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 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 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.

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 Local scour around complex pier groups and combined piles at semi-integral bridge

2014 ◽  
Vol 62 (2) ◽  
pp. 108-116 ◽  
Author(s):  
Shatirah Akib ◽  
Afshin Jahangirzadeh ◽  
Hossein Basser
Keyword(s):  
Experimental Study ◽  
Laboratory Experiments ◽  
Bridge Piers ◽  
Scour Depth ◽  
Flow Depth ◽  
Flow Discharge ◽  
Integral Bridge ◽  
Integral Bridges ◽  
Equilibrium Scour Depth ◽  
The Relationship

Abstract This research presents an experimental study on the scouring mechanism at semi-integral bridge piers. Based on laboratory experiments, this study focuses on the relationship between scour depth in complex pier groups and combined piles bridge and various parameters including the variation of inflow velocity, distance, and time. 1 200 data were collected for flow velocity and scour. The flow pattern and scour were analyzed for different flow discharges and flow depths. The results showed that the scour development with respect to time was greater for higher flow depth and bigger flow discharge at semi-integral bridges. In addition, the equilibrium scour depth increased with the approach flow depth around piers at semi-integral bridges. Velocity distribution also affected the scour development. It decreased when approaching the bridge but increased from upstream to downstream of the flume.

scholarly journals Experimental Investigation of Scour Prediction Methods for Offshore Tripod and Hexapod Foundations

2020 ◽  
Vol 8 (11) ◽  
pp. 856
Author(s):  
Xuan Ni ◽  
Leiping Xue
Keyword(s):  
Laboratory Experiments ◽  
Prediction Methods ◽  
Scour Depth ◽  
Effective Diameter ◽  
Bed Sediment ◽  
Clear Water ◽  
Pile Groups ◽  
Steady Current ◽  
Complex Shapes ◽  
Equilibrium Scour Depth

Scour prediction is essential for the design of offshore foundations. Several methods have been proposed to predict the equilibrium scour depth for monopiles. By introducing an effective diameter, such methods could also be applied to predicting scour depth for pile groups. Yet, there are still difficulties in estimating the equilibrium scour depth of foundations in complex shapes, such as the tripod foundation. This study investigates the clear-water scour around the tripod and hexapod foundations through laboratory experiments, with uniform bed sediment and steady current. Here, the authors propose an approach to calculate the effective diameter for the tripod and hexapod models, which is similarly as for the pile groups. Three widely-used methods in predicting equilibrium scour depth have been evaluated, and the best method is recommended.

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 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 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
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