Os transformadores de potência elétrica produzem um elevado nível de ruído que em alguns casos gera desconforto à comunidade vizinha. O presente trabalho desenvolve um modelo estrutural de elementos nitos que, com carregamento adequado, é capaz de reproduzir o deslocamento, medido durante a operação, de um transformador de potência elétrica. Este modelo estrutural é utilizado para calcular a redução do deslocamento das superfícies deste transformador decorrentes do emprego de absorvedores dinâmicos de vibração. Este modelo estrutural foi desenvolvido para estimar o número de absorvedores dinâmicos, sua massa e sua localização que permitiria reduzir o ruído acústico emitido por este transformador de potência até alcançar níveis de intensidade de som em comformidade com a legislação brasileira. / Electrical power transformers produce a high level of noise, which, in some cases, generate discomfort to the surrounding community. The present work develops a structural model by the Finite Element Method that, with adequate loading conditions, is capable of reproducing the displacement, measured during operation, of the transformer tank. The structural model has been used to compute the displacement reduction of the transformer surfaces by using dynamic vibration absorbers. The structural model was developed to estimate the number of dynamic absorbers, the mass and localization that could reduce the acoustic noise to levels of intensity of sound in accordance to the Brazilian law.

Absorvedores de vibração são comumente usados em aplicações com intuito de reduzir indesejadas amplitudes de vibração de estruturas e maquinas vibrantes. O conceito de um absorvedor de vibração linear consiste na ideia de projetar um subsistema com frequência de ressonância coincidente com uma dada frequência de interesse, tal que a amplitude de vibração do sistema primário e significativamente reduzida quando comparada a situação original, sem o absorvedor de vibração. Porem, uma deficiência dos absorvedores de vibração lineares típicos e sua estreita faixa de frequência de operação. Para superar essa deficiência, muitas tentativas de solução usando subsistemas não lineares tem sido propostas na literatura, ja que se apropriadamente projetados, eles podem aumentar a faixa de frequência de absorção de vibração e/ou melhorar a redução das amplitudes de vibração do sistema primário. Contudo, a síntese e o projeto de tais absorvedores não lineares não e tão simples e direta como no caso linear. Baseado na geometria de uma topologia proposta e encontrada na literatura, que compreende a inclusão de uma montagem do tipo snap through truss no lugar da mola linear do absorvedor de vibração, este trabalho tem intenção de apresentar um estudo sobre o projeto e otimização de um absorvedor dinâmico de vibrações não linear. Portanto, o efeito dos parâmetros do absorvedor e analisado quanto as perspectivas de redução das amplitudes de vibração do sistema principal como também de aumento da faixa de frequência de operação. A analise paramétrica do absorvedor foi promovida para responder questões sobre as variáveis de projeto, tanto físicas como geométricas. Realizou-se otimização do absorvedor com objetivo de sintoniza-lo a frequência de trabalho desejada, através de busca extensiva e algoritmos genéticos. Os resultados mostram que o absorvedor não linear proposto pode ser mais efetivo que seu correspondente linear em ambos os aspectos, na redução da máxima amplitude de vibração e no aumento da faixa de frequência de absorção. Portanto, apesar da dificuldade inicial de projeto, esse tipo de absorvedor representa uma alternativa interessante na atenuação das amplitudes de vibração ao longo de uma extensa faixa de frequência. / Dynamic vibration absorbers are commonly used in several applications in order to reduce undesired vibration amplitudes of vibrating machinery and structures. The concept of a linear vibration absorber is based on the idea of designing a subsystem with a resonance frequency coincident with a given frequency of interest such that the vibration amplitude of the primary system is significantly reduced when compared to the original situation (without the vibration absorber). But one of the known handicaps of typical linear vibration absorbers is their narrow frequency range of operation. To overcome this handicap, a number of tentative solutions have been proposed in the literature using nonlinear subsystems. If properly designed, they could enlarge the frequency range of vibration absorption and/or improve vibration reduction of the primary system. However, the synthesis and design of such nonlinear absorbers are not as straightforward as for their linear counterpart. A proposed design found in the open literature consists of replacing the linear spring of the vibration absorber by a nonlinear snap-through truss. This work aims to present a study on the design and optimization of a nonlinear dynamic vibration absorber based on snap-through absorber geometry. The effect of the absorber parameters was analyzed on both, the primary system vibration amplitude reduction and the frequency range of operation. Parametric analyses of the absorber were carried out to answer questions about the physical and geometric design variables. The absorber optimization was performed in two different ways, by extensive search and genetic algorithms, in order to tune it in the desired working frequency. The results show that the proposed nonlinear vibration absorber may be more effective than its linear counterpart both in terms of maximum vibration amplitude reduction and absorption frequency-range. Therefore, despite the increased design complexities such an absorber is an interesting alterna- tive in attenuating vibration amplitudes over a wide frequency range.

Les matériaux absorbants électromagnétiques, ou « Radar Absorbing Materials » (RAM), ont été créés à la fois aux USA et en Allemagne lors de la seconde guerre mondiale. Les applications des absorbants appartiennent principalement aux domaines de la Compatibilité ElectroMagnétique (CEM) et de la discrétion radar. Ces absorbants sont lourds et encombrants. Au travers de cette thèse, nous cherchons à développer une solution pour pallier à ces inconvénients grâce aux absorbants à métamatériaux. Les métamatériaux sont des composites artificiels présentant des propriétés électromagnétiques que l'on ne retrouve pas dans la nature. En utilisant ce type de matériaux, nous pouvons obtenir des absorbants ultras fins, et par l'optimisation et la conception couvrir des bandes larges en fréquence. Nous proposons donc plusieurs formes basiques d'absorbant à métamatériaux. De ces formes, nous présentons un modèle théorique et développons les techniques pour définir leur fréquence de fonctionnement et les paramètres nécessaires pour obtenir une absorption totale. Puis nous étudions plus en détail nos différents prototypes à travers des simulations et des mesures. Nous étudions aussi le couplage des absorbants à métamatériaux avec des absorbants traditionnels pour créer un type d'absorbant inédit. / Electromagnetic absorbing materials, or "Radar Absorbing Materials" (RAM), were created in the U.S. and Germany at the same time during the Second World War. Applications of absorbers are mainly in the field of ElectroMagnetic Compatibility (EMC) and radar stealth. These absorbers are heavy and bulky. In this thesis, we seek to develop a solution to overcome these drawbacks using metamaterial absorbers. Metamaterials are artificial composites with electromagnetic properties that are not found in nature. By using this type of material, we can obtain ultra-thin absorbers over a wide band of frequency by optimizing the design. We introduce several basic forms of metamaterial absorbers. From these geometries, we present a theoretical model and we develop techniques to define their operating frequency and parameters required to achieve total absorption. Then we study in detail our various prototypes with simulations and measurements. We also study the coupling of metamaterial absorbers with traditional ones to create a new type of absorber.

Excitabilité et structures localisées sont des phénomènes universels qui ont été observés dans une grande variété de systèmes. Chacun des deux phénomènes a des propriétés intéressante pour des applications potentielles, surtout dans l'optique. L'excitabilité est la propriété intrinsèque du neurone, elle décrit sa réponse à une stimulation: pour des stimulations en-dessous d'un certain seuil, le neurone reste dans son état de repos mais quand la stimulation dépasse ce seuil, il émet une impulsion dont la taille ne dépend pas de la force de la stimulation. Les structures localisées dans les systèmes optiques sont des pics de surintensité qui coexistent avec un fond homogène sur la section transversale spatialement étendue d'une cavité laser. Dans cette thèse nous avons étudié l'apparition de ces deux phénomènes non-linéaires dans des microcavités à semi-conducteur, pour lesquelles les applications dans le traitement tout-optique de l'information sont prometteuse. En outre, nous avons étudié la possibilité de trouver un nouveau phénomène à l'intersection entre les deux: les structures localisées excitables. D'une part nous avons étudié les propriétés des structures localisées qui se forment dans un laser à solitons. Celui-ci est constitué par deux laser à semiconducteur à cavité verticale (VCSEL) mutuellement couplées dans une configuration de laser avec absorbant saturable (LSA). Nous observons l'émissions aléatoire et localisée d'impulsions que nous affirmons être la première évidence expérimentale de structures localisées excitables. D'autre part nous avons démontré le comportement excitable d'un laser avec signal injecté par la possibilité de contrôler les impulsions excitable grâce à une perturbation externe appropriée. Nous avons également réalisé des simulations numériques qui montrent l'existence des structures localisées excitables dans un modèle de VCSEL avec absorbant saturable. / Excitability and localized structures are universal phenomena, observed in various systems. Both possess interesting properties for potential applications, especially in optics. Excitability is the intrinsic property of the neuron defining its response to an external stimulus: for a sub-threshold stimulus the neuron stays quiescent; for a super-threshold stimulus, it emits a well-calibrated pulse independent on the strength of the stimulus. Localized structures in optics are bright intensity peaks coexisting with a homogeneous low intensity background. They appear in the transverse section of spatially-extended laser resonators. We study the occurrence of these nonlinear phenomena in semiconductor microcavities since the applications in all-optical processing of information are promising. Moreover we investigate the possibility of a novel kind of localized structure which stands at the intersection of these two phenomena: the excitable localized structures. On the one hand we study the properties of localized structures arising from a cavity soliton laser composed of two mutually coupled broad-area VCSELs in a LSA (Laser with Saturable Absorber) configuration . We report on the observation of a random and localized emission of pulses which we claim to be the first experimental evidence of noise-triggered excitable localized structures whose excitability is induced by inhomogeneities and drift. On the other hand we demonstrate the excitability in an optically injected laser by showing the control of excitable pulses by means of an external perturbation. We also perform numerical simulations which reveal the existence of excitable localized structures in a model of broad area VCSEL with saturable absorber.

Le travail présenté dans cette thèse est dédié à l’étude d’un absorbeur bistable continu basé sur le principe du "Nonlinear Energy Sink" (NES) et son utilisation pour l’atténuation des vibrations d’un système mécanique à plusieurs degrés de liberté sous excitation acoustique. Le modèle analytique du comportement linéaire de l’absorbeur ainsi que le modèle numérique complet ont été présentés, analysés et validés par des séries d’expériences. Le complexité du transfert énergétique ciblé ("Targeted Energy Transfer" ou TET) entre l'absorbeur et le système primaire à contrôler n’a pas permis une description analytique simple. Nous avons donc choisi de concentrer cette étude sur l’exploration expérimentale et numérique de l’absorbeur couplé à des systèmes mécaniques sous excitations harmonique et aléatoire ainsi que sur l’identification des mécanismes de transfert d’énergie. Le système couplé a montré une dynamique très riche du fait de différents régimes de TET qui ont été décrits dans la littérature pour d’autres types de NES. Ce projet a été financé par Saint-Gobain. L’absorbeur a été adapté pour l’application prévue par la direction industrielle de la thèse: contrôle des vibrations de la double paroi sous excitation acoustique afin d’améliorer l’isolation acoustique fournie par le système.Les connaissances qualitatives sur la dynamique de l’absorbeur obtenues à partir des résultats expérimentaux et numériques, ainsi que l’analogie avec les autres types de NES, ont permis la création d’un absorbeur qui répond à la problématique posée. Les moyens pour l’optimisation et le développement de l’absorbeur ont été identifiés et les simulations préliminaires ont été fournies. / The work presented in this thesis is dedicated to the study of a continuous bistable absorber based on the principle of Nonlinear Energy Sink (NES) and its use for the vibration mitigation of a many-degree-offreedom mechanical systems under acoustic excitation. The analytical model of the linear behavior of the absorber and its complete numerical model were presented, analyzed and validated by series of experiments. The complexity of the Targeted Energy Transfer (TET) between the absorber and the primary system did not allow a simple analytical description. We have chosen to concentrate this study on the experimental and numerical exploration of the absorber coupled to mechanical systems under harmonic and random excitations, as well as on the identification of the mechanisms of energy transfer. The coupled system have shown very rich dynamics as it possessed different regimes of TET, which were earlier described in literature for other types of NES. This project was funded by Saint-Gobain. The absorber was adapted for the application foreseen by the industrial supervisors of the PhD: the vibration control of partitioning double walls under acoustic excitation so that to improve the acoustic isolation provided by the system. The qualitative knowledge on the absorber dynamics obtained from the experimental and numerical results, as well as the analogy with the other types of NES, permitted the creation of an absorber which corresponds to the problematic. The ways for the further optimization and development of the absorber were identified and preliminary simulations were provided.

This dissertation can be divided into two parts project goals. The first one is the synthesis of rhenium (Re) complexes which are potential reverse saturable absorber (RSA) materials. The second one is the polymerization of ruthenium (Ru) polypyridyl monomers to have an oligomer ensemble for solar light harvesting purposes. THE FIRST part starts with an introduction to optical limiting materials (OLM) (chapter 1). The main discussion in chapter 4 is about the photophysical properties and energy-transfer reactions for three series of facial Re(I) tri-carbonyl complexes. The complexes are of the general type fac-[Re(CO)3(N-N)Cl], where Cl is the chloride and N-N are novel mono functionalized aryl-oligo(p-phenylene-vinylene) bipyridine (bpy) ligands. These series is as a result of changing the aryl group of the ligands to either anthracene or pyrene, and di-alkoxy attachments of phenyl ring in anthracene bipyridine ligands. The synthesis of the bpy ligands involved attaching various aryls by utilizing successive multi-step Wittig-Horner reactions (chapter 2). The ligands were later reacted with Re pentacarbonyl chloride to obtain the complexes. Chromium complexes synthesis is also included (chapter 3). The characterization involved 1H NMR, ESI-MS and elemental analysis. There is also another set of ligands where the aryl group is di-methylaminophenyl where the solvatochromic emission properties of the ligands were studied but were not coordinated to metals. The excited-state properties using both the nanosecond (ns) and picosecond (ps) time resolved transient absorption (TA) of Re(I) complexes shows strong positive excited-state absorption signals in 500-800 nm range. From the TA (ps) and time-resolved infrared of the carbonyl region, the excited state forms instantaneously after excitation. Their observed lifetimes are relatively long (2 μs-40 μs range) and they increase as the phenylene-vinylene linker increases. The excited state triplet energies values for the complexes were obtained experimentally using energy transfer method from the simple Sandros relation. They decreases as the π-conjugated phenylene-vinylene linker decreases, this is because the extended backbone bridge serves to lower the energy of the triplet excited state. Lastly, the Re(I) complexes triplet-triplet molar extinction coefficients(δex) were measured by energy transfer to a standard method and their ratios to the ground state molar absorptivity(δg ) are all (δex/δg ≥40) at 530nm which make them potential candidates for RSA. THE SECOND part involves RAFT polymerization of two new acrylamide functionalized Ru(II) polypyridyl monomers. Photoinduced electron transfer reactions for the obtained Ru oligomers and complexes were done using 10-methylphenothiazine (MPT) quencher (chapter 8). The synthesized acrylamide functionalized bipyridine ligand (chapter 6) was reacted with complex precursors cis-[Ru(L)2Cl2] where the ligand (L) is either 2,2’- bipyridine or biquinoline (chapter 7). The obtained Ru(II) photosensitizers acts as energy donating and accepting respectively. The attachment of these Ru complexes to oligomer backbone as side chains is by a C11 alkyl linker. 1H NMR, UV-Vis spectroscopy, and differential pulse voltammetry (DPV) were used to characterize the ligand, monomers and oligomers. The excited state REDOX potentials were determined using the cyclic voltammetry (CV) values and steady state emission values converted to electron volt (eV). Lastly, the TAs (ns) obtained in the presence of MPT electron donating quencher was in agreement with the ones calculated/ predicted from spectroelectrochemistry. These efforts are toward the goal of making a panchromatic solar light collector in the visible region (chapter 5). / acase@tulane.edu

<p>The optical efficiency of a commercially available sputter deposited spectrally selective solar absorber was improved. The main purposes were to decrease the thermal emittance, increase the solar absorbtance of the absorber and to protect the substrate from degradation due to environmental influence. The adhesion properties between the corrosion-protecting barrier and the substrate were also studied. This project was focused on process improvements that are realistic to implement in industrial production.</p><p>The thermal emittance of the absorber was decreased from 0.12 to 0.06 by changing the material of the corrosion-protecting layer from nickel-chromium to copper-nickel. Copper-nickel was less sensitive to variations in the sputter parameters than nickel-chromium. A novel method that could simplify the search for alternative corrosion resistant materials with a low thermal emittance has been purposed. Since resistivity data usually exist or can easily be measured and infrared measurements require more sophisticated measurements, the Hagen-Rubens relation was investigated for copper-nickel and nickel-chromium alloys. The dc-resistivity was found to be related to the infrared emittance or the integrated thermal emittance for alloys in their solid soluble fcc phase.</p><p>The solar absorbtance was increased when a graded index absorbing coating was tailored for a crossover of the reflectance from low to high reflectance at about 2.5 µm. The solar absorber graded index coating was optimized for nickel metal content in nickel oxide and a solar absorptance of 0.89-0.91 was achieved. The solar absorptance was further increased to 0.97 when an antireflection coating was added on top of the absorbing layer.</p><p>Finally, extrapolation algorithms were developed to assure correct determination of the thermal emittance for coatings on glass since modern spectrometers that do not cover the complete wavelength interval required to calculate the thermal emittance of surfaces at room temperatures accurately. The error arising from the extrapolation algorithms were smaller than the noise from the optical measurements. Similar strategies can be used for other surfaces.</p>

<p>Recently, materials such as hole conductors (CuI, CuSCN) and light absorbers (Ru-complexes, CuInS₂) have been actively investigated for application in nanocrystalline solar cells. In this thesis combinations of these materials have been studied.</p><p>In the first part of the thesis, various methods were applied to characterize the electronic structure and photoconversion mechanism of the dye molecule Ru(dcbpyH₂)₂(NCS)₂ when combined with materials for the use in photovoltaic devices. Specifically, the adsorption and electronic structure of the dye molecules adsorbed to semiconductors were investigated by means of photoelectron spectroscopy. The results indicate a chemical bond between the dye molecules and the hole conductors (CuI, CuSCN) via the NCS- groups. In addition, preparation of a TiO₂/Ru-dye/CuI solid state model system was studied <i>in situ</i>. These experiments showed a partial breaking of the TiO₂-dye bond caused by CuI evaporation. Photovoltage measurements were also performed. These investigations showed a shift in the light absorption threshold of the dye molecules adsorbed onto the hole conductors (CuI and CuSCN), indicating new defect states at the dye/CuSCN interface. Also, charge accumulation and transport in solar cells with CuSCN were compared to liquid electrolyte cells. Measurements showed that the lifetime and transport time of electrons in solar cells with CuSCN are much shorter than in electrolyte cells.</p><p>In the second part of the thesis, the deposition of CuInS₂ onto various metal oxides by spray pyrolysis has been studied with x-ray diffraction and photoelectron spectroscopy. The measurements showed that the morphologies of the substrates play a significant role in the formation of CuInS₂ layers. Also, the presence of CdS at TiO₂ has a positive influence on the formation of CuInS₂.</p>

A large body of literature exists regarding linear and nonlinear dynamic absorbers, but the vast majority of it deals with linear primary structures. However, nonlinearity is a frequency occurrence in engineering applications. Therefore, the present thesis focuses on the mitigation of vibrations of nonlinear primary systems using nonlinear dynamic absorbers. Because most existing contributions about their design rely on optimization and sensitivity analysis procedures, which are computationally demanding, or on analytic methods, which may be limited to small-amplitude motions, this thesis sets the emphasis on a tuning procedure of nonlinear vibration absorbers that can be computationally tractable and treat strongly nonlinear regimes of motion. The proposed methodology is a two-step procedure relying on a frequency-energy based approach followed by a bifurcation analysis. The first step, carried out in the free vibration case, imposes the absorber to possess a qualitatively similar dependence on energy as the primary system. This gives rise to an optimal nonlinear functional form and an initial set of absorber parameters. Based upon these initial results, the second step, carried out in the forced vibration case, exploits the relevant information contained within the nonlinear frequency response functions, namely, the bifurcation points. Their tracking in parameter space enables the adjustment of the design parameter values to reach a suitable tuning of the absorber. The use of the resulting integrated tuning methodology on nonlinear vibration absorbers coupled to systems with nonlinear damping is then investigated. The objective lies in determining an appropriate functional form for the absorber so that the limit cycle oscillation suppression is maximized. Finally, the proposed tuning methodology of nonlinear vibration absorbers may impose the use of complicated nonlinear functional forms whose practical realization, using mechanical elements, may be difficult. In this context, an electro-mechanical nonlinear vibration absorber relying on piezoelectric shunting possesses attractive features as various functional forms for the absorber nonlinearity can be achieved through proper circuit design. The foundation of this new approach are laid down and the perspectives are discussed.

The optical efficiency of a commercially available sputter deposited spectrally selective solar absorber was improved. The main purposes were to decrease the thermal emittance, increase the solar absorbtance of the absorber and to protect the substrate from degradation due to environmental influence. The adhesion properties between the corrosion-protecting barrier and the substrate were also studied. This project was focused on process improvements that are realistic to implement in industrial production. The thermal emittance of the absorber was decreased from 0.12 to 0.06 by changing the material of the corrosion-protecting layer from nickel-chromium to copper-nickel. Copper-nickel was less sensitive to variations in the sputter parameters than nickel-chromium. A novel method that could simplify the search for alternative corrosion resistant materials with a low thermal emittance has been purposed. Since resistivity data usually exist or can easily be measured and infrared measurements require more sophisticated measurements, the Hagen-Rubens relation was investigated for copper-nickel and nickel-chromium alloys. The dc-resistivity was found to be related to the infrared emittance or the integrated thermal emittance for alloys in their solid soluble fcc phase. The solar absorbtance was increased when a graded index absorbing coating was tailored for a crossover of the reflectance from low to high reflectance at about 2.5 µm. The solar absorber graded index coating was optimized for nickel metal content in nickel oxide and a solar absorptance of 0.89-0.91 was achieved. The solar absorptance was further increased to 0.97 when an antireflection coating was added on top of the absorbing layer. Finally, extrapolation algorithms were developed to assure correct determination of the thermal emittance for coatings on glass since modern spectrometers that do not cover the complete wavelength interval required to calculate the thermal emittance of surfaces at room temperatures accurately. The error arising from the extrapolation algorithms were smaller than the noise from the optical measurements. Similar strategies can be used for other surfaces.