The study applies in vivo technique for profiling hemodynamics and wall shear stress (WSS) distribution in human coronary arteries. The methodology involves fusion of 2D Intra Vascular Ultra Sound and Bi-plane angiograms to reproduce the 3D arterial geometry. This geometry is then used in a Computational Fluid Dynamics (CFD) module for flow modeling. The Walburn and Schneck constitutive relation was used to represent the non-Newtonian blood rheology. The methodology is applied to study the relationship between WSS and Neointimal Hyperplasia (NIH) in two groups of diabetic patients after being treated separately with bare metal stents (BMS) and Sirolimus Eluting Stents (SES). The stent assignments were blinded until the end of the study. The study was repeated for the patients after 9 months. The predicted WSS ranged from (0.1- 8 N/m2) and was categorized into five classes: low ( < 1 N/m2); low-normal (1-2 N/m2); normal (2-3 N/m2); high-normal (3-4 N/m2); high ( > 4 N/m2). The results indicate NIH in 5 of the patients treated with BMS and none in SES cases. These results correlate with our predicted WSS distribution.

No description available.

Le contrôle des écoulements vise à modifier le comportement naturel d’un écoulement fluidique. Dans le domaine des transports, contrôler les phénomènes fluidiques tels que le décollement peut permettre d’économiser du carburant, d’améliorer les performances des véhicules ou encore d’assurer davantage la sécurité des passagers. Dans ce contexte, des capteurs avec de fines résolutions temporelle et spatiale sont requis afin de connaître l’écoulement à contrôler et adapter en temps réel le contrôle. Dans ce travail, l’objectif a été de développer des micro-capteurs de frottement et de pression pour les mesures en écoulements turbulents et le contrôle de décollement. Tout d’abord un micro-capteur calorimétrique a été conçu et réalisé par des techniques de microfabrication pour mesurer simultanément le frottement pariétal et la direction de l’écoulement. Le micro-capteur a ensuite été intégré en paroi d’une soufflerie afin de réaliser son étalonnage statique et dynamique et d’étudier sa sensibilité à la direction de l’écoulement. Troisièmement, le micro-capteur calorimétrique a été utilisé pour caractériser des écoulements décollés. Plusieurs micro-capteurs avec électronique miniaturisée ont été intégrés avec succès dans une maquette de volet et des essais de contrôle actif ont été réalisés. Enfin, la quatrième partie concerne le développement d’un micro-capteur de pression et d’un micro-capteur multi-paramètres réunissant les deux technologies. L’ensemble de ces micro-capteurs ont été caractérisés avec succès et montrent des résultats prometteurs pour caractériser les écoulements turbulents et permettre la mise en place de contrôle d’écoulement en boucle fermée. / Flow control aims at artificially changing the natural behaviour of a flow. In transport industries, controlling fluidic phenomena such as boundary layer separation allows saving fuel and power, improving vehicles performances or insuring passenger’s safety. In this context, sensors with accurate spatial and temporal resolution are required. Such devices enable to estimate the flow to control and allow real-time adaptation of the control. In this work, the objective is to develop wall shear stress and pressure micro-sensors for turbulent flows measurements and flow separation control.Firstly, a calorimetric micro-sensor was designed and realized using micromachining techniques for measuring simultaneously the wall shear stress amplitude and the flow direction. Secondly, the micro-sensor was flush-mounted at the wall of a wind tunnel for static and dynamic calibrations. Thirdly, it was used to characterized separated flows. Several configurations were studied: separation on airfoil profile, separation and reattachment downstream a 2D square rib and the separation on a flap model. Several micro-sensors with embedded electronics were successfully integrated on a flap model and active flow control experiments were performed. Finally, the fourth part of the document concerns the development of a pressure micro-sensor and the development of a multi-parameter micro-sensor combining both technologies.All these micro-sensors have been successfully realized and characterized and demonstrate promising results for measuring turbulent flows and implementing closed loop reactive flow control

Turbulent mixed convection is a complicated flow where the buoyancy and shear forces compete with each other in affecting the flow dynamics. This thesis deals with the near wall dynamics in a turbulent mixed convection flow over an isothermal horizontal heated plate. We distinguish between two types of mixed convection ; low-speed mixed convection (LSM) and high-speed mixed convection (HSM). In LSM the entire boundary layer, including the near-wall region, is dominated by buoyancy; in HSM the near-wall region, is dominated by shear and the outer region by buoyancy. We show that the value of the parameter (* = ^ determines whether the flow is LSM or HSM. Here yr is the friction length scale and L is the Monin-Obukhov length scale. In the present thesis we proposed a model for the near-wall dynamics in LSM. We assume the coherent structure near-wall for low-speed mixed convection to be streamwise aligned periodic array of laminar plumes and give a 2d model for the near wall dynamics, Here the equation to solve for the streamwise velocity is linear with the vertical and spanwise velocities given by the free convection model of Theerthan and Arakeri [1]. We determine the profiles of streamwise velocity, Reynolds shear stress and RMS of the fluctuations of the three components of velocity. From the model we obtain the scaling for wall shear stress rw as rw oc (UooAT*), where Uoo is the free-stream velocity and AT is the temperature difference between the free-stream and the horizontal surface.A similar scaling for rw was obtained in the experiments of Ingersoll [5] and by Narasimha et al [11] in the atmospheric boundary layer under low wind speed conditions. We also derive a formula for boundary layer thickness 5(x) which predicts the boundary layer growth for the combination free-stream velocity Uoo and AT in the low-speed mixed convection regime.

This thesis presents a detailed, two-dimensional analysis of the performance of multi-element guard-heated hot-film wall shear stress microsensors for turbulent flows. Previous studies of conventional, single-element sensors show that a significant portion of heat generated in the hot-film travels through the substrate before reaching the fluid, causing spectral and phase errors in the wall shear stress signal and drastically reducing the spatial resolution of the sensor. Earlier attempts to reduce these errors have focused on reducing the effective thermal conductivity of the substrate. New guard-heated microsensor designs proposed to overcome the severe deficiencies of the conventional design are investigated in this thesis. Guard-heaters remove the errors associated with substrate heat conduction, by forcing zero temperature gradient at the edges and bottom face of the hot-film, and hence, block the indirect heat transfer to the flow. Air and water flow over the sensors are studied numerically to investigate design, performance and signal strength of the guard-heated sensors. Our results show, particularly for measurements in low-conductivity fluids such as air, that edge guard-heating needs to be supplemented by a sub-surface guard-heater, to make substrate conduction errors negligible. With this two-plane guard-heating, a strong non-linearity in the standard single-element designs can be corrected, and spectral and phase errors arising from substrate conduction can be eliminated. / Graduate / 0548 / etrati@uvic.ca

This dissertation deals with instabilities of thin liquid films up to entrainment of drops. Four types of instabilities have been classified depending on the type of structure and process on the liquid film surface: two-dimensional slow waves, two-dimensional fast waves, three-dimensional waves, solitary waves and entrainment of drops from the film surface. This thesis analyzes the physical principles of instabilities and deals with the mathematical formulation of the problem. Shear and pressure forces acting on the surface of the liquid film are identified as the cause of instabilities. Mathematical models for predicting instabilities are demonstrated using approaches based on solving the Orr-Sommerfeld equation and the equations of motion in integral form. Models of shear and pressure forces acting on the surface of the film and selected models of film thickness are presented. The work is focused on the prediction of the initiation of two-dimensional waves using the integral approach. Shear stress and pressure forces acting on the liquid film surface have been modeled using the simulation of air flow over a solid surface. Finally, criteria for drop entrainment are presented with their dependence on air velocity and film thickness.

<p>The fluid dynamics of blood in the systemic circulation modulates production of nitric oxide (NO), a potent vasodilator. Non-invasive techniques such as the flow-mediated dilation (FMD) test and physiologic phenomena associated with autonomic stress induce hyperemia and subsequently higher levels of wall shear stress (WSS), stimulating endothelial nitric oxide synthase (eNOS) expression. In the current clinical practice, WSS–a key regulator of endothelial function–is commonly estimated assuming a parabolic velocity distribution, despite the evidence that the temporal changes of pulsatile blood flow over the cardiac cycle modulate vasodilation in mammals. This work investigates the effect of cardiovascular stress on local WSS distributions and the potential for near-wall accumulation of nitrite, the vasoactive storage form of NO in the bloodstream. The specific aims of the project are therefore as follows: 1) develop a reduced-order model of the major systemic vasculature at rest, during a flight-or-flight response, and under moderate levels of aerobic exercise; 2) derive a velocity-driven Womersley solution for pulsatile flow to support accurate estimation of pulsatile WSS in the clinical setting; and 3) quantify cumulative transport of nitrite in a multiscale model of bifurcating vasculature utilizing computational fluid dynamics (CFD). Development of these open-source, translatable methods enable accurate quantification of hemodynamics and species transport during cardiovascular stress. Results detailed herein extend our knowledge about regulation of regional blood flow during autonomic stress, suggest a convergent evolutionary theory for having a complete circle of Willis, and potentially clarify reproducibility concerns associated with the FMD test. </p>

No description available.

Cardiovascular diseases are among the leading causes of deaths worldwide, but the fluid mechanics of many of these conditions and the devices used to treat them are only partially understood. This goal of this dissertation was to develop new experimental techniques that would enable translational research into two of these conditions. The first set of experiments examined <i>in-vitro</i> the changes in Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) caused by the implantation of coronary stents into the arteries of the heart using Particle Image Velocimetry. These experiments featured one-to-one scaling, commercial stents, and realistic flow and pressure waveforms, and are believed to be the most physiologically accurate stent experiments to date. This work revealed distinct differences in WSS and OSI between the different stent designs tested, and showed that changes in implantation configuration also affected these hemodynamic parameters. Also, the production of vortices near the stent struts during flow reversal was noted, and an inverse correlation between WSS and OSI was described. The second set of experiments investigated Left Ventricular Diastolic Dysfunction (LVDD) using phase contrast magnetic resonance imaging (pcMRI). Using this technique, ten patients with and without LVDD were scanned and a 2D portrait of blood flow through their heart was obtained. To augment this data, pressure fields were calculated from the velocity data using an omni-directional pressure integration scheme coupled with a proper-orthogonal decomposition-based smoothing. This technique was selected from a variety of methods from the literature based on an extensive error analysis and comparison. With this coupled information, it was observed that healthy patients exhibited different flow patterns than diseased patients, and had stronger pressure differences during early filling. In particular, the ratio of early filling pressure to late filling pressure was a statistically significant predictor of diastolic dysfunction. Based on these observations, a novel hypothesis was presented that related the motion of the heart walls to the observed flow patterns and pressure gradients, which may explain the differences observed clinically between healthy and diseased patients. / Ph. D.

Abdominal aortic aneurysm (AAA) is characterized by a bulge in the abdominal aorta. AAA development is mostly asymptomatic, but such a bulge may suddenly rupture, which is associated with a high mortality rate. Unfortunately, there is no medication that can prevent AAA from expanding or rupturing. Therefore, patients with detected AAA are monitored until treatment indication, such as maximum AAA diameter of 55 mm or expansion rate of 1 cm/year. Models of AAA development may help to understand the disease progression and to inform decision-making on a patient-specific basis. AAA growth and remodeling (G&amp;R) models are rather complex, and before the challenge is undertaken, sound clinical validation is required. In Paper A, an existing thick-walled model of growth and remodeling of one layer of an AAA slice has been extended to a two-layered model, which better reflects the layered structure of the vessel wall. A parameter study was performed to investigate the influence of mechanical properties and G&amp;R parameters of such a model on the aneurysm growth. In Paper B, the model from Paper A was extended to an organ level model of AAA growth. Furthermore, the model was incorporated into a Fluid-Solid-Growth (FSG) framework. A patient-specific geometry of the abdominal aorta is used to illustrate the model capabilities. In Paper C, the evolution of the patient-specific biomechanical characteristics of the AAA was investigated. Four patients with five to eight Computed Tomography-Angiography (CT-A) scans at different time points were analyzed. Several non-trivial statistical correlations were found between the analyzed parameters. In Paper D, the effect of different growth kinematics on AAA growth was investigated. The transverse isotropic in-thickness growth was the most suitable AAA growth assumption, while fully isotropic growth and transverse isotropic in-plane growth produced unrealistic results. In addition, modeling of the tissue volume change improved the wall thickness prediction, but still overestimated thinning of the wall during aneurysm expansion. / Bukaortaaneurysm (AAA) kännetecknas av en utbuktning hos aortaväggen i buken. Tillväxt av en AAA är oftast asymtomatisk, men en sådan utbuktning kan plö̈tsligt brista, vilket har hög dödlighet. Tyvärr finns det inga mediciner som kan förhindra AAA från att expandera eller brista. Patienter med upptä̈ckt AAA hålls därför under uppsikt tills operationskrav är uppnådda, såsom maximal AAA-diameter på 55 mm eller expansionstakt på 1 cm/år. Modeller för AAA-tillväxt kan bidra till att öka förståelsen för sjukdomsförloppet och till att förbättra beslutsunderlaget på en patientspecifik basis. AAA modeller för tillväxt och strukturförändring (G&amp;R) är ganska komplicerade och innan man tar sig an denna utmaning krävs de god klinisk validering. I Artikel A har en befintlig tjockväggig modell för tillväxt av ett skikt av en AAA-skiva utö̈kats till en två-skiktsmodell. Denna modell återspeglar bättre den skiktade strukturen hos kärlväggen. Genom en parameterstudie undersö̈ktes påverkan av mekaniska egenskaper och G&amp;R-parametrar hos en sådan modell för AAA-tillväxt. I Artikel B utvidgades modellen från Artikel A till en organnivå-modell för AAA-tillväxt. Vidare inkorporerades modellen i ett “Fluid–Solid–Growth” (FSG) ramverk. En patientspecifik geometri hos bukaortan användes för att illustrera möjligheterna med modellen. I Artikel C undersöktes utvecklingen av patientspecifika biomekaniska egenskaper hos AAA. Fyra patienter som skannats fem till åtta gånger med “Computed Tomography-Angiography” (CT-A) vid olika tillfällen analyserades. Flera icke triviala statistiska samband konstaterades mellan de analyserade parametrarna. I Artikel D undersöktes effekten av olika tillväxt-kinematik för AAA tillväxt. En modell med transversellt-isotrop-i-tjockleken-tillväxt var den bäst lämpade för AAA tillväxt, medans antagandet om fullt-isotrop-tillväxt och transversellt-isotrop-i-planet-tillväxt producerade orimliga resultat. Dessutom gav modellering av vävnadsvolymsförändring ett förbättrat väggtjockleks resultat men en fortsatt överskattning av väggförtunningen under AAA-expansionen. / <p>QC 20161201</p>