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.

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.

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 Effect of Mean Velocity-to-Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 883
Author(s):  
Nargess Moghaddassi ◽  
Seyed Habib Musavi-Jahromi ◽  
Mohammad Vaghefi ◽  
Amir Khosrojerdi
Keyword(s):  
Experimental Investigation ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Scour Depth ◽  
Incipient Motion ◽  
Mean Velocity ◽  
Straight Path ◽  
Meandering Channel ◽  
Bed Topography ◽  
The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity-to-critical velocity ratios have been tested at the upstream straight path to determine the meander’s incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity-to-critical velocity ratios. In addition, the upstream bend’s effect on the downstream bend was investigated. Results indicated that the maximum scour depth at the downstream bend increased as a result of changing the mean velocity-to-critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by, respectively, 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend’s incipient motion was observed for the mean velocity-to-critical velocity ratio of 0.89, while the downstream bend’s incipient motion occurred for the ratio of 0.78.

scholarly journals Design of a new hybrid artificial neural network method based on decision trees for calculating the Froude number in rigid rectangular channels

2016 ◽  
Vol 64 (3) ◽  
pp. 252-260 ◽  
Author(s):  
Isa Ebtehaj ◽  
Hossein Bonakdari ◽  
Amir Hossein Zaji ◽  
Charles Hin Joo Bong ◽  
Aminuddin Ab Ghani
Keyword(s):  
Decision Trees ◽  
Incipient Motion ◽  
Rigid Boundary ◽  
Sediment Bed ◽  
Economical Design ◽  
Rectangular Channels ◽  
Wide Range ◽  
Practical Engineering ◽  
Artificial Neural Network Method ◽  
Bed Thickness

Abstract A vital topic regarding the optimum and economical design of rigid boundary open channels such as sewers and drainage systems is determining the movement of sediment particles. In this study, the incipient motion of sediment is estimated using three datasets from literature, including a wide range of hydraulic parameters. Because existing equations do not consider the effect of sediment bed thickness on incipient motion estimation, this parameter is applied in this study along with the multilayer perceptron (MLP), a hybrid method based on decision trees (DT) (MLP-DT), to estimate incipient motion. According to a comparison with the observed experimental outcome, the proposed method performs well (MARE = 0.048, RMSE = 0.134, SI = 0.06, BIAS = -0.036). The performance of MLP and MLP-DT is compared with that of existing regression-based equations, and significantly higher performance over existing models is observed. Finally, an explicit expression for practical engineering is also provided.

scholarly journals On the effect of cross sectional shape on incipient motion and deposition of sediments in fixed bed channels

2014 ◽  
Vol 62 (1) ◽  
pp. 75-81 ◽  
Author(s):  
Mir-Jafar-Sadegh Safari ◽  
Mirali Mohammadi ◽  
Golezar Gilanizadehdizaj
Keyword(s):  
Cross Sections ◽  
Research Work ◽  
Fixed Bed ◽  
Deposition Condition ◽  
Incipient Motion ◽  
Rigid Boundary ◽  
Cross Sectional ◽  
Motion Equations ◽  
Sectional Shape ◽  
Minimum Velocity

Abstract The condition of incipient motion and deposition are of the essential issues for the study of sediment transport. This phenomenon is of great importance to hydraulic engineers for designing sewers, drainage, as well as other rigid boundary channels. This is a study carried out with the objectives of describing the effect of cross-sectional shape on incipient motion and deposition of particles in rigid boundary channels. In this research work, the experimental data given by Loveless (1992) and Mohammadi (2005) are used. On the basis of the critical velocity approach, a new incipient motion equation for a V-shaped bottom channel and incipient deposition of sediment particles equations for rigid boundary channels having circular, rectangular, and U-shaped cross sections are obtained. New equations were compared to the other incipient motion equations. The result shows that the cross-sectional shape is an important factor for defining the minimum velocity for no-deposit particles. This study also distinguishes incipient motion of particles from incipient deposition for particles. The results may be useful for designing fixed bed channels with a limited deposition condition.

Seismic Response Analysis of Twin-Tower Building with Enlarged Base

2014 ◽  
Vol 912-914 ◽  
pp. 1534-1537
Author(s):  
Shao Bo Zhang ◽  
Ke Lun Wei ◽  
Bi Jian Xiao
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Boundary Conditions ◽  
Seismic Response ◽  
Time History ◽  
Response Analysis ◽  
Rigid Boundary ◽  
Finite Element Software ◽  
Elastic Boundary ◽  
Elastic Boundary Conditions

This paper adopts large finite element software ANSYS to establish finite element model of twin-tower building with enlarged base, uses dynamic time history analysis method for seismic response calculation, compare and analyze the calculation results of twin-tower building with enlarged base under elastic boundary conditions and rigid boundary conditions. The results showe that dynamic response for model under elastic boundary conditions is larger than dynamic response for model under rigid boundary conditions, and elastic boundary conditions is more close to the actual situation.

scholarly journals EXPERIMENTS ON THE DENSITY OF TSUNAMI INUNDATION WATER AND ITS INFLUENCE ON THE TSUNAMI RUN-UP AND DEPOSIT

2018 ◽  
pp. 41
Author(s):  
Hideo Matsutomi ◽  
Fumiko Konno
Keyword(s):  
Small Scale ◽  
Distance Ratio ◽  
Sediment Grain Size ◽  
Tsunami Inundation ◽  
Deposit Thickness ◽  
Historical Tsunami ◽  
Run Up ◽  
Tsunami Run Up ◽  
Tsunami Sediment ◽  
Sediment Deposit

For the sophistication of the tsunami load, future and historical tsunami scale evaluations, the dependency of the density of tsunami inundation water with sediment on the hydraulic quantities, and then the dependencies of the tsunami run-up distance, sediment deposit distance, mean sediment deposit thickness on the density of the tsunami inundation water are examined through a devised small-scale hydraulic experiment. Within the experimental range of this study, it is verified that the density of the tsunami inundation water depends on the Froude number of the incident tsunami inundation flow and the sediment grain size, and the relative tsunami run-up distance (= the run-up distance of the inundation water with sediment/the run-up distance of the inundation water without sediment (= fresh water)), ratio of the tsunami sediment deposit distance to the tsunami run-up distance, ratio of the mean tsunami sediment deposit thickness to the tsunami sediment deposit distance depend on the density of the tsunami inundation water, and four empirical expressions for those dependencies are proposed.

Effect of fully blocked non-rigid boundary conditions on detonation wave

2018 ◽  
Vol 116 ◽  
pp. 52-60 ◽  
Author(s):  
Qingwei Guan ◽  
Wentao Ji ◽  
Xingqing Yan ◽  
Jianliang Yu ◽  
Futong Yao ◽  
...  
Keyword(s):  
Detonation Wave ◽  
Boundary Conditions ◽  
Rigid Boundary

scholarly journals Effect of Mean Velocity to Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

2021 ◽  
Author(s):  
Nargess Moghaddassi ◽  
Seyed Habib Musavi-Jahromi ◽  
Mohammad Vaghefi ◽  
Amir Khosrojerdi
Keyword(s):  
Experimental Investigation ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Scour Depth ◽  
Incipient Motion ◽  
Mean Velocity ◽  
Straight Path ◽  
Meandering Channel ◽  
Bed Topography ◽  
The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity to critical velocity ratios have been tested at the upstream straight path to determine the meander's incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity to critical velocity ratios. In addition, the upstream bend's effect on the downstream bend has been investigated. Results indicated that the maximum scour depth at the downstream bend has increased as a result of changing the mean velocity to critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by respectively 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend's incipient motion was observed for the mean velocity to critical velocity ratio of 0.89, while the downstream bend was equal to 0.78.

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