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1
Trabelsi, Faouzi. "Pulsatile flow in a conical tube". Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6604.
Testo completoAbstract (sommario):
The present study of pulsatile flow in a conical tube, although fundamental in nature, may be used to determine blood flow characteristics in cannulae. For the experimental study, a transparent conical tube was connected to a mock circulation loop. Pulsatile flow was supplied by a pump ("artificial heart"), with controlled "pulse rate" and systolic time period ratio. Tests include flow visualization, pressure measurement with miniature piezo-resistive pressure transducers and velocity measurement with a two-component, frequency shifted, fibre optic, laser Doppler velocimeter. Flow visualization has revealed the formation of a high speed jet in the core of the conical tube during "diastole" as well as the appearance of separated and recirculating regions near the inclined wall. The formation of weak backflow ("regurgitation") was also observed during "systole", especially immediately upstream of the valve. Pressure variation in the tube was fairly complex, containing substantial fluctuations that are caused by the opening and closing of the valve. Measurements of the axial velocity along the centerline of the test section demonstrate an emerging downstream asymmetry of the "active" part of the velocity cycle, which is a clear indication of separation and recirculation in the conical tube. A large set of measurements have been analyzed in order to describe the detailed flow pattern during the cycle. Reverse flow took place at both the conical and the straight sections of the tube. However, in the conical section, the flow shows more unsteady and complex variation during the cycle. Also, the reverse flow near the wall region in the conical section occurred earlier in the diastolic phase, which is a clear indication of separation caused by the expansion. (Abstract shortened by UMI.)
2
Ascough, John. "Pulsatile flow in curved elastic tubes". Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/32000.
Testo completoAbstract (sommario):
Wall shear stresses are thought to have an influence on the formation of deposits of blood fats on the linings of the arteries, in atherosclerosis. Measuring velocities close to an artery wall to determine wall shears is difficult in view of the thinness of the boundary layer. Analytical solutions are limited to simple geometries and numerical analyses of three-dimensional, unsteady blood flows are expensive in terms of computational time. In the present study, finite element analyses of blood flow in models representative of the human aorta are based on two-dimensional sections in order to reduce the computational requirement.
3
Li, Hong-yu Graduate School of Biomedical Engineering Faculty of Engineering UNSW. "Mechanism studies for crossflow microfiltration with pulsatile flow". Awarded by:University of New South Wales. Graduate School of Biomedical Engineering, 1995. http://handle.unsw.edu.au/1959.4/17858.
Testo completoAbstract (sommario):
The mechanism of how pulsatile flow affects flux behaviour in crossflow micro-filtration was investigated. The effects of pulsatile flow were sub-divided into shear effects and backflushing effects. A servo-valve hydraulic piston pump was applied to generate pulsatile flows in the membrane module with particular waveforms. Four types of fluid pulsation with specific flow-rate and pressure waveforms were produced for experimental tests. Two parameters, /dVcf\dt/ maxand Pmin, were examined independently for their effect during pulsatile flow, which was estimated by comparing the cake resistance during steady flow and pulsatile flow at the same mean crossflow velocity, trans-membrane pressure and membrane resistance. Filtration tests for all the pulsatile flows with clean water confirmed that pulsatility only affects cake depositions. Without particles, no flux improvement was obtained. The results for the microfiltration of 0.5g/1 silica suspension showed that for pulsatile flows without backflushing (i.e. no negative transmembrane pressure peak), the fluid pulsation decreased cake resistance when the shear related parameter /dVcf\dt/max exceeded a critical value for each given waveform. When the instantaneous transmembrane pressure reached negative values, i.e. back-flushing occurred, the cake resistance was reduced for all pressure waves tested. Cake resistance was reduced more for more negative P min. With two of the waveforms tested, the cake resistance was almost completely eliminated. In contrast, the shear affected cake resistance reduction differently for each waveform. Comparing cake reduction results for different pulsatile waveforms, it was found that, for the square wave, the cake resistance reduction was higher for both shear and backflushing effect tests, while for the short spike waveform, the cake resistance reduction was lower. The flux waveforms were seen to follow the variations in transmembrane pressure. The flux response time was longer than the time required for the pressure changes, but was not dependent on the direction of the pressure change.
4
Moschandreou, Terry. "Heat transfer with pulsatile flow in a tube". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq21326.pdf.
Testo completo
5
Rajamohan, Divakar. "Developing Pulsatile Flow in a Deployed Coronary Stent". University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1131920589.
Testo completo
6
Bridges, Ronald Craig II. "Pulsatile flow of a chemically-reacting non-linear fluid". Texas A&M University, 2003. http://hdl.handle.net/1969.1/5892.
Testo completoAbstract (sommario):
Many complex biological systems, such as blood and polymeric materials,
can be approximated as single constituent homogeneous fluids whose properties
can change because of the chemical reactions that take place. For instance, the
viscosity of such fluids could change because of the chemical reactions and the
flow. Here, I investigate the pulsatile flow of a chemically-reacting fluid whose
viscosity depends on the concentration of a species (constituent) that is governed
by a convection-reaction-diffusion equation and the velocity gradient, which can
thicken or thin the fluid. I study the competition between the chemical reaction
and the kinematics in determining the response of the fluid.
The solutions to the equations governing the steady flow of a chemicallyreacting,
shear-thinning fluid are obtained analytically. The solution for the velocity
exhibits a parabolic-type profile reminiscent of the Newtonian fluid profile, if
the fluids are subject to the same boundary conditions. The full equations associated
with the fluid undergoing a pulsatile flow are studied numerically. A comparison
of the shear-thinning/chemical-thinning fluid to the shear-thinning/chemicalthickening
fluid using a new non-dimensional parameterâÂÂthe competition number
(CN) shows that both the shear-thinning effects and the chemical-thinning/thickening
effects play a vital role in determining the response of the fluid. For the parameter
values chosen, the effects of chemical-thinning/thickening dominate the majority
of the domain, while the effects due to shear-thinning are dominant only in a small
region near the boundary.
7
Paciocco, Michael C. "Measurements of pulsatile flow in an idealized ventricular assist device". Thesis, University of Ottawa (Canada), 2009. http://hdl.handle.net/10393/28314.
Testo completoAbstract (sommario):
Ventricular Assist Devices (VAD) are mechanical pumps connected to the human circulatory system in order to assist the left ventricle of diseased hearts in pumping blood to the body. Currently, both pulsatile and non-pulsatile VAD are used, primarily as a bridge to heart transplantation, with new generation devices under development to become alternatives to transplantation. Negative interactions between the biological components of the flow and the mechanical system, such as poor washout, recirculation, thrombosis and hemolysis need to be minimized in order to improve performance and longevity of both the device and the patient.
The present research is an experimental study of flow in a highly idealized, diaphragm-type, pulsatile-flow VAD. Its objective is to document in detail the motions of the fluid and the diaphragm so that they can be used for the validation of ongoing numerical simulations of flows in such devices, and more generally to assist in validation of computational methods involving fluid-structure interaction. Measurements of the flow field were collected using both Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV). The PIV system was used to measure the instantaneous velocity variation along each of six different planes at several different times during the cycle, whereas the two component LDV system was used to measure the time-dependent velocity at several points of interest over the entire cycle. The images recorded by the PIV system camera have also been used to determine the instantaneous shape and position of the diaphragm at different times during the cycle.
Representative and averaged PIV images showed that the inlet jet created a core vortex in the VAD that is the primary means of mixing. The development and motion of this vortex over the VAD operational cycle was documented for use in future modelling. A previously unobserved vortex was also documented. This vortex appeared in the vertical plane, beneath the inlet jet at peak injection, and moved along the path of the jet during the injection phase. It is believed that this vortex is created by the interaction of the inlet jet and the diaphragm in motion during injection and represents a region of recirculation in the flow, as well as possible flow separation. Other regions of recirculation were identified in the area directly adjacent to the outlet jet during ejection of the flow, and along the surface of the VAD directly opposite of the outlet tube just prior to the beginning of the ejection cycle. Areas of stagnant flow were also observed, particularly in the inlet and outlet tubes in periods of inactivity. The flow during ejection was localized in the region of the VAD directly adjacent to the outlet tube. The ejection has a longer period and a lower peak velocity than the injection.
The motion of the VAD diaphragm was also studied and it was found that the diaphragm deformation was influenced by the inlet jet. The diaphragm shape was nearly axisymmetric during some parts of the cycle, but highly skewed during other parts. Small-scale motions were also present in the diaphragm, and fluctuated from one cycle to another, adding to irregularities in the flow. Dimensional analysis of the flow strongly suggested that the unsteady nature of the flow was the dominant feature of the flowfield.
Recommendations for future experimental work include the addition of valves and a mock circulatory loop, as well as the use of different settings for the LDV and PIV systems for different parts of the VAD and different parts of the cycle.
8
Lieber, Baruch Barry. "Ordered and random structures in pulsatile flow through constricted tubes". Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/13011.
Testo completo
9
Moore, James E. Jr. "Steady and pulsatile flow visualization in the human abdominal aorta". Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/16351.
Testo completo
10
Lau, Anna. "Effect of pulsatile flow on liquid phase packed bed adsorption". Thesis, University of Bath, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362237.
Testo completo
11
Hume, Struan. "Pulsatile Flow in Computational Modelling of Thrombosis in Cerebral Aneurysms". Master's thesis, Faculty of Health Sciences, 2019. http://hdl.handle.net/11427/31581.
Testo completoAbstract (sommario):
Ngoepe and Ventikos have developed one of a growing number of computational models of thrombosis of cerebral aneurysms designed with consideration towards clinical use and research. Their model, amongst many others, utilizes computationally inexpensive steady flow conditions. However, pulsatile flow better characterizes blood flow in-vivo. Steady flow is an acceptable approximation of pulsatile flow from a fluid dynamics perspective, but there is no prior evidence suggesting whether it is an acceptable approximation when considering clot formation within a flowing environment. To this end a pulsatile flow model has been created in ANSYS® Fluent, and a function from Ngoepe and Ventikos’s computational model that simulates the release of thrombin, a chemical responsible for clotting activation, has been implemented. The output of this simulation is compared to the output of an otherwise identical simulation utilizing Particle-Image-Velocimetry (PIV) validated steady flow conditions, to determine whether clotting outcome of Ngoepe and Ventikos’s model, amongst others, differs with pulsatile flow This experiment revealed that the concentration of thrombin required for clotting activation is generated in nearly half the time when utilizing pulsatile flow over steady flow. Pulsatile flow creates unsteady flow patterns within the aneurysm, which create an environment where less thrombin is carried out of the aneurysm and into the regular bloodstream. This indicates that steady flow approximations for realistic clotting in computational models of thrombosis of cerebral aneurysms without strong consideration for the effects of pulsatile flow are inaccurate.
12
Dave, Parth Pranavbhai. "Numerical simulation of blood flow in arterial stenosis under steady and pulsatile flow conditions". Thesis, Wichita State University, 2011. http://hdl.handle.net/10057/3949.
Testo completoAbstract (sommario):
Cardiovascular diseases (CVDs) are among the leading causes of death in the world. In
this study, an attempt was made to model the flow dynamics of blood in abnormally narrowed
artery. Finite volume solver FLUENT was used for the analysis with the aim of understanding
the consequences of increasing the degree of stenosis using a two-equation turbulence model.
The compliant nature of the artery was neglected, and Newtonian behavior of the blood flow was
assumed for the larger arteries. Steady-flow simulations with 75% area reductions were used to
establish the validity of the current models by employing the standard and transitional variant of
the k turbulence models. Subsequently, it was found that transitional k model was
suitable for the low Reynolds number internal flows associated with the transition to turbulence,
although only a minor departure in terms of the turbulence intensity peak was observed.
Unsteady blood flow was introduced by employing a sinusoidal pulsatile waveform at the
inlet. The pulsatile nature of the blood flow was investigated in the range of the constriction ratio
from 60% to 90%, with an inlet-specified pulse. It was hypothesized that the severity of the
stenosis played a major role in the initiation of the turbulence, since no major turbulence was
reported for the 60% and 75% area reductions, while increasing the constriction ratio of 90%
significantly altered the flow dynamics and triggered the transition to turbulence much earlier
than anticipated. The outcome of current numerical efforts was expressed in terms of wall shear
stress, a hemodynamically relevant parameter.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.
13
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.
Testo completo
14
Wendling, Fabrice. "Simulation of doppler ultrasound signals for a laminar, pulsatile, nonuniform flow". Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/16875.
Testo completo
15
Holmlund, Petter. "Computational fluid dynamic simulations of pulsatile flow in stenotic vessel models". Thesis, Umeå universitet, Institutionen för fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-93007.
Testo completo
16
Leefe, Simon Edric. "Pulsatile flow testing and development of prosthetic heart valves in conduits". Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335930.
Testo completo
17
Wang, Wanxin Graduate School of Biomedical Engineering Faculty of Engineering UNSW. "Improvements to the performance of membrane systems by applying collapsible-tube-induced pulsatile flow". Awarded by:University of New South Wales. Graduate School of Biomedical Engineering, 2006. http://handle.unsw.edu.au/1959.4/24350.
Testo completoAbstract (sommario):
The major drawback of crossflow membrane filtration is that permeate flux declines with time as a result of the increase in total membrane resistance. Pulsatile flow is well known to reduce the resistance and enhance permeate flux. This study applied pulsatile flow induced by the oscillation of a collapsible tube to microfiltration and ultrafiltration, to improve filtration performance expressed as permeate flux enhancement and backflushable resistance reduction. Three membranes (ceramic tubular microfiltration, PVDF spiral-wound microfiltration and PS hollow-fibre ultrafiltration) and two media (bentonite suspension and whey solution) were used. In bentonite pulsatile microfiltration with the tubular membrane, up to 300% of permeate flux enhancement and 90% of backflushable resistance reduction were achieved. In bentonite and whey pulsatile microfiltration with the spiral-wound membrane, moderate improvements were gained: for bentonite, the highest increase in permeate flux was 51% and decrease in backflushable resistance was 45%; for whey, the highest permeate flux enhancement and backflushable resistance reduction were 36% and 38% respectively. In ultrafiltration of both media, no significant performance improvement was found. This is thought due in the one case to the relatively minute membrane pore size, and in the other to the large irreversible resistance created by whey solution. Transmural pressure at the collapsible tube downstream end indicates the tube compression and influences the pulsation vigour. Increasing the transmural pressure was an effective way to improve filtration performance. In bentonite microfiltration with the tubular membrane, increasing crossflow velocity was also effective, but increasing transmembrane pressure was not. Analysis of pulsatility parameters showed that the pulsatile flow always resulted in enhanced wall shear, and induced pore backflush always in the tubular membrane and sometimes in the HF membrane. These mechanistic findings helped to understand the filtration performance improvements. The analysis of energy consumption in bentonite microfiltration with the tubular membrane clearly demonstrated the benefit of applying the collapsible-tube-induced pulsatile flow in energy utilisation. The system specific energy could be reduced more than 70 % relative to the equivalent steady microfiltration permeate flux. For a given specific energy, the permeate flux could be increased by a factor of nearly four.
18
Molla, Md Mamun. "LES of pulsatile flow in the models of arterial stenosis and aneurysm". Thesis, University of Glasgow, 2009. http://theses.gla.ac.uk/905/.
Testo completoAbstract (sommario):
The Large Eddy Simulation (LES) technique is used to simulate the different types of Newtonian and non-Newtonian pulsatile blood flow in a constricted as well as in a dilated channel to gain insight of the transition-to-turbulent blood flow due to the arterial stenosis and aneurysm. In the stenosed model, a cosine shape stenosis is placed at the upper wall of a 3D channel which reduces the cross-sectional area, whereas the aneurysm which is also placed at the upper wall dilates the channel cross-sectional area. In LES, a top-hat spatial grid-filter is applied to the Navier-Stokes equations of motion to separate the large scale flows, which carry the majority of the energy, from the small scale known as sub-grid scale (SGS).The large scale flows are resolved fully while the unresolved SGS motions are modelled using two different dynamic models to determine the Smagorinsky constant at each time step. Initially, an additive sinusoidal pulsatile velocity profile is used at the inlet of the model stenosis to generate the unsteady oscillating flow and a comparison is made between the results obtained by the additive and non-additive pulsation. Secondly, the physiological pulsatile flow in the same model stenosis is investigated, where the physiological pulsation is generated at the inlet using the first four harmonics of the Fourier series of pressure pulse. A comparison between the LES and the coarse Direct Numerical Simulation (DNS) results is drawn and the effects of the various harmonics of pressure pulse, length and percentage of the stenosis on the flow field are examined. Transition-to-turbulent physiological flow through the model of a double stenosis and an aneurysm is also investigated. Finally, the physiological pulsatile flow in a model of single stenosis is investigated using the various non-Newtonian blood viscosity models and the results are compared with the Newtonian model. For the additive sinusoidal pulsation case the maximum ratio of the SGS to molecular viscosity is 0.709 and for the non-additive case is 0.78 while Re =2000. The shape of the post-stenotic re-circulation region is totally different between the additive and non-additive case. In the additive case the upper wall pressure drop is larger than the non-additive case. Due to the large amplitude of the oscillation, transition happens earlier and the peak turbulent kinetic energy occurs at the post-lip of the stenosis. The intensity of the turbulent kinetic energy is higher in the additive sinusoidal pulsation case than the physiological pulsation. The maximum contribution of the SGS motion to the large -scale motion is 37.4 percent for the first harmonic physiological pulsation while 97 percent contribution from the first four harmonics case for Re =2000. The centreline turbulent kinetic energy is slightly higher in the first harmonic case than the first four harmonics. For the higher area reduction of the stenosis, the stress drop at the upper wall, the maximum shear stress at the lower wall and the turbulent kinetic energy increased. The intensity of the shear stress and the turbulent kinetic energy decreased when the length of the stenosis is increased. The break frequency of the energy spectra found from -5/3 to -10/3 for the velocity fluctuations and from -5/3 to -7/3 for the pressure fluctuations. Due to the presence of the second stenosis, the stress drop, the adverse pressure gradient and the turbulent intensity of the flow enhance significantly. Inside the aneurysm a large re-circulation region exists and the flow is turbulent for a asymmetric aneurysm and maximum turbulent intensity occurs between the centre and the ending segment of the aneurysm. Owing to the effects of the non-Newtonian viscosity, the length of the post-stenotic re-circulation region increased as well as the streamwise velocity and the turbulent kinetic energy decreased.
19
Hägglund, Jesper. "Simulated cerebrospinal fluid motion due to pulsatile arterial flow : Master Thesis Project". Thesis, Umeå universitet, Institutionen för fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-182508.
Testo completoAbstract (sommario):
All organs, including the brain, need a pathway to remove neurotoxic extracellular proteins. In the brain this is called the glymphatic system. The glymphatic system works by exchanging proteins from interstitial fluids to cerebrospinal fluids. The extracellular proteins are then removed through the cerebrospinal fluid drains. The glymphatic system is believed to be driven by arterial pulsatility, cerebrospinal fluid production and respiration. Cerebrospinal fluids enters the brain alongside arteries. In this project, we investigate if a simulated pulsatile flow in a common carotid artery can drive cerebrospinal fluid flow running along the artery, using computational simulations of a linearly elastic and fluid-structure multiphysical model in COMSOL. Our simulations show that a heartbeat pulse increases the arterial radius of the common carotid artery by 6 %. Experimental data, assessed using 4D magnetic resonance imaging of a living human, show an increase of 13 %. Moreover, our results indicate that arterial displacement itself is not able to drive cerebrospinal fluid flow. Instead, it seems to create a back and forth flow that possibly could help with the protein exchange between the cerebrospinal and interstitial fluids. Overall, the results indicate that the COMSOL Multiphysics linearly elastic model is not ideal for approximations of soft non-linearly elastic solids, such as soft polydimethylsiloxane and artery walls work for stiffer materials. The long term aim is to simulate a part of the glymphatic system and the present work is a starting point to reach this goal. As the simulations in this work are simplified there are more things to test in the future. For example, using the same geometries a non-linear elastic model could be tested. The pulsatile waveform or the geometry could be made more complex. Furthermore the model could be scaled down to represent a penetrating artery in the brain instead of the common carotid artery.
20
Wang, Yuyan. "Simulation of pulsatile flow in baffled permeable channel for membrane filtration system". Thesis, University of Bath, 1993. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332793.
Testo completo
21
Nguyen, Minh Chau. "Hydrodynamic transport phenomena in suspension of microalgae : particle separation using pulsatile flow". Thesis, Université Paris Cité, 2021. http://www.theses.fr/2021UNIP7174.
Testo completoAbstract (sommario):
La séparation des particules est nécessaire dans de nombreuses applications en chimie, physique, biologie, domaines médicaux et biotechnologie. Par exemple, la récolte de biomasse, qui est l'une des étapes clés de la production de biocarburants à partir des microalgues et des cyanobactéries, est un processus complexe et coûteux (20-30 % du coût total) en raison de la petite taille et aussi de la faible différence entre la densité des micro-organismes et celle de leurs milieux de culture. Ainsi, de nouvelles techniques peu coûteuses sont nécessaires pour remplacer ou améliorer le processus de la séparation. Tandis que plusieurs méthodes passives et actives ont été proposées pour la séparation des particules en écoulement stationnaire, l'écoulement pulsé a reçu moins d'attention. Le but de cette étude est de déterminer les effets de la pulsation d'écoulement sur la séparation des particules dans un microcanal du type « double Y». Seulement l'un des deux écoulements entrants contient des particules et l'efficacité de la séparation est définie comme le rapport entre le nombre des particules s'échappant de la sortie opposée et le nombre total des particules. Les cellules mortes et motiles de Chlamydomonas reinhardtii sont respectivement utilisées comme particules passives et actives. Des expériences microfluidiques et des simulations sont réalisées pour chaque partie de l'étude et les principaux résultats sont résumés ci-dessous: Pour les particules passives: - Lorsque les écoulements entrants dans le microcanal sont stationnaires, le seul paramètre qui permet de contrôler la séparation des particules est le rapport entre les débits aux entrées. L'efficacité de la séparation augmente avec l'augmentation de ce rapport. Pour approcher l'efficacité maximale (0,5), ce rapport doit être supérieur à 20, ce qui n'est pas toujours pratique. - Lorsque les écoulements entrants sont pulsés avec un déphasage, le réglage de ce déphasage peut contrôler l'efficacité de la séparation. - Lorsque 0,5 < amplitude de pulsation < 2 et 1 s < période de pulsation < 10 s, l'efficacité de la séparation augmente avec le déphasage de sorte qu'un déphasage de 180° aboutit à une efficacité maximale. Une tendance similaire est observée pour des valeurs plus élevées de l'amplitude (comme beta = 5) uniquement si la période de pulsation est suffisamment petite. Pour les particules actives: - Les particules actives (cellules motile) n'obéissent pas au protocole de contrôle imposé par la pulsation à l'entrée du système. Comme les particules actives choisissent aléatoirement leur sortie du microcanal, l'efficacité de la séparation reste toujours proche de 0,5. Par conséquent, la pulsation de l'écoulement (seule) ne présente aucun avantage par rapport à un écoulement stationnaire pour la séparation des particules actives. - Cependant, lorsque le comportement phototactique des algues est activé, l'avantage de la pulsation devient évident. En présence d'une stimulation lumineuse, l'efficacité de la séparation augmente respectivement jusqu'à 65 % et 75 % dans les écoulements stationnaires et pulsés. Bien que nos expériences soient menées sur une algue modèle (Chlamydomonas reinhardtii), une simulation numérique a démontré que l'idée d'utiliser un écoulement pulsé peut être étendue à la séparation de toutes autres particules actives stimulées par un champ externe attractif ou répulsif. Ainsi, les applications potentielles peuvent aller au-delà de la récolte des algues pour le control et l'amélioration des processus de séparation, de sélection ou d'accumulation sans avoir besoin de composants mécaniques ou de substances chimiquesParticle separation is an important requirement in chemistry, physics, biology, medical domains and biotechnology. For instance, the conventional biomass harvesting which is one of the key steps in production of biofuels from non-feed stocks such as microalgae and cyanobacteria, is a complex and costly process (20-30% of total cost) due to the small size and low-density difference of the photosynthesis microorganisms and their growth media. Thus, novel low-cost techniques are required to substitute or improve the downstream separation process. While a variety of active and passive techniques have been proposed for the separation process in steady flows, pulsatile flow has received much less attention. The purpose of this study is to determine the effects of flow pulsation on the separation of particles in a double Y-microchannel. Only one of the two entering flows contains the particles and the separation efficiency is defined as the ratio of the particles escaping from the opposite outlet to the total number of particles. Dead and motile cells of Chlamydomonas reinhardtii are used as passive and active particles, respectively. Both experiments and simulations are carried out for each part of the study. The key results can be summarized as follows: For passive particles: - When the inlet flows are in a steady regime, the only parameter that allows controlling the particle separation/distribution is the ratio between the flow rates at the inlets. The separation efficiency increases with increasing this ratio. To approach the maximum efficiency (0.5), this ratio should be more than 20, which is not always practical. - When the inlet flows are pulsating with a phase shift, adjusting the phase shift between the inlet flows can control the separation efficiency. - When 0.5 < pulsation amplitude < 2 and 1 s < pulsation period < 10 s, the separation efficiency increases with the phase shift such that phi = 180° gives the highest efficiency. A similar trend can be observed for higher values of amplitude (like beta = 5) only if the pulsation period is small enough. For active particles: - Active particles (motile cells) do not obey the control protocol imposed at the inlet of the system. The separation efficiency remains around 0.5 implying that active particles choose their exit from the microchannel randomly. Therefore, pulsation (alone) shows no advantage for separation of the active particles compared to a steady flow. - However, when the phototactic behavior of the algae is coupled with pulsatile flow features, the advantage of pulsation becomes clear. In the presence of light stimulation, the separation efficiency increases to 65% and 75% in steady and pulsatile flows respectively. Although the experiments are conducted on the well-known model alga, Chlamydomonas reinhardtii, a simplified numerical simulation demonstrated that the idea can be extended to any other active particle stimulated by an attractive or repulsive external field. Thus, the potential applications of pulsatile flow can go beyond algae harvesting to control and improve separation, selection or accumulation processes without using any mechanical component or chemical substance
22
Mingalev, Stanislav. "Le Comportement de la bulle et des particules, l’écoulement pulsatile et le flux péristaltique". Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0361/document.
Testo completoAbstract (sommario):
Dans cette thèse on cherche à étudier le flux péristaltique des liquides dans un canal à onde de pression déterminée aux confins. Dans la plupart des recherches de systèmes de transportation péristaltiques la variation des coordonnées de la paroi est prédéfinie pour les raisons de commodité. Cependant les parois d’organes creux (comme oesophage intestin grêle, côlon urètre, vaisseaux lymphatiques) dont le fonctionnement consiste à transmettre des produits par la voie péristaltique, sont dotées de barorécepteurs – capteurs qui perçoivent la pression dans la couche limite de fluides et servent à réguler le calibre des vaisseaux. Pour créer le modèle du comportement des systèmes biologiques pareils il nous semble plus adéquat de prédéfinir l’onde de pression aux confins des vaisseaux. Cette approche réalisée dans notre thèse permet de découvrir et décrire des effets nouveaux, inexplorés auparavant. Dans cette thèse nous étudions aussi l’influence des pulsations transversales des parois du canal sur la transmission du produit dues aux chutes de pression. Cet objectif est apparu lors de la détermination de la viscosité du liquide utilisant la méthode des canaux compressibles (squeezing flow viscometry). Des problèmes similaires sont assez répandus dans l’étude d’une variété des systèmes biologiques, en particulier, des mouvements de lubrification des articulations ou des micro-vaisseaux des muscles. Nous avons aussi étudié l’influence du son sur l’interaction d’une particule solide tombante et d’une bulle de gaz montante dans le liquide. La pertinence de ce travail est liée à l’importance de recherche des solutions possibles pour augmenter l’efficacité de flottation, méthode d’enrichissement basée sur l’accrochage des particules minérales par des bulles de gazThe thesis studies the peristaltic flow of fluid in a channel with the specified pressure wave at the boundary. The law of wall’s coordinate variation isn’t determined a priori. It is found from the initially definite law of pressure-variation on the wall. This way is based on the fact that some hollow organs change diameter under the signals of baroreceptors (sensors that detects the pressure). We studied the effects of various parameters on flow rate and structure of flow. Besides we studied the influence of vibration on the peristaltic flow under long wave approximation. The paper also considers the influence of the wall transverse pulsation on the fluid transport under the pressure drop. This problem arises in defining the liquid viscosity by squeezing flow viscometry. The same problems occur in analyzing different biological systems, including the lubricant movement in joints or in the microvessels of working muscles. The influence of sound on the interaction of a solid particle and a gas bubble in fluid is studied as well
23
Nejadmalayeri, Alireza. "Numerical simulation of pulsatile blood flow across a tilting–disk mechanical heart valve". Thesis, Wichita State University, 2007. http://hdl.handle.net/10057/1526.
Testo completoAbstract (sommario):
To overcome several clinical challenges involving mechanical heart valves, accurate numerical simulation of blood flow through these devices has been of interest. Since heart disease is the leading cause of death around the world, the hemodynamic study of the heart is of extraordinary interest in the field of bio fluid dynamics. Recent numerical/experimental investigations have shown that mechanical heart valves inherit the “production of sufficiently large shear and turbulent stresses to cause clinical problems such as hemolysis.” Due to several parameters including the non-Newtonian behavior of blood, pulsatile waveform, strong blood and tissue interactions, clinical difficulties, etc., experimental examination of blood flow in the heart and its valves is a very difficult task. Therefore, comprehensive numerical analysis of this complex fluid-structure system is essential. However, precise experimental investigations are still imperative for developing appropriate and accurate turbulence models and for validating numerical techniques.In the current computational effort, the first set of objectives was numerical investigations of vortex shedding behind a two-dimensional tilting-disk mechanical heart valve in a straight channel, which is a simplified representation of the mitral position, using first- and several higher-order finite volume schemes as well as examination of the non-Newtonian viscosity effects on shedding frequency and amplitude. For the low Reynolds number (low inflow), both first- and higher-order schemes resulted in identical shedding frequencies; however, higher-order schemes improved the shedding amplitude. For pulsatile inflow, the first-order scheme was found to be in better qualitative and quantitative agreement with previous investigations. Careful scrutiny of the findings revealed that higher-order schemes implemented in the code produced too much dispersion error for applications in the present study. In addition, non-Newtonian viscosity did not affect the overall flow structure, although it caused significant shear-thinning for both types of inflow. Furthermore, numerical simulations of laminar Newtonian and non-Newtonian blood flow across 2D and 3D models of a Björk-Shiley tilting-disk mechanical heart valve in the aortic position with sinuses of valsalva (valve replacements are more common in the aortic position) under steady and physiological pulsatile inflows were performed to investigate the three dimensional effects as well as the influences of pulsatile waveform and non-Newtonian nature of blood on the overall flow structure. The results of grid and time-step independency tests as well as validation with previous investigations were satisfactory. Obvious differences of various flow parameters between 2D and 3D analyses clarified noticeable breakup of symmetry by the third dimension. Similar to the 2D case in a straight channel, it was observed that the non-Newtonian viscosity did not affect significantly the maximal velocity components and maximal vorticity magnitude, although it caused substantial shear-thinning and altered the overall flow structure, particularly during the regurgitation phase. It was found that three-dimensional effects were much smaller for the non-Newtonian viscosity model than the Newtonian model at all time levels. Indeed, the non-Newtonian behavior resulted in a “less complex vortical flow” and consequently “less probability of blood cell damage” compared to the Newtonian fluid. Since the longer the blood cells are trapped in the vortices, the more chance of hemodynamic damage, it is essential to consider the non-Newtonian behavior of blood in the analysis.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering
"July 2007."
24
Ruo, Jeanny Bin-chin. "In vitro continuous monitoring of cardiac output using ultrasound doppler in pulsatile flow". Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/10224.
Testo completo
25
Hong, Say Yenh. "Fluid structure interaction modeling of pulsatile blood flow in serial pulmonary artery stenoses". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112571.
Testo completoAbstract (sommario):
Motivated by the physiological phenomena of collapse and flow limitation for a serial pulmonary artery stenosis, we investigated the three-dimensional influence of spatial configuration on the wall motion and hemodynamic. Our numerical study focused on the effect of two geometrical parameters: the relative distance and the angular orientation between the two stenoses. The collapse of a compliant arterial stenosis may cause flow choking, which would limit the flow reserve to major vital vascular beds such as the lungs, potentially leading to a lethal ventilation-perfusion mismatch. Flow through a stenotic vessel is known to produce flow separation downstream of the throat. The eccentricity of a stenosis leads to asymmetric flow where the high velocity jets impinge on the sidewall, thereby inducing significant dissipation. The additional viscous dissipation causes a higher pressure drop for a flow through a stenotic vessel, than in a straight compliant vessel. It is likely that some particular morphology would have a higher vulnerability to the fluid induced instability of buckling (divergence), under physiological pulsatile flow. It was found that fluid pressure distribution have substantial implication for the downstream wall motion, under conditions of strong coupling between nonlinear vessel geometries, and their corresponding asymmetric flow. The three-dimensional fluid structure interaction problem is solved numerically by a finite element method based on the Arbitrary Lagrangian Eulerian formulation, a natural approach to deal with the moving interface between the flow and vessel. The findings of this investigation reveal that the closeness between stenoses is a substantial indication of wall collapse at the downstream end. Moreover, the results suggest a close link between the initial angular orientation of the distal stenosis (i.e. the constriction direction) and the subsequent wall motion at the downstream end. For cases showing evidence of preferential direction of wall motion, it was found that the constricted side underwent greater cumulative displacement than the straight side, suggestive of significant wall collapse.
26
Nejadmalayeri, Alireza Hoffmann Klaus A. "Numerical simulation of pulsatile blood flow across a tilting-disk mechanical heart valve /". Thesis, A link to full text of this thesis in SOAR, 2007. http://hdl.handle.net/10057/1526.
Testo completo
27
Bastos, Carlos Alberto da Costa. "A model for the simulation of Doppler ultrasound signals from pulsatile blood flow". Phd thesis, Instituições portuguesas -- -Universidade de Aveiro -- -Departamento de Electrónica e Telecomunicações, 1999. http://dited.bn.pt:80/6564.
Testo completoAbstract (sommario):
The Doppler ultrasonic blood flow detector estimates
non-invasively the velocity of blood in the circulatory system. It has been
extensively used in the last four decades for the detection of stenoses in the
circulation.The development of new signal processing techniques for the Doppler
signal requires test signals with known or measurable characteristics. This is
very difficult to achieve with Doppler signals obtained in vivo because of the
variability of blood flow between persons and with physiological state, for
example blood pressure. A model for generating simulated Doppler signals whose
characteristics are controllable and/or measurable is a useful tool because it
permits the test of new processing techniques under controlled conditions. It
permits also the study of the effect of various factors on the Doppler
spectrum. Usually these effects cannot be isolated with in vivo
measurements.During this work a model for the generation of simulated Doppler
ultrasound signals was developed. It comprised two sub-models one for blood
flow in the human lower limb and the other for generating simulated signals
from the blood velocity field and the instrument's characteristics.Blood flow
in the lower limb was modelled by an electric analogue for the lower limb
vascular tree. Each artery was modelled by a lossy transmission line and the
peripheral vascular beds by three-element Windkessel models. The
electric analogue circuit was implemented with the SPICE circuit simulator. To
simulate the inter-action of the blood cells with the ultrasonic field the
vessel was divided into small elemental volumes whose contributions were added
together to generate the simulated Doppler signal. The model assumed
irrotational laminar flow and some other simplifying approximations.The
characteristics of the signals generated by the model were similar to those
expected for the Doppler signal. The model was used to study the influence of
blood acceleration, sample volume size and data segment duration on the root
mean square (rms) width of the Doppler spectrum. A simple formula was derived
for estimating the Doppler rms spectral width from the individual contribution
of non-stationarity broadening, intrinsic broadening, window broadening and the
range of blood velocities passing through the sample volume.In addition closed
form expressions were derived for the Doppler power spectrum due solely to the
range of blood velocities passing through a Gaussian sample volumes placed in
irrotational laminar flow with a velocity profile obeying a simple power law.
Closed form expressions were also obtained for the root mean square spectral
width in the special case of a spherically symmetric Gaussian sample volume
placed in the centre of the vessel.O detector ultra-sónico de fluxo sanguíneo usa o efeito Doppler para estimar de forma não invasiva a velocidade do sangue na circulação. Tem sido bastante usado nas últimas quatro décadas para detectar a presença de estenoses.O desenvolvimento de novas técnicas de processamento do sinal Doppler necessita de sinais de teste cujas características sejam conhecidas ou possam ser medidas com precisão. Isto é difícil de obter com sinais Doppler medidos in vivo devido à elevada variação do fluxo sanguíneo de pessoa para pessoa e também com o estado fisiológico da pessoa no momento da medida, por exemplo a tensão arterial influencia significativamente o fluxo sanguíneo. Um modelo para gerar sinais Doppler simulados cujas características sejam controláveis e/ou mensuráveis é uma ferramenta bastante útil, pois permite que as novas técnicas de processamento do sinal Doppler sejam testadas em condições controladas. Permite, também, estudar o efeito de vários factores que afectam o espectro do sinal Doppler. Habitualmente o efeito individual dos vários factores não pode ser identificado quando são usados sinais medidos in vivo.Neste trabalho foi desenvolvido um modelo para gerar sinais Doppler ultra-sónicos simulados. O modelo contém dois sub-modelos, um para o fluxo sanguíneo nos membros inferiores de um ser humano e outro para gerar os sinais simulados a partir do campo de velocidades do sangue e das características do instrumento.O fluxo sanguíneo nos membros inferiores foi simulado com um análogo eléctrico para a rede vascular dos membros inferiores. Cada artéria foi simulada por uma linha de transmissão com perdas e as redes vasculares periféricas por um circuito Windkessel com três elementos. O circuito eléctrico foi implementado com o simulador de circuitos SPICE.Para simular a interacção entre os glóbulos vermelhos e o campo de ultra-sons o vaso sanguíneo foi dividido em pequenos volumes elementares. As contribuições dos volumes elementares foram todas somadas para gerar o sinal Doppler simulado. O modelo fez algumas aproximações como sejam, por exemplo, considerar o fluxo sanguíneo laminar e sem rotação.As características dos sinais gerados pelo modelo são bastante parecidas com as esperadas para o sinal Doppler real. O modelo desenvolvido foi usado para estudar a influência que a aceleração sanguínea, o tamanho do volume de amostragem e a duração da janela de amostragem têm na largura de banda eficaz do espectro do sinal Doppler. Foi deduzida uma fórmula que estima a largura de banda eficaz a partir das contribuições individuais do alargamento espectral devido à não estacionaridade, do alargamento espectral intrínseco, do alargamento espectral devido à duração da janela de amostragem e ainda da gama das velocidades que passam pelo volume de amostragem. Foram, ainda, deduzidas expressões em forma fechada para o espectro de potência do sinal Doppler devido unicamente à gama de velocidades que atravessam um volume de amostragem com forma Gaussiana colocado num perfil de velocidades com forma exponêncial. Foram, também, obtidas expressões para a largura de banda eficaz no caso especial do volume de amostragem Gaussiano ter simetria esférica e estar colocado no centro do vaso sanguíneo.
28
Yun, Brian Min. "Simulations of pulsatile flow through bileaflet mechanical heart valves using a suspension flow model: to assess blood damage". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/53378.
Testo completoAbstract (sommario):
Defective or diseased native valves have been replaced by bileaflet mechanical heart valves (BMHVs) for many years. However, severe complications still exist, and thus blood damage that occurs in BMHV flows must be well understood. The aim of this research is to numerically study platelet damage that occurs in BMHV flows. The numerical suspension flow method combines lattice-Boltzmann fluid modeling with the external boundary force method. This method is validated as a general suspension flow solver, and then validated against experimental BMHV flow data. Blood damage is evaluated for a physiologic adult case of BMHV flow and then for BMHVs with pediatric sizing and flow conditions. Simulations reveal intricate, small-scale BMHV flow features, and the presence of turbulence in BMHV flow. The results suggest a shift from previous evaluations of instantaneous flow to the determination of long-term flow recirculation regions when assessing thromboembolic potential. Sharp geometries that may induce these recirculation regions should be avoided in device design. Simulations for predictive assessment of pediatric sized valves show increased platelet damage values for potential pediatric valves. However, damage values do not exceed platelet activation thresholds, and highly damaged platelets are found far from the valve. Thus, the increased damage associated with resized valves is not such that pediatric valve development should be hindered. This method can also be used as a generic tool for future evaluation of novel prosthetic devices or cardiovascular flow problems.
29
Helmlinger, Gabriel. "Effect of pulsatile flow on the intracellular free calcium concentration of cultured vascular endothelial cells". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/16707.
Testo completo
30
Loth, Francis. "Velocity and wall shear measurements inside a vascular graft model under steady and pulsatile flow conditions". Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/15907.
Testo completo
31
Fatouraee, Nasser. "The role of fluid flow and mass transfer in the atherosclerosis of the human carotid artery under pulsatile flow conditions". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0020/NQ48539.pdf.
Testo completo
32
Lee, Kyung Eun. "The effect of geometrical configurations on physiological pulsatile flow in ideal and realistic vessel geometries". Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485736.
Testo completo
33
Aslan, Seda. "A Computational Fluid Dynamics Study on Bidirectional Glenn Shunt Flow with an Additional Pulsatile Flow Through a modified Blalock-Taussig Shunt". ScholarWorks@UNO, 2017. http://scholarworks.uno.edu/td/2294.
Testo completoAbstract (sommario):
The blood flow through the Bidirectional Glenn shunt (BGS) and modified Blalock-Taussig shunt (mBTS) to the pulmonary arteries (PAs) was analyzed using Computational Fluid Dynamics. This study consisted of the steady and pulsatile cases. In case one, the results of blood flow through the BGS for the Newtonian and non-Newtonian viscosity models were compared. Case two focused on having an additional pulsatile blood flow through the mBTS using the non-Newtonian Carreau viscosity model. The geometries were created based on the angiograms. In case one, boundary conditions to be specified at the inlets were obtained from the flow rate measurements via Doppler flow studies in children and young adults. The averaged velocities were obtained from these flow rates and specified as parabolic velocity profiles at the inlets. The average PA pressures were obtained from the catheterization data and specified at the branches of the PA outlets. In case two, boundary conditions at the same inlets were constant during the cardiac cycle. The pulsatile PA and aortic pressure tracings obtained from the catheterization data were specified at the outlets and mBTS inlet, respectively. A comparison is made between the first and second case results.
34
Hellström, Fredrik. "Numerical computations of the unsteady flow in turbochargers". Doctoral thesis, KTH, Strömningsfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12742.
Testo completoAbstract (sommario):
Turbocharging the internal combustion (IC) engine is a common technique to increase the power density. If turbocharging is used with the downsizing technique, the fuel consumption and pollution of green house gases can be decreased. In the turbocharger, the energy of the engine exhaust gas is extracted by expanding it through the turbine which drives the compressor by a shaft. If a turbocharged IC engine is compared with a natural aspirated engine, the turbocharged engine will be smaller, lighter and will also have a better efficiency, due to less pump losses, lower inertia of the system and less friction losses. To be able to further increase the efficiency of the IC engine, the understanding of the highly unsteady flow in turbochargers must be improved, which then can be used to increase the efficiency of the turbine and the compressor. The main objective with this thesis has been to enhance the understanding of the unsteady flow in turbocharger and to assess the sensitivity of inflow conditions on the turbocharger performance. The performance and the flow field in a radial turbocharger turbine working under both non-pulsatile and pulsatile flow conditions has been assessed by using Large Eddy Simulation (LES). To assess the effects of different operation conditions on the turbine performance, different cases have been considered with different perturbations and unsteadiness of the inflow conditions. Also different rotational speeds of the turbine wheel were considered. The results show that the turbine cannot be treated as being quasi-stationary; for example,the shaft power varies for different frequencies of the pulses for the same amplitude of mass flow. The results also show that perturbations and unsteadiness that are created in the geometry upstream of the turbine have substantial effects on the performance of the turbocharger. All this can be summarized as that perturbations and unsteadiness in the inflow conditions to the turbine affect the performance. The unsteady flow field in ported shroud compressor has also been assessed by using LES for two different operational points. For an operational point near surge, the flow field in the entire compressor stage is unsteady, where the driving mechanism is an unsteadiness created in the volute. For an operational point far away from surge, the flow field in the compressor is relatively much more steady as compared with the former case. Although the stable operational point exhibits back-flow from the ported shroud channels, which implies that the flow into the compressor wheel is disturbed due to the structures that are created in the shear layer between the bulk flow and the back-flow from the ported shroud channels.QC20100622
35
Ghalichi, Farzan. "Pulsatile laminar and turbulent blood flow simulation in large stenosed arteries and stenosed carotid artery bifurcation". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0013/NQ36272.pdf.
Testo completo
36
Bathe, Mark 1975. "A fluid-structure interaction finite element analysis of pulsatile blood flow through a compliant stenotic artery". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9842.
Testo completo
37
Patel, Karnal. "Design and development of a pulsatile axial flow blood pump as a left ventricular assist device". Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/11085.
Testo completoAbstract (sommario):
Each year all over the world, Millions of patients from infants to adults are diagnosed with heart failure. A limited number of donor hearts available for these patients results in a tremendous demand of mechanical circulatory support (MCS) system, either in the form of total artificial heart (TAH) or a ventricular assist device (VAD). Physiologically MCS are expected to provide heart; a time to rest and potential recovery by unloading the ventricle, while maintaining the adequate peripheral as well as coronary circulation. Existing ventricular assist devices (VAD) have employed either displacement type pulsatile flow pumping systems or continuous flow type centrifugal/rotodynamic pumps systems. Displacement type devices produce a pulsatile outflow, which has significant benefits on vital organ function and end organ recovery. Continuous flow devices are small and can be placed within body using minimal invasive procedures, in addition they reduces infection as well as mechanical failure related complications. Despite availability of success stories for both types of pumping systems, the selection of the either of them is an ongoing debate. This thesis aims to merge the advantages of displacement pumps (pulsatile flow) and axial-flow pumps (continuous flow) into a novel left vertical assist device (LVAD), by designing a novel minimal invasive, miniature axial-flow pump producing pulsating outflow for the patients having early heart failure and myocardial infarction as a Bridge-To-Recovery (BTR) or Bridge-To-Decision (BTD) device. The design of VAD, the experimental setup and dedicated control system were developed for the in vitro evaluation of pulsatile flow. Computational fluid dynamics (CFD) had been employed for the detail investigation of pulsatile flow. In addition, CFD was also applied to optimize the pulse generation for low haemolysis levels. Outcome of the study produces comprehensive understanding for the generation of pulsatile flow using an axial flow pump. Further, it provides the means of generating a controlled pulse that can regulate flow rate for varying heart rate within low haemolysis levels.
38
Vieira, Junior Francisco Ubaldo. "Analise do perfil hidrodinamico em diferentes modelos de bombas de roletes utilizadas em circulação extracorporea". [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/309535.
Testo completoAbstract (sommario):
Orientador: Reinaldo Wilson VieiraTese (doutorado)- Universidade Estadual de Campinas, Faculdade de Ciencias Medicas
Made available in DSpace on 2018-08-14T08:18:06Z (GMT). No. of bitstreams: 1 VieiraJunior_FranciscoUbaldo_D.pdf: 9716061 bytes, checksum: 94d31e9715d7d77c249963888ed77562 (MD5) Previous issue date: 2009
Resumo: Introdução: Dentre os equipamentos utilizados em circulação extracorpórea, as bombas de roletes têm grande importância, com modelos disponíveis de vários fabricantes. O ajuste dos roletes é um fator importante nas taxas de hemólise e o potencial hemolítico difere em cada um deles. Pesquisadores nem sempre abordam detalhes sobre os perfis do leito rígido supondo que as formas padronizadas de ajuste garantem valores iguais e comparáveis para todos os modelos de bombas de roletes. Dispomos principalmente de dois métodos para o ajuste de bombas de roletes e nenhum deles considera as características de impulsão do fluido, definida pelo perfil do leito rígido. Objetivo: O objetivo desse trabalho é analisar o perfil hidrodinâmico de três diferentes modelos de bombas de roletes comercializados no Brasil e sua influência no fluxo e refluxo. Materiais e Métodos: Foram utilizados tubos de silicone de 9,5x1,6; 9,5x2,4; 13x2,4 mm de diâmetro de dois fornecedores diferentes. Os testes foram realizados em solução fisiológica e solução análoga ao sangue. O perfil hidrodinâmico de três bombas de roletes foi realizado por medidas de velocidade de queda e calibração dinâmica. Foi investigada a variação das medidas de velocidade de queda com o tempo e testes de compressão em equipamento servo-hidráulico. Os refluxos foram visualizados em aspirador de sangue e reservatório de cardiotomia com medidas simultâneas. Resultados: Os perfis hidrodinâmicos apresentaram diferenças em suas variâncias para medidas de velocidade de queda (P<0,01) e calibração dinâmica (P<0,0001). A tensão residual nos tubos de silicone ocasionou redução nas medidas de velocidade de queda com o tempo (P<0,0002) e foram confirmadas pelos testes de compressão (P<0,0001). Conclusão: Os ajustes realizados pelos métodos de velocidade de queda e calibração dinâmica são dependentes da forma do leito rígido. Comparações envolvendo bombas de roletes devem ser feitas com cautela. A tensão residual em tubos de silicone compromete a repetitividade dos ajustes feitos pelo método de velocidade de queda.
Abstract: Introduction: Among the equipment used in cardiopulmonary bypass, roller pumps have great importance, with models available from several manufacturers. The roller adjustment is an important factor in the rates of hemolysis and the hemolytic potential differs in adjustment. Researchers do not always address details on the profiles of the raceway accepting that the forms of standardized settings ensure equal and comparable values for all models of roller pumps. There are two methods for setting roller pumps and none considers the dynamic characteristics of the fluid, defined by the profile of the raceway. Objective: The aim of this study is to analyze the hydrodynamic profile of three different models of roller pumps commercialized in Brazil and its influence on the flow and back flow. Materials and methods: We used silicone tubes of 9.5x1.6, 9.5 x2.4 and 13x2.4 mm in diameter from two different suppliers. The tests were performed in saline and solution analogous to blood. The hydrodynamic profile in three roller pumps was achieved by measurements of drop rate and dynamic calibration. The drop rate variations were investigated in silicone tubes by measurements of drop rate and the compression tests in servo-hydraulic equipment. Retrograde flows were viewed in blood aspirator and cardiotomy reservoir. Results: The hydrodynamic profiles showed differences in their variances for measurements of drop rate (P <0.01) and dynamic calibration (P <0.0001). The residual stress in the silicone tubes caused reduction in drop rate with time (P<0.0002) and were confirmed by compression tests (P <0.0001). Conclusion: The adjustments made by the methods of drop rate and dynamic calibration are dependent on the raceway profile. Comparisons involving roller pumps must be made with caution. The residual stress in the silicone tubes compromises repeatability of adjustments made by the drop rate method.
Doutorado
Pesquisa Experimental
Doutor em Cirurgia
39
Hellström, Fredrik. "Numerical computations of the unsteady flow in a radial turbine". Licentiate thesis, KTH, Mechanics, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4660.
Testo completoAbstract (sommario):
Non-pulsatile and pulsatile flow in bent pipes and radial turbine has been assessed with numerical simulations. The flow field in a single bent pipe has been computed with different turbulence modelling approaches. A comparison with measured data shows that Implicit Large Eddy Simulation (ILES) gives the best agreement in terms of mean flow quantities. All computations with the different turbulence models qualitatively capture the so called Dean vortices. The Dean vortices are a pair of counter-rotating vortices that are created in the bend, due to inertial effects in combination with a radial pressure gradient. The pulsatile flow in a double bent pipe has also been considered. In the first bend, the Dean vortices are formed and in the second bend a swirling motion is created, which will together with the Dean vortices create a complex flow field downstream of the second bend. The strength of these structures will vary with the amplitude of the axial flow. For pulsatile flow, a phase shift between the velocity and the pressure occurs and the phase shift is not constant during the pulse depending on the balance between the different terms in the Navier- Stokes equations.
The performance of a radial turbocharger turbine working under both non-pulsatile and pulsatile flow conditions has also been investigated by using ILES. To assess the effect of pulsatile inflow conditions on the turbine performance, three different cases have been considered with different frequencies and amplitude of the mass flow pulse and different rotational speeds of the turbine wheel. The results show that the turbine cannot be treated as being quasi-stationary; for example, the shaft power varies with varying frequency of the pulses for the same amplitude of mass flow. The pulsatile flow also implies that the incidence angle of the flow into the turbine wheel varies during the pulse. For the worst case, the relative incidence angle varies from approximately −80° to +60°. A phase shift between the pressure and the mass flow at the inlet and the shaft torque also occurs. This phase shift increases with increasing frequency, which affects the accuracy of the results from 1-D models based on turbine maps measured under non-pulsatile conditions.
For a turbocharger working under internal combustion engine conditions, the flow into the turbine is pulsatile and there are also unsteady secondary flow components, depending on the geometry of the exhaust manifold situated upstream of the turbine. Therefore, the effects of different perturbations at the inflow conditions on the turbine performance have been assessed. For the different cases both turbulent fluctuations and different secondary flow structures are added to the inlet velocity. The results show that a non-disturbed inlet flow gives the best performance, while an inflow condition with a certain large scale eddy in combination with turbulence has the largest negative effect on the shaft power output.
40
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.
Testo completo
41
Sadrizadeh, Sasan. "Instabilities in Pulsating Pipe Flow of Shear-Thinning and Shear-Thickening Fluids". Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-82037.
Testo completoAbstract (sommario):
In this study, we have considered the modal and non-modal stability of fluids with shear-dependent viscosity flowing in a rigid straight pipe. A second order finite-difference code is used for the simulation of pipe flow in the cylindrical coordinate system. The Carreau-Yasuda model where the rheological parameters vary in the range of 0.3 < n < 1.5 and 0.1 < λ < 100 is represents the viscosity of shear- thinning and shear thickening fluids. Variation of the periodic pulsatile forcing is obtained via the ratio Kω/Kο and set between 0.2 and 20. Zero and non-zero streamwise wavenumber have been considered separately in this study. For the axially invariant mode, energy growth maxima occur for unity azimuthal wave number, whereas for the axially non-invariant mode, maximum energy growth can be observed for azimuthal wave number of two for both Newtonian and non-Newtonian fluids. Modal and non-modal analysis for both Newtonian and non-Newtonian fluids show that the flow is asymptotically stable for any configuration and the pulsatile flow is slightly more stable than steady flow. Increasing the maximum velocity for shear-thinning fluids caused by reducing power-low index n is more evident than shear-thickening fluids. Moreover, rheological parameters of Carreau-Yasuda model have ignored the effect on the peak velocity of the oscillatory components. Increasing Reynolds number will enhance the maximum energy growth while a revers behavior is observed by increasing Womersley number.
42
Hatoum, Hoda. "Fluid Mechanics of Transcatheter Aortic Valve Replacement". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1541781379381912.
Testo completo
43
Tala, Chiragkumar D. "Numerical simulation of steady and pulsatile flow in stenosed tapered artery and abdominal aortic aneurysm using κ-ω model". Thesis, Wichita State University, 2010. http://hdl.handle.net/10057/3751.
Testo completoAbstract (sommario):
The effect of hemodynamics on cardiovascular disease (CVD) is very important since
CVD is the number one killer nationwide and around the globe. Coronary artery disease (CAD),
also called arteriosclerosis, is a common disease found in human arteries, including coronary
arteries and the common carotid artery. The abdominal aorta is also affected by atherosclerotic
aneurysm.
Formation of atherosclerosis obstructs the blood flow in arteries and changes the
hemodynamics pattern. Numerical and experimental modeling in a tapered artery using turbulent
models has been untouched so far. To investigate the cause of atherosclerosis and atherosclerotic
aneurysm, simulations were done using the finite volume method via FLUENT 6.3.26.
Wilcox’s two-equation standard κ-ω model was used for numerical simulation of a
tapered artery and abdominal aortic aneurysm. The tapered artery had a diameter reduction of 25
percent at the stenosed area. The two-equation turbulence κ-ω model was employed on a
geometry to validate the numerical results with velocity profiles of experimental results. Blood
was assumed to be Newtonian in all simulations.
The main objectives of this thesis were as follows:
1. To study the shear stress and blood streamlines of tapered artery at different Reynolds
number using the κ-ω model.
2. To simulate the pulsatile flow conditions on a tapered artery and abdominal aortic
aneurysm.
3. To predict and validate the kick-start of atherosclerosis based on hemodynamic
conditions.
4. To study the effect of turbulent viscosity on shear stress.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.
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Young, Angela Chien-hsin. "The role of Krüppel-Like factor 2 in mediating the atheroprotective functions of pulsatile laminar flow in vascular endothelium". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3319814.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed September 4, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 107-117).
45
Kalpakli, Vester Athanasia. "Vortices in turbulent curved pipe flow-rocking, rolling and pulsating motions". Doctoral thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145311.
Testo completoAbstract (sommario):
This thesis is motivated by the necessity to understand the flow structure of turbulent flows in bends encountered in many technical applications such as heat exchangers, nuclear reactors and internal combustion engines. Flows in bends are characterised by strong secondary motions in terms of counter-rotating vortices (Dean cells) set up by a centrifugal instability. Specifically the thesis deals with turbulent flows in 90° curved pipes of circular cross-section with and without an additional motion, swirling or pulsatile, superposed on the primary flow. The aim of the present thesis is to study these complex flows in detail by using time-resolved stereoscopic particle image velocimetry to obtain the three-dimensional velocity field, with complementary hot-wire anemometry and laser Doppler velocimetry measurements. In order to analyse the vortical flow field proper orthogonal decomposition (POD) is used. The so called ``swirl-switching'' is identified and it is shown that the vortices instantaneously, ``rock'' between three states, viz. a pair of symmetric vortices or a dominant clockwise or counter-clockwise Dean cell. The most energetic mode exhibits a single cell spanning the whole cross-section and ``rolling'' (counter-)clockwise in time. However, when a honeycomb is mounted at the inlet of the bend, the Dean vortices break down and there is strong indication that the ``swirl-switching'' is hindered. When a swirling motion is superimposed on the incoming flow, the Dean vortices show a tendency to merge into a single cell with increasing swirl intensity. POD analysis show vortices which closely resemble the Dean cells, indicating that these structures co-exist with the swirling motion. In highly pulsating turbulent flow at the exit of a curved pipe, the vortical pattern is diminished or even eliminated during the acceleration phase and then re-established during the deceleration. In order to investigate the effect of pulsations and curvature on the performance of a turbocharger turbine, highly pulsating turbulent flow through a sharp bend is fed into the turbine. Time-resolved pressure and mass-flow rate measurements show that the hysteresis loop in the pressure-ratio-mass-flow plane, may differ significantly between straight and curved inlets, however the mean operating point is only slightly affected.QC 20140523
46
Kvitting, John-Peder Escobar. "Quantification of cardiovascular flow and motion : aspects of regional myocardial function and flow patterns in the aortic root and the aorta /". Linköping : Univ, 2004. http://www.bibl.liu.se/liupubl/disp/disp2004/med832s.pdf.
Testo completo
47
Maurer, Éric. "Etude du rôle des étapes initiales d'adhérence des plaquettes sanguines et du flux pulsatile dans l'agrégation plaquettaire". Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAJ009/document.
Testo completoAbstract (sommario):
Lors d'une lésion vasculaire, les plaquettes adhèrent, s’activent et agrègent pour former un clou hémostatique qui stoppe le saignement. Dans un contexte pathologique, l’agrégation plaquettaire mène à la formation d’un thrombus qui peut obstruer une artère malade et entrainer des pathologies ischémiques graves. Les agents antiplaquettaires actuels, qui ciblent l’activation et l’agrégation des plaquettes, ont une efficacité reconnue, mais ont pour limites, la récurrence d'événements ischémiques et le risque hémorragique. L’objectif central de ma thèse a été d’explorer l’importance des étapes initiales d’adhérence des plaquettes aux protéines sous-endothéliales et du rôle du flux sanguin dans l’agrégation des plaquettes. J’ai pu montrer qu’un anticorps dirigé contre la GPIbβ, RAM.1, réduit la signalisation du complexe GPIb-V-IX et la formation de thrombi sans affecter l'hémostase. J’ai également mis en évidence que la fibronectine cellulaire fibrillaire est une surface thrombogène qui assure l’adhérence, l'activation, l'agrégation et l'activité pro-coagulante des plaquettes. Enfin, mes travaux indiquent que la pulsatilité du flux sanguin possède un rôle inverse sur la croissance des thrombi en conditions physiologique et pathologique. En conclusion, ce travail met en lumière l’importance des étapes initiales d’adhérence des plaquettes et de la pulsatilité du flux sanguin dans l’agrégation plaquettaireFollowing vascular injury, blood platelets adhere, become activated and aggregate to form a hemostatic plug which stops the bleeding. In a pathological context, platelet aggregation can also lead to the formation of an occlusive thrombus, responsible for lifethreatening ischemic events. Current antiplatelet drugs targeting platelet activation and aggregation, have a recognized efficacy, but also present some limitations including the recurrence of ischemic events and the risk of bleeding. The aim of my thesis was to explore the importance of the initial step of platelet adhesion to subendothelial proteins and the role of pulsatile blood flow in platelet aggregation. I provided evidence that RAM.1 an antibody directed against GPIbβ, reduces GPIb signaling and thrombus formation without affecting hemostasis. My work also showed that fibrillar cellular fibronectin is a thrombogenic surface which supports efficient adhesion, activation, aggregation and procoagulant activity of platelets. Finally, I observed that the pulsatility of the blood flow has an inverse role in the growth of thrombi in physiological and pathological settings. In conclusion, this work highlights the importance of initial stages of platelet adhesion and of the blood flow pulsatility in platelet aggregation
48
Sinatra, Francy L. "Understanding the Interaction Between Blood Flow and an Applied Magnetic Field". Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3518.
Testo completoAbstract (sommario):
Hemodynamic monitoring is extremely important in the accurate measurement of vital parameters. Current methods are highly invasive or noncontinuous, and require direct access to the patient’s skin. This study intends to explore the modulated magnetic signature of blood method (MMSB) to attain blood flow information. This method uses an applied magnetic field to magnetize the iron in the red blood cells and measures the disturbance to the field with a magnetic sensor [1]. Exploration will be done by experimentally studying in-vitro, as well as simulating in COMSOL the alteration of magnetic fields induced by the flow of a magnetic solution. It was found that the variation in magnetic field is due to a high magnetization of blood during slow flow and low magnetization during rapid flow. The understanding of this phenomenon can be used in order to create a portable, non-invasive, continuous, and accurate sensor to monitor the cardiovascular system.
49
Ashtekar, Koustubh D. "Guidewire Flow Obstruction Effect on Diagnosis of Coronary Lesion Severity: In-Vitro Experimental and Numerical Study". Cincinnati, Ohio : University of Cincinnati, 2006. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1163376181.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of Cincinnati, 2006.Advisor: Dr. Rupak K. Banerjee. Title from electronic thesis title page (viewed May 15, 2008). Includes abstract. Keywords: Coronary stenosis; guidewire; diagnosis; FFR; CFR; Steady and pulsatile flow; Pressure drop coefficient; Diffuser performance coefficient. Includes bibliographical references.
50
Gaw, Richelle Leanne. "The effect of red blood cell orientation on the electrical impedance of pulsatile blood with implications for impedance cardiography". Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/39448/1/Richelle_Gaw_Thesis.pdf.
Testo completoAbstract (sommario):
Impedance cardiography is an application of bioimpedance analysis primarily used in a research setting to determine cardiac output. It is a non invasive technique that measures the change in the impedance of the thorax which is attributed to the ejection of a volume of blood from the heart. The cardiac output is calculated from the measured impedance using the parallel conductor theory and a constant value for the resistivity of blood. However, the resistivity of blood has been shown to be velocity dependent due to changes in the orientation of red blood cells induced by changing shear forces during flow. The overall goal of this thesis was to study the effect that flow deviations have on the electrical impedance of blood, both experimentally and theoretically, and to apply the results to a clinical setting. The resistivity of stationary blood is isotropic as the red blood cells are randomly orientated due to Brownian motion. In the case of blood flowing through rigid tubes, the resistivity is anisotropic due to the biconcave discoidal shape and orientation of the cells. The generation of shear forces across the width of the tube during flow causes the cells to align with the minimal cross sectional area facing the direction of flow. This is in order to minimise the shear stress experienced by the cells. This in turn results in a larger cross sectional area of plasma and a reduction in the resistivity of the blood as the flow increases. Understanding the contribution of this effect on the thoracic impedance change is a vital step in achieving clinical acceptance of impedance cardiography. Published literature investigates the resistivity variations for constant blood flow. In this case, the shear forces are constant and the impedance remains constant during flow at a magnitude which is less than that for stationary blood. The research presented in this thesis, however, investigates the variations in resistivity of blood during pulsataile flow through rigid tubes and the relationship between impedance, velocity and acceleration. Using rigid tubes isolates the impedance change to variations associated with changes in cell orientation only. The implications of red blood cell orientation changes for clinical impedance cardiography were also explored. This was achieved through measurement and analysis of the experimental impedance of pulsatile blood flowing through rigid tubes in a mock circulatory system. A novel theoretical model including cell orientation dynamics was developed for the impedance of pulsatile blood through rigid tubes. The impedance of flowing blood was theoretically calculated using analytical methods for flow through straight tubes and the numerical Lattice Boltzmann method for flow through complex geometries such as aortic valve stenosis. The result of the analytical theoretical model was compared to the experimental impedance measurements through rigid tubes. The impedance calculated for flow through a stenosis using the Lattice Boltzmann method provides results for comparison with impedance cardiography measurements collected as part of a pilot clinical trial to assess the suitability of using bioimpedance techniques to assess the presence of aortic stenosis. The experimental and theoretical impedance of blood was shown to inversely follow the blood velocity during pulsatile flow with a correlation of -0.72 and -0.74 respectively. The results for both the experimental and theoretical investigations demonstrate that the acceleration of the blood is an important factor in determining the impedance, in addition to the velocity. During acceleration, the relationship between impedance and velocity is linear (r2 = 0.98, experimental and r2 = 0.94, theoretical). The relationship between the impedance and velocity during the deceleration phase is characterised by a time decay constant, ô , ranging from 10 to 50 s. The high level of agreement between the experimental and theoretically modelled impedance demonstrates the accuracy of the model developed here. An increase in the haematocrit of the blood resulted in an increase in the magnitude of the impedance change due to changes in the orientation of red blood cells. The time decay constant was shown to decrease linearly with the haematocrit for both experimental and theoretical results, although the slope of this decrease was larger in the experimental case. The radius of the tube influences the experimental and theoretical impedance given the same velocity of flow. However, when the velocity was divided by the radius of the tube (labelled the reduced average velocity) the impedance response was the same for two experimental tubes with equivalent reduced average velocity but with different radii. The temperature of the blood was also shown to affect the impedance with the impedance decreasing as the temperature increased. These results are the first published for the impedance of pulsatile blood. The experimental impedance change measured orthogonal to the direction of flow is in the opposite direction to that measured in the direction of flow. These results indicate that the impedance of blood flowing through rigid cylindrical tubes is axisymmetric along the radius. This has not previously been verified experimentally. Time frequency analysis of the experimental results demonstrated that the measured impedance contains the same frequency components occuring at the same time point in the cycle as the velocity signal contains. This suggests that the impedance contains many of the fluctuations of the velocity signal. Application of a theoretical steady flow model to pulsatile flow presented here has verified that the steady flow model is not adequate in calculating the impedance of pulsatile blood flow. The success of the new theoretical model over the steady flow model demonstrates that the velocity profile is important in determining the impedance of pulsatile blood. The clinical application of the impedance of blood flow through a stenosis was theoretically modelled using the Lattice Boltzman method (LBM) for fluid flow through complex geometeries. The impedance of blood exiting a narrow orifice was calculated for varying degrees of stenosis. Clincial impedance cardiography measurements were also recorded for both aortic valvular stenosis patients (n = 4) and control subjects (n = 4) with structurally normal hearts. This pilot trial was used to corroborate the results of the LBM. Results from both investigations showed that the decay time constant for impedance has potential in the assessment of aortic valve stenosis. In the theoretically modelled case (LBM results), the decay time constant increased with an increase in the degree of stenosis. The clinical results also showed a statistically significant difference in time decay constant between control and test subjects (P = 0.03). The time decay constant calculated for test subjects (ô = 180 - 250 s) is consistently larger than that determined for control subjects (ô = 50 - 130 s). This difference is thought to be due to difference in the orientation response of the cells as blood flows through the stenosis. Such a non-invasive technique using the time decay constant for screening of aortic stenosis provides additional information to that currently given by impedance cardiography techniques and improves the value of the device to practitioners. However, the results still need to be verified in a larger study. While impedance cardiography has not been widely adopted clinically, it is research such as this that will enable future acceptance of the method.