Strongly localised plasmons in metallic nano-structures offer exciting characteristics for guiding and focusing light on the nano-scale, opening the way for the development of new types of sensors, circuitry and improved resolution of optical microscopy. The work presented in this thesis focuses on two major areas of plasmonics research - nano-focusing structures and nano-sized waveguides. Nano-focusing structures focus light to an area smaller than the wavelength and will find applications in sensing, efficiently coupling light to nano-scale devices, as well as improving the resolution of near field microscopy. In the past the majority of nano-focusing structures have been nano-scale cones or tips, which are capable of focusing light to a spot of nano-scale area whilst enhancing the light field. The alternatives are triangular nano-focusing structures which have received far less attention, and only one type of triangular nano-focusing structure is known – a sharp V-groove in a metal substrate. This structure focuses light to a strip of nano-scale width, which may lead to new applications in microscopy and sensing. The difficulty with implementing the V-groove is that the structure is not robust and is quite difficult to fabricate. This thesis aims to develop new triangular nano-focusing devices which will overcome these difficulties, whilst still producing an intense light source on the nano-scale. The two proposed structures presented in this thesis are a metallic wedge submerged in uniform dielectric and a tapered metal film lying on a dielectric substrate, the latter being the easier to fabricate and the more structurally sound and robust. The investigation is performed using the approximation of continuous electrodynamics, the geometrical optics approximation and the zero-plane method. The second aim of this thesis is to investigate plasmonic waveguides and couplers for the development of nano-optical circuitry, more compact photonic devices and sensors. The research will attempt to fill the gaps in the current knowledge of the V-groove waveguide, which consists of a sharp triangular groove in a metal substrate, and the gap plasmon waveguide, which consists of a rectangular slot in a thin metal film. The majority of this work will be performed using the author’s in house finite-difference time-domain algorithm and FEMLAB as well as the effective medium method and geometric optics approximation. The V-groove may be used as either a nano-focusing or waveguiding device. As a waveguide the V-groove is one of the most promising plasmonic waveguides in the optical regime. However, there exist quite a number of gaps in the current knowledge of V-groove waveguides which this thesis will attempt to fill. In particular, the effect of rounded groove tip on plasmon propagation has been assessed for the V-groove. The investigation of rounded groove tip is important, as due to modern fabrication processes it’s not possibly to produce an infinitely sharp groove, and the existing literature has not considered the impact of this problem. The thesis will also investigate the impacts of the inclusion of dielectric filling in the groove on plasmon propagation parameters. This research will be important for optimising the propagation characteristics of the mode for certain applications, but it may also lead to easier methods of fabricating the V-groove device and prevent oxidation of the metal film. The gap plasmon waveguide is easier to fabricate than the V-groove, and is a new type of sub-wavelength waveguide which displays many advantages over other types of plasmon waveguides, including ease of fabrication, almost 100% transmission around sharp bends, sub-wavelength localisation and long propagation distances of the guided mode, etc. This waveguide may prove invaluable in the development of compact photonic devices. In the past the modes supported by this structure were not thoroughly analysed and the possibility of using this structure to develop sub-wavelength couplers for sensing and nano-optical circuits was not considered in detail. This thesis aims to resolve these issues. In conclusion, the results of this thesis will lead to a better understanding of Vgroove and gap plasmon waveguide devices for the development of nano-optical circuits, compact photonic devices and sensors. This thesis also proposes two new nano-focusing structures which are easier to fabricate than the V-groove structure and will lead to applications in sensing, coupling light efficiently into nano-scale devices and improving the resolution of near-field microscopy.

The area of powertrain dynamics has received considerable attention over a number of years. The recent introduction of more stringent emission requirements together with economic pressure has led to a particular focus on increasing powertrain efficiency. This has seen the incorporation of on-board, real-time measurements to predict system behaviour and engine condition. In this domain, accurate models for all powertrain components are important. One strategy to improve accuracy is to evaluate the assumptions made when deriving each model and then to address the simplifications that may introduce large errors. To this end, the aim of the work presented in this dissertation was to investigate the consequences of some of the more common assumptions and simplifications made in low frequency torsional powertrain models, and to propose improved models where appropriate. In particular, the effects of piston-tocylinder friction, crank/gudgeon pin offset, and the torsional behaviour of tyres were studied. Frequency and time domain models were used to investigate system behaviour and model predictions were compared with measurements on a small single cylinder engine. All time domain engine and powertrain models also include a variable inertia function for each reciprocating mechanism. It was found that piston-to-cylinder friction can increase the apparent inertia variation of a single reciprocating engine mechanism. This has implications for the nonlinear behaviour of engines and the drivetrains they are connected to. The effect of crank/gudgeon pin offset also modified the nonlinear behaviour of the mechanism. Though, for typical (small) gudgeon offset values these effects are small. However, for large offset values, achievable practically with crank offset, the modification to the nonlinear behaviour should not be ignored. The low frequency torsional damping properties of a small pneumatic tyre were found to be more accurately represented as hysteretic rather than viscous. Time domain modelling was then used to extend the results to a multi-cylinder engine powertrain and was achieved using the Time Domain Receptance (TDR) method. Various powertrain component TDRs were developed using Laplacians. Powertrain simulations showed that piston-to-cylinder friction can provide additional excitation to the system.

Nos sistemas de distribuição de alta e média tensão tem-se aumentado a utilização de linhas de distribuição de energia subterrâneas ou cabos subterrâneos. A ocorrência de faltas nas linhas afeta negativamente a qualidade da energia e o correto funcionamento da rede. O processo que leva a uma falta nos cabos é gradual e está caracterizado por uma série de subciclos de faltas incipientes associadas a uma tensão de arco. Estas, muitas vezes, passam despercebidas e, eventualmente, resultam em uma falta permanente. Os métodos clássicos de localização de faltas como as metodologias baseadas no cálculo da impedância aparente, as baseadas na inteligência artificial e as baseadas nas ondas viajantes são, habitualmente, aplicadas ao sistema depois de uma falta permanente acontecer e precisam de um ou mais ciclos do sinal para entregar uma resposta razoável. No entanto, as faltas nos cabos são um processo gradual, de curta duração (entre ¼ e ½ ciclo do sinal) e seria desejável localizar a falta incipiente antes de tornar-se permanente. Nesse contexto, esta pesquisa aborda o problema de localização de faltas incipientes. Assim, nesta tese propõe-se uma nova técnica de localização de faltas incipientes usando medições em um terminal, no domínio do tempo e que utiliza componentes de fase. Desta forma, são desenvolvidas duas novas formulações do modelo elétrico do sistema de distribuição com cabos subterrâneos durante uma falta incipiente. A abordagem proposta considera simultaneamente na sua formulação características da falta incipiente e dos sistemas de distribuição de energia, como a tensão de arco, o modelo Π nominal de parâmetros concentrados do cabo subterrâneo, o desequilíbrio do sistema e a condição da carga. A estimativa da distância da falta, junto com os parâmetros da falta incipiente, é obtida a partir da solução de um sistema sobredeterminado de equações lineares pela aplicação do método de mínimos quadrados ponderados não negativos. As formulações propostas permitem estimar a distância da falta em termos da reatância da linha até a falta. Além disso, é proposto um processo de compensação de corrente para estimar a corrente de falta; é aplicado um pré-processamento dos dados de entrada para suavizar o efeito do ruído que pode conter o sinal e, é aplicado um pós-processamento dos resultados para refinar e entregar a melhor estimativa obtida durante o processo de localização da falta. O desempenho da técnica proposta é avaliado mediante estudos de casos simulados em um circuito real de distribuição no Alternative Transients Program (ATP/EMTP) considerando análises de sensibilidade e comparativa. Também, o modelo da falta incipiente foi programado utilizando a ferramenta de MODELS do ATP/EMTP. Os resultados obtidos, considerando faltas incipientes simuladas que avaliam a influência da variação da magnitude de tensão de arco, do ruído aleatório inserido na tensão de arco, da distância da falta, da taxa de amostragem, do carregamento do sistema, do modelo de tensão de arco e de incertezas nas medições, indicam claramente que a abordagem proposta possui validade como técnica de localização de faltas incipientes, apresentando erros médios globais de 1,60% e 0,93%, respectivamente para cada formulação proposta. / The use of underground power distribution lines or underground cables in the high and medium voltage distribution systems has increased dramatically in recent years. The fault occurrence in the distribution lines negatively affects the power quality and the correct network operation. The process which leads to a fault in underground cables is gradual and is characterized by a series of sub-cycles of incipient faults associated with an arc voltage. These often are unnoticed and, eventually, results in a permanent fault. Classical fault localization methods such as the based-impedance, the based on artificial intelligent and the based on traveling waves are, usually, applied to the system after a permanent fault occurrence and need one or more signal cycles for providing a reasonable response. However, the faults in cables are a gradual process, with short duration (between ¼ to ½ of signal cycle) and would be desirable to locate the fault before this becomes a permanent fault. In this context, this research approaches the incipient faults location problem. Thus, in this thesis is proposed a new incipient fault location technique using single-end terminal measurement, in time-domain and employing phase components. In this way, two new formulations of the electrical model of the distribution system with underground cables during an incipient fault are developed. The proposed approach considers simultaneously in its formulation, incipient fault type and power distribution systems characteristics as arc voltage, unbalanced operation, load conditions and complete line model. The fault distance estimation, together with the incipient fault parameters, it is obtained from the solution of an overdetermined linear system of equations by the application of the non-negative weighted least squares estimator method. The proposed formulations allow estimating the fault distance in terms of the line reactance up to the fault. In addition, a load current compensation strategy is proposed to reduce its effect in the fault current estimation; an input data pre-processing is applied to smooth out the noise effect and a post-processing of the results is performed for estimation refinement and to provide the best estimate obtained during the fault location process. The proposed technique performance is evaluated through simulated cases studies in a real-life distribution network with underground cable data in the Alternative Transients Program (ATP/EMTP) considering sensitivity and comparative analyzes. Also, the fault model was programmed using the MODELS tool of ATP/EMTP. The obtained results, considering simulated incipient faults, which evaluate the influence of variations in the arc voltage magnitude, random noise percentage inserted in the arc voltage, fault distance, sampling rate, load dynamics, the arc voltage model and uncertainties in measurements, indicate clearly that the proposed approach is valid as incipient faults location technique, showing overall average errors of 1,60% and 0,93%, respectively for each proposed formulation.

Ce travail de thèse a été réalisé dans le cadre d'un contrat avec l'ANR (ANR-09-VERS-013 « THID ») et porte sur le développement d'une nouvelle génération de tags Chipless à bas coûts fonctionnant dans le domaine THz, pour des applications d'identification et/ou authentification unitaire des articles commerciaux, des papiers d'identités, des personnes pour le contrôle d'accès... Les structures proposées, constituées d'un empilement périodique de couches diélectriques d'indices de réfraction différents, utilisent les propriétés particulières des cristaux photoniques 1D de présenter une réponse électromagnétique entrecoupée de bandes interdites photoniques (BIP). Toute perturbation de la périodicité de la structure engendre des pics dans les bandes interdites qui sont utilisés pour coder une information binaire. Cette structuration particulière des matériaux permet donc de manipuler précisément une signature électromagnétique. Pour des raisons liées à l'industrialisation (facilité de fabrication en masse) et aussi de coût, nous avons retenu des matériaux de base déjà couramment utilisés dans l'industrie papetière : le papier et le polyéthylène. Le choix de ces matériaux, qui doivent allier contraste d'indice élevé et faible absorption, représente une étape cruciale dans ce travail. Ainsi, à partir des résultats expérimentaux obtenus par spectroscopie THz dans le domaine temporel (THz-TDS) sur un grand nombre de matériaux, nous avons pu concevoir deux familles de tags sur la base de ces différents matériaux. Par ailleurs, nous avons développé deux méthodes de codage d'une information binaire, toutes deux basées sur l'absence ou la présence de pics dans une BIP, pics dont la position et le nombre dépendent bien évidemment des défauts de périodicité introduits. Pour des applications liées à l'identification, des capacités de codage de près de 20 bits ont été démontrées. Nous avons aussi montré que la richesse d'information contenue dans la réponse électromagnétique de ces Tags THz peut être utilisée pour les applications liées à l'authentification unitaire, en utilisant comme critère de discrimination le coefficient d'autocorrélation. Nous avons ainsi pu évaluer les performances d'un test d'authentification basé sur ce critère dans différents domaines d'analyse : temporel, fréquentiel et temps-fréquence. Nous avons montré qu'une étude du spectrogramme (combinant temps et fréquence) est ainsi bien plus pertinente qu'une étude dans les seuls domaines temporel ou fréquentiel. / This thesis work deals with the development of a new generation of low-cost Chipless tags operating in the THz frequency domain, it has been supported by the french national agency for research (ANR-09-VERS-013 « THID » ). It covers a wide area of applications such as the identification and/or unitary authentication of commercial items, identity papers, access control…To manufacture these tags, we proposed to use a periodic stack of dielectric material layers with different refractive index and whose thickness is of the order of the wavelength, commonly known as a one dimensional photonic crystal. The electromagnetic signature of such a structure exhibits photonic bandgaps (PBG), i.e. frequency windows in which light propagation is prohibited. We suggested modifying the periodicity of the crystal to create defect levels (peaks) for example in the 1st PBG to encode binary information. This particular structure allows to precisely tuned an electromagnetic signature. To ensure a mass and cost effective industrialization, we retained basic materials which are widely used in the pulp and paper industry: paper and polyethylene. The choice of these materials, which must combine high index contrast and low absorption, represents the first and a crucial step in this work. We characterize a wide range of materials using classical THz time domain spectroscopy (THz-TDS) and we propose two families of tags based on paper and polyethylene. Furthermore, we developed two methods to encode binary information, both based on the absence or presence of peaks in a PBG, peaks whose number and position depend on the introduced defects of periodicity. In a real identification test, a coding capacity of nearly 20-bit has been demonstrated. We also showed that the information contained in the electromagnetic response of these THz tags can be used for other applications related to the unitary authentication and by using the correlation coefficient as criterion for discrimination of the different signatures. Therefore, we evaluate the performance of an authentication test based on this criterion in various analysis domains: time, frequency and time-frequency. We showed that a study of the spectrogram (combining time and frequency representation) is much more relevant than a study in the only time or frequency domain.

A reflectometria no domínio do tempo permite estimar o teor de umidade de um meio através da sua correlação com a constante dielétrica. Uma sonda helicoidal TDR, que pode ser cravada em conjunto outros ensaios de penetração in situ para a estimativa do teor de umidade em diversas profundidades, tem aplicação interessante para a investigação geotécnica do subsolo. No presente trabalho, uma sonda TDR foi adaptada e utilizada em conjunto ao ensaio CPT para caracterização de um perfil de solo arenoso não saturado que ocorre na região de Bauru (SP). A calibração dessa sonda foi feita em laboratório especificamente para esse solo. As equações de calibração que mostraram os melhores resultados foram definidas correlacionando a constante dielétrica, condutividade elétrica aparente e a massa específica seca com o teor de umidade. Com o intuito de melhorar a acurácia na determinação do teor de umidade em campo e eliminar possíveis interferências no registro da onda eletromagnética, foram efetuadas modificações em algumas características do projeto original dessa sonda. Tais modificações consistiram em separar os eletrodos condutores e as partes metálicas da sonda, e eliminar o cabo coaxial de extensão, conectando a sonda diretamente a um cabo coaxial de 12 m de comprimento. Tais mudanças levaram a uma melhoria significativa na determinação do perfil de teor de umidade do local estudado. Os valores de teor de umidade de campo determinados usando o TDR ao longo de 8 m de profundidade foram comparados com os valores de referência obtidos de amostras deformadas retiradas com trado mecânico. O erro médio na estimativa do perfil de teor de umidade gravimétrico utilizando a sonda TDR helicoidal foi de 1.61%, na última campanha de ensaios realizados. Os resultados dessa pesquisa indicam que esta ferramenta é adequada para estimar do perfil de teor de umidade para uso em conjunto com o ensaio CPT. / The time domain reflectometry allows estimating the moisture content of a medium by means of its correlation with the dielectric constant. A coil TDR probe, which can be driven into the ground together with others in situ penetration tests, can be used to estimate the moisture content at different depths. It is an interesting approach for geotechnical site characterization. In this work, a coil TDR probe was adapted and used in combination with the CPT test for the site characterization of an unsaturated sandy soil profile which occurs in the region of Bauru (SP). The probe calibration was performed in laboratory specifically for that soil. The calibration equation, which presented the best results, were defined correlating the dielectric constant, electrical conductivity and dry density with the moisture content. In order to improve the accuracy for determining the water content in the field and to eliminate possible interference on the electromagnetic wave registration, modifications were made in some characteristics of the original design of this probe. Such modifications consisted in separating the conductive electrodes from the metal parts of the probe, and eliminating the coaxial extension cable, connecting the probe directly to a coaxial cable 12 m long. Such changes have led to a significant improvement in the determination of the moisture content profile of the studied site. The moisture content values determined in situ by using the TDR along 8 m depth were compared with reference values obtained from disturbed soil samples collected using mechanical augers. The root mean square error of the gravimetric water content profile using the TDR coil probe was 1.61% in the last test campaign. The results of this research indicate that this tool is suitable to estimate the gravimetric moisture content together with the CPT test.

Power transformers are quite costly and essential to provide reliable electrical power system operation. Besides their maintenance or substitution costs, transformer failures must be taken into account, since its will have a large impact on the utility financial health due to the temporary loss of power delivery capability. Concerning transformer failure statistics, investigations carried out in many utilities in the world reveal that the effect of electromechanical stress caused by short-circuit currents is a relevant cause of failure in such equipment and they cause onerous financial damage. Failures caused by mechanical stress due to external short-circuit and due to inrush currents are an important aspect to be considered. The excessive strength caused in transformer conductors/windings due to electromagnetic forces can reduce the transformer lifetime or even cause irreversible damages of them. Therefore, the investigation of the harmful effects caused by transient phenomena becomes imperative. With this in mind, this work aims at investigating the electromagnetic forces and mechanical stresses due to external short-circuit and inrush currents inside the transformer. The studies are carried out using a time domain transformer model based on magnetomotive forces and magnetic reluctances, which allows simulating the transformer transient and steady state behavior regarding the electric, magnetic and mechanical aspects. The methodology is applied in two transformer models operating under rated and short-circuit conditions. Due to the lack of mechanical stress experimental values, a comparative performance analysis is obtained by comparing the simulated results and the well accepted results from finite element program. The results obtained from simulations are evaluated through of the impacts provoked in the variables used to analyze the mechanical stresses which occur in the transformers due to short-circuit and inrush currents. From the mechanical stress calculated it is presented a methodology that establishes a correlation between the phenomena here investigated and the impact in the transformer lifetime. This can assist, previously, in the reduction of the number of unexpected failures and, consequently, in financial damages. / Transformadores de potência são dispositivos fundamentais para a operação de sistemas de potência e têm um peso significativo no custo total de uma instalação. Além dos custos de manutenção e substituição, as falhas nos transformadores devem ser levadas em consideração, no sentido de manter tanto a continuidade do fornecimento de energia como os padrões mínimos de qualidade estabelecidos para o insumo energia elétrico, aliado ao equilíbrio financeiro das empresas. Estudos realizados por concessionárias de diversos países deixam evidentes os enormes prejuízos financeiros das empresas do setor elétrico, devido às falhas mecânicas em transformadores. Defeitos provocados pelos esforços mecânicos decorrentes de correntes de curtos-circuitos passantes e correntes de inrush se constituem como importantes causadores de falhas em transformadores. Os esforços adicionais causados nos condutores/bobinas de transformadores, devido ao acréscimo das forças eletromagnéticas resultantes, podem, em alguns casos, vir a reduzir a vida útil de transformadores ou até mesmo provocar a sua perda total. A investigação dos efeitos danosos causados pelos fenômenos mencionados, portanto, torna-se imperativa. Nessa perspectiva, a presente tese tem por objetivo investigar as forças eletromagnéticas e o estresse mecânico resultantes de cor- rentes de curtos-circuitos passantes e correntes de energização que se estabelecem no interior de transformadores. Para alcançar tal propósito, é empregada uma modelagem computacional no domínio do tempo baseada em forças magnetomotrizes e relutâncias magnéticas. Este modelo permite simulações de fenômenos de regime transitório e per- manente, além de possibilitar o acesso às grandezas elétricas, magnéticas e mecânicas. A metodologia é aplicada a dois modelos de transformadores operando em condições nominais e em curto-circuito. Devido às dificuldades de se encontrar publicações que contenham valores de referência para validar a metodologia proposta, os resultados são comparados aos correspondentes obtidos de um tradicional e bem aceito pacote do Método dos Elementos Finitos. Os resultados oriundos das simulações são avaliados em termos do grau de impacto que é provocado nas grandezas utilizadas para aferir os esforços mecânicos a que fica submetido um transformador, quando de sua energização ou na ocorrência de curtos-circuitos passantes. A partir dos esforços mecânicos determinados é apresentada uma proposta de metodologia que estabelece uma correlação entre os fenômenos aqui estudados e o impacto sobre a vida útil de transformadores, que pode auxiliar, de maneira preditiva, na redução do número de falhas inesperadas e, em conseqüência, nos prejuízos financeiros decorrentes. / Doutor em Ciências

Nos sistemas de distribuição de alta e média tensão tem-se aumentado a utilização de linhas de distribuição de energia subterrâneas ou cabos subterrâneos. A ocorrência de faltas nas linhas afeta negativamente a qualidade da energia e o correto funcionamento da rede. O processo que leva a uma falta nos cabos é gradual e está caracterizado por uma série de subciclos de faltas incipientes associadas a uma tensão de arco. Estas, muitas vezes, passam despercebidas e, eventualmente, resultam em uma falta permanente. Os métodos clássicos de localização de faltas como as metodologias baseadas no cálculo da impedância aparente, as baseadas na inteligência artificial e as baseadas nas ondas viajantes são, habitualmente, aplicadas ao sistema depois de uma falta permanente acontecer e precisam de um ou mais ciclos do sinal para entregar uma resposta razoável. No entanto, as faltas nos cabos são um processo gradual, de curta duração (entre ¼ e ½ ciclo do sinal) e seria desejável localizar a falta incipiente antes de tornar-se permanente. Nesse contexto, esta pesquisa aborda o problema de localização de faltas incipientes. Assim, nesta tese propõe-se uma nova técnica de localização de faltas incipientes usando medições em um terminal, no domínio do tempo e que utiliza componentes de fase. Desta forma, são desenvolvidas duas novas formulações do modelo elétrico do sistema de distribuição com cabos subterrâneos durante uma falta incipiente. A abordagem proposta considera simultaneamente na sua formulação características da falta incipiente e dos sistemas de distribuição de energia, como a tensão de arco, o modelo Π nominal de parâmetros concentrados do cabo subterrâneo, o desequilíbrio do sistema e a condição da carga. A estimativa da distância da falta, junto com os parâmetros da falta incipiente, é obtida a partir da solução de um sistema sobredeterminado de equações lineares pela aplicação do método de mínimos quadrados ponderados não negativos. As formulações propostas permitem estimar a distância da falta em termos da reatância da linha até a falta. Além disso, é proposto um processo de compensação de corrente para estimar a corrente de falta; é aplicado um pré-processamento dos dados de entrada para suavizar o efeito do ruído que pode conter o sinal e, é aplicado um pós-processamento dos resultados para refinar e entregar a melhor estimativa obtida durante o processo de localização da falta. O desempenho da técnica proposta é avaliado mediante estudos de casos simulados em um circuito real de distribuição no Alternative Transients Program (ATP/EMTP) considerando análises de sensibilidade e comparativa. Também, o modelo da falta incipiente foi programado utilizando a ferramenta de MODELS do ATP/EMTP. Os resultados obtidos, considerando faltas incipientes simuladas que avaliam a influência da variação da magnitude de tensão de arco, do ruído aleatório inserido na tensão de arco, da distância da falta, da taxa de amostragem, do carregamento do sistema, do modelo de tensão de arco e de incertezas nas medições, indicam claramente que a abordagem proposta possui validade como técnica de localização de faltas incipientes, apresentando erros médios globais de 1,60% e 0,93%, respectivamente para cada formulação proposta. / The use of underground power distribution lines or underground cables in the high and medium voltage distribution systems has increased dramatically in recent years. The fault occurrence in the distribution lines negatively affects the power quality and the correct network operation. The process which leads to a fault in underground cables is gradual and is characterized by a series of sub-cycles of incipient faults associated with an arc voltage. These often are unnoticed and, eventually, results in a permanent fault. Classical fault localization methods such as the based-impedance, the based on artificial intelligent and the based on traveling waves are, usually, applied to the system after a permanent fault occurrence and need one or more signal cycles for providing a reasonable response. However, the faults in cables are a gradual process, with short duration (between ¼ to ½ of signal cycle) and would be desirable to locate the fault before this becomes a permanent fault. In this context, this research approaches the incipient faults location problem. Thus, in this thesis is proposed a new incipient fault location technique using single-end terminal measurement, in time-domain and employing phase components. In this way, two new formulations of the electrical model of the distribution system with underground cables during an incipient fault are developed. The proposed approach considers simultaneously in its formulation, incipient fault type and power distribution systems characteristics as arc voltage, unbalanced operation, load conditions and complete line model. The fault distance estimation, together with the incipient fault parameters, it is obtained from the solution of an overdetermined linear system of equations by the application of the non-negative weighted least squares estimator method. The proposed formulations allow estimating the fault distance in terms of the line reactance up to the fault. In addition, a load current compensation strategy is proposed to reduce its effect in the fault current estimation; an input data pre-processing is applied to smooth out the noise effect and a post-processing of the results is performed for estimation refinement and to provide the best estimate obtained during the fault location process. The proposed technique performance is evaluated through simulated cases studies in a real-life distribution network with underground cable data in the Alternative Transients Program (ATP/EMTP) considering sensitivity and comparative analyzes. Also, the fault model was programmed using the MODELS tool of ATP/EMTP. The obtained results, considering simulated incipient faults, which evaluate the influence of variations in the arc voltage magnitude, random noise percentage inserted in the arc voltage, fault distance, sampling rate, load dynamics, the arc voltage model and uncertainties in measurements, indicate clearly that the proposed approach is valid as incipient faults location technique, showing overall average errors of 1,60% and 0,93%, respectively for each proposed formulation.

La tomographie optique diffuse (TOD) est une modalité d’imagerie biomédicale 3D peu dispendieuse et non-invasive qui permet de reconstruire les propriétés optiques d’un tissu biologique. Le processus de reconstruction d’images en TOD est difficile à réaliser puisqu’il nécessite de résoudre un problème non-linéaire et mal posé. Les propriétés optiques sont calculées à partir des mesures de surface du milieu à l’étude. Dans ce projet, deux méthodes de reconstruction non-linéaire pour la TOD ont été développées. La première méthode utilise un modèle itératif, une approche encore en développement qu’on retrouve dans la littérature. L’approximation de la diffusion est le modèle utilisé pour résoudre le problème direct. Par ailleurs, la reconstruction d’image à été réalisée dans différents régimes, continu et temporel, avec des mesures intrinsèques et de fluorescence. Dans un premier temps, un algorithme de reconstruction en régime continu et utilisant des mesures multispectrales est développé pour reconstruire la concentration des chromophores qui se trouve dans différents types de tissus. Dans un second temps, un algorithme de reconstruction est développé pour calculer le temps de vie de différents marqueurs fluorescents à partir de mesures optiques dans le domaine temporel. Une approche innovatrice a été d’utiliser la totalité de l’information du signal temporel dans le but d’améliorer la reconstruction d’image. Par ailleurs, cet algorithme permettrait de distinguer plus de trois temps de vie, ce qui n’a pas encore été démontré en imagerie de fluorescence. La deuxième méthode qui a été développée utilise l’apprentissage machine et plus spécifiquement l’apprentissage profond. Un modèle d’apprentissage profond génératif est mis en place pour reconstruire la distribution de sources d’émissions de fluorescence à partir de mesures en régime continu. Il s’agit de la première utilisation d’un algorithme d’apprentissage profond appliqué à la reconstruction d’images en TOD de fluorescence. La validation de la méthode est réalisée avec une mire aux propriétés optiques connues dans laquelle sont inséres des marqueurs fluorescents. La robustesse de cette méthode est démontrée même dans les situations où le nombre de mesures est limité et en présence de bruit. / Abstract : Diffuse optical tomography (DOT) is a low cost and noninvasive 3D biomedical imaging technique to reconstruct the optical properties of biological tissues. Image reconstruction in DOT is inherently a difficult problem, because the inversion process is nonlinear and ill-posed. During DOT image reconstruction, the optical properties of the medium are recovered from the boundary measurements at the surface of the medium. In this work, two approaches are proposed for non-linear DOT image reconstruction. The first approach relies on the use of iterative model-based image reconstruction, which is still under development for DOT and that can be found in the literature. A 3D forward model is developed based on the diffusion equation, which is an approximation of the radiative transfer equation. The forward model developed can simulate light propagation in complex geometries. Additionally, the forward model is developed to deal with different types of optical data such as continuous-wave (CW) and time-domain (TD) data for both intrinsic and fluorescence signals. First, a multispectral image reconstruction algorithm is developed to reconstruct the concentration of different tissue chromophores simultaneously from a set of CW measurements at different wavelengths. A second image reconstruction algorithm is developed to reconstruct the fluorescence lifetime (FLT) of different fluorescent markers from time-domain fluorescence measurements. In this algorithm, all the information contained in full temporal curves is used along with an acceleration technique to render the algorithm of practical use. Moreover, the proposed algorithm has the potential of being able to distinguish more than 3 FLTs, which is a first in fluorescence imaging. The second approach is based on machine learning techniques, in particular deep learning models. A deep generative model is proposed to reconstruct the fluorescence distribution map from CW fluorescence measurements. It is the first time that such a model is applied for fluorescence DOT image reconstruction. The performance of the proposed algorithm is validated with an optical phantom and a fluorescent marker. The proposed algorithm recovers the fluorescence distribution even from very noisy and sparse measurements, which is a big limitation in fluorescence DOT imaging.

This thesis addresses the development of a weakly non-linear Higher Order Time Domain Rankine Panel Method (TDRPM) for the linear and weakly non-linear seakeeping analysis of floating offshore structures, including wave-current interaction effects. A higher order boundary elements method is adopted based on the body geometry description using Non-uniform Rational B-splines (NURBS) formulation, which can be generated by many standard Computed Aided Design (CAD) softwares widely available, and the several computed quantities (velocity potential, free surface elevation and others) are described using a B-spline formulation of arbitrary degree. The problem is formulated considering wave-current-body interactions up to second order effects, these ones considering the terms obtained by interaction of zero/first order quantities. In order to provide numerical stability, the Initial Boundary Value Problem (IBVP) is formulated in terms of the velocity potential and the local acceleration potential, the later used to predict the hydrodynamic pressure accurately. The zeroth order problem is solved using the double-body linearization instead of the Neumman-Kelvin one in order to allow bluff bodies simulation, leading to very complex expressions regarding the m-terms computation. The method adopts the Rankine sources as Green\'s function, which are integrated using Gauss quadrature in the entire domain, but for the self-influence terms that are integrated using a desingularized procedure. The numerical method is verified initially considering simplified geometries (sphere and circular cylinder) for both, first and second-order computations, with and without current effects. The derivatives of the velocity potential are verified by comparing the numerical m-terms to the analytical solutions for a hemisphere under uniform flow. The mean and double frequency drift forces are computed for fixed and floating structures and the quantities involved in these computations (wave runup, velocity field) are also compared to literature results, including the free floating response of a sphere under current effects. Two practical cases are also studied, namely the wave-induced second order responses of a semi-submersible platform and the wavedrift-damping effect evaluated through the equilibrium angle of a turret moored FPSO. For the former, some specific model tests were designed and conducted in a wave-basin. / Essa tese aborda o desenvolvimento de um método de Rankine de ordem alta no domínio do tempo (TDRPM) para o estudo de problemas lineares e fracamente não lineares, incluindo o efeito de corrente, envolvendo sistemas flutuantes. O método de ordem alta desenvolvido considera a geometria do corpo como descrita pelo padrão Non-uniform Rational Basis Spline (NURBS), que está disponível em diverso0s softwares de Computed Aided Design (CAD) disponíveis, sendo as diversas funções (potencial de velocidades, elevação da superfície-livre e outros) descritos usando B-splines de grau arbitrário. O problema é formulado considerando interações onda-corrente-estrutura para efeitos de até segunda ordem, os de ordem superior sendo calculados considerando as interações somente dos termos de ordem inferior. Para garantir a estabilidade numérica, o problema de contorno com valor inicial é formulado0 com relação ao potencial de velocidade e de parcela local do potencial de acelerações, este para garantir cálculos precisos da pressão dinâmica. O problema de ordem zero é resolvido usando a linearização de corpo-duplo ao invés da linearização de Neumman-Kelvin para permitir a análise de corpos rombudos, o que requer o cálculo de termos-m de grande complexidade. O método adota fontes de Rankine como funções de Green, que são integradas através de quadratura de Gauss-Legendre no domínio todo, exceto com relação aos termos de auto-influência que adotasm um procedimento de dessingularização. O método numérico é inicialmente verificado considerando corpos de geometria simplificada (esfera e cilindro), considerando efeitos de primeira e segunda ordens, com e sem corrente. As derivadas do potencial de velocidade são verificadas comparando os termos-m obtidos numericamente com soluções analíticas disponíveis para a esfera em fluído infinito. As forças de deriva média e dupla-frequência são calculadas para estruturas fixas e flutuantes, sendo as funções calculadas (elevação da superfície, campo de velocidade) comparadas com resultados disponíveis na literatura, incluindo o movimento da esfera flutuante sob a ação de corrente e ondas. São também estudados dois casos de aplicação prática, a resposta de segunda ordem de uma plataforma semi-submersível e o efeito de wave-drift damping para o ângulo de equilíbrio de uma plataforma FPSO ancorada através de sistema turred. No caso da semi-submersível, os ensaios foram projetados e realizados em tanque de provas.

A produção de petróleo e gás em campos brasileiros é cada vez mais proveniente de regiões com águas profundas e situadas longe da costa, chegando a distâncias de mais de 100 km, como, por exemplo, na Bacia de Campos ou de Santos. Devido à falta de infra-estrutura e às características do petróleo desses campos, a cadeia de abastecimento e o sistema de exportação da produção possuem grande importância para a indústria offshore. Uma maneira usual para a exportação da produção é através de dutos submarinos, onde o óleo e/ou a gás flui das plataformas diretamente para o continente. Com esta infra-estrutura é possível a utilização de sistemas de produção sem capacidade de armazenamento e, conseqüentemente, torna-se desnecessário o uso de navios para o alívio da produção. No entanto, devido à qualidade do óleo e às distâncias entre os poços e a costa em alguns campos brasileiros, a utilização dos oleodutos mostra-se uma solução pouco viável. Por este motivo, é bastante comum o uso de FPSOs ou semi-submersíveis conectadas a sistemas auxiliares, como o FSO (Floating Storage and Offloading). Nas plataformas, outra característica importante e desejada é tornar viável o uso de um sistema de completação seca (árvore de Natal acima da linha dágua) com o objetivo de diminuir, significativamente, os custos operacionais envolvidos. Esse tipo de completação é utilizado, com excelência, por unidade do tipo TLWP ou Spar, devido ao baixo nível dos movimentos e acelerações observadas nestas plataformas. Entretanto, as condições ambientais severas amplificam as dificuldades para encontrar um sistema com grande capacidade de armazenamento e que permita o uso de completação seca. Neste contexto, pesquisadores e engenheiros estão sendo obrigados a desenvolver novos conceitos capazes de atender a essa demanda. Desta forma, uma nova solução, considerando um FPSO e uma TLWP operando a uma curta distância e trabalhando de forma acoplada com a conexão garantida por cabos sintéticos vem sendo estudada. Essencialmente, o grande atrativo deste conceito é o fato de que toda a produção e o armazenamento são concentrados no FPSO e a TLWP é responsável pela perfuração e extração dos hidrocarbonetos através de risers verticais. Assim o sistema trabalhando de forma conjunta possui capacidade de armazenamento e permite o uso da completação seca. Nesta dissertação, foi realizado um estudo sobre a evolução deste novo conceito, dividido em três fases. A primeira focada no dimensionamento do sistema de conexão e ancoragem das unidades e em uma investigação da interação hidrodinâmica entre as unidades de forma a mostrar a viabilidade do sistema. A segunda fase, focada na validação dos resultados por meio da comparação com os testes realizados no modelo em escala do NMRI (National Maritime Research Institute - Japão). Finalmente, a terceira fase, com foco no redimensionamento do sistema de amarração e no sistema de conexão, com base nos resultados obtidos na segunda fase. / The oil and gas production in Brazilian fields are commonly found in deep water and situated far away from the coast, reaching distances of more than 100 km as, for example, in the Campos Basin or Santos Basin. Due to the heavy oil and lack of pipeline infrastructure found in these fields, not only subsea equipments that must support high pressure but also logistics problems such as supply chain and production exportation system play an important role for the offshore industry. A usual way to export the production is to concentrate it in hubs of submarine pipelines which flows the oil or gas from the platforms to the continent. This infrastructure makes possible the use of no storage production systems and, consequently, releases the use of the shuttle tanks employment. However, due to the quality of the oil and the distances between the wells and the coast, some Brazilian fields do not allow the use of the pipelines to export their production. For this reason, is quite common to use FPSO and semi-submersible aided by auxiliary systems such as the FSO (Floating Storage and Offloading) units. Another important and desired characteristic of production platforms is to make it feasible to install a dry Christmas tree system aiming to decrease, significantly, operational costs involved. This feature is performed, with excellence, by TLWP and Spar units due to the low level of motions and accelerations observed in these platforms. Harsh environmental conditions can bring difficulties to find a solution of a system with both storage and dry tree system capability. In this context, researchers and engineers are being forced to develop new technological systems capable to support this demand. In this way, a new solution considering a FPSO and a TLWP coupled in a short distance by synthetic ropes has being studied. Essentially, the attractive feature of this concept is the fact that the production is performed by the FPSO whereas the TLWP is responsible to support the risers and drilling facilities turning the system coupled, equipped with a dry Christmas tree and with the possibility to storage the production. By now, the concept evolution has been divided in three phases. The first phase concerned about an advanced research focusing on the connection and mooring system development and the hydrodynamic interaction between the units and having in mind the verification of the concept feasibility. The second phase, concerned about the results validation by a comparison with scale model tests performed in the NMRI (National Maritime Research Institute Japan). Finally, the third phase, has the focus in the mooring and connection system resizing based on the results obtained on second phase.