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

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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MEASUREMENT OF BED FRICTION IN TIDAL INLETS

Coastal Engineering Proceedings ◽

10.9753/icce.v15.98 ◽

1976 ◽

Vol 1 (15) ◽

pp. 98 ◽

Cited By ~ 4

Author(s):

A.J. Mehta ◽

R.J. Byrne ◽

J.T. DeAlteris

Keyword(s):

Shear Stress ◽

Friction Factor ◽

Gulf Coast ◽

Flow Characteristics ◽

Bed Shear Stress ◽

Stress Regime ◽

Cross Sectional ◽

The Times ◽

The Stability ◽

Bed Friction

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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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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Climate Change Impacts on Coastal Wave Dynamics at Vougot Beach, France

Journal of Marine Science and Engineering ◽

10.3390/jmse9091009 ◽

2021 ◽

Vol 9 (9) ◽

pp. 1009

Author(s):

Pushpa Dissanayake ◽

Marissa L. Yates ◽

Serge Suanez ◽

France Floc’h ◽

Knut Krämer

Keyword(s):

Climate Change ◽

Shear Stress ◽

Sediment Transport ◽

Climate Change Impacts ◽

Wave Climate ◽

Bed Shear Stress ◽

Storm Events ◽

Climate Scenarios ◽

Wave Dynamics ◽

Waves And Currents

Wave dynamics contribute significantly to coastal hazards and were thus investigated at Vougot Beach by simulating both historical and projected future waves considering climate change impacts. The historical period included a major storm event. This period was projected to the future using three globally averaged sea level rise (SLR) scenarios for 2100, and combined SLR and wave climate scenarios for A1B, A2, and B1 emissions paths of the IPCC. The B1 wave climate predicts an increase in the occurrence of storm events. The simulated waves in all scenarios showed larger relative changes at the beach than in the nearshore area. The maximum increase of wave energy for the combined SLR and wave scenarios was 95%, while only 50% for the SLR-only scenarios. The effective bed shear stress from waves and currents showed different spatial variability than that of the wave height, emphasizing the importance of interactions between nearshore waves and currents. Increases in the effective bed shear stress (combined scenarios: up to 190%, and SLR-only scenarios: 35%) indicate that the changes in waves and currents will likely have significant impacts on the nearshore sediment transport. This work emphasizes that combined SLR and future wave climate scenarios need to be used to evaluate future changes in local hydrodynamics and their impacts. These results provide preliminary insights into potential future wave dynamics at Vougot Beach under different climate change scenarios. Further studies are necessary to generalize the results by investigating the wave dynamics during storm events with different hydrodynamical conditions and to evaluate potential changes in sediment transport and morphological evolution due to climate change.

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PROBABILITY OF EXCEEDING THE CRITICAL SHEAR STRESS FOR SAND MOTION IN SPECIFIC WAVE AND CURRENT CONDITIONS

Coastal Engineering Proceedings ◽

10.9753/icce.v33.sediment.4 ◽

2012 ◽

Vol 1 (33) ◽

pp. 4

Author(s):

Pierre-Yves Henry ◽

Alf Tørum ◽

Øivind Artsen ◽

Dag Myrhaug ◽

Muk Chen Ong

Keyword(s):

Shear Stress ◽

Critical Shear Stress ◽

Bed Shear Stress ◽

Random Waves ◽

Flow Conditions ◽

Flume Experiments ◽

Natural Sand ◽

Waves And Currents ◽

Mobility Parameter ◽

A Current

This study is focusing on the threshold of sand motion under random waves combined with a following current. The analysis is based on some flume experiments realized over a natural sand bed for different flow conditions (waves and currents). The main result comes as a map of the probability to exceed the threshold of sand motion, as a function of a wave and a current mobility parameter. These observations are compared to methods predicting the bed shear stress using an equivalent monochromatic wave, and links between the probability of exceeding the critical shear stress for initiation of sand motion and the calculated maximum bed shear stress are found.

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Erosion of fine sediments from a rough bed

E3S Web of Conferences ◽

10.1051/e3sconf/20184005058 ◽

2018 ◽

Vol 40 ◽

pp. 05058

Author(s):

Michele Trevisson ◽

Olivier Eiff

Keyword(s):

Shear Stress ◽

Sediment Supply ◽

Critical Conditions ◽

Bed Shear Stress ◽

Flow Conditions ◽

Flume Experiments ◽

Gravel Beds ◽

Fine Sediments ◽

Sediment Bed ◽

Rough Bed

Gravel beds in river systems represent important aquatic habitats, which may be endangered by the introduction of large amounts of fine sediments. In order to better understand the interaction between fine sediments and coarse immobile beds in sediment supply-limited systems, a series of flume experiments was conducted. The main goal was to determine under what conditions erosion stops. The experiments were performed over a bed of regularly arranged spheres. Plastic particles were taken as sediment and the erosion was investigated under uniform flow conditions for variable bed shear stress conditions just above critical conditions. The system was observed to behave in two different ways: with higher bed shear stress fine sediments were completely washed out, whilst with lower stress the sediment bed reached a stable level just above the equator of the spheres.

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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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