abstract: Cerebral aneurysms are pathological balloonings of blood vessels in the brain, commonly found in the arterial network at the base of the brain. Cerebral aneurysm rupture can lead to a dangerous medical condition, subarachnoid hemorrhage, that is associated with high rates of morbidity and mortality. Effective evaluation and management of cerebral aneurysms is therefore essential to public health. The goal of treating an aneurysm is to isolate the aneurysm from its surrounding circulation, thereby preventing further growth and rupture. Endovascular treatment for cerebral aneurysms has gained popularity over traditional surgical techniques due to its minimally invasive nature and shorter associated recovery time. The hemodynamic modifications that the treatment effects can promote thrombus formation within the aneurysm leading to eventual isolation. However, different treatment devices can effect very different hemodynamic outcomes in aneurysms with different geometries. Currently, cerebral aneurysm risk evaluation and treatment planning in clinical practice is largely based on geometric features of the aneurysm including the dome size, dome-to-neck ratio, and parent vessel geometry. Hemodynamics, on the other hand, although known to be deeply involved in cerebral aneurysm initiation and progression, are considered to a lesser degree. Previous work in the field of biofluid mechanics has demonstrated that geometry is a driving factor behind aneurysmal hemodynamics. The goal of this research is to develop a more combined geometric/hemodynamic basis for informing clinical decisions. Geometric main effects were analyzed to quantify contributions made by geometric factors that describe cerebral aneurysms (i.e., dome size, dome-to-neck ratio, and inflow angle) to clinically relevant hemodynamic responses (i.e., wall shear stress, root mean square velocity magnitude and cross-neck flow). Computational templates of idealized bifurcation and sidewall aneurysms were created to satisfy a two-level full factorial design, and examined using computational fluid dynamics. A subset of the computational bifurcation templates was also translated into physical models for experimental validation using particle image velocimetry. The effects of geometry on treatment were analyzed by virtually treating the aneurysm templates with endovascular devices. The statistical relationships between geometry, treatment, and flow that emerged have the potential to play a valuable role in clinical practice. / Dissertation/Thesis / Doctoral Dissertation Bioengineering 2016

abstract: A moving overlapping mesh methodology that achieves spectral accuracy in space and up to second-order accuracy in time is developed for solution of unsteady incompressible flow equations in three-dimensional domains. The targeted applications are in aerospace and mechanical engineering domains and involve problems in turbomachinery, rotary aircrafts, wind turbines and others. The methodology is built within the dual-session communication framework initially developed for stationary overlapping meshes. The methodology employs semi-implicit spectral element discretization of equations in each subdomain and explicit treatment of subdomain interfaces with spectrally-accurate spatial interpolation and high-order accurate temporal extrapolation, and requires few, if any, iterations, yet maintains the global accuracy and stability of the underlying flow solver. Mesh movement is enabled through the Arbitrary Lagrangian-Eulerian formulation of the governing equations, which allows for prescription of arbitrary velocity values at discrete mesh points. The stationary and moving overlapping mesh methodologies are thoroughly validated using two- and three-dimensional benchmark problems in laminar and turbulent flows. The spatial and temporal global convergence, for both methods, is documented and is in agreement with the nominal order of accuracy of the underlying solver. Stationary overlapping mesh methodology was validated to assess the influence of long integration times and inflow-outflow global boundary conditions on the performance. In a turbulent benchmark of fully-developed turbulent pipe flow, the turbulent statistics are validated against the available data. Moving overlapping mesh simulations are validated on the problems of two-dimensional oscillating cylinder and a three-dimensional rotating sphere. The aerodynamic forces acting on these moving rigid bodies are determined, and all results are compared with published data. Scaling tests, with both methodologies, show near linear strong scaling, even for moderately large processor counts. The moving overlapping mesh methodology is utilized to investigate the effect of an upstream turbulent wake on a three-dimensional oscillating NACA0012 extruded airfoil. A direct numerical simulation (DNS) at Reynolds Number 44,000 is performed for steady inflow incident upon the airfoil oscillating between angle of attack 5.6 and 25 degrees with reduced frequency k=0.16. Results are contrasted with subsequent DNS of the same oscillating airfoil in a turbulent wake generated by a stationary upstream cylinder. / Dissertation/Thesis / Doctoral Dissertation Aerospace Engineering 2016

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Mingjun Wei / In this study, a global Proper Orthogonal Decomposition (POD)-Galerkin based Reduced Order model (ROM) is proposed. It is extended from usual fixed-domain problems to more general fluid-solid systems with moving boundaries/interfaces. The idea of the extension is similar to the immersed boundary method in numerical simulations which uses embedded forcing terms to represent boundary motions and domain changes. This immersed boundary method allows a globally defined fixed domain including both fluid and solid, where POD-Galerkin projection can be directly applied. However, such a modified approach cannot get away with the unsteadiness of boundary terms which appear as time-dependent coefficients in the new Galerkin model. These coefficients need to be pre-computed for prescribed periodic motion, or worse, to be computed at each time step for non-prescribed (e.g. with fluid-structure interaction) or non-periodic situations. Though computational time for each unsteady coefficient is smaller than the coefficients in a typical Galerkin model, because the associated integration is only in the close neighborhood of moving boundaries. The time cost is still much higher than a typical Galerkin model with constant coefficients. This extra expense for moving-boundary treatment eventually undermines the value of using ROMs. An aggressive approach is to decompose the moving boundary/domain to orthogonal modes and derive another low-order model with fixed coefficients for boundary motion. With this domain decomposition, an approach including two coupled low-order models both with fixed coefficients is proposed. Therefore, the new global ROM with decomposed approach is more efficient. Though the model with the domain decomposition is less accurate at the boundary, it is a fair trade-off for the benefit on saving computational cost. The study further shows, however, that the most time-consuming integration in both approaches, which come from the unsteady motion, has almost negligible impact on the overall dynamics. Dropping these time-consuming terms reduces the computation cost by at least one order while having no obvious effect on model accuracy. Based on this global POD-Galerkin based ROM with forcing term, an improved ROM which can handle the parametric variation of body motions in a certain range is also presented. This study shows that these forcing terms not only represent the moving of the boundary, but also decouple the moving parameters from the computation of model coefficients. The decoupling of control parameters provides the convenience to adapt the model for the prediction on states under variation of control parameters. An improved ROM including a shit mode seems promising in model adaptation for typical problems in a fixed domain. However, the benefit from adding a shit mode to model diminishes when the method is applied to moving-boundary problems. Instead, a combined model, which integrates data from a different set of parameters to generate the POD modes, provides a stable and accurate ROM in a certain range of parametric space for moving-boundary problems. By introducing more data from a different set of parameters, the error of the new model can be further reduced. This shows that the combined model can be trained by introducing more and more information. With the idea of the combined model, the improved global ROM with forcing terms shows impressive capability to predict problems with different unknown moving parameters, and can be used in future parametric control and optimization problems.

Le secteur du bâtiment est le plus gros consommateur d'énergie au niveau mondial. Pour en réduire l'impact environnemental, l'utilisation de solutions passives pour améliorer le confort est nécessaire. Malgré ce constat, la climatisation est de plus en plus utilisée dans les DROM-COM. Le développement de la ventilation naturelle est incontournable pour inverser cette tendance. Les méthodes multizones, modèles historiques de la simulation thermique du bâtiment, peinent à décrire ce type d'écoulement. Les modèles de mécanique des fluides numériques (MFN) sont prometteurs pour lever ce frein à l'utilisation de la ventilation naturelle.Ce manuscrit traite de l'adaptation d'un code de résolution directe des équations de Navier-Stokes à la description d'écoulements d'air dans le bâtiment. À cette fin, le développement, l'implémentation et la comparaison de différents types de conditions aux limites en pression sur les ouvertures ont été nécessaires. Ce travail nous a permis d'étudier le comportement d'une chambre soumise à de la convection naturelle et mixte. Pour intégrer ces développements à une simulation de bâtiment, nous avons développé un objet qui appelle le code de MFN sur un serveur de calcul distant depuis un environnement multizone de façon transparente. Le refroidissement partiel des murs d'une cavité soumise à de la convection naturelle a pu être simulé à l'aide de cette méthode. / The building sector is the global largest energy consumer. To reduce environmental impact of buildings, passive tools must be developed. Still, air conditioning is increasingly used in the DROM-COM. The development of natural ventilation is essential to reverse this trend. Multizone models are not really suited for describing natural ventilation flows. Computational fluid dynamics (CFD) seem to be a promising way too model those flows.This thesis deals with the adaptation of a direct resolution of the Navier-Stokes equations code to describe airflows in buildings. The development, implementation and comparison of different types of pressure boundary conditions on the openings were required. The behavior of a room subjected to natural and mixed convection has been studied thanks to this work. To integrate this model into a building simulation, a “black box” object that transparently calls the CFD code on a remote server from a multizone environment has been developed. Partial cooling of the walls of a cavity subjected to natural convection has been simulated using this method.

Buscando compreender o comportamento hidrodinâmico de um reator anaeróbio de fluxo ascendente (UASB), o presente trabalho teve por objetivo desenvolver um modelo numérico utilizando ferramentas de Fluidodinâmica Computacional (CFD) para a simulação do comportamento do escoamento trifásico (líquido, gás e sólido) em um reator UASB utilizado na produção de biogás a partir da vinhaça, e validar este modelo utilizando técnicas de Velocimetria de Partículas por Imagem (PIV). Para tanto, inicialmente foi projetado o reator UASB e em seguida foram desenvolvidas a geometria e a malha. As simulações foram executadas no software Fluent, utilizando uma malha com 528.000 volumes de controle. Foram inicialmente realizadas simulações do escoamento monofásico do líquido e em seguida simulações bifásicas gás/líquido e sólido/líquido foram realizadas adotando-se uma abordagem Euleriana-Euleriana, isotérmica, transiente e tridimensional. Por fim, os modelos bifásicos já validados foram associados em um modelo trifásicos. Técnicas de PIV foram utilizadas na validação dos modelos bifásicos e do trifásico. Na etapa de validação dos modelos numéricos, foi verificada uma diferença máxima entre resultados experimentais e computacionais menor de 4% para todos os casos. Foi verificado que a força de arraste é a que exerce a maior influência no perfil do escoamento gás/líquido. Com relação ao escoamento sólido/líquido, o modelo de Gidaspow foi escolhido para o cálculo do coeficiente de arraste, após comparação com resultados experimentais. Nas simulações trifásicas, verificou-se o gás foi o principal responsável pela qualidade da mistura dentro do reator, reduzindo de 44% o percentual de zonas mortas no reator no caso sólido/líquido para 0,02% no caso trifásico e aumentando em cerca de oito vezes a magnitude da velocidade das fases sólida e líquida. O sistema de distribuição de gás exerceu forte influência no perfil do escoamento, tendo induzido recirculação interna no reator. A compreensão do escoamento permitirá otimizações no processo e no reator de forma a buscar o aumento da eficiência de tratamento bem como da geração de biogás. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2017-06-26T17:27:11Z No. of bitstreams: 1 Dissertacao Camila DBastiani.pdf: 3648057 bytes, checksum: 6fcb0f38708ea3a24444be3ab47dd30b (MD5) / Made available in DSpace on 2017-06-26T17:27:11Z (GMT). No. of bitstreams: 1 Dissertacao Camila DBastiani.pdf: 3648057 bytes, checksum: 6fcb0f38708ea3a24444be3ab47dd30b (MD5) Previous issue date: 2017-06-26 / PETROBRAS, Brasil. / Aiming to understand the hydrodynamics of a Upflow Anaerobic Sludge Blanket (UASB) reactor, this work aimed to apply multiphase modeling through computational fluid dynamics (CFD) to assess the behavior of the three phase flow (liquid, gas and solid) in a UASB reactor, which is used in the biogas production using vinasse as substrate and the to validate the results using Particle Image Velocimetry (PIV) techniques. Therefore, the UASB reactor was designed and then the geometry and mesh were developed. The simulations were performed using the software Fluent and a mesh with 528.000 control volumes. Initially, monophasic simulations of the liquid phase were carried out. Next, two phase simulations were performed considering the pairs of phases gas/liquid and solid/liquid. An Eulerian-Eulerian approach was adopted, together with isothermal, transient and tridimensional conditions. After validated, the two-phase models (solid/liquid and gas/liquid) were combined into a three-phase model. PIV was used for the experimental validation of the two and three-phase models. The numerical model validation showed maximum differences lower than 4% between experimental and computational results for the three cases (gas/liquid, solid/liquid and liquid/gas/solid). Numerical results showed that the drag force plays the major role on the gas/liquid flow profile. Regarding the solid/liquid flow, Gidaspow model was chosen to estimate the drag force coefficient after comparisons between numerical and experimental results. Three-phase simulations showed that the gas was the main responsible for the mixing quality within the reactor. Dead zones were reduced from 44% in the solid/liquid simulations to 0,02% in the three-phase simulations and the liquid and solid velocity magnitude increased in about eight times. The configuration of the gas distribution system played a major role on the overall flow profile and drove liquid recirculation along the axial position. Understanding the multiphase flow within this reactor will allow optimizations on the process as well as on the reactor, in order to seek an increase on the efficiency both in the treatment and biogas in the production.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016. / This work presents the computational uid dynamics (CFD) analysis of a light road vehicle. Simulations are conducted using the lattice Boltzmann method (LBM) with the wall adapting local eddy (WALE) turbulence model. Simulations include and compare the use of a rolling road, rotating wheels, adaptive re nement as well as showing comparison with a Reynolds-averaged Navier-Stokes (RANS) solver and the Spalart- Allmaras (SA) turbulence model. The lift coe cient of the vehicle for the most part was seen to show a much greater di erence and inconsistencies when compared to drag from the comparisons of solvers, turbulence models, re nement and the e ect of rolling road. Determining the drag of a road vehicle can be easily achieved and veri ed using multiple solvers and methods, however, the lift coe cient and its validation require a greater understanding of the vehicle ow eld as well as the solvers, turbulence models and re nement levels capable of correctly simulating the turbulent regions around a vehicle. Using the presented method, it was found that the optimisation of vehicle aerodynamics can easily be done alongside the design evolution from initial low-drag shapes to the nal detail design, ensuring aerodynamic characteristics are controlled with aesthetic change.

Nos últimos anos, a utilização da energia eólica vem apresentando uma tendência de aumento. Um dos principais aspectos para determinar a viabilidade técnica e econômica de uma instalação eólica é a avaliação precisa da distribuição das velocidades de vento na área de aproveitamento. A instalação de turbinas eólicas em áreas com terrenos complexos tem determinado a necessidade de aprimorar a metodologia de previsão do campo de velocidades do vento visando à melhor determinação da distribuição dos equipamentos e aproveitamento do potencial existente. Neste contexto, esta dissertação apresenta um estudo sobre a aplicação da Dinâmica dos Fluidos Computacional - CFD para avaliação do potencial eólico e o comportamento do vento sobre um modelo de uma superfície de topografia complexa. Resultados numéricos com diferentes alternativas de modelagem do problema são comparados com dados de um experimento em túnel de vento, visando determinar a metodologia adequada para avaliação do problema proposto. As simulações numéricas do escoamento de ar sobre o terreno são realizadas com o uso do programa ANSYS-Fluent 13.0, que utiliza o método de volumes finitos para a solução das equações de Navier-Stokes com médias de Reynolds (RANS). O estudo é dividido em três casos. No primeiro caso, a rugosidade superficial é negligenciada e o problema de fechamento é contornado com a utilização do modelo de turbulência k ω SST. No segundo caso, a rugosidade superficial é estipulada de acordo com modelo utilizado no ensaio experimental e o problema de fechamento é contornado com a utilização do modelo de turbulência k - ε. No terceiro caso, a rugosidade superficial também é estipulada de acordo com modelo utilizado no ensaio experimental e o problema de fechamento é contornado com a utilização do modelo de turbulência k ω SST. Os resultados das simulações são apresentados de forma que se possa observar o perfil de velocidades adimensional sobre a superfície da geometria para cada caso, para que seja possível verificar o campo de velocidades sobre a superfície em estudo. O resultado das simulações são comparados com dados experimentais obtidos em túnel de vento: verifica-se um comportamento similar nos perfis de velocidade alcançados. Através da análise do campo de velocidades sobre a superfície em estudo, pode-se obter a localização que apresenta o melhor potencial eólico de uma região. Este processo é conhecido como Micrositing. / In recent years the use of wind energy has shown an increasing. A key aspect to determine the technical and economic viability for the wind power plant is the accurate assessment of the distribution of wind speeds in the area of utilization. The installation of wind turbines in areas with complex terrain has determined the necessity of improve the methodology for the prediction of wind velocity field in order to better determine the distribution of equipment and utilization of existing potential. In this context this work presents a study on the application of computational fluid dynamics to evaluate the wind potential and the behavior of the wind on a model of a complex surface topography. Numerical results with different alternatives for modeling the problem are compared with data from an experiment in wind tunnel to determine the appropriate methodology for evaluation of the problem. The numerical simulations of the air flow over the terrain are performed using the ANSYS Fluent 13.0 which uses the finite volumes method for solving the Reynolds Averaged Navier Stokes (RANS) equation. The study is divided in three cases. In the first one, the surface roughness is neglected and the closure problem is solved by k ω SST turbulence model. In the second case, the surface roughness is stipulated according to the model used in the experimental test and the closure problem is solved by k ε turbulence model. In the third case, the surface roughness is stipulated according to the model used in the experimental test and the closure problem is solved by k ω SST turbulence model. The simulation results are presented so that one can observe the dimensionless velocity profile on the surface in each case in order to check the velocity field on the surface under investigation. These results are compared with experimental data obtained in wind tunnel which shows consistency with them. By analyzing the velocity field on the surface, it can be verified that the exact location where there is the best wind potential of a region. This process is called Micrositing.

The aims of this thesis are to develop and validate a robust and efficient algorithm for the numerical solution of the equations of General Relativistic Hydrodynamics, to implement the algorithm in a computationally efficient manner, and to apply the resulting computer code to the problem of perturbed Bondi-Hoyle-Lyttleton accretion onto a Kerr black hole. The algorithm will also be designed to evolve the space-time metric, and standardised tests will be applied to this aspect of the algorithm. The algorithm will use up-to-date High-Resolution Shock-Capturing numerical schemes that have been developed for the stable and accurate solution of complex systems of equations. It will be built around the Adaptive Mesh Refinement and overlapping, curvilinear grid methodologies in order to extend these schemes to the efficient solution of two and three-dimensional problems. When implementing the algorithm, we will use previously written code libraries, where appropriate, to avoid excessive software development. We will validate the algorithm against standard test-cases for Special and General Relativistic Hydrodynamics, and for Einstein's equations for the evolution of the space-time metric. The methodologies we use will be tested to ensure that they lead to the stable and accurate numerical solution of these problems. Finally, the implemented algorithm will be applied to the problem of Bondi-Hoyle-Lyttleton flow onto a Kerr black hole in three dimensions. It will be validated against existing exact and numerical solutions of the problem, and then be used to perform an extensive parametric study of the problem, varying the spin of the black hole and the incident wind direction, and allowing for the perturbation of the fluid density upstream of the black hole. We will then analyze the results of the study, and present the complete set of results on a DVD accompanying this thesis.

A presente dissertação investiga o comportamento do escoamento em um túnel de cavitação, através de simulações fluido-dinâmicas computacionais, excluindo a bomba de circulação. Para tanto um extenso estudo buscou selecionar a abordagem numérica e configurações de simulação mais adequadas, de uma forma a reproduzir as características hidrodinâmica inerentes à operação do túnel. Portanto, as informações referentes à perda de carga, uniformidade no perfil de velocidade, tendência de cavitação, descolamento e altura da camada limite foram apreciadas. Esse estudo foi direcionado por dados provenientes de métodos empíricos da literatura, resultados experimentais do próprio túnel pesquisado e de outros túneis. Em geral, os resultados foram satisfatórios, pois a perda de carga estimada foi semelhante ao obtido experimentalmente. Além de serem identificados os trechos com efeito desfavorável na uniformidade do escoamento, foram determinadas a distribuição de pressão nas aletas e o perfil de velocidade incidente na bomba. / This study deals with a cavitation tunnel flow (except the pump region) through computational fluid dynamic simulations. Therefore, previously one made a literature survey to aid the selection of the most appropriate techniques and simulation settings to simulate the hydrodynamic characteristics of the tunnel. The pressure drop, uniformity of the velocity profile, existence of cavitation, detachment and height of the boundary layer were evaluated. This study used empirical methods and also experimental results. The results were satisfactory, as long as the estimated pressure drop was close to the one obtained experimentally. In addition, it was forecasted low flow uniformity in some parts of the tunnel, the pressure distribution on the fins and the incident velocity profile at the pump.

Nos últimos anos, a utilização da energia eólica vem apresentando uma tendência de aumento. Um dos principais aspectos para determinar a viabilidade técnica e econômica de uma instalação eólica é a avaliação precisa da distribuição das velocidades de vento na área de aproveitamento. A instalação de turbinas eólicas em áreas com terrenos complexos tem determinado a necessidade de aprimorar a metodologia de previsão do campo de velocidades do vento visando à melhor determinação da distribuição dos equipamentos e aproveitamento do potencial existente. Neste contexto, esta dissertação apresenta um estudo sobre a aplicação da Dinâmica dos Fluidos Computacional - CFD para avaliação do potencial eólico e o comportamento do vento sobre um modelo de uma superfície de topografia complexa. Resultados numéricos com diferentes alternativas de modelagem do problema são comparados com dados de um experimento em túnel de vento, visando determinar a metodologia adequada para avaliação do problema proposto. As simulações numéricas do escoamento de ar sobre o terreno são realizadas com o uso do programa ANSYS-Fluent 13.0, que utiliza o método de volumes finitos para a solução das equações de Navier-Stokes com médias de Reynolds (RANS). O estudo é dividido em três casos. No primeiro caso, a rugosidade superficial é negligenciada e o problema de fechamento é contornado com a utilização do modelo de turbulência k ω SST. No segundo caso, a rugosidade superficial é estipulada de acordo com modelo utilizado no ensaio experimental e o problema de fechamento é contornado com a utilização do modelo de turbulência k - ε. No terceiro caso, a rugosidade superficial também é estipulada de acordo com modelo utilizado no ensaio experimental e o problema de fechamento é contornado com a utilização do modelo de turbulência k ω SST. Os resultados das simulações são apresentados de forma que se possa observar o perfil de velocidades adimensional sobre a superfície da geometria para cada caso, para que seja possível verificar o campo de velocidades sobre a superfície em estudo. O resultado das simulações são comparados com dados experimentais obtidos em túnel de vento: verifica-se um comportamento similar nos perfis de velocidade alcançados. Através da análise do campo de velocidades sobre a superfície em estudo, pode-se obter a localização que apresenta o melhor potencial eólico de uma região. Este processo é conhecido como Micrositing. / In recent years the use of wind energy has shown an increasing. A key aspect to determine the technical and economic viability for the wind power plant is the accurate assessment of the distribution of wind speeds in the area of utilization. The installation of wind turbines in areas with complex terrain has determined the necessity of improve the methodology for the prediction of wind velocity field in order to better determine the distribution of equipment and utilization of existing potential. In this context this work presents a study on the application of computational fluid dynamics to evaluate the wind potential and the behavior of the wind on a model of a complex surface topography. Numerical results with different alternatives for modeling the problem are compared with data from an experiment in wind tunnel to determine the appropriate methodology for evaluation of the problem. The numerical simulations of the air flow over the terrain are performed using the ANSYS Fluent 13.0 which uses the finite volumes method for solving the Reynolds Averaged Navier Stokes (RANS) equation. The study is divided in three cases. In the first one, the surface roughness is neglected and the closure problem is solved by k ω SST turbulence model. In the second case, the surface roughness is stipulated according to the model used in the experimental test and the closure problem is solved by k ε turbulence model. In the third case, the surface roughness is stipulated according to the model used in the experimental test and the closure problem is solved by k ω SST turbulence model. The simulation results are presented so that one can observe the dimensionless velocity profile on the surface in each case in order to check the velocity field on the surface under investigation. These results are compared with experimental data obtained in wind tunnel which shows consistency with them. By analyzing the velocity field on the surface, it can be verified that the exact location where there is the best wind potential of a region. This process is called Micrositing.