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

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.

scholarly journals A Review on the Self-Cleansing Design Criteria for Sewer System

2014 ◽  
Vol 5 (2) ◽  
pp. 1-7 ◽  
Author(s):  
Charles H.J. Bong
Keyword(s):  
Shear Stress ◽  
Adverse Effects ◽  
Critical Velocity ◽  
Critical Shear Stress ◽  
The Self ◽  
Design Criteria ◽  
Sewer System ◽  
Hydraulic Behavior ◽  
Sediment Deposits ◽  
Viable Approach

 Sediment deposits in sewer system had been known to have adverse effects on the hydraulic performance of the system and also on the environment. Thus, the need for sewer system to carry sediment has been recognized for many years and self-cleansing criteria have been proposed in the literature for design purposes. Conventionally, a minimum critical velocity or critical shear stress was specified and although this approach had been successful in many cases; it was appreciated that a minimum critical velocity or critical shear stress which is unrelated to the characteristics and concentration of the sediment or the hydraulic behavior of the sewer could not properly represent the ability of the sewer flows to transport sediments. A more viable approach for self-cleansing design is to incorporate some aspect of the sediment and sewer characteristics into the design criteria; hence, various self-cleansing design criteria for sewer have been proposed in the literature. This paper presents a review on the various self-cleansing design criteria for sewer and proposed some further studies that could be conducted to improve the existing self-cleansing design criteria.

Sediment deposit thickness and its effect on critical velocity for incipient motion

2016 ◽  
Vol 74 (8) ◽  
pp. 1876-1884 ◽  
Author(s):  
C. H. J. Bong ◽  
T. L. Lau ◽  
A. Ab. Ghani ◽  
N. W. Chan
Keyword(s):  
Boundary Conditions ◽  
Critical Velocity ◽  
Sediment Deposition ◽  
Incipient Motion ◽  
Rigid Boundary ◽  
Densimetric Froude Number ◽  
Deposit Thickness ◽  
Velocity Equation ◽  
Deposition Thickness ◽  
Sediment Deposit

The understanding of how the sediment deposit thickness influences the incipient motion characteristic is still lacking in the literature. Hence, the current study aims to determine the effect of sediment deposition thickness on the critical velocity for incipient motion. An incipient motion experiment was conducted in a rigid boundary rectangular flume of 0.6 m width with varying sediment deposition thickness. Findings from the experiment revealed that the densimetric Froude number has a logarithmic relationship with both the thickness ratios ts/d and ts/y0 (ts: sediment deposit thickness; d: grain size; y0: normal flow depth). Multiple linear regression analysis was performed using the data from the current study to develop a new critical velocity equation by incorporating thickness ratios into the equation. The new equation can be used to predict critical velocity for incipient motion for both loose and rigid boundary conditions. The new critical velocity equation is an attempt toward unifying the equations for both rigid and loose boundary conditions.

Period Formula for Reinforced Concrete Buildings with Infill Walls

2016 ◽  
Vol 857 ◽  
pp. 177-182 ◽  
Author(s):  
Arijit Banik ◽  
Lipika Halder
Keyword(s):  
Reinforced Concrete ◽  
Linear Regression Analysis ◽  
Multiple Linear Regression Analysis ◽  
Fundamental Period ◽  
Support Condition ◽  
Global Response ◽  
Building Height ◽  
Building Models ◽  
Time Period ◽  
New Equation

The calculation of fundamental time period of vibration is a crucial step in seismic design and analysis of the structures to assess global response of the structure. Different international code proposed empirical expressions considering only height for bare frame structures and height and width of the buildings with infill to estimate the fundamental time period. This paper summaries the effect of the following parameters of building height, bay width, number of bays, cracked or un-cracked section of the structural member and support condition at the base on the fundamental time period of reinforced concrete bare frame and buildings with infill. Modal analysis of 360 building models with selected parameters is investigated in this study. A new equation, which is a function of the selected parameters (building height, bay width, number of bays, type of support condition, cracked or un-cracked sections and type of frame chosen for analysis) is also proposed using multiple linear regression analysis for predicting the fundamental period of buildings. The proposed simple model, including the building height, bay width, number of bays, type of support condition, cracked or un-cracked sections and type of frame chosen for analysis, showed better estimate in predicting the fundamental period of buildings compared to the code equations.

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

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.

Verification of equations for incipient motion studies for a rigid rectangular channel

2013 ◽  
Vol 67 (2) ◽  
pp. 395-403 ◽  
Author(s):  
Charles Hin Joo Bong ◽  
Tze Liang Lau ◽  
Aminuddin Ab. Ghani
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Experimental Work ◽  
Rectangular Channel ◽  
Incipient Motion ◽  
Deposit Thickness ◽  
Motion Studies ◽  
New Equation ◽  
Discrepancy Ratio ◽  
Sediment Deposit

The current study aims to verify the existing equations for incipient motion for a rigid rectangular channel. Data from experimental work on incipient motion from a rectangular flume with two different widths, namely 0.3 and 0.6 m, were compared with the critical velocity value predicted by the equations of Novak & Nalluri and El-Zaemey. The equation by El-Zaemey performed better with an average discrepancy ratio value of 1.06 compared with the equation by Novak & Nalluri with an average discrepancy ratio value of 0.87. However, as the sediment deposit thickness increased, the equation by El-Zaemey became less accurate. A plot on the Shields Diagram using the experimental data had shown the significant effect of the sediment deposit thickness where, as the deposit becomes thicker, the dimensionless shear stress θ value also increased. A new equation had been proposed by incorporating the sediment deposit thickness. The new equation gave improved prediction with an average discrepancy ratio value of 1.02.

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