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1
Doty, Sherry D. „Fluid shear stress effects on fibronectin in endothelial cells“. Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/19073.
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2
Zhou, Fangbin. „Inertial effects upon suspension shear flows : instability issue“. Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/10056.
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Helmlinger, Gabriel. „Effects of pulsatile laminar shear stress on cultured vascular endothelial cells“. Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/16738.
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4
Baker, William John Jr. „The effects of population doubling on the shear stress response of bovin aortic endothelial cells“. Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/19600.
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5
Akbary, Hamid. „Effects of extra strain rates on uniform shear flow and their relevance to impeller flows“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23857.pdf.
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Shuaib, Norshah Hafeez. „Numerical simulation of thin film flow including surface shear and gravitational effects“. Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420340.
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7
Drumright-Clarke, Mary Ann. „Numerical simulations that characterize the effects of surfactant on droplets in shear flow“. Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/26895.
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Numerical simulations utilizing the code SURFER++ with the incorporation of an insoluble surfactant in the VOF scheme were conducted to characterize the effects of surfactant on a drop in shear flow. The drop is suspended in a matrix liquid. A parameter called reduction, which specifically relates to a percentage decrease in effective surface tension, is used to measure the surfactant amount on the interface. In a model system where reduction = 0.1, viscosity ratio = 1 and density ratio = 1, it was found that stable drops tend to be more elongated and less inclined to the primary flow direction than drops unexposed to surfactant. This can be explained by the location of surfactant at the interface as the drop evolves. Breaking drops also show a flattened angle, but exhibit shorter necks and faster time to break than similar drops without surfactant. As reduction increases, various physical characteristics of the drops change across Reynolds number.Ph. D.
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Magid, Richard. „Engineering molecular reporters to investigate the effects of shear stress upon endothelial cells“. Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/13754.
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9
Ziegler, Thierry. „Effects of a laminar steady-state flow-induced shear stress on the proliferation of cultured endothelial cells“. Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/17663.
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10
Mehrabadi, Marmar. „Effects of red blood cells and shear rate on thrombus growth“. Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53082.
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Thrombosis formation upon rupture or erosion of an atherosclerotic plaque can lead to occlusion of arteries. An occlusive thrombus is the most common cause of clinical events such as angina, myocardial infarction, ischemic attacks and strokes. Occlusive thrombi can cause ischemic cardiac arrest in less than an hour. Thrombosis formation requires rapid platelet accumulation rates exceeding thrombosis lysis and embolization rates. Hemodynamics greatly affects platelet accumulation rate through affecting platelet transport to the surface of a growing thrombus. The presence of red blood cells (RBCs) in blood increases platelet transport rate by several orders of magnitude compared to transport due to Brownian motion. Margination of platelets towards the vessel walls also results in higher platelet concentration at the RBC-depleted layer relative to the bulk. In this thesis, we studied the effects of hemodynamics on thrombus growth. We investigated the effects of important flow and particle properties on margination of particles in RBC suspensions by direct numerical simulation (DNS) of cellar blood flow. We derived a scaling law for margination length. Based on this scaling law, margination length increases cubically with channel height and is independent of shear rate. Using DNS, we verified the proposed scaling law for margination length in straight channels. We also showed that rigidity and size both lead to particle margination. We show that platelet margination can be explained by RBC-enhanced shear-induced diffusion of platelets in the RBC-filled region combined with platelet trapping in the RBC-free region. A simple continuum model is introduced based on the proposed mechanism. Using an experimental correlation for effective diffusivity in blood, the continuum model can recover experimental results from the literature over a wide range of tube diameters. We created an in vitro experimental model of thrombosis with and without RBCs. Surprisingly, we found that rapid thrombus growth does not require enhanced platelet transport in the presence of RBCs at high shear. Instead, our results suggest that thrombus growth rate at high shear is dependent on the availability of vWF-A1 domains as opposed to convective transport of platelets. Finally, we obtained empirical correlations for thrombus growth and lag time based on flow parameters by using an in vitro model of thrombosis. We developed a simple model for predicting thrombus formation using the obtained empirical correlations. We demonstrated the capability of the model in predicting thrombus formation over a wide range of experimental geometries. This model may be useful for designing blood-contacting devices to avoid unwanted thrombosis.
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Wayman, Brian H. „Arterial Response to Local Mechanical Variables: The Effects of Circumferential and Shear Stress“. Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/22611.
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Arteries respond to changes in global mechanical parameters (pressure, flow rate, and longitudinal stretching) by remodeling to restore local parameters (circumferential stress, shear stress, and axial strain) to baseline levels. Because a change in a single global parameter results in changes of multiple local parameters, the effects of individual local parameters on remodeling remain unknown. This study uses a novel approach to study remodeling in organ culture based on independent control of local mechanical parameters. The approach is illustrated by studying the effects of circumferential and shear stress on remodeling-related biological markers. Porcine carotid arteries were cultured for three days at a circumferential stress of 50 kPa or 150 kPa or, in separate experiments, a shear stress of 0.75 Pa or 2.25 Pa. At high circumferential stress, matrix synthesis, smooth muscle cell proliferation, and cell death are significantly greater, but matrix metalloproteinase-2 (MMP-2) and pro-MMP-2 activity are significantly less. In contrast, biological markers measured were unaffected by shear stress. Applications of the proposed approach for improved understanding of remodeling, optimizing mechanical conditioning of tissue engineered arteries, and selection of experimentally motivated growth laws are discussed.
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Miller, Leigh Ann. „Wall shear stress distribution and the effects of branch angle on a human coronary artery model“. Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/16088.
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13
Coleman, Sarah Elizabeth. „The development of an in vitro flow simulation device to study the effects of arterial shear stress profiles on endotheilial cells“. Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/11657.
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Mechanical forces are important regulators of cell function in many tissues including, for example, bone and components of the cardiovascular system. The endothelial lining of blood vessels has been shown to respond in an atheroprotective manner to unidirectional, laminar flow-induced shear stress and in an atherogenic manner to oscillating and low levels of shear. We have developed a cone and plate shear apparatus to simulate fluid shear stress on endothelial cells in vitro. The significant feature of this apparatus is that, unlike other in vitro flow systems, it accurately produces varying levels of shear stress, consistent with those created in vivo during the cardiac cycle. Flow characteristics of this system were verified by computational fluid dynamics (CFD) and laser Doppler velocimetry (LDV). Cellular responses were monitored by cell morphology and protein expression. These responses are consistent with in vivo responses as well as previous work using other in vitro flow systems.
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Derakhshandeh, Maziar. „Flow-induced crystallization of high-density polyethylene : the effects of shear, uniaxial extension and temperature“. Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37669.
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The effects of shear, uniaxial extension and temperature on the flow-induced crystallization of two different types of two high-density polyethylenes (a metallocene and a Ziegler-Natta HDPE) are examined using rheometry. Shear and uniaxial extension experiments were performed at temperatures below and well above the peak melting point of the polyethylene’s in order to characterize their flow-induced crystallization behavior at rates relevant to processing. Generally, strain and strain rate found to enhance crystallization in both shear and elongation. In particular, extensional flow was found to be a much stronger stimulus for polymer crystallization compared to shear. At temperatures well above the melting peak point (up to 25°C), polymer crystallized under elongational flow, while there was no sign of crystallization under simple shear. A modified Kolmogorov crystallization model (Kolmogorov AN (1937) On the statistics of the crystallization process on metals. Bull Akad Sci. USSR, Class Sci, Math Nat. 1:355–359) proposed by Tanner (Tanner RI (2009) Stretching, shearing and solidification, Chem Eng Sci, 64:4576-4579) was used to describe the crystallization kinetics under both shear and elongational flow. The model was found to predict the FIC behaviour under low deformation rates and various temperatures well; however the predictions for the higher rates were not satisfactory.
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Kolli, Kranthi Kumar. „Domain Effects in the Finite / Infinite Time Stability Properties of a Viscous Shear Flow Discontinuity“. Connect to this title, 2008. http://scholarworks.umass.edu/theses/204/.
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Weston, Matthew W. „Characterization of the shear stress on the aortic valve leaflet surface and its effects on cellular biosynthetic activity“. Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/9369.
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Coleman, Sarah Elizabeth. „The development of an in vitro flow simulation device to study the effects of arterial shear stress profiles on endothelial cells“. Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-07072005-220718/.
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Thesis (M. S.)--Biomedical Engineering, Georgia Institute of Technology, 2006.Hanjoong Jo, Ph.D., Committee Chair ; Don P. Giddens, Ph.D., Committee Member ; W. Robert Taylor, M.D., Ph.D., Committee Member ; Ajit Yoganathan, Ph.D., Committee Member.
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Reshko, Mykhaylo. „Gyrokinetic simulations of the effects of equilibrium E X B flow shear on microinstabilities and transport in tokamaks“. Thesis, University of York, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516656.
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Li, Wei. „Mechanical Effects of Flow on CO2 Corrosion Inhibition of Carbon Steel Pipelines“. Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1461751721.
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20
Silas, Kevin Alexander. „Phase Transform Time Delay Estimation to Counteract Spectral Haystacking Effects in Jet Exhaust Flow Measurements“. Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/104892.
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This study determined a superior data processing technique for correlating an acoustic signal passing through a subsonic jet engine exhaust in order to estimate the traversal time of the signal. Thrust measurement is possible with enough time delay estimates across different portions of the exhaust. This preliminary study did not take the full array of data necessary to measure thrust, but did validate key aspects of the measurement process. The turbulent shear layers of the exhaust spectrally broaden the signal, creating the appearance of spectral "haystacks", making traditional correlation methods unworkable. An experiment was performed to evaluate the ability of a novel sound source to produce a signal from which a reliable and precise time delay estimate could be found. The test apparatus was installed on either side of a Honeywell TFE731-2 turbofan research engine exhaust cone, with the source and receivers placed near the jet exit plane. The signal was then directed across the jet exhaust. This flow environment is considered an extreme challenge for accurate acoustic signal propagation. A key contribution of this paper is the determination that the Phase Transform processor of the Generalized Cross-Correlation (GCC) method produces the most reliable time delay estimates, for the given signal and flow conditions. Several alternative time delay estimators and GCC processors were examined and evaluated on this data. A proposed explanation is provided for why this time delay estimation technique produces the most accurate results, as well as explanations for why the technique became less reliable as the flow environment became more challenging, with an observed 22% anomalous TDE selection rate for the N1Corr = 60% and N1Corr = 70% conditions combined, versus only 6% for the idle and N1Corr = 50% conditions combined. This paper also details the development and first use of a novel acoustic source that produces a two-tone narrowband signal emanating from a single point – the dual Hartmann generator.Master of Science
This study builds on a Computational Tomography (CT) technique that uses an acoustic signal and an array of receivers to measure the velocity and temperature of a gas flow field. In particular, the velocity and temperature field tested involves multiple turbulent and disruptive elements, requiring a loud and specifically designed signal. As such, a novel acoustic signal generator, the dual Hartmann generator, was designed that is both loud and produces a specific two-toned signal. The key contribution of the study was to process the data, comparing the sets of transmitted and received signals, in order to estimate the time delay amongst receiver pairs – a key input in the CT method. Traditional cross-correlation methods were inadequate, and multiple alternatives were evaluated. The Phase Transform (PHAT) technique showed the most promise, and an explanation is given for why this technique is most suitable for this type of signal.
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Rajabi, Jaghargh Ehsan. „Effects of hemodynamic stresses on the remodeling parameters in arteriovenous fistula“. University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427962400.
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Milbank, Juliette, und milbank@turbulenflow com au. „Investigation of fluid-dynamic cavity oscillations and the effects of flow angle in an automotive context using an open-jet wind tunnel“. RMIT University. Aerospace, Mechanical & Manufacturing Engineering, 2005. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090723.121800.
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Aeroacoustic whistles are a significant source of customer complaints to automotive manufacturers. Whistles can occur on many such components, but the relative position and configuration of rearview mirrors means they are a more problematic source of tonal noise on vehicles. The low subsonic complex turbulent flow, combined with small cavity scales, determines the possible whistle mechanisms. The one considered to be most problematic, fluid-dynamic cavity resonance, is the topic of this research thesis. The research scope is limited to the automotive environment of external rearview mirrors and the fluid-dynamic resonance mechanism: low subsonic Mach number, M = 0.05 - 0.13; laminar boundary layers; and two-dimensional, acoustically compact cavities. The low unit-cost of rearview mirrors and the desire to have simple identification and prediction schemes, that could be used by production engineers, determined an empirical approach. A search of the existing literature revealed that there were some data on cavities of the above scale in low Mach number flow, but quoted errors in empirical descriptions were large and there was very little research on the effects of flow yaw angle on the chosen resonance mechanism. The research therefore aims to determine whether existing empirical descriptions of fluid-dynamic cavity resonance are suitable for the prediction of the resonance characteristics, with sufficient accuracy to enable unambiguous identification of the presence of the resonance and its mechanism. A second aim is to investigate the effects of a feature of the automotive flow environment, flow yaw angle, on the resonance. Flow yaw angle is determined by those components of the flow in the same plane as the surface in which the cavity is situated. An experimental program was undertaken using a purpose-built aeroacoustic wind tunnel and a simple cavity model. Testing with two types of cavity configurations, as well as flow visualisation, investigated the main features of the resonance in time-averaged yawed flow. Within the scope of this thesis, it is shown that fluid-dynamic cavity resonance characteristics can be accurately identified by a simple empirical model, even in yawed flow. Various descriptors allow identification of the resonance threshold, stage, frequency and relative amplitude in non-yawed flow, while the frequency and stage can also be identified in yawed flow. The relative decrease in resonance amplitude in yawed flow, although identified for these experiments, would depend on the degree of spanwise variation in the boundary layer characteristics for a given cavity configuration. The results also identify significant issues with testing in a free jet tunnel, due to the nature of fluid-dynamic cavity resonance and the fluctuation energy content in free shear layers. Despite this, the thesis aims are achieved, and appropriate design guidelines are produced for automotive designers.
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Yang, Jinyue. „Impedance eduction of acoustic liners with complex sound fields and shear flows“. Electronic Thesis or Diss., Le Mans, 2024. http://www.theses.fr/2024LEMA1023.
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Les traitements acoustiques sont largement utilisés pour réduire les émissions sonores des moteurs d'avions. Pour leur développement, il est essentiel de pouvoir mesurer l’impédance acoustique de ces traitements et d'étudier leur comportement en présence d’écoulement. Cette thèse vise à évaluer la performance de la méthode directe de mesure dans des conditions réalistes, en particulier lorsque l'on considère de grands conduits, des modes acoustiques d'ordres élevés et des vitesses d'écoulement représentatives des nacelles d'aéronefs. L'étude est d'abord basée sur des simulations numériques avec une méthode multimodale. Ensuite, le banc d’essai, MAINE Flow, permet de valider et de démontrer expérimentalement les méthodes proposées et les conclusions.Dans les grands conduits, le champ acoustique est plus complexe que dans les petits, pour la même gamme de fréquences. Ainsi, la mesure d'impédance est un défi, qui est également perturbé par le bruit dû à la présence de l'écoulement. Ce travail conçoit d’abord la configuration expérimentale et des antennes de microphones, pour réaliser une mesure d'impédance précise dans de grands conduits. Ensuite, la validité de l'hypothèse d'écoulement uniforme qui est souvent appliquée est évaluée, et l’effet d’un écoulement cisaillé est étudié, en particulier dans le cas de conduits de grandes tailles. Finalement, différentes ondes incidentes entraînent des comportements différents de la méthode de mesure. Par conséquent, l'influence du champ acoustique incident est aussi étudiéeAcoustic liners are widely used to reduce noise emissions in aircraft engines. The investigation of liners behavior is essential for their development. Impedance eduction is thus commonly implemented to measure its acoustic impedance in presence of flow. The work in this thesis aims to study the performance of the direct eduction method under realistic conditions, especially when considering large ducts, high-order acoustic modes and flow velocities representative of aircraft nacelles. The study is first based on numerical simulations with a multimodal method. Then the MAINE Flow facility is used for experimental validation and demonstration of the proposed methods and conclusions.In large ducts, the sound field is more complex compared to small ducts in the same frequency range. Therefore, the impedance eduction is challenging, and also because it is also perturbed by the background noise due to the presence of flow. The first task is to design microphone arrays for the experimental facility with the aim of performing accurate impedance eduction in large ducts. The second objective is to investigate the effects of shear flow. Impedance eduction is commonly implemented under the hypothesis of uniform mean flow. However, it is reasonable to question the validity of the uniform flow hypothesis, especially when considering large ducts. The third task is to study the influence of the incident sound field. In large ducts, the sound field contains higher-order modes, and different incident waves result in different behavior of the impedance eduction. It is thus necessary to study how the incident acoustic field affects the eduction results in the presence of flow
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Twycross-Lewis, Richard. „Micro flow chambers for studies on effects of the spatial gradient of the fluid shear stress on cultured endothial cells“. Thesis, Queen Mary, University of London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417841.
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Xing, Yun. „Effects of Mechanical Forces on the Biological Properties of Porcine Aortic Valve Leaflets“. Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6828.
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Cardiac valves are dynamic, sophisticated structures which interact closely with the surrounding hemodynamic environment. Altered mechanical stresses, including pressure, shear and bending stresses, are believed to cause changes in valve biology, but the cellular and molecular events involved in these processes are not well characterized. Therefore, the overall goal of this project is to determine the effects of pressure and shear stress on porcine aortic valve leaflets biology.
Results from the pressure study showed that elevated constant pressure (140 and 170 mmHg) causes significant increases in collagen synthesis. The increases were 37.5% and 90% for 140 and 170 mmHg, respectively. No significant differences in DNA and sGAG synthesis were observed under constant pressure. In the cyclic pressure study, the effects of both pressure magnitude and pulse frequency were studied. With the frequency fixed at 1.167 Hz, collagen and sGAG synthesis increased proportionally with mean pressure level. At a fixed pressure level (80-120 mmHg), collagen and sGAG synthesis were slightly increased by 25% and 14% at 0.5 Hz, respectively. DNA synthesis was significantly increased by 72% at 2 Hz. An experiment combining high magnitude (150-190 mmHg) and high frequency (2 Hz) demonstrated significant increases in collagen and sGAG synthesis (collagen: 74%, sGAG: 56%), but no significant changes in cell proliferation.
Shear levels ranging from 1 to 80 dyne/cm2 were studied. Scanning electron microscopy results indicated that 48 hrs exposure to shear stress did not alter the circumferential alignment of endothelial cells. Collagen synthesis was significantly enhanced at 9 and 25 dyne/cm2, but not different from static controls under other shear conditions. Leaflets denuded of the endothelium were exposed to identical shear stress and showed very different responses. Collagen synthesis was not affected at any shear levels, but sGAG content was increased at shear of 9, 25 and 40 dyne/cm2.
Further studies showed that the increases in collagen synthesis under pressure or shear stress was concurrent with a decline in the expression and activities of cathepsins L and S. This converse relationship between collagen synthesis and cathepsin activity indicated that cathepsins might be involved in valvular ECM remodeling.
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Godoy, Ruben D. „Lethal and sub-lethal effects of hydrodynamic forces on animal cell culture“. Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1206393724.
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Raya, Akhila. „Fundamental Study of the Initial Bacterial Attachment of Pseudomas aeruginosa, Pseudomas putida and Escherichia coli“. University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1258171437.
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Paraschiv, Ioana. „Shear flow stabilization of Z-pinches“. abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3264527.
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Selomulya, Cordelia Chemical Engineering & Industrial Chemistry UNSW. „The Effect of Shear on Flocculation and Floc Size/Structure“. Awarded by:University of New South Wales. Chemical Engineering and Industrial Chemistry, 2002. http://handle.unsw.edu.au/1959.4/18226.
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The effect of shear on the evolution of floc properties was investigated to analyse the flocculation mechanisms. Little fundamental attention has been given to the shear influence that often creates compact aggregates, while the floc characteristics might differ in other aggregating conditions. It is thus crucial to understand how flocs evolve to steady state, if their properties are to be 'tailored' to suit subsequent solids-liquid separation processes. In this work, flocculation of monodisperse latex particles of various sizes (60, 380, and 810 nm diameter) via electrolyte addition was carried out in a couette-flow and also in shear fields generated by an axial-flow impeller (Fluid foil A310) and a radial-flow impeller (Rushton R100) in standard mixing tanks. A small-angle light scattering technique was used to acquire information regarding the time variation of floc properties in a non-intrusive manner. The structure was quantified by a measure of fractal dimension, signifying the degree of floc compactness. Estimates of the average floc mass were also obtained from the aggregate scattering patterns. By monitoring the changes in floc structure and mass, corresponding to the size evolution; mechanisms of floc formation, fragmentation, and restructuring were identified. Aggregates of 60 and 380 nm particles were observed to grew larger initially, before decreasing to their equilibrium sizes at moderate shear rates (32 - 100 s-1) in a homogeneous shear environment. Floc restructuring at large length scales occurred extensively, and was responsible for the drop in size, particularly at the early stage of the process. Aggregates of 810 nm particles did not, however, display this behaviour. Flocs of larger primary particles were presumably susceptible to breakage rather than deformation, as they were weaker under comparable conditions. Denser aggregates were found when restructuring transpired, while comparatively tenuous flocs were observed when formation and breakage kinetics were the governing mechanisms. The disparity in floc behaviour at higher shear rates (246 s-1 - 330 s-1) was less apparent. The intense hydrodynamic stresses in those instances inevitably caused fragmentation, regardless of the intrinsic particle properties; hence the observed floc compaction was the product of break-up and re-aggregation. A population balance model, incorporating variation in floc structure, displayed comparable trends in size evolution; verifying that restructuring indeed took an important role under certain flocculation conditions. Similar phenomena were likewise observed with the flocculation in stirred tanks. The results reinforced findings in literature; that while circulation time controlled the process kinetics; the floc size was determined by the turbulent stresses. In addition, the maximum shear levels also influenced the floc structures, with denser aggregates produced in a shear field generated using the radial-flow impeller at equivalent energy dissipation per-unit mass. A correlation between non-dimensional floc factor that embodied the aggregate size and structure, and aggregation factor comprising the significant parameters from flocculation conditions, was proposed. The proposed relationship takes into account aspects such as the aggregate structure, interparticle forces, and particle concentration that are often overlooked in existing relationships, which usually only relate the maximum floc size to the applied energy dissipation rate. It thus provides an improved manner of presenting general flocculation data, as well as a means to predict floc properties produced under a specific aggregation condition. Future studies with increasingly complex systems that resemble real conditions are recommended in order to establish a practical understanding of the flocculation mechanisms, for the purpose of optimising the aggregate properties.
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Si-Ameur, Mohamed. „Simulations numériques de mélanges turbulents dans les écoulements cisaillés supersoniques“. Université Joseph Fourier (Grenoble ; 1971-2015), 1994. http://www.theses.fr/1994GRE10214.
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L'etude du melange turbulent dans des ecoulements cisailles supersoniques, couche de melange confinee entre parois et jet faiblement sous detendu, est abordee a l'aide de simulations numeriques tridimensionnelles instationnaires. Un code aux volumes finis est utilise dans cette optique. La technique de simulation des grandes echelles a ete utilisee, les effets sous-maille etant pris en compte par les proprietes de l'algorithme numerique ppm qui filtre les concentrations de vorticite a petite echelle. Cette technique nous a permis de considerer certains caracteres des ecoulements reels: prise en compte des parois, simulation explicite du developpement spatial, resolution a des echelles de l'ordre de la taille des dispositifs reels. Les effets de parois sont etudies en approximation bidimensionnelle et en situation reelle tridimensionnelle. Les resultats montrent que les calculs bidimensionnels sont peu realistes pour representer le caractere tridimensionnel de l'ecoulement. Les zones de melange sont analysees qualitativement et quantitativement. La formation de sous-couches au niveau de la zone de melange est evidente pour m#c 0. 6. Une schematisation d'un modele de melange dans une couche de melange compressible est proposee
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Hodgkinson, Richard. „The effect of extensional flow on shear viscosity“. Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/18327/.
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Shear rheology is conventionally studied under pure shearing flows, rather than more realistic mixed flows. Moving parallel surfaces and capillary rheometery are examples of the former, whilst the latter occurs whenever a flow accelerates or decelerates creating an additional component of extension, e.g. on passing through an industrial extrusion die. We postulate and gather supporting evidence that shear rheology is a function of not only shear, but both shear and extension rate, a factor with important consequences for fibre spinning and extrusion operations. The direction, as well as rate, of extensional deformation is important. A novel two-phase flow, planar extension experiment is developed and the surface coatings necessary to control the interface structure identified. Shear viscosity evolution is monitored, in-situ, under extensional flow, by optically measuring shear rates either side of a test fluid – reference fluid interface; issues due to optical refraction are critically addressed. Preliminary evidence is shown for a 1.2wt% 4x10^6 MW PEO solution that parallel (+ve) extensional flow, on the order of 11.5s-1 , causes a reduction in shear viscosity, and perpendicular (-ve) causes an increase in shear viscosity, supporting the hypothesis. A framework for a comparison experiment, with the same shear history but without extension, is presented. As part of this work, design criteria for planar hyperbolic extensional channels are critically assessed. In particular, expanding a hyperbola entrance region would maximise total Hencky strain, yet this region is almost never given rationalised consideration in literature. In this region the basis for the hyperbolic profile breaks down, and a new profiling strategy and channel form are presented, which is found to only differ significantly in this inlet region. A useful design limit of 130 degrees on channel inlet angle is identified. The new profile is compared to a hyperbolic profile through the use of CFD for wall slip flow, and a slight improvement in extension rate uniformity along the centreline found. Deviations are contrasted against assumptions made in the profiling strategy: comments are made with regards the possibility for “internal” shear to occur, and non-uniform extension rates are accordingly found to exist between streamlines in these channels despite the use of full wall slip in the simulations.
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Brown, Nicholas J. „The effect of wall waviness on shear flow instabilities“. Thesis, Imperial College London, 2007. http://hdl.handle.net/10044/1/1275.
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This thesis is concerned with the effect of wall waviness on shear flow instability, specifically for the incomprehensiblc flow in a channel. We investigate the stability of the flow in a channel with fixed wavy boundaries using two methods. Firstly the disturbance evolution is calculated using the parabolised stability equations (PSE), which apply to the flow stability at finite Reynolds number, and are solved using a finite-difference marching scheme, marching in the downstream direction. Secondly we employ the triple-deck formulation for channel flow which is valid at asymptotically high Reynolds number and the problem is solved using Floquet theory, making use of the periodic coefficients appearing in the disturbance equations. The mean flow for the PSE analysis is obtained by linearising the Navier-Stokes equations using a perturbation method, valid for small amplitude boundary waviness, Δ. We solve the linear PSE using this periodic mean flow, and it is found that increasing Δ stabilises plane Poiseuille flow near the nose of the neutral curve but has a destabilising effect on the lower branch for higher Reynolds numbers. The nonlinear PSE are used to study thc stability of 2-D finite amplitude waves, and are able to demonstrate the existence of suporcritical equilibrium amplitude solutions, as well as threshold amplitudes separating growing and decaying solutions in the subcritical regime. Wall waviness is found to have a stabilising effect on subcritical disturbances, raising the amplitude needed for instability to occur. Using Floquet theory and decomposing the disturbance equations into Fourier modes enables the high Reynolds number problem to be formulated as an eigenvalue problem. The waviness is found to be able to produce a destabilising effect in agreement with the results for the linear PSE near the lower branch. The method of multiple scales is used to study the wavy channel flow stability at high Reynolds number in the limit of small Δ, which gives an O(Δ 2) correction to the flat boundary eigenvalue, λ. When λ = ±i μ, for boundary wavenumber, μ, we find a degeneracy in the intermediate O(Δ) system of equations due to a resonance ktween a neutrally stable flat-boundary T-S wave and the boundary wave of equal wave-length. New asymptotic scalings are derived in this case to obtain a valid solution.
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Pantano-Rubino, Carlos. „Compressibility effects in turbulent nonpremixed reacting shear flows /“. Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9981965.
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Topayev, Sultan. „Taylor-Couette flow for shear-thinning fluids“. Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0301.
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On s’intéresse aux instabilités secondaires dans un écoulement de Taylor-Couette en grand entrefer pour un fluide rhéofluidifiant. Des études théorique, expérimentale et numérique ont été mises en œuvre. D’un point de vue théorique, une analyse faiblement non linéaire a été développée en régime dit TVF (Taylor Vortex Flow) pour rendre compte des premiers effets de la non linéarité de la loi de comportement sur la structure de l’écoulement. Le comportement rhéologique du fluide est décrit par le modèle de Carreau. Des effets significatifs du caractère rhéofluidifiant ont été mis en évidence : Les rouleaux de Taylor ont une taille plus petite et sont écrasés contre le cylindre intérieur. Le jet radial sortant est plus fin et beaucoup plus intense que le jet radial entrant. Par conservation de débit, la zone de jet radial entrant est plus étendue. Ces modifications sont probablement à l’origine des instabilités des rouleaux de Taylor observées expérimentalement et numériquement. Le dispositif expérimental utilisé est constitué de deux cylindres coaxiaux, où le cylindre intérieur est en rotation et le cylindre extérieur est fixe. Le rapport des rayons est "eta = 0.4" et le rapport d’aspect "L = 32". Les fluides utilisés sont des solutions de xanthane à différentes concentrations ainsi qu’une solution de glycérole, comme fluide newtonien de référence. La structure de l’écoulement est déterminée par visualisation et par mesures de vitesse par PIV 2D. Pour la solution de glycérole, après la bifurcation primaire à "Re = Re_c", le régime TVF stationnaire reste stable jusqu’à pratiquement "7 Re_c". A partir de cette dernière valeur, les rouleaux de Taylor perdent leur stabilité vis-à-vis de perturbations azimutales. Dans le cas des solutions de xanthane, les valeurs du nombre de Reynolds à partir desquelles, les rouleaux de Taylor apparaissent sont en accord avec la théorie linéaire comme dans le cas Newtonien. En augmentant le nombre de Reynolds, les rouleaux de Taylor deviennent instables, mais cette-fois-ci vis-à vis de perturbations axiales. Ces instabilités peuvent être considérées comme des instabilités d’Eckhaus généralisées. Elles se caractérisent par un processus récurrent de création et d’appariement de rouleaux. L’augmentation du nombre de sites où se produit ce processus conduit à un écoulement chaotique (turbulence de phase). Il convient de noter que plus les effets rhéofluidifiants sont importants, et plus la gamme de Re où le régime TVF est stable, est réduite. Ces résultats ont été confirmés par une simulation numérique 2D des équations de conservation instationnaires, en utilisant le solveur de FreeFem++. Le cas des fluides rhéofluidifiants avec seuil de contrainte a été entamé , en se focalisant sur le cas particulier où il existe une zone non-cisaillée attachée au cylindre extérieurThis work deals with secondary instabilities in a Taylor-Couette flow with a wide gap in the case of shear-thinning fluids. Theoretical, experimental and numerical approaches are used. From theoretical point of view, a weakly nonlinear analysis has been done to account for the nonlinear effects of constitutive law on the flow structure of the Taylor Vortex Flow (TVF) regime. The shear-thinning behavior of the fluid are characterized by the Carreau model. Significant effects of shear-thinning have been demonstrated: Taylor vortices are smaller in size and shifted toward the inner cylinder. The radial outflow jet is thinner and stronger than the radial inflow jet. This asymmetry leads to an increase of the radial inflow zone. These changes in the flow structure are probably the origin of the secondary instabilities of Taylor vortices observed experimentally and numerically. The experimental setup consist of two coaxial cylinders where the inner cylinder is rotating and the outer one is at rest. The radius ratio is "eta = 0.4" and the aspect ratio is "L = 32". The fluids used are aqueous xanthan gum solutions at different concentrations and aqueous glycerol solution as a reference Newtonian fluid. The flow structure is analyzed through the visualization and by the 2D PIV velocity measurements. For the aqueous glycerol solution, once the primary bifurcation is reached at "Re = Re_c", the stationary TVF regime remains stable up to practically "Re = 7 Re_c". From this values the Taylor vortices lose its stability with respect to azimuthal disturbances. In the case of the aqueous xanthan gum solutions the values of the Reynolds number from which the Taylor vortices appear are in agreement with a linear theory as for the case of Newtonian fluid. By increasing the Reynolds number, the Taylor vortices become unstable, but with respect to axial disturbances. There instabilities can be considered as generalized Eckhaus instabilities. They are characterized by the continuous processes of creation and merging of vortices. The increase in the number of axial positions where these processes occur leads to the chaotic flow (phase turbulence). It should be noted that the stronger shear-thinning effects, the smaller the range of stable TVF regime. These results have been confirmed by a 2D numerical simulation of unsteady conservation equations, using PDE solver Freefem++. The case of shear-thinning with a stress-yield was started as well, focusing on the particular case when the unyielded zone is attached to the outer cylinder
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Akaiwa, Michiro. „The electrorheological effect in static squeeze-flow“. Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367103.
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Khan, Konika Moushumi Chemical Sciences & Engineering Faculty of Engineering UNSW. „The effect of floc microstructure and shear on dewatering processes“. Awarded by:University of New South Wales. Chemical Sciences & Engineering, 2007. http://handle.unsw.edu.au/1959.4/40547.
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This work investigated the effect of floc microstructure (size and fractal structure) and shear forces on dewatering processes, which are crucial for environmental and economical aspects in many industries. Due to limitations inherent In experimental investigations, a numerical code using the discrete element method and including some novel force models (polymer bridging force, elastic bending moment and a modified concept of rolling friction torque) was developed to simulate the consolidation behavior of flocculated systems. The code showed good agreement with experimental results. The elastic behavior of aggregates is known to depend on the backbone structure (stress bearing structure of the aggregate). However, there is little known about backbone structure. It was found that backbone represents a fractal structure with a fractal dimension value close to 1 and increasing with increase of aggregate mass fractal dimension. The dewatering process was characterized by compressive and hindered settling behavior. The numerical study of compressive rheology with different aggregate microstructure showed that the compaction results from a reduction of the correlation length rather than increase in fractal dimension. The compressive behavior is consistent with theoretical models at higher compressive stresses but is not well described at low compressive stresses. A semi- empirical model is presented describing the compressive rheology in both regions via a correction factor derived using dimensional analysis. The hindered settling behavior was in good agreement with the theoretical model based on the assumption of self similar structure. The investigation revealed that shear effect is not due entirely to hydrodynamics and can arise from the particle bonding mechanism alone. The study showed that low shear increases compressibility but high shear is detrimental. At low shear, bond bending at local voids results in solid densification. High shear increases kinetic energy and kinetic repulsion of the particles. The effect of shear is analogous to the anomalous behavior of the water density- temperature function. At low temperature bond breakage increases the density and at high temperature thermal expansion decreases the density. The investigation showed that shear increases the permeability due to bending of the structure in the shear direction, resulting in large pores.
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Denison, Tracy Adam. „The effect of fluid shear stress on growth plate“. Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29603.
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Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Boyan, Barbara; Committee Co-Chair: Schwartz, Zvi; Committee Member: Bonewald, Lynda; Committee Member: Jo, Hanjoong; Committee Member: Sambanis, Athanassios. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Vlachos, Bill Vaseleos. „Effect of shear layer modelling on the simulated flow in a cavity“. Thesis, University of Hertfordshire, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369760.
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Rotenberry, James Michael Saffman P. G. Saffman P. G. „Effect of compliant boundaries on weakly nonlinear shear waves in channel flow /“. Diss., Pasadena, Calif. : California Institute of Technology, 1989. http://resolver.caltech.edu/CaltechETD:etd-02152007-075746.
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Soontaranun, Wit. „Effect of flow on the miscibility of partially miscible polymer blends“. Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266261.
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Canto, Maya Christian M. „Effect of Wall Shear Stress on Corrosion Inhibitor Film Performance“. Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1447954894.
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Thoumine, Olivier. „Effect of steady and pulsatile laminar shear stress on extracellular matrix and focal contact-associated proteins of endothelial cells“. Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/17079.
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Hadinata, Chitiur, und chitiurh@yahoo com au. „Flow-induced crystallization of polybutene-1 and effect of molecular parameters“. RMIT University. Civil, Environmental and Chemical Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080212.163803.
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There are two main goals of this thesis: to investigate the flow-induced crystallization behaviour of Polybutene-1 (PB-1 samples, and to study the effects of molecular parameters on the crystallization behaviour While flow-induced crystallization is not a new area in polymer research, well-defined experimental methods that allow access to high flow rate range comparable to that encountered in real processing are still lacking. Two types of flow are considered: shear and uniaxial elongational. Regarding the second aim, several molecular parameters considered are: molecular weight, molecular weight distribution, isotacticity, presence of nucleating agents, and copolymer content. For this purpose an array of PB-1 samples were used. It is found that each of these parameters can have significant effect on the crystallization behaviour. Mainly rheological methods were utilized to conduct the flow-induced crystallization experiments. Crystallization onset time is define d from the change in viscosity or other related parameters. The experiments begin with low shear rate range, to ensure that the results are comparable with literature data. In this range we encounter the quasi-quiescent onset time at very small. shear rates, which draws an interesting comparison with another physical parameter, the gel time. Beyond a critical flow rate a decrease in the onset time is seen, and a plateau-and-slope trend is evident for a curve of onset time vs. shear rate. Using a combination of three experimental methods, shear rates ranging from Q0001 - 500 s-1 are successfully achieved, and a good agreement between these methods is observed. Furthermore, a normalization procedure is introduced, which yields temperature-invariant curves for the mentioned range of shear rate. For the uniaxial elongation flow, the Elongational Viscosity Fixture (EVF) is employed, with the strain rate ranging from 0.0001 - 10 s'. A greater reduction in onset time as compared to shear (at the same shear/strain r ate) is observed, and the difference in the onset times for shear and elongation already reaches more than one decade for a flow rate of 10 5. This quantitative comparison is particularly important; since not so many data on elongation-induced crystallization are available in the literature. Finally, the thesis compares several flow induced crystallization models that can be useful as prediction tools and selects one of these models to be compared with the experimental data. A qualitative agreement is found, however, for better quantitative prediction the model still needs to be.
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Gonzales, Joaquin Uranga. „Effect of Exercise-Induced Blood Flow Patterns on Endothelial Function“. University of Toledo / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1208977525.
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Fox, Michael. „Statistical structure of plasma turbulence from BES measurements in MAST and the effect of flow shear“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:9d109810-79e7-4403-bb4c-f58b7acbd6c1.
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The suppression of turbulent transport is a key requirement for enabling nuclear fusion to become a viable energy source. One possible route to achieving this suppression is through toroidal flow shear. We investigate the effect that flow shear has on the structure of turbulence by analysing data from both measurements of the fluctuating intensity field using the Beam-Emission-Spectroscopy (BES) diagnostic on the spherical tokamak MAST, as well as from numerical simulations of the fluctuating density field in MAST. We develop a procedure to map from the correlation parameters of the intensity field to the correlation parameters of the density field. This procedure is illustrated using the MAST BES system and the validity of the underlying assumptions is tested on fluctuating density fields generated by direct numerical simulations using the gyrokinetic code GS2. By using this procedure, we demonstrate how, in experiment, the flow shear associated with the differential toroidal rotation of tokamak plasmas breaks an underlying symmetry of the turbulent fluctuations imposed by the up-down symmetry of the magnetic equilibrium. Indeed, in both experimental BES measurements and gyrokinetic simulations, this symmetry breaking in ion-scale turbulence in MAST is shown to manifest itself as a tilt of the spatial correlation function and a finite skew in the distribution of the fluctuating intensity (density) field. The tilt is a statistical expression of the "shearing" of the turbulent structures by the mean flow. The skewness of the distribution is related to the emergence of long-lived density structures in sheared, near-marginal plasma turbulence. The extent to which these effects are pronounced is argued (with the aid of the simulations) to depend on the distance from the non- linear stability threshold. Away from the threshold, the symmetry is effectively restored.
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Davis, John Matthew. „An investigation into the effect of surface-mounted circular obstructions on flow driven diffusion flames“. Cincinnati, Ohio : University of Cincinnati, 2009. http://www.ohiolink.edu/etd/view.cgi?acc_num=ucin1236291952.
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Thesis (M.S.)--University of Cincinnati, 2009.Advisors: Peter Disimile PhD (Committee Chair), Paul Orkwis PhD (Committee Member), Shaaban Abdallah PhD (Committee Member), Norman Toy PhD (Committee Member). Title from electronic thesis title page (viewed April 22, 2009). Includes abstract. Keywords: Shear Flow; Surface Mounted Obstructions; Boundary Layer; Flame Stability. Includes bibliographical references.
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Ghoma, Mohamed I. „The Effect of Wall Jet Flow on Local Scour Hole“. Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5501.
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This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study.
In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations.
The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.
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Yakhoub, Hamat Abderrahmane. „Effect of high shearing on rheological/structural properties of highly concentrated w/o emulsions /“. Thesis, [S.l. : s.n.], 2009. http://dk.cput.ac.za/cgi/viewcontent.cgi?article=1064&context=td_cput.
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Zillinger, Christian [Verfasser]. „Linear Inviscid Damping for Monotone Shear Flows, Boundary Effects and Sharp Sobolev Regularity / Christian Zillinger“. Bonn : Universitäts- und Landesbibliothek Bonn, 2015. http://d-nb.info/1077290055/34.
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Ghoma, Mohamed Ibrahem. „The effect of wall jet flow on local scour hole“. Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5501.
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This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study. In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations. The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.