scholarly journals The 3-D Morphology Evolution of Spur Dike Scour under Clear-Water Scour Conditions

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1583 ◽  
Author(s):  
Li Zhang ◽  
Hao Wang ◽  
Xianqi Zhang ◽  
Bo Wang ◽  
Jian Chen
Keyword(s):  
Shear Stress ◽  
Morphological Evolution ◽  
Golden Section ◽  
Evolution Process ◽  
Bed Shear Stress ◽  
Clear Water ◽  
Power Functions ◽  
Spur Dike ◽  
Evolution Characteristics ◽  
Scour Hole

By changing the alignment angle of spur dike, this study focused on the evolution of scour hole morphology in three alignments under clear-water scour conditions, including the 3-D structure of the scour hole, 2-D profile morphological evolution process and the evolution characteristics of the local bed shear stress. The results show that the plane area and volume of the scour hole both are power functions over time, which is similar to the evolution characteristics of scour depth. Local scour includes three stages: The initial stage, development stage and balance stage. The local bed shear stress presents successively: τb > τc, τb = τc and τb < τc. Based on this characteristic, the evolution mechanism between scour hole morphology and the local bed shear stress is further clarified. Furthermore, although the alignment of the spur dike significantly affects the longitudinal and vertical dimension erosion rates of the scour hole, the scour hole morphology is not only relatively constant but also has a specific proportion, and the evolution process is orderly in the whole process of evolution. To the scouring equilibrium state, the length of the scour hole on the upstream and downstream of the spur dike is approximately in line with the golden section feature. The related results provide technical support for scour parameter design and scour hole protection of spur dike in flood period.

scholarly journals Three-Dimensional Flow Characteristics in Slit-Type Permeable Spur Dike Fields: Efficacy in Riverbank Protection

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 964 ◽  
Author(s):  
Shampa ◽  
Yuji Hasegawa ◽  
Hajime Nakagawa ◽  
Hiroshi Takebayashi ◽  
Kenji Kawaike
Keyword(s):  
Shear Stress ◽  
Longitudinal Velocity ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Efficient Solutions ◽  
Staggered Grid ◽  
Bed Shear Stress ◽  
Experimental Conditions ◽  
Alluvial Rivers ◽  
Spur Dike

This paper focuses on finding efficient solutions for the design of a highly permeable pile spur (or slit type) dike field used in morphologically dynamic alluvial rivers. To test the suitability of different arrangements of this type of permeable pile spur dike field, laboratory experiments were conducted, and a three-dimensional multiphase numerical model was developed and applied, based on the experimental conditions. Three different angles to the approach flow and two types of individual pile position arrangements were tested. The results show that by using a series of slit-type spurs, the approach velocity of the flow can be considerably reduced within the spur dike zone. Using different sets of angles and installation positions, this type of permeable spur dike can be used more efficiently than traditional dikes. Notably, this type of spur dike can reduce the longitudinal velocity, turbulence intensity, and bed shear stress in the near-bank area. Additionally, the deflection of the permeable spur produces more transverse flow to the opposite bank. Arranging the piles in staggered grid positions among different spurs in a spur dike field improves functionality in terms of creating a quasi-uniform turbulence zone while simultaneously reducing the bed shear stress. Finally, the efficacy of the slit-type permeable spur dike field as a solution to the riverbank erosion problem is numerically tested in a reach of a braided river, the Brahmaputra–Jamuna River, and a comparison is made with a conventional spur dike field. The results indicate that the proposed structure ensures the smooth passing of flow compared with that for the conventional impermeable spur structure by producing a lower level of scouring (low bed shear stress) and flow intensification.

Development of an Analysis Methodology for Pressure Flow Scour Under Flooded Bridge Decks Using Commercial CFD Software

2010 ◽  
Author(s):  
Dipankar Biswas ◽  
Steven A. Lottes ◽  
Pradip Majumdar ◽  
Milivoje Kostic
Keyword(s):  
Shear Stress ◽  
Turbulence Model ◽  
Critical Shear Stress ◽  
Scour Depth ◽  
Bed Shear Stress ◽  
Cfd Analysis ◽  
Flow Conditions ◽  
Pressure Flow ◽  
Scour Hole ◽  
Bridge Failure

Bridges are a significant component of the ground transportation infrastructure in the United States. With about sixty percent of bridge failures due to hydraulic causes, primarily scour, application of computational fluid dynamics (CFD) analysis techniques to the assessment of risk of bridge failure under flood conditions can provide increased accuracy in scour risk assessment at a relatively low cost. The analysis can be used to make optimum use of limited federal and state funds available to maintain and replace bridges and ensure public safety while traveling on the nation’s roads and highways during and after floods. Scour is the erosion of riverbed material during high flow conditions, such as floods. When scouring of the supporting soil around the piers and abutments of bridges takes place, risk of bridge failure increases. A simulation methodology to conservatively predict equilibrium shape and size of the scour hole under pressure flow conditions for flooded bridge decks using commercial CFD software was developed. The computational methodology has been developed using C++ to compute changes in the bed contour outside of the CFD software and generate a re-meshing script to change the bed boundary contour. STAR-CD was used to run the hydrodynamic analysis to obtain bed shear stress, and a BASH script was developed to automate cycling between computing bed shear stress with the CFD software and computing changes in the bed contour due to scour predicted using the computed shear stress for the current bed contour. A single-phase moving boundary formulation has been developed to compute the equilibrium scour hole contour that proceeds through a series of quasi-steady CFD computations. It is based on CFD analysis of the flow fields around the flooded bridge deck and shear stress computed at the bed modeled as a rough wall. A high Reynolds number k-ε turbulence model with standard wall functions, based on a Reynolds-Averaged Navier-Stokes (RANS) turbulence model, was used to compute bed shear stress. The scour sites on the bed were identified as those sites where the computed shear stress exceeded the critical shear stress computed from a published correlation for flat bed conditions. Comparison with experimental data obtained from the Turner-Fairbank Highway Research Center (TFHRC), McLean, VA, USA, revealed larger discrepancies than anticipated between the bridge inundation ratio and the scour hole depth. Although scour hole slopes were small for the cases tested, a correction to critical shear stress to account for bed slope was also tested. It did not significantly improve the correlation between CFD prediction and experimental observations. These results may be a consequence of using only excess shear stress above critical as a criteria for scour when other physical mechanisms also contribute to the initiation of scour. Prediction of scour depth using federal guidelines over predicts scour depth by as much as an order of magnitude in some cases. Over prediction is acceptable for purposes of ensuring bridge safety. CFD methods for scour prediction can be a significant improvement of current methods as long as under prediction of scour depth is avoided. Conservative scour prediction using CFD methods can be achieved by using conservative values of parameters such as critical shear stress and effective bed roughness.

Modelling of three-dimensional flow velocities in a deep hole in the East Channel of the Mackenzie Delta, Northwest Territories

2007 ◽  
Vol 34 (10) ◽  
pp. 1312-1323 ◽  
Author(s):  
Bahram Gharabaghi ◽  
Chris Inkratas ◽  
Spyros Beltaos ◽  
Bommanna Krishnappan
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Bed Shear Stress ◽  
Mackenzie Delta ◽  
Stress Distributions ◽  
Deep Hole ◽  
Flow Conditions ◽  
Scour Hole ◽  
Scour Holes ◽  
The Stability

The Mackenzie River has several anomalous deep scour holes in a number of river channels in its delta. Proposed gas pipeline crossings have renewed interest in studying the stability of these scour holes. The main goal of this research project was to study flow velocity and bed shear stress distributions for a 30 m deep hole in the East Channel of the Mackenzie Delta as a first step toward assessing the stability of the scour hole and the risk of its migration during various flow conditions. In this study, a three-dimensional (3D) finite element flow model, FLUENT, using the renormalization group (RNG) k-ε turbulence model (where k is the turbulent kinetic energy and ε is the turbulence dissipation rate) was set up for the scour hole and calibrated using detailed measurements of 3D flow velocities, obtained with an acoustic doppler current profiler. The numerical model was then applied to predict flow velocity and bed shear stress distributions in and around the scour hole for three flow conditions (720, 1000, and 1400 m3/s). Results indicate that two vortices are formed in the river elbow above the scour hole. As the flow rate changed, the sizes of the vortices varied. The region upstream of the hole experienced the greatest magnitudes of bed shear stress.Key words: computational fluid dynamics, finite element, bed shear stress, deep hole, flow reversal.

Efficient non-hydrostatic modelling of flow and bed shear stress in a pier scour hole

2014 ◽  
Vol 41 (5) ◽  
pp. 450-460 ◽  
Author(s):  
S. Pournazeri ◽  
S.S. Li ◽  
F. Haghighat
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Local Maximum ◽  
Bedload Transport ◽  
Bed Shear Stress ◽  
Pier Scour ◽  
Law Of The Wall ◽  
Scour Hole ◽  
The Law ◽  
Wall Method

Predicting 3-D flow in a pier scour hole and the associated bed shear stress τb is important for the safe and economical design of bridge piers. This paper combines layered, hydrostatic hydrodynamic computations with non-hydrostatic pressure corrections, exploring a new modelling approach for efficient and reliable predictions of 3-D flow velocity. The law of the wall method is used for estimating τb. Its suitability for incorporation into layered models for bedload transport and pier scour simulations is also discussed. The predicted flow shows realistic features: strong downward flow adjacent to the upstream nose of a circular pier, vortex motions in the vertical and horizontal direction, and meandering flow wakes. The velocity results compare well with available experimental data. In the approach region, τb is uniform. It attains a local maximum immediately before flow enters the scour hole and then drops non-linearly in the scour-hole region toward the pier. In the wake region, τb has very low values. The τb predictions are consistent with the experimental data. In multi-layer models, when applying the law of wall method, one should use near-bed velocities as opposed to bottom-layer velocities to obtain more reliable τb estimates and avoid noisy results, which can cause a numerical instability problem in bedload transport simulations.

Experimental Study on the Effect of Froude Number on Temporal Variation of Scour around a T Shaped Spur Dike in a 90 Degree Bend

2011 ◽  
Vol 147 ◽  
pp. 75-79 ◽  
Author(s):  
Mohammad Vaghefi ◽  
Masoud Ghodsian ◽  
Arash Adib
Keyword(s):  
Experimental Study ◽  
Temporal Variation ◽  
Froude Number ◽  
Average Diameter ◽  
Clear Water ◽  
Spur Dike ◽  
Outer Banks ◽  
The Past ◽  
Scour Hole ◽  
Spur Dikes

In the past few decades, the use of spur dikes for stability of the outer banks of rivers has attracted the attention of hydraulic engineers. Setting spur dikes in the flow’s direction leads to local scour around the spur dike and changes the topography of the bed. This paper deals with the study of the temporal variation of the scour hole and topography of the bed around a T shaped spur dike located in a 90 degree bend. The experiments were carried out in a channel with a 90 degrees bend. Uniform sediments having an average diameter of 1.28mm were used under clear water condition. The effects of Froude number on the amount and the geometry of scour hole around a T shaped spur dike and the time variation of scour were investigated.

Geometry of developing and equilibrium scour holes at bridge piers in gravel

2010 ◽  
Vol 37 (4) ◽  
pp. 544-552 ◽  
Author(s):  
Reda Diab ◽  
Oscar Link ◽  
Ulrich Zanke
Keyword(s):  
Shear Stress ◽  
Bridge Piers ◽  
Scour Depth ◽  
Bed Shear Stress ◽  
Clear Water ◽  
Square Cylinders ◽  
Scour Holes ◽  
Laser Distance Sensor ◽  
Distance Sensor ◽  
Spatio Temporal

Experimental results on scour at circular and square cylinders in uniform gravel under the clear-water scour condition are presented. Nonintrusive, high-resolution topographic measurements of developing and equilibrium scour holes were performed during running experiments with an experimental installation using a laser distance sensor (LDS) and precision step motors. Measurements were taken by the LDS in different azimuthal half-planes with θ = 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 135°, 150°, 165°, and 180° to study the spatio-temporal variation of geometric properties of scour holes. Experiments were conducted over 40 h until equilibrium, with bed shear stress equal to 95% of the critical bed shear stress for the initiation of sediment motion at the undisturbed plane gravel bed having a d50 of 3.25 mm. Results show that scour in gravel progresses more slowly around the square cylinder, where steeper slopes than at the circular cylinder are observed. During experiments the scour slopes do not exceed the observed repose angle of the sediment particles. Maximum scour depth in different azimuthal half-planes and scoured volume are well correlated with the maximum scour depth at azimuthal half-plane with θ = 0°.

scholarly journals Three-Dimensional Numerical Investigations of the Flow Pattern and Evolution of the Horseshoe Vortex at a Circular Pier during the Development of a Scour Hole

2021 ◽  
Vol 11 (15) ◽  
pp. 6898
Author(s):  
Ahmed M. Helmi ◽  
Ahmed H. Shehata
Keyword(s):  
Shear Stress ◽  
Flow Structure ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Horseshoe Vortex ◽  
Bed Shear Stress ◽  
Scour Hole ◽  
Scouring Depth ◽  
Mean Size ◽  
Stress Variations

In the current study, a three-dimensional CFD model is utilized to investigate the variation of the flow structure and bed shear stress at a single cylindrical pier during scour development. The scour development is presented by seven solidified geometries of the scour hole, collected during previous experimental work at different scour stages. Different turbulence models are evaluated and the (k-ω) model is chosen due to its relative accuracy in capturing the flow oscillation and vortex shedding at the pier downstream side with personal computer computational and storage resources. The numerical results are verified against dimensionless parameters from different previous experimental works. This research describes in detail the flow structure and bed shear stress variations through seven stages of the scour hole development. The dimensionless area-averaged circulation coefficient (Ψi) is developed to evaluate the changes in the vortex strength through the scouring process by eliminating the calculation area effect. It was concluded that the circulation in the (Y) direction is the main driving factor in the development of the scour hole more than the circulation in the (X) direction. The ratio between the horseshoe vortex (HV) mean size and the scouring depth (DV/dS) in addition to the location of the maximum bed shear stress are investigated during different stages of the scour development.

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