Film flow of a suspension has been investigated both experimentally and theoretically. Gravity-driven free-surface inclined plane flow of a suspension of neutrally buoyant particles has been investigated using a stereoscopic particle imaging velocimetry technique. Particles have been shown to migrate away from the solid surface, and the film thickness has been shown to decrease as the fluid moves down the inclined plane. The free surface has been characterized using a light reflection technique, which shows that surface topography is affected by the inclination angle, and the particle concentration. This flow has been modeled based on a suspension normal stress approach. A boundary condition at the free surface has been examined, and model predictions have been compared with experimental results. The model predicts that the film thickness, relative to its initial value, will decrease with the bulk particle concentration. The thin film flow over the inner cylinder in partially filled Couette flow of a suspension has been experimentally investigated as well as modeled. Concentration bands have been shown to form under a variety of different fill fractions, bulk particle concentrations, inclination angles, ratio of inner to outer cylinder, and rotation rates of the inner cylinder. The banding phenomena ranges from a regime where bands are small, mobile and relatively similar in concentration to the bulk, to a regime where the concentration bands are larger, stationary, and where the space between them is completely devoid of particles. The role of the film thickness in the band formation process has been investigated, and has led to a model for the band formation process based on a difference in the rate that fluid can drain from height fluctuations relative to the particles.

Extreme hydrological events associated with global warming are likely to produce an increasing number of flooding scenarios resulting in significant bridge inundation and associated damages. During large floods, the presence of a bridge in an open channel triggers a highly turbulent flow field including 3D complex coherent structures around bridge structures. These turbulence structures are highly energetic and possess high sediment entrainment capacity which increases scouring around the bridge foundation and consequently lead to structural stability problems or even failure of the structure. Hence, understanding the complex turbulent flow field for these extreme flow conditions is crucial to estimate the failure risks for existing bridges and better design of future bridges. This research employs the method Large Eddy Simulation (LES) to predict accurately the 3D turbulent flow around bridge structures. The LES code is refined with a novel free surface algorithm based on the Level Set Method (LSM) to determine the complex water surface profiles. The code is used to analyze the hydrodynamics of compound channel flow with deep and shallow overbanks, free flow around a bridge abutment, pressure flow with a partially submerged bridge deck and bridge overtopping flow. All simulations are validated with data from complementary physical model tests under analogous geometrical and flow conditions. Primary velocity, bed shear stress, turbulence characteristics and 3D coherent flow structures are examined thoroughly for each of the flow cases to explain the hydrodynamics of these complex turbulent flows.

A numerical solution algorithm based on finite volume method is developed for unsteady, two-dimensional, depth-averaged shallow water flow equations. The model is verified using test cases from the literature and free surface data obtained from measurements in a laboratory flume. Experiments are carried out in a horizontal, rectangular channel with vertical solid boxes attached on the sidewalls to obtain freesurface data set in flows where three-dimensionality is significant. Experimental data contain both subcritical and supercritical states. The shallow water equations are solved on a structured, rectangular grid system. Godunov type solution procedure evaluates the interface fluxes using an upwind method with an exact Riemann solver. The numerical solution reproduces analytical solutions for the test cases successfully. Comparison of the numerical results with the experimental two-dimensional free surface data is used to illustrate the limitations of the shallow water equations and improvements necessary for better simulation of such cases.

A soleira lateral desempenha um papel importante nos reservatórios de detenção/ retenção (off-line), atuando na captação das vazões afluentes e evitando possíveis enchentes, problema em destaque nos períodos chuvosos das principais capitais brasileiras. Um melhor entendimento do seu comportamento hidráulico possibilitará o desenvolvimento de estruturas laterais mais eficientes. O presente trabalho tem como objetivo criar um modelo da soleira lateral através da tecnologia CFD (Dinâmica dos Fluidos Computacional) e validá-lo através de experimentos em modelo reduzido do Laboratório de Hidráulica da Escola Politécnica da USP. A partir disso, explorar as características hidráulicas do modelo de CFD, como o comportamento dos níveis dágua e a distribuição de velocidades. No estudo da validação estudaram-se três tipos de refinamento de malhas e três modelos de turbulência (k-, k- (RNG) e SST k-). O modelo computacional validado é composto pela malha 3, com um refinamento cerca de 342000 elementos (hexaédricos predominante), e o modelo de turbulência k- (RNG), que apresentaram a maior precisão dos resultados. A análise da distribuição de velocidades possibilitou visualizar uma região de mínima velocidade abaixo da soleira lateral, e também quantificar uma região de baixas velocidades no início da soleira, onde é pequena a eficiência das vazões escoadas. Através do comportamento da superfície dágua foi possível visualizar a região de influência do dispositivo lateral no canal principal. A comparação do coeficiente de descarga do modelo de CFD com trabalhos de outros pesquisadores, um nacional e outro internacional, mostrou a representatividade do modelo criado para condições diferentes. A ferramenta CFD é promissora para o estudo de estruturas hidráulicas, contribuindo para o seu desenvolvimento e aperfeiçoamento. / The side weir plays an important role in the detention / retention tanks (off-line), operating in the uptake of water inflow and preventing possible flooding, which is a highlighted problem on rainy periods of the main Brazilian capitals. A better understanding of the hydraulic behavior allows the development of more efficient lateral structures. This work aims at creating a model of the side weir through CFD technology (Computational Fluid Dynamics) and validating it through experiments on a reduced model of the Laboratório de Hidráulica da Escola Politécnica da USP. Thereafter, explore the hydraulic characteristics of the CFD model, like the behavior of water levels and the velocity distribution. In the validation study, three types of mesh refinement and three turbulence models were studied (k-, k- (RNG) and SST k-). The computational model is validated by the composite mesh 3 with a refinement about 342,000 elements (hexahedral predominant), and the turbulence model k- (RNG), which had the highest precision of results. Analysis of the velocities distribution allowed us to visualize a region of minimum velocity below the side weir, and also to quantify a region of low velocities at the beginning of the weir, where the efficiency of overflows is small. Through water surface behavior it was possible to visualize the influence region of the side device in the main channel. A comparison of discharge coefficient of the CFD model between other works (one national and the other one international) showed the representativeness of the model created for different conditions. The CFD is a promising tool for the study of hydraulic structures, contributing to its development and improvement.

Ice sheets and glaciers constitute an enormous water storage, currently corresponding to a potential sea level rise of almost 70 meters if all ice was to melt completely. The ice sheets are dynamic components of the global climate system and numerical modeling is a useful tool that can help us understand and predict how the ice sheets develop. The most accurate model available for ice sheets is given by the Stokes equations, but to solve them for a real ice sheet on a relevant time scale would be way too computationally costly. Instead approximations of the Stokes equations are used such as the Shallow Ice Approximation (SIA). The SIA is valid for areas where the aspect ratio, the ice thickness divided by the horizontal extent of the ice, is small. In this project equations for temperature and surface evolution were implemented in a Matlab version of SIA. The model already had algorithms implemented for computation of stresses, velocities and pressures for an ice sheet with fixed geometry and temperature. Implementation of temperature and free surface equations also made the problem time-dependent. The result was evaluated by solving a simple test problem and comparing the solution to a full Stokes solution obtained with the code ElmerIce. The SIA solution was closer to the Stokes solution when the aspect ratio ε and slope α were decreased simultaneously such that ε=arctanα, but a similar improvement was also obtained when only the slope was decreased. The differences between the two solutions were satisfyingly small for both temperature, surface location and velocities for an aspect ratio of ε= 7.8 10−4 and ε=arctanα.

This thesis addresses aspects of the transport of bubbles and capsules (a thin elastic membrane enclosing a viscous fluid) by means of a viscous flow in complex vessel geometries. It focusses on two related themes: (i) the trapping of air bubbles in a sudden streamwise tube expansion and (ii) the extreme deformation of bubbles and capsules in a localised tube constriction. Air bubbles of different volumes were trapped in a tube with a square cross-section, which contains a sudden streamwise expansion in tube width. The liquid filling the tube was driven by constant volume-flux flow, and experiments were performed in both millimetric and micrometric tubes to identify the range of flow rates for which bubbles could get trapped. The gradients in surface energy generated by the broadening of the bubble into the expansion depend strongly on bubble volume and the expansion length. It is shown that in order for a trapped bubble to release from the expansion, the work of the pressure forces due to flow past the bubble must exceed the change in surface energy required to squeeze into the narrower channel. This criterion for trapping was verified by direct pressure measurements and a capillary static model, which uses three-dimensional Surface Evolver calculations. The extreme deformation of bubbles and capsules was investigated using a localised constriction of the tube width. Both bubbles and capsules were shown to adopt highly contorted configurations and exhibit broadly similar features over a wide range of flow rates, suggesting that the deformation was primarily imposed by the geometry through viscous shear forces. However, bubbles and capsules also display distinguishing features. Bubbles can breakup and exhibit thinning of the rear of the bubble at a critical flow rate, which is associated with a divergence of the rear tip speed and curvature. In contrast, the capsule membrane can wrinkle and fold, and the membrane thickness imposes the value of the maximum curvature locally available to the capsule.

Secondary currents are one of the important features that characterize flow in river bends and confluences. Fluid particles follow a helical path instead of moving nearly parallel to the axis of the channel. The local imbalance between the vertically varying centrifugal force and the cross-stream pressure gradient results in generating the secondary flow and raising a typical motion of the helical flow. A number of studies, including experimental or mathematical, have been conducted to examine flow characteristics in curved open channels, river meanders, or confluences. In this research, the influence of secondary currents is studied on the elevation of water surface and the hydraulic structures in channel bends and confluences by employing a 3D OpenFOAM numerical model. The research implements the 3D OpenFOAM numerical model to simulate the horizontal distribution of the flow in curved rivers. In addition, the progress in unraveling and understanding the bend dynamics is considered. The finite volume method in (OpenFOAM) software is used to simulate and examine the behavior of secondary current in channel bends and confluences. Thereafter, a comparison between the experimental data and a numerical model is conducted. Two sets of experimental data are used; the data provided by Rozovskii (1961) for sharply curved channel, and the dataset provided by Shumate (1998) for confluent channel. Two solvers in (OpenFOAM) software were selected to solve the problem regarding the experiment; InterFoam and PisoFoam. The InterFoam is a transient solver for incompressible flow that is used with open channel flow and Free Surface Model. The PisoFoam is a transient solver for incompressible flow that is used with closed channel flow and Rigid-Lid Model. Various turbulence models (i.e. Standard k-ε, Realizable k-ε, LRR, and LES) are applied in the numerical model to assess the accuracy of turbulence models in predicting the behaviour of the flow in channel bends and confluences. The accuracies of various turbulence models are examined and discussed.

Laser metal deposition is one of the most versatile methods in the expanding field of additive manufacturing. Its outstanding advantage is its capability to process a variety of metallic materials for the freeform fabrication of objects having sound mechanical properties. The process is used in applications of rapid manufacturing, components repair and surface coating. During recent years, modelling has been increasingly used to study and improve the laser metal deposition process. However, most models have focused on analysing individual stages of the deposition process and thus have not thoroughly dealt with the occurrence of mutually-influencing phenomena. This work presents a new numerical model that, starting from the simulation of powder particles in the deposition head, integrates the important phenomena and interactions that govern the dynamics of a powder stream and a deposition melt pool, within a single model for the first time.The resulting model is comprehensive enough to allow the prediction of the morphology of deposited tracks and structures and the heat flows during their creation; as well as the flexibility to simulate, in principle, any deposition shape. The model has been demonstrated using the settings of an actual laser metal deposition system, and has been applied to study clad formation in the deposition of single tracks, layers, walls and simple three-dimensional structures. Moreover, the model has been used to study the formation of irregularities and excessive mass deposition. A new sensor-less deposition control technique based on the simulation and testing of different deposition strategies prior to actual deposition, is proposed. As a demonstration of this control technique, the model has also been used to study the case where excessive deposition develops at intersecting or cornered tracks. Improved deposition strategies have been tested using the model and applied to real deposits. A two fold improvement in layer height control has been achieved in the case of cornered layers.The outcome of the work presented in this thesis can be applied in further studies and prediction of laser deposited shapes for real applications. Furthermore, it can be potentially used for improvement of the laser metal deposition technology through the simulation of deposition strategies prior to actual processing.

O objetivo deste trabalho é desenvolver um método numérico capaz de simular escoamentos viscoelásticos com superfícies livres governados pela equação constitutiva não-linear PTT (Phan-Thien-Tanner). Neste trabalho foram apresentados três métodos numéricos para simular escoamentos viscoelásticos modelados pela equação PTT. Dois desses métodos foram desenvolvidos para simular escoamentos viscoelásticos bidimensionais enquanto o terceiro método foi desenvolvido para simular escoamentos viscoelásticos tridimensionais. Estes métodos numéricos foram incorporados aos ambientes de simulação FreeDow2D e FreeDow3D, extendendo estes ambientes para escoamentos viscoelásticos descritos por uma equação constitutiva não-linear. Inicialmente, uma descrição de FreeDow2D e FreeDow3D é apresentada. As equações governantes para escoamentos descritos pelo modelo PTT são dadas na forma de tensorial e as formulações matemáticas para obtenção dos métodos numéricos são apresentadas. As equações que descrevem os métodos numéricos são resolvidas pela técnica de diferenças finitas numa malha deslocada e o fluido é representado por partículas arcadoras usando o método Marker-and-Cell. As condições de contorno para cada tipo de contorno são descritas em detalhes e o cálculo do tensor extra-tensão no contorno rígido é obtido utilizando as idéias de Tomé et al. [84] para o modelo Oldroyd-B. Seguindo a metodologia de Alves et al. [2], a solução analítica do modelo PTT para escoamentos totalmente desenvolvidos em um canal bidimensional é apresentada em detalhes. Esta solução analítica é então usada para validar o método numérico desenvolvido neste trabalho. Os métodos numéricos desenvolvidos nesse trabalho foram aplicados para simular os seguintes problemas: um jato de fluido viscoelástico incidindo numa placa rígida; o inchamento do extrudado e o problema de uma gota esférica de fluido viscoelástico incidindo perpendicularmente contra uma superfície rígida plana / The aim of this work is to develop a numerical method capable of simulating viscoelastic free surface flows governed by the non-linear constitutive equation PTT (Phan-Thien-Tanner). In this work three numerical methods to simulate vicoelastic Flows of fluids modelled by the PTT equation are presented. Two of these methods were developed to simulate two-dimensional viscoelastic flows while the third method was developed to simulate three-dimensional viscoelastic flows. These numerical methods were incorporated into the codes FreeFlow2D and FreeFlow3D, extending these codes to viscoelastic flows described by the non-linear constitutive equation PTT. Initially, a description of FreeFlow2D and FreeFlow3D is presented. The governing equations for flows described by the PTT model are given in index form and the mathematical formulations for obtaining the numerical methods are presented. The equations describing the numerical methods are solved by the finite difference method on a staggered grid and the fluid is modelled using a Marker-and-Cell type method. The boundary conditions for each type of boundary are described in details and the calculation of the extra-stress tensor on rigid boundaries is performed using the ideas of Tomé et al. [84] for an Oldroyd-B Fluid. Following the methodology presented by Alves et al. [2], the analytic solution of the PTT model for fully developed flows in a two-dimensional channel is presented in details. This analytic solution is then used to validate the numerical method developed in this work. Finally, the numerical methods developed in this work were applied to simulate viscoelastic flows such as a viscoelastic jet flowing onto a rigid plate, the extrudate swell of viscoelastic fluids and the simulation of a viscoelastic drop hitting a rigid plate

Este trabalho descreve um método para expandir a aplicabilidade do sistema FreeFlow-2D para problemas de escoamentos de fluidos multifásicos. Este método permite a simulação de escoamento de fluido multifásico, incompressível e com superfície livre. Um número arbitrário de fases com propriedades diferentes pode ser utilizado. Tensões superficial e interfacial são também consideradas. A técnica numérica utilizada baseia-se no GENSMAC (Generalized-Simplified-Marker-and-Cell) e consideram-se propriedades variáveis de acordo com a posição da interface durante o escoamento. O campo de velocidade é computado utilizando-se às equações de Navier-Stokes discretizadas por esquema de diferença finita numa malha deslocada. O método foi implementado em três módulos: Modelador, Simulador e Visualizador. A validação foi efetuada comparando-se os resultados numéricos com resultados analíticos e experimentais. O método mostrou-se robusto e computacionalmente eficiente para os problemas considerados. / This work describes a method to expand the applicability of the system FreeFlow-2D in multi-phase flows problems. This method allows the simulation of incompressible free surface multi-phase flows. An arbitrary number of phases having different properties can be used. Surface and interface tension effects are also considered. The numerical technique is based on the GENSMAC (Generalized-Simplified-Marker-and-Cell) and it considers the properties varying according to the position of the interfaces in the flow. The velocity field is computed using the Navier-Stokes equations discretized by finite-difference on stagered grid. The method was implemented in three modules: the modeling module, the simulation module, and the visualization module. The validation was effected by comparing numerical results with analytical and experimental results. The method shown to be robust and computationally efficient in the problems considered.