Orientador: José Roberto Nunhez / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-19T04:07:53Z (GMT). No. of bitstreams: 1 AlvarezCastro_HelverCrispiniano_M.pdf: 3784043 bytes, checksum: bc88cbde39ba881df9a43aee4f3ba52c (MD5) Previous issue date: 2011 / Resumo: Este Trabalho tem por objetivo desenvolver um modelo de simulação dinâmica para um tanque de mistura de diesel de larga escala localizado na refinaria da Petrobras em Paulínia. O tanque é utilizado na área de produtos acabados médios da Petrobras. Neste sentido, o objetivo principal deste projeto inclui estimar o perfil de velocidade, tempo de mistura e a potência que o agitador requer para sua homogeneização, visando otimizar a operação destes tanques na Petrobras. O referido tanque de armazenamento e mistura de óleo diesel possui uma capacidade nominal de 24000 m3, o fluido possui densidade de 0,86 kg/ m3; O projeto do tanque esta baseado na norma API 650. Para a simulação utilizam-se técnicas baseadas em fluidodinâmica computacional (CFD). O método utilizado é o dos volumes finitos. Para atingir o objetivo proposto, utiliza-se o software comercial CFX versão 12.1. O software resolve numericamente as equações discretas de conservação de massa, momento e um modelo de turbulência associado ao modelo. O SST ( Shear Stress Transport Model ) é usado para se estimar a turbulência. A região do fluido é dividida em um grande número de volumes de controle, sendo construído um modelo de tanque equipado com uma entrada lateral de um misturador tipo naval . O modelo do impelidor foi fornecido pela PETROBRAS / Abstract: The aim of this work is the development of a computational model for large storage diesel mixing vessels. The tank studied is located at REPLAN (Refinery of Paulínia). This vessel is used for products with intermediate viscosity. It is intended to estimate velocity profiles, mixing time and energy consumption required for its homogenization, with a view to optimize its operation. This storage vessel has a nominal capacity of 24000 m3, the fluid has a specific mass of 0.86 kg/m3. The tank design follows the API 650 especifications. The model uses Computational Fluid Dynamics (CFD) techniques. It is based on the finite volume method. The commercial CFX 12.1 software was used to get the numerical data. This software solves numerically the discrete form of the mass, momentum and species conservation equations and the turbulence model associated to the general tank model. The SST ( shear Stress transport turbulence model ) is used to estimate the turbulence. The tank is divided into a great number of control volumes. The model of the vessel considers a lateral flow impeller (similar to a naval type impeller). The characteristics of the impeller was given by PETROBRAS / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

Orientador: Amauri Garcia / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-04T03:14:59Z (GMT). No. of bitstreams: 1 Ferreira_IvaldoLeao_D.pdf: 8636771 bytes, checksum: fb3623e9e0a9c93143f4b34ba87844cf (MD5) Previous issue date: 2004 / Resumo: o presente trabalho analisa as influências do teor de soluto, do superaquecimento e do coeficiente global de transferência de calor metal/fluido (hg), na macrossegregação inversa durante a solidificação unidirecional vertical ascendente de ligas binárias AI-Cu e ternária AI-Cu-Si. Os perfis experimentais de segregação ao longo dos lingotes para as ligas AI4,5%Cu, AI-6,2%Cu, AI-8,I%Cu e Al-8,I%Cu-3%Si são comparados com as predições teóricas fomecidas por modelos numérico e analítico, com perfis transitórios de (hg) sendo determinados em cada experimento. O modelo analítico é baseado num modelo analítico de transferência de calor [Garcia, 2001], acoplado a uma formulação clássica para a redistribuição local de soluto proposta por Flemings e Nereo (Flemings e Nereo, 1967]. O modelo numérico é aquele proposto por V oller [V oller, 1997], com modificações introduzidas levando em consideração diferentes propriedades termofisicas para as fases líquida e sólida, coeficiente global de transferência de calor metal/fluido variável com o tempo e malha com distribuição de comprimento de nós variável ao longo do domínio, o que garantiu a precisão dos resultados sem aumento excessivo do número de nós. AIém dessas modificações, fez-se necessária à mudança no critério de convergência para melhor representar os gradientes térmicos e taxas de resfriamento. Um modelo semi-analítico para a macrossegregação inversa, baseado na solução por variável de similaridade, é aplicado para validação do modelo numérico. Observa-se que as predições numéricas apresentam boa concordância com as medidas experimentais, e que as predições analíticas, apesar de sua relativa simplicidade, também é capaz de representar satisfatoriamente os resultados experimentais, exceto para condições de elevado superaquecimento. O modelo numérico é aplicado com sucesso para a situação de solidificação de ligas multicomponentes, representada pela liga Al-8,1%Cu-3%Si, onde é observada boa representatividade dos resultados experimentais / Abstract: The present work focuses on the influences of alloy solute content, melt superheat, and meta1/fluid heat transfer coefficients on inverse segregation during upward solidification of AI-Cu and AI-Cu-Si alloys. The experimental segregation profiles of AI4,5 wt % Cu, AI-6,2 wt % Cu, AI-8,1 wt % Cu and AI-8,1 wt % Cu-3 wt % Si alloys are compared with theoretical predictions fumished by analytical and numerica1 models, with transient (hg) profiles being determined in each experimento The analytical model is based on an ana1ytica1 heat transfer model coupled with the classica1loca1 solute redistribution equation proposed by Flemings and Nereo. The numerica1 model is that proposed by V oller, with some changes introduced to take into account different thermophysica1 properties for liquid and solid phases, time variable meta1/fluid interface heat-transfer coefficient, and a variable space grid along the domain in order to assure the accuracy of results without raising the number of nodes. Furthermore, changes in the convergence criterion were necessary to improve the accuracy of the therma1 gradients and solidification rates ca1culated numerlcally. A sophisticated semi-ana1ytica1 solution for the inverse segregation based on the similarity variable is carried out to valida te the numerica1 model. It is observed that the numerical predictions generally conform with the experimental segregation measurements and that the predicted analytical segregation, despite its simplicity, also compares favorably with the experimental scatter except for high melt superheat. The numerical model is successfully applied for a situation of multicomponent alloy solidification, Le., AI-8,1 wt % Cu-3 wt % Si alloy, and it is found be in good agreement with experimental results / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Orientador: Antonio Carlos Bannwart / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências / Made available in DSpace on 2018-08-22T09:34:42Z (GMT). No. of bitstreams: 1 Gaspari_EduardoFerreira_D.pdf: 3211545 bytes, checksum: 80820e359cf9df0a39b228d34978524f (MD5) Previous issue date: 2013 / Resumo: Utilizando um método numérico especializado em problemas hiperbólicos chamado Riemann Solver, é feito um estudo para avaliar o processo de evolução de roll waves em canais fechados. Todo o estudo se baseia em fenômenos de propagação de ondas hiperbólicas do tipo ondas de gravidade. Foi utilizado um modelo unidimensional para representar a dinâmica das roll waves. Inicialmente foi feita uma análise das velocidades características envolvidas, a qual indicou, para o arranjo estratificado, um fraco acoplamento entre os fenômenos de propagação de onda mais relacionados com a compressibilidade dos fluidos e os fenômenos de propagação de ondas mais relacionados com a variação hidrostática na seção transversal do canal. Os resultados desta análise foram utilizados para justificar uma modelagem de roll wave considerando os fluidos como incompressíveis. Testes numéricos também foram feitos, demonstrando que a hipótese de fluidos incompressíveis não leva a uma perda de qualidade na modelagem de ondas de gravidade em canais fechados. Foi observada a fragilidade da hipótese de perfil hidrostático de pressão nos modelos de dois fluidos e é proposta uma modificação para este perfil de pressão considerando os efeitos dinâmicos devido à forma rugosa da interface em um escoamento estratificado instável. São feitas comparações com resultados experimentais de literatura para o filme de líquido em regime laminar e foram feitos experimentos para o filme de líquido em regime turbulento. As comparações entre as simulações e os resultados experimentais demonstrando que o modelo proposto é consistente / Abstract: Using a Riemann Solver numerical method, a study to evaluate the process of evolution of roll waves in closed channels was implemented. The whole study is based on the phenomena of hyperbolic gravity waves propagation. It was used a one-dimensional model to represent the dynamics of roll waves. Initially an analysis of the propagation wave velocities involved on to the stratified flow was done, a weak coupling between the wave propagation phenomena more closely related to fluid compressibility and wave propagation phenomena more closely related to the change in the void fraction, due the gravity waves, was verified. The results of this analysis were used to justify a roll wave modeling considering the fluids as incompressible. Numerical tests were also performed, showing that the hypothesis of incompressible fluids does not lead to a loss of quality in the modeling of gravity waves in closed channels. It was observed a fragility of the hydrostatic pressure profile assumption to modeling unstable stratified flow. It was proposed a modification to this pressure profile, considering the dynamic effects of the roughness interface. Comparisons were made with experimental results from the literature for the liquid film in laminar and experiments made for the film of liquid in turbulent flow. This comparison between simulations and experimental results demonstrate that the proposed model is consistent / Doutorado / Explotação / Doutor em Ciências e Engenharia de Petróleo

Orientador: Kátia Lucchesi Cavalca Dedini / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-26T15:33:06Z (GMT). No. of bitstreams: 1 Vieira_LeonardoCarpinetti_D.pdf: 8387504 bytes, checksum: c4ddda686a98c9562fec4c86ff5f3a1c (MD5) Previous issue date: 2014 / Resumo: Este trabalho possui como principal objetivo analisar a influência da variação da temperatura e, consequentemente, da viscosidade do fluido lubrificante sobre o comportamento de mancais axiais lubrificados de geometria fixa. Foi implementado numericamente, para isto, um modelo termohidrodinâmico (THD) baseado na resolução da Equação de Reynolds generalizada e da Equação de Energia através do Método dos Volumes Finitos (MVF), permitindo a obtenção da distribuição de pressão e da distribuição de temperatura ao longo do filme de óleo presente entre o mancal estacionário e o colar do eixo em movimento. Os resultados de capacidade de carga axial do mancal e o seu comportamento dinâmico, cuja análise é feita através dos coeficientes equivalentes de rigidez e amortecimento do lubrificante, são comparados com os resultados obtidos através de um modelo exclusivamente hidrodinâmico (HD), isotérmico e isoviscoso, previamente desenvolvido, buscando-se compreender o grau de influência da variação da temperatura na análise de mancais deste tipo. A influência de uma gama de parâmetros geométricos envolvidos, tais como comprimento angular da rampa e do segmento e inclinação da rampa, também é analisada, com o objetivo de se definir parâmetros geométricos ótimos do mancal que resultam em uma maior capacidade de carga axial. A influência de parâmetros de operação, tais como velocidade de rotação e espessura mínima de fluido, também é analisada. Resultados experimentais obtidos através de uma bancada de testes montada com um turbocompressor são utilizados para se validar os resultados do modelo implementado numericamente e analisar o comportamento de um sistema real capaz de funcionar a velocidades de rotação muito altas e sujeito a esforços axiais abruptos e elevados / Abstract: The main aim of this work is to analyse the influence of the temperature variation and, as consequence, the viscosity variation of the lubricant fluid on the behaviour of lubricated fixed-geometry thrust bearings. For this purpose, a thermohydrodynamic (THD) model, based on the solution of the Generalized Reynolds¿ Equation and of the Energy Equation by use of a Finite Volume Method, was developed, enabling the calculation of both pressure and temperature distribution along the fluid film present between the stationary bearing and the rotating collar. The results of axial load capacity of the bearing and its dynamic behaviour, characterised by the equivalent stiffness and damping coefficients, are compared to the results obtained by a previously developed purely hydrodynamic (HD), isothermal and isoviscous model, with the objective of understanding the influence of the temperature variation on the analysis of this type of bearings. The influence of several geometric parameters, such as pad length, ramp length and slope of the ramp, is also analysed, with the objective of defining the optimum values that lead to a higher load capacity. Also, the influence of operating parameters as speed and minimum film thickness on the behaviour of the system is studied. Experimental results, obtained at a test rig mounted with a small turbocharger are used to validate the simulated results and analyse the behaviour of a real system, capable of supporting high speeds of rotation and severe and abrupt external loads / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Organic semiconductors provide an alternative set of basis materials to fabricate electronic devices like PN Junctions, LEDs, and FETs. These materials have several benefits over traditional inorganic semiconductors including their mechanical flexibility, reliance on renewable resources, and inexpensive large-scale manufacturability. Despite the contemporary device implementations with organic semiconductors, a solid-state electrically-pumped organic laser diode does not exist. However, organically-based lasers do exist by utilizing the organic material strictly for optical gain. The challenge occurs when charge carriers appear in the organic material. The charge carriers must reach a concentration such that population inversion occurs producing optical gain. However, between the overlapping emission and absorption spectra of the organic material and insufficient carrier concentrations, positive optical gain remains elusive in electrically-pumped organic diodes. Organic device simulation provides a faster method of testing organic materials and device structures for positive optical gain based on known organic physics. The results generated from simulation provide key information in development of physical organic devices. This project produces a simulator capable of modeling current density and optical density with the intent of testing various device structures that allow for lazing in organic materials.

This thesis is based on the series of scholarly article dedicated to the issue of pumping in the differential scanning chamber of an environmental scanning microscope. The thesis is based on Danilatos’s study where the pumping of the differential pumped chamber is solved by means of the Monte Carlo statistical method. The thesis analyzes gas flow in the experimental chamber using the Pipot tube. The analyses will be used for the design of the experimental chamber which will serve for the experimental evaluation of the flow results in the chamber using the continuum mechanics.

<p><a>Direct chill (DC) casting is the main production method for wrought aluminum alloys. In this semi-continuous process, significant heat is extracted through a narrow, solidified shell by impinging water jets. A combination of rapid cooling and inoculation of the liquid metal with heterogenous nucleation sites (grain refiner) produces the proper conditions for equiaxed solidification. As equiaxed grains nucleate and grow in the slurry, they are transported by natural convection until their eventual coalescence into a rigid mush. The preferential accumulation of these solute-depleted grains in localized regions of the casting can lead to long range composition differences known as macrosegregation. Because macrosegregation cannot be mitigated by subsequent processing, it is critical to understand and prevent its development during casting. </a></p> <p>Numerical models are often used to gain insight into the interplay of the different transport phenomena that cause macrosegregation. The formation of mobile equiaxed grains creates a multiphase system with many moving interfaces, causing several modeling challenges. In principle, a model could be formulated in terms of local instantaneous variables describing the evolution of these interfaces, however the associated computational cost prohibits its extension to the length scale of industrial castings. For this reason, macroscopic transport equations are mathematically formulated using volume averaging methods. Two different volume-averaged model formulations can be distinguished in the solidification literature. The first approach is the multiphase formulation, which solves separate sets of governing equations for each phase that are coupled using microscale interfacial balances. While this approach retains closure models to describe the behavior of the sub-grid interfaces, these interfacial models introduce significant uncertainty that is propagated through the model. The second approach is the mixture formulation, which solves a single set of governing equations for the mixture and utilizes more pragmatic closure relationships. While this approach significantly reduces the complexity and computational cost of the model, previous formulations have oversimplified the microscale transport. Recognizing the advantages and disadvantages of both formulations, a mixture model is rigorously derived, retaining appropriate relationships for the grain structure and microsegregation behavior in equiaxed solidification </p> <p>Implementation of this model into a 3-D finite volume method (FVM) code using a co-located grid is discussed along with appropriate treatment of the discontinuous body forces and phase mass fluxes across the interface between the slurry and rigid mush. More specifically, body forces in the momentum equation are treated at the face-centers of a control volume to prevent erroneous velocity oscillations near this interface, and a diffuse phase flux method is proposed to reduce the sensitivity of composition predictions to the numerical grid. The proposed methods are verified across a wide range of conditions present in equiaxed solidification. </p> <p>This model is then used to investigate the role of grain motion on macrosegregation development in equiaxed solidification, specifically in horizontal and vertical DC casting. In horizontal DC casting, the casting axis is perpendicular to gravity and there is a tendency for grains to accumulate along the bottom of the ingot. Feeding liquid metal through a constrained inlet near the bottom suspends grains in the slurry, both reducing the overall macrosegregation and improving the macrosegregation symmetry in the ingot. In vertical DC casting, the casting axis is parallel to gravity and there is a tendency for grains to accumulate in the center of the ingot. It is determined by a combination of simulations in the current work and previous experimental results that a strong localized jet at the centerline can suspend grains in the slurry and reduce negative centerline segregation. The change in segregation is attributed to a combination of reducing the accumulation of solute-depleted grains near the centerline and thinning the rigid mush where solidification shrinkage pulls enriched liquid away from the centerline. The strong localized jet also causes significant refinement and homogenization of the grain structure, which improves the mechanical properties of the ingot. These studies indicate that it is beneficial for DC casting practices to move towards agitated or stirred melts, and away from conventional practices which promote thermal stratification and localized accumulation of equiaxed grains.</p>

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13021号 / 論農博第2831号 / 新制||農||1042(附属図書館) / 学位論文||H28||N4967(農学部図書室) / 32949 / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 藤原 正幸, 教授 村上 章, 准教授 宇波 耕一 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

For a structure designed to interact with the surrounding fluid, structural deformation under loads induced by fluid flows is an important factor to consider, and one which is traditionally difficult to account for analytically. Coupling the finite element method for structural analysis with the finite volume method for the determination of fluid response allows for accurate simulation of the pressure and shearing loads applied by the fluid onto the fluid-structure interface, while also determining localized structural displacements that would cause changes to the geometry of the interface. This work seeks to simulate the behavior of cylinders with varying heights and stiffnesses under external flows with low Reynolds numbers. To address structural deformation accurately in the simulation, a morphing and remapping algorithm is applied to the fluid-structure interface. With additional consideration for anisotropy in the structure's elasticity, these analyses could potentially support the development of flexible components that deform in predetermined ways under anticipated fluid loads, allowing for simpler and more efficient solutions to control flow scenarios that traditionally require moving components and control surfaces.

No description available.