MEASUREMENT OF BED FRICTION IN TIDAL INLETS

The flow characteristics and the stability of a tidal inlet are governed, among other factors, by the channel bed friction. In order to determine the bed shear stress regime and the frictional characteristics, near-bed velocity profiles were obtained at the throat sections of two inlets, John's Pass and Blind Pass, on the Gulf Coast of Florida. A specially designed steel cage with five current meters in a vertical array was used to obtain the profiles in the bottom one meter of the flow. The profiles were found to be logarithmic but it is noted that, especially near the times of slack water, the effect of inertia becomes significant. However, during the major part of the flood or ebb flow period, frictional effects are dominant. In the fully rough regime of flow, the bed-shear stress - velocity relationship is found to follow the square law, with a constant, characteristic friction factor and Manning's n for each inlet. This friction factor is used in hydraulic formulas, based on uniform, steady open channel flow relationships, to obtain the tidal prism - throat cross-sectional area ratio, which is then compared with that obtained from flow discharge measurements. Agreements and discrepancies in the comparison are discussed. The relationship between the bed shear stress at incipient motion and the grain size at the bed is reviewed, and it is noted that the observed relationship at the two inlets does not agree with the well-known correlation of Shields for uniform sandy beds.

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

Water ◽

10.3390/w12040964 ◽

2020 ◽

Vol 12 (4) ◽

pp. 964 ◽

Cited By ~ 1

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.

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

Canadian Journal of Civil Engineering ◽

10.1139/l07-054 ◽

2007 ◽

Vol 34 (10) ◽

pp. 1312-1323 ◽

Cited By ~ 8

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.

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STABILITY AGAINST WAVES AND CURRENTS OF GRAVEL RUBBLE MOUNDS OVER PIPELINES AND FLAT GRAVEL BEDS

Coastal Engineering Proceedings ◽

10.9753/icce.v32.structures.59 ◽

2011 ◽

Vol 1 (32) ◽

pp. 59

Author(s):

Alf Tørum ◽

Øivind Arntsen ◽

Colin Kuester

Keyword(s):

Shear Stress ◽

Laboratory Tests ◽

Statistical Distribution ◽

Irregular Waves ◽

Bed Shear Stress ◽

Gas Pipelines ◽

Gravel Beds ◽

Waves And Currents ◽

The Stability ◽

Oil Gas

For different reasons oil/gas pipelines or parts of oil/gas pipelines have to be covered with rubble mounds. The question is then what the size of the stones/gravel in the mound should be to withstand waves and currents of the area. In order to obtain more information on the stability of gravel mounds over pipelines, laboratory tests in a wave/current flume have been carried out and are summarized herein. In addition data from other similar investigations elsewhere are discussed. A brief analysis of the stability of a flat gravel bed subjected to irregular waves has also been included, using the concept of the statistical distribution of the bed shear stress.

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Effects of salinity and particle concentration on sediment hydrodynamics and critical bed-shear-stress for erosion of fine grained sediments used in wetland restoration projects

Proceedings of the International Association of Hydrological Sciences ◽

10.5194/piahs-367-435-2015 ◽

2015 ◽

Vol 367 ◽

pp. 435-441 ◽

Cited By ~ 3

Author(s):

M. Ghose-Hajra ◽

A. McCorquodale ◽

G. Mattson ◽

D. Jerolleman ◽

J. Filostrat

Keyword(s):

Shear Stress ◽

Mississippi River ◽

Particle Concentration ◽

Gulf Coast ◽

Open Water ◽

Distribution Model ◽

Bed Shear Stress ◽

Sediment Distribution ◽

Fine Grained ◽

Term Performance

Abstract. Sea-level rise, the increasing number and intensity of storms, oil and groundwater extraction, and coastal land subsidence are putting people and property at risk along Louisiana’s coast, with major implications for human safety and economic health of coastal areas. A major goal towards re-establishing a healthy and sustainable coastal ecosystem has been to rebuild Louisiana’s disappearing wetlands with fine grained sediments that are dredged or diverted from nearby rivers, channels and lakes to build land in open water areas. A thorough geo-hydrodynamic characterization of the deposited sediments is important in the correct design and a more realistic outcome assessment of the long-term performance measures for ongoing coastal restoration projects. This paper evaluates the effects of salinity and solid particle concentration on the re-suspension characteristics of fine-grained dredged sediments obtained from multiple geographic locations along the Gulf coast. The critical bed-shear-stress for erosion has been evaluated as a function of sedimentation time. The sediment hydrodynamic properties obtained from the laboratory testing were used in a numerical coastal sediment distribution model to aid in evaluating sediment diversions from the Mississippi River into Breton Sound and Barataria Bay.

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Efficiency prediction for storage chambers using computational fluid dynamics

Water Science & Technology ◽

10.2166/wst.1996.0202 ◽

1996 ◽

Vol 33 (9) ◽

pp. 163-170 ◽

Cited By ~ 4

Author(s):

Virginia R. Stovin ◽

Adrian J. Saul

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Shear Stress ◽

Particle Tracking ◽

Critical Value ◽

Complex Geometries ◽

Bed Shear Stress ◽

Breadth Ratio ◽

Computational Fluid Dynamics Cfd ◽

Simulated Flow

Research was undertaken in order to identify possible methodologies for the prediction of sedimentation in storage chambers based on computational fluid dynamics (CFD). The Fluent CFD software was used to establish a numerical model of the flow field, on which further analysis was undertaken. Sedimentation was estimated from the simulated flow fields by two different methods. The first approach used the simulation to predict the bed shear stress distribution, with deposition being assumed for areas where the bed shear stress fell below a critical value (τcd). The value of τcd had previously been determined in the laboratory. Efficiency was then calculated as a function of the proportion of the chamber bed for which deposition had been predicted. The second method used the particle tracking facility in Fluent and efficiency was calculated from the proportion of particles that remained within the chamber. The results from the two techniques for efficiency are compared to data collected in a laboratory chamber. Three further simulations were then undertaken in order to investigate the influence of length to breadth ratio on chamber performance. The methodology presented here could be applied to complex geometries and full scale installations.

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Particle Responses to Near-Bed Shear Stress in a Shallow, Wave- and Current-Driven Environment

10.1002/essoar.10507100.1 ◽

2021 ◽

Author(s):

Grace Chang ◽

Galen Egan ◽

Joseph D McNeil ◽

Samuel McWilliams ◽

Craig Jones ◽

...

Keyword(s):

Shear Stress ◽

Bed Shear Stress

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Simulation of the Load Evolution of an Anchoring System under a Blasting Impulse Load Using FLAC3D

Shock and Vibration ◽

10.1155/2015/972720 ◽

2015 ◽

Vol 2015 ◽

pp. 1-8 ◽

Cited By ~ 3

Author(s):

Xigui Zheng ◽

Jinbo Hua ◽

Nong Zhang ◽

Xiaowei Feng ◽

Lei Zhang

Keyword(s):

Shear Stress ◽

Dynamic Response ◽

Axial Force ◽

Mechanical Characteristics ◽

Oscillation Amplitude ◽

Anchoring System ◽

Impulse Load ◽

The Stability ◽

Calculation Software ◽

Dynamic Perturbation

A limitation in research on bolt anchoring is the unknown relationship between dynamic perturbation and mechanical characteristics. This paper divides dynamic impulse loads into engineering loads and blasting loads and then employs numerical calculation software FLAC3Dto analyze the stability of an anchoring system perturbed by an impulse load. The evolution of the dynamic response of the axial force/shear stress in the anchoring system is thus obtained. It is revealed that the corners and middle of the anchoring system are strongly affected by the dynamic load, and the dynamic response of shear stress is distinctly stronger than that of the axial force in the anchoring system. Additionally, the perturbation of the impulse load reduces stress in the anchored rock mass and induces repeated tension and loosening of the rods in the anchoring system, thus reducing the stability of the anchoring system. The oscillation amplitude of the axial force in the anchored segment is mitigated far more than that in the free segment, demonstrating that extended/full-length anchoring is extremely stable and surpasses simple anchors with free ends.

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