Orientador: Sávio Souza Venâncio Vianna / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-24T13:25:34Z (GMT). No. of bitstreams: 1 Ferreira_TatieleDalfior_M.pdf: 4562241 bytes, checksum: 69c742236e806f040cfc237f2ba91cf4 (MD5) Previous issue date: 2014 / Resumo: Este trabalho tem como objetivo desenvolver um modelo matemático capaz de prever o tamanho de nuvem de gás inflamável formada em uma típica plataforma de petróleo considerando condições reais de ventilação e de operação de uma planta de processo. Para tanto, foi realizado um estudo de dispersão de gás inflamável (gás natural) na plataforma em questão utilizando Fluidodinâmica Computacional (CFD). Os resultados deste estudo de dispersão serviram como base para a construção do modelo matemático utilizando Metodologia de Superfície de Resposta. Tal modelo permite o cálculo do tamanho de nuvem de gás inflamável no ambiente estudado usando duas variáveis principais: a taxa não-dimensional de vazamento (que contabiliza a relação entre a taxa de vazamento de gás e a taxa de ventilação na plataforma) e a direção adimensional de vazamento (que computa a relação entre as direções de vazamento de gás e do vento). O modelo desenvolvido mostrou-se eficaz, pois foi capaz de prever com considerável grau de confiabilidade os tamanhos de nuvem de gás inflamável quando comparados aos valores fornecidos por simulações com CFD / Abstract: This work proposes the development of a mathematical correlation for prediction of flammable gas cloud size in a typical offshore module. Real conditions regarding the ventilation and process plant operation were considered. A dispersion study of natural gas release in the module was conducted using Computational Fluid Dynamics (CFD) and the state of art as far as the gas dispersion modelling is concerned. A mathematical model was built based on the numerical results and Response Surface Methodology (RSM). The approach comprises into a single mathematical model the most relevant independent variables. The response surface curves calculate the flammable gas cloud volume as a function of the non-dimensional leak rate (that concerns the ventilation and the gas release rate) and the non-dimensional leak direction (which comprises the wind direction and the leak direction). The developed model had proved to be effective. It was able to predict flammable gas volume and good agreement with CFD results was observed / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestra em Engenharia Química

Mechanical conditioning has been shown to promote tissue formation in a wide variety of tissue engineering efforts. However the underlying mechanisms by which external mechanical stimuli regulate cells and tissues are not known. This is particularly relevant in the area of heart valve tissue engineering owing to the intense hemodynamic environments that surround native valves. Some studies suggest that oscillatory shear stress (OSS) caused by time-varying flow environments, play a critical role in engineered tissue formation derived from bone marrow derived stem cells (BMSCs). There is strong evidence to support this hypothesis in tissue engineering studies of bone. From observing native heart valve dynamics, OSS can be created by means of pulsatility or by cyclic specimen geometry changes. However, quantification of the individual or combined effects of these variables for the maximization of OSS environments in vitro is to date, not known. Accordingly, in this study we examined and quantified the role that i) physiologically relevant scales of pulsatility and ii) changes in geometry as a function of specimen flexure, have in creating OSS conditions for dynamic culture of tissue. A u-shaped custom made bioreactor capable of producing flow stretch and flexure was used. Computational Fluid Dynamic (CFD) simulations were performed through Ansys CFX (Ansys, Pittsburgh, PA) for both steady and pulsatile flow. We have shown that OSS can be maximized by inducing pulsatile flow over straight scaffolds. We believe that OSS promotes BMSCs tissue formation.

The objective of this study is to identify the optimal designs of converging-diverging supersonic and hypersonic nozzles that perform at maximum uniformity of thermodynamic and flow-field properties with respect to their average values at the nozzle exit. Since this is a multi-objective design optimization problem, the design variables used are parameters defining the shape of the nozzle. This work presents how variation of such parameters can influence the nozzle exit flow non-uniformities. A Computational Fluid Dynamics (CFD) software package, ANSYS FLUENT, was used to simulate the compressible, viscous gas flow-field in forty nozzle shapes, including the heat transfer analysis. The results of two turbulence models, k-e and k-ω, were computed and compared. With the analysis results obtained, the Response Surface Methodology (RSM) was applied for the purpose of performing a multi-objective optimization. The optimization was performed with ModeFrontier software package using Kriging and Radial Basis Functions (RBF) response surfaces. Final Pareto optimal nozzle shapes were then analyzed with ANSYS FLUENT to confirm the accuracy of the optimization process.

Orientador: Sávio Souza Venâncio Vianna / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-26T16:12:11Z (GMT). No. of bitstreams: 1 FerreiraJunior_ElmodeSena_M.pdf: 18188081 bytes, checksum: 2b445e8828a2a2b90c9a27c3379a7d74 (MD5) Previous issue date: 2015 / Resumo: A simulação numérica é de grande importância em diversas áreas da engenharia, tais como otimização e manutenção de processo químico, bem como na indústria do petróleo e segurança do processo. O Fire Dynamics Simulator (FDS) é um código de Fluidodinâmica Computacional com base na simulação das grandes escalas. Este foi desenvolvido pelo Instituto Nacional de Padrões e Tecnologia (NIST). O código FDS foi originalmente projetado para modelar baixo fluxo de velocidade comumente encontrados em cenários de incêndio. Assim, o FDS não é adequado para simulação de casos onde o número de Mach é elevado. Para superar esta limitação, este trabalho propõe um novo modelo dedicado às características próximas da saída do jato a fim de permitir o FDS simular cenários de jatos e dispersão de gás. A abordagem também reduz significativamente o tempo da simulação computacional. A ferramenta proposta é uma alternativa livre e confiável para a modelagem de dispersão de gás. Os resultados são amplamente discutidas e um estudo de caso de uma plataforma é apresentado. A comparação com os resultados experimentais, bem como um pacote CFD comercial mostram boa concordância / Abstract: The numerical simulation is of great importance in various areas of engineering such as optimization and maintenance of chemical process, petroleum industry and process safety. The Fire Dynamics Simulator (FDS) is a Computational Fluid Dynamics (CFD) code based on Large Eddy Simulation (LES) modeling and developed by National Institute of Standards and Technology (NIST). FDS code was originally designed to model low speed flow commonly found in fire scenarios. Hence, FDS is not suitable for modeling high Mach number cases. To overcome this limitation this work proposes a novel model dedicated to the near field jet characteristics in order to enable FDS to simulate jet scenarios and gas dispersion. The approach also reduces the computational time significantly as far as turbulent jet flows are concerned. The proposed tool is a free and reliable alternative for gas dispersion modeling. Results are extensively discussed and case study for a typical offshore site is presented. Comparison with experimental results as well as commercial CFD package show good agreement / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

Inspired by the pectoral flippers of the humpback whale, the use of spanwise waviness in wings has been considered in the literature as a possible way of delaying the stall, and possibly also reducing the drag coefficient, allowing for improved aerodynamic characteristics. In order to provide a better understanding of this flow control mechanism, the present work investigates numerically the effect of the waviness on the flow around infinite wings with a NACA0012 profile. The study consists of direct numerical simulations employing the spectral/hp method, which is available through the nektar++ library. Considering the high computational cost of the simulations performed, several improvements were introduced to the method, making it more efficient and allowing higher Reynolds numbers to be analysed. These improvements to the method include a coordinate transformation technique to treat the waviness, changes to the parallelism strategy, and an adaptive polynomial order refinement procedure. Initially, simulations were performed for a very low value of the Reynolds number Re = 1, 000, allowing the three-dimensional flow structures to be observed in de- tail. In this case, the results show that the waviness leads to a decrease in the lift-to-drag ratio, accompanied by a strong reduction in the fluctuations of the lift force. The reduction in the lift-to-drag ratio is the combined effect of lower drag and lift forces, and is associated with a regime where the flow remains attached behind the peaks of the leading edge while there are distinct regions of flow separation behind the troughs. Then, simulations with Re = 10, 000 were considered. For high angles of attack, the results for this case are similar to the lower Re, with the waviness leading to separation behind the troughs and reducing both the lift and the drag. However, for a lower angle of attack the waviness leads to a large increase in the lift coefficient. This was observed to be related to the fact that flow around the straight wing is laminar in this case, with the waviness inducing transition to a turbulent state. Finally, the case Re = 50, 000 was considered, with the results showing a good agreement with experiments presented in the literature. / Inspirado na nadadeira peitoral da baleia jubarte, o uso de ondulações ao longo da envergadura de asas tem sido considerado na literatura como uma possível maneira de atrasar o estol, e possivelmente também reduzir o arrasto, levando a melhores características aerodinâmicas. Com o objetivo de obter um melhor entendimento desse mecanismo de controle do escoamento, o presente trabalho investiga numericamente o efeito de ondulações no escoamento ao redor de asas infinitas com o perfil NACA0012. O estudo consiste de simulações diretas do escoamento usando o método espectral/hp, que está disponível através da biblioteca nektar++. Considerando o alto custo computacional das simulações realizadas, diversas melhorias foram introduzidas no método, tornando-o mais eficiente e permitindo que números de Reynolds mais elevados fossem analisados. Essas melhorias ao método incluem uma técnica de mudança de coordenadas para tratar a ondulação, mudanças na estratégia de paralelismo e um procedimento de refinamento usando ordem polinomial variável. Inicialmente, simulações foram realizadas para um número de Reynolds muito baixo Re = 1, 000, o que permitiu observar as estruturas tridimensionais do escoamento em detalhe. Nesse caso, os resultados mostram que a ondulação leva a uma diminuição da razão sustentação-arrasto, combinada com uma forte redução das flutuações da força de sustentação. A redução da razão sustentação-arrasto é consequência de uma combinação de arrasto e sustentação mais baixos e está associada a um regime no qual o escoamento permanece colado atrás dos picos do bordo de ataque, enquanto que regiões distintas de escoamento separado estão presentes atrás dos vales. Em seguida, simulações com Re = 10, 000 foram consideradas. Para ângulos de ataque elevados, os resultados neste caso são similares àqueles com Re mais baixo, com a ondulação levando a separação atrás dos vales e provocando reduções na sustentação e no arrasto. No entanto, para um ângulo de ataque mais baixo a ondulação leva a um grande aumento na força de sustentação. Foi observado que isso está relacionado ao fato de que o escoamento ao redor da asa lisa é laminar neste caso, com a ondulação induzindo a transição para um estado turbulento. Finalmente, o caso Re = 50, 000 foi considerado, com os resultados apresentando uma boa concordância com experimentos apresentados na literatura.

O foco desta pesquisa é a análise computacional da cavitação em válvula borboleta utilizando o software comercial Ansys CFX versão 14. Dentre várias aplicações, a válvula pode ser utilizada no controle da vazão de água para lavagem de gases oriundos do processo de fabricação do aço num conversor LD. Foi estabelecido como parâmetros constantes de simulação, a pressão a montante e jusante respectivamente em 150 e 60 kPa e a temperatura de 80C. O objetivo deste trabalho é conhecer, através da simulação computacional, os ângulos em que a cavitação torna-se crítica na válvula borboleta, mapeando as áreas de cavitação, que será validada pelo equacionamento da válvula, de acordo com a norma da ISA. Será analisado o escoamento do fluído, priorizando a variável pressão e diferencial de pressão através da válvula, variando os ângulos do obturador de 10 em 10 graus, até o ângulo de 70. Em seguida, serão feitas novas simulações com as temperaturas de 50, 60, 70 e 90C, haja vista que, a vaporização da água está diretamente relacionada, não somente com a pressão, mas também com a temperatura do fluído. A escolha desta válvula para estudo dá-se pelo fato de ter uma alta recuperação de pressão a jusante, levando ao colapso as bolhas de vapor, quando a pressão se eleva acima da pressão de vapor da água, resultando no fenômeno físico denominado por cavitação, alvo de análise e mapeamento desta pesquisa. O regime de escoamento do fluído newtoniano é turbulento e utilizou-se a técnica de volumes finitos idealizada por Patankar, para resolução numérica, e o software comercial CFX versão 14 da Dinâmica de Fluidos Computacional. Foi utilizada a geometria e condições de contorno operacionais de uma válvula borboleta para investigar as regiões as quais ocorrem possibilidades de desgaste e focos de cavitação. / The focus of this study is a computational analysis of cavitation in butterfly valve using a commercial software named Ansys CFX version 14. Among several applications, the valve may be used in controlling water flow for gas washing originating from the washing process in a steelmaking converter LD. Therefore, the constant pressure upstream and downstream respectively at 150 and 60 kPa and de 80C , was established as constant simulation parameter. The purpose of this study is find out, using a computer simulation, which angles at the cavitation becomes critical in the butterfly valve, and mapping the areas of cavitation, which will be validated by the valve equation, according to ISA standards. Therefore, the flow of the fluid will be analyzed, prioritizing the variable and the differential constant pressure through the valve by varying the obturators angles from 10 to 10 degrees, until it comes to a 70 angle. To achieve this purpose, new simulations will be made with temperatures of 50, 60, 70 and 90 degrees, considering that the water vaporization is directly related to not only the pressure but also the temperature of the fluid. In this study, the butterfly valve was chosen because of its high downstream pressure recovery, leading to collapse of the vapor bubbles, when the pressure is elevated above the water vapour pressure, resulting in the physical phenomenon known as cavitation, which is the target analysis and mapping of this study. The Newtonians flow regime was found turbulent and to numerical solution was used the technique of finite volume designed by Patankar, by using commercial software CFX version 14.0 of Computational Fluid Dynamics. Was used both geometric and operational contour of a butterfly valve project to investigate in which part and conditions of a valve can occur potential wear and cavitations spots.

Den här rapporten presenterar ett examensarbete som har utförts på Boliden Mineral AB. Arbetet handlar om att förbättra pumphoarnas konstruktion för att minimera slitage och sedimentering av slurryn. Pumphoarna sitter i anslutning till slurrypumparna i anrikningsverket för att reglera flödet av slurry. Arbetet följer Boliden Mineral ABs egna projektmodell, från början till slut. Syftet med projektet är att få bättre kunskap om pumphoarna, hur slurryn rör sig samt hur och var slitage uppstår. Målet med projektet är att utveckla en standardiserad design av pumphoar för slurrypumpning, samt att standardisera sättet för att ta fram dessa i framtiden. Nuvarande konstruktion av Bolidenområdets pumpho utvärderas med hjälp av CFD-simuleringar. Resultatet visar slitage som uppstår vid pumphons inlopp, områden där sedimentering kan förekomma samt strömlinjer för partiklarna i slurryn. Nya koncept för att förbättra pumphons konstruktion tas fram. Koncepten genereras för att minimera slitaget vid inloppet på pumphon samt minska risken för sedimentering av slurryn. De framtagna koncepten utvärderas med hjälp av CFD-simuleringar, på samma sätt som för den nuvarande konstruktionen. Koncepten jämfördes sedan med den nuvarande pumphon. En kombination av två koncept valdes som den slutgiltiga konstruktionen då den uppfyllde arbetets mål bäst.

A computational fluid dynamics (CFD) methodology is presented to predict density stratified flows in the near-field of ships and submarines. The density is solved using a higher-order transport equation coupled with mass and momentum conservation. Turbulence is implemented with a k-ε/k-ω based Delayed Detached Eddy Simulation (DDES) approach, enabling explicit solution of larger energy-containing vortices in the wake. Validation tests are performed for a two-dimensional square cavity and the three-dimensional stratified flow past a sphere, showing good agreement with available data. The near-field flow of the self-propelled Research Vessel Athena advancing in a stably stratified fluid is studied, as well as the operation in stratified flow of the notional submarine Joubert BB2 also in self-propelled condition. The resulting density, velocity, pressure and turbulent quantities at the exit plane of the near-field computation contain a description of the relevant scales of the flow and can be used to compute the far-field stratified flow, including internal waves. The generation of internal waves is shown in the case of the submarine for two different conditions, one with the pycnocline located at the propeller centerline, and the second with the pycnocline located slightly below the submarine, concluding that distance to the pycnocline strongly affects the internal wave generation due to the presence of the vessel. It is also shown that, as in the case of surface waves, the generation of internal waves requires energy that results in an increase in resistance. For the case of the surface ship the near field wakes are mostly affected by the separation at the wet transom and propeller mixing. However, in the case of the underwater vessel, the disturbance of the background density profile by the presence of the submarine affects the near-field wakes. Finally, the dead-water phenomenon, which occurs at very low Froude numbers, is studied for R/V Athena. Though the dead water problem has been studied in the literature using potential flow methods, this thesis presents the first attempt at using computational fluid dynamics (CFD) to analyze the flow. Results show that, while CFD can reproduce trends observed in potential flow studies, viscous effects are significant in the wake and the friction coefficient.

In order to evaluate a biologically relevant measure of exposure, inhalable samplers are designed to match the aspiration efficiency of the human head. Human inhalability is evaluated in wind tunnel studies using mannequins as human surrogates or using numerical and computational methods. There has been differences between human aspiration efficiency estimates using wind tunnel studies and computational fluid dynamics (CFD) modeling, particularly for larger particle sizes (>68 µm). The objective of this dissertation was to evaluate biases in low velocity inhalability studies in an effort to explain the discrepancies in results between experimental and computational inhalability studies. This research addressed the phenomena of secondary aspiration on human facial skin, evaluated the appropriateness of mannequin surfaces as surrogates for humans, and evaluated the performance of the thin-walled reference sampler in low velocities to quantify potential biases in low velocity inhalability studies. The first study determined a realistic coefficient of restitution (CoR) for human facial skin over a range of ages under nine environmental conditions. This study found human facial skin is non-uniform across the face and identified significant interaction between age and sampling location, indicating that how CoR varies with age is dependent on the location sampled. The second study applied the average CoR values for forehead, cheeks and nose in CFD simulations to evaluate the effect of secondary aspiration on human aspiration efficiency estimates and determine how refined the CoR value needed to be to accurately model human aspiration efficiency. This study identified significant increases in aspiration when allowing for particle bounce, but no significant differences between uniform CoRs of 0.5, 0.8 and 1.0, indicating differences between different mannequin surfaces and particle interactions would have minimal effect on aspiration efficiency estimates. The third study evaluated the performance of a horizontally-aligned reference sampler in low wind speeds (0.1 to 0.4 m s-1). While significant differences from unity were identified, differences ranged from -1 to 6% and would have a negligible effect on sampler efficiency estimates. The use of a horizontally-aligned isokinetic reference sampler was found to be appropriate in freestream velocities ranging from 0.1 to 0.4 m s-1.

Oxide inclusions are among the most commonly reported defects in ferrous and non-ferrous castings. They affect the surface quality, machinability, and mechanical performance of a cast part. Air entrainment during mold filling is the main source of the oxygen that is consumed in inclusion formation. A quantitative understanding of the formation mechanisms or the prediction of final amounts and locations of oxide inclusions in metal castings is not available. Ductile iron experiments are conducted to study the formation of oxide inclusions during pouring. Oxide inclusions are measured by serial sectioning of the solidified castings. The effect of different gating systems, section thicknesses, and surface orientations on the inclusion formation and final distribution is studied. In addition, a computational model is developed for predicting the formation, motion and final location of oxide inclusions during pouring of metal castings, with the focus on the important mechanism of generation of oxide inclusions due to air entrainment during mold filling. The developed model calculates the local air entrainment rate as a function of the turbulent kinetic energy and the magnitude of the normal velocity gradient of the liquid metal at the liquid-air interface. The turbulent kinetic energy is estimated from the sum of the squares of the fluctuating velocity components relative to a spatially averaged mean velocity. The air entrainment model is implemented in a casting simulation software and validated by comparing its predictions to experimental air entrainment measurements for a circular water jet plunging into a quiescent pool. The liquid velocity, diameter and the turbulence intensity dependence is determined by a single entrainment coefficient. Oxide inclusions are then generated at the liquid-air interface, transported with the melt flow under the combined influences of drag and buoyancy, and captured by the solidifying casting surface. The developed model provides a powerful technique for predicting the oxide inclusion formation and final location.