Showing papers on "Shear stress published in 2021"

Permeability Evolution of Two-Dimensional Fracture Networks During Shear Under Constant Normal Stiffness Boundary Conditions

Abstract: The permeability evolution of fractal-based two-dimensional discrete fracture networks (DFNs) during shearing under constant normal stiffness (CNS) boundary conditions is numerically modeled and analyzed based on a fully coupled hydromechanical (HM) model. The effects of fractal dimension, boundary normal stiffness and hydraulic pressure on the evolutions of mechanical behaviors, aperture distributions and permeability are quantitatively investigated. The results show that with increasing confining pressure from 0 to 30 MPa, the permeability decreases from the magnitude of 10−13 m2 to 10−16 m2, which is generally consistent with previous models reported in the literature. With the increment of shear displacement from 0 to 500 mm, the variations in shear stress, normal stress and normal displacement exhibit the same patterns with the conceptual model. As shear advances, the permeability evolution exhibits a three-stage behavior. In the first stage, the permeability decreases due to the compaction of fractures induced by the increasing shear stress from 0 to the peak value. In the second stage, the permeability holds almost constant values under constant normal load (CNL) boundary conditions, whereas that under CNS boundary conditions decreases by approximately one order of magnitude. Under CNS boundary conditions, although the aperture of shearing fracture increases enhancing its own permeability, the apertures of surrounding fractures are compacted due to the simultaneous increases in the normal and shear stresses, which result in the decrease in the total permeability of DFNs. When the fractal dimension increases from 1.4 to 1.5, the permeability increases following exponential functions in the early stage of shear, which fail to characterize the permeability in the residual stage due to the complex flow path distributions. At the start of shear, the ratio of permeability perpendicular to the shear direction to that parallel to shear decreases approximately from 1.0 to 0.5 and then gradually decreases from 0.5 to 0.3 in the residual stage. The hydraulic pressure tends to open up the fractures and enhances the permeability. The magnitude in permeability enhancement is of approximately the same order with the increase in the hydraulic pressure.

Leveraging Elasticity to Uncover the Role of Rabinowitsch Suspension through a Wavelike Conduit: Consolidated Blood Suspension Application

Abstract: The present work presents a mathematical investigation of a Rabinowitsch suspension fluid through elastic walls with heat transfer under the effect of electroosmotic forces (EOFs). The governing equations contain empirical stress-strain equations of the Rabinowitsch fluid model and equations of fluid motion along with heat transfer. It is of interest in this work to study the effects of EOFs, which are rigid spherical particles that are suspended in the Rabinowitsch fluid, the Grashof parameter, heat source, and elasticity on the shear stress of the Rabinowitsch fluid model and flow quantities. The solutions are achieved by taking long wavelength approximation with the creeping flow system. A comparison is set between the effect of pseudoplasticity and dilatation on the behaviour of shear stress, axial velocity, and pressure rise. Physical behaviours have been graphically discussed. It was found that the Rabinowitsch and electroosmotic parameters enhance the shear stress while they reduce the pressure gradient. A biomedical application to the problem is presented. The present analysis is particularly important in biomedicine and physiology.

Laboratory investigation on erosion threshold shear stress of cohesive sediment in Karkheh Dam

Abstract: The awareness of the transmission of the sticky sediments for the development and maintenance of reservoirs and water transfer network is very important. This research was carried out to recognize and understand the dynamic behavior of fine-sticky sediments to obtain the necessary information for the Karkheh dam reservoir management. Sediment samples were taken from the four different points located in the dam reservoir. Liquidity and plasticity behaviors and their indices of the samples that were combined together were determined by doing the Atterberg limits experiment. To investigate the initial erosion threshold shear stress, the impact of consolidation and sediment depth were examined by cylindrical settling columns. Using a circular flume in, Shahrekord University Lab, the concentration process, changes of eroded sediments, shear stress threshold of erosion, erosion rates, etc. in different consolidation periods (3, 14 and 30 days) were studied. The results showed that the concentration of eroded sediments is a function of time for the consolidation of reservoir sediment and bed shear stress and also observed that the duration of consolidation time is an effective factor on critical erosion shear stress. So, the threshold shear stress values for consolidation time of 3, 14 and 30 days were, 0.16, 0.22, 0.31 N/m2, respectively. The results of the erosion rate suggest an inverse relationship between this parameter and the life of the settled sediments based on the results the best flow shear stress for sediment removal by flashing from the Karkheh dam reservoir should be greater than 0.31 N/m2.

Back propagation modeling of shear stress and viscosity of aqueous Ionic-MXene nanofluids

Abstract: Back-propagation modeling of viscosity and shear stress of Ionic-MXene nanofluid is carried out in this work. The data for Ionic-MXene nanofluid of 0.05, 0.1, and 0.2 mass concentration (mass%) are collected from the experimental analysis. Shear stress and viscosity as a function of shear rate and mass% of MXene nanoparticles is used as input. Additionally, viscosity as a function of temperature and % of MXene nanoparticles is collected separately. Based on the possible combinations, five back-propagation algorithms are developed. In each algorithm, five models depending upon the number of neurons in the hidden layer are used. The training and testing of all the models in each algorithm are performed. Statistical analysis of the network output is done to evaluate the accuracy of models by finding the losses in terms of mean squared error (MAE), root-mean-squared error, mean absolute error, (MAE), and error deviation. Model 1 is found to have lower accuracy than the remaining models as the number of neurons in its hidden layer is only one. The performance evaluation metrices of the back-propagation model show that the error involved is acceptable. The training and testing of the algorithms are satisfactory as the network output is found to be in comfortably good agreement with the desired experimental output.

The fluid shear stress sensor TRPM7 regulates tumor cell intravasation.

Abstract: Tumor cell intravasation preferentially occurs in regions of low fluid shear because high shear is detrimental to tumor cells. Here, we describe a molecular mechanism by which cells avoid high shear during intravasation. The transition from migration to intravasation was modeled using a microfluidic device where cells migrating inside longitudinal tissue-like microchannels encounter an orthogonal channel in which fluid flow induces physiological shear stresses. This approach was complemented with intravital microscopy, patch-clamp, and signal transduction imaging techniques. Fluid shear-induced activation of the transient receptor potential melastatin 7 (TRPM7) channel promotes extracellular calcium influx, which then activates RhoA/myosin-II and calmodulin/IQGAP1/Cdc42 pathways to coordinate reversal of migration direction, thereby avoiding shear stress. Cells displaying higher shear sensitivity due to higher TRPM7 activity levels intravasate less efficiently and establish less invasive metastatic lesions. This study provides a mechanistic interpretation for the role of shear stress and its sensor, TRPM7, in tumor cell intravasation.

The influence of inlet velocity profile on predicted flow in type B aortic dissection

Abstract: In order for computational fluid dynamics to provide quantitative parameters to aid in the clinical assessment of type B aortic dissection, the results must accurately mimic the hemodynamic environment within the aorta. The choice of inlet velocity profile (IVP) therefore is crucial; however, idealised profiles are often adopted, and the effect of IVP on hemodynamics in a dissected aorta is unclear. This study examined two scenarios with respect to the influence of IVP-using (a) patient-specific data in the form of a three-directional (3D), through-plane (TP) or flat IVP; and (b) non-patient-specific flow waveform. The results obtained from nine simulations using patient-specific data showed that all forms of IVP were able to reproduce global flow patterns as observed with 4D flow magnetic resonance imaging. Differences in maximum velocity and time-averaged wall shear stress near the primary entry tear were up to 3% and 6%, respectively, while pressure differences across the true and false lumen differed by up to 6%. More notable variations were found in regions of low wall shear stress when the primary entry tear was close to the left subclavian artery. The results obtained with non-patient-specific waveforms were markedly different. Throughout the aorta, a 25% reduction in stroke volume resulted in up to 28% and 35% reduction in velocity and wall shear stress, respectively, while the shape of flow waveform had a profound influence on the predicted pressure. The results of this study suggest that 3D, TP and flat IVPs all yield reasonably similar velocity and time-averaged wall shear stress results, but TP IVPs should be used where possible for better prediction of pressure. In the absence of patient-specific velocity data, effort should be made to acquire patient's stroke volume and adjust the applied IVP accordingly.

Rheology and application of buoyant foam concrete for digital fabrication

Abstract: In the fresh state, conventional lightweight foam concrete (LWFC) has low yield stress which challenges shape retention and buildability in digital construction. Several literatures attempt to address the rheological performance of 3D printable lightweight foam concrete (3DP-LWFC) in essence. This research presents a comprehensive rheological characterisation with controlled shear rate tests and flow curve tests over different foam volume fractions and densities of 700, 1000 and 1400 kg/m3. LWFC is appropriately adapted for extrusion-based 3D printing in the experimental program by incorporating a small amount of nanopowder (replacing 2% of cement mass) for increased yield shear stress, and calcium sulfoaluminate cement replacing 10% of cement mass for improved thixotropy in the fresh state. Accordingly, this raises the yield stress to 347–812 Pa for 700–1400 kg/m3 LWFC compared to static yield stress below 100 Pa of conventional LWFC, improves thixotropic performance in terms of the rate of reflocculation (Rthix 0.21–3.15 Pa/s) and rate of structuration (Athix 0.06–1.02 Pa/s), viscosity (2.5–3.4 Pa⋅s), and elastic shear modulus evolution. Foam volume is found to significantly influence the rheological properties. To analyse the constructability, shape retention and buildability are investigated, resulting in up to 15 deposited filament layers to be reached in a buildability test. Lastly, a practical example is presented whereby a facade element is printed with 3DP-LWFC at a wet density less than 1000 kg/m3, yielding a lightweight element with buoyant characteristics that further expands the application potential of 3D concrete printing.

Ohmic heating and chemical reaction effect on MHD flow of micropolar fluid past a stretching surface

Abstract: The current article discuss the interaction between the Ohmic heating and chemical reaction impact on MHD micropolar fluid flow past a stretching surface in the existence of chemical reaction using Runge–Kutta–Fehlberg method (RKF-45) along with the shooting procedure. By applying some similarity transformations, the governing equations were changed to ODEs. Numerical consequences were calculated for many values of pertinent factors on flow, angular velocity, thermal, mass transfer are exposed graphically and the numerical outcomes of the skin friction, couple stress at the wall, Nusselt number, Sherwood number are entered in tabulated form. With an increase of the material parameter, the velocity, couple stress, Sherwood number, Nusselt number, and temperature, concentration, and shear stress increase, while temperature, concentration, and shear stress decreases.

Scale effect of shear mechanical properties of non-penetrating horizontal rock-like joints

Abstract: From the perspective of macroscopic scale, the majority of natural rock mass should be categorized as non-penetrating jointed rock mass. The existing researches in the field of scale effect of joint properties were mainly implemented on penetrating joints, which contradicts engineering practice, and is of high possibility to make the strength estimation of large natural jointed rock mass inaccurate, leading to serious loss of life and property. In response to such case, a series of numerical calculations of direct shear test on non-penetrating horizontal rock-like joints with different scales were carried out by PFC in this paper, to investigate the scale effect of shear mechanical properties of non-penetrating horizontal rock-like joints. First, the model microparameters were calibrated by three physical experiments to guarantee the precise reproduction of the mechanical performances of target rock and joint. Next, the particle parameters (average particle size dave and radius ratio μ) of model were changed, the effect of particle size on joint strength was studied by direct shear calculation, and the determining method for the values of dave and μ was suggested. Then, based on two distribution forms of non-penetrating horizontal rock-like joint (type I and type II joints), the numerical shear tests were conducted on jointed rock models with different persistence rations and model scales, and the variations of shear stress displacement curve and strength characteristics were analyzed. The results indicate: The lower the persistence ration λ of the joint, the more obvious the negative scale effect of joint shear strength. Besides, the scale effect of shear strength gradually decreases when λ > 0.5 for type I joints while λ > 0.8 for type II joints and the scale effects of joint strength parameters only emerge in the case of λ < 0.2.

Influence of shear deformation during asymmetric rolling on the microstructure, texture, and mechanical properties of the AZ31B magnesium alloy sheet

Abstract: In this study, the changes in the microstructure, texture, and mechanical properties of the AZ31B magnesium alloy sheet after asymmetric rolling (ASR) in different shear deformations during each pass are reported. A high shear strain is induced along the sheet thickness when the velocity ratio of the upper and lower rollers is 1.8. In the case of the sheet processed via ASR in the reverse shear deformation along the rolling direction (RASR), the grain refinement, weak basal texture, and improved structural homogeneity result in better mechanical properties than those of the sheet processed via symmetric rolling (SR). However, in the case of the sheet processed via ASR in the single shear deformation along the rolling direction (UASR), shear bands containing dynamically recrystallized grains and larger numbers of dislocation are formed, tilting the peak intensity of the pole figure away from the normal direction. Moreover, the shear band with an average grain size of 5 μm causes severe structural inhomogeneity, which results in bad mechanical properties than the other two sheets. Furthermore, the twin mode changes from the double twin of the SR sheet to the extension twin of the ASR sheet under shear strain. The extension twin contributes to the optimization of the mechanical properties. Finally, the strength and elongation of the sheets processed via RASR are simultaneously improved to 250.3 MPa and 12.5%, respectively.

Heat and mass transfer on unsteady mhd flow through an infinite oscillating vertical porous surface

Abstract: M. Veera Krishna, M. Gangadhar Reddy, & A.J. Chamkha Department of Mathematics, Rayalaseema University, Kurnool, Andhra Pradesh 518007, India Department of Science and Humanities, Sri Venkateswara Institute of Science and Technology, Kadapa, Andhra Pradesh 516003, India Faculty of Engineering, Kuwait College of Science and Technology, Doha District, Kuwait Center of Excellence in Desalination Technology, King Abdulaziz University, P.O. Box 80200, Jeddah 21589, Saudi Arabia

Shear relaxation governs fusion dynamics of biomolecular condensates

Abstract: Phase-separated biomolecular condensates must respond agilely to biochemical and environmental cues in performing their wide-ranging cellular functions, but our understanding of condensate dynamics is lagging. Ample evidence now indicates biomolecular condensates as viscoelastic fluids, where shear stress relaxes at a finite rate, not instantaneously as in viscous liquids. Yet the fusion dynamics of condensate droplets has only been modeled based on viscous liquids, with fusion time given by the viscocapillary ratio (viscosity over interfacial tension). Here we used optically trapped polystyrene beads to measure the viscous and elastic moduli and the interfacial tensions of four types of droplets. Our results challenge the viscocapillary model, and reveal that the relaxation of shear stress governs fusion dynamics. These findings likely have implications for other dynamic processes such as multiphase organization, assembly and disassembly, and aging.

Sub-micron moulding topological mass transport regimes in angled vortex fluidic flow

Abstract: Shear stress in dynamic thin films, as in vortex fluidics, can be harnessed for generating non-equilibrium conditions, but the nature of the fluid flow is not understood. A rapidly rotating inclined tube in the vortex fluidic device (VFD) imparts shear stress (mechanical energy) into a thin film of liquid, depending on the physical characteristics of the liquid and rotational speed, ω, tilt angle, θ, and diameter of the tube. Through understanding that the fluid exhibits resonance behaviours from the confining boundaries of the glass surface and the meniscus that determines the liquid film thickness, we have established specific topological mass transport regimes. These topologies have been established through materials processing, as spinning top flow normal to the surface of the tube, double-helical flow across the thin film, and spicular flow, a transitional region where both effects contribute. The manifestation of mass transport patterns within the film have been observed by monitoring the mixing time, temperature profile, and film thickness against increasing rotational speed, ω. In addition, these flow patterns have unique signatures that enable the morphology of nanomaterials processed in the VFD to be predicted, for example in reversible scrolling and crumbling graphene oxide sheets. Shear-stress induced recrystallisation, crystallisation and polymerisation, at different rotational speeds, provide moulds of high-shear topologies, as ‘positive’ and ‘negative’ spicular flow behaviour. ‘Molecular drilling’ of holes in a thin film of polysulfone demonstrate spatial arrangement of double-helices. The grand sum of the different behavioural regimes is a general fluid flow model that accounts for all processing in the VFD at an optimal tilt angle of 45°, and provides a new concept in the fabrication of novel nanomaterials and controlling the organisation of matter.

Effective viscosity and Reynolds number of non-Newtonian fluids using Meter model

Abstract: The Meter model (a four-parameter model) captures shear viscosity–shear stress relationship (S-shaped type) of polymeric non-Newtonian fluids. We devise an analytical solution for radial velocity profile, average velocity, and volumetric flow rate of steady-state laminar flow of non-Newtonian Meter model fluids through a circular geometry. The analytical solution converts to the Hagen–Posseuille equation for the Newtonian fluid case. We also develop the formulations to determine effective viscosity, Reynolds number, and Darcy’s friction factor using measurable parameters as available rheological models do not correctly define these parameters for a given set of flow condition in circular geometry. The analytical solution and formulations are validated against experimental data. The results suggest that the effective Reynolds number and effective friction factor estimated using the proposed formulation help characterize non-Newtonian fluid flow through a circular geometry in laminar and turbulent flows.

Effects of initial static shear stress orientation on cyclic behavior of calcareous sand

Abstract: The current study investigated the effect of the initial static shear stress orientation on the liquefaction behavior of Hormuz Island calcareous sand. An experimental study was performed using nin...