scholarly journals Scour Characteristics and Equilibrium Scour Depth Prediction around Umbrella Suction Anchor Foundation under Random Waves

2021 ◽  
Vol 9 (8) ◽  
pp. 886
Author(s):  
Ruigeng Hu ◽  
Hongjun Liu ◽  
Hao Leng ◽  
Peng Yu ◽  
Xiuhai Wang
Keyword(s):  
Numerical Simulation ◽  
Present Model ◽  
Euler Number ◽  
Horseshoe Vortex ◽  
Scour Depth ◽  
Random Waves ◽  
Depth Prediction ◽  
Equilibrium Scour Depth ◽  
Scour Morphology ◽  
Good Agreement

A series of numerical simulation were conducted to study the local scour around umbrella suction anchor foundation (USAF) under random waves. In this study, the validation was carried out firstly to verify the accuracy of the present model. Furthermore, the scour evolution and scour mechanism were analyzed respectively. In addition, two revised models were proposed to predict the equilibrium scour depth Seq around USAF. At last, a parametric study was carried out to study the effects of the Froude number Fr and Euler number Eu for the Seq. The results indicate that the present numerical model is accurate and reasonable for depicting the scour morphology under random waves. The revised Raaijmakers’s model shows good agreement with the simulating results of the present study when KCs,p < 8. The predicting results of the revised stochastic model are the most favorable for n = 10 when KCrms,a < 4. The higher Fr and Eu both lead to the more intensive horseshoe vortex and larger Seq.

scholarly journals Experimental Study of Local Scour around Tripod Foundation in Combined Collinear Waves-Current Conditions

2021 ◽  
Vol 9 (12) ◽  
pp. 1373
Author(s):  
Ruigeng Hu ◽  
Xiuhai Wang ◽  
Hongjun Liu ◽  
Yao Lu
Keyword(s):  
Laboratory Experiments ◽  
Euler Number ◽  
General Trend ◽  
Scour Depth ◽  
Dimensionless Time ◽  
Structural Elements ◽  
Scour Hole ◽  
Main Column ◽  
Equilibrium Scour Depth ◽  
Scour Morphology

A series of laboratory experiments were conducted in a wave-current flume to investigate the scour evolution and scour morphology around tripod in combined waves and current. The tripod model was made using the 3D printing technology, and it was installed in seabed with three installation angles α = 0°, 90°and 180° respectively. In the present study, the scour evolution and scour characteristic were first analyzed. Then, the equilibrium scour depth Seq was investigated. Furthermore, a parametric study was carried out to study the effects of Froude number Fr and Euler number Eu on equilibrium scour depth Seq respectively. Finally, the effects of tripod’s structural elements on Seq were discussed. The results indicate that the maximum scour hole appeared underneath the main column for installation angle α = 0°, 90° and 180°. The Seq for α = 90° was greater than the case of α = 0° and α = 180°, implying the tripod suffered from more severe scour for α = 90°. When KC was fixed, the dimensionless time scale T* for α = 90° was slightly larger than the case of α = 0° and α = 180° and the T* was linearly correlated with Ucw in the range of 0.347 < Ucw < 0.739. The higher Fr and Eu both resulted in the greater scour depth for tripod in combined waves and current. The logarithmic formula can depict the general trend of Seq and Fr (Eu) for tripod in combined waves and current.

Effects of Sand-Clay Mixtures on Scour Around Vertical Piles Due to Long-Crested and Short-Crested Nonlinear Random Waves

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Coastal Ocean ◽  
Stochastic Method ◽  
Offshore Wind ◽  
Pile Foundations ◽  
Scour Depth ◽  
Regular Wave ◽  
Random Waves ◽  
Offshore Wind Turbines ◽  
Equilibrium Scour Depth ◽  
Nonlinear Random Waves

This note provides a practical stochastic method by which the effects of sand-clay mixtures on the maximum equilibrium scour depth around vertical piles exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. This is made by using the regular wave formulas for scour depth for sand-clay mixtures by Dey et al. (2011, Scour at Vertical Piles in Sand-Clay Mixtures Under Waves,” J. Waterway, Port, Coastal, Ocean Eng., 137(6), pp. 324–331) and the stochastic method presented by Myrhaug and Ong (2013, “Scour Around Vertical Pile Foundations for Offshore Wind Turbines Due to Long-Crested and Short-Crested Nonlinear Random Waves,” ASME J. Offshore Mech. Arctic Eng., 135(1), p. 011103). Thus the present results are supplementary to those presented in the latter reference. An example calculation is provided.

Equilibrium Scour Prediction for Uniform and Non-Uniform Cylindrical Structures Under Clear Water Conditions

2016 ◽  
Author(s):  
Nicholas S. Tavouktsoglou ◽  
John M. Harris ◽  
Richard R. Simons ◽  
Richard J. S. Whitehouse
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Euler Number ◽  
Offshore Structures ◽  
Scour Depth ◽  
Flow Conditions ◽  
Mean Flow ◽  
Cylindrical Structures ◽  
Cylindrical Structure ◽  
Equilibrium Scour Depth

Offshore Gravity Base Foundations (GBFs) are often designed with non-uniform cylindrical geometries. Such structures interact with the local hydrodynamics which amplify the adverse dynamic pressure gradient, which is responsible for all flow and scour phenomena including the bed shear stress amplification. In this study a method for predicting the effect non-uniform cylindrical structure geometries have on local scour around offshore structures under the forcing of a unidirectional current is presented. The interaction of the flow field with the sediment around these complex structures is described in terms of non-dimensional parameters that characterize the similitude of water-sediment movement. The paper presents insights in the influence a form of the Euler number has on the equilibrium scour around uniform and non-uniform cylindrical structures. Here the Euler number is defined as the depth averaged pressure gradient (calculated using potential flow theory) divided by the product of the square of mean flow velocity and the fluid density. The insights are confirmed through a series of experiments where the equilibrium scour was monitored for different types of structures and flow conditions. The results of this study show that the Euler number is a more appropriate parameter for describing the scour potential of a structure compared to using the equivalent pile diameter. The experimental data show that an increasing Euler number yields an increase in the non-dimensional equilibrium scour. The results of this study also suggest that an increase in the water depth yields a decrease in the equilibrium scour depth for the conical, cylindrical base structures and truncated cylinders and an increase in the equilibrium scour depth for the uniform cylinders which can also be explained in terms of changes in the Euler number. Finally, the Buckingham π theorem in conjunction with the experimental data was used to derive a simple shape correction factor that could be used to determine the scour depth of a non-uniform cylindrical structure based on the equilibrium scour produced for the same flow conditions by a uniform cylinder.

scholarly journals Numerical Simulation of Local Scour around Three Cylindrical Piles in a Tandem Arrangement

Water ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 3623
Author(s):  
Jyh-Haw Tang ◽  
Aisyah Dwi Puspasari
Keyword(s):  
Numerical Simulation ◽  
Experimental Study ◽  
Numerical Model ◽  
Experimental Studies ◽  
Horseshoe Vortex ◽  
Local Scour ◽  
Scour Depth ◽  
Pile Groups ◽  
Tandem Arrangement ◽  
Flow Acceleration

Scouring is one of the most common potential causes of bridge pile foundation failure, with loss of life, economic and environmental impacts. Comprehensive studies on the numerical simulation of local scour around pile groups are still limited. This paper presents a numerical simulation using Flow-3D software to calculate the maximum sediment scour depth and investigate the mechanism around the groups of three cylinders in a tandem arrangement. A validation using the experimental study was carried out to confirm the reliability of the present numerical model. By using the Van Rijn transport rate equation and RNG k-ε turbulence model, the results of time evolution of scour depth and bed elevation contour show good agreement with the experimental study. The numerical simulation of three cylinders in a tandem arrangement were conducted with pile spacing ratios, G/D of 2 and 3. The local scour is affected by the horseshoe vortex from the downflow driven by the downward pressure gradient and rotates in front of the pile and the high bed shear stress, triggered by flow acceleration. The deepest maximum local scour depth is always obtained by the front pile as a shield pile, followed by the piles behind. The trend of the maximum local scour depth in a tandem arrangement is in accordance with the experimental studies and has a better agreement than previous numerical studies with the same model setup. This means that the numerical model used to simulate pile groups is accurate and capable of calculating the depth of sediment scour.

Scour Around Vertical Pile Foundations for Offshore Wind Turbines Due to Long-Crested and Short-Crested Nonlinear Random Waves

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Order Theory ◽  
Offshore Wind ◽  
Wave Crest ◽  
Random Wave ◽  
Scour Depth ◽  
Height Distribution ◽  
Random Waves ◽  
Equilibrium Scour Depth ◽  
Nonlinear Random Waves ◽  
Wave Induced

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around vertical piles exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall wave crest height distribution (Forristall, 2000, “Wave Crest Distributions: Observations and Second-Order Theory,” J. Phys. Oceanogr., 30, pp. 1931–1943) representing both 2D and 3D nonlinear random waves, and using the regular wave formulas for scour depth by Sumer et al. (1992, “Scour Around Vertical Pile in Waves,” J. Waterway, Port, Coastal, Ocean Eng., 114(5), pp. 599–641). An example calculation is provided. Tentative approaches to related random wave-induced scour cases are also suggested.

scholarly journals Equilibrium Scour-Depth Prediction around Cylindrical Structures

2017 ◽  
Vol 143 (5) ◽  
pp. 04017017 ◽  
Author(s):  
N. S. Tavouktsoglou ◽  
J. M. Harris ◽  
R. R. Simons ◽  
R. J. S. Whitehouse
Keyword(s):  
Scour Depth ◽  
Cylindrical Structures ◽  
Depth Prediction ◽  
Equilibrium Scour Depth

scholarly journals The Equilibrium Scour Depth around a Pier under the Action of Collinear Waves and Current

2020 ◽  
Vol 8 (1) ◽  
pp. 36 ◽  
Author(s):  
Ainal Hoque Gazi ◽  
Subhrangshu Purkayastha ◽  
Mohammad Saud Afzal
Keyword(s):  
Velocity Profile ◽  
Arbitrary Shape ◽  
Scour Depth ◽  
Mathematical Equation ◽  
Flowing Fluid ◽  
Scour Hole ◽  
Sediment Particles ◽  
Equilibrium Scour Depth ◽  
Work Done ◽  
Good Agreement

In this paper, a mathematical equation is developed for the equilibrium scour depth considering an arbitrary shape of the scour hole around a pier under the action of collinear waves and current. A power-law current velocity profile is assumed for the purpose of the analysis. The equilibrium scour depth is obtained by equating the work done by the flowing fluid while interacting with the pier under the action of the collinear waves and the current and the work done by the total volume of the sediment particles removed from the scour hole, respectively. The equilibrium scour depths predicted by the model show good agreement with the experimental and numerical results available in the literature.

Two-Phase Model for Simulating Current-Induced Scour Beneath Subsea Pipelines at Different Initial Elevations

2018 ◽  
Author(s):  
Jun Y. Lee ◽  
Jasmin B. T. McInerney ◽  
Fauzi A. Hardjanto ◽  
Shuhong Chai ◽  
Remo Cossu ◽  
...  
Keyword(s):  
Numerical Results ◽  
Scour Depth ◽  
Flow Conditions ◽  
Eulerian Model ◽  
Two Phase ◽  
Mesh Dependency ◽  
Steady Current ◽  
Equilibrium Scour Depth ◽  
Subsea Pipelines ◽  
Good Agreement

When a subsea pipeline is laid on an uneven seabed, the pipeline can have an initial elevation, potentially compromising its on-bottom stability; scouring due to flow conditions around the pipe can further exacerbate the problem. We assess the capability of the two-phase Eulerian-Eulerian OpenFOAM solver, twoPhaseEulerFoam, in terms of predicting the equilibrium scour depth beneath a pipe at different initial elevations under a steady current for the live bed condition. The predictions were found to be in good agreement with published experimental and numerical results; however, similar to a recent study involving another two-phase Eulerian-Eulerian model, the scour time scale was under-predicted. The predicted equilibrium scour depth was seen to decrease with an increase in the initial pipe elevation. The numerical results were also compared to predictions that were made using previous empirical equations. The most comprehensive equation to date showed a good agreement with the present numerical results. We conclude that this open-source solver, twoPhaseEulerFoam, can be used to predict the equilibrium scour depth beneath subsea pipelines, with short computation times and negligible mesh dependency.

Modeling of mass transfer in biofilms in oscillatory flow conditions using k-ɛ turbulence model

2003 ◽  
Vol 3 (1-2) ◽  
pp. 201-207
Author(s):  
H. Nagaoka ◽  
T. Nakano ◽  
D. Akimoto
Keyword(s):  
Numerical Simulation ◽  
Mass Transfer ◽  
Turbulence Model ◽  
Uptake Rate ◽  
Oscillatory Flow ◽  
Substrate Uptake ◽  
Flow Conditions ◽  
Mass Transfer Mechanism ◽  
Substrate Uptake Rate ◽  
Good Agreement

The objective of this research is to investigate mass transfer mechanism in biofilms under oscillatory flow conditions. Numerical simulation of turbulence near a biofilm was conducted using the low Reynold’s number k-ɛ turbulence model. Substrate transfer in biofilms under oscillatory flow conditions was assumed to be carried out by turbulent diffusion caused by fluid movement and substrate concentration profile in biofilm was calculated. An experiment was carried out to measure velocity profile near a biofilm under oscillatory flow conditions and the influence of the turbulence on substrate uptake rate by the biofilm was also measured. Measured turbulence was in good agreement with the calculated one and the influence of the turbulence on the substrate uptake rate was well explained by the simulation.

Field Observation and Simulation of Sediment Resuspension in a Shallow Lake

1988 ◽  
Vol 20 (6-7) ◽  
pp. 263-270 ◽  
Author(s):  
K. Otsubo ◽  
K. Muraoka
Keyword(s):  
Numerical Simulation ◽  
Shallow Lake ◽  
Water Wave ◽  
Field Data ◽  
Sediment Resuspension ◽  
Field Research ◽  
Lake Kasumigaura ◽  
Bed Erosion ◽  
Current Water ◽  
Good Agreement

The dispersion and resuspension of sediments in Takahamairi Bay basin of Lake Kasumigaura were studied by means of field research and numerical simulation. The field data on wind direction and velocity, lake current, water wave, and turbidity were shown. Based on these results, we discuss how precipitated sediments were resuspended in this shallow lake. To predict the turbidity and the depth of bed erosion, a simulation model was established for this lake. The calculated turbidity showed good agreement with the field data. According to the simulated results, the turbidity reaches 200 ppm, and the bed is eroded several millimeters deep when the wind velocity exceeds 12 m/s in the lake.

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