Experimental Study on the Fluid Mud Transportation Under Currents with Fluctuating Water Surface

2016 ◽  
Vol 11 (5) ◽  
pp. 982-988
Author(s):  
Chunrong Liu ◽  
◽  
Wenyu Yang ◽  
Bo Wu ◽  
Huhe Aode ◽  
...  
Keyword(s):  
Experimental Study ◽  
Shear Stress ◽  
Cross Section ◽  
Water Surface ◽  
Bed Shear Stress ◽  
Fluid Mud ◽  
Water Currents ◽  
Series Of Experiments ◽  
Surface Fluctuation ◽  
Over Time

A series of experiments conducted to study fluid mud movement in currents with a fluctuating water surface involved measuring fluid mud yield stress, bed shear stress, and water surface fluctuation. To observe fluid mud movement, we dyed a sheet of fluid mud in the water flume cross-section red. We then calculated the fluid mud transportation velocity based on mud sheet displacement over time. Experiments showed that water surface fluctuation plays an important role in fluid mud movement. Under conditions of water surface fluctuation, we were able to observe fluid mud oscillation in the case that the interface of the water and fluid mud is clear. After several oscillation cycles, fluid mud is transported downstream by water currents.

scholarly journals Laboratory studies on bedload transport under unsteady flow conditions

2018 ◽  
Vol 66 (1) ◽  
pp. 23-31 ◽  
Author(s):  
Magdalena M. Mrokowska ◽  
Paweł M. Rowiński ◽  
Leszek Książek ◽  
Andrzej Strużyński ◽  
Maciej Wyrębek ◽  
...  
Keyword(s):  
Shear Stress ◽  
Sediment Yield ◽  
Water Surface ◽  
Bedload Transport ◽  
Bed Shear Stress ◽  
Surface Slope ◽  
Stream Power ◽  
Transport Dynamics ◽  
Water Surface Slope ◽  
Total Sediment

Abstract Two sets of triangular hydrographs were generated in a 12-m-long laboratory flume for two sets of initial bed conditions: intact and water-worked gravel bed. Flowrate ranging from 0.0013 m3 s-1 to 0.0456 m3 s-1, water level ranging from 0.02 m to 0.11 m, and cumulative mass of transported sediment ranging from 4.5 kg to 14.2 kg were measured. Then, bedload transport rate, water surface slope, bed shear stress, and stream power were evaluated. The results indicated the impact of initial bed conditions and flow unsteadiness on bedload transport rate and total sediment yield. Difference in ratio between the amount of supplied sediment and total sediment yield for tests with different initial conditions was observed. Bedload rate, bed shear stress, and stream power demonstrated clock-wise hysteretic relation with flowrate. The study revealed practical aspects of experimental design, performance, and data analysis. Water surface slope evaluation based on spatial water depth data was discussed. It was shown that for certain conditions stream power was more adequate for the analysis of sediment transport dynamics than the bed shear stress. The relations between bedload transport dynamics, and flow and sediment parameters obtained by dimensional and multiple regression analysis were presented.

Streamlining of Bridge Piers as Scour Countermeasures

2015 ◽  
Vol 2521 (1) ◽  
pp. 162-171 ◽  
Author(s):  
Junhong Li ◽  
Junliang Tao
Keyword(s):  
Shear Stress ◽  
Cross Section ◽  
Cross Sections ◽  
Turbulence Intensity ◽  
Computational Cost ◽  
Three Dimensional ◽  
Test Cases ◽  
Bridge Scour ◽  
Bed Shear Stress ◽  
Cfd Simulations

Bridge scour is one of the most critical causes of bridge failure. Existing scour countermeasures either passively prevent the development of scour holes by stabilizing the critical shear zone or actively reduce the turbulence intensity in the vicinity of the pier surface. This paper proposes streamlining of the bridge pier as an option to reduce turbulence intensity actively in the local zone and thus decrease overall local scour potential. The effect of the curvature of the pier cross section was evaluated with computational fluid dynamics (CFD) simulations. To reduce computational cost, two-dimensional CFD simulations were conducted to model the flow fields around test cases having different pier cross sections. Simulation results were systematically analyzed and compared to evaluate the effect of streamlining on the flow field. The cross section that resulted in the smallest value of the maximum bed shear stress was selected as the optimal cross section for the subsequent three-dimensional (3-D) study, which investigated the vortex structures around the pier. Results from this 3-D simulation were compared with those from two other test cases, in which piers had cross-section shapes that are commonly seen in practice. The pier model with the optimal cross section was found to significantly reduce the downward velocity in front of the piers, the maximum bed shear stress, and the overall scour potential. These findings are expected to inform the design of optimal streamlined piers for newly proposed bridges, which could diminish the overall scour potential around piers.

scholarly journals Modeling Bed Shear Stress Distribution in Rectangular Channels Using the Entropic Parameter

Entropy ◽  
2020 ◽  
Vol 22 (1) ◽  
pp. 87 ◽  
Author(s):  
Domenica Mirauda ◽  
Maria Grazia Russo
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Cross Section ◽  
Open Channel ◽  
Shear Stress Distribution ◽  
Open Channels ◽  
Channel Cross Section ◽  
Small Scale ◽  
Large Set ◽  
Bed Shear Stress

The evaluation of bed shear stress distribution is fundamental to predicting the transport of sediments and pollutants in rivers and to designing successful stable open channels. Such distribution cannot be determined easily as it depends on the velocity field, the shape of the cross section, and the bed roughness conditions. In recent years, information theory has been proven to be reliable for estimating shear stress along the wetted perimeter of open channels. The entropy models require the knowledge of the shear stress maximum and mean values to calculate the Lagrange multipliers, which are necessary to the resolution of the shear stress probability distribution function. This paper proposes a new formulation which stems from the maximization of the Tsallis entropy and simplifies the calculation of the Lagrange coefficients in order to estimate the bed shear stress distribution in open-channel flows. This formulation introduces a relationship between the dimensionless mean shear stress and the entropic parameter which is based on the ratio between the observed mean and maximum velocity of an open-channel cross section. The validity of the derived expression was tested on a large set of literature laboratory measurements in rectangular cross sections having different bed and sidewall roughness conditions as well as various water discharges and flow depths. A detailed error analysis showed good agreement with the experimental data, which allowed linking the small-scale dynamic processes to the large-scale kinematic ones.

Comparison of Different Methods to Calculate Bed Shear Stress

1992 ◽  
Vol 25 (8) ◽  
pp. 131-140 ◽  
Author(s):  
M. R. Kabir ◽  
H. Torfs
Keyword(s):  
Shear Stress ◽  
Velocity Profile ◽  
Cross Section ◽  
Friction Velocity ◽  
Rectangular Cross Section ◽  
Reference Level ◽  
Bed Shear Stress ◽  
Rough Bed ◽  
Channel Slope

Precise velocity profile measurements were carried out in a fully developed, subcritical and supercritical flow on a smooth and a rough bed in a flume with a rectangular cross section. In both cases different approaches were used to calculate the friction velocity, u*, and comparisons were made. The influence of the reference level (hypothetical bed level) has been discussed. Friction velocities calculated from the velocity profile are very sensitive to the hypothetical bed level. For a smooth bed the determination of the reference level does not present any difficulties. However, for a rough bed this level shows dependency on the channel slope.

Interfacial Shear in Two-Phase Wavy Flow in Closed Horizontal Channels

1974 ◽  
Vol 96 (2) ◽  
pp. 97-102 ◽  
Author(s):  
E. Kordyban
Keyword(s):  
Shear Stress ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Cross Section ◽  
Water Surface ◽  
Interfacial Shear Stress ◽  
Interfacial Shear ◽  
Channel Cross Section ◽  
Two Phase ◽  
The Waves

The interfacial shear stress for air flowing over a wavy water surface was determined experimentally in a closed horizontal channel by measuring the pressure drop and the structure of the water surface. The wall shear stress was measured with the aid of a Preston gauge. The range of tests included the conditions where the waves were large in comparison to the channel cross section. The equivalent sand roughness determined from the resistance formula for rough walls in fully turbulent flow was found to be related to the rms wave height through ks = 32Δh.

scholarly journals BED SHEAR STRESS IN UNSTEADY FLOW

2011 ◽  
Vol 1 (32) ◽  
pp. 8 ◽  
Author(s):  
Paul Andrew Guard ◽  
Peter Nielsen ◽  
Tom E Baldock
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Pressure Gradient ◽  
Water Surface ◽  
Free Stream ◽  
Shear Stresses ◽  
Bed Shear Stress ◽  
Horizontal Pressure Gradient ◽  
Friction Factors ◽  
Horizontal Pressure

Standard engineering methods of estimating bed shear stress using friction factors can fail spectacularly in unsteady hydrodynamic conditions. This paper demonstrates this fact using direct measurements of bed shear stresses under irregular waves using a shear plate apparatus. The measurements are explained in terms of the influence of the horizontal pressure gradient and the shear stresses acting on the surface of the plate. The horizontal fluid velocity at the edge of the boundary layer and the water surface elevation and slope were also measured. The paper demonstrates that the water surface measurements can be used to obtain accurate estimates of the forces on the bed, by employing Fourier analysis techniques or an innovative convolution integral method. The experimental results indicate that an offshore bed shear stress may be recorded while the free stream velocity remains onshore at all times. This demonstrates the failure of the standard engineering friction factor method in this scenario, since negative friction factors would be required. Important questions are raised regarding the appropriate definition for the bed shear stress when the vertical gradient of the shear stress is large. It is shown that it is problematic to define a single value for a “bed” shear stress in the presence of a strong horizontal pressure gradient. It is also argued that the natural driver for any model used to predict bed shear stress is the pressure gradient (or its proxy the free stream acceleration), rather than the velocity. This allows for accurate calculation of both acceleration effects (more rapid acceleration leads to a thinner boundary layer and higher shear stress) and also the direct action of the horizontal pressure gradient.

Fractal dimensions of cohesive sediment during settling in steady state flow with different initial sediment concentrations

2005 ◽  
Vol 32 (4) ◽  
pp. 658-664 ◽  
Author(s):  
M Stone ◽  
B G Krishnappan
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Suspended Solids ◽  
Fractal Dimensions ◽  
Sediment Concentration ◽  
Cohesive Sediment ◽  
Image Analysis System ◽  
Bed Shear Stress ◽  
Annular Flume ◽  
Over Time

Morphology of particle populations of cohesive sediment were examined during settling experiments in an annular flume with different initial sediment concentrations (200 and 350 mg/L) at constant bed shear stress (0.121 N/m2) using fractal dimensions. The area, longest axis, and perimeter of suspended solids were measured with light microscopy and an image-analysis system to determine three fractal dimensions (D, D1, D2). The ratio between the initial and steady state (time T = 300 min) sediment concentration was 0.54 for both experimental runs and is a function of bed shear stress, not the initial sediment concentration. The fractal dimension D changed from 1.32 at the start of the experiment to 1.36 at steady state, which represents an increase in shape irregularity of larger particles over time compared with smaller particles. At steady state, D1 and D2 were 1.19 and 1.66, respectively. Small increases in D1 and D2 over time indicated a change in morphology towards longer and more elongated particles. The D2 measurements in the present study indicate that differential sedimentation is the predominant flocculation mechanism of cohesive sediments in the flume settling experiments. Fractal dimensions of suspended solids were not significantly different at steady state as a function of initial sediment concentration.Key words: particle morphology, fractal dimensions, cohesive sediment, flocculation, deposition, annular flume.

scholarly journals Experimental study on the bed shear stress under breaking waves

2017 ◽  
Vol 31 (3) ◽  
pp. 308-316 ◽  
Author(s):  
Si-yu Hao ◽  
Yun-feng Xia ◽  
Hua Xu
Keyword(s):  
Experimental Study ◽  
Shear Stress ◽  
Breaking Waves ◽  
Bed Shear Stress
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