On the radial structure of planetary rings

1984 ◽  
Vol 75 ◽  
pp. 431-437 ◽  
Author(s):  
A.W. Harris ◽  
W.R. Ward
Keyword(s):  
Shear Stress ◽  
Optical Depth ◽  
Orbital Velocity ◽  
Planetary Rings ◽  
Radial Gradient ◽  
Viscous Shear Stress ◽  
Viscous Shear ◽  
Radial Structure ◽  
Uniform Ring ◽  
Increasing Function

ABSTRACTA ring of particles in orbit about a planet experiences a viscous shear stress due to the radial gradient of orbital velocity. This stress tends to spread the ring with time. At low optical depth (τ ≲ 0.5), and again at high optical depth (τ ≳ 2), the shear stress is an increasing function of optical depth. In the intermediate range (0.5 ≲ x ≲ 2), stress may decrease with increasing τ, leading to a diffusive instability which will tend to break an Initially uniform ring into ringlets of high and low optical depths.

scholarly journals Shear models and parametric analysis of the PVC geomembrane-cushion interface in a high rock-fill dam

PLoS ONE ◽  
2021 ◽  
Vol 16 (1) ◽  
pp. e0245245
Author(s):  
Yun-Feng Liu ◽  
Ke Gu ◽  
Yi-Ming Shu ◽  
Xian-Lei Zhang ◽  
Xin-Xin Liu ◽  
...  
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Three Dimensional ◽  
Viscous Friction ◽  
Hydraulic Pressure ◽  
Viscous Shear Stress ◽  
Box Counting ◽  
Viscous Shear ◽  
The Stability ◽  
Hysteresis Friction

As a type of flexible impermeable material, a PVC geomembrane must be cooperatively used with cushion materials. The contact interface between a PVC geomembrane and cushion easily loses stability. In this present paper, we analyzed the shear models and parameters of the interface to study the stability. Two different cushion materials were used: the common extrusion sidewall and non-fines concrete. To simulate real working conditions, flexible silicone cushions were added under the loading plates to simulate hydraulic pressure loading, and the loading effect of flexible silicone cushions was demonstrated by measuring the actual contact areas under different normal pressures between the geomembrane and cushion using the thin-film pressure sensor. According to elastomer shear stress, there are two main types of shear stress between the PVC geomembrane and the cushion: viscous shear stress and hysteresis shear stress. The viscous shear stress between the geomembrane and the cement grout was measured using a dry, smooth concrete sample, then the precise formula parameters of the viscous shear stress and viscous friction coefficient were obtained. The hysteresis shear stress between the geomembrane and the cushion was calculated by subtracting the viscous shear stress from the total shear stress. The formula parameters of the hysteresis shear stress and hysteresis friction coefficient were calculated. The three-dimensional box-counting dimensions of the cushion surface were calculated, and the formula parameters of the hysteresis friction were positively correlated with the three-dimensional box dimensions.

An Experimental Study of the Flow Structures in Vegetated Open Channels

2014 ◽  
Vol 522-524 ◽  
pp. 941-949
Author(s):  
Xu Yue Hu ◽  
Kun Jiang ◽  
Hua Qiang Ren ◽  
Xiao Xiong Shen
Keyword(s):  
Shear Stress ◽  
Reynolds Stress ◽  
Turbulence Intensity ◽  
Flow Structures ◽  
Vegetation Distribution ◽  
Measuring Point ◽  
Vegetation Height ◽  
Water Flows ◽  
Viscous Shear Stress ◽  
Viscous Shear

To investigate the effects of vegetation on flow Reynolds stress and turbulence intensity,an experiment was performed with plastic rods and artificial waterweeds in a slope-variable laboratory flume; an acoustic Doppler velocimeter was used to measure the instantaneous velocity at different points on the vertical line under different conditions; Turbulence parameters at each measuring point were calculated, such as Reynolds stress and turbulence intensity; The effects of vegetation on flow structures were analyzed through comparison with the turbulence characteristics of uniform open channel flows without vegetation distribution. The experimental results show that the turbulent constant Reynolds stress layer exists in water flows with vegetation distribution compared with the water flows without vegetation distribution. Without vegetation distribution, the viscous shear stress at the flume bed mainly affects the area between the bed and the level at a depth about 30% of the water depth. With vegetation distribution, the effect of the viscous shear stress at the bed weakens.The highest flow turbulence intensity with vegetation distribution occurs within the range of vegetation height.

scholarly journals Three-dimensional extent of flow stagnation in transcatheter heart valves

2019 ◽  
Vol 16 (154) ◽  
pp. 20190063 ◽  
Author(s):  
Vrishank Raghav ◽  
Chris Clifford ◽  
Prem Midha ◽  
Ikechukwu Okafor ◽  
Brian Thurow ◽  
...  
Keyword(s):  
Shear Stress ◽  
Heart Valves ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Flow Loop ◽  
Low Velocity ◽  
Viscous Shear Stress ◽  
Velocity Magnitude ◽  
Flow Stagnation ◽  
Viscous Shear

The recent unexpected discovery of thrombosis in transcatheter heart valves (THVs) has led to increased concerns of long-term valve durability. Based on the clinical evidence combined with Virchow's triad, the primary hypothesis is that low-velocity blood flow around the valve could be a primary cause for thrombosis. However, due to limited optical access in such unsteady three-dimensional biomedical flows, measurements are challenging. In this study, for the first time, we employ a novel single camera volumetric velocimetry technique to investigate unsteady three-dimensional cardiovascular flows. Validation of the novel volumetric velocimetry technique with standard planar particle image velocimetry (PIV) technique demonstrated the feasibility of adopting this new technique to investigate biomedical flows. This technique was used to quantify the three-dimensional velocity field in the vicinity of a validated, custom developed, transparent THV in a bench-top pulsatile flow loop. Large volumetric regions of flow stagnation were observed in the neo-sinus throughout the cardiac cycle, with stagnation defined as a velocity magnitude lower than 0.05 m s −1 . The volumetric scalar viscous shear stress quantified via the three-dimensional shear stress tensor was within the range of low shear-inducing thrombosis observed in the literature. Such high-fidelity volumetric quantitative data and novel imaging techniques used to obtain it will enable fundamental investigation of heart valve thrombosis in addition to providing a reliable and robust database for validation of computational tools.

High-Resolution Measurements of Velocity and Shear Stress in Leakage Jets From Bileaflet Mechanical Heart Valve Hinge Models

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Ewa Klusak ◽  
Alessandro Bellofiore ◽  
Sarah Loughnane ◽  
Nathan J. Quinlan
Keyword(s):  
Shear Stress ◽  
High Resolution ◽  
Flow Field ◽  
Heart Valve ◽  
Temporal Resolution ◽  
Mechanical Heart Valve ◽  
Small Scale ◽  
Bileaflet Mechanical Heart Valve ◽  
Viscous Shear Stress ◽  
Viscous Shear

In flow through cardiovascular implants, hemolysis, and thrombosis may be initiated by nonphysiological shear stress on blood elements. To enhance understanding of the small-scale flow structures that stimulate cellular responses, and ultimately to design devices for reduced blood damage, it is necessary to study the flow-field at high spatial and temporal resolution. In this work, we investigate flow in the reverse leakage jet from the hinge of a bileaflet mechanical heart valve (BMHV). Scaled-up model hinges are employed, enabling measurement of the flow-field at effective spatial resolution of 167 μm and temporal resolution of 594 μs using two-component particle image velocimetry (PIV). High-velocity jets were observed at the hinge outflow, with time-average velocity up to 5.7 m/s, higher than reported in previous literature. Mean viscous shear stress is up to 60 Pa. For the first time, strongly unsteady flow has been observed in the leakage jet. Peak instantaneous shear stress is up to 120 Pa, twice as high as the average value. These high-resolution measurements identify the hinge leakage jet as a region of very high fluctuating shear stress which is likely to be thrombogenic and should be an important target for future design improvement.

The effect of turbulent viscous shear stress on red blood cell hemolysis

2014 ◽  
Vol 17 (2) ◽  
pp. 178-185 ◽  
Author(s):  
Jen-Hong Yen ◽  
Sheng-Fu Chen ◽  
Ming-Kai Chern ◽  
Po-Chien Lu
Keyword(s):  
Shear Stress ◽  
Blood Cell ◽  
Red Blood Cell ◽  
Viscous Shear Stress ◽  
Viscous Shear
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