Influence de la turbulence sur la force tractrice dans les canaux rectangulaires lisses

1984 ◽  
Vol 11 (3) ◽  
pp. 655-662 ◽  
Author(s):  
Karol Rohan ◽  
Gérald Pilon
Keyword(s):  
Shear Stress ◽  
Flow Measurement ◽  
Shear Stresses ◽  
Rectangular Channels ◽  
Maximal Shear Stress ◽  
Local Shear ◽  
The Mean ◽  
The University ◽  
New Procedures ◽  
Local Shear Stress

A specific research program was undertaken at the University of Sherbrooke in order to develop new procedures to determine the mean and the maximal shear stress found by means of velocity distribution measurements. For this purpose, the noninvasive flow measurement technique of laser velocimetry was employed.For smooth rectangular channels, a function between local velocity and local shear stress was developed, which includes nondimensional parameters such as the form factor of the cross section, the slope of the energy grade line, and the Reynolds number. This function can also be employed to estimate the value of maximal instantaneous shear stresses.

A Numerical Study of the Contact Mechanics and Sub-Surface Stress Effects Experienced Over a Range of Machined Surface Coatings in Rough Surface Contacts

2003 ◽  
Vol 125 (4) ◽  
pp. 720-730 ◽  
Author(s):  
A. Kadiric ◽  
R. S. Sayles ◽  
Xiao Bo Zhou ◽  
E. Ioannides
Keyword(s):  
Shear Stress ◽  
Root Mean Square ◽  
Surface Coatings ◽  
Root Mean Square Roughness ◽  
Shear Stresses ◽  
Elastic Contact ◽  
Mean Square ◽  
Clear Trend ◽  
Local Shear ◽  
Local Shear Stress

The paper employs a rough-surface numerical elastic contact method designed to analyze Hertzian elastic contact effects of surface coatings. In particular the paper explores the differences in the surface contact mechanics and the resulting sub-surface stresses experienced over a range of differing coating material-properties, thickness, and machined roughness levels in a quantitative manner. The effect of a range of surface roughness properties and in particular root mean square roughness (σ) and correlation length β*, on the magnitude and depth of maximum shear stresses in the layer under individual asperities is investigated. This is done for a hard and stiff, and also for a soft and compliant coating, and for two coating thicknesses in each case. The results suggest that the magnitude of the local shear stress increases with increasing ratio σ/β* approximately linearly. The depth of the maximum local shear stress is found to correlate best with β*, however a further clear trend is observed between this depth and the number of profile peaks. The depth also shows a relation to the ratio σ/β* but the correlation in this case is weaker with significant deviations. Neither the magnitude nor the depth of shear stresses shows any significant trend in relation to the roughness (σ) alone. The tensile stresses at the interface, and the subsequent potential for delamination, are also investigated and found to be significant. Approximate correlation between the magnitude of interface tensile stress and root mean square roughness is achieved, but no clear trend in relation to correlation length is evident.

scholarly journals Coupling between a glacier and a soft bed: I. A relation between effective pressure and local shear stress determined from till elasticity

1999 ◽  
Vol 45 (149) ◽  
pp. 31-40 ◽  
Author(s):  
Neal R. Iverson ◽  
Robert W. Baker ◽  
Roger LeB. Hooke ◽  
Brian Hanson ◽  
Peter Jansson
Keyword(s):  
Shear Stress ◽  
Shear Strain ◽  
Water Pressure ◽  
Shear Stresses ◽  
Effective Pressure ◽  
Interface Shear ◽  
Shear Moduli ◽  
Ring Shear ◽  
Local Shear ◽  
Local Shear Stress

AbstractTo predict the distribution of motion beneath glaciers on soft beds, the strength of the coupling between the ice and the bed and its variation with effective pressure must be known. A record of shear strain, acquired with a tiltmeter emplaced in till beneath Storglaciären, Sweden, indicates that fluctuations in water pressure cause variations in the local shear stress on the bed and that the bed deforms elastically in response to these variations. To estimate the shear stress from the elastic component of the total shear strain, the shear modulus of the till was measured in relaxation tests conducted in the laboratory with a ring-shear device. After accounting for the elastic compliance of the device, these tests yielded shear moduli of about 1000 and 1800 kPa at confining pressures of 85 and 280 kPa, respectively. These values are comparable to those of other granular materials undergoing recoverable shear strains of the same magnitude. The local shear stress on the till, calculated by applying the measured shear moduli to the tilt record, scales with Pe1.7, where Pe is the effective pressure. This relation implies that as Pe decreases at the ice/till interface, shear stresses on the till are reduced and concentrated elsewhere on the bed, perhaps where the till is absent or the glacier is frozen to the bed. When compared with the strength of the till determined from ring-shear tests, this relation also accounts for the lack of permanent deformation at depth in the bed during periods of low Pe and indicates that most basal motion was by sliding or ploughing.

scholarly journals Coupling between a glacier and a soft bed: I. A relation between effective pressure and local shear stress determined from till elasticity

1999 ◽  
Vol 45 (149) ◽  
pp. 31-40 ◽  
Author(s):  
Neal R. Iverson ◽  
Robert W. Baker ◽  
Roger LeB. Hooke ◽  
Brian Hanson ◽  
Peter Jansson
Keyword(s):  
Shear Stress ◽  
Shear Strain ◽  
Water Pressure ◽  
Shear Stresses ◽  
Effective Pressure ◽  
Interface Shear ◽  
Shear Moduli ◽  
Ring Shear ◽  
Local Shear ◽  
Local Shear Stress

AbstractTo predict the distribution of motion beneath glaciers on soft beds, the strength of the coupling between the ice and the bed and its variation with effective pressure must be known. A record of shear strain, acquired with a tiltmeter emplaced in till beneath Storglaciären, Sweden, indicates that fluctuations in water pressure cause variations in the local shear stress on the bed and that the bed deforms elastically in response to these variations. To estimate the shear stress from the elastic component of the total shear strain, the shear modulus of the till was measured in relaxation tests conducted in the laboratory with a ring-shear device. After accounting for the elastic compliance of the device, these tests yielded shear moduli of about 1000 and 1800 kPa at confining pressures of 85 and 280 kPa, respectively. These values are comparable to those of other granular materials undergoing recoverable shear strains of the same magnitude. The local shear stress on the till, calculated by applying the measured shear moduli to the tilt record, scales withPe1.7, wherePeis the effective pressure. This relation implies that asPedecreases at the ice/till interface, shear stresses on the till are reduced and concentrated elsewhere on the bed, perhaps where the till is absent or the glacier is frozen to the bed. When compared with the strength of the till determined from ring-shear tests, this relation also accounts for the lack of permanent deformation at depth in the bed during periods of lowPeand indicates that most basal motion was by sliding or ploughing.

Roughness Influence on Turbulent Flow Through Annular Seals

1994 ◽  
Vol 116 (2) ◽  
pp. 321-328 ◽  
Author(s):  
Victor Lucas ◽  
Sterian Danaila ◽  
Olivier Bonneau ◽  
Jean Freˆne
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Mixing Length ◽  
Local Shear ◽  
Wall Shear ◽  
Local Shear Stress

This paper deals with an analysis of turbulent flow in annular seals with rough surfaces. In this approach, our objectives are to develop a model of turbulence including surface roughness and to quantify the influence of surface roughness on turbulent flow. In this paper, in order to simplify the analysis, the inertial effects are neglected. These effects will be taken into account in a subsequent work. Consequently, this study is based on the solution of Reynolds equation. Turbulent flow is solved using Prandtl’s turbulent model with Van Driest’s mixing length expression. In Van Driest’s model, the mixing length depends on wall shear stress. However there are many numerical problems in evaluating this wall shear stress. Therefore, the goal of this work has been to use the local shear stress in the Van Driest’s model. This derived from the work of Elrod and Ng concerning Reichardt’s mixing length. The mixing length expression is then modified to introduce roughness effects. Then, the momentum equations are solved to evaluate the circumferential and axial velocity distributions as well as the turbulent viscosity μ1 (Boussinesq’s hypothesis) within the film. The coefficients of turbulence kx and kz, occurring in the generalized Reynolds’ equation, are then calculated as functions of the flow parameters. Reynolds’ equation is solved by using a finite centered difference method. Dynamic characteristics are calculated by exciting the system numerically, with displacement and velocity perturbations. The model of Van Driest using local shear stress and function of roughness has been compared (for smooth seals) to the Elrod and Ng theory. Some numerical results of the static and dynamic characteristics of a rough seal (with the same roughness on the rotor as on the stator) are presented. These results show the influence of roughness on the dynamic behavior of the shaft.

scholarly journals Stress-gradient Coupling in Glacier Flow: IV. Effects of the “T” Term

1986 ◽  
Vol 32 (112) ◽  
pp. 342-349 ◽  
Author(s):  
Barclay Kamb ◽  
Keith A. Echelmeyer
Keyword(s):  
Shear Stress ◽  
Coupling Theory ◽  
Longitudinal Stress ◽  
Longitudinal Flow ◽  
Stress Gradients ◽  
Flow Coupling ◽  
Flow Response ◽  
Longitudinal Variations ◽  
Local Shear ◽  
Local Shear Stress

AbstractThe “T term” in the longitudinal stress-equilibrium equation for glacier mechanics, a double y-integral of ∂2τxy/∂x2 where x is a longitudinal coordinate and y is roughly normal to the ice surface, can be evaluated within the framework of longitudinal flow-coupling theory by linking the local shear stress τxy at any depth to the local shear stress τB at the base, which is determined by the theory. This approach leads to a modified longitudinal flow-coupling equation, in which the modifications deriving from the T term are as follows: 1. The longitudinal coupling length is increased by about 5%. 2. The asymmetry parameter σ is altered by a variable but small amount depending on longitudinal gradients in ice thickness h and surface slope α. 3. There is a significant direct modification of the influence of local h and α on flow, which represents a distinct “driving force” in glacier mechanics, whose origin is in pressure gradients linked to stress gradients of the type ∂τxy/∂x. For longitudinal variations in h, the “T force” varies as d2h/dx2 and results in an in-phase enhancement of the flow response to the variations in h, describable (for sinusoidal variations) by a wavelength-dependent enhancement factor. For longitudinal variations in α, the “force” varies as dα/dx and gives a phase-shifted flow response. Although the “T force” is not negligible, its actual effect on τB and on ice flow proves to be small, because it is attenuated by longitudinal stress coupling. The greatest effect is at shortest wavelengths (λ 2.5h), where the flow response to variations in h does not tend to zero as it would otherwise do because of longitudinal coupling, but instead, because of the effect of the “T force”, tends to a response about 4% of what would occur in the absence of longitudinal coupling. If an effect of this small size can be considered negligible, then the influence of the T term can be disregarded. It is then unnecessary to distinguish in glacier mechanics between two length scales for longitudinal averaging of τb, one over which the T term is negligible and one over which it is not.Longitudinal flow-coupling theory also provides a basis for evaluating the additional datum-state effects of the T term on the flow perturbations Δu that result from perturbations Δh and Δα from a datum state with longitudinal stress gradients. Although there are many small effects at the ~1% level, none of them seems to stand out significantly, and at the 10% level all can be neglected.The foregoing conclusions apply for long wavelengths λh. For short wavelengths (λ h), effects of the T term become important in longitudinal coupling, as will be shown in a later paper in this series.

Comparison of void fraction change and local shear stress fluctuation in channel flow

2018 ◽  
Vol 2018 (0) ◽  
pp. OS3-5
Author(s):  
Hayato NAKAMURA ◽  
Satoshi OGAMI ◽  
Yoshihiko OISHI ◽  
Hideki KAWAI ◽  
Yuichi MURAI
Keyword(s):  
Shear Stress ◽  
Channel Flow ◽  
Void Fraction ◽  
Stress Fluctuation ◽  
Local Shear ◽  
Local Shear Stress

scholarly journals The Brachial Artery Remodels to Maintain Local Shear Stress Despite the Presence of Cardiovascular Risk Factors

2009 ◽  
Vol 29 (4) ◽  
pp. 606-612 ◽  
Author(s):  
William B. Chung ◽  
Naomi M. Hamburg ◽  
Monika Holbrook ◽  
Sherene M. Shenouda ◽  
Mustali M. Dohadwala ◽  
...  
Keyword(s):  
Risk Factors ◽  
Shear Stress ◽  
Cardiovascular Risk ◽  
Cardiovascular Risk Factors ◽  
Brachial Artery ◽  
Local Shear ◽  
Local Shear Stress
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