Academic literature on the topic 'Wall shear rates'
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Journal articles on the topic "Wall shear rates"
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Duncan, D. D., C. B. Bargeron, S. E. Borchardt, O. J. Deters, S. A. Gearhart, F. F. Mark, and M. H. Friedman. "The Effect of Compliance on Wall Shear in Casts of a Human Aortic Bifurcation." Journal of Biomechanical Engineering 112, no. 2 (May 1, 1990): 183–88. http://dx.doi.org/10.1115/1.2891170.
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Rigid and compliant casts of a human aortic bifurcation were subjected to physiologically realistic pulsatile fluid flows. At a number of sites near the wall in the approximate median plane of the bifurcation of these models, fluid velocity was measured with a laser Doppler velocimeter, and wall motion (in the case of the compliant cast) was determined with a Reticon linescan camera. The velocity and wall motion data were combined to estimate the instantaneous shear rates at the cast wall. Analysis showed that at the outer walls the cast compliance reduced shear rates, while at the walls of the flow divider the shear rate was increased.
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Deters, O. J., C. B. Bargeron, F. F. Mark, and M. H. Friedman. "Measurement of Wall Motion and Wall Shear in a Compliant Arterial Cast." Journal of Biomechanical Engineering 108, no. 4 (November 1, 1986): 355–58. http://dx.doi.org/10.1115/1.3138628.
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Initial measurements of the time-varying wall shear rate at two sites in a compliant cast of a human aortic bifurcation are presented. The shear rates were derived from flow velocities measured by laser Doppler velocimetry (LDV) near the moving walls of the cast. To derive these shear rate values, the distance from the velocimeter sampling volume to the cast wall must be known. The time variation of this distance was obtained from LDV measurements of the velocity of the wall itself.
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Stel, HV, KS Sakariassen, PG de Groot, JA van Mourik, and JJ Sixma. "Von Willebrand factor in the vessel wall mediates platelet adherence." Blood 65, no. 1 (January 1, 1985): 85–90. http://dx.doi.org/10.1182/blood.v65.1.85.85.
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Abstract A monoclonal antibody directed against the von Willebrand factor moiety (vWF) of factor VIII-von Willebrand factor (FVIII-vWF), which blocks ristocetin-induced platelet aggregation as well as the binding of FVIII- vWF to platelets in the presence of ristocetin, inhibited platelet adherence to human artery subendothelium when present in normal flowing blood. This monoclonal antibody, CLB-RAg 35, inhibited platelet adherence as a function of the shear rate. At wall shear rates below 500 s-1, platelet adherence was not affected, but at higher shear rates platelet adherence was gradually inhibited, reaching an average of 11% of the normal value at 2,500 s-1. Indirect immunofluorescence established the reactivity of CLB-RAg 35 with vWF present in artery subendothelium. Pretreatment of normal vessel walls with this antibody inhibited adherence of platelets in blood from a patient with severe homozygous von Willebrand's disease and in blood from normal individuals. The inhibition was shear-rate dependent and significant at high shear rates (2,500 s-1). By adding increasing amounts of purified FVIII-vWF to normal blood, the inhibition was gradually overcome. These data indicate that vWF present in the vessel wall contributes appreciably to platelet adherence. At high wall shear rates, platelet adherence is mediated virtually completely by both plasma FVIII-vWF and vWF in the vessel wall. At low wall shear rates (below 500 s-1), platelet adherence occurs independent of FVIII-vWF in plasma and vWF in the vessel wall.
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Stel, HV, KS Sakariassen, PG de Groot, JA van Mourik, and JJ Sixma. "Von Willebrand factor in the vessel wall mediates platelet adherence." Blood 65, no. 1 (January 1, 1985): 85–90. http://dx.doi.org/10.1182/blood.v65.1.85.bloodjournal65185.
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A monoclonal antibody directed against the von Willebrand factor moiety (vWF) of factor VIII-von Willebrand factor (FVIII-vWF), which blocks ristocetin-induced platelet aggregation as well as the binding of FVIII- vWF to platelets in the presence of ristocetin, inhibited platelet adherence to human artery subendothelium when present in normal flowing blood. This monoclonal antibody, CLB-RAg 35, inhibited platelet adherence as a function of the shear rate. At wall shear rates below 500 s-1, platelet adherence was not affected, but at higher shear rates platelet adherence was gradually inhibited, reaching an average of 11% of the normal value at 2,500 s-1. Indirect immunofluorescence established the reactivity of CLB-RAg 35 with vWF present in artery subendothelium. Pretreatment of normal vessel walls with this antibody inhibited adherence of platelets in blood from a patient with severe homozygous von Willebrand's disease and in blood from normal individuals. The inhibition was shear-rate dependent and significant at high shear rates (2,500 s-1). By adding increasing amounts of purified FVIII-vWF to normal blood, the inhibition was gradually overcome. These data indicate that vWF present in the vessel wall contributes appreciably to platelet adherence. At high wall shear rates, platelet adherence is mediated virtually completely by both plasma FVIII-vWF and vWF in the vessel wall. At low wall shear rates (below 500 s-1), platelet adherence occurs independent of FVIII-vWF in plasma and vWF in the vessel wall.
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Fatemi, Ray S., and Stanley E. Rittgers. "Derivation of Shear Rates From Near-Wall LDA Measurements Under Steady and Pulsatile Flow Conditions." Journal of Biomechanical Engineering 116, no. 3 (August 1, 1994): 361–68. http://dx.doi.org/10.1115/1.2895743.
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Atherosclerosis, thrombosis, and intimal hyperplasia are major forms of cardiovascular diseases in the United States. Previous studies indicate a significant correlation between hemodynamics, in particular, wall shear rate, and pathology of the arterial walls. While results of these studies implicate morphologic and functional changes related to wall shear rate magnitude, a standard technique for wall shear rate measurement has not been established. In this study, theoretical and in-vitro experimental fully developed steady and physiologic pulsatile flow waveforms have been used to obtain velocity profiles in the near-wall region. The estimated wall shear rates from these results are compared to the theoretical value to assess the accuracy of the approximating technique. Experimentally obtained results from LDA suggest that in order to minimize the error in velocity data, and subsequently, the wall shear rate, the first measured velocity has to be 500 μm away from the wall. While a linear approximation did not produce errors larger than 16.4 percent at peak systole, these errors substantially increased as the velocity magnitudes decreased during late systole and diastole. Overall, a third degree polynomial curve fit using four points produced the most accurate estimation of wall shear rate through out the cardiac cycle. Results of higher degree curve-fitting functions can be unpredictable due to potential oscillations of the function near the wall. Hence, based on the results of this study, use of a linear approximation is not recommended; a third degree curve-fitting polynomial, using four points provided the most accurate approximation for these flow waveforms.
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Wang, Shixin, Haiqing Liu, Yue Wang, Yizhi Qiao, Liang Wang, Jie Bai, Tim K. T. Tse, Cruz Y. Li, and Yunfei Fu. "Experimental Study on the Seismic Performance of Shear Walls with Different Coal Gangue Replacement Rates." Applied Sciences 12, no. 20 (October 20, 2022): 10622. http://dx.doi.org/10.3390/app122010622.
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To replace conventional concrete with coal gangue concrete in the construction industry, lateral cyclic loading tests were applied to three shear walls with different coal gangue replacement rates in this study, in which the replacement rate of coal gangue was 0%, 50%, and 100%. The load‒displacement hysteretic curves and backbone curves of the shear walls obtained from tests were analyzed to compare the failure process and seismic performance of each shear wall. The results indicate that the stress performance and failure morphology of coal gangue concrete shear walls and conventional concrete shear walls are extremely similar, and the characteristics of the hysteretic and backbone curves are approximately the same. With the increase in the coal gangue replacement rate, the bearing capacity and ductility of the three shear walls gradually decrease, the strength degradation gradually becomes significant, and the energy dissipation capacity becomes worse, but the difference is not obvious, and all of them can meet the requirements of seismic performance. In addition, with the increase in the coal gangue replacement rate, the stiffness degradation gradually slows, so it is feasible to construct a shear wall using coal gangue concrete instead of conventional concrete.
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Ben Driss, A., J. Benessiano, P. Poitevin, B. I. Levy, and J. B. Michel. "Arterial expansive remodeling induced by high flow rates." American Journal of Physiology-Heart and Circulatory Physiology 272, no. 2 (February 1, 1997): H851—H858. http://dx.doi.org/10.1152/ajpheart.1997.272.2.h851.
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The effects of chronic increase in aortic blood flow on arterial wall remodeling were investigated in vivo with the use of an aortocaval fistula (ACF) model in rats. Phasic hemodynamics and aortic wall structure upstream and downstream in 30 male Wistar rats with ACF and 30 sham-operated rats were compared immediately and 2 mo after the ACF was opened in anesthetized rats. Opening the ACF upstream acutely decreased aortic pressure (-30%, P < 0.001) and increased aortic blood velocity (x12, P < 0.001), blood flow (x9, P < 0.001), wall shear stress (x10, P < 0.001) and guanosine 3',5'-cyclic monophosphate (cGMP) wall content (+50%, P < 0.01). After 2 mo, aortic pressure decreased (-22%, P < 0.001) and aortic blood velocity, diameter, and blood flow increased (+114%, P < 0.001; +60%, P < 0.001; and +250%, P < 0.001; respectively) compared with the control group. Aortic wall shear stress and cGMP wall content dropped over time and tended to recover control values; aortic wall tensile stress was higher than in the control group (P < 0.05). Medial cross-sectional area and elastin and collagen contents increased (+38%, P < 0.01; +50%, P < 0.01; and +30%, P < 0.05, respectively) and were associated with smooth muscle cell hypertrophy) (+23%, P < 0.05), despite a decrease in arterial wall thickness (-13%, P < 0.01). Opening the ACF downstream acutely decreased aortic pressure (-30%, P < 0.001) without any change in aortic blood velocity, diameter, blood flow, shear stress, and cGMP wall content. After 2 mo, pressure, blood velocity, shear stress, and cGMP wall content decreased (-22%, P < 0.001; -31%, P < 0.01; -46%, P < 0.02; and -50%, P < 0.05; respectively) and diameter and blood flow were unchanged; smooth muscle cell hypertrophy and hypoplasia were the only observed changes in the aortic wall structure. These results suggest that both shear and tensile stresses are involved in the aortic wall remodeling. Increase in shear stress likely induces expansive remodeling in relation to flow-dependent vasodilation, whereas increase in tensile stress is responsible for medial hypertrophy and fibrosis.
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Bao, Quan, Xin Meng, Mingcheng Hu, Jian Xing, Dan Jin, He Liu, Jie Jiang, and Yanwei Yin. "Simulation analysis of aneurysm embolization surgery: Hemorheology of aneurysms with different embolization rates (CTA)." Bio-Medical Materials and Engineering 32, no. 5 (September 3, 2021): 295–308. http://dx.doi.org/10.3233/bme-211225.
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BACKGROUND: Embolization degree acts as an important factor affecting recurrence of aneurysm. OBJECTIVE: To analyze the role of hemodynamics parameters of different degrees of embolization in the occurrence, development and post-treatment of aneurysms, and to determine the specific factors causing the occurrence and recurrence of aneurysms after hemodynamics treatment. Our study provides a theoretical basis for the prevention and treatment of aneurysms. METHODS: Computed tomography angiography data of a patient with cerebral aneurysm was used to model 0%, 24%, 52%, 84% and 100% of endovascular embolization, respectively. The time average wall shear stress, time average wall shear stress, oscillatory shear index, hemodynamics formation index and relative retentive time were used to analyze the changes of hemodynamics indexes in different embolic models. RESULTS: With the increase of embolic rate, the values of time average wall shear stress, time average wall shear stress grade and aneurysm index formation gradually increased, and the values of relative retention time gradually decreased. Oscillatory shear index was higher in patients with incomplete embolization and decreased in patients with complete embolization. CONCLUSIONS: As the degree of embolization increased, the blood flow tended to stabilize, reducing the risk of cerebral aneurysm rupture, and finding that the wall of the vessel junction was susceptible to injury.
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McNally, Andrew, A. George Akingba, and Philippe Sucosky. "Effect of arteriovenous graft flow rate on vascular access hemodynamics in a novel modular anastomotic valve device." Journal of Vascular Access 19, no. 5 (March 1, 2018): 446–54. http://dx.doi.org/10.1177/1129729818758229.
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Purpose: Perturbed vascular access hemodynamics is considered a potential driver of intimal hyperplasia, the leading cause of vascular access failure. To improve vascular access patency, a modular anastomotic valve device has been designed to normalize venous flow between hemodialysis periods while providing normal vascular access during hemodialysis. The objective of this study was to quantify the effects of arteriovenous graft flow rate on modular anastomotic valve device vascular access hemodynamics under realistic hemodialysis conditions. Methods: Modular anastomotic valve device inlet and outlet flow conditions and velocity profiles were measured by ultrasound Doppler in a vascular access flow loop replicating arteriovenous graft flow rates of 800, 1000, and 1500 mL/min. Fluid–structure interaction simulations were performed to identify low wall shear stress regions on the vein wall and to characterize them in terms of temporal shear magnitude, oscillatory shear index, and relative residence time. The model was validated with respect to the Doppler measurements. Results: The low wall shear stress region generated downstream of the anastomosis under low and moderate arteriovenous graft flow rates was eliminated under the highest arteriovenous graft flow rate. Increase in arteriovenous graft flow rate from 800 to 1500 mL/min resulted in a substantial increase in wall shear stress magnitude (27-fold increase in temporal shear magnitude), the elimination of wall shear stress bidirectionality (0.20-point reduction in oscillatory shear index), and a reduction in flow stagnation (98% decrease in relative residence time). While the results suggest the ability of high arteriovenous graft flow rates to protect the venous wall from intimal hyperplasia–prone hemodynamics, they indicate their adverse impact on the degree of venous hemodynamic abnormality.
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Colace, Thomas Vincent, and Scott L. Diamond. "Direct Observation of Von Willebrand Factor Elongation and Fiber Formation On Collagen During Acute Whole Blood Exposure to Pathological Flow." Blood 120, no. 21 (November 16, 2012): 1070. http://dx.doi.org/10.1182/blood.v120.21.1070.1070.
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Abstract Abstract 1070 Under conditions of pathological shear rate, von Willebrand Factor (vWF) undergoes conformational changes and self aggregation. We sought to visualize this phenomenon using a novel microfluidic model of stenosis and understand its role in thrombus formation in elevated shear rate environments. In severe stenosis, vWF experiences millisecond exposures to pathological wall shear rates (gw). Distinct from shear experiments that last many seconds, we deployed microfluidic devices for single-pass perfusion of whole blood or platelet free plasma (PFP) over fibrillar type 1 collagen (< 50 msec transit time) at pathological gw or spatial wall shear rate gradient (grad gw). Using fluorescent anti-vWF, long thick vWF fibers (>20 mm) bound to collagen were visualized at constant gw > 30,000 s−1 during perfusion of PFP, a process enhanced by EDTA. Rapid acceleration or deceleration of EDTA-PFP at grad gw = ± 5.5 × 105 to 4.3 × 107 s−1/cm did not promote vWF deposition when gw < 30,000. At 19,400 s−1, EDTA-blood perfusion resulted in rolling vWF-platelet nets, while blood perfusion (normal Ca2+) generated large vWF/platelet deposits that repeatedly embolized and were blocked by anti-GP1b or the aIIbβ3 inhibitor GR144053 and did not require shear gradients. Blood perfusion at venous shear rate (200 s−1) produced a stable platelet deposit that was a substrate for massive but unstable vWF-platelet aggregates when flow was increased to 7800 s−1. Supported by collagen and enhanced by platelet GP1b and aIIbβ3, vWF fiber formation occurred during acute exposures to pathological gw but did not require wall shear rate gradients. Figure 1 A, Platelet free citrated-plasma was treated with 1 μg/mL fluorescently labeled anti-vWF and 5 mM EDTA. The plasma samples were perfused over a collagen type 1 surface at local wall shear rates of 30,000, 62,400 and 125,000 s−1 from left to right. Long fibers of vWF (>20 μm) appeared at shear rates above ∼30,000 s−1, with more fibers appearing at higher shear rates. The bar indicates 15 μm. Figure 1. A, Platelet free citrated-plasma was treated with 1 μg/mL fluorescently labeled anti-vWF and 5 mM EDTA. The plasma samples were perfused over a collagen type 1 surface at local wall shear rates of 30,000, 62,400 and 125,000 s−1 from left to right. Long fibers of vWF (>20 μm) appeared at shear rates above ∼30,000 s−1, with more fibers appearing at higher shear rates. The bar indicates 15 μm. Disclosures: No relevant conflicts of interest to declare.
Dissertations / Theses on the topic "Wall shear rates"
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Köhler, Uwe. "3D phase contrast MRI : velocity-field visualisation and wall shear rate calculation in major arteries." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/22384.
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Approximately half of all deaths in the developed world arise from cardiovascular disease, primarily caused by the deposition of atheroma within major arteries. It has been observed that atheroma is deposited preferentially in regions along the outer wall of bifurcations, and along the distal part of the inner wall of bends. These are regions associated with disturbances of the blood flow that display abnormal shear rate (spatial velocity gradient at the vessel wall). Thus, in order to facilitate clinical diagnoses, it is important to visualise the structure and haemodynamic properties of arteries and veins. Magnetic resonance imaging (MRI) is well suited for volume imaging and can be made sensitive to flow. Quantitative velocity measurements are possible using phase contrast (PC) MRI. The aim of this project was the provision of a method that provides information on wall shear rate vectors using MRI. To handle the large number of images acquired in PC MRI automated flow detection algorithms were developed. Three different algorithms were identified: one operating on magnitude MRI images only and two methods which additionally use the velocity information generated from in-vivo and in-vitro acquisitions. These algorithms are based on an edge detection method and were tested on phantoms. The post processing steps necessary to calculate wall shear stress involved the fit of smooth functions to the velocity data, the detection of walls and the calculation of the wall shear rate vector based on that information. Fitting a smooth function removed residual noise and allowed the calculation of spatial derivatives. The velocity data was satisfactorily described by a segmented fifth order polynomial fit. One method of vessel wall reconstruction was based on the fitted velocity field, while another one utilised the detected flow regions. Using the surface position and normals, the wall shear rate was calculated from the shear stress tensor. All post-processing steps were integrated in a purpose built program that enabled graphical user interactions. The calculated wall shear rate values were quantitatively verified with experiments on various phantoms and simulations, and qualitatively compared with computational fluid dynamics calculations. It is shown that a method to calculate reliably wall shear rate directly from time averaged PC MRI acquisitions has been established.
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Blake, James R. "On the assessment of blood velocity and wall shear rate in arteries with Doppler ultrasound : a validation study." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/4195.
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Cardiovascular disease, mostly atherosclerosis, is responsible for one third of all deaths globally, rising to more than 50% in the Western World. Risk factors include smoking, diet, and familial history. Doppler ultrasound can provide estimates of blood velocity and wall shear rate. Clinically, maximum velocity is used to categorise patients for surgery, although Doppler velocity measurement is prone to errors and in need of validation. Wall shear stress—which can be derived from wall shear rate—plays a role in disease initiation and progression, although its clinical utility is unclear due to difficulties associated with its measurement. This thesis investigates the use of Doppler ultrasound as a tool to estimate blood velocity and wall shear rate. A simplified method for estimation of wall shear rate in healthy arteries is developed that uses spectral Doppler ultrasound. This method is based upon the theory of oscillatory flow in rigid pipes, requiring two measurements that are readily available with clinical ultrasound machines. This method is compared to a similar method based on colour flow imaging. The spectral Doppler method underestimated the theoretic value of wall shear rate by between 7 and 22%, with results varying between phantoms. Errors for the colour method were on average 35% greater. Test measurements from one healthy volunteer demonstrated that this method can be applied in-vivo. In more advanced stages of disease, peak velocity distal to a stenosis is of clinical interest and the simplified method for wall shear rate estimation is invalid. Steady flow in a series of simplified stenosis geometries was studied using a dual-beam Doppler system to obtain velocity vectors. These measurements were compared with data from an equivalent system that used particle image velocimetry (PIV) and was considered the gold standard. For Reynolds numbers at the stenosis throat of less than 800, flow remained laminar over the region studied, although distal flow separation did occur. For higher throat Reynolds numbers—corresponding to more severe stenoses or increased flow rates—asymmetric recirculation regions developed; the transition to turbulence occurred more proximally, with a corresponding reduction in stenotic jet and recirculation length. Qualitative agreement was observed in the velocity profile shapes measured using ultrasound and PIV at throat Reynolds numbers less than 800. Above this threshold the qualitative agreement between the velocity profiles became poorer as both downstream distance and the degree of stenosis increased. Peak axial velocity distal to the stenosis was underestimated, on average, by 15% in the ultrasound system. Estimation of shear rate remained difficult with both experimental techniques. Under a Newtonian approximation, the normalised wall shear stresses agree qualitatively. Under pulsatile flow conditions using an idealised flow waveform, superior qualitative agreement was observed in the velocity profiles at diastole than at systole. Similar to the steady flow behaviour, this agreement deteriorated with stenosis severity. The current generation of clinical ultrasound machines are capable of estimating the wall shear rate in healthy arteries. In the presence of significant arterial disease, errors in the peak velocity may result in mis-selection of patients for surgery, while estimation of the wall shear stress remains extremely problematic; particularly with identifying the wall location and measuring velocities close to the wall.
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Gliah, Omemah Rajab. "In Vitro Investigation of Cell-Free Layer Formation in Microchannels: Dependency on the Red Blood Cell Aggregation and Field of Shear." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37211.
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Red blood cells (RBCs) form approximately 40 to 45% of the human blood volume, and their behaviour and characteristics are the main determinant of blood properties, such as viscosity. RBCs are deformable species and stack together under low shear rate to form aggregates or rouleaux. Flowing RBCs migrate away from the wall leaving a cell-depleted layer known as the cell-free layer (CFL). This layer contributes to the blood viscosity and exchange between the RBCs and the target cells: a thinner CFL enhances the exchange process by reducing the diffusion distance. The formation of this CFL, however, is not yet completely understood.
The goal of this study is to improve the understanding of the formation of the CFL in the micro-flow. This was accomplished by studying the effects of changing both the flow rate and the microchannel geometry on blood flow in microchannels.
In this work, 10% hematocrit human blood suspensions were prepared in native plasma and flowed through poly-dimethylsiloxane (PDMS) microchannels of 100 μm x 34 μm cross-section. Investigation of the flowing cells was performed by using micro particle image velocimetry (μPIV) coupled with a high-speed camera. First, the high-speed camera images were processed with customized Matlab programs to detect and measure the CFL thickness and the RBC aggregates sizes. Second, the blood flow velocity profiles were measured using μPIV in order to determine the actual flow rate, the RBCs’ centerline velocity, and the shear rate.
The results showed that the increase in both flow rate and shear rate significantly reduced the CFL thickness and RBC aggregates size. Comparison of the upstream and downstream measurements in the bifurcating microchannel showed that the change in microchannel geometry did not significantly influence CFL thickness and RBC aggregate size, while within the daughter branches, RBCs tended to flow close to the inner wall resulting in an undetectable CFL at the inner wall and in a larger CFL at the outer wall of the branch. These in vitro results quantitatively relate CFL thickness and RBC aggregate size at different shear rates. The findings are of immediate interest regarding the understanding of microcirculation and improved designs of microchips.
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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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Prado, Cibele Maria. "Estiramento ou fluxo turbilhonar e baixa tensão de cisalhamento influem diferentemente no remodelamento aórtico em ratos." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/17/17143/tde-15012007-141715/.
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O presente estudo foi realizado para investigar a relação entre forças hemodinâmicas locais e remodelamento intimal e medial nos segmentos pré-estenose e pós-estenose da parede da aorta abdominal de ratos submetidos à estenose acentuada. Foram utilizados ratos Wistar machos divididos em dois grupos: sham-operado, grupo controle em que a aorta foi apenas manipulada, e grupo estenosado, animais submetidos à cirurgia de estenose da aorta abdominal. As aortas demonstraram duas respostas remodeladoras distintas e diferentes ao estímulo hemodinâmico induzido pela coarctação infra-diafragmática. A primeira é o remodelamento no segmento pré-estenótico hipertensivo com tensão circunferencial da parede aumentada associada com estresse tensional normal, fluxo laminar e tensão de cisalhamento normal. As células endoteliais eram heterogêneas, aumentadas em tamanho e alongadas em direção ao fluxo. Além disso, observou-se conspícuas placas neointimais difusamente distribuídas e espessamento medial. Nossos achados sugerem que a tensão circunferencial da parede aumentada devido a hipertensão tem papel fundamental no remodelamento desse segmento através de efeitos biomecânicos sobre o estresse oxidativo e expressão aumentada de TGF-?. A segunda é o remodelamento no segmento pós-estenótico normotenso com fluxo turbilhonar e baixa tensão de cisalhamento na parede associados a tensão circunferencial da parede e estresse tensional normais. As células endoteliais apresentavam-se semelhantes aos controles, exceto por alterações fenotípicas focais associadas à presença de conspícuas placas neointimais focalmente distribuídas, similares mas muito maiores que as encontradas no segmento pré-estenose. Mais estudos são necessários para se determinar como as forças mecânicas do fluxo turbilhonar e da baixa tensão de cisalhamento na parede são detectadas e traduzidas em sinais bioquímicos para as células e convertidas em alterações fenotípicas patofisiologicamente relevantes.The present investigation was carried out to evaluate the relationship between local hemodynamic forces and intimal and medial remodeling in the proximal and distal segments of the arterial walls of rats in relation to severe stenosis of the aorta. Male Wistar young rats were divided randomly into: operated group, animals submitted to surgical abdominal aorta stenosis, and sham-operated group, a control group of animals submitted to sham operation to simulate abdominal aorta stenosis. Constricted aortas showed two distinct adaptive remodeling responses to hemodynamic stimuli induced by coarctation. The first is remodeling in the hypertensive prestenotic segment with increased circumferential wall tension associated with normal tensile stress, laminar flow/normal wall shear stress. The remodeling in this segment is characterized by enlarged heterogeneous endothelial cells, elongated in the direction of the blood flow, diffusely distributed neointimal plaques, appearing as discrete bulging toward the vascular lumen, and medial thickening. Our findings suggest that increased circumferential wall tension due to hypertension play a pivotal role in the remodeling of the prestenotic segment through biomechanical effects on oxidative stress and increased TGF-? expression. The second is remodeling in the normotensive poststenotic segment with turbulent flow/low wall shear stress and normal circumferential wall tension and tensile stress. The remodeling in this segment is characterized by groups of endothelial cells with phenotypic alterations and focally distributed neointimal plaques, similar but many of them larger than those found in the prestenotic segments. Further studies are needed to determine how the mechanical forces of turbulent flow/low shear stress are detected and transduced into biochemical signaling by the cells of the artery walls and then converted into pathophysiologic relevant phenotypic changes.
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Shamu, John. "On the measurement and application of cement grout rheological properties." Licentiate thesis, KTH, Jord- och bergmekanik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-251745.
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The rheological properties of cement-based grouts play a key role in determining the final spread in grouted rock formations. Rheologically, cement grouts are known to be complex thixotropic fluids, but their steady flow behavior is often described by fitting the simple Bingham constitutive law to flow curve data. The resultant Bingham parameters are then used in grouting design of e.g. tunnels, to estimate the penetration length. Since cement grouts are thixotropic suspensions, the interpretation of their flow curves as obtained from flow sweeps in concentric cylinder rotational rheometers is often complicated by: the presence of wall slip, sedimentation and unstable flow at low shear rates. A systematic approach to study these effects within the constraints of the concentric cylinder geometry (Couette) and for different cement grout concentrations was carried out as part of the Licentiate research work. Of particular interest was the influence of geometry and flow sweep measurement interval on flow curves, including the characteristic unstable flow branch that appears at applied shear rates that are below the critical shear rate. The unstable flow branch observed below the critical shear rate has been described as a characteristic feature in the flow curves of thixotropic suspensions, e.g. cement grouts, laponite. From a practical standpoint, this information can then be readily used to improve rheological measurements of cement grouts. The existence of the critical shear rate below which no stable flow occurs, plus the complex wall slip phenomenon are then discussed by considering how they affect actual spread in rough and smooth rock fractures. Another major part of the research presented in this thesis relates to the measurement of model yield stress fluid (YSF), i.e. Carbopol, velocity profiles within the radial flow geometry. Radial flow between parallel plates, is an idealized fundamental flow configuration that is often used as a basis for grout spread estimation in planar rock fractures. Compared to other flow configurations with YSFs, e.g. channels, only a limited amount of work has presented analytical solutions, numerical models and especially experimental work for radial flow. Thus, as a first step towards more systematic studies of the plug flow region of YSFs in radial flow the current work presents the design, manufacture and for the first time velocity profile measurements that were conducted by using the pulsed Ultrasound Velocity Profiling (UVP) technique. The current observations for tests carried out with different disk spacings and flow rates show a distinct plug region, coupled with wall slip effects for the Carbopol model YSF fluid that was used. The theoretically predicted velocity profiles and the measured ones agree reasonably well, and the main discrepancies are discussed. Future studies, would then be targeted at improving the current experimental setup, for detailed measurements of the plug flow region along the radial length, which remains a challenging issue for studies on YSFs and engineering applications such as rock grouting design.Cementbaserade injekteringsmedels reologiska egenskaper har en stor påverkan på strömning och inträngningslängd i sprickigt berg. Medlens reologi är komplex, inklusive tixotropi, men strömningen beskrivs ändå oftast med den enkla linjära Bingham modellen i injekteringssammanhang. De två parametrarna från denna modell, flytgräns och viskositet, används sedan inom injekteringsdesign, för t.ex. tunnlar och dammar, för att bedöma inträngningen. Eftersom cementbaserade medel är tixoptropa suspensioner försvåras utvärderingen vid mätning med konventionella rotationsviskometrar på grund av glidning vid fasta begränsningsytor, sedimentation/separation av partiklarna och instabila flöden vid låga deformationshastigheter. En systematisk mätprocedur för att studera ovanstående problem med rotationsviskometer och koncentriska cylindrar samt olika vanliga vattencementtal, har utförts inom ramen för detta licentiatarbete. Av särskilt intresse har varit att studera effekten av olika geometrier och tidsintervallet mellan mätningarna, inklusive den instabila delen av flödeskurvan då deformationshastigheten är lägre än ett kritiskt värde. Denna del av kurvan har i litteraturen beskrivits som karakteristisk för tixotropa suspensioner, som t.ex. cementbaserade injekteringsmedel. Praktiskt kan ovanstående kunskap användas för att förbättra mätningen av de reologiska egenskaperna. Existensen av en kritisk deformationshastighet under vilken det inte finns något stabilt flöde, i kombination med glidning vid fasta begränsningsytor, diskuteras särskilt med hänsyn till dess påverkan på faktisk inträngning i släta och råa bergsprickor. Ett annat fokus i licentiatarbetet har varit att studera icke-Newtonska modellvätskors (Carbopol) radiella strömning mellan parallella plattor. Denna typ av strömningsgeometri används ofta som en idealiserad konfiguration för strömning i bergsprickor. I jämförelse med andra enklare geometrier, finns endast en begränsad forskning utförd för denna geometri både då det gäller analytiska och numeriska beräkningar men framförallt då det gäller experiment. Som ett första steg inför en mer systematisk undersökning av icke-Newtonsk radiella strömning presenteras i detta arbete framtagandet av en fysisk laboratoriemodell där hastighetsprofilerna mellan plattorna för första gången visualiserats med hjälp av ultraljud. De utförda mätningarna med tre olika öppningar mellan plattorna sam tre olika värden på det konstanta flödet, visar på en distinkt plugg som är ett resultat av vätskans flytgräns samt glidning i gränsskiktet mellan vätskan och plattornas fasta begränsningsytor. En jämförelse mellan uppmätta hastighetsprofiler och analytiskt beräknade diskuteras där resultaten överensstämmer relativt väl, med beaktande av de långtgående förenklade antaganden som krävs för beräkningarna. Fortsatta studier kommer att fokuseras på att förbättra laboratoriemodellen för en mer detaljerad studie av icke-Newtonska vätskors strömning och hur pluggen utvecklas under den radiella inträngningen, vilket fortsättningsvis är av betydelse för design av injektering i bergsprickor.
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Mnekbi, Djebali Cheima. "Rhéologie des polymères fondus à hauts taux de cisaillement : application à la microinjection." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00820185.
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La rhéologie à hauts taux de cisaillement pour deux polymères, le PEHD semi-cristallin et le PMMA amorphe a été étudiée. Des outils de rhéométrie classique, un rhéomètre plan-plan en mode dynamique, et un rhéomètre capillaire, ont été utilisés dans des conditions extrêmes (avec des filières pour la rhéométrie capillaire de diamètres allant jusqu'à 0,3 mm) mais les dépouillements de ces résultats ont été fait suivant les hypothèses conventionnelles en négligeant les instabilités et les phénomènes physiques qui interviennent lors de ces écoulements.Nous avons par la suite développé un modèle mathématique de l'écoulement dans un capillaire pour rendre compte de l'importance des différents phénomènes physiques qui peuvent avoir lieu dans des écoulements extrêmes, à savoir l'échauffement et la piezodépendance de la viscosité, la compressibilité et le glissement à la paroi. Les résultats du modèle développé ont été comparés avec les résultats expérimentaux.Nous avons aidé au développement d'une presse de microinjection originale et nous l'avons testée avec un moule de plaque instrumenté d'épaisseur allant jusqu'à 0,2 mm. Nous avons montré qu'il était possible de réaliser des pièces de qualité ce qui est avéré par des mesures de pression, vitesse et de température bien reproductibles. Nous avons exploité les données rhéologiques expérimentales dans la modélisation de la phase de remplissage avec le logiciel de calcul Rem3D. Des corrélations entre les mesures expérimentales et les calculs ont été réalisées en comparant l'évolution des pressions dans le système d'alimentation et dans l'empreinte.
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(9818900), Ian Mcneilly. "Electrochemical characterisation of a unique rotating parallel disc device for flow-accelerated corrosion research." Thesis, 2011. https://figshare.com/articles/thesis/Electrochemical_characterisation_of_a_unique_rotating_parallel_disc_device_for_flow-accelerated_corrosion_research/13459733.
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"This thesis presents the electrochemical characterisation of a novel device that has been designed to facilitate the study of flow-accelerated corrosion (FAC) at a metal electrode under high shear rate flow conditions"--P. 1.
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Lee, Tsung-Ming, and 李宗明. "Calculations of shear rate along arterial wall." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/80058989936120156630.
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碩士國立成功大學
航空太空工程學系
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Acoording to the research of predecessors, a blood vessel disease is not only relevant to the distribution of shear stress of arterial wall , but the formation of a blood vessel disease is also influenced by the function of the platelet to the arterial wall . Based upon this testimony, the reserach of thesis deals with numerical simulation flow under different conditions , and the distribution of shear rate along arterial wall and adhension of platelets are discussed . In the process of reseachch , two sorts of flow field are analyzed : the flow field with barriers on the bottom wall, and the one of a bran- ching tube. The simulation of flow field employs SIMPLER algorithm with finite volume method , nonstaggered grid and body fitted coordinated . As for the grid generation , the flow field is divided into two sub-regions,which can be more easily handled. Calculations are performed iteratively between the subregions. Treatment of the interface is discussed briefly. The numerical results are compared with the available exp- erimental data . A parameter which is the ratio of nomal vel- ocity gradient tangential velocity gradient is used to chara- cterized the adhesion of platelet on the walls.
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Bhowmick, Anjan K. "Seismic Analysis and Design of Steel Plate Shear Walls." Phd thesis, 2009. http://hdl.handle.net/10048/787.
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A nonlinear finite element model was developed to study the behaviour of unstiffened steel plate shear walls. The model was validated using the results from quasi-static and dynamic experimental programs. With the validated finite element model, the performance of 4-storey and 8-storey Type D (ductile) and Type LD (limited-ductility) steel plate shear walls with moment-resisting beam-to-column connections was studied under spectrum-compatible seismic records.
A design procedure that aims to achieve optimal seismic behaviour for steel plate shear walls was proposed. The proposed method uses the concepts of indirect capacity design principles of CAN/CSA-S16-01 to identify the infill plates that are likely to yield in the design earthquake. The proposed method was used for the design of two 4-storey and one 8-storey shear walls. Design axial forces and moments in the boundary columns for the shear walls were shown to be in good agreement with nonlinear seismic analysis results. Results also showed that some of the other capacity design methods available generally underestimate the maximum design forces in the columns, while others can be overly conservative. The effect of loading rate on the dynamic behaviour of steel plate shear walls was also investigated, as was the P-Delta effect in terms of its influence on seismic demand in shear and flexure.
A shear strength model of the infill plate with circular openings at any location was developed based on a strip model where all the strips with perforations were partially discounted. A design method for steel plate shear walls with perforations was introduced. The method was applied for the design of boundary columns of a 4-storey steel plate shear wall with perforations. The predicted design forces in the columns for the 4-storey perforated shear wall agreed well with the forces obtained from nonlinear seismic analysis.
Finally, an improved simple formula for estimating the fundamental period of steel plate shear walls was developed by regression analysis of the period data obtained from frequency analysis of series of steel plate shear walls. In addition, the effectiveness of a shearflexure cantilever formulation for determining fundamental periods and P-Delta effects of steel plate shear walls was studied.Structural Engineering
Book chapters on the topic "Wall shear rates"
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Somwanshi, Praveen M., K. Muralidhar, and Sameer Khandekar. "Wall Shear Rates Generated During Coalescence of Pendant and Sessile Drops." In Fluid Mechanics and Fluid Power – Contemporary Research, 33–42. New Delhi: Springer India, 2016. http://dx.doi.org/10.1007/978-81-322-2743-4_4.
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Berrich-Betouche, Emma, Fethi Aloui, and Jack Legrand. "Radial Distribution of Mass Transfer and Wall Shear Instantaneous Rates in Couette-Taylor Flow." In Exergy for A Better Environment and Improved Sustainability 1, 583–99. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-62572-0_38.
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Berrich, Emna, Fethi Aloui, and Jack Legrand. "Effect on Wall Shear Rates of Taylor Vortex Instabilities Induced by Progressive Variation of the Inner Cylinder." In Progress in Clean Energy, Volume 1, 891–908. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-16709-1_65.
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Kuroda, Akiyoshi, Nobuhide Kasagi, and Masaru Hirata. "Direct Numerical Simulation of Turbulent Plane Couette-Poiseuille Flows: Effect of Mean Shear Rate on the Near-Wall Turbulence Structures." In Turbulent Shear Flows 9, 241–57. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-78823-9_16.
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Ishida, Fujimaro, Masanori Tsuji, Satoru Tanioka, Katsuhiro Tanaka, Shinichi Yoshimura, and Hidenori Suzuki. "Computational Fluid Dynamics for Cerebral Aneurysms in Clinical Settings." In Acta Neurochirurgica Supplement, 27–32. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-63453-7_4.
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AbstractHemodynamics is thought to play an important role in the pathogenesis of cerebral aneurysms and recent development of computer technology makes it possible to simulate blood flow using high-resolution 3D images within several hours. A lot of studies of computational fluid dynamics (CFD) for cerebral aneurysms were reported; therefore, application of CFD for cerebral aneurysms in clinical settings is reviewed in this article.CFD for cerebral aneurysms using a patient-specific geometry model was first reported in 2003 and it has been revealing that hemodynamics brings a certain contribution to understanding aneurysm pathology, including initiation, growth and rupture. Based on the knowledge of the state-of-the-art techniques, this review treats the decision-making process for using CFD in several clinical settings. We introduce our CFD procedure using digital imaging and communication in medicine (DICOM) datasets of 3D CT angiography or 3D rotational angiography. In addition, we review rupture status, hyperplastic remodeling of aneurysm wall, and recurrence of coiled aneurysms using the hemodynamic parameters such as wall shear stress (WSS), oscillatory shear index (OSI), aneurysmal inflow rate coefficient (AIRC), and residual flow volume (RFV).
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Jehle, Markus, Bernd Jähne, and Ulrich Kertzscher. "Direct Estimation of the Wall Shear Rate Using Parametric Motion Models in 3D." In Lecture Notes in Computer Science, 434–43. Berlin, Heidelberg: Springer Berlin Heidelberg, 2006. http://dx.doi.org/10.1007/11861898_44.
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Reneman, Robert S., Theo Arts, Dick W. Slaaf, and Geert Jan Tangelder. "Wall Shear Rate in Arterioles: Least Estimates from in Vivo Recorded Velocity Profiles." In Biomechanical Transport Processes, 197–204. Boston, MA: Springer US, 1990. http://dx.doi.org/10.1007/978-1-4757-1511-8_22.
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Haggag, Y., A. Nassef, A. Sallam, and A. Mansour. "An In-Vitro Comparative Study of the Wall Shear Rate Produced by the Central Axis Prosthetic Heart Valve Using a Laser Doppler Anemometer." In Interfaces in Medicine and Mechanics—2, 464–73. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3852-9_51.
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"Wall Shear Rates Induced by a Single Cavitation Bubble Collapse." In Proceedings of the 10th International Symposium on Cavitation (CAV2018), 1097–103. ASME Press, 2018. http://dx.doi.org/10.1115/1.861851_ch208.
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Carvalho, Violeta, Diogo Lopes, João Silva, Hélder Puga, Rui A. Lima, José Carlos Teixeira, and Senhorinha Teixeira. "Comparison of CFD and FSI Simulations of Blood Flow in Stenotic Coronary Arteries." In Computational Fluid Dynamics [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.102089.
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Cardiovascular diseases are amongst the main causes of death worldwide, and the main underlying pathological process is atherosclerosis. Over the years, fatty materials are accumulated in the arterial which consequently hinders the blood flow. Due to the great mortality rate of this disease, hemodynamic studies within stenotic arteries have been of great clinical interest, and computational methods have played an important role. Commonly, computational fluid dynamics methods, where only the blood flow behavior is considered, however, the study of both blood and artery walls’ interaction is of foremost importance. In this regard, in the present study, both computational fluid dynamics and fluid-structure interaction modeling analysis were performed in order to evaluate if the arterial wall compliance affects considerably the hemodynamic results obtained in idealized stenotic coronary models. From the overall results, it was observed that the influence of wall compliance was noteworthy on wall shear stress distribution, but its effect on the time-averaged wall shear stress and on the oscillatory shear index was minor.
Conference papers on the topic "Wall shear rates"
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Moritzer, Elmar, Marius Wittke, and Gilmar Heiderich. "Numerical simulation of residence time, shear rates and throughput in single screw extruders considering wall shear rates." In MATERIALS CHARACTERIZATION USING X-RAYS AND RELATED TECHNIQUES. Author(s), 2019. http://dx.doi.org/10.1063/1.5088292.
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Corbett, Scott C., Amin Ajdari, Ahmet U. Coskun, and Hamid N.-Hashemi. "Effect of Blood Viscosity on Thrombosis Potential Near a Step Wall Transition." In ASME 2009 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2009. http://dx.doi.org/10.1115/sbc2009-206629.
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Thrombosis and hemolysis are two problems encountered when processing blood in artificial organs. Physical factors of blood flow alone can influence the interaction of proteins and cells with the vessel wall, induce platelet aggregation and influence coagulation factors responsible for the formation of thrombus, even in the absence of chemical factors in the blood. These physical factors are related to the magnitude of the shear rate/stress, the duration of the applied force and the local geometry. Specifically, high blood shear rates (or stress) lead to damage (hemolysis, platelet activation), while low shear rates lead to stagnation and thrombosis [1].
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Agelinchaab, M., and M. F. Tachie. "Three-Dimensional Turbulent Wall Jets." In ASME 2009 Fluids Engineering Division Summer Meeting. ASMEDC, 2009. http://dx.doi.org/10.1115/fedsm2009-78542.
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Particle image velocimetry (PIV) measurements were carried out on generic three-dimensional turbulent wall jets. The wall jets were created from a long circular pipe at Reynolds number based on the jet exit velocity (Uj) and inside diameter of pipe (d) of Rej = Ujd/v = 7680 to 19500. The profiles of the mean velocities, turbulence intensities and Reynolds shear stresses in the streamwise/wall-normal and streamwise/lateral planes are presented. Consistent with previous results, the profiles of the mean velocities and turbulent statistics are independent of Reynolds number. The mean velocity attained self-similarity before the turbulence quantities. The decay rate and spread rates obtained in the present study fall in between the values reported in previous studies. The contours of the two-point velocity correlations in the inner region of the 3D wall jet are qualitatively similar to those reported in boundary layer studies. The results from proper orthogonal analysis revealed that large scale structures are largely responsible for the distribution of the streamwise turbulence intensity and Reynolds shear stresses than the distribution of the wall-normal turbulence intensity.
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Arora, Ravi, Eric Daymo, Anna Lee Tonkovich, Laura Silva, Rick Stevenson, Mike Lamont, and Jan Lerou. "Non-Newtonian Flow Behavior in Microchannels for Emulsion Formation." In ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2006. http://dx.doi.org/10.1115/icnmm2006-96205.
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Emulsion formation within microchannels enables smaller mean droplet sizes for new commercial applications such as personal care, medical, and food products among others. When operated at a high flow rate per channel, the resulting emulsion mixture creates a high wall shear stress along the walls of the narrow microchannel. This high fluid-wall shear stress of continuous phase material past a dispersed phase, introduced through a permeable wall, enables the formation of small emulsion droplets — one drop at a time. A challenge to the scale-up of this technology has been to understand the behavior of non-Newtonian fluids under high wall shear stress. A further complication has been the change in fluid properties with composition along the length of the microchannel as the emulsion is formed. Many of the predictive models for non-Newtonian emulsion fluids were derived at low shear rates and have shown excellent agreement between predictions and experiments. The power law relationship for non-Newtonian emulsions obtained at low shear rates breaks down under the high shear environment created by high throughputs in small microchannels. The small dimensions create higher velocity gradients at the wall, resulting in larger apparent viscosity. Extrapolation of the power law obtained in low shear environment may lead to under-predictions of pressure drop in microchannels. This work describes the results of a shear-thinning fluid that generates larger pressure drop in a high-wall shear stress microchannel environment than predicted from traditional correlations.
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Mejia, Juan, Rosaire Mongrain, Richard Leask, Olivier F. Bertrand, and Josep Cabau-Rodes. "Transient and Non-Newtonian Effects on the Wall Shear Stress Distribution of a Stented Artery." In ASME 2009 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2009. http://dx.doi.org/10.1115/sbc2009-206735.
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For the last few decades stents have played a central role in the treatment of artherosclerosis. Although bare-metal stents (BMS) have significantly reduced levels of restenosis rates by 20 or 30% [1], restenosis rates remain high at around 25% [1]. The introduction of drug-eluting stents have reduced restenosis rates even further [2], but are associated with high risk of late thrombosis [3].
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Browne, L. D., P. Griffin, and M. T. Walsh. "Quantifying Turbulent Wall Shear Stress in an Arteriovenous Graft Using Large Eddy Simulation." In ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80709.
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Hemodialysis patients require a vascular access capable of accommodating the high blood flow rates required for effective dialysis treatment. The arteriovenous graft is one such access. However, this access type suffers from reduced one year primary & secondary patency rates of 59–90% and 50–82% respectively [1]. The main contributor to the failure of this access is stenosis via the development of intimal hyperplasia (IH) that predominately occurs at the venous anastomosis. It is hypothesized that the resulting transitional to turbulent flow regime within the venous anastomosis contributes to the development of IH. The aim of this study is to investigate the influence of this transitional to turbulent behavior on wall shear stress within the venous anastomosis via the use of large eddy simulation.
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Bark, David L., Andrea N. Para, and David N. Ku. "Shear Rate Characteristics of Growing Thrombus on a Stenosis in a Coronary Sized Vessel." In ASME 2009 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2009. http://dx.doi.org/10.1115/sbc2009-206766.
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Arterial thrombosis can lead to acute myocardial infarction or stroke. Thrombosis has been found to occur on atherosclerotic lesions and can fully occlude the blood vessel. Atheromas create a stenosis in the flow field. Thrombus forming in these regions is characteristically composed mostly of platelets with the addition of von Willebrand Factor (vWF) and polymerized fibrin. Previous studies of thrombosis under arterial-like stenotic flow conditions have shown that the thrombus growth rate increases under increasing shear rates up to 40000 s−1 [1]. The obstructive atheroma can lead to wall shear rates even greater than 40 times the average wall shear rate for an artery [2]. The shear rate dependency can be ascribed to mass transport [3]. Additionally, it can be ascribed to platelet binding mechanisms, such as vWF, that dominate at high shear, while other binding mechanisms, such as fibrinogen, bind at lower shear in the arteries [4].
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McGah, Patrick M., James J. Riley, Alberto Aliseda, Daniel F. Leotta, and Kirk W. Beach. "Incomplete Restoration of Homeostatic Shear Stress Within Arteriovenous Fistulae." In ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80458.
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Arteriovenous fistulae are created surgically to provide an adequate access for dialysis in patients with End-Stage Renal Disease (ESRD). Producing an autogenous shunt linking an artery and a vein in the peripheral circulation bypasses the high resistance capillary bed in order to provide the necessary flow rates at sites easily accessible for dialysis. In successful fistulae, venous flow rates can easily exceed 1000 mL/min. It has long been recognized that the hemodynamics constitute the primary external influence on the remodeling process [1]; The high flow rate, together with the exposure of the venous tissue to the high arterial pressure, leads to a rapid process of wall remodeling that may end in a mature access or in failure. Recent hemodynamic simulations [2,3] have computed very high viscous wall shear stresses within fistulae; Stresses > 15Pa have been reported which are much greater than what is typically considered normal (i.e. homeostatic, ≈ 1Pa). Both sustained high shear and sustained low shear have been hypothesized to cause pathological venous remodeling (i.e. intimal hyperplasia) which causes stenoses and threatens fistula patency. The role of high vs. low shear stress in effecting patency remains unclear. Given the high failure rate of dialysis access sites (up to 50% require surgical revision within one year [4]), understanding the dynamics of blood flow within the fistula is a necessary step in understanding the remodeling, and ultimately, in improving clinical outcomes.
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Hammad, Khaled J. "Influence of Non-Newtonian Rheology on Mass Transfer From a Biofluid in Separated and Reattached Flows." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-86809.
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Influence of the rheological model selection on the flow and mass transfer behavior of human blood in a separated and reattached flow region is investigated. Newtonian and non-Newtonian hemorheological models that account for the yield stress and shear-thinning characteristics of blood are used. The conservation of mass, momentum, and species equations as well as the Herschel-Bulkley constitutive equation are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the impact of flow restriction and rheological modelling on blood-borne oxygen exchange with the confining walls. The wall mass transfer rates within the separated and reattached regions display a strong dependency on the used hemorheological model. Newtonian and non-Newtonian models result in a peak wall mass transfer rate within the recirculation region. However, non-Newtonian models that account for the yield stress and shear-thinning effects predict a substantial, highly localized, drop in the wall mass transfer rates of oxygen, at the reattachment point.
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Weydahl, Erlend, Aland Santamarina, and James E. Moore. "Effects of Rapid Curvature Changes on Flow Through Coronary Artery Models." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0020.
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Abstract The localized nature of atherosclerosis has led to extensive study of blood flow patterns and their possible involvement in atherogenesis. Vessel geometry has always been considered a primary factor in determining blood flow patterns. In the coronary arteries, the geometry varies dynamically due to myocardial contraction. The effects of physiologic axial (Moore et al., 1994) and lateral (Delfino et al., 1994) vessel movement on coronary blood flow patterns have been shown to be important in producing oscillations in wall shear stress. Those studies were limited to straight vessels that translated in one direction only. Previous studies of flow in curved tubes with time-varying curvature showed that large quasi-static wall shear rate amplitudes relative to the static case when the curvature change was 50% of the mean curvature (Santamarina et al., 1997). The largest variation in wall shear rate from the minimum curvature to the maximum curvature was 52%, and was found at the mid-wall location (halfway between the inner and outer wall of curvature along the circumference) for the highest mean curvature ratio studied (δ = 0.12). A comparison of the shear rate amplitudes found in a tube whose radius of curvature varies dynamically at 1 Hz to the variations noted in the quasi-static analysis revealed differences of less than 1%. Changes in the mean wall shear rate predicted with the dynamic analysis were less than 7%, relative to the wall shear rate at the static mean radius of curvature. It was concluded that, although the change in curvature creates a relatively large shear rate amplitude, the fact that the curvature varies dynamically at 1 Hz is not important in predicting wall shear rates.