scholarly journals Fracture Unclogging: A Numerical Study of Seismically Induced Viscous Shear Stresses in Fluid‐Saturated Fractured Rocks

2019 ◽  
Vol 124 (11) ◽  
pp. 11705-11727 ◽  
Author(s):  
Nicolás D. Barbosa ◽  
Jürg Hunziker ◽  
Simón Lissa ◽  
Erik H. Saenger ◽  
Matteo Lupi
Keyword(s):  
Fractured Rocks ◽  
Numerical Study ◽  
Shear Stresses ◽  
Viscous Shear

Endwall Boundary Layer Development in a Multistage Low-Speed Compressor With Tandem Stator Vanes

2021 ◽  
Author(s):  
Michael Hopfinger ◽  
Volker Gümmer
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Shear Stresses ◽  
Flow Area ◽  
Stage Design ◽  
Low Speed ◽  
Boundary Layer Development ◽  
Viscous Shear ◽  
Layer Development ◽  
Highly Loaded

Abstract The development of viscous endwall flow is of major importance when considering highly-loaded compressor stages. Essentially, all losses occurring in a subsonic compressor are caused by viscous shear stresses building up boundary layers on individual aerofoils and endwall surfaces. These boundary layers cause significant aerodynamic blockage and cause a reduction in effective flow area, depending on the specifics of the stage design. The presented work describes the numerical investigation of blockage development in a 3.5-stage low-speed compressor with tandem stator vanes. The research is aimed at understanding the mechanism of blockage generation and growth in tandem vane rows and across the entire compressor. Therefore, the blockage generation is investigated as a function of the operating point, the rotational speed and the inlet boundary layer thickness.

scholarly journals Mathematical Models and Evaluation Software for Stress-Strain State of the Earth’s Lithosphere

2019 ◽  
pp. 51-66
Author(s):  
Alexander O. Faddeev ◽  
Svetlana A. Pavlova ◽  
Tatiana M. Nevdakh
Keyword(s):  
Mathematical Model ◽  
Strain State ◽  
Uniform Grid ◽  
Shear Stresses ◽  
Stress Strain ◽  
Gravitation Field ◽  
Vertical Movements ◽  
Stress Strain State ◽  
The Earth ◽  
Viscous Shear

Introduction. For the purposes of this article, geodeformation processes mean processes associated with deformations arising from the movement of species and blocks of the lithosphere at various depths, including surfaces. The objective is to reconstruct geodynamic stress fields, which cause modern shifts and deformations in the Lithosphere. A mathematical model and software for estimating the stress-strain state of the Earth Lithosphere are considered. Materials and Methods.For mathematical modeling of stresses, isostatically reduced data on abnormal gravitation field were used. The methods of continuum mechanics and methods of the theory of differential equations were used to design a model for estimating the stressstrain state of the Earth Lithosphere. For processing input, intermediate and outcoming data, the Fourier transform method of spectral analysis for constructing grid functions and spectral-temporal method were used. To model for the stress-strain state of the Lithosphere globally, stress calculation was corrected on the basis of sputnik-derived velocity data at the surface of the earth crust. The data on the rates of horizontal and vertical movements at the surface of the Earth crust were processed to obtain a distribution of velocities in the uniform grid embracing longitudes and latitudes. The processing procedure was carried out on the basis of the Kraiging method. The software was developed in Borland Delphi 7.0 programming environment. Results. Based on the data on the abnormal gravitation field in isostatic reduction and information on the distribution of velocities of horizontal motions on the surface of the Earth crust, a mathematical model of the stress-strain state of the Lithosphere was constructed. With the help of the obtained mathematical model and software complex, the stress-strain state of the Lithosphere was calculated at various depth using elastic and elastic-viscous models, and maps of equipotential distribution of shear elastic-viscous deformations in the lithosphere at the depth of 10 km were constructed. Discussion and Conclusion. The presented mathematical model and software allow restoring fields of both elastic and elastic-viscous deformations that is fundamental for quantification of elastic-viscous shear stresses deep in the Earth Lithosphere.

Numerical study of hemodynamics after stent implantation during the cardiac cycle

2021 ◽  
Vol 15 (2) ◽  
pp. 8016-8028
Author(s):  
Abdelhakem Belaghit ◽  
B. Aour ◽  
M. Larabi ◽  
A. A. Tadjeddine ◽  
S. Mebarki
Keyword(s):  
Blood Flow ◽  
Stent Implantation ◽  
Cardiac Cycle ◽  
Numerical Study ◽  
Shear Stresses ◽  
Flow Profile ◽  
Hemodynamic State ◽  
Dynamics Simulations ◽  
Medical Planning

The descending aortic aneurysm is one of the most catastrophic cardiovascular emergencies resulting in high mortality worldwide. Clinical observations have pointed out that stent implantation in the sick aorta should probably allow stabilization of the hemodynamic state of the patient's aorta. To better understand the hemodynamic impact of a stent-treated aneurysm, numerical simulations are used to evaluate hemodynamic parameters. These latter including flow profile, velocity distribution, aortic wall pressure and shear stress, which are difficult to measure in vivo. It should be noted that the numerical modeling assists in medical planning by providing patterns of blood circulation, in particular, the distribution of pressures and shear stresses in the wall. In this context, the pulsatile blood flow in the aneurysmal aorta with stent is studied by CFD (Computational Fluid Dynamics) simulations. Realistic boundary conditions time dependent are prescribed at the level of the different arteries of the complete aorta models. The hemodynamic profile of the aneurysmal aorta with stent was analyzed by contour planes of velocity vectors, pressures and shear stresses at different times during the cardiac cycle. The obtained results made it possible to show the effect of the stent on the improvement of the blood flow by solving the problems of hemodynamic disturbances in the aorta.  The methodology used in this work has revealed detailed and necessary information for the cases studied and shows the interest of the numerical tool for diagnosis and surgery.

Cartesian Based Finite Volume Formulation for LES of Mixed Convection in a Vertical Turbulent Pipe Flow

2002 ◽  
Author(s):  
Xiaofeng Xu ◽  
Joon Sang Lee ◽  
R. H. Pletcher
Keyword(s):  
Finite Volume ◽  
Pipe Flow ◽  
Stokes Equations ◽  
Numerical Study ◽  
Turbulent Pipe Flow ◽  
Shear Stresses ◽  
Turbulent Heat ◽  
Subgrid Scale ◽  
Wall Boundary Conditions ◽  
High Heating

A numerical study was performed to investigate the effects of heating and buoyancy on the turbulent structures and transport in turbulent pipe flow. Isoflux wall boundary conditions with low and high heating were imposed. The compressible filtered Navier-Stokes equations were solved using a second order accurate finite volume method. Low Mach number preconditioning was used to enable the compressible code to work efficiently at low Mach numbers. A dynamic subgrid-scale stress model accounted for the subgrid-scale turbulence. The results showed that strong heating caused distortions of the flow structures resulting in reduction of turbulent intensities, shear stresses, and turbulent heat flux, particularly near the wall. The effect of heating was to raise the mean streamwise velocity in the central region and reduce the velocity near the wall resulting in velocity distributions that resembled laminar profiles for the high heating case.

scholarly journals Sound radiation in turbulent channel flows

2003 ◽  
Vol 475 ◽  
pp. 269-302 ◽  
Author(s):  
ZHIWEI HU ◽  
CHRISTOPHER L. MORFEY ◽  
NEIL D. SANDHAM
Keyword(s):  
Mach Number ◽  
Sound Radiation ◽  
Fourth Power ◽  
Shear Stresses ◽  
Far Field ◽  
Good Resolution ◽  
Reynolds Stresses ◽  
Rigid Boundary ◽  
Frequency Spectra ◽  
Viscous Shear

Lighthill’s acoustic analogy is formulated for turbulent channel flow with pressure as the acoustic variable, and integrated over the channel width to produce a two-dimensional inhomogeneous wave equation. The equivalent sources consist of a dipole distribution related to the sum of the viscous shear stresses on the two walls, together with monopole and quadrupole distributions related to the unsteady turbulent dissipation and Reynolds stresses respectively. Using a rigid-boundary Green function, an expression is found for the power spectrum of the far-field pressure radiated per unit channel area. Direct numerical simulations (DNS) of turbulent plane Poiseuille and Couette flow have been performed in large computational domains in order to obtain good resolution of the low-wavenumber source behaviour. Analysis of the DNS databases for all sound radiation sources shows that their wavenumber–frequency spectra have non-zero limits at low wavenumber. The sound power per unit channel area radiated by the dipole distribution is proportional to Mach number squared, while the monopole and quadrupole contributions are proportional to the fourth power of Mach number. Below a particular Mach number determined by the frequency and radiation direction, the dipole radiation due to the wall shear stress dominates the far field. The quadrupole takes over at Mach numbers above about 0.1, while the monopole is always the smallest term. The resultant acoustic field at any point in the channel consists of a statistically diffuse assembly of plane waves, with spectrum limited by damping to a value that is independent of Mach number in the low-M limit.

A Numerical Study of Friction in Isothermal EHD Rolling-Sliding Sphere-Plane Contacts With Spinning

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
H. Dormois ◽  
N. Fillot ◽  
W. Habchi ◽  
G. Dalmaz ◽  
P. Vergne ◽  
...  
Keyword(s):  
Film Thickness ◽  
Numerical Study ◽  
Friction Reduction ◽  
Shear Stresses ◽  
Fluid Viscosity ◽  
Stress Distributions ◽  
Eyring Model ◽  
Element Approach ◽  
Transverse Shear Stresses ◽  
Shear Heating

This paper presents a study of the spinning influence on film thickness and friction in EHL circular contacts under isothermal and fully flooded conditions. Pressure and film thickness profiles are computed with an original full-system finite element approach. Friction was thereafter investigated with the help of a classical Ree–Eyring model to calculate the longitudinal and transverse shear stresses. An analysis of both the velocity and shear stress distributions at every point of the contact surfaces has allowed explaining the fall of the longitudinal friction coefficient due to the occurrence of opposite shear stresses over the contact area. Moreover in the transverse direction spinning favors large shear stresses of opposite signs, decreasing the fluid viscosity by non-Newtonian effects. These effects have direct and coupled consequences on the friction reduction that is observed in the presence of spinning. They are expected to further decrease friction in real situations due to shear heating.

scholarly journals Numerical Study of Lorentz Force Interaction with Micro Structure in Channel Flow

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4286
Author(s):  
Shabbir Ahmad ◽  
Kashif Ali ◽  
Sohail Ahmad ◽  
Jianchao Cai
Keyword(s):  
Heat Transfer ◽  
Differential Equations ◽  
Viscous Dissipation ◽  
Numerical Study ◽  
Nonlinear Differential Equations ◽  
Thermal Control ◽  
Shear Stresses ◽  
Fluid Temperature ◽  
X Rays ◽  
Micro Particles

The heat transfer Magnetohydrodynamics flows have been potentially used to enhance the thermal characteristics of several systems such as heat exchangers, electromagnetic casting, adjusting blood flow, X-rays, magnetic drug treatment, cooling of nuclear reactors, and magnetic devices for cell separation. Our concern in this article is to numerically investigate the flow of an incompressible Magnetohydrodynamics micropolar fluid with heat transportation through a channel having porous walls. By employing the suitable dimensionless coordinates, the flow model equations are converted into a nonlinear system of dimensionless ordinary differential equations, which are then numerically treated for different preeminent parameters with the help of quasi-linearization. The system of complex nonlinear differential equations can efficiently be solved using this technique. Impact of the problem parameters for microrotation, temperature, and velocity are interpreted and discussed through tables and graphs. The present numerical results are compared with those presented in previous literature and examined to be in good contact with them. It has been noted that the imposed magnetic field acts as a frictional force which not only increases the shear stresses and heat transfer rates at the channel walls, but also tends to rotate the micro particles in the fluid more rapidly. Furthermore, viscous dissipation may raise fluid temperature to such a level that the possibility of thermal reversal exists, at the geometric boundaries of the domain. It is therefore recommended that external magnetic fields and viscous dissipation effects may be considered with caution in applications where thermal control is required.

Numerical Study on the Pulsatile Flow Characteristics of Proximal Anastomotic Models

2005 ◽  
Vol 219 (5) ◽  
pp. 361-379 ◽  
Author(s):  
L P Chua ◽  
J-M Zhang ◽  
S C M Yu ◽  
D N Ghista ◽  
Y S Tan
Keyword(s):  
Flow Separation ◽  
Patency Rate ◽  
Numerical Study ◽  
Flow Characteristics ◽  
High Time ◽  
Shear Stresses ◽  
Proximal Anastomosis ◽  
Haemodynamic Parameters ◽  
Simulation Results ◽  
Wall Shear

Haemodynamics was widely believed to correlate with anastomosis restenosis. Utilizing the haemodynamic parameters as indicator functions, distal anastomosis was redesigned by some researchers so as to improve the long-term graft patency rate. However, there were few studies upon the proximal anastomosis. Therefore, in this study, flow characteristics and distributions of the haemodynamic parameters in proximal anastomosis under physiological flow condition have been investigated numerically for three different grafting angles: namely, 45° forward facing, 45° backward facing, and 90° anastomotic joints. The simulation results showed a flow separation region along the graft inner wall immediately after the heel at peak flow phase and it decreased in size with the grafting angle shifting from 45° forward facing to 45° backward facing. At the same time, a pair of vortex was found in the cross-sectional planes of the 45° backward facing and 90° grafts. In addition, stagnation point was found along the graft outer wall with small shifting during the physiological cycle. High spatial and temporal wall shear stresses gradients (WSSG) were observed around the anastomotic joint. Low time-averaged wall shear stress (WSS) with elevated oscillation shear index (OSI) was found near the middle of anastomosis at the aorta wall and along the graft inner wall respectively, while high time-averaged WSS with low OSI was found at the heel, the toe, and the region downstream of the toe. These regions correlated to early lesion growth. Elevated time-averaged WSSG was found at the same region, where the elevated low-density lipoprotein (LDL) permeability was observed as reported in the literature. The existence of nearly fixed stagnating location, flow separation, vortex, high time-averaged WSS with low OSI, low time-averaged WSS with elevated OSI, and high time-averaged WSSG may lead to graft stenosis. Moreover, the simulation results obtained were consistent with those of experimental measurements. Based on the validated simulation results, the 45° backward-facing graft was found to have the lowest variation range of time-averaged WSS and the lowest segmental average of WSSG among the three models investigated. The 45° backward-facing graft is thus recommended for the bypass operation with expected higher patency rate.

On the Lubrication of Short Porous Journal Bearings—Use of the Brinkman Model

1995 ◽  
Vol 117 (1) ◽  
pp. 196-199 ◽  
Author(s):  
Jaw-Ren Lin ◽  
Chi-Chuan Hwang
Keyword(s):  
Pressure Gradient ◽  
Journal Bearings ◽  
Shear Stresses ◽  
Brinkman Model ◽  
Eccentricity Ratio ◽  
Lubrication Performance ◽  
Viscous Shear ◽  
Permeability Parameter

Based on the Brinkman model (MB), this paper concerns the more realistic influence of viscous shear stresses on the lubrication performance of short porous journal bearings. Compared with those using the zero pressure gradient assumption (ZPGA), the effect of LPGA provides an improvement in the bearing performance, especially when the thick-walled bearing has higher permeability parameter or the journal operates at higher eccentricity ratio.

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