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.

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.

Linear stability analysis of channel inception: downstream-driven theory

2000 ◽  
Vol 419 ◽  
pp. 239-262 ◽  
Author(s):  
NORIHIRO IZUMI ◽  
GARY PARKER
Keyword(s):  
Shear Stress ◽  
Stability Analysis ◽  
Froude Number ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Critical Shear Stress ◽  
Resistance Coefficient ◽  
Critical Depth ◽  
Sheet Flow ◽  
Characteristic Wavelength

A linear stability analysis of incipient channellization on hillslopes is performed using the shallow-water equations and a description of the erosion of a cohesive bed. The base state consists of a laterally uniform Froude-subcritical sheet flow down a smooth, downward-concave hillslope profile. The downstream boundary condition consists of the imposition of a Froude number of unity. The process of channellization is thus driven from the downstream end. The flow and bed profiles describe a base state that migrates at constant, slow speed in the upstream direction due to bed erosion. Transverse perturbations corresponding to a succession of parallel incipient channels are introduced. It is found that these perturbations grow in time, so describing incipient channellization, only when the characteristic spacing between incipient channels is on the order of 6–100 times the Froude-critical depth divided by the resistance coefficient. The characteristic wavelength associated with maximum perturbation growth rate is found to scale as 10 times the Froude-critical depth divided by the resistance coefficient. Evaluating the friction coefficient as on the order of 0.01, an estimate of incipient channel spacing on the order of 1000 times the Froude-critical depth is obtained. The analysis reveals that downstream-driven channellization becomes more difficult as (a) the critical shear stress required to erode the bed becomes so large that it approaches the Froude-critical shear stress reached at the downstream boundary and (b) the Froude number of the subcritical equilibrium flow attained far upstream approaches unity. Alternative mechanisms must be invoked to explain channellization on slopes high enough to maintain Froude-supercritical sheet flow.

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.

scholarly journals ANALISIS ANGKUTAN SEDIMEN DASAR (BED LOAD) PADA SALURAN IRIGASI MATARAM YOGYAKARTA

Teknisia ◽  
2021 ◽  
Vol XXVI (1) ◽  
Author(s):  
Anggi Hermawan ◽  
◽  
Erwin Afiato ◽  
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Froude Number ◽  
Critical Shear Stress ◽  
Bed Load ◽  
Cross Sectional ◽  
Logarithmic Curve ◽  
Agricultural Areas ◽  
The Relationship ◽  
Downstream Area

In the last decade, the problem that has occurred in the Yogyakarta Mataram irrigation channel is the occurrence of sedimentation in the channel. This has an impact on reducing the cross-sectional discharge capacity of the canal and resulting in the supply of irrigation discharge to agricultural areas to be not optimal, so that agricultural productivity in the Mataram Irrigation Area will also not be optimal. The sediment transport (bed load) that occurs in an open channel can be approached using the empirical equation, including the Einstein, Meyer - Peter Muller and Frijlink equations. Sediment transport events that occur in the channel are stated based on the magnitude of the flow shear stress which exceeds the critical shear stress of the sediment particles. The quantity of sediment transport in the channel is stated on the logarithmic curve of the relationship between the froude number (fr) to the sediment transports (qb). The Curve explains that the increase in the froude number (fr) that occurs on each section of the channel will be directly proportional to the increase in the quantity of transport sediment (qb). The largest sediment transport occurred at the site of the Gambang and Nambongan channel section with a prediction of sediment transport of 3.57 m3/day and 3.67 m3/day, respectively. Thus, the potential for sediment transport that will settle in the downstream area is 3.67 m3/day.

scholarly journals ANALYSIS OF CHARACTERISTICS OF SEVERAL BENDS ON SIDOAN RIVER

2021 ◽  
Vol 8 (4) ◽  
pp. 46-57
Author(s):  
Rinawati ◽  
M. Galib Ishak ◽  
Rudi Herman
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Shear Velocity ◽  
High Water ◽  
Sliding Velocity ◽  
Hydraulic Simulation ◽  
Velocity Relationship ◽  
Riverbed Sediment ◽  
River Bends ◽  
The Stability

Researching the behavior of the river. Especially at the bend, where the morphology of the river is not always straightforward. Flow velocity high water and grinding at river bends occur at different points. This research was conducted on five adjacent bends on the Sidoan River section. This study examined the condition of riverbed sediment, knowing the stability of riverbed sediment granules based on shearing velocity, and stability of riverbed sediment granules based on shear stress. The method used in this study is geometric measurement. Q50 discharge calculation. produces hydraulic simulation. d50 sediment diameter. HEC-RAS software simulation and Shields graphs analysis. The results of the study on five bends for Q50 discharge are the condition of the riverbed in five bends all moving, the critical shear velocity relationship and flow depth are directly proportional, the highest condition at bend 2, otherwise the lowest condition at bend 3. The relationship between particle dimensions and shear velocity is inversely proportional to the value of sliding velocity. if the particle dimensions are small then the large shear stress occurs at bend 5 and vice versa, the dimensions of large particles then the small shear velocity occurs at bend 4, sliding velocity is directly proportional to the shear stress. The highest critical shear stress at bend 2, while the lowest condition at bend 4, the greater the radius of the bend the scouring was deeper.

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
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