Shear Stress Analysis Research Articles

Numerical study of airfoil stall cells using a very wide computational domain

The formation of stall cells over a NACA 0012 airfoil at a Reynolds number of one million has been investigated numerically, using unsteady Reynolds-averaged Navier–Stokes (URANS) and delayed detached-eddy simulation (DDES) approaches. The simulations are performed with a very wide computational domain (10 chord length) to minimize the influence of spanwise periodic boundary conditions. For the URANS simulations, four different spanwise mesh resolutions are tested to determine the minimum resolution required to capture the formation of stall cells. Both URANS and DDES results show a sudden decrease in lift and increase in drag between 16° and 17° angle of attack, accompanied by a significant change of separated flow patterns. Stall cell structures are observed clearly in the URANS solutions between 17° and 19° with a spanwise spacing of about 1.4 to 1.8 chord length, which agrees well with a theoretical prediction based on the slope of the lift curve in this angle-of-attack range. The DDES results show much more complex flow patterns over the airfoil at these high angles of attack, although the spectral analysis of wall shear stress suggests the existence of flow structures having a similar spanwise length scale to the stall cells.

Computational fluid dynamics analysis of wall shear stresses between human and rat nasal cavities

Toxicology studies often use laboratory animals as surrogates for human subjects because of the relatively similar nasal anatomy that allows data extrapolation between species. An understanding of nasal airflow patterns, particularly wall shear stress can help better understand the causes of toxicant distribution and local dosimetry. A laminar, steady state flow was used to simulate light inhaled air. The WSS produced inside a human nasal cavity was compared with a rat nasal cavity. The results showed that averaged WSS was highest in the anterior nasal region, i.e. vestibule (rat - 755 mPa and human - 153 mPa). In the human model, the lower septal wall, and nasopharynx region also exhibited high WSS regions. Local high WSS regions on the nasal cavity wall were identified by plotting the WSS distribution as 3D contour maps on a normalised 2D domain. This visualisation technique displays peaks for locally high WSS values which were primarily caused by the airway geometry intruding into the airflow paths and causing high shear. Velocity vectors on the 2D domain also correlated high WSS with flow acceleration that was caused by a reduction in the cross-sectional area of a local region in the nasal passage.

Nano-scale elastic–plastic properties and indentation-induced deformation of amorphous silicon carbide thin film

Controllable low-temperature (500°C) deposition of amorphous a-SiC ceramic films on Si(100) was achieved using a pulsed dc-magnetron puttering system in a mixture of CH4/Ar. The nanoscale elastic-plastic response of the film upon contact loading was systematically characterized and analyzed by depth sensing nanoindentation technique using a Berkovich tip indenter. The mean values for elastic modulus and hardness were found to be 170±10 and 11.0±0.8GPa, respectively. The onset of elastic-plastic transition occurred with contact loading of 70µN at a depth of 10nm. By coupling the Hertzian contact theory and Johnson's cavity model, the critical shear stress (7.7GPa), yielding strength (14.4GPa), plastic zone size (30–300nm), and plastic work ratio (0.18–0.40) of a-SiC thin film under nanoindentation were determined. Based on the experimental results, the resolved shear stress analysis and deformation behavior were found to be consistent with the interpretation that the deformation behavior was associated with local readjustment of small clusters of atoms. The deformation mechanism was also explained on the basis of shear transformation zones (STZs) amorphous plasticity theory.

Control of submerged hollow fiber membrane fouling caused by fine particles in photocatalytic membrane reactors using bubbly flow: Shear stress and particle forces analysis

In current work, bubbly flow was applied to control membrane fouling in photocatalytic membrane reactors (PMRs) under different aeration rate. The fine particles of TiO2 (d0.5 = 1.75 μm) in combination with natural organic matter (NOM) in suspended solutions were employed to conduct membrane fouling experiments in a submerged hollow fiber membrane tank. The results revealed that bubbly flow was an efficient approach to mitigate membrane fouling, leading to a rapidly decreasing fouling rate (dTMP/dt) (0.0908–0.0069 kPa/min) with the aeration increase. Additionally, computational fluid dynamics (CFD) simulations were implemented to calculated shear stress distribution on the spatial point of the membrane surface. Based on the detailed CFD simulation results, it was observed that the mean shear stress (0.505–2.111 Pa) increased rapidly with the increase of air flow rate (0–3.2 L/min). Furthermore, the forces exerted on the fine particles were analyzed in terms of calculated shear stress. It was quantitatively demonstrated that the streaming particles were prone to deposit on the vicinity of the layer and the particles deposited on the layer cannot be removed by hydrodynamics forces. It is expected that this study would be basis for further improvement of hydrodynamic condition design induced by bubbly flow in PMRs.

Dynamic modelling of the steering performance of an articulated tracked vehicle using shear stress analysis of the soil

The steering performance is one of the major concerns in special engineering vehicle fields. This study aims to investigate the steering performance of an articulated tracked vehicle. An improved dynamic steering model for an articulated tracked vehicle is proposed when considering the shear stress–shear displacement relation of the soil at the track–ground interface. In this model, the mechanical, kinematic and dynamic models of the articulated unit are constructed to evaluate the movement performance of the articulated unit, and the kinematic and dynamic models of the front vehicle and the rear vehicle are developed to evaluate the steering performance. The created dynamic model is then applied to analyse the steering performance of a specific articulated tracked vehicle. A mechanically controlled united simulation model and actual tests of an articulated tracked vehicle are utilized to verify the established steering model. The results of the comparisons show the effectiveness of the proposed dynamic steering model.

Wall Shear Stress Analysis in Stenosed Carotid Arteries with Different Shapes of Plaque

Atherosclerosis is a disease caused due to formation of plaque into the artery. Increase in plaque affects the wall shear stress. The present study is performed to calculate wall shear stress in different geometries of stenosed carotid artery. A 2D model of different geometries is generated using CFD for Non- Newtonian model. After this WSS of different geometries of stenosed arteries is calculated and compared. Wall Shear Stress (WSS) of carotid arteries with smooth plaque, irregular plaque, cosine plaque and artery with blood clot is calculated. It is found that with increase of plaque in common carotid artery WSS increases. Irregular plaque causes highest WSS. Wall Shear Stress of opposite walls of carotid artery is compared where one wall is having blood clot into it and other one is healthy.

２個の楕円空孔を有する等方性弾性体に面外せん断荷重が作用する問題の解析

２個の楕円空孔を有する等方性弾性体に面外せん断荷重が作用する問題の解析

Contact Stress and Shear Stress Analysis of Spur Gear Using ANSYS and Theoretical

Contact Stress and Shear Stress Analysis of Spur Gear Using ANSYS and Theoretical

Time-Resolved Particle Image Velocimetry Measurements with Wall Shear Stress and Uncertainty Quantification for the FDA Nozzle Model.

We present advanced particle image velocimetry (PIV) processing, post-processing, and uncertainty estimation techniques to support the validation of computational fluid dynamics analyses of medical devices. This work is an extension of a previous FDA-sponsored multi-laboratory study, which used a medical device mimicking geometry referred to as the FDA benchmark nozzle model. Experimental measurements were performed using time-resolved PIV at five overlapping regions of the model for Reynolds numbers in the nozzle throat of 500, 2000, 5000, and 8000. Images included a twofold increase in spatial resolution in comparison to the previous study. Data was processed using ensemble correlation, dynamic range enhancement, and phase correlations to increase signal-to-noise ratios and measurement accuracy, and to resolve flow regions with large velocity ranges and gradients, which is typical of many blood-contacting medical devices. Parameters relevant to device safety, including shear stress at the wall and in bulk flow, were computed using radial basis functions. In addition, in-field spatially resolved pressure distributions, Reynolds stresses, and energy dissipation rates were computed from PIV measurements. Velocity measurement uncertainty was estimated directly from the PIV correlation plane, and uncertainty analysis for wall shear stress at each measurement location was performed using a Monte Carlo model. Local velocity uncertainty varied greatly and depended largely on local conditions such as particle seeding, velocity gradients, and particle displacements. Uncertainty in low velocity regions in the sudden expansion section of the nozzle was greatly reduced by over an order of magnitude when dynamic range enhancement was applied. Wall shear stress uncertainty was dominated by uncertainty contributions from velocity estimations, which were shown to account for 90-99% of the total uncertainty. This study provides advancements in the PIV processing methodologies over the previous work through increased PIV image resolution, use of robust image processing algorithms for near-wall velocity measurements and wall shear stress calculations, and uncertainty analyses for both velocity and wall shear stress measurements. The velocity and shear stress analysis, with spatially distributed uncertainty estimates, highlights the challenges of flow quantification in medical devices and provides potential methods to overcome such challenges.

Assessment of nanofluids for laminar convective heat transfer: A numerical study

In this article, a numerical study of laminar forced convective heat transfer in a circular tube is presented, incorporating entropy generation and wall shear stress analysis. Three different nanofluids, Al2O3–water, ZrO2–water and TiO2–water, are considered under constant heat flux boundary condition using single phase approach. Performance of nanofluids is compared with the base fluid by keeping the Reynolds number, mass flow rate and discharge criteria constant for various volume fractions of nanoparticles. A non linear dependence of base fluid thermo-physical properties with temperature is considered in this study. For same Reynolds number comparison criteria, the heat transfer coefficient for nanofluids is found to be significantly higher as compared to the base fluid. However, for same mass flow rate and same discharge comparison criteria, an increment in the heat transfer coefficient is found to be insignificant. The performance factor is found to be poor for the nanofluids and also, it decreases with an increase in particle loading. However, it is nearly similar for all kinds of comparisons. The entropy generation decreases for the nanofluids under same Reynolds number comparison, but the decrement is found to be negligible for the other two comparison bases. The wall shear stress increases with an increase in particle loading for all three comparisons.

A theoretical analysis of a spacer filled flat plate membrane distillation modules using CFD: Part I: velocity and shear stress analysis

This work presents the theoretical analysis of the velocity and shear stress in a flat plate direct contact membrane distillation system. ANSYS CFX was used to create 3-D CFD model to study the effect of different hydrodynamic angles on the velocity profiles and shear stress. The membrane was assumed fully permeable and the heat and mass transfer mechanisms through the membrane were modelled by implementing FORTRAN user-subroutines at the boundary intersection between the feed and permeate side. Three hydrodynamic angles were tested: αf =45°,αf=90° and αf=0°. Results have shown that for the system examined, the alignment of the flow does not depend on the increasing Reynolds number. Two types of flow were identified: zig- zag pattern in the bulk flow and flow parallel to the filaments. The types of flow observed depended on the hydrodynamic angle. Finally, it was further shown that the most favourable configuration was when the system was operating with a hydrodynamic angle αf=45° as it produced better mixing and enhanced shear stress resulting in higher fluxes and the least desirable configuration was when the hydrodynamic angle αf=0°.

Simulation of the Interaction of Plastic Deformation in Shear Bands with Deformation-Induced Martensitic Phase Transformation in the VHCF Regime

The experimental observation of the microstructural deformation behavior of a metastable austenitic stainless steel tested at the real VHCF limit indicates that plastic deformation is localized and accumulated in shear bands and martensite formation occurs at grain boundaries and intersecting shear bands. Based on these observations a microstructure-sensitive model is proposed that accounts for the accumulation of plastic deformation in shear bands (allowing irreversible plastic sliding deformation) and considers nucleation and growth of deformation-induced martensite at intersecting shear bands. The model is numerically solved using the two-dimensional (2-D) boundary element method. By using this method, real simulated 2-D microstructures can be reproduced and the microstructural deformation behavior can be investigated within the microstructural morphology. Results show that simulation of shear band evolution is in good agreement with experimental observations and that prediction of sites of deformation-induced martensite formation is possible in many cases. The analysis of simulated shear stresses in most critical slip systems under the influence of plastic deformation due to microstructural changes contributes to a better understanding of the interaction of plastic deformation in shear bands with deformation-induced martensitic phase transformation in the VHCF regime.

Computational simulation of carotid stenosis and flow dynamics based on patient ultrasound data – A new tool for risk assessment and surgical planning

PurposeThere is nowadays extensive experimental and computational investigation on the pathophysiology of atherosclerosis, searching correlations between its focal nature and local hemodynamic environment. The goal of this work is to present a methodology for patient-specific hemodynamics study of the carotid artery bifurcation based on the use of ultrasound (US) morphological and blood flow velocity patient data. Materials/methodsSubject-specific studies were performed for two patients, using a developed finite element code. Geometrical models were obtained from the acquisition of longitudinal and sequential cross-sectional ultrasound images and boundary conditions from Doppler velocity measurements at the common carotid artery. ResultsThere was a good agreement between ultrasound imaging data and computational simulated results. For a normal and a stenosed carotid bifurcation the velocity, wall shear stress (WSS) and WSS descriptors analysis illustrated the extremely complex hemodynamic behavior along the cardiac cycle. Different patterns were found, associated with morphology and hemodynamic patient-specific conditions. High values of time-averaged WSS (TAWSS) were found at stenosis site and for both patients TAWSS fields presented low values within areas of high oscillating shear index and relative residence time values, corresponding to recirculation zones. ConclusionSimulated hemodynamic parameters were able to capture the disturbed flow conditions in a normal and a stenosed carotid artery bifurcation, which play an important role in the development of local atherosclerotic plaques. Computational simulations based on clinic US might help improving diagnostic and treatment management of carotid atherosclerosis.

MECHANICAL STRESS IN ABDOMINAL AORTIC ANEURYSMS USING ARTIFICIAL NEURAL NETWORKS

Combination of numerical modeling and artificial intelligence (AI) in bioengineering processes are a promising pathway for the further development of bioengineering sciences. The objective of this work is to use Artificial Neural Networks (ANN) to reduce the long computational times needed in the analysis of shear stress in the Abdominal Aortic Aneurysm (AAA) by finite element methods (FEM). For that purpose two different neural networks are created. The first neural network (Mesh Neural Network, MNN) creates the aneurysm geometry in terms of four geometrical factors (asymmetry factor, aneurism diameter, aneurism thickness, aneurism length). The second neural network (Tension Neural Network, TNN) combines the results of the first neural network with the arterial pressure (new factor) to obtain the maximum stress distribution (output variable) in the aneurysm wall. The use of FEM for the analysis and design of bioengineering processes often requires high computational costs, but if this technique is combined with artificial intelligence, such as neural networks, the simulation time is significantly reduced. The shear stress obtained by the artificial neural models developed in this work achieved 95% of accuracy respect to the wall stress obtained by the FEM. On the other hand, the computational time is significantly reduced compared to the FEM.

Role of Flow in Lymphatic Vessel Remodeling and Patterning

Fluid shear forces have established roles in blood vascular development and function, but whether such forces also play important roles in the low flow, low pressure lymphatic system is unknown. Testing the role of fluid forces in vivo has been difficult because mechanical or genetic perturbations that alter flow often have direct effects on endothelial cells and vessel growth. Here, we investigate the functional role of fluid shear force in lymphatic vessel development using mice deficient in the platelet-specific receptor CLEC2, in which blood back-fills the lymphatic network and blocks lymph flow. CLEC2-deficient animals exhibit normal growth of the primary mesenteric lymphatic plexus, but fail to remodel this plexus into a hierarchical structure typical of collecting vessels and fail to form lymphatic valves. In vitro studies in which lymphatic endothelial cells were exposed to a specific lymphatic flow regimen reveal that low, reversing shear stress is sufficient to induce expression of genes required for lymphatic valve development. Shear stress studies and analysis of CLEC2-deficient mesenteric lymphatics identify GATA2 as an upstream transcriptional regulator of this lymphatic valve genetic program. These studies provide in vivo evidence that fluid forces regulate vascular development even in the low flow lymphatic system.

Unsteady polar fluid model of blood flow through taperedω-shape stenosed artery: Effects of catheter and velocity slip

In this paper, we considered the pulsatile flow of blood through catheterized tapered artery in the presence of an ω-shaped stenosis. Blood flow is modelled as homogeneous incompressible couple stress fluid. Further the effects of velocity slip at the arterial wall are also examined. The analysis is carried out analytically and closed form solutions are obtained with the assumption of mild stenosis. In the present study, we analyze the effects of various fluid and geometric parameters on the physiological parameters such as resistance to flow and shear stress at the wall. The variation in the resistance to the flow and wall shear stress with respect to stenosis size (∊,ψ), radius of the catheter (Rc), couple stress fluid parameters (β,ω), Reynolds number (Re) and pulsatile parameter (σ) has been studied. In particular shear stress at the wall is reckoned at both the locations corresponding to the maximum height of the stenosis. It has been observed that this physiological parameter is independent of the location of the maximum height in case of nontapered artery while these locations significantly impact the shear stress at the wall in case of tapered artery. The locations of the critical and maximum heights with corresponding annular radii are summarized in the form of Table 1. We also focussed our attention on the analysis of the wall shear stress over the entire stenosis region for various values of the geometric and fluid parameters. It is observed that the impedance and wall shear stress are increasing with increase in the radius of catheter and stenosis size while they are decreasing as the tapered parameter and the couple stress fluid parameters are increasing. It is observed that slip velocity and diverging tapered artery facilitate the fluid flow.

Nanoindentation study of size effect on shear transformation zone size in a Ni–Nb metallic glass

An apparent reduction in both size and amount of shear bands was observed, as the sample converted from 45μm ribbon to 1.8μm film in a Ni–Nb metallic glass. Such size effect on the macroscopic plastic characteristic could be intrinsically related to the scale variation of the shear transformation zone (STZ). Statistical analysis of the maximum shear stress, which is based on the distribution of first pop-in events in nanoindentation, was employed to estimate the STZ volume and atoms it contains. The result indicates that the STZ size decreases from 83 atoms in the ribbon to 36 atoms in the film. This phenomenon was consistent with the result by another experimental method based on the strain rate sensitivity (SRS). Upon nanoindentation creep test, STZ sizes with 44 atoms and 18 atoms were calculated for the ribbon and film, respectively. The variation trend of the STZ size was discussed in terms of free volume content combined with internal stress which arises during the film deposition and the local atomic structure changes recognized by EXAFS measurement.

The New Options to Reduce Shear Stress into Foundation Structure

This paper deals with analysis of shear stress into foundation structure with applied rheological sliding joint into foundation structures. Rheological sliding joint can create an important part of the building in case that the foundation structure is placed on undermined territory. Buildings which are situated on the edge of settlement trough are often loaded with horizontal deformation from the subsoil. Horizontal deformations then cause shear stress into foundation bottom and tensile forces into foundation. These foundations have to be reinforced a lot or can be structurally modified and can be built on the concrete base layer with rheological sliding joint from different materials. The sliding joint can be created from some different materials but it is often created from asphalt belts. This method was discovered and researched in the 80th at first. Not many materials were on market in this time nevertheless calculation method to determination of shear stress was discovered. Sliding joint was also patented in 1985. Today it was constructed new testing equipment for new tests at the Faculty of Civil Engineering on VŠB – Technical University of Ostrava because the asphalt belts can have very different properties. The testing equipment also allows include effect of ambient temperature. Ambient temperature is monitored because of strong effect on asphalt behavior. The shear response is monitored at the laboratory test and analysis is provided based on results from these experiments. The main objective of this research is to determine calculation method to design sliding into real building. Shear stress into foundation bottom is the most important outcome because from it can be calculated tensile forces and bending moments in foundation structure on which foundation will be assessed. If the settlement trough parameters are known it can be calculated the velocity of deformation in the subsoil. From velocity of subsoil's deformation can be calculated shear stress and also tensile forces and bending moment according to old method and according to Czech standard (ČSN 73 0039 - Building on undermined areas). Calculations are limited to type of applied asphalt belt because the equation for friction's calculation is based on old materials (only two types of oxidized asphalt belts which were in this time on our market). New results and comparison are obtained from new test.

1A23 胃内のせん断応力の数値解析(OS11-2:生体流れの計算バイオメカニクス:疾病の再現および診断・治療への応用(2))

1A23 胃内のせん断応力の数値解析(OS11-2:生体流れの計算バイオメカニクス:疾病の再現および診断・治療への応用(2))

Evaluation of incipient motion for sediment transport of mining waste rock using critical shear stress analysis

There have been concerns that excess sediment load of mining waste rock, also known as chat, into nearby alluvial streams with which have increased flooding risks due to the aggradation and destabilisation of the channel. The goal of this project was to gain a better understanding of the conditions required for fluvial transport and assess the frequency at which those conditions were met. Before this goal could be achieved at field-scale, and the initial objective of determining the critical shear stress required for initiation of fluvial transport of chat, was identified. To determine the critical shear stress required for initiation of transport, a bench-scale laboratory experiment was done in a hydraulic flume with chat collected from an impacted stream viz., Tar Creek, Oklahoma, USA. The empirical critical shear stress required for transport was slightly less than values suggested for general use of sediment transport. This difference is shown to be due to angular characteristics of the chat. The impact of this study and determination of critical shear stress enables the development and calibration of hydraulic and sediment transport modelling of cherty mining waste rock.