Variation Of Shear Stress Research Articles

Study on the Influence of Temperature–Magnetic Field Coupling on the Mechanical Properties of Magnetorheological Fluids

The composition of a magnetorheological fluid (MRF) usually includes magnetic particles, a carrier fluid, and additives. Among them, the magnetic particles and carrier fluid are the main sources of the mechanical properties of the MRF. The changes of the related properties of the two will affect the mechanical properties of the MRF directly or indirectly. Herein, first, the temperature–magnetic field characteristics are analyzed during the MRF working process. Then, the influence mechanism of temperature and magnetic field changes on the properties of the magnetic particles and carrier liquid are analyzed. On this basis, the traditional Bingham model is improved and optimized, in which the temperature variable is introduced to represent the effect of temperature–magnetic field coupling on the shear stress of the MRF. Finally, parameter fitting and simulation are carried out for the optimized model, and the self‐made shear stress of the MRF measuring device with temperature‐control function is used to experimentally verify the accuracy of the optimized model. The comparison and verification of the results show that the optimized model can better represent the variation of shear stress of an MRF with temperature and magnetic field than the traditional Bingham model.

AC Electric-Field Assistant Architecting Ordered Network of Ni@PS Microspheres in Epoxy Resin to Enhance Conductivity.

By using the low loading of the conductor filler to achieve high conductivity is a challenge associated with electrically conductive adhesion. In this study, we show an assembling of nickel-coated polystyrene (Ni@PS) microspheres into 3-dimensional network within the epoxy resin with the assistance of an electric field. The morphology evolution of the microspheres was observed with optical microscopy and scanning electron microscopy (SEM). The response speed of Ni@PS microsphere to the electric field were investigated by measuring the viscosity and shear stress variation of the suspension at a low shear rate with an electrorheological instrument. The SEM results revealed that the Ni@PS microspheres aligned into a pearl-alike structure. The AC impedance spectroscopy confirmed that the conductivity of this pearl-alike alignment was significantly enhanced when compared to the pristine one. The maximum enhancement in conductivity is achieved at 15 wt. % of Ni@PS microspheres with the aligned composites about 3 orders of magnitude as much as unaligned one, typically from ~10−5 S/m to ~10−2 S/m.

Estimating Effective Normal Stress During Slow Slip Events From Slip Velocities and Shear Stress Variations

AbstractTheoretical analyses using a rate‐ and state‐dependent friction law have shown quasistatic and stable slip behaviors following velocity weakening. We estimated spatiotemporal slip distributions for six slow slip events (SSEs) off the Boso Peninsula, Japan, from Global Navigation Satellite System data and plotted their shear stress variations vs. slip velocity, here called “trajectories.” Most trajectories are similar to theoretical stable trajectories, implying that the Boso SSEs represent a quasistatic and stable process, and that the gradient of the trajectories during slip acceleration is equal to the product of the friction coefficients of the slipping plates (a–b) and the effective normal stress (). Taking (a–b) = −0.003, we estimate that the effective normal stresses during the SSEs were 10–50 MPa at 12.5–20.5 km depth. These values are much smaller than the lithostatic pressures at those depths, implying high pore pressures on the slow slip interface.

Transient response analysis of FG-CNTRC curved composite panel under multi-directional initially stresses resting on nonpolonomial elastic foundation

Due to importance of exploring novel ways to protect systems from detrimental influences of thermal shock phenomenon, this study aims at analyzing the transient coupled poro/thermoelasticity response of functionally graded CNT reinforced (FG-CNTR) nanocomposite panels surrounded by non-polynomial kind of elastic foundation. In addition to thermal shock, the mentioned nanocomposite structure is subjected to initial mechanical loads in different orientations. As the accuracy of the results is of high prominence to guarantee reliability of the practical designs, the governing equations are developed on the basis of the exact type of elasticity theory known as three-dimensional form. Also, analytical solution is determined by applying Navier approach to solve the governing differential equations for simply-supported boundaries. Energy balance equation is utilized to determine the temperature gradient of the cylindrical panel considering the assumptions that the internal surface is fully isolated and the external one is subjected to thermal shock loading. Modified type of Dunber and Abate’s approach is implemented to inverse the Laplace transform in order to map the response of the system from Laplace into time domain. Convergence of the determined deflection, shear stresses, and temperature versus passing time is analyzed and confirmed. The acquired numerical results elucidate the role of different factors such as mid-radius to thickness ratio, volume-fraction, and scattering pattern of CNT in the transient coupled poro/thermoelasticity response of the FG-CNTR nanocomposite cylindrical panel. As a valuable result, it is found that increasing the volume-fraction of CNT applies negative impacts on the variation of the transverse shear stress.

Channeling the Force: Piezo1 Mechanotransduction in Cancer Metastasis.

Cancer metastasis is one of the leading causes of death worldwide, motivating research into identifying new methods of preventing cancer metastasis. Recently there has been increasing interest in understanding how cancer cells transduce mechanical forces into biochemical signals, as metastasis is a process that consists of a wide range of physical forces. For instance, the circulatory system through which disseminating cancer cells must transit is an environment characterized by variable fluid shear stress due to blood flow. Cancer cells and other cells can transduce physical stimuli into biochemical responses using the mechanosensitive ion channel Piezo1, which is activated by membrane deformations that occur when cells are exposed to physical forces. When active, Piezo1 opens, allowing for calcium flux into the cell. Calcium, as a ubiquitous second-messenger cation, is associated with many signaling pathways involved in cancer metastasis, such as angiogenesis, cell migration, intravasation, and proliferation. In this review, we discuss the roles of Piezo1 in each stage of cancer metastasis in addition to its roles in immune cell activation and cancer cell death.

Critical Shear Stress for Erosion of Sand-Mud Mixtures and Pure Mud

The erosion threshold of sand-mud mixtures is investigated by analyzing the momentum balance of a sand particle or a mud parcel in the mixture bed surface, and a formula for the critical shear stress of sand-mud mixtures is developed, which also applies for pure sand and mud. The developed formula suggests that the variation of the critical shear stress of sand-mud mixtures over mud content is mainly caused by the varying dry bulk density of the mud component in the mixture. The developed formula reproduces well the variation of the critical shear stress of sand-mud mixtures over mud content and can predict the critical shear stress of both sand-mud mixtures and pure mud in the process of consolidation. The developed formula promises to be convenient for application by relating the critical shear stress to mud content and the dry bulk density of sediment.

Effects of varying shear stress profiles on the regulation of pulmonary artery endothelial cell gene expression: a focus on selected mediators of vascular tone, inflammation and angiogenesis

Abstract Background Pulmonary arterial hypertension (PAH) is a complex pathology characterized by obliterative vascular remodeling that leads to right heart failure and death. Predisposition to PAH is associated with mutations in the BMPR2 gene in approximately 70–80% of familial cases and around 30% for that of sporadic PAH. The study of the pathogenetic basis of PAH is often performed in static endothelial cultures. Such two-dimensional, isolated cell microenvironments fail to consider the heterogeneity in mechanical stress acting on endothelial cells in various regions of the pulmonary vascular tree. In the remodeled pulmonary vasculature, low and oscillatory shear stress is observed in the proximal pulmonary artery with high shear stress in distal pre-capillary pulmonary arterioles. Therefore, the impact of varied shear profiles (including both laminar and oscillatory flow) on pulmonary artery endothelial cell (and that of BMPR2-deplete) gene expression of common vasoactive (EDN1, ENOS), proinflammatory (IL6, IL8) and angiogenic mediators (ANG2, VEGFA), are poorly described. Purpose To evaluate the effects of shear stress magnitude, including unidirectional and oscillatory flow on BMPR2-knockdown human pulmonary artery endothelial cell (HPAEC) gene expression of EDN1, ENOS, IL6, IL8, ANG2 and VEGFA. Methods HPAECs were transfected with siRNA directed against BMPR2 (siB2) or with a non-targeting control (siCon). Cells were exposed to 10 hours of laminar or oscillatory flow (1Hz; 1.5 dyn/cm2, 15 dyn/cm2 or 90 dyn/cm2) using a parallel-plate fluid flow chamber system. Measurement of mRNA expression was performed using qPCR. Results Shear stress intensity and flow type (unidirectional and oscillatory) mediated diverse effects on HPAEC gene expression across the markers studied. Changes in gene expression were calculated relative to that of static siCon-transfected HPAECs and in such a manner are summarized as fold changes in the table below. Asterisks are shown where significant fold differences are reported. *P≤0.05, **P≤0.01, ***P≤0.001, ****P≤0.0001. aP≤0.05, bP≤0.05, cP≤0.05, denote comparisons between groups. Of note, no significant differences in gene expression were observed between static siCon and static siB2. Conclusions For the markers studied, different magnitudes of shear stress and flow profiles (together with BMPR2 loss) exhibit varied patterns of gene expression in the pulmonary vascular endothelium. As such, this illustrates the need for wider study of in vitro endothelial-shear stress interactions in understanding mechanisms of remodeling in PAH. Funding Acknowledgement Type of funding sources: None. Table 1

Numerical analysis of surface foundation subjected to strike–slip faulting: model boundaries, pre-softening volumetric response, parametric study

The paper investigates strike-slip fault rupture propagation through dense sand and its interaction with surface foundations, employing 3D finite element (FE) modelling. Two soil constitutive models (implemented in Abaqus through user subroutines) are employed for this purpose: (i) a recently developed simple yet efficient model with a Mohr–Coulomb yield criterion, which incorporates post-yield isotropic frictional hardening and softening (MC–HS model); and (ii) the basic version of the more sophisticated hypoplastic model for sand. Both models are calibrated on the basis of monotonic triaxial compression tests (and an additional oedometer test for the hypoplastic model), conducted as part of this study. The numerical predictions are comparatively assessed against centrifuge model test results. In accord with the centrifuge model tests, the free-field analyses with the MC-HS model reveal a complex fault pattern at the ground surface, consisting of Riedel (R) shears. These are the surficial manifestation of complex 3D structures of helicoidal geometry, attributed to the spatial variation of shear stresses within the overburden soil due to the imposed bedrock offset. The development of R shears is primarily controlled by the pre-softening volumetric soil response in monotonic compression and soil dilation. The latter is underestimated by the basic hypoplastic model, thus predicting the formation of a single straight shear band instead of R shears. A parametric study is conducted employing the validated MC-HS model, exploring fault rupture–soil–foundation interaction. Foundation response is shown to be sensitive to the surficial fault pattern (R shears vs. single fault trace), but the mechanism (rotational vs. translational) and foundation distress are not affected to the same extent. A two-step design strategy is outlined, requiring a free-field analysis to capture the surficial fault pattern, followed by a minimum of four interaction analyses, varying the fault-normal and fault-parallel foundation location.

Understanding an irregular pattern of fracture slip from laboratory earthquake using machine learning

A series of direct-shear experiments on a sawcut fracture under a multi-stage reduction in normal stress shows slip transition behaviors from stick-slip to stable sliding. The irregular slip pattern near the stability transition is traditionally considered unexplainable and unpredictable. This study utilizes a support vector machine (SVM) to classify the fracture slip behaviors and to predict new, unseen slip events. The results exhibit that the SVM trained by the acoustic emission amplitude well predicts the variation of shear stress near the stability transition, and the prediction accuracy slightly decreases with more irregular slip events occurred in the transition stage. The prediction for a fast rupture is more accurate than that for a slow rupture as relatively weak signals from a slow rupture are more sensitive at the same attenuation level. Understanding the irregular slip pattern allows us to better explain the occurrence of Parkfield tremors in California and provides more insights into the mechanisms of repeating earthquakes.

Neutrophil extracellular traps in feline cardiogenic arterial thrombi: a pilot study.

The aim of this study was to investigate the spatial distribution of neutrophil extracellular traps (NETs) in cardiogenic arterial thromboembolism (CATE). Specifically, we aimed to examine the related structural features of NETs in feline arterial thrombi in relation to their arterial locations. Paraffin-embedded aortic bifurcations from nine cats with hypertrophic cardiomyopathy (four with CATE and five without) were deparaffinized, and NETs were identified by immunodetection based on colocalization of cell-free DNA, citrullinated histone H3 and neutrophil elastase. The distribution of NETs in thrombi within the aortic bifurcations and common iliac arteries (CIAs) was compared based on their proximity to the descending aorta (proximal, mid, distal). Ten random fields per section were captured at × 10 and × 20 magnification for each section of the clot and analyzed. The distributions of NETs in thrombi within the aortic bifurcation and CIAs were found to differ in relation to their assigned zones (proximal, mid, distal; P = 0.04); NETs were concentrated mostly in the proximal region in the aortic bifurcations (47.56%, interquartile range [IQR] 14.07-77.95) and CIAs (44.69%, IQR 24.65-85.28), compared with the distal regions (2.69%, IQR 0.10-50.04 [P = 0.027]; 7.08%, IQR 1.27-59.33 [P = 0.02]). The variation in NET distribution within arterial thrombi may shed light on the pathogenesis of thrombus growth. This may be due to possible neutrophil entrapment or variations in shear stress.

Effect of thermal radiation on MHD three dimensional natural convective Couette flow in presence of thermo-diffusion and chemical reaction

This paper analyzes the effect of thermal radiation on MHD three dimensional natural convective Couette flow of an incompressible, viscous and electrically conducting fluid with uniform magnetic field. The plates are taken vertically upward. The magnetic field is applied normal to the plates. The governing equations are solved using simple perturbation technique. The effect of various parameters like M , Pr , R , Re , Gr , Gm etc. are studied graphically on dimensionless velocity, temperature and concentration. Also the variations in shear stress ( τ ), Nusselt number ( Nu ) and Sherwood number ( Sh ) for different physical parameters are presented in tables.

Influence of porosity distribution on static and buckling responses of porous functionally graded plates

This article studies the effect of porosity distribution on static and buckling response of a functionally graded (FG) porous plate with all its four edges simply supported and subjected to a transverse load. The plate’s displacement field is approximated based on an inverse hyperbolic shear deformation theory (IHSDT) involving five variables. In this theory, inplane displacements vary as an inverse hyperbolic function through the plate thickness, so account for non-linear variation of transverse shear stresses and satisfies traction free boundary conditions on the surfaces of plate without the need of any shear correction factors. The governing equations of motion are derived using the principle of virtual work, and thus, the expressions of its strain energy and work done are obtained. Effective material properties of porous plate are assumed with an additional term of porosity in the direction of thickness. Power-law is used for continuous variation of material properties along the thickness direction. In this study, five types of porosity distribution functions are considered. The effect of the porosity parameter, the power-law exponent, side-thickness ratio, and aspect ratio on the static and buckling responses of the porous FG plate is evaluated. In problem-solving, the Navier solution technique is used to obtain the exact solutions. The non-dimensional deflections and critical buckling loads of FG porous plate are thus obtained. The results are compared with available results in the literature, and good agreement is found. Moreover, the results are presented to study the effects of various parameters on the dimensionless deflections, stresses, and critical uni-axial and bi-axial buckling loads.

Three-dimensional direct numerical simulation of flow induced by an oscillating sphere close to a plane boundary

The dynamic interaction of submerged spherical structures with ocean waves alters the local flow field and is responsible for the movement of sediments over the seabed, which would have detrimental effects on the ecosystems. The present research aims to gain insight into the effect of a plane boundary on the vorticity dynamics and shear modifications on the plane boundary induced by the flow due to an oscillating sphere. The flow field around an oscillating sphere close to a plane boundary is investigated numerically by three-dimensional direct numerical simulation of the Navier–Stokes equations. The sphere oscillates perpendicular to the plane boundary modeling the seabed. The flow structure, resulting mean and fluctuating shear stress distribution on the plane boundary, and the Lagrangian particle transport are investigated as a function of the sphere oscillation amplitude, Reynolds number, and the distance of the sphere from the plane boundary. The systematic correlations for the variation of maximum shear stress on the plane boundary are estimated from scaling parameters. The time-mean results are then linked to the Lagrangian particle transport where it is observed that the Lagrangian path lines track the mean streamlines closely. Further, the particles at the stagnation zone cease drifting and oscillate about a constant mean position. The practical significance of this result is that a ring of zero mean shear on the seabed is found toward where particles congregate. This provides a guide for the optimum location for the mooring anchors, minimizing the risk of anchor scour or undermining.

Modifications of structural, dielectric and ferroelectric properties induced by porosity in BaTiO3 ceramics with phase coexistence

The modifications of structural and functional properties induced by the gradual increase of porosity from 4 vol% to 26 vol% produced by addition of polymeric sacrificial templates in BaTiO3 ceramics were investigated in detail. With respect to other previous studies concerning porous ceramics, the present ones show a phase superposition around room temperature, whose relative amount impact on their functional properties. Low/high porosity favours the orthorhombic/tetragonal symmetry, respectively. Permittivity and polarisation (both irreversible and reversible ones) regularly decrease when reducing ceramic density, while dc tunability and P(E) loops of denser ceramics have shown peculiar features at intermediate fields, i.e. modifications of hysteretic-nonhysteretic character of ε(E) dependences at about± (8–10) kV/cm and wasp-waisted P(E) loops. To explain such effects, a simplified Landau-based approached considering variable shear stress contributions (higher in dense ceramics, lower in porous ones) was developed to examine the stability of orthorhombic/tetragonal states as a function of stress and applied field levels. The simulations indicated for dense ceramics the possibility of a field-induced structural transformation at intermediate field range overlapped on the general trend of stress-induced increasing of orthorhombic amount. The porosity-induced modification of properties in BaTiO3 ceramics is related to the value of porosity itself which reduces the amount of ferroelectric active phase, to possible modifications of pore connectivity at various porosity levels, but also by modifications of internal stress level induced by porosity, which impact on the polymorph phase composition.

Applications of deep learning to the assessment of red blood cell deformability.

Measurement of abnormal Red Blood Cell (RBC) deformability is a main indicator of Sickle Cell Anemia (SCA) and requires standardized quantification methods. Ektacytometry is commonly used to estimate the fraction of Sickled Cells (SCs) by measuring the deformability of RBCs from laser diffraction patterns under varying shear stress. In addition to estimations from model comparisons, use of maximum Elongation Index differences (ΔEImax) at different laser intensity levels was recently proposed for the estimation of SC fractions. Implement a convolutional neural network to accurately estimate rigid-cell fraction and RBC concentration from laser diffraction patterns without using a theoretical model and eliminating the ektacytometer dependency for deformability measurements. RBCs were collected from control patients. Rigid-cell fraction experiments were performed using varying concentrations of glutaraldehyde. Serial dilutions were used for varying the concentration of RBC. A convolutional neural network was constructed using Python and TensorFlow. Measurements and model predictions show that a linear relationship between ΔEImax and rigid-cell fraction exists only for rigid-cell fractions less than 0.2. The proposed neural network architecture can be used successfully for both RBC concentration and rigid-cell fraction estimations without a need for a theoretical model.

Stress distribution in the walls of major arteries: implications for atherogenesis.

There is a correlation between the sites of atheroma development and stress points in the arterial system. Generally, pulse pressure results in stresses acting on the vascular vessel, including longitudinal stress, radial or normal stress, tangential stress or hoop stress and shear stress. This paper explores the relationship between arterial wall shear stress and pulsatile blood pressure with the aim of furthering the understanding of atherogenesis and plaque progression. We computed the magnitude of the shear stresses within the carotid bifurcation geometry of a patient and calculated the increase in shear stress levels that would occur when the blood pressure and pulse pressures rise during exertion. We also determined in which layer of the artery wall the maximum shear stress is located, and computed the shear stress at different levels within the media. We used the theory of laminate analysis, (Classical Laminate Plate Theory), to analyse the stress distribution on the carotid artery wall. Computational Fluid Dynamics (CFD) analysis was used on anatomy based on a CT angiogram of the carotid bifurcation of a patient with a 90% stenosis on the right side and 10% on the left. The pulsatile non-Newtonian blood flow with a resting blood pressure of 120/80 mmHg and an exertion pressure of 200/100 mmHg was simulated and the resultant forces were transferred to an ANSYS Composite PrepPost (ACP) model for wall shear stress analysis. A multilayer elastic, anisotropic, and inhomogeneous arterial wall (intima, internal elastic lamina, media, external elastic lamina, and adventitial layers) was modelled and the shear stress magnitudes and change over time between the layers was calculated. Shear stress in the individual composite layers is far greater than that acting on the endothelium (less than 5 Pa). At rest, the maximum variation of shear stress in the arterial wall occurs in the intima (138 Pa) and adventitia (135 Pa). The medial layer has the lowest variation of shear stress. Under severe exertion, the maximum shear stress magnitude in the intimal layer and the adjacent medial layer is near the ultimate stress level. The maximum/minimum shear stress ratios during the cardiac cycle vary most widely in the innermost part of the media, adjacent to the intima, with a four-fold ratio increase. This compares with a less than two-fold increase in all the other layers including the intima and adventitia, making the inner media the most vulnerable layer to mechanical injury. This study showed that the magnitude of exertion-induced shear stress approaches the ultimate stress limit in the intima and the immediate adjacent medial layer. The variation in stress is maximal in the inner layer of the media. These findings correlate the site of atheroma development with the most vulnerable site for injury in the media and emphasise the impact of pulse pressure. Further biological studies are required to ascertain whether this leads to injury that initiates atheroma that then precipitates an injury/healing cycle.

Numerical study of the dam-break waves and Favre waves down sloped wet rigid-bed at laboratory scale

The bed slope and the tailwater depth are two important ones among the factors that affect the propagation of the dam-break flood and Favre waves. Most previous studies have only focused on the macroscopic characteristics of the dam-break flows or Favre waves under the condition of horizontal bed, rather than the internal movement characteristics in sloped channel. The present study applies two numerical models, namely, large eddy simulation (LES) and shallow water equations (SWEs) models embedded in the CFD software package FLOW-3D to analyze the internal movement characteristics of the dam-break flows and Favre waves, such as water level, the velocity distribution, the fluid particles acceleration and the bed shear stress, under the different bed slopes and water depth ratios. The results under the conditions considered in this study show that there is a flow state transition in the flow evolution for the steep bed slope even in water depth ratio α = 0.1 (α is the ratio of the tailwater depth to the reservoir water depth). The flow state transition shows that the wavefront changes from a breaking state to undular. Such flow transition is not observed for the horizontal slope and mild bed slope. The existence of the Favre waves leads to a significant increase of the vertical velocity and the vertical acceleration. In this situation, the SWEs model has poor prediction. Analysis reveals that the variation of the maximum bed shear stress is affected by both the bed slope and tailwater depth. Under the same bed slope (e.g., S0 = 0.02), the maximum bed shear stress position develops downstream of the dam when α = 0.1, while it develops towards the end of the reservoir when α = 0.7. For the same water depth ratio (e.g., α = 0.7), the maximum bed shear stress position always locates within the reservoir at S0 = 0.02, while it appears in the downstream of the dam for S0 = 0 and 0.003 after the flow evolves for a while. The comparison between the numerical simulation and experimental measurements shows that the LES model can predict the internal movement characteristics with satisfactory accuracy. This study improves the understanding of the effect of both the bed slope and the tailwater depth on the internal movement characteristics of the dam-break flows and Favre waves, which also provides a valuable reference for determining the flood embankment height and designing the channel bed anti-scouring facility.

Ligand and precatalyst offerings expand

The bed slope and the tailwater depth are two important ones among the factors that affect the propagation of the dam-break flood and Favre waves. Most previous studies have only focused on the macroscopic characteristics of the dam-break flows or Favre waves under the condition of horizontal bed, rather than the internal movement characteristics in sloped channel. The present study applies two numerical models, namely, large eddy simulation (LES) and shallow water equations (SWEs) models embedded in the CFD software package FLOW-3D to analyze the internal movement characteristics of the dam-break flows and Favre waves, such as water level, the velocity distribution, the fluid particles acceleration and the bed shear stress, under the different bed slopes and water depth ratios. The results under the conditions considered in this study show that there is a flow state transition in the flow evolution for the steep bed slope even in water depth ratio α = 0.1 (α is the ratio of the tailwater depth to the reservoir water depth). The flow state transition shows that the wavefront changes from a breaking state to undular. Such flow transition is not observed for the horizontal slope and mild bed slope. The existence of the Favre waves leads to a significant increase of the vertical velocity and the vertical acceleration. In this situation, the SWEs model has poor prediction. Analysis reveals that the variation of the maximum bed shear stress is affected by both the bed slope and tailwater depth. Under the same bed slope (e.g., S0 = 0.02), the maximum bed shear stress position develops downstream of the dam when α = 0.1, while it develops towards the end of the reservoir when α = 0.7. For the same water depth ratio (e.g., α = 0.7), the maximum bed shear stress position always locates within the reservoir at S0 = 0.02, while it appears in the downstream of the dam for S0 = 0 and 0.003 after the flow evolves for a while. The comparison between the numerical simulation and experimental measurements shows that the LES model can predict the internal movement characteristics with satisfactory accuracy. This study improves the understanding of the effect of both the bed slope and the tailwater depth on the internal movement characteristics of the dam-break flows and Favre waves, which also provides a valuable reference for determining the flood embankment height and designing the channel bed anti-scouring facility.

Three-Dimensional Numerical Investigations of the Flow Pattern and Evolution of the Horseshoe Vortex at a Circular Pier during the Development of a Scour Hole

In the current study, a three-dimensional CFD model is utilized to investigate the variation of the flow structure and bed shear stress at a single cylindrical pier during scour development. The scour development is presented by seven solidified geometries of the scour hole, collected during previous experimental work at different scour stages. Different turbulence models are evaluated and the (k-ω) model is chosen due to its relative accuracy in capturing the flow oscillation and vortex shedding at the pier downstream side with personal computer computational and storage resources. The numerical results are verified against dimensionless parameters from different previous experimental works. This research describes in detail the flow structure and bed shear stress variations through seven stages of the scour hole development. The dimensionless area-averaged circulation coefficient (Ψi) is developed to evaluate the changes in the vortex strength through the scouring process by eliminating the calculation area effect. It was concluded that the circulation in the (Y) direction is the main driving factor in the development of the scour hole more than the circulation in the (X) direction. The ratio between the horseshoe vortex (HV) mean size and the scouring depth (DV/dS) in addition to the location of the maximum bed shear stress are investigated during different stages of the scour development.

Clot Formation Under Physiological Flow Conditions Is Altered in Sickle Cell Disease As Measured By a Multiparameter Microfluidic System

Background: While the hallmark of sickle cell disease (SCD) is vaso-occlusion, it is now clear that hypercoagulation plays a prominent role in the pathophysiology of SCD (Sparkenbaugh 2017). Consistent with this prothrombotic state, SCD patients remain at increased risk for thromboembolic events (Naik 2014) such as pulmonary embolism and deep vein thrombosis. In addition, sickle red blood cells (RBC) are known to biochemically contribute to the hypercoaguable state through hemolysis or enhanced PS exposure (Whelihan 2016, Litvinov 2017). However, no studies have examined the biophysical contribution of RBCs to clot formation in SCD, especially under physiologic flow conditions. As both the increased stiffness and adhesion of the sickle RBC (Kasschau 2016) biophysically amplify the frequency and duration of interactions with the developing clot, we hypothesize that enhanced RBC incorporation occurs in sickle cell clots under physiologic flow conditions. Furthermore, as the altered shape and stiffness of sickle RBCs decreases the packing density in clots (Tutwiler 2015, Strauss 2015), we also hypothesize that the application of fluidic forces to the clots likely causes instability potentially leading to thromboemboli. This highlights the need for an assay that studies both clot formation and stability under flow conditions.Innovation: While studying these events in vivo remains the most physiologically relevant approach, the inability to control the cellular and physical parameters renders mechanistic studies to be extremely challenging. Moreover, while in vitro microfluidics offer the unique ability to precisely control parameters known to affect clot formation, including shear stress, hematocrit, platelet count, and oxygen tension, these devices typically cannot be used for extended time studies due to confounding systemic clotting throughout the fluidic. To that end, we developed a novel multi-parameter microfluidic that precisely controls the spatial location of clot initiation and formation for extended (>30 mins) in vitro studies of developing clots using recalcified citrated whole blood (Figure 1a). Our easy-to-use system combines on-chip calcification (Lehmann 2015) to reduce systemic clotting, simple assembly methods (Myers 2017), and protein micropatterning using collagen and tissue factor. Brightfield and fluorescent microscopy was used to examine the flow of blood over this patch to observe the clot formation process, structure, and stability.Results: The device performed as designed and maintained perfusion for at least 45 minutes with each trial for healthy AA donors (Figure 1b). Our preliminary images qualitatively show that clots from SS patients on hydroxyurea are larger than AA clots (Figure 1b-c). Quantitative measurements of the clot areas indicate that the clot size is significantly higher in SCD blood (n=3 patients, Mann-Whitney, p= 0.007) than in blood from healthy AA subjects (n=21) (Figure 1d). This suggests that even in the modern age of hydroxyurea therapy, patients remain in a prothrombotic state. Furthermore, after SCD whole blood clots were formed in our microfluidic system, force applied via continuous exposure to high shear stress of ~3000 dynes/cm2 in the microfluidic created clot fragments composed primarily of RBCs. The creation of these fragments suggests decreased clot stability and has implications for micro-thromboemboli (Figure 1e). These results support our hypothesis that enhanced RBC incorporation in SCD alters the structure and stability of whole blood clots. Ongoing studies are focused on defining the compositional variability and susceptibility to embolism.Conclusion and Relevance: Ongoing studies involve integrating and varying shear stress, hematocrit, platelet count, and oxygen tension to determine how these multiple parameters interact to affect the incorporation of sickle RBCs in thrombi, as our novel microfluidic enables real time visualization of clot formation and clot stability under physiologic flow conditions (Figure 2). Our device allows us to examine the stability of these clots under shear stress and the propensity for emboli formation. Collectively, these studies will lead to a better understanding of the prothrombotic state of SCD and how the sickle RBCs interacts with platelets and the coagulation cascade. [Display omitted] DisclosuresLam:Sanguina, LLC: Equity Ownership.