline is grounded or left open circuited at the extremities of the zone of influence. Effect of earth resistivity and anti-corrosive coatings on induced voltage has also been studied. For mitigating the induced voltage on the pipeline,numerous low resistive earthings have been suggested. Results show that significant reduction in induced voltage can be achieved as the number of earth points is increased.