O concreto é um dos materiais de construção civil mais versáteis, podendo se adaptar a formas diversas quando em seu estado fresco e resistindo a grandes cargas de compressão em seu estado rígido. No entanto, em estruturas mais densamente armadas ou com geometrias mais complexas, pode-se apresentar dificuldades para a moldagem, causando falhas no preenchimento da forma, o que reduz a capacidade resistente da peça e sua vida útil. Neste trabalho foi utilizado o método de partículas lagrangeanas Moving Particle Semi-Implicit (MPS) como base para um simulador para o estudo do comportamento do escoamento de pastas e argamassas cujo comportamento pode se aproximado por modelos reológicos como Bingham e Herschel-Bulkley. Foram propostos módulos para a simulação da viscosidade não-newtoniana, variação térmica no processo de cura e modelagem de turbulência. Para modelar a variação de viscosidade de um fluido não-newtoniano foi utilizado o modelo de Herschel-Bulkley. O modelo de Herschel-Bulkley possui uma singularidade para taxas de deformação muito pequenas, que resulta em valores de viscosidade infinitas, dificuldade contornada pela solução proposta por Papanastasiou (1987). Na modelagem térmica foram analisados dois modelos de dissipação, sendo um original do método e outro calculado por meio do divergente do gradiente utilizando os modelos de partículas e que teria melhores resultados para o cálculo da dissipação térmica. Também foi modelada a convecção térmica, utilizando para isso a hipótese de Boussinesq. A reação de hidratação do concreto foi modelada utilizando uma equação do tipo Hill para representar a elevação de temperatura obtida por meio um ensaio adiabático. Para complementar as simulações, foi utilizado o modelo de turbulência Detached Eddy Simulation (DES), baseado no método Large Eddy Simulation (LES), que utiliza um modelo de parede para simular a interação do fluido. Para a implementação deste modelo de turbulência foi proposto um algoritmo para o cálculo da distância da partícula de fluido à parede. Este algoritmo utiliza estruturas de dados já existentes no método de partículas de modo que sua execução requer muito menos recursos que a busca binária. Apesar do trabalho ter se guiado pela simulação do concreto fresco, que é um material particularmente complexo, outros escoamentos encontrados na engenharia civil também podem ser beneficiados pelo método, como os estudos do escoamento em sistemas prediais de água e esgoto, do escoamento e prevenção de erosão em rios e córregos, do escorregamento de encostas, dos reatores para depuração de esgotos, entre outros. / The concrete is one of the more versatile civil construction materials, it can adapt to various forms when in its fresh state while resisting to high compression loads in its rigid state. However, in some cases like densely reinforced concrete structures and complex geometry concrete structures can present issues to the casting, and failure in proper form filling can occur. These failures can reduce the resistance and the lifetime of the structure. This work used a simulator based on the lagrangean particle method called Moving Particle Semi-Implicit (MPS) to study the concrete behavior in its distinctive characteristics. Also, this work proposed modules to simulate the non-Newtonian viscosity, the thermal process of concrete cure and to model the turbulent flow. To model the variation of viscosity of a non-Newtonian fluid, the Herschel-Bulkley model, which relates the shear stress with the strain rate, was applied. The Herschel-Bulkley model has a singularity at low strain rates, which results in infinite viscosities. To overcome this issue, Papanastasiou (1987) proposed a modification in the model in order to eliminate the singularity. For the thermal modeling, two models for thermal dissipation were compared, the original method and other calculated from the divergence of gradient using the differential operators for the particle model and that could present improved results for the thermal dissipation calculation. Also, the thermal convection was modeled using the Boussinesq hypothesis. The hydration reaction of the concrete was modeled using a Hill type equation to reproduce the temperature elevation. In addition, a Detached Eddy Simulation (DES) based turbulence model with a simple wall model in the interaction of wall and fluid was applied in the simulations. To improve the turbulence model, an algorithm to calculate the distance between fluid and the nearest wall particle was proposed. The algorithm uses already calculated information from particles so that the execution requires much less resources than a binary search. Although the work has been focused on to the modeling of fresh concrete simulation, which is a particularly complex material, other flows found in civil engineering can also be benefited by the method, such as studies of drainage in water and sewage systems, drainage and prevention of erosion into rivers and streams, prevention and damage mitigation of landslides, reactors for sewage treatment among many others.

O concreto é um dos materiais de construção civil mais versáteis, podendo se adaptar a formas diversas quando em seu estado fresco e resistindo a grandes cargas de compressão em seu estado rígido. No entanto, em estruturas mais densamente armadas ou com geometrias mais complexas, pode-se apresentar dificuldades para a moldagem, causando falhas no preenchimento da forma, o que reduz a capacidade resistente da peça e sua vida útil. Neste trabalho foi utilizado o método de partículas lagrangeanas Moving Particle Semi-Implicit (MPS) como base para um simulador para o estudo do comportamento do escoamento de pastas e argamassas cujo comportamento pode se aproximado por modelos reológicos como Bingham e Herschel-Bulkley. Foram propostos módulos para a simulação da viscosidade não-newtoniana, variação térmica no processo de cura e modelagem de turbulência. Para modelar a variação de viscosidade de um fluido não-newtoniano foi utilizado o modelo de Herschel-Bulkley. O modelo de Herschel-Bulkley possui uma singularidade para taxas de deformação muito pequenas, que resulta em valores de viscosidade infinitas, dificuldade contornada pela solução proposta por Papanastasiou (1987). Na modelagem térmica foram analisados dois modelos de dissipação, sendo um original do método e outro calculado por meio do divergente do gradiente utilizando os modelos de partículas e que teria melhores resultados para o cálculo da dissipação térmica. Também foi modelada a convecção térmica, utilizando para isso a hipótese de Boussinesq. A reação de hidratação do concreto foi modelada utilizando uma equação do tipo Hill para representar a elevação de temperatura obtida por meio um ensaio adiabático. Para complementar as simulações, foi utilizado o modelo de turbulência Detached Eddy Simulation (DES), baseado no método Large Eddy Simulation (LES), que utiliza um modelo de parede para simular a interação do fluido. Para a implementação deste modelo de turbulência foi proposto um algoritmo para o cálculo da distância da partícula de fluido à parede. Este algoritmo utiliza estruturas de dados já existentes no método de partículas de modo que sua execução requer muito menos recursos que a busca binária. Apesar do trabalho ter se guiado pela simulação do concreto fresco, que é um material particularmente complexo, outros escoamentos encontrados na engenharia civil também podem ser beneficiados pelo método, como os estudos do escoamento em sistemas prediais de água e esgoto, do escoamento e prevenção de erosão em rios e córregos, do escorregamento de encostas, dos reatores para depuração de esgotos, entre outros. / The concrete is one of the more versatile civil construction materials, it can adapt to various forms when in its fresh state while resisting to high compression loads in its rigid state. However, in some cases like densely reinforced concrete structures and complex geometry concrete structures can present issues to the casting, and failure in proper form filling can occur. These failures can reduce the resistance and the lifetime of the structure. This work used a simulator based on the lagrangean particle method called Moving Particle Semi-Implicit (MPS) to study the concrete behavior in its distinctive characteristics. Also, this work proposed modules to simulate the non-Newtonian viscosity, the thermal process of concrete cure and to model the turbulent flow. To model the variation of viscosity of a non-Newtonian fluid, the Herschel-Bulkley model, which relates the shear stress with the strain rate, was applied. The Herschel-Bulkley model has a singularity at low strain rates, which results in infinite viscosities. To overcome this issue, Papanastasiou (1987) proposed a modification in the model in order to eliminate the singularity. For the thermal modeling, two models for thermal dissipation were compared, the original method and other calculated from the divergence of gradient using the differential operators for the particle model and that could present improved results for the thermal dissipation calculation. Also, the thermal convection was modeled using the Boussinesq hypothesis. The hydration reaction of the concrete was modeled using a Hill type equation to reproduce the temperature elevation. In addition, a Detached Eddy Simulation (DES) based turbulence model with a simple wall model in the interaction of wall and fluid was applied in the simulations. To improve the turbulence model, an algorithm to calculate the distance between fluid and the nearest wall particle was proposed. The algorithm uses already calculated information from particles so that the execution requires much less resources than a binary search. Although the work has been focused on to the modeling of fresh concrete simulation, which is a particularly complex material, other flows found in civil engineering can also be benefited by the method, such as studies of drainage in water and sewage systems, drainage and prevention of erosion into rivers and streams, prevention and damage mitigation of landslides, reactors for sewage treatment among many others.

Orientador: Maria Virgínia Costa Scarpa / Coorientador: Marlus Chorilli / Banca: Renata Fonsenca Vianna Lopez / Banca: Leila Aparecida Chiavacci / Resumo: Amplamente utilizado no tratamento de vários tipos de câncer e na psoríase, o metotrexato (MTX) é um quimioterápico, estruturalmente análogo do ácido fólico, que apesar de sua eficácia apresenta uma série de efeitos adversos, sendo a hepatotoxicidade o mais grave. Atualmente os sistemas nanoestruturados líquido-cristalinos de fase lamelar estão sendo utilizados como dispositivos para liberação modificada de fármacos, sendo vantajosos na liberação tópica de várias substâncias, conforme suas características de interação com o estrato córneo e as outras camadas da pele, evitando assim efeitos adversos sistêmicos. Os objetivos deste trabalho foram desenvolver sistemas nanoestruturados líquido-cristalinos de fase lamelar, acrescidos de MTX, caracteriza-los do ponto de vista físico, realizar a análise estrutural das formulações, através de microscopia de luz polarizada (MLP), espalhamento de raios-X a baixo ângulo (SAXS) e suas propriedades reológicas, executar os testes de estabilidade preliminar (TEP) das formulações, validar o método analítico para a quantificação de MTX por CLAE e executar ensaios de liberação, permeação e retenção in vitro. As formulações preparadas a partir da mistura do poliéter funcional siloxano (Dow Corning® 5329) como tensoativo, com silicone fluido de co-polímero glicol (Dow Corning® 193C) como fase oleosa titulados em fase aquosa, composta por tampão fosfato de potássio monobásico 0,01M pH 7,4, apresentaram fases líquido-cristalinas do tipo lamelar, confirmados pelos ensaios de MLP e SAXS. Os TEPs evidenciaram que as formulações A, B e C mantiveram-se estáveis durante o período do estudo. Os estudos do comportamento reológico das formulações apresentaram-se como fluidos pseudoplásticos não-newtonianos tixotrópicos ... / Abstract: Widely used in the treatment of some types of cancer, the methotrexate (MTX) is a chemotherapeutic, structurally analog of the folic acid, although its effectiveness, presents a series of adverse effect, being the most serious hepatotoxicity. Currently, the liquid crystal lamellar phase is being used of devices for modified release of drug demonstrated to be advantageous in the release topic of some substances, given to the characteristics of interaction with the stratum corneun and other layers of the skin, avoiding systemic adverse effects. The aims of this research had been to develop and to characterize liquid crystalline nanostructure systems of lamellar phase, increased of MTX of the physical point of view, also carry through the structural analysis of the formulations through by polarized light microscopy (PLM), small-angle X-ray scattering (SAXS) and rheological properties. Perform stability studies of the chosen formulations, validate the analytical method of quantification of MTX for High Performance Liquid Chromatography (HPLC) and carry through release assay, cutaneous permeation and skin retention in vitro for the chosen formulations. The formulations prepared by the mixture of polyether functional siloxane as surfactant, with silicone polyether copolymer as oily phase and phosphate buffer 0,01M pH 7,4 as aqueous phase demonstrating lamellar liquid-crystalline phases, confirmed by assays of PLM and SAXS. The stability studies showed that formulations A, B and C remained stable throughout the period of the study. The study of the rheological behavior of the formulations presented as not Newtonian pseudoplastic fluid and thixotropic ... / Mestre

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2016-10-05T18:21:53Z No. of bitstreams: 1 2016 - Jo?o Pedro Chalfun Haouche Meneses.pdf: 6719960 bytes, checksum: ac9a27b5731b19e4693f71fae09adefe (MD5) / Made available in DSpace on 2016-10-05T18:21:53Z (GMT). No. of bitstreams: 1 2016 - Jo?o Pedro Chalfun Haouche Meneses.pdf: 6719960 bytes, checksum: ac9a27b5731b19e4693f71fae09adefe (MD5) Previous issue date: 2016-01-25 / Petrobras / The drilling of wells in salt layers faces major challenges in Brazil?s oil industry. Drilling in such layers requires the development of new technologies and operational procedures to make the process economically viable. One of the main problems is the dissolution of the salt layers in water-based drilling fluids. An uncontrolled dissolution presents a potential risk for the operation and can cause abrupt changes in the properties of the fluids. The main objective of this work was to study the effects of the dissolution of sodium chloride particles in non-Newtonian fluids containing xanthan gum. The study was divided into three parts, rheological experiments, kinetics experiments in a mixing tank and a mathematical modeling. The rheological experiments aimed at studies of the effect of the addition of saline particles on the rheology of non-Newtonian fluids, the effect of the concentration of suspended particles in the rheology of saturated fluids and the effect of the size of suspended particles in the rheology of saturated fluids. The Einstein equation was used to calculate the apparent viscosity of saturated fluids, taking into account the effect of the concentration of salt particles in suspension. The experiments in the mixing tank aimed at the study of the kinetics of dissolution with time in different operating conditions. Fluids were prepared using different concentrations of xanthan gum and different initial concentrations of sodium chloride. The effects of the viscosifier concentration and the initial concentration gradient were evaluated. A phenomenological model was used to represent the dissolution process, which provides the variation of the concentration of the fluid, the variation of the volume fraction of solids, the variation of the particles mean diameter and the variation of the interfacial mass transfer area as a function of time. In the rheology studies, it was verified that the addition of sodium chloride to the non-Newtonian fluid, in the studied conditions, increased the apparent viscosity of the solution. The increase of the concentration of suspended sodium chloride particles increased the apparent viscosity of the suspensions. The increase of the size of the suspended particles decreased the apparent viscosity of the suspension. Statistical tests were made in order to evaluate the statistical relevance of the performed studies. In the kinetics study, the convective mass transfer coefficient was estimated and simulations were made for the other variables of the process. The estimations showed that the xanthan gum concentration in the fluid and the initial sodium chloride concentration in the fluid affect the mass transfer coefficient. The average relative error observed for the simulations was 2,2%. / A perfura??o de po?os em camadas salinas enfrenta grandes desafios na ind?stria de petr?leo do Brasil. A perfura??o em tais camadas exige o desenvolvimento de novas tecnologias e procedimentos operacionais para tornar a perfura??o economicamente vi?vel. Um dos principais problemas enfrentados ? a dissolu??o das camadas de sais em fluidos de perfura??o base ?gua. Uma dissolu??o descontrolada apresenta um risco em potencial para a opera??o, podendo causar mudan?as bruscas nas propriedades dos fluidos. Este trabalho teve como principal objetivo estudar os efeitos da dissolu??o de part?culas de cloreto de s?dio em fluidos n?o-Newtonianos contendo goma xantana. O estudo foi dividido em tr?s partes, experimentos reol?gicos, experimentos de cin?tica em um tanque de mistura e modelagem matem?tica. Os experimentos reol?gicos tiveram como objetivo os estudos do efeito da adi??o de part?culas salinas na reologia de fluidos n?o-Newtonianos, do efeito da concentra??o de part?culas suspensas na reologia de fluidos saturados e do efeito do tamanho das part?culas suspensas na reologia de fluidos saturados. A equa??o de Einstein foi utilizada para calcular a viscosidade aparente dos fluidos saturados levando em conta o efeito da concentra??o de part?culas salinas em suspens?o. Os experimentos no tanque de mistura tiveram como objetivo o estudo da cin?tica de dissolu??o com o tempo em diferentes condi??es operacionais. Foram preparados fluidos com diferentes concentra??es de goma xantana e diferentes concentra??es iniciais de cloreto de s?dio. Foi analisado o efeito da concentra??o do viscosificante na cin?tica de dissolu??o bem como o efeito do gradiente de concentra??o inicial. Um modelo fenomenol?gico foi utilizado para representar o processo de dissolu??o, o qual prev? as varia??es da concentra??o do fluido, a varia??o da fra??o volum?trica de s?lidos, a varia??o do di?metro m?dio das part?culas e a varia??o da ?rea interfacial de transfer?ncia de massa em fun??o do tempo. Nos estudos de reologia, verificou-se que a adi??o de cloreto de s?dio ao fluido n?o-Newtoniano, nas condi??es estudadas, aumentou a viscosidade aparente da solu??o. O aumento da concentra??o de part?culas suspensas de cloreto de s?dio provocou um aumento na viscosidade aparente das suspens?es. O aumento do tamanho das part?culas suspensas de cloreto de s?dio diminuiu a viscosidade aparente da suspens?o. Testes estat?sticos foram feitos para analisar a relev?ncia estat?stica dos estudos realizados. No estudo da cin?tica, o coeficiente convectivo de transfer?ncia de massa foi estimado e simula??es foram feitas para as demais vari?veis do processo. As estima??es mostraram que a concentra??o de goma xantana no fluido e a concentra??o inicial de cloreto de s?dio no fluido influenciam o coeficiente de transfer?ncia de massa. O erro relativo m?dio simula??es observado para as simula??es foi de 2,2%.

La méthode LS-STAG est une méthode de type frontière immergée/cut-cell pour le calcul d’écoulements visqueux incompressibles qui est basée sur la méthode MAC pour grilles cartésiennes décalées, où la frontière irrégulière est nettement représentée par sa fonction level-set, résultant en un gain significatif en ressources informatiques par rapport aux codes MFN commerciaux utilisant des maillages qui épousent la géométrie. La version 2D est maintenant bien établie et ce manuscrit présente son extension aux géométries 3D avec une symétrie translationnelle dans la direction z (configurations extrudées 3D). Cette étape intermédiaire sera considérée comme la clé de voûte du solveur 3D complet, puisque les problèmes de discrétisation et d’implémentation sur les machines à mémoire distribuée sont abordés à ce stade de développement. La méthode LS-STAG est ensuite appliquée à divers écoulements newtoniens et non-newtoniens dans des géométries extrudées 3D (conduite axisymétrique, cylindre circulaire, conduite cylindrique avec élargissement brusque, etc.) pour lesquels des résultats de références et des données expérimentales sont disponibles. Le but de ces investigations est d’évaluer la précision de la méthode LS-STAG, d’évaluer la polyvalence de la méthode pour les applications d’écoulement dans différents régimes (fluides newtoniens et rhéofluidifiants, écoulement laminaires stationnaires et instationnaires, écoulements granulaires) et de comparer ses performances avec de méthodes numériques bien établies (méthodes non structurées et de frontières immergées) / The LS-STAG method is an immersed boundary/cut-cell method for viscous incompressible flows based on the staggered MAC arrangement for Cartesian grids where the irregular boundary is sharply represented by its level-set function. This approach results in a significant gain in computer resources compared to commercial body-fitted CFD codes. The 2D version of LS-STAG method is now well-established and this manuscript presents its extension to 3D geometries with translational symmetry in the z direction (3D extruded configurations). This intermediate step will be regarded as the milestone for the full 3D solver, since both discretization and implementation issues on distributed memory machines are tackled at this stage of development. The LS-STAG method is then applied to Newtonian and non-Newtonian flows in 3D extruded geometries (axisymmetric pipe, circular cylinder, duct with an abrupt expansion, etc.) for which benchmark results and experimental data are available. The purpose of these investigations is to evaluate the accuracy of LS-STAG method, to assess the versatility of method for flow applications at various regimes (Newtonian and shear-thinning fluids, steady and unsteady laminar to turbulent flows, granular flows) and to compare its performance with well-established numerical methods (body-fitted and immersed boundary methods)

Made available in DSpace on 2014-12-02T11:16:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-06-27Bitstream added on 2014-12-02T11:21:14Z : No. of bitstreams: 1 000693706.pdf: 2880957 bytes, checksum: 43d4b15dffaa346d602b5f57917996d4 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Amplamente utilizado no tratamento de vários tipos de câncer e na psoríase, o metotrexato (MTX) é um quimioterápico, estruturalmente análogo do ácido fólico, que apesar de sua eficácia apresenta uma série de efeitos adversos, sendo a hepatotoxicidade o mais grave. Atualmente os sistemas nanoestruturados líquido-cristalinos de fase lamelar estão sendo utilizados como dispositivos para liberação modificada de fármacos, sendo vantajosos na liberação tópica de várias substâncias, conforme suas características de interação com o estrato córneo e as outras camadas da pele, evitando assim efeitos adversos sistêmicos. Os objetivos deste trabalho foram desenvolver sistemas nanoestruturados líquido-cristalinos de fase lamelar, acrescidos de MTX, caracteriza-los do ponto de vista físico, realizar a análise estrutural das formulações, através de microscopia de luz polarizada (MLP), espalhamento de raios-X a baixo ângulo (SAXS) e suas propriedades reológicas, executar os testes de estabilidade preliminar (TEP) das formulações, validar o método analítico para a quantificação de MTX por CLAE e executar ensaios de liberação, permeação e retenção in vitro. As formulações preparadas a partir da mistura do poliéter funcional siloxano (Dow Corning® 5329) como tensoativo, com silicone fluido de co-polímero glicol (Dow Corning® 193C) como fase oleosa titulados em fase aquosa, composta por tampão fosfato de potássio monobásico 0,01M pH 7,4, apresentaram fases líquido-cristalinas do tipo lamelar, confirmados pelos ensaios de MLP e SAXS. Os TEPs evidenciaram que as formulações A, B e C mantiveram-se estáveis durante o período do estudo. Os estudos do comportamento reológico das formulações apresentaram-se como fluidos pseudoplásticos não–newtonianos tixotrópicos ... / Widely used in the treatment of some types of cancer, the methotrexate (MTX) is a chemotherapeutic, structurally analog of the folic acid, although its effectiveness, presents a series of adverse effect, being the most serious hepatotoxicity. Currently, the liquid crystal lamellar phase is being used of devices for modified release of drug demonstrated to be advantageous in the release topic of some substances, given to the characteristics of interaction with the stratum corneun and other layers of the skin, avoiding systemic adverse effects. The aims of this research had been to develop and to characterize liquid crystalline nanostructure systems of lamellar phase, increased of MTX of the physical point of view, also carry through the structural analysis of the formulations through by polarized light microscopy (PLM), small-angle X-ray scattering (SAXS) and rheological properties. Perform stability studies of the chosen formulations, validate the analytical method of quantification of MTX for High Performance Liquid Chromatography (HPLC) and carry through release assay, cutaneous permeation and skin retention in vitro for the chosen formulations. The formulations prepared by the mixture of polyether functional siloxane as surfactant, with silicone polyether copolymer as oily phase and phosphate buffer 0,01M pH 7,4 as aqueous phase demonstrating lamellar liquid-crystalline phases, confirmed by assays of PLM and SAXS. The stability studies showed that formulations A, B and C remained stable throughout the period of the study. The study of the rheological behavior of the formulations presented as not Newtonian pseudoplastic fluid and thixotropic ...

The polymers are integral part of vast number of products used in day to day life due to their anomalous viscoelastic behaviour. The remarkable flow behaviour exhibited by the polymeric fluids including rod climbing, extrudate swell, tube-less siphon, viscoelastic jet, elastic recoil and sharkskin instability is attributed to the complex microstructures in the polymeric liquids that arise due to the interactions of long chain polymer molecules with each other and with the surrounding fluid particles. The significance of polymer in transportation, packaging, pharmaceutical, chemical, biomedical, textiles, food and polymer processing industries highlights the requirement to comprehend the complex rheology of polymeric fluids. First, we investigate the flow features exhibited by different shear thinning vis-coelastic fluids in rectangular cavities over a wide range of depth to width ratio. We have developed a viscoelastic flow solver in order to perform numerical simulations of highly elastic flow of viscoelastic fluids. In particular, we discuss the simulations of flows of constant viscosity Boger and shear thinning viscoelastic fluids in the complex flow problems using different constitutive equations. The effects of elasticity and inertia on the flow behaviour of two shear thinning vis-coelastic fluids modeled using Giesekus and linear PTT constitutive equations in rectangular cavities is studied. The size of the primary eddies and critical aspect ratio over which the corner eddies merge to yield a second primary eddy in deep cavities is discussed. We demonstrate that the flow in the shallow and deep cavities can be characterized using Weissenberg number, defined based on the shear rate, and Deborah number, specified based on the convective time scale, respectively. The study of flow in driven cavities is important in understanding of the mixing process during synthesis of blends and composites. Next, we study two phase polymeric flow in confined geometries. Nowadays, polymer processing industries prefer to develop newer polymer with the desired material properties mechanically by mixing and blending of different polymer components instead of chemically synthesizing fresh polymer. The microstructure of blends and emulsions following drop deformation, breakup and coalescence during mixing determines its macroscopic interfacial rheology. We developed a two phase viscoelastic flow solver using volume conserving sharp interface volume-of-fluid (VOF) method for studying the dynamics of single droplet subjected to the complex flow fields. We investigated the effects of drop and matrix viscoelasticity on the motion and deformation of a droplet suspended in a fully developed channel flow. The flow behaviour exhibited by Newtonian-Newtonian, viscoelastic-Newtonian, Newtonian-viscoelastic and viscoelastic-viscoelastic drop-matrix systems is presented. The difference in the drop dynamics due to presence of constant viscosity Boger fluid and shear thinning viscoelastic fluid is represented using FENE-CR and linear PTT constitutive equations, respectively. The presence of shear thinning viscoelastic fluid either in the drop or the matrix phase suppresses the drop deformation due to stronger influence of matrix viscoelasticity as compared to the drop elasticity. The shear thinning viscoelastic drop-matrix system further restricts the drop deformation and it displays non-monotonic de-formation. The constant viscosity Boger fluid droplet curbs the drop deformation and exhibits flow dynamics identical to the shear thinning viscoelastic droplet, thus indicating that the nature of the drop viscoelasticity has little influence on the flow behaviour. The matrix viscoelasticity due to Boger fluid increases drop deformation and displays non-monotonic deformation. The drop deformation is further enhanced in the case of Boger fluid in viscoelastic drop-matrix system. Interestingly, the pressure drop due to the presence of viscoelastic drop in a Newtonian matrix is lower than the single phase flow of Newtonian fluid. We also discuss the effects of inertia, surface tension, drop to matrix viscosity ratio and the drop size on these drop-matrix systems. Finally, we investigate the emulsion rheology by studying the motion of a droplet in the square lid driven cavity flow. The viscoelastic effects due to constant viscosity Boger fluid and shear thinning viscoelastic fluid are illustrated using FENECR and Giesekus rheological relations, respectively. The presence of viscoelasticity either in drop or matrix phase boosts the drop deformation with the drop viscoelasticity displaying intense deformation. The drop dynamics due to the droplet viscoelasticity is observed to be independent of the nature of vis-coelastic fluid. The shear thinning viscoelastic matrix has a stronger influence on the drop deformation and orientation compared to the Boger fluid matrix. The different blood components, cells and many materials of industrial importance are viscoelastic in nature. Thus, the present study has significant applications in medical diagnostics, drug delivery, manufacturing and processing industries, study of biological flows, pharmaceutical research and development of lab-on-chip devices.

In the first part of this thesis we are concerned with the constitutive the- ory for incompressible fluids characterized by a continuous monotone rela- tion between the velocity gradient and the Cauchy stress. We, in particular, investigate a class of activated fluids that behave as the Euler fluid prior activation, and as the Navier-Stokes or power-law fluid once the activation takes place. We develop a large-data existence analysis for both steady and unsteady three-dimensional flows of such fluids subject either to the no-slip boundary condition or to a range of slip-type boundary conditions, including free-slip, Navier's slip, and stick-slip. In the second part we show that the W−1,q norm is localizable provided that the functional in question vanishes on locally supported functions which constitute a partition of unity. This represents a key tool for establishing local a posteriori efficiency for partial differential equations in divergence form with residuals in W−1,q . In the third part we provide a novel analysis for the pressure convection- diffusion (PCD) preconditioner. We first develop a theory for the precon- ditioner considered as an operator in infinite-dimensional spaces. We then provide a methodology for constructing discrete PCD operators for a broad class of pressure discretizations. The...

<p><b>Part I: Micromechanics of dense suspensions</b></p><p>Particulate suspensions are ubiquitous in the industry & nature. Fresh concrete, uncured solid rocket fuel, & biomass slurries are typical industrial applications, while milk & blood are examples of naturally occurring suspensions. These suspensions exhibit many non-Newtonian properties like rate-dependent rheology & normal stresses. Other than volume fraction, particle material, inter-particle interactions determine the rheological behavior of suspension. The average inter-particle gaps between the neighboring particles decrease significantly as the suspension volume fraction approaches the maximum packing fraction in dense suspensions. So, in this regime, the short-ranged non-contact interactions are important. In addition, the particles come into contact due to asperities on their surfaces. The surface asperities are present even in the case of so-called smooth particles, as particles in real suspensions are not perfectly smooth. Hence, contact forces become one of the essential factors to determine the rheology of suspensions.</p><p> </p><p>Part I of this thesis investigates the effects of microscopic inter-particle interactions on the rheological properties of dense suspensions of non-Brownian particles by employing discrete particle simulations. We show that increasing the roughness size results in a rise in the viscosity & normal stress difference in the suspensions. Furthermore, we observe that the jamming volume fraction decreases with the particle roughness. Consequently, for suspensions close to jamming, increasing the asperity size reduces the critical shear rate for shear thickening (ST) transition, resulting in an early onset of discontinuous ST (DST, a sudden jump in the suspension viscosity) in terms of volume fraction, & enhances the strength of the ST effect. These findings are in excellent agreement with the recent experimental measurements & provide a deeper understanding of the experimental findings. Finally, we propose a constitutive model to quantify the effect of the roughness size on the rheology of dense ST suspensions to span the entire phase-plane. Thus, the constitutive model and the experimentally validated numerical framework proposed can guide experiments, where the particle surface roughness is tuned for manipulating the dense suspension rheology according to different applications. </p><p> </p><p>A typical dense non-Brownian particulate suspension exhibits shear thinning (decreasing viscosity) at a low shear rate followed by a Newtonian plateau (constant viscosity) at an intermediate shear rate values which transition to ST (increasing viscosity) beyond a critical shear rate value and finally, undergoes a second shear-thinning transition at an extremely high shear rate values. This part unifies & quantitatively reproduces all the disparate rate-dependent regimes & the corresponding transitions for a dense non-Brownian suspension with increasing shear rate. The inclusion of traditional hydrodynamic interactions, attractive/repulsive DLVO (Derjaguin and Landau, Verwey and Overbeek), contact interactions, & constant friction reproduce the initial thinning as well as the ST transition. However, to quantitatively capture the intermediate Newtonian plateau and the second thinning, an additional interaction of non-DLVO origin & a decreasing coefficient of friction, respectively, are essential; thus, providing the first explanation for the presence these regimes. Expressions utilized for various interactions and friction are determined from experimental measurements, resulting in an excellent quantitative agreement with previous experiments. </p><p><br></p><p><b>Part II: Motion in a stratified fluid</b></p><p>Density variations due to temperature or salinity greatly influence the dynamics of objects like particles, drops, and microorganisms in oceans. Density stratification hampers the vertical flow & substantially affects the sedimentation of an isolated object, the hydrodynamic interactions between a pair, and the collective behavior of suspensions in various ways depending on the relative magnitude of stratification inertia (advection), and viscous (diffusion) effects. This part investigates these effects and elicits the hydrodynamic mechanisms behind some commonly observed fluid-particle transport phenomena in oceans, like aggregation in horizontal layers. The physical understanding can help us better model these phenomena and, hence, predict their geophysical, engineering, ecological, and environmental implications. </p><p><br></p><p>We investigate the self-propulsion of an inertial swimmer in a linear density stratified fluid using the archetypal squirmer model, which self-propels by generating tangential surface waves. We quantify swimming speeds for pushers (propelled from the rear) and pullers (propelled from the front) by direct numerical solution. We find that increasing stratification reduces the swimming speeds of swimmers relative to their speeds in a homogeneous fluid while reducing their swimming efficiency. The increase in the buoyancy force experienced by these squirmers due to the trapping of lighter fluid in their respective recirculatory regions as they move in the heavier fluid is one of the reasons for this reduction. Stratification also stabilizes the flow around a puller, keeping it axisymmetric even at high inertia, thus leading to otherwise absent stability in a homogeneous fluid. On the contrary, a strong stratification leads to instability in the motion of pushers by making the flow around them unsteady 3D, which is otherwise steady axisymmetric in a homogeneous fluid. Data for the mixing efficiency generated by individual squirmers explain the trends observed in the mixing produced by a swarm of squirmers. </p><p><br></p><p>In addition, the ubiquitous vertical density stratification in aquatic environments significantly alters the swimmer interactions affecting their collective motion &consequently ecological and environmental impact. To this end, we numerically investigate the interactions between a pair of model swimming organisms with finite inertia in a linear density stratified fluid. Depending on the squirmer inertia and stratification, we observe that the squirmer interactions can be categorized as i) pullers getting trapped in circular loops, ii) pullers escaping each other with separating angle decreasing with increasing stratification, iii) pushers sticking to each other after the collision and deflecting away from the collision plane, iv) pushers escaping with an angle of separation increasing with stratification. Stratification also increases the contact time for squirmer pairs. The results presented can help understand the mechanisms behind the accumulation of planktonic organisms in horizontal layers in a stratified environment like oceans and lakes. </p><p><br></p><p>Much work has been done to understand the settling dynamics of spherical particles in a homogeneous and stratified fluid. However, the effects of shape anisotropy on the settling dynamics in a stratified fluid are not entirely understood. To this end, we perform numerical simulations for settling oblate and prolate spheroids in a stratified fluid. We find that both the oblate and prolate spheroids reorient to the edge-wise and partially edge-wise orientations, respectively, as they settle in a stratified fluid completely different from the steady-state broad-side on orientation observed in a homogeneous fluid. We observe that reorientation instabilities emerge when the velocity magnitude of the spheroids falls below a particular threshold. We also report the enhancement of the drag on the particle from stratification. The torque due to buoyancy effects tries to orient the spheroid in an edge-wise orientation, while the hydrodynamic torque tries to orient it to a broad-side orientation. The buoyancy torque dominates below the velocity threshold, resulting in reorientation instability.<br></p>

[pt] Esta dissertação investiga escoamentos multifásicos de deslocamento de fluidos em geometrias anulares envolvidas em operações de cimentação de poços com fluidos espumados. A cimentação desempenha um papel relevante na integridade de poços e algumas aplicações requerem pastas leves com alta resistência à compressão, e o cimento espumado atende a este propósito. Para modelar adequadamente a complexidade do escoamento - que compreende comportamento não-newtoniano e elevada compressibilidade - um modelo tridimensional de dinâmica computacional de fluidos (CFD) foi desenvolvido a partir do código aberto OpenFOAM. As equações de conservação da massa, momento e fases são solucionadas em uma geometria anular, considerando o efeito da pressão na densidade e na reologia dos fluidos, e o método Volume of Fluid (VoF) foi usado para capturar a interface entre fluidos. Os modelos foram validados com soluções exatas para escoamento monofásico axissimétrico com fluidos incompressíveis e compressíveis, e com modelos constitutivos newtonianos e não-newtonianos. Além disso, simulações multifásicas estimaram a eficiência de deslocamento do fluido de perfuração pela pasta de cimento em diferentes condições – constraste de densidade e de viscosidade, ecentricidade e vazões de bombeio – e com diferentes correlações para a reologia dos fluidos espumados. Finalmente, simulações de deslocamento com fluidos com densidade e reologia constante (não-espumados) foram utilizadas para comparação. Os resultados indicam que a eficiência no deslocamento com a técnica de cimentação espumada é superior em condições similares e ilustra que as pastas espumadas são menos suceptíveis a gerarem falhas quanto condições desafiadoras estão presentes. / [en] This master dissertation investigates multiphase displacement flow in annular geometries involved in well cementing operations with foamed cement slurries and spacers. Well cementing plays a relevant role in well integrity and some applications require combining a low-density cement slurry with high compressive strength, and foamed cement suits this purpose. To properly model the displacement complexity involving foamed fluids flow - pressure and temperature dependent densities and non-Newtonian rheology - a 3-dimensional computational fluid dynamics (CFD) model was developed from the open-source OpenFOAM toolbox. The mass, momentum and phase conservation equations are solved in an annular geometry, taking the effect of pressure in the fluid density and rheology, and the volume-of-fluid (VoF) method was used to capture the interface between the fluids. The models were validated using exact solutions for axisymmetric single-phase flow with incompressible and compressible fluids, and Newtonian and non-Newtonian constitutive models. Further, multiphase simulations were performed to estimate the removal efficiency of the drilling fluid by the foamed cement slurry/spacer in different conditions – density and viscosity contrast, eccentricities, and flow rate - and with different correlations for the foamed cement rheological behavior. Finally, the displacement simulations with constant density and rheology displacing fluids (unfoamed) were performed and used to compare the results with the foamed displacing fluids. The results indicate that the displacement efficiency with a foamed cement technique outperforms constant density lightweight cement slurries with similar conditions and are much less sensitive to impairment when challenging conditions are present.