We introduce new methods based on the L2 Optimal Transport (OT) problem and the Navier-Stokes equations to approximate a fluid velocity field from images obtained with Particle Image Velocimetry (PIV) measurements. The main idea is to consider two successive images as the initial and final densities in the OT problem, and to use the associated OT flow as an estimate of the underlying physical flow. We build a simple but realistic model for PIV data, and use it to analyze the behavior of the transport map in this situation. We then design and implement a series of post-processing filters created to improve the quality of the numerical results, and we establish comparisons with traditional cross-correlation algorithms. These results indicate that the OT-PIV procedure performs well on low to medium seeding densities, and that it gives better results than typical cross-correlation algorithms in some cases. Finally, we use a variational method to project the OT velocity field on the space of solutions of the Navier-Stokes equations, and extend it to the rest of the fluid domain, outside the particle locations. This extension provides an effective filtering of the OT solution beyond the local post-processing filters, as demonstrated by several numerical experiments. / Graduate

Blending processes in a silo minimise the fluctuations in the property of bulk solids with the blending performance being strongly influenced by the flow pattern and operating mode among other process parameters such as batch size and type of input fluctuations. An accurate prediction of flow characteristics such as flow channel boundary and velocity profiles is important for understanding and quantifying the blending performance, thereby increasing the scope for new design by minimising the number of expensive pilot scale experiments required. In this thesis, the Discrete Element Method (DEM) is deployed to predict and understand the flow characteristics and blending of cylindrical plastic pellets in a planar flat bottom silo and a multi-flow blender (a silo with an insert and a blending tube). The predictions are validated against high-resolution velocity measurements analysed using Particle Image Velocimetry (PIV) technique. A planar model silo was built to measure the flow of pellets using PIV technique. The existing GeoPIV Matlab module was customised to extract the velocity fields in the Eulerian frame of reference and its accuracy has been verified. The developed tool was then applied to quantitatively investigate the mechanism of evolution of flow in a flat bottom silo and the dependency of the state of developed flow on the depth of the planar silo. It was shown that the development of flow during discharge can be divided into two stages: a rapid upward propagation of plug flow followed by a widening of the flow channel with increasing shearing boundaries. The size of the flow channel was found to be increasing with the depth of the silo. For the 100 mm deep silo, the flow is three dimensional with significant retardation in velocity at the frontal walls, whilst a negligible retardation was found for the 20 and 40 mm deep model silos. The thickness and frontal wall friction in planar silos thus play an important role in the development of flow patterns in model silos. In this thesis, DEM model calibration relating the macro-scale bulk friction and micro- scale particle friction at different rolling friction values was developed from DEM simulations of Jenike direct shear box. During the direct shear simulation, a constant normal force was achieved with the use of a shear lid geometry made with glued spheres thereby eliminating the use of a traditional servo control function. The influence of particle rotations and rolling friction on the limiting bulk friction for different particle sliding friction coefficients was explored. The accuracy of the calibration data was assessed by simulating the flow in a flat bottom silo and comparing the model predictions of flow rate, velocity profiles and flow channel boundary with the experiments. A good quantitative agreement was found between the experiment and simulations. The DEM model predictions were also compared with the kinematic model. Following the validation of the model, it was shown that the frontal friction and rolling friction are the influential parameters in simulating the flow patterns such as semi-mass and internal flow. It was further shown that flow transits from semi-mass flow to internal flow with the increase of frontal wall friction. The drastic influence of frontal wall friction on stress, flow patterns and force chains were analysed highlighting its implications on interpretations in 2D test silos. Finally, the developed DEM and PIV tools are employed to investigate blending in a flat bottom and multi-flow blender silo for different flow patterns. The analysis showed that the blending is more effective with the internal flow when compared to semi-mass flow in a flat bottom silo, in both continuous and discontinuous modes for a variety of process conditions such as batch size, the number of recirculation and frequency of input fluctuations. An algorithm was developed to evaluate the blending performance from the spatially averaged Eulerian velocity fields. The flow in a relatively large-scale multi-flow blender comprising nearly 606,000 particles, thereby fully replicating the test silo, was simulated and the challenges in reproducing the test conditions of continuous and discontinuous modes of operation were discussed. The flow patterns and blending were first analysed from the experiments in different configurations of the insert. Using the same input parameters for the model, it was shown that the model predictions of the velocity profiles along the height of the silo are in good agreement with the experiments. Internal flow, mixed flow and mass flow were predicted for the diverging, straight and converging insert configurations respectively and the blending performance for each of these configurations suggests an optimal configuration of the blender thereby demonstrating the potential of PIV and DEM in design optimisation. The possibility of conducting the DEM simulations under increased gravity in order to reduce the computational time has also been explored.

New technologies are constantly developing towards the goal of increasing the performance of gas turbine engines while reducing pollutant emissions. The design of the combustion system is vital in the drive to reduce pollutants in order to meet legislative targets. As part of this, the fuel injector is crucial in preparing the fuel for combustion through atomization and correct mixing with the air flow. Thus, it is desirable to develop techniques to allow the analysis of performance in these key criteria and improve the understanding of both fuel injector aerodynamics and fuel atomisation. Particle Image Velocimetry (PIV) allows for spatially resolved velocity data of flow fields to be recorded and therefore enables the inspection of flow behaviour.

No description available.

abstract: The application of novel visualization and modeling methods to the study of cardiovascular disease is vital to the development of innovative diagnostic techniques, including those that may aid in the early detection and prevention of cardiovascular disorders. This dissertation focuses on the application of particle image velocimetry (PIV) to the study of intracardiac hemodynamics. This is accomplished primarily though the use of ultrasound based PIV, which allows for in vivo visualization of intracardiac flow without the requirement for optical access, as is required with traditional camera-based PIV methods. The fundamentals of ultrasound PIV are introduced, including experimental methods for its implementation as well as a discussion on estimating and mitigating measurement error. Ultrasound PIV is then compared to optical PIV; this is a highly developed technique with proven accuracy; through rigorous examination it has become the “gold standard” of two-dimensional flow visualization. Results show good agreement between the two methods. Using a mechanical left heart model, a multi-plane ultrasound PIV technique is introduced and applied to quantify a complex, three-dimensional flow that is analogous to the left intraventricular flow. Changes in ventricular flow dynamics due to the rotational orientation of mechanical heart valves are studied; the results demonstrate the importance of multi-plane imaging techniques when trying to assess the strongly three-dimensional intraventricular flow. The potential use of ultrasound PIV as an early diagnosis technique is demonstrated through the development of a novel elasticity estimation technique. A finite element analysis routine is couple with an ensemble Kalman filter to allow for the estimation of material elasticity using forcing and displacement data derived from PIV. Results demonstrate that it is possible to estimate elasticity using forcing data derived from a PIV vector field, provided vector density is sufficient. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2015

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

Este trabalho representa o início de uma série de pesquisas que visam o estudo da turbulência e de sua relação com processos de mistura e trocas gasosas entre ar e água, através de experimentos com grades oscilantes. Seu objetivo foi o projeto e a construção de um tanque de grade oscilante, equipamento que gera turbulência com intensidade controlável. Após a construção do tanque, experimentos para medições de velocidade turbulenta foram feitos, com uso de uma técnica de velocimetria a laser. Uma grade de 9x9 barras foi usada na agitação do fluido, com uma amplitude de oscilação de 3 cm, para 4 diferentes freqüências de oscilação. Adquiriu-se 9600 imagens do movimento do fluido, em 6 regiões do tanque, para a obtenção dos campos de velocidade turbulenta, calculados através do software Visiflow e de um programa computacional desenvolvido neste trabalho. Os gráficos criados a partir dos campos possibilitaram a observação do decaimento espacial da turbulência e da região de sua produção. Os campos médios de velocidade mostraram-se bem inferiores aos campos instantâneos, indicando a existência de baixo escoamento médio do fluido. As condições de isotropia e a homogeneidade espacial da turbulência são mais aproximadas à medida que se afasta da grade. A intensidade turbulenta produzida é diretamente relacionada com a freqüência de oscilação. O número de imagens para a obtenção de uma média representativa da velocidade turbulenta neste equipamento parece ser dependente da freqüência de oscilação da grade. Isto aponta para a necessidade de estabelecer corretamente as condições para os cálculos estatísticos em escoamentos turbulentos / This work presents the project and construction of a tank with an oscillating grid, equipment which provides for the experimental studies of turbulence and its relation to mixing processes and gas transfer across fluid interface. Experiments were carried out with the use of digital particle image velocimetry technique, to investigate the properties of the produced turbulence. A grid made of 9x9 square bars was used to stir the water, with a stroke of 3 cm and 4 different oscillation frequencies. A number of 9600 images were acquired, in 6 regions of the tank, for the generation of the turbulent velocity fields through the software Visiflow and a computational program developed in this work. The results showed that the current equipment, with a new concept for the grid oscillation system, can be conveniently useful for studies in this research field. Average velocity fields appeared to be considerably smaller than the instantaneous velocity fields, which leads to the existence of nearly-stationary turbulence in the water volume. Nearly-isotropic turbulence and spatial homogeneity were approximate as the measurements distanced from the grid. The turbulent intensity was directly dependent on the oscillation frequency. The spatial decay of the turbulence and the region near the grid where it is produced could also be observed. The number of images necessary for the calculus of reliable root-mean-square turbulent velocities seems to be dependent on the oscillation frequency of the grid. It results in the necessity of establishing correct statistical analysis of turbulent flows

Red blood cells (RBCs) form approximately 40 to 45% of the human blood volume, and their behaviour and characteristics are the main determinant of blood properties, such as viscosity. RBCs are deformable species and stack together under low shear rate to form aggregates or rouleaux. Flowing RBCs migrate away from the wall leaving a cell-depleted layer known as the cell-free layer (CFL). This layer contributes to the blood viscosity and exchange between the RBCs and the target cells: a thinner CFL enhances the exchange process by reducing the diffusion distance. The formation of this CFL, however, is not yet completely understood. The goal of this study is to improve the understanding of the formation of the CFL in the micro-flow. This was accomplished by studying the effects of changing both the flow rate and the microchannel geometry on blood flow in microchannels. In this work, 10% hematocrit human blood suspensions were prepared in native plasma and flowed through poly-dimethylsiloxane (PDMS) microchannels of 100 μm x 34 μm cross-section. Investigation of the flowing cells was performed by using micro particle image velocimetry (μPIV) coupled with a high-speed camera. First, the high-speed camera images were processed with customized Matlab programs to detect and measure the CFL thickness and the RBC aggregates sizes. Second, the blood flow velocity profiles were measured using μPIV in order to determine the actual flow rate, the RBCs’ centerline velocity, and the shear rate. The results showed that the increase in both flow rate and shear rate significantly reduced the CFL thickness and RBC aggregates size. Comparison of the upstream and downstream measurements in the bifurcating microchannel showed that the change in microchannel geometry did not significantly influence CFL thickness and RBC aggregate size, while within the daughter branches, RBCs tended to flow close to the inner wall resulting in an undetectable CFL at the inner wall and in a larger CFL at the outer wall of the branch. These in vitro results quantitatively relate CFL thickness and RBC aggregate size at different shear rates. The findings are of immediate interest regarding the understanding of microcirculation and improved designs of microchips.

Background: Nowadays, one of the medical problem is rolling cell adhesion. Rolling cell adhesion is a complex process that requires the analysis of the challenging environment such as body fluid and is the process responsible for recruiting the cell to specific organs. In order to explore the rolling cell adhesion, mathematical model is proposed. Different image processing methods are created, such as optical flow - Lucas Kanade algorithm, and other type of methods related to mechanical fluid, namely PIV (Particle Image Velocimetry). Aim: The aim of this master thesis is the identification of challenges while using PIV in live cell images and propose the algorithm, which may analyze the rolling cell adhesion problem. Methods: In order to understand properly the rolling cell adhesion problem from biological site, literature review combined with the expert consultation is performed. According to gather information, mathematical model is proposed. Particle Image Velocimetry is explained according to literature review, where at the beginning the expert recommends some books as a primary research. As a result of this research, PIV challenges are identified and generally PIV idea is explained. Then two experiments are performed. The first experiment evaluates detection algorithms and the second one, analyses track algorithm vs. PIV. In order to evaluate the mentioned algorithms, some evaluation method are selected and some criteria are defined. Unfortunately the found methods are not perfect, therefore a new method related to performance evaluation using time series is proposed. Thesis result: The result of this thesis is a proposition of the algorithm, which can be used in the rolling cell adhesion. The algorithm is formed according to the detailed exploration of the rolling cell adhesion and analysis of the selected algorithms related to the image analysis during the theoretical research and experiments.

D'une part, les équations de Navier-Stokes permettent de décrire les écoulements fluides, la littérature est riche de méthodes numériques permettant la résolution de celle-ci. D'autre part, nous sommes capables de mesurer de manière non-intrusive différentes caractéristique d'un écoulement (champ de vitesse et pression, etc.). Dans le cadre de cette thèse, nous nous intéressons aux techniques d'assimilation de données qui combinent les modèles numériques avec les observations afin de déterminer une meilleure approximation du système. Cette thèse s'articule autour de l'assimilation de donnée variationnelle (4DVar) qui est plus précise par construction. Nous avons mené une première application sur la reconstruction de la hauteur et vitesse de la surface libre d'un fluide contenu dans un récipient rectangulaire à fond plat. L'écoulement est modélisé par les équations de shallow water et résolues numériquement. Les observations de l'évolution de la hauteur de la surface libre ont été prélevées par un capteur de profondeur (Kinect). Nous avons comparé les résultats de la reconstruction par 4DVar avec plusieurs version de la méthode d'assimilation hybride 4DEnVar. Enfin, nous avons appliqué la technique 4DVar à la reconstruction volumique de l'aval d'un sillage de cylindre à Reynolds 300. L'écoulement turbulent a été simulé par un code DNS parallèle Incompact3D. La reconstruction a été effectué en combinant tout d'abord des observations synthétiques en trois dimension, puis en combinant des observations de plans orthogonales en stéréo PIV. / In the one hand, flow dynamics are usually described by the NavierStokes equations and the literature provides a wide range of techniques to solve such equations. On the other hand, we can nowadays measure different characteristics of a flow (velocity, pressure, temperature etc...) with non-intrusive Particle Image Velocimetry techniques. Within this thesis, we take interest in the data assimilation techniques, that combine a dynamics model with measurements to determine a better approximation of the system. This thesis focus on the classic variational assimilation technique (4DVar) which ensures a high accuracy of the solution by construction. We carry out a first application of the 4DVar technique to reconstruct the characteristics (height and velocity field) of a uni directional wave at its free surface. The fluid evolution is simulated by the shallow water equations and solved numerically. We use a simple experimental setup envolving a depth sensor (Kinect sensor) to extract the free surface height. We compared the results of the 4DVar reconstruction with different versions of the hybrid data assimilation technique 4DEnVar. Finally, we apply the 4DVar technique to reconstruct the downstream of a three dimensional cylinder wake at Reynolds 300. The turbulent flow is simulated by the high-performance multi-threading DNS code Incompact3d. This dynamics model is first combined with synthetic three dimensional observations, then with real orthogonal-plane stereo PIV observations to reconstruct the full three dimensional flow.