scholarly journals PREDICTION OF EQUILIBRIUM SCOUR HOLES USING OPTIMIZATION PROCEDURES

2020 ◽  
pp. 12
Author(s):  
Xerxes Mandviwalla ◽  
Jesper Roland Kjaergaard Qwist ◽  
Erik Damgaard Christensen
Keyword(s):  
Equilibrium Shape ◽  
Optimization Procedure ◽  
Bed Load ◽  
Scour Depth ◽  
Transient Solution ◽  
Marine Structures ◽  
Scour Hole ◽  
Scour Holes ◽  
Speed Up ◽  
Equilibrium Scour Depth

This paper presents an optimization procedure that finds the equilibrium scour depth under a pipeline. Even though much knowledge on scour is available for the most typical marine structures such as a vertical circular monopile of a horizontal pipelines the calculation of the scour depth complex and time-consuming as the transient solution is often modelled as well. In this paper we present a optimization procedure that combined with a computational fluid dynamics, and a model of the bed load finds the equilibrium shape of a scour hole. This can potentially speed up the calculation of the shape of the equilibrium scour hole with a factor of 100. However, it comes with a coast as we will not model the transition and the time scale of the scour hole development.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/LpKq9Twj7zo

scholarly journals Physical model study of bedrock scour downstream of dams due to spillway plunging jets

2020 ◽  
Vol 62 (3) ◽  
Author(s):  
A Bosman ◽  
G R Basson
Keyword(s):  
Physical Model ◽  
Linear Regression Analysis ◽  
Scour Depth ◽  
Model Study ◽  
Fissured Rock ◽  
Scour Hole ◽  
Plunging Jets ◽  
Concrete Blocks ◽  
Rock Bed ◽  
Equilibrium Scour Depth

The erosive power of a free-falling high-velocity water jet, flowing from a dam spillway, could create a scour hole downstream of the dam, endangering the foundation of the dam. Despite extensive research since the 1950s, there is presently no universally agreed method to predict accurately the equilibrium scour depth caused by plunging jets at dams. These formulae yield a large range of equilibrium scour dimensions. The hydrodynamics of plunging jets and the subsequent scour of a rectangular, horizontal and vertical fissured rock bed were investigated in this study by means of a physical model. Equilibrium scour hole geometries for different fissured dimensions (simulated with rectangular concrete blocks tightly prepacked in a regular rectangular matrix), for a range of flow rates, plunge pool depths, and dam height scenarios were experimentally established with 31 model tests. From the results, non-dimensional formulae for the scour hole geometry were developed using multi-linear regression analysis. The scour depth results from this study were compared to various analytical methods found in literature. The equilibrium scour hole depth established in this study best agrees with that predicted by the Critical Pressure method.

scholarly journals Experimental Scours by Impinging Twin-Propeller Jets at Quay Wall

2020 ◽  
Vol 8 (11) ◽  
pp. 872
Author(s):  
Yonggang Cui ◽  
Wei Haur Lam ◽  
Zhi Chao Ong ◽  
Lloyd Ling ◽  
Chee Loon Siow ◽  
...  
Keyword(s):  
Scour Depth ◽  
Water Tank ◽  
Quay Wall ◽  
Depth Position ◽  
Scour Hole ◽  
Scour Holes ◽  
Horseshoe Vortices ◽  
Three Stages ◽  
Deposition Height ◽  
The Relationship

Experiments were conducted to investigate the seabed scour holes due to the interaction between the twin-propeller jet and quay wall. Vertical quay wall was modelled by using a polyvinyl chloride (PVC) plastic plate in a water tank. The relationship between the positions of the propeller and the vertical quay wall was designed according to the actual working conditions of a ship entering and leaving a port. Propeller-to-wall distance and rotational speed were changed to observe the various scour conditions. The scour depth was measured by using an Acoustic Doppler Velocimeter (ADV). Primary scour hole was found within the jet downstream and secondary scour hole occurred beneath of the propeller. Third scour hole was found close to the quay wall due to horseshoe vortices. The maximum scour position of this third scour hole was found at the jet centre near the quay wall. Temporal formation of scour holes can be divided into three stages: axial scour formation, obstructed scour expansion and equilibrium stages. The quantitative relationships for six characteristic parameters of the scour pit were established including the maximum scour depth (εmax,q), maximum scour depth position (Xm,q), maximum scour width (Wm,q), length of main scour pit (XS,q), maximum deposition height (ZD,q), and location of maximum deposition height (XD,q).

scholarly journals Improving the 2D Numerical Simulations on Local Scour Hole around Spur Dikes

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1462
Author(s):  
Chung-Ta Liao ◽  
Keh-Chia Yeh ◽  
Yin-Chi Lan ◽  
Ren-Kai Jhong ◽  
Yafei Jia
Keyword(s):  
Numerical Simulation ◽  
Three Dimensional ◽  
Local Scour ◽  
Bridge Piers ◽  
Scour Depth ◽  
Foundation Design ◽  
Mobile Bed ◽  
Scour Hole ◽  
Scour Holes ◽  
Spur Dikes

Local scour is a common threat to structures such as bridge piers, abutments, and dikes that are constructed on natural rivers. To reduce the risk of foundation failure, the understanding of local scour phenomenon around hydraulic structures is important. The well-predicted scour depth can be used as a reference for structural foundation design and river management. Numerical simulation is relatively efficient at studying these issues. Currently, two-dimensional (2D) mobile-bed models are widely used for river engineering. However, a common 2D model is inadequate for solving the three-dimensional (3D) flow field and local scour phenomenon because of the depth-averaged hypothesis. This causes the predicted scour depth to often be underestimated. In this study, a repose angle formula and bed geometry adjustment mechanism are integrated into a 2D mobile-bed model to improve the numerical simulation of local scour holes around structures. Comparison of the calculated and measured bed variation data reveals that a numerical model involving the improvement technique can predict the geometry of a local scour hole around spur dikes with reasonable accuracy and reliability.

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.

scholarly journals Hydrodynamic Structure with Scour Hole Downstream of Bed Sills

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 186 ◽  
Author(s):  
Mouldi Ben Meftah ◽  
Francesca De Serio ◽  
Diana De Padova ◽  
Michele Mossa
Keyword(s):  
Flow Velocity ◽  
Phenomenological Theory ◽  
Scour Depth ◽  
Shear Stresses ◽  
Alluvial Channels ◽  
Spectral Exponent ◽  
Turbulence Measurements ◽  
Scour Hole ◽  
Hydrodynamic Structure ◽  
Equilibrium Scour Depth

Experimental turbulence measurements of scour hole downstream of bed sills in alluvial channels with non-cohesive sediments are investigated. Using an Acoustic Doppler Velocimeter (ADV), the flow velocity-field within the equilibrium scour hole was comprehensively measured. In this study, we especially focus on the flow hydrodynamic structure in the scour hole at equilibrium. In addition to the flow velocity distribution in the equilibrium scour hole, the turbulence intensities, the Reynolds shear stresses, the turbulent kinetic energy, and the turbulent length scales are analyzed. Since the prediction of equilibrium scour features is always very uncertain, in this study and based on laboratory turbulence measurements, we apply the phenomenological theory of turbulence to predict the maximum equilibrium scour depth. With this approach, we obtain a new scaling of the maximum scour depth at equilibrium, which is validated using experimental data, satisfying the validity of a spectral exponent equal to −5/3. The proposed scaling shows a quite reasonable accuracy in predicting the equilibrium scour depth in different hydraulic structures.

scholarly journals Scour Induced by Single and Twin Propeller Jets

Water ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 1097 ◽  
Author(s):  
Yonggang Cui ◽  
Wei Haur Lam ◽  
Tianming Zhang ◽  
Chong Sun ◽  
Gerard Hamill
Keyword(s):  
Normal Distribution ◽  
Maximum Depth ◽  
Scour Depth ◽  
Scour Hole ◽  
Scour Holes ◽  
Ship Propeller ◽  
Gaussian Normal Distribution

Single and twin ship propeller jets produce scour holes with deposition dune. The scour hole has a maximum depth at a particular length downstream within the propeller jet. Existing equations are available to predict maximum scour depth and the corresponding scour length downstream. Experiments conducted with various physical propeller models, rotational speeds, propeller-to-propeller distances and bed clearances are presented. The measurements allowed a better understanding of the mechanism of temporal scour and deposition formation for scour caused by single-propeller and twin-propeller. Results show that the propeller jet scour profiles can be divided into three zones, which are the small scour hole, primary scour hole and deposition dune. An empirical 2D scour model is proposed to predict the scour profile for both a single-propeller and twin-propeller using a Gaussian normal distribution.

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.

scholarly journals Secondary Currents with Scour Hole at Grade Control Structures

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 319
Author(s):  
Mouldi Ben Meftah ◽  
Diana De Padova ◽  
Francesca De Serio ◽  
Michele Mossa
Keyword(s):  
Secondary Flow ◽  
Control Structure ◽  
Scour Depth ◽  
Control Structures ◽  
Secondary Currents ◽  
Scour Hole ◽  
Grade Control ◽  
Flow Motion ◽  
The Cross ◽  
Equilibrium Scour Depth

Most studies on local scouring at grade control structures have principally focused on the analysis of the primary flow field, predicting the equilibrium scour depth. Despite the numerous studies on scouring processes, secondary currents were not often considered. Based on comprehensive measurements of flow velocities in clear water scours downstream of a grade control structure in a channel with non-cohesive sediments, in this study, we attempted to investigate the generation and turbulence properties of secondary currents across a scour hole at equilibrium condition. The flow velocity distributions through the cross-sectional planes at the downstream location of the maximum equilibrium scour depth clearly show the development of secondary current cells. The secondary currents form a sort of helical-like motion, occurring in both halves of the cross-section in an axisymmetric fashion. A detailed analysis of the turbulence intensities and Reynolds shear stresses was carried out and compared with previous studies. The results highlight considerable spatial heterogeneities of flow turbulence. The anisotropy term of normal stresses dominates the secondary shear stress, giving the impression of its crucial role in generating secondary flow motion across the scour hole. The anisotropy term shows maximum values near both the scour mouth and the scour bed, caused, respectively, by the grade control structure and the sediment ridge formation, which play fundamental roles in maintaining and enhancing the secondary flow motion.

Estimating Equilibrium Scour Depth at Cylindrical Piers in Experimental Studies

2011 ◽  
Vol 137 (9) ◽  
pp. 1089-1093 ◽  
Author(s):  
Gonzalo Simarro ◽  
Cristina M. S. Fael ◽  
António H. Cardoso
Keyword(s):  
Experimental Studies ◽  
Scour Depth ◽  
Equilibrium Scour Depth

Numerical Investigation of Local Scour Around Submerged Pipeline in Shoaling Conditions

2018 ◽  
Author(s):  
Ming-ming Liu ◽  
Ming Zhao ◽  
Lin Lu
Keyword(s):  
Water Waves ◽  
Slope Angle ◽  
Suspended Load ◽  
Local Scour ◽  
Navier Stokes ◽  
Bed Load ◽  
Scour Depth ◽  
Two Dimensional ◽  
Sediment Mass ◽  
Subsea Pipelines

Water waves play an important role in local scour around subsea pipelines laid on the sandy seabed, especially in shallow water regions. In this paper, a two-dimensional numerical model is employed to predict local scour around submarine pipelines under water waves in shoaling condition. The motion of water under waves is simulated by solving the Reynolds Averaged Navier-Stokes (RANS) equations. The evolution of the seabed surface near the pipeline is predicted by solving the conservation of the sediment mass, which transport in the water in the forms of bed load and suspended load. The main aim of this study is to investigate the effect of the seabed slope on the scour profiles and scour depth. To achieve this aim, numerical simulations of scour around a pipeline on a flat seabed and on a slope seabed with a slope angle of 15° are conducted for various wave conditions.

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