Decrease In Shear Stress Research Articles

Numerical predictions of shear stress and cyclic stretch in pulmonary hypertension due to left heart failure.

Isolated post-capillary pulmonary hypertension (Ipc-PH) occurs due to left heart failure, which contributes to 1 out of every 9 deaths in the United States. In some patients, through unknown mechanisms, Ipc-PH transitions to combined pre-/post-capillary PH (Cpc-PH) and is associated with a dramatic increase in mortality. Altered mechanical forces and subsequent biological signaling in the pulmonary vascular bed likely contribute to the transition from Ipc-PH to Cpc-PH. However, even in a healthy pulmonary circulation, the mechanical forces in the smallest vessels (the arterioles, capillary bed, and venules) have not been quantitatively defined. This study is the first to examine this question via a computational fluid dynamics model of the human pulmonary arteries, arterioles, venules, and veins. Using this model, we predict temporal and spatial dynamics of cyclic stretch and wall shear stress with healthy and diseased hemodynamics. In the normotensive case for large vessels, numerical simulations show that large arteries have higher pressure and flow than large veins, as well as more pronounced changes in area throughout the cardiac cycle. In the microvasculature, shear stress increases and cyclic stretch decreases as vessel radius decreases. When we impose an increase in left atrial pressure to simulate Ipc-PH, shear stress decreases and cyclic stretch increases as compared to the healthy case. Overall, this model predicts pressure, flow, shear stress, and cyclic stretch that providing a way to analyze and investigate hypotheses related to disease progression in the pulmonary circulation.

A layer-wise formulation for transient response of composite sandwich panel in the exposure of thermal shock loading by considering novel linear and torsional elastic foundation

In order to present practical ways to decline the adverse effects of thermal shock loading from the perspective of improving structural design, authors of this study put their main focus on the analysis of transient coupled poro-thermo-elastic behavior of the sandwich cylindrical panel under multi-directional initially stresses with functionally graded carbon nanotube reinforced (FG-CNTRC) face-layers and polymeric core resting on novel elastic foundation. With the aid of compatibility conditions, the sandwich structure with three layers are modeled. To guarantee the accuracy of the calculations, authors define the governing equations of the system within the context of the exact three-dimensional form of elasticity theory. Additionally, the Navier approach is employed as the analytical solution to find the response of the simply-supported structure in the content of shear stresses and transverse deflection. Dubner and Abate method is utilized to inverse the Laplace transform in order to determine the time history of the system. Convergence of the stress and deflections of the system with respect to passing time is examined and verified. The parametric study reveals that utilizing each of the CNT scattering patterns through the radial direction of the face-layers is useful for protecting specific proportion of the thickness against the applied thermal shock. Moreover, by tracking the effect of increasing the damper coefficient of the surrounding foundation on the different components of the stress, it is revealed that increasing this factor leads to increase of the transverse shear stress and decrease of the normal shear stress.

A parametric study on the behavior of RC and FRC deep beams with and without CFRP strengthening using ANSYS

Deep beams are common elements in concrete structures such as bridges, water tanks, etc. Deep beams were designed by using the strut-and-tie model (STM) method without any web reinforcement using ACI 318-14 with a shear span to depth ratio (a/d =1). RC deep beams show brittle failure by crushing of struts under applied load. Fiber reinforced concrete (FRC) is a better alternative for the reinforced concrete beam without web reinforcement as it contains fibers such as a ramid, steel, etc. The fibers used were steel fibers of 1% volume, and aspect ratio of 60. The use of carbon fiberreinforced polymer (CFRP) for strengthening the deep beams is utilized and a comparison between reinforced concrete(RC) and fiber-reinforced concrete (FRC) deep beams with and without CFRP strengthening is carried out using (Analysis of Systems) ANSYS 18.1. The mid-span deflections were significantly decreased and improved shear strength was observed in CFRP strengthened deep beams and FRC deep beam in comparison of RC deep beam. The ultimate loads for a maximum deflection value were compared in all the deep beams and RC frame with embedded carbonfiber reinforced polymer (RC-CFRP), fiber reinforced concrete carbon-fiber reinforced polymer(FRC-CFRP) and FRC deep beams showed 29.4%, 42.47% and 32.05% improvement, respectively, when compared with the RC deep beam. A total of 43.4% decrease in deflection and 74% decrease in shear stress was observed in FRC deep beam. The deflection and stress values in strengthened beams were comparatively lesser. In this study, deflection was observed to decrease by 74.4% and 82%, and shear stress decreased by 92% and 93.5% in the strengthened RC and FRC deep beam, respectively, compared to the deep beam RC model. It is suggested that strengthened FRC is a better alternative to RC deep beams.

Numerical Investigation of Turbulence Production Under Two-Phase Flow in a Simulation of Electrical Submersible Pump Performance

Abstract Investigating the characteristics of gas–liquid two-phase flow in a centrifugal pump is critical for evaluating pump performance. In this study, a numerical simulation was performed to understand the effects of gas–liquid turbulence formation in the impeller channels on the performance of a single-stage centrifugal pump. The focus was on the inlet gas volume fraction (IGVF) at constant flowrate and constant impeller speed on the flow structure in the impeller and the pressure surging characteristics. The correlation between Reynolds shear stress and turbulent kinetic energy on pump performance is shown by examining pressure, velocity, turbulent kinetic energy, and gas volume fraction (GVF). The model verification is verified using the theoretical pump pressure head determined by the manufacturer, which demonstrated adequate uncertainty (μ<5%) for a flowrate of 250 L/min. The results show a 9.41% decrease in wall shear stresses when the in-situ GVF varies between 1% and 10%. Wall shear stresses combined with circulation resulted in a 3.76% decrease in turbulent kinetic energy, while the contribution of turbulence to pump performance degradation is minimal. Other factors such as gas entrapment, impeller inlet blockage due to bubble coalescence, pressure gradient, and bubble size had a much greater impact on performance. The performance decreased dramatically by 26.53% when the GVF increased from 1% to 10%. The proposed flow structure can be further investigated together with the wall shear stress and circulation phenomena, such as vorticity and shear layers in the context of two-phase flow.

Effects of Velocity Fluctuations of Upper Flow on Turbulent Structure of Atmospheric Boundary Layer

The effects of velocity fluctuations of upper flow on turbulent structure of atmospheric boundary layer were experimentally investigated. The atmospheric boundary layer was reproduced in a wind tunnel. In order to produce various velocity fluctuations in the upper flow, three kinds of turbulence grids were set to the entrance of the test section. The streamwise and spanwise velocities were simultaneously measured by using hot-wires anemometer. Turbulence statistics were estimated. The vertical profiles of Reynolds shear stress, Ruw, for M25 and M50 decrease as z/L increase, on the other hands, those for M75 increase. The ratio of the integral length scale, λ(GT)/λ(ABT), for M75 were higher than those for M25, M50 at 0.33≦z/L ≦0.67 in the upper region of the atmospheric boundary layer. The joint probability density functions of u and w for M75 show the strong negative correlation in the upper region of the atmospheric boundary layer. It is suggested that the effects on the turbulent structure of the atmospheric boundary layer depends on the scale of velocity fluctuations of the upper flow.

Finite element analysis of the flange with different fillet radius in tubular wind tower

Today’s modern world has more demand for electricity to perform most of the activities. In this regard, wind turbines are used to convert the wind energy into electrical power, where turbines are mounted at the top of the tower called wind tower. To meet the high power generation demand, the wind energy towers will have to become taller because winds are stronger at higher altitudes. In the present, work Modal analysis of the wind tower is done using ANSYS, and Campbell diagram is plotted to check the frequency of resonance between the tower natural frequency and the natural frequency of the rotating blades. Considering the different fillet radius in the flanges, the critical conditions are simulated under the same loading condition. Finite Element Analysis (FEA) results show that by increasing the fillet radius the Equivalent stress, Maximum principle stress and, Maximum shear stress decreases. The safety of the tower is ensured through the Campbell diagram where the excitation frequency of any blade is not crossing the exciter box.

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

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.

Analysis of laminar boundary-layer separation in retarded flow over bodies of revolution

The laminar boundary-layer separation phenomenon is an interesting and important aspect of boundary-layer flows. It occurs in various physical situations because of a decrease in wall shear stress caused by retarded flow velocity, among other things. Flow separation can be prevented or delayed by utilizing bodies of revolution because the surface transverse curvature produces a favorable pressure gradient, which in turn increases the wall shear stress that keeps the flow attached to the surface. Bodies of revolution, whose body contours follow a power-law form, also play a vital role in delaying flow separation. Bodies of revolution of varying cross sections and involving surface transverse curvature are utilized to examine their effects on flow separation. In particular, a convex transverse curvature has been considered owing to its effects on the nature of the favorable pressure gradient, which delays the flow separation. A Görtler-type retarded flow velocity was considered in this study to investigate the flow separation process. A detailed analysis is provided to understand the flow separation by calculating the separation points under various assumptions. It has been observed that the body contour exponent n and the convex transverse curvature parameter k play an assistive role in the delay of boundary-layer separation even under the influence of strong retardation. The results are presented through various tables and graphs to highlight the role of the power-law exponent of external velocity m, convex transverse curvature parameter k, and body contour exponent n on the separation points.

Ecohydraulics of Surrogate Salt Marshes for Coastal Protection: Wave–Vegetation Interaction and Related Hydrodynamics on Vegetated Foreshores at Sea Dikes

Vegetation on foreshores in close vicinity to sea dikes may prove beneficial as regulating ecosystem service in the context of coastal defense, dike safety, and flood protection by reducing loads on these defense structures. Predominantly, a decrease in wave heights and bottom shear stresses is hypothesized, which calls for an inclusion in design procedures of coastal defense structures. In contrast to heterogeneous and variable salt marsh vegetation, this study uses surrogate vegetation models for systematic hydraulic experiments in a wave flume, without modeling specific plant species a priori. Froude-scale experiments are performed in order to investigate the effect of salt marsh vegetation on the wave transformation processes on the foreshore and wave run-up at sea dikes. The effect of plant and wave properties on wave transmission, energy dissipation, and wave run-up at a 1:6 sloped smooth dike are presented and discussed, focusing on the wave–vegetation–structure interaction. Vegetated foreshores can contribute to wave attenuation, where an increasing relative vegetation height hv/h results in decreased wave run-up on the dike by up to 16.5% at hv/h = 1.0.

Change of physical and chemical properties of asphaltene-resin-paraffin deposits deposits in tubing

The paper analyzes the geological and physical characteristics of the White Tiger field, deep and estuary samples of oil and asphaltene-resin-paraffin (ARP) deposits, which revealed the main factors leading to the intensive accumulation of asphaltenes on tubing surface during oil production. First of all, these are high formation temperatures (80-120°C) in combination with high paraffin separation temperature (57°C) and a relatively large oil depth (up to 4,500 m). Experimental studies were carried out and chemical reagents consisting of a mixture of polyvinyl acetate and organic solvents were selected (naphthalene, toluene, aromatic derivatives), which affect paraffin separation, which, in turn, leads to a decrease in viscosity and dynamic shear stress at the same temperature, as well as a decrease in oil congelation temperature thereby promoting the inhibition of asphaltene-resin-paraffin deposits by interacting with an activator for gel formation, adsorption on the surface of rocks, i.e. preventing the formation of asphaltene during oil production.

Numerical analysis of hydrodynamics influenced by a deformed bed due to a near-bank vegetation patch

Abstract This study uses a 2D hydro-morphological model to analyze hydrodynamics over flat and deformed beds with a near-bank vegetation patch. By varying the patch density, the generalized results show that the hydrodynamics over deformed beds differs a lot from those over flat beds. It is found that the deformed bed topography leads to an apparent decrease in longitudinal velocity and bed shear stress in the open region and longitudinal surface gradient for the entire vegetated reach. However, the transverse flow motion and transverse surface gradient in the region of the leading edge and trailing edge is enhanced or maintained, suggesting the strengthening of secondary flow motion. Interestingly, the deformed bed topography tends to alleviate the horizontal shear caused by the junction-interface horizontal coherent vortices, indicating that the turbulence-induced flow mixing is highly inhibited as the bed is deformed. The interior flow adjustment through the patch for the deformed bed requires a shorter distance, La, which is related to the vegetative drag length, (Cda)−1, with a logarithmic formula (La = 0.4ln[(Cda)−1] + b, with b = 3.83 and 4.03 for the deformed and flat beds). The sloping bed topographic effect in the open region accelerating the flow may account for the quick flow adjustment.

Numerical investigation of the effect of convex transverse curvature and concave grooves on the turbulent boundary layer along a cylinder in axial flow

Axisymmetric turbulent boundary layers that develop around streamwise oriented long cylinder-like objects can be found in many applications, such as towed array sonars or marine seismic streamers. In many of these applications, turbulent fluctuations within the boundary layer flow can have a negative impact compared with laminar flow conditions. The aim of the present work is to design a surface modification that influences the turbulent boundary layer around a cylinder in axial flow in order to reduce turbulent fluctuations. To design the surface we consider recent findings regarding the turbulence damping effects of groove-like surface structures and combine these insights with the effect of convex transverse curvature on turbulence. We use large-eddy simulations to investigate the flow around a cylinder of modified design and around a reference circular cylinder. Both flows have a radius-based Reynolds number of Rea≈1.23⋅104. The modified design leads to a 20 % decrease in the average wall shear stress and results in local reductions in the turbulent intensities, Reynolds stress, the temporal velocity spectrum, and the turbulent dissipation rate. The analysis within the anisotropy-invariant space reveals a tendency towards flow relaminarization. However, the new design has no effect on turbulent pressure fluctuations. We provide suggestions on how to further improve the surface design to achieve even greater flow stabilization.

A detailed hydrothermal investigation of a helical micro double-tube heat exchanger for a wide range of helix pitch length

The present study was numerically inquired the heat transfer performance and fluid flow characteristic of a helical micro double-tube heat exchanger (HMDTHX) using the finite volume method. The tube length was considered to be constantly equal to 30 mm, and 12 different configurations were modeled by changing in turn number and pitch length (P) for Reynolds numbers of 50, 100, 150, and 200. The findings indicated that the heat transfer would enhance by applying any helix angle in the straight tube. However, it had an optimum point which varied by Reynolds number (Re). Rising Re caused overall heat transfer coefficient (OHTC), pressure drop, and pumping power augment for all cases. Increasing P in overall reduced OHTC, pressure drop, and pumping power which had different maximum points between P = 0.5 to 3. Maximum overall heat transfer coefficient (OHTC) enhancement was equal to 45% for Re = 200 and P = 2. Also, maximum effectiveness was 11.5% for P = 2 and Re = 200. Moreover, a 42% maximum increment was achieved for pressure drop, pumping power, and friction factor at Re = 200 and P = 2. Shear stress for Re = 100 to 200 showed that the values are almost the same for P = 0.5 and 1. Then by increasing P, the shear stress decreases. While, for Re = 50, a maximum is seen at P = 2. The temperature distribution was indicated that the maximum temperature of the straight tube and helical tube are the same, but the difference is in the average temperature, which was 3.2 K between straight and helical tubes. Finally, by investigating the velocity contour, it was determined that a secondary flow through the HMDTHX, affected by centrifugal force, was existed, enhancing the fluid flow turbulency and heat transfer rate.

Numerical Simulation of the Geothechnical Effects on Local Scour in Inclined Pier Group with FLow-3D Softaware

When the bridge piers are located in front of the water flow, vortices are formed against it and due to their activity, the materials of the river bed are eroded around the bridge piers and the scouring hole is created. If the foundation depth and bridge pier piles are insufficient, the bridge will fail.The study of total shear stress in the flow bed at different leveling of the pile caps shows that the highest shear stress is created when the pile cap position is at the same level as the river bed; by installing the pile cap at a lower level than the river bed, the maximum shear stress decreases. This may be due to the fact that in this case, the distance between the pier group increases and the presence of the second pier decreases the flow rate in the pier group and different pier in the one pier group acts as the two independent piers in the formation of the flow pattern. By comparing the final longitudinal sections of the scouring at different leveling of the pile cap, it is concluded that the largest reduction in scouring depth occurs in aerofoil-shaped pile caps and pile caps with the sharper nose and better aerodynamic shapes are good options to control the horseshoe vortices and will reduce the scouring depth around the inclined pier group.

Effect of linear and Mooney\u2013Rivlin material model on carotid artery hemodynamics

Atherosclerosis is one of the most common cardiovascular diseases leading to high morbidity. The study of arterial dynamics using fluid–structure interaction (FSI) technique by taking into account the physiology of flow, the critical hemodynamic parameters can be determined which plays a crucial role in predictive medicine. Due to advances in the computational facilities, coupled field analysis such as FSI can facilitate understanding of the mechanics of stenosis progression and its early diagnosis. In this study a two-way FSI analysis is carried out using modified Navier–Stokes equations as the governing equations of blood flow for determining hemodynamic parameters. The arterial wall has been described at different linear elastic modulus and compared with hyperelastic Mooney–Rivlin model to evaluate the effect of different arterial stiffness on hemodynamics. The Mooney–Rivlin model predicts flow reduction with the severe backflow at arterial bifurcation resulting in decreased shear stress and oscillatory behavior. Furthermore, these findings may be used in understanding the advantages and disadvantages of using hyperelastic artery model in numerical simulations to better understand and predict the variable that causes cardiovascular diseases and as a diagnostic tool. In the present study, variation due to change in arterial wall properties such as linear elastic and Mooney Rivlin hyperelastic and its influence on hemodynamics are investigated.

Influence of Interfacial Oxidation on Friction in Structural Superlubricity

We present the results of friction experiments performed by manipulation of oxidized platinum nanoislands on highly oriented pyrolytic graphite (HOPG) substrates through atomic force microscopy (AFM). The oxidation of the platinum nanoislands, performed via mild plasma exposure, is confirmed through X-ray photoelectron spectroscopy (XPS) and high-resolution energy-dispersive X-ray spectroscopy (EDX), the latter of which reveals partial oxidation on the sliding surfaces of the nanoislands. Oxidized platinum nanoislands are found to exhibit higher friction than non-oxidized islands, with a ~ 70% increase in mean shear stress over the investigated contact size regime. An increase in chemical interaction forces between the oxidized platinum and the graphite substrate is proposed to explain the increase in friction forces. Our results reveal that alteration of interfacial chemistry through oxidation leads to a noticeable modulation of friction forces, but not a total breakdown of the superlubric state (as evidenced by the signature observation of decreasing shear stress with increasing contact size), providing further feasibility for the design of superlubric mechanical systems to be operated under ambient conditions.Graphic

Simulation of Fluid-Structure Interaction in Extracorporeal Membrane Oxygenation Circulatory Support Systems.

Extracorporeal membrane oxygenation (ECMO) is a vital mechanical circulatory support modality capable of restoring perfusion for the patient in circulatory failure. Despite increasing adoption of ECMO, there is incomplete understanding of its effects on systemic hemodynamics and how the vasculature responds to varying levels of continuous retrograde perfusion. To gain further insight into the complex ECMO:failing heart circulation, computational fluid dynamics simulations focused on perfusion distribution and hemodynamic flow patterns were conducted using a patient-derived aorta geometry. Three case scenarios were simulated: (1) healthy control; (2) 90% ECMO-derived perfusion to model profound heart failure; and, (3) 50% ECMO-derived perfusion to model the recovering heart. Fluid-structure interface simulations were performed to quantify systemic pressure and vascular deformation throughout the aorta over the cardiac cycle. ECMO support alters pressure distribution while decreasing shear stress. Insights derived from computational modeling may lead to better understanding of ECMO support and improved patient outcomes.

Time-Dependent Response of a Recycled C&D Material-Geotextile Interface under Direct Shear Mode.

Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate.

Investigation of Unstable Failure Potential of a Shear Slip Using DEM at an Underground Mine

Geological structures and discontinuities subjected to the perturbations posed by mining operations in underground mining can be re-activated and cause fault-slip rockbursts. This study investigates geomechanical stability in terms of shear slip behavior along discontinuities using 3DEC with focusing on sudden changes of shear stress and shear displacement. A direct shear test is performed using a continuously yielding joint model to examine the evolution of shear stress and shear displacement on this joint. Further, this continuously yielding joint model is applied in major discontinuities of an underground mine to examine whether an unstable shear slip behavior exists, which is represented by a significant shear stress decrease and a shear displacement increase. By referring to geological mapping of this mine, four cases are developed and each case is set up with one type of major discontinuities with identically simulated mining operations. Results imply that the amplitude of shear stress decrease and shear displacement increase along discontinuities substantially increases with the depth due to higher virgin stresses and mining-induced stresses at greater depths. The discontinuity parallel to the interface between footwall and orebody is the least safe case and subjects to the largest potential of triggering seismic events. Keywords: Shear slip behavior, Unstable failure, Mining-induced seismicity, Continuously yielding joint model, DEM.

Computational Fluid Dynamic Study of Blockage in Artery With and Without Bypass

In complex vessel geometry different temporal, spatial variation takes place which occur under pulsatile conditions. The high Wall Shear Stress (WSS) at the wall affected by the disturbed flow may ultimately lead to endothelial cell dysfunction, which leads to atherogenesis and thrombosis. The present study observes WSS and streamlines due to stenosis with and without By-pass Artery. It was found that by adding bypass Artery there is tremendous decrease in wall shear stress in the stenosis. Reverse flow of blood through stenosis was observed in 30° Bypass Models. Hence the blood flow stabilizes and can be reached at optimum level in 50% stenosed artery. Based on this paper findings, it can be deduced that there would be a low risk of further atherosclerosis when the bypass artery is added.