Essen, Universiẗat, Diss., 2005--Duisburg.

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

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology. / Pulsed Ultrasound Velocimetry combined with Pressure Difference (PUV+PD) measurement is a non-invasive in-line rheometric technique which is used to analyse the complex flow properties of industrial fluids for quality control purposes. Cape Peninsula University of Technology (CPUT) and Technical Research Institute of Sweden (SP) have developed and patented a new PUV+PD based system, called Flow-Viz™. Despite this advancement, the system and ultrasound sensor technology have not been fully tested and evaluated in a wide range of industrial fluids. Acoustic characterisation tests were carried out at SP, with the aim of understanding the ultrasound beam properties after propagating through industrial stainless steel (316L) pipe walls. For these tests, a high-precision robotic XYZ-scanner and needle hydrophone setup were used. Different ultrasound sensor configurations were mounted to a stainless steel pipe while using different coupling media between the transducer-to-wedge and sensor wedge-to-pipe boundaries. The ultrasound beam propagation after the wall interface was measured by navigating the needle hydrophone within a predefined 2-dimensional spatial grid. The most suitable coupling material was determined from the acoustic characterisation, and then used in the in-line rheological characterisation tests to evaluate the performance of the Flow-VizTM rheometric unit against conventional tube viscometry. The in-line rheological tests were conducted with bentonite, kaolin and Carboxymethyl cellulose (CMC) model fluids. The flow loop used consisted of three different pipe test sections; and two concentrations of each fluid were tested in order to ascertain the consistency of the measurements. The in-line rheological tests showed good agreement (±15%) between the two techniques and Flow-VizTM was able to provide important data at very low shear rates. Acoustic characterisation indicated that variations in the beam properties were highly dependent on the acoustic couplants used to mount the sensors to the stainless steel pipes. Furthermore, the in-line results showed the effectiveness of Flow-VizTM as an industrial rheometer. The non-invasive ultrasound sensor technology, was for the first time acoustically characterised through stainless steel. This information will now be used to further optimise the unique technology for advanced industrial applications, e.g. oil drilling fields, complex cement grout and food processing applications.

Questões de aeração forçada ou natural estão intimamente ligadas à capacidade de autodepuração dos corpos hídricos, ou seja, oxidar substâncias agressivas para resultar em baixo teor de toxicidade. Uma das etapas do processamento de efluentes consiste na dissolução de oxigênio em água e, para realizar essa dissolução, utilizam-se aeradores que são unidades (tanques) onde o ar é borbulhado no meio líquido, o qual se desloca em um regime contínuo de escoamento. Esta pesquisa refere-se à obtenção experimental de valores de viscosidade turbulenta para inserção em modelagem fenomenológica da transferência de oxigênio das bolhas de ar para o meio líquido. Tais modelos, se bem realísticos, podem contribuir aos estudos de gestão de recursos hídricos ou em operações nos tratamentos de efluentes líquidos. O método experimental empregado foi a velocimetria por imagem de partículas, no qual foi possível obter velocidades instantâneas do fluido (água). Estas consideram o movimento turbulento, que é o principal responsável pelo transporte de oxigênio da superfície para o seio do corpo hídrico, sendo que essa superfície pode ser livre para o ambiente, ou a superfície de uma bolha. Praticamente, o método consiste em correlacionar posições de partículas traçadoras em suspensão no fluido, as quais são assumidas ter a mesma velocidade do fluido. As posições consecutivas para fornecer a trajetória e a velocidade foram obtidas por imagens capturadas em uma freqüência definida através de uma câmera digital, onde a luz do laser contrastou as partículas em uma área desejada com uma precisão elevada. Então, nessa área (um plano), foi possível correlacionar um perfil de velocidades. Assim, os valores de viscosidade turbulenta foram obtidos para serem usados em modelagem da transferência de oxigênio, os quais poderão contribuir nos estudos de aeração em corpos hídricos. / Problems involving natural or forced aeration are intimately bind to the reaeration of water bodies. Pollutants are oxidized to yield low toxicity conditions. One of the steps of wastewater treatment consists in dissolving oxygen in water. To perform this, aeration tanks are used where bubbling air crosses the continuous liquid flow. This research focuses on the experimental determination of turbulent viscosity values to be used in modeling of oxygen transfer from air bubbles to the bulk liquid. Such models, if realistic enough, may contribute to water resources management studies or in wastewater treatment operations. Particle image velocimetry method was used, by means of which it became possible to obtain instantaneous velocities of the fluid (water). These velocities embody the turbulent flow, which is the main responsible for oxygen transport from the surface to the bulk liquid. This surface may be either facing the atmosphere or the interior of a bubble. In practice, the method consists in correlating tracking particles suspended in the liquid, which are supposed to have the same velocity of the fluid. The successive positions that give path and speed were obtained by images took in predefined intervals by a digital camera. The laser light illuminated the particles in a predefined area with high precision, making possible to determine velocity profiles. Turbulent viscosity values were so determined and may be used in the modeling of oxygen transfer, which may contribute to water body aeration studies.

Uma vez que a maioria das complicações relacionadas ao funcionamento das próteses de válvulas cárdicas é devida aos distúrbios de escoamento, a sua caracterização hidrodinâmica é um auxílio útil no projeto de novas válvulas. Simulações do escoamento pulsátil através de próteses de válvulas cardíacas começaram há cerca de 60 anos, por meio do desenvolvimento de diferentes simuladores cardíacos, melhorando a interpretação dos resultados clínicos. Para o presente estudo, um simulador cardíaco foi desenvolvido completamente na Escola Politécnica da Universidade de São Paulo, no Departamento de Engenharia Mecânica, para estudar o fluxo através de próteses mitrais e aórticas. A sua concepção é baseada na geometria e na fisiologia do lado esquerdo do coração humano, no estado da arte desses simuladores e na norma ISO 584:2010. Neste trabalho, o simulador cardíaco desenvolvido foi aplicado para estudar experimentalmente o fluxo pulsátil através de próteses cardíacas mitrais biológicas de pericárdio bovino. Para tanto, após a validação do simulador para algumas freqüências cardíacas, as biopróteses foram submetidas a ensaios de velocimetria não invasiva, por meio de um equipamento Particle Image Velocimetry (PIV). Os experimentos, que se concentraram principalmente logo após o começo da diástole, mostraram qualitativamente uma diferença significativa no escoamento intraventricular em função de dois posicionamentos das biopróteses, defasadas entre si de 180º no sentido do seu eixo longitudinal. Além disso, produziram significativas mudanças no escoamento próximo à prótese aórtica considerada. Com a continuidade deste estudo, os resultados poderão induzir a um dado procedimento clínico. / Since most complications related to the operation of prosthetic heart valves are due to disturbances of flow, their hydrodynamic characterization is a useful aid in the design of new prostheses. Simulations of pulsatile flow in cardiac prostheses began nearly 60 years ago, through the development of different mock human circulatory systems, improving the clinical results interpretation. A complete design of a cardiac simulator was developed at Polytechnic School of USP, Mechanical Engineering Department, to study mitral and aortic prosthetic heart valves. The simulator design is based on the both geometry and physiology of the left side of the human heart, on state-of-art studies and also considering the ISO 584:2010 standard. The cardiac simulator was applied to pulsatile flow testing of bovine pericardium mitral prosthetic valves. For this, after the cardiac simulator validation for some heart rates, the bioprostheses were assayed by noninvasive velocimetry technics, i.e., a Particle Image Velocimetry (PIV) system. The testing, which mainly were focused on just after the beginning of diastole, qualitatively have showed a significant difference in the intraventricular flow according two different positions for the bioprostheses, dephased of 180° in the direction of their longitudinal axis. Moreover, they produced significant changes in flow close to the aortic prosthesis considered. Future works may lead to a particular medical procedure.