scholarly journals FLOW VISUALISATION AROUND A SOLID SPHERE ON A ROUGH BED UNDER REGULAR WAVES

2012 ◽  
Vol 1 (33) ◽  
pp. 32
Author(s):  
Hela Vidura Vithana ◽  
Richard Robert Simons ◽  
Martin Hyde
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Solid Sphere ◽  
Spherical Particles ◽  
Flow Visualisation ◽  
Incipient Motion ◽  
Exponential Relationship ◽  
Pressure Transducers ◽  
Motion Data ◽  
Rough Bed

Flow visualization using Volumetric Three-component Velocimetry (V3V) was carried out during laboratory tests to determine threshold shear stress and forces on idealized spherical stones. Incipient motion tests consisted of light weight spherical particles of specific gravity=1.19-2.65 and diameter=9.6mm-31.8mm. In-line and uplift forces on a 50mm sphere sitting on a rough bed of similar spheres were measured using pressure transducers linked to tappings on the sphere surface. It was found that the Shields critical shear stress and stone protrusion has an exponential relationship. At an exposure of 0.2d and less, bed protection is remarkably stable. Incipient motion data for currents are applicable for waves when the flow is fully developed.

Study on Incipient Motion of Consolidated Cohesive Fine Sediment

2012 ◽  
Vol 204-208 ◽  
pp. 354-358
Author(s):  
Jun Wang ◽  
Wei Guo ◽  
Hai Tao Xu ◽  
Zhong Wu Jin ◽  
Yin Jun Zhou
Keyword(s):  
Particle Size ◽  
Shear Stress ◽  
Critical Shear Stress ◽  
Fine Sediment ◽  
Weight Increase ◽  
Unit Weight ◽  
Incipient Motion ◽  
Mean Particle Size ◽  
Dry Unit Weight ◽  
The One

The incipient motion mechanism of cohesive fine sediment is different to the one of non-cohesive sediment. It is related to the consolidation while being influenced by the dry unit weight and particle size. By means of the rectangle piping flume, the influence mechanism of dry unit weight and particle size to critical shear stress of cohesive fine sediment is studied. Experimental results show that on the condition of consolidation, the influence of dry unit weight to incipient motion is divided into two different stages, one is that when dry unit weight increase quickly, but the influence to incipient motion is not greatly, another is that when dry unit weight increase slowly, but the influence to incipient motion is very greatly, the critical dry unit weight to two stages decline as mean particle size decrease. So the mean particle size is finer, the degree of dry unit weight influence to critical shear stress is stronger, and the incipient motion is more difficult when consolidation last longer; it is also shown consolidation is more disadvantageous to incipient motion.

scholarly journals Assessment of Critical Shear Stress and Threshold Velocity in Shallow Flow with Sand Particles

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 994
Author(s):  
Reza Shahmohammadi ◽  
Hossein Afzalimehr ◽  
Jueyi Sui
Keyword(s):  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Critical Shear Stress ◽  
Flow Region ◽  
Transitional Flow ◽  
Incipient Motion ◽  
Sediment Particle ◽  
Threshold Velocity ◽  
Threshold Conditions ◽  
Sand Particles

In this study, the incipient motion of four groups of sand, ranging from medium to very coarse particles, was experimentally examined using an acoustic Doppler velocimeter (ADV) in different water depths under the hydraulically transitional flow condition. The transport criterion of the Kramer visual observation method was used to determine threshold conditions. Some equations for calculating threshold average and near-bed velocities were derived. Results showed that the threshold velocity was directly proportional to both sediment particle size and water depth. The vertical distributions of the Reynolds shear stress showed an increase from the bed to about 0.1 of the water’s depth, after performing a damping area, then a decrease toward the water surface. By extending the linear portion of the Reynolds shear stress in the upper zone of the damping area to the bed, the critical shear stress, particle shear Reynolds number, and critical Shields parameter were calculated. Results showed that the critical Shields parameter was located under the Shields curve, showing no sediment motion. This indicates that the incipient motion of sediment particles occurred with smaller bed shear stress than that estimated using the Shields diagram in the hydraulically transitional flow region. The reason could be related to differences between the features of the present experiment and those of the experiments used in the development of the Shields diagram, including the approaches to determine and define threshold conditions, the accuracy of experimental tools to estimate critical shear stress, and sediment particle characteristics. Therefore, the change in the specifications of experiments from those on which the Shields diagram has been based led to the deviation between the estimation using the Shields diagram and that of real threshold conditions, at least in the hydraulically transitional flow region with sand particles.

Critical shear stress for incipient motion of sand/gravel streambeds

2001 ◽  
Vol 37 (8) ◽  
pp. 2273-2283 ◽  
Author(s):  
Audrey B. Shvidchenko ◽  
Gareth Pender ◽  
Trevor B. Hoey
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Incipient Motion

DEPOSITION THICKNESS AND ITS EFFECT ON CRITICAL SHEAR STRESS FOR INCIPIENT MOTION OF SEDIMENTS

2016 ◽  
Vol 78 (9-4) ◽  
Author(s):  
Charles Hin Joo Bong ◽  
Frederik Josep Putuhena ◽  
Tze Liang Lau ◽  
Aminuddin Ab. Ghani
Keyword(s):  
Boundary Condition ◽  
Shear Stress ◽  
Linear Regression Analysis ◽  
Critical Shear Stress ◽  
Multiple Linear Regression Analysis ◽  
Incipient Motion ◽  
Rigid Boundary ◽  
Sediment Deposits ◽  
Deposition Thickness ◽  
New Equation

There are evidences in existing literatures suggesting the incipient motion values for any particle size is substantially lower for rigid boundary condition as compared to loose boundary condition.  The objective of the current study is to determine the effect of sediment deposition thickness on the critical shear stress for incipient motion. Experimental works for incipient motion were carried out in a rectangular flume with varying sediment deposits thickness. Results showed that the sediment deposits thickness has effect on the critical shear stress at low sediment deposits thickness and the effect will slowly diminish as the sediment deposits thickness increases. Multiple linear regression analysis was performed on the experimental data to develop a new critical shear stress equation.  The best regression model has   value of 0.69;    value of 0.60;  value of 0.009 and Mallow’s  value of 3.00. The new equation appears to be more consistent as compared to existing incipient motion equations for rigid boundary condition by having 80% of the predicted data falls within the acceptable discrepancy ratio when tested with data from other authors. The new equation can be used to determine critical shear stress values for self-cleansing sewerage design and other related engineering applications

scholarly journals Experimental Analysis of Incipient Motion for Uniform and Graded Sediments

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1874
Author(s):  
Khabat Khosravi ◽  
Amir H. N. Chegini ◽  
Luca Mao ◽  
Jose F. Rodriguez ◽  
Patricia M. Saco ◽  
...  
Keyword(s):  
Shear Stress ◽  
Froude Number ◽  
Critical Shear Stress ◽  
Shear Velocity ◽  
Incipient Motion ◽  
Critical Flow Velocity ◽  
Relative Roughness ◽  
Motion Condition ◽  
Gravel Size ◽  
Bed Slope

So far, few studies have focused on the concept of critical flow velocity rather than bed shear stress for incipient sediment motion. Moreover, few studies have focused on sediment mixtures (graded sediment) and shape rather than uniform sediment for incipient motion condition. Different experiments were conducted at a hydraulic laboratory at the University of Guilan in 2015 to determine hydraulic parameters on the incipient motion condition. The aim of this study is to conduct a comparison between uniform and graded sediments, and a comparison between round and angular sediments. Experiments included rounded uniform bed sediments of 5.17, 10.35, 14 and 20.7 mm, angular uniform sediment of 10.35 mm, and graded sediment. Results demonstrated that angular sediment has a higher critical shear velocity than rounded sediment for incipient motion. Results also showed that for a given bed sediment, although critical shield stress and relative roughness increased with the bed slope, the particle Froude number (based on critical velocity) decreased. In terms of the sediment mixture, the critical shear stress (Vc*) was higher for the graded sediment than for the three finer uniform sediment sizes. The finer fractions of the mixture have a higher particle Froude number than their corresponding uniform sediment value, while the coarser fractions of the mixture showed a lower stability than their corresponding uniform sediment value. Results demonstrated that the reduction in the particle Froude number was more evident in lower relative roughness conditions. The current study provides a clearer insight into the interaction between initial sediment transport and flow characteristic, especially particle Froude number for incipient motion in natural rivers where stream beds have different gravel size distribution.

scholarly journals Effects of relative submergence and bed slope on sediment incipient motion under decelerating flows

2015 ◽  
Vol 63 (4) ◽  
pp. 295-302 ◽  
Author(s):  
Ramin Bolhassani ◽  
Hossein Afzalimehr ◽  
Subhasish Dey
Keyword(s):  
Experimental Study ◽  
Shear Stress ◽  
Critical Shear Stress ◽  
Incipient Motion ◽  
Grain Sizes ◽  
Bed Slope ◽  
Sediment Incipient Motion

Abstract This paper presents the results of an experimental study to quantify the effects of bed slope and relative submergence on incipient motion of sediment under decelerating flows. Experiments were conducted in an experimental tilting-flume of 8 m long 0.4 m wide and 0.6 m deep with glass-walls. Three uniform sediments with median grain sizes of 0.95, 1.8 and 3.8 mm and three bed slopes of 0.0075, 0.0125 and 0.015 were used under decelerating flow. The main conclusion is that the Shields diagram, which is commonly used to evaluate the critical shear stress, is not suitable to predict the critical shear stress under decelerating flows.

scholarly journals Computation of Critical Shear Stress for Non-Uniform Sediment

2019 ◽  
Vol 8 (3) ◽  
pp. 1402-1406
Keyword(s):  
Shear Stress ◽  
Flood Control ◽  
Critical Shear Stress ◽  
Incipient Motion ◽  
Alluvial Rivers ◽  
Motion Condition ◽  
Load Transport ◽  
Bed Load Transport ◽  
College Of Engineering ◽  
Critical Process

Civil engineers associated with water resources development come across various kinds of problems related to alluvial rivers and channels like Floods, Meandering and Flood Control, Sediment Load Computation, Silting of Reservoir, erosion etc. To define incipient motion condition is very critical process and is of prime important for design any hydraulic structure. Many investigators study the critical shear stress at incipient condition. For uniform as well as non-uniform sediments. Many came up with the formulae to describe the incipient condition still there is a scope to study these parameters. In this present study, the incipient motion conditions. for non-uniform sediment is tried to compute based on various parameters with the help of experimentation. Experiments on critical shear stress and bed load transport of different fractions for non-uniform sediment are reported in this study. Study of hydraulic parameter such as depth, velocity, discharge, sediment characteristics etc. were investigated with the help of experiments. Experiments were conducted in a 10-meter-long, 0.30-meter-wide and 0.45-meter-deep tilting flume in P.G Hydraulic Lab of BV(DU) College of Engineering, Pune. The results were obtained, analysed and conclusion were made.

Sign in / Sign up

Export Citation Format

Share Document