In this study, a progressive failure analysis is used to investigate leakage in internally pressurized non-circular composite cylinders. This type of approach accounts for the localized loss of stiffness when material failure occurs at some location in a structure by degrading the local material elastic properties by a certain factor. The manner in which this degradation of material properties takes place depends on the failure modes, which are determined by the application of a failure criterion. The finite-element code STAGS, which has the capability to perform progressive failure analysis using different degradation schemes and failure criteria, is utilized to analyze laboratory scale, graphite-epoxy, elliptical cylinders with quasi-isotropic, circumferentially-stiff, and axially-stiff material orthotropies. The results are divided into two parts. The first part shows that leakage, which is assumed to develop if there is material failure in every layer at some axial and circumferential location within the cylinder, does not occur without failure of fibers. Moreover before fibers begin to fail, only matrix tensile failures, or matrix cracking, takes place, and at least one layer in all three cylinders studied remain uncracked, preventing the formation of a leakage path. That determination is corroborated by the use of different degradation schemes and various failure criteria. Among the degradation schemes investigated are the degradation of different engineering properties, the use of various degradation factors, the recursive or non-recursive degradation of the engineering properties, and the degradation of material properties using different computational approaches. The failure criteria used in the analysis include the noninteractive maximum stress criterion and the interactive Hashin and Tsai-Wu criteria. The second part of the results shows that leakage occurs due to a combination of matrix tensile and compressive, fiber tensile and compressive, and inplane shear failure modes in all three cylinders. Leakage develops after a relatively low amount of fiber damage, at about the same pressure for three material orthotropies, and at approximately the same location. / Master of Science

An investigation was conducted to determine the effect of organized flow pulsations on mean heat transfer from a single cylinder, in-line arrangements and perpendicular arrangements of cylinders. Pulsation frequencies of up to twice the natural vortex shedding frequency and zero to peak. amplitudes as high as 36 percent were used. Pulsations were sinusoidal with at least 93 percent of the power at the fundamental frequency. Turbulence levels (Tu=0.5 percent) were not altered by the addition of unsteady flow. Reynolds number ranged from 23,000<Re<49,000. Results for heat transfer on the front and back of the cylinder are given for a constant wall temperature boundary condition. Heat transfer measurements were made by applying a heat balance to a thick walled copper tube divided into four individually heated segments with guard. heaters located at each end. Mean heat transfer was found to increase for all three arrangements when organized flow pulsations were applied. For a single cylinder and for perpendicular arrangements, heat transfer increases were found primarily on the back of the cylinder. For in-line arrangements, increases occurred mostly on the front of the cylinder. for the range of pitch ratio most useful to heat exchanger design, in-line arrangements were found to have a higher Nusselt number than perpendicular arrangements. / Master of Science

No description available.

This Master thesis deals with the requirements for the quality of ISO standard compliant pneumatic cylinders, which are machined and assembled by a local manufacturer. According to the philosophy of continuous improvement, this thesis describes the project to decrease the number of air leaks detected by automatic testing machines. The main benefits of the thesis are the improvement of the design of pneumatic cylinders and the improvement of their assembly procedure leading to a reduction in the number of air leaks from pneumatic cylinders on automatic test equipment. It also provides an overview and general procedure for selecting, analyzing, implementing measures and taking further opportunities to improve the quality management system of pneumatic cylinders in the company.

Le caractère entièrement sans contact de la technique d'Ultrasons-Laser en fait un outil de premier choix pour étudier la propagation des ondes acoustiques dans diverses géométries. Les problèmes rencontrés lors du couplage de transducteurs piézoélectriques sur une surface courbe sont ainsi évités et l'étude de structures cylindriques de diverses tailles, notamment à l'échelle du micron, peut être envisagée. Le développement de l'acoustique picoseconde dans les années 80 a permis, en effet, de générer des ultrasons de très haute fréquences (>GHz) présentant des longueurs d'onde de l'ordre de quelques nanomètres. Il devient alors possible de sonder des couches minces de tailles microniques à sub-microniques. Une extension de ces travaux au cas de fibres de diamètres micrométriques est ici proposée. Le mécanisme de génération acoustique par laser nécessite quel'échantillon soit optiquement absorbant. Plusieurs régimes de génération sont abordés suivant la fluence laser et la longueur de pénétration optique. Des modèles semi-analytiques de la génération acoustique dans des structures cylindriques optiquement absorbantes sont ainsi proposés. Une première approche, s'intéresse à la modélisation de la propagation dans un multi-couche cylindrique pour lequel la source acoustique est distribuée selon un profil d'intensité imposée par l'absorption de l'impulsion optique. Une seconde approche consiste à rechercher la fonction de Green d'une source enfouie. Une convolution par la distribution de source permet ensuite de calculer la réponse du cylindre. Une validation expérimentale est menée sur un barreau de verre de 5 mm de diamètre à l'aide d'un laser Nd:Yag délivrant des impulsions de 5ns. Une confrontation expérience/théorie est enfin proposée pour une fibre de tungstène de 5 microns de diamètre étudiée par un dispositif d'acoustique picoseconde. Enfin, des expériences similaires ont été réalisées sur des fibres de carbone d'un diamètre de 5 et 10 microns et ont permis d'évaluer localement leur indice optique complexe ainsi que leur élasticité transverse. / Having emerged in the 80s, the laser ultrasonics technique with its non-contact generation and detection process overpasses the difficulties of coupling piezoelectric transducers with curved surfaces. With the picosecond ultrasonics technique it is now possible to generate acoustic waves with very high frequency (>GHz) and very short wavelengths of few nanometers giving access to micrometric and sub-micrometric samples probing. To date, the acoustic generation for cylinders opaque at a given laser wavelength where the acoustic source is located at the cylinder surface was investigated. In this PhD thesis, an extension of this work is proposed in the case of micro-fibers where taking into account the optical penetration depth becomes essential. Semi-analytical models for acoustic waves generation and propagation in a optically absorptive cylinder are derived. In a first way, we adapt modelling techniques used to calculate the response of elastically heterogeneous materials to the case of an homogeneous material with a radially distributed source imposed by the optical absorption. In a second model, the radial displacement for an inner point source is derived, in a 2D Fourier domain. The response to a volume-source distribution along a radius is obtained as a convolution of the above Green function with the corresponding source distribution caused by optical absorption. Two inverse transforms are then applied. Picosecond ultrasonics experiments are performed for different micrometric fibers and compared with calculated waveforms for different optical absorptive properties. Experiments made on carbon micro-fibers have permitted to locally evaluate the transverse elasticity of the fibers as well as their complex optical index.

O problema das vibrações induzidas por vórtices em cilindros flexíveis inclinados em relação ao perfil de correnteza incidente é estudado através de uma abordagem experimental. Este tema se mostra de grande importância e aplicação na Engenharia Naval e Oceânica uma vez que são diversas as estruturas que se encaixam nesta descrição, como são o casos dos risers e linhas de amarração. Apesar de extensa, a literatura técnica especializada no assunto é focada em simplificações, tais como os estudos de cilindros rígidos fixos, cilindros rígidos montados em base elástica e cilindros flexíveis verticais ou lançados em catenária livre. A questão da inclinação é abordada em termos do Principio da Independência que diz que as forças e a frequência de emissão de vórtices em um cilindro inclinado são iguais as de um cilindro vertical se considerada apenas a parcela da correnteza normal à direção de inclinação. Estudos anteriores mostraram que este princípio é válido somente em algumas condições específicas e poucos deles apresentam resultados para cilindros flexíveis. Com base nisso, um ensaio em escala reduzida em tanque de reboque foi realizado com um modelo de linha composto por um tubo de silicone preenchido com microesferas de aço e condições de contorno articuladas em suas extremidades, o que conferiu características inerciais e geométricas ideais para a obtenção do fenômeno. Além da configuração vertical (? = 0°), que é o caso de referência, o modelo foi estudado em outras quatro inclinações com a vertical: ? = 10°, 20°, 30° e 45°. Estas inclinações foram ensaiadas para cinco diferentes azimute: ? = 0°, 45°, 90°, 135° e 180°, resultando em vinte e uma configurações de inclinação. Os resultados são analisados em termos da decomposição modal da vibração da linha, ou seja, são apresentadas amplitudes e frequências de oscilação ocorridas em cada um dos modos de vibrar. Além disso são realizadas análises espectrais, gráficos de evolução espaço-temporal, trajetórias de pontos ao longo do modelo flexível, entre outros. Frequências naturais, coeficientes de amortecimento e trações no topo são apresentados, complementarmente, como resultados de caracterização do modelo. Os estudos apontaram para uma validade do PI com algumas ressalvas, principalmente influenciadas pela diferença nas frequências do primeiro e segundo modo que é crescente com o aumento da inclinação. Além disso conclusões importantes sobre a coexistência modal, em regiões de ressonância e/ou de transição da dominância modal, foram obtidas. / The vortex-induced vibration problem in flexible cylinders yawed in relation to the incident current profile is studied through an experimental approach. This topic has great importance and application on Naval and Oceanic Engineering once there are multiple structures that fit into this description, such as risers and mooring lines. Though extensive, technical literature specialized on this topic is focused on simplifications such as the study of fixed rigid cylinders, elastic base rigid cylinders and flexible cylinders assembled vertically or launched in free hanging catenary. The inclination issue is addressed in the terms of the Principle of Independence which states that the forces and frequency shedding in an inclined cylinder are equal to those of a vertical cylinder if only considered the current component normal to the inclination plane. Previous studies showed that this principle is valid only on some specific conditions and few of them showed results to flexible systems. Based on this, a scaled tow tank test was performed with a line model composed of a silicone tube filled with steel microspheres and articulated end conditions, which offered the ideal inertial and geometrical conditions to obtaining the phenomenon. Besides the vertical configuration (? = 0°), which is the reference case, the model was studied in other four inclinations with the vertical: ? = 10°,20°, 30° and 45°. These inclinations were tested for five different azimuth directions: ? = 0°, 45°, 90°, 135° and 180°, resulting in 21 configurations. The results are analyzed on terms of the modal decomposition of the line motions, that is, amplitudes and oscillation frequencies are presented for each one of the vibration modes. Furthermore other analyzes are made, as spectral graphs, spatio-temporal evolution graphs, line points trajectories, among others. Natural frequencies, damping coefficients and tensions at the top are presented, complementarly, as results of the model characterization. The studies pointed to a validity of the IP with some reservations, mainly influenced by the difference in of the first and second mode frequencies that is increasing with the yaw increase. In addition, important conclusions about modal coexistence in regions of resonance and / or transition of modal dominance were obtained.

Vazamentos em tubos pressurizados geram ondas acústicas que se propagam através das paredes destes tubos, as quais podem ser captadas por acelerômetros ou por sensores de emissão acústica. O conhecimento de como estas paredes podem vibrar, ou de outro modo como as ondas acústicas se propagam neste meio, é fundamental em um processo de detecção e localização da fonte de vazamento. Neste trabalho, foi implementado um modelo analítico, através das equações de movimento da casca cilíndrica, com o objetivo de entender o comportamento da superfície do tubo em função de uma excitação pontual. Como a superfície cilíndrica é um meio fechado na direção circunferencial, ondas que iniciaram sua jornada, a partir de uma fonte pontual sobre a superfície, se encontrarão com outras que já completaram a volta na casca cilíndrica, tanto no sentido horário como no anti-horário, gerando interferências construtivas e destrutivas. Após um tempo suficiente, uma estacionariedade é atingida, criando pontos de picos e vales na superfície da casca, os quais podem ser visualizadas através de uma representação gráfica do modelo analítico criado. Os resultados teóricos foram comprovados através de medidas realizadas em uma bancada de testes composta de um tubo de aço terminado em caixa de areia, simulando a condição de tubo infinito. Para proceder à localização da fonte pontual sobre a superfície, adotou-se o processo de solução inversa, ou seja, conhecidos os sinais dos sensores dispostos na superfície do tubo, determina-se através do modelo teórico onde a fonte que gerou estes sinais pode estar. / Leaks in pressurized tubes generate acoustic waves that propagate through the walls of these tubes, which can be captured by accelerometers or by acoustic emission sensors. The knowledge of how these walls can vibrate, or in another way, how these acoustic waves propagate in this material is fundamental in the detection and localization process of the leak source. In this work an analytic model was implemented, through the motion equations of a cylindrical shell, with the objective to understand the behavior of the tube surface excited by a point source. Since the cylindrical surface has a closed pattern in the circumferential direction, waves that are beginning their trajectory will meet with another that has already completed the turn over the cylindrical shell, in the clockwise direction as well as in the counter clockwise direction, generating constructive and destructive interferences. After enough time of propagation, peaks and valleys in the shell surface are formed, which can be visualized through a graphic representation of the analytic solution created. The theoretical results were proven through measures accomplished in an experimental setup composed of a steel tube finished in sand box, simulating the condition of infinite tube. To determine the location of the point source on the surface, the process of inverse solution was adopted, that is to say, known the signals of the sensor disposed in the tube surface, it is determined through the theoretical model where the source that generated these signals can be.

Vazamentos em tubos pressurizados geram ondas acústicas que se propagam através das paredes destes tubos, as quais podem ser captadas por acelerômetros ou por sensores de emissão acústica. O conhecimento de como estas paredes podem vibrar, ou de outro modo como as ondas acústicas se propagam neste meio, é fundamental em um processo de detecção e localização da fonte de vazamento. Neste trabalho, foi implementado um modelo analítico, através das equações de movimento da casca cilíndrica, com o objetivo de entender o comportamento da superfície do tubo em função de uma excitação pontual. Como a superfície cilíndrica é um meio fechado na direção circunferencial, ondas que iniciaram sua jornada, a partir de uma fonte pontual sobre a superfície, se encontrarão com outras que já completaram a volta na casca cilíndrica, tanto no sentido horário como no anti-horário, gerando interferências construtivas e destrutivas. Após um tempo suficiente, uma estacionariedade é atingida, criando pontos de picos e vales na superfície da casca, os quais podem ser visualizadas através de uma representação gráfica do modelo analítico criado. Os resultados teóricos foram comprovados através de medidas realizadas em uma bancada de testes composta de um tubo de aço terminado em caixa de areia, simulando a condição de tubo infinito. Para proceder à localização da fonte pontual sobre a superfície, adotou-se o processo de solução inversa, ou seja, conhecidos os sinais dos sensores dispostos na superfície do tubo, determina-se através do modelo teórico onde a fonte que gerou estes sinais pode estar. / Leaks in pressurized tubes generate acoustic waves that propagate through the walls of these tubes, which can be captured by accelerometers or by acoustic emission sensors. The knowledge of how these walls can vibrate, or in another way, how these acoustic waves propagate in this material is fundamental in the detection and localization process of the leak source. In this work an analytic model was implemented, through the motion equations of a cylindrical shell, with the objective to understand the behavior of the tube surface excited by a point source. Since the cylindrical surface has a closed pattern in the circumferential direction, waves that are beginning their trajectory will meet with another that has already completed the turn over the cylindrical shell, in the clockwise direction as well as in the counter clockwise direction, generating constructive and destructive interferences. After enough time of propagation, peaks and valleys in the shell surface are formed, which can be visualized through a graphic representation of the analytic solution created. The theoretical results were proven through measures accomplished in an experimental setup composed of a steel tube finished in sand box, simulating the condition of infinite tube. To determine the location of the point source on the surface, the process of inverse solution was adopted, that is to say, known the signals of the sensor disposed in the tube surface, it is determined through the theoretical model where the source that generated these signals can be.

Gallium nitride (GaN)-based light-emitting diodes (LEDs) with cylindrical nanostructures have been the subject of significant research interest in the past decade, due to the potential of such structures to increase light extraction efficiency and deliver highly directional light emission. Nanorod LEDs, where the light emission is within the nanocylinder, have the additional potential to increase internal quantum efficiency and emit in colours previously thought impractical with GaN-based LEDs. Optical modelling of nanostructured LEDs is usually carried out using finite-difference time-domain methods, which are computationally intensive and do not always provide sufficient insight into the physics underlying the simulation results. This thesis proposes an intuitive, quasi-analytic method based on modal expansion. It is found that it is possible to calculate the far field diffraction patterns of all guided modes supported by a single nanorod, with full consideration of Fabry-Perot effects, in minutes using a standard office desktop computer. Focus is placed on the case of a nanorod of radius 140 nm, for which angular photoluminescence measurements were available to provide a means of validating the model. Consideration of the guided modes alone provides a compelling explanation for gross features in the measured data where none previously existed. It is shown that, using a standard equation from a textbook, it is possible to calculate how much each of the guided and radiation modes of a single nanorod is excited by a Hertzian dipole of known position and orientation with respect to the nanorod geometry. When interference between these modes is considered, it is possible to calculate the total far field angular emission pattern due to that dipole. Comparing these patterns with photoluminescence measurements allows one to infer the locations and orientations of dipole current sources; the results are found to be consistent with those of cathodoluminescence studies.

Este trabalho tem como propósito investigar através do método Design Construtal a influência do espaçamento (S0) entre cilindros de seção transversal elíptica na maximização da densidade de transferência de calor em um escoamento externo sob efeito de convecção forçada. A razão de aspecto (r) entre os eixos vertical e horizontal dos cilindros elípticos também é um parâmetro avaliado. O estudo proposto é assumido bidimensional, incompressível, laminar e permanente. O regime de escoamento é dirigido por uma diferença de pressão ΔP, que se mantém através do domínio e é governada pelo número de Bejan (Be). Foram avaliados escoamentos com quatro diferentes números de Bejan, Be = 102, 103, 5.103, 104. O fluido que escoa através do domínio possui as propriedades termofisicas definidas pelo número de Prandtl, Pr = 0,72. O método Design Construtal, associado à busca exaustiva, foi empregado para determinar as restrições, graus de liberdade e o objetivo na avaliação geométrica do sistema A solução numérica das equações de conservação de massa, quantidade de movimento e energia foram resolvidas baseadas no método de volumes finitos, através do código comercial de dinâmica dos fluidos computacional FLUENT®. As geometrias e malha do domínio computacional foram desenvolvidas no pacote GAMBIT®. Como resultados, obteve-se que os casos ótimos apresentaram resultados consideravelmente melhores do que as demais configurações, onde se obteve ganhos de desempenho na densidade de transferência de calor de 50% a 97% em relação às configurações de menor desempenho estudadas. Além disso, foi possível verificar que o sistema adapta sua geometria ótima para cada condição de escoamento, a fim de proporcionar a melhor arquitetura de fluxo para atender ao objetivo térmico de maximizar a transferência de calor em um menor espaço físico, atendendo os princípios da Teoria Construtal. / This work investigates, through the Construtal Design method, the influence of the spacing (S0) between cylinders with elliptic cross in the maximization of the heat transfer density in an external flow with forced convection. The aspect ratio (r) between the vertical and horizontal axes of the elliptical cylinders is also evaluated. The proposed study is assumed twodimensional, incompressible, laminar and permanent. The flow regime is directed by a pressure difference ΔP, which is governed by the Bejan number (Be). The flows were evaluated for different values of the Bejan number, Be = 102, 103, 5.103, 104. The fluid flowing through the domain has its thermophysical properties defined by Prandtl number, Pr = 0.72. The Construtal Design method, associated with the exhaustive search, was used to determine the restrictions, degrees of freedom and objective in the geometric evaluation of the system. The numerical solution of the mass conservation, momentum and energy equations is solved based on the finite volume method, using the commercial fluid dynamics software FLUENT ®. The geometries and mesh of the computational domain were developed in the GAMBIT® package. The results show that the optimal cases performs considerably better than the other configurations, with an increase in the heat transfer density of 50% to 97% in comparison to the performance of lower level cases studied. In addition, it was possible to verify that the system adapts its optimal geometry to every flow condition in order to provide a better flow architecture that meets the thermal objective of maximizing a heat transfer in a smaller physical space in agreement with the principles of the Constructal Theory.