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Patrick Segers - One of the best experts on this subject based on the ideXlab platform.
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a simulation environment for validating ultrasonic blood flow and vessel wall imaging based on fluid structure interaction simulations ultrasonic assessment of arterial distension and wall Shear Rate
Medical Physics, 2010Co-Authors: Abigail Swillens, Joris Degroote, Jan Vierendeels, Lasse Lovstakken, Patrick SegersAbstract:Purpose: Ultrasound(US) is a commonly used vascular imaging tool when screening for patients at high cardiovascular risk. However, current blood flow and vessel wall imaging methods are hampered by several limitations. When optimizing and developing new ultrasound modalities, proper validation is required before clinical implementation. Therefore, the authors present a simulation environment integrating ultrasound and fluid-structure interaction (FSI) simulations, allowing construction of synthetic ultrasoundimages based on physiologically realistic behavior of an artery. To demonstRate the potential of the model for vascular ultrasound research, the authors studied clinically relevant imaging modalities of arterial function related to both vessel wall deformation and arterial hemodynamics: Arterial distension (related to arterial stiffness) and wall Shear Rate (related to the development of atherosclerosis) imaging. Methods: An in-house code (“TANGO”) was developed to strongly couple the flow solver FLUENT and structural solver ABAQUS using an interface quasi-Newton technique. FIELD II was used to model realistic transducer and scan settings. The input to the FSI-US model is a scatterer phantom on which the US waves reflect, with the scatterer displacement derived from the FSI flow and displacement fields. The authors applied the simulation tool to a 3D straight tube, representative of the common carotid artery (length: 5 cm; and inner and outer radius: 3 and 4 mm). A mass flow inlet boundary condition, based on flowmeasured in a healthy subject, was applied. A downstream pressure condition, based on a noninvasively measured pressure waveform, was chosen and scaled to simulate three different degrees of arterial distension (1%, 4%, and 9%). The RF data from the FSI-US coupling were further processed for arterial wall and flowimaging. Using an available wall tracking algorithm, arterial distensibility was assessed. Using an autocorrelation estimator, blood velocity and Shear Rate were obtained along a scanline. Results: The authors obtained a very good agreement between the flow and the distension as obtained from the FSI-US model and the reference FSI values. The wall application showed a high sensitivity of distension measurements to the measurement location, previously reported based onin vivo data. Interestingly, the model indicated that strong reflections between tissue transitions can potentially cloud a correct measurement. The flowimaging application demonstRated that Maximum Shear Rate was underestimated for a relevant simulation setup. Moreover, given the difficulty of measuring near-wall velocities with ultrasound, maximal Shear Rate was obtained at a distance from the wall [0.812 mm for the anterior and 0.689 mm for the posterior side (9% distension case)]. However, ultrasound Shear Rates correlated well with the FSI ground truth for all distension degrees, suggesting that correction of the severe underestimation by ultrasound might be feasible in certain flow conditions. Conclusions: The authors demonstRated a simulation environment to validate and develop ultrasonic vascular imaging. An elaboRate technique to integRate FSI andFIELD IIultrasound simulations was presented. This multiphysics simulation tool was applied to two imaging applications where distensible ultrasound phantoms are indispensable: Wall distension and Shear Rate measurement. Results showed that the method to couple fluid-structure interaction and ultrasound simulations provides realistic RF signals from the tissue and the blood pool.
Michel Y. Jaffrin - One of the best experts on this subject based on the ideXlab platform.
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Comparison between rotating disk and vibratory membranes in the ultrafiltration of oil-in-water emulsions
Desalination, 2007Co-Authors: N. Moulai-mostefa, Omar Akoum, Luhui Ding, M. Nedjihoui, Michel Y. JaffrinAbstract:The purpose of this work is to compare the effects of hydrodynamic parameters on the permeate flux provided by two different dynamic filtration systems using same membrane material and same fluids. Tested systems were rotating disk module and a VSEP pilot with a circular vibrating membrane. Test fluid consisted of oil in water emulsion of cutting fluid. The characteristic Shear Rate was taken to be the Maximum one at the membrane. It was varied by changing the rotation speed of the disk or by changing the vibration frequency of the VSEP. The highest permeate fluxes were obtained with rotating disks equipped with vanes. With the VSEP, the flux decreases with time. However, the fouling limitation disappears completely for a disk equipped with vanes. In the two systems, the flux is mainly governed by the Maximum Shear Rate and not by details of internal flow and can be increased to very high levels by increasing rotation speed or vibration amplitude.
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A hydrodynamic comparison between rotating disk and vibratory dynamic filtration systems
Journal of Membrane Science, 2004Co-Authors: Michel Y. Jaffrin, Luhui Ding, Omar Akoum, Ambroise BrouAbstract:Abstract The purpose of this work is to compare the effects of various hydrodynamic parameters (transmembrane pressure, Shear Rate, fluid viscosity and solute concentration) on the permeate flux provided by two different dynamic filtration systems using same membrane material and same fluids. Tested systems were two rotating disk modules designed in our laboratory and a VSEP pilot with a circular vibrating membrane. Tests fluids consisted of baker’s yeast microfiltration (MF) at 0.2 μm and of UHT skim milk ultrafiltration (UF) at 50 kDa. The characteristic Shear Rate was taken to be the Maximum one (γm) at the membrane outer rim in each module. It was varied by changing the rotation speed of the disk or by changing the vibration frequency of the VSEP. The highest permeate fluxes were obtained with rotating disks equipped with vanes because they geneRated the largest Shear Rates. But in MF, when the disk speed was adjusted to produce the same Maximum Shear Rate as in the VSEP, permeate fluxes variations with time in both modules were identical at the same TMP and yeast concentration. Flux variations with TMP were also very close in this case. In concentration tests by MF at constant speed or frequency, permeate fluxes (J) in L h−1 m−2 provided by the two rotating disks (with and without vanes) and the VSEP were well correlated by a single equation, J = 4.3 × 10−6γm1.46, where the Shear Rate was varied by the concentration change. Permeate fluxes were also similar in UF of milk for the VSEP and rotating disk when Shear Rates were matched. The variation of permeate flux with Shear Rate at constant concentration for the two rotating disks systems with and without vanes was correlated by a single equation J = 0.136γm0.594, while the corresponding equation for the VSEP was J = 0.110γm0.587. Our data suggest that, in these devices, the flux is mainly governed by the Maximum Shear Rate and not by details of internal flow and can be increased to very high levels by increasing rotation speed or vibration amplitude or by equipping the disk with large vanes. This information can be used for scaling up industrial systems.
Thomas Kiorboe - One of the best experts on this subject based on the ideXlab platform.
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predatory and suspension feeding of the copepod acartia tonsa in turbulent environments
Marine Ecology Progress Series, 1995Co-Authors: Enric Saiz, Thomas KiorboeAbstract:The copepod Acartia tonsa exhibits 2 different feeding modes: when feeding on small phytoplankton cells it sets up a feeding current and acts as a suspension feeder; when feeding on motile prey it acts as an ambush feeder. We examined experimentally the effects of small-scale turbulence on feeding Rates in these 2 modes. The different feeding behaviours were triggered by offering the copepods diatoms Thalassiosira weissfloqii and ciliates Strombidium sulcatum, respectively. Turbulence at 5 different intensities (energy dissipation Rate, E, between 4 X I O ~ and 3.7 X 10' cm2 s ~ ) was geneRated by an oscillating grid. In ambush feeding mode, low (realistic) intensities of turbulence (E = 1 0 ' ~ to 1 0 ~ cm2 s ~ ) enhanced clearance Rates by up to a factor of 4 above those observed in calm water Higher intensities of turbulence ( E = 10-' to 10' cm2 s ~ ) resulted in a depression of clearance Rates, although the Rates were still significantly higher than those observed in calm water. The depression of clearance Rates at high turbulence intensities was due partly to a decline in capture success, but mainly to a decrease in reactive distance, because turbulence interferes with prey perception by disturbing the hydrodynamical signal geneRated by motile prey. The negative effects were evident only at turbulence intensities exceeding those normally encountered by A tonsa in its natural habitat. In suspension feeding mode, low intensities of ambient turbulence (E = I O ~ to 10-2 cm2 s-" had negligible effects on clearance Rates, while at higher turbulence intensities (E = 10-I to 10' cm2 s ~ ) we observed a negatlve effect (depression of clearance Rate). The negative effects become evident when ambient turbulent fluid Shear approaches the Maximum Shear Rate of the copepod's feeding current, and we hypothesize that at these intensities the feeding current is eroded. Again the negative effects were observed only at turbulence intensities higher than those typically experienced by A. tonsa in the sea. The differential response to turbulence of the 2 feeding behaviours, including the negative effects, were accuRately predicted by encounter Rate and feeding behaviour models proposed by korboe & Saiz (1995; Mar Ecol Prog Ser 122:135-145). Because feeding behaviour is specific to the prey (phytoplankton vs mot~le prey), and because ambush-mode feeding is much more dependent on turbulence than suspensionmode feeding, our findings suggest that prey selection in A. tonsa may be partly governed by turbulence in the ocean. This may explain why rnicrozooplankton at times dominates the diet of A. tonsa and other copepods, even though it is numerically scarce relative to phytoplankton in the environment.
Weibin Liang - One of the best experts on this subject based on the ideXlab platform.
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measurement of lubricant viscosity and detection of boundary slip at high Shear Rates
Tribology International, 2016Co-Authors: Yonggang Meng, Yu Tian, Jun Zhang, Weibin LiangAbstract:Abstract A novel rheometer with the Maximum Shear Rate of 10 5 s −1 has been fabricated to measure lubricant viscosity and to detect solid/liquid boundary slip. The gap between two parallel plates is controlled in the range from 20 to 500 μm and the viscous Shear torque is measured with a feed-backed laser reflection technique. Test results of the perfluoropolyethers (PFPE) coated sample indicated that the viscous Shear resistance is reduced by about 15–20% compared with the bare plate, implying that possible boundary slip occurred at the liquid/solid interface and a slip length of order 10 μm was extrapolated.
David N. Ku - One of the best experts on this subject based on the ideXlab platform.
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High Shear Thrombus Formation under Pulsatile and Steady Flow
Cardiovascular Engineering and Technology, 2014Co-Authors: Lauren D. C. Casa, David N. KuAbstract:Most previous studies have investigated in vitro thrombus formation under steady flow conditions at physiological Shear Rates, though occlusive thrombosis leading to myocardial infarction and stroke forms under elevated Shear Rates and pulsatile flow. Two reports of pulsatile flow on thrombosis have yielded conflicting results. In the present study, we quantify the effect of very high Shear, reversing pulsatile flow relevant to coronary thrombosis on platelet deposition leading to occlusive thrombus formation. Whole porcine blood was perfused in a collagen-coated, tubular, stenotic test section under pulsatile or steady flow. Pulsatile flow was geneRated with a frequency of 60 beats per minute and large magnitude excursions similar to a coronary artery waveform. Alternatively, steady flow conditions from a pressure driven system created Shear Rates matched to the Maximum (16000 s^−1), mean (3800 s^−1), and an intermediate (6500 s^−1) Shear Rates corresponding to the pulsatile system. Thrombus growth in thickness was recorded using a high-resolution CCD attached to a microscope. Steady flow recreated pulsatile flow thrombus formation in most cases. Lag time, t _lag, thrombus growth Rate, dV/dt , and time to occlusion, t _occ, did not show statistically significant differences between pulsatile flow and steady flow with matched mean Shear Rate. Pulsatile flow conditions yielded t _occ = 5.5 ± 2.8 min, which was not significantly different compared to a steady mean Shear Rate condition with t _occ = 6.2 ± 1.7 min. Similarly, occlusion times for steady intermediate and steady Maximum Shear Rate conditions were not significantly difference from pulsatile flow conditions yielding t _occ of 4.6 ± 2.9 and 4.6 ± 1.8 min, respectively. In contrast, lag time for steady flow at Maximum Shear Rate of 16000 s^−1 was decreased to 26.1 s compared to pulsatile flow ( t _lag = 42.7 s, p = 0.03), steady mean flow ( t _lag = 60.9 s, p = 0.02), and steady intermediate flow ( t _lag = 39.9 s, p = 0.01). Occlusive thrombus formation under high Shear, pulsatile conditions may be modeled in vitro using steady flow with matched mean Shear Rate with respect to occlusion time, lag time, and growth Rate. Our results indicate that the magnitude of Shear Rate more strongly affects thrombus growth characteristics than flow pulsatility for an arterial frequency.