Equilibrium Scour-Depth Prediction around Cylindrical Structures

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.

Download Full-text

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

Journal of Marine Science and Engineering ◽

10.3390/jmse9080886 ◽

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.

Download Full-text

Estimating Equilibrium Scour Depth at Cylindrical Piers in Experimental Studies

Journal of Hydraulic Engineering ◽

10.1061/(asce)hy.1943-7900.0000410 ◽

2011 ◽

Vol 137 (9) ◽

pp. 1089-1093 ◽

Cited By ~ 27

Author(s):

Gonzalo Simarro ◽

Cristina M. S. Fael ◽

António H. Cardoso

Keyword(s):

Experimental Studies ◽

Scour Depth ◽

Equilibrium Scour Depth

Download Full-text

Discussion of “ Scour‐Depth Prediction Under Armoring Conditions ” by Deva K. Borah (October, 1989, Vol. 115, No. 10)

Journal of Hydraulic Engineering ◽

10.1061/(asce)0733-9429(1991)117:8(1084.2) ◽

1991 ◽

Vol 117 (8) ◽

pp. 1084-1084 ◽

Cited By ~ 1

Author(s):

Ryszard Błażejewski

Keyword(s):

Scour Depth ◽

Depth Prediction

Download Full-text

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

Journal of the South African Institution of Civil Engineering ◽

10.17159/2309-8775/2020/v62n3a4 ◽

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.

Download Full-text

Experimental investigation of the equilibrium scour depth below submerged pipes both in live-bed and clear-water regimes under the wave effect

Applied Ocean Research ◽

10.1016/j.apor.2018.08.010 ◽

2018 ◽

Vol 80 ◽

pp. 49-56 ◽

Cited By ~ 2

Author(s):

Mustafa Dogan ◽

Aysegul Ozgenc Aksoy ◽

Yalcin Arisoy ◽

Mehmet Sukru Guney ◽

Vahid Abdi

Keyword(s):

Experimental Investigation ◽

Scour Depth ◽

Clear Water ◽

Wave Effect ◽

Water Regimes ◽

Equilibrium Scour Depth

Download Full-text

Scour Depth Prediction for Asa Dam Bridge, Ilorin, Using Artificial Neural Network

International Journal of Engineering Research in Africa ◽

10.4028/www.scientific.net/jera.47.53 ◽

2020 ◽

Vol 47 ◽

pp. 53-62

Author(s):

Samson Olalekan Odeyemi ◽

Mutiu Adelodun Akinpelu ◽

Rasheed Abdulwahab ◽

Kazeem Adeshina Dauda ◽

Stella Chris-Ukaegbu

Keyword(s):

Economic Value ◽

Economic Life ◽

Scour Depth ◽

Bridge Scour ◽

Average Flow Velocity ◽

Sediment Size ◽

The North ◽

Depth Prediction ◽

Pile Cap ◽

Artificial Neural

Bridge Scour is the localized loss of the geomaterials around the foundation of a bridge as a result of the movement of water around it. Scour is a great risk to the stability of a bridge’s foundation, thus leading to collapse, loss of lives and setback in a nation’s socio-economic life. Artificial Neural Networks (ANN) are collections of simple, highly connected processing elements that learn according to sets of input parameters and use that to simulate the networks of nerve cells of humans or animal central nervous system. The Asa Dam Bridge, one of the longest bridges in Ilorin, Kwara State, Nigeria, has five (5) spans of 20m each. The bridge connects Ilorin to the Ogbomosho Express way (leading to the western part of the country) and the Eyenkorin-Jebba road (leading to the north). Thus, the bridge has a high economic value. In this research, factors such as flow depth, average flow velocity of the river and median sediment size were investigated to show how they affect the depth of scour around the bridge pile foundation. Data were taken for a period of 48 weeks and ANN was applied to predict and generate a model that shows how these factors relate to the scour depth of the riverbed. The model revealed that the hydraulic parameters and soil grading around the pile cap of Asa River Bridge bears significant influence on the scour depth of its foundation. The model was compared with five (5) other established scour equations.

Download Full-text

Scour around Spur Dike in Sand–Gravel Mixture Bed

Water ◽

10.3390/w11071417 ◽

2019 ◽

Vol 11 (7) ◽

pp. 1417 ◽

Cited By ~ 4

Author(s):

Manish Pandey ◽

Wei Haur Lam ◽

Yonggang Cui ◽

Mohammad Amir Khan ◽

Umesh Kumar Singh ◽

...

Keyword(s):

Water Depth ◽

Velocity Ratio ◽

Maximum Error ◽

Length Ratio ◽

Scour Depth ◽

Spur Dike ◽

Particle Ratio ◽

Cause Of Failure ◽

Equilibrium Scour Depth ◽

Sediment Mixture

Scour is the main cause of failure for spur dike. The accurate prediction of scour around spur dike is essential to design a spur dike. The present study focuses on the maximum scour depth in equilibrium condition and parameters, which influence it in a sand–gravel mixture bed. Outcomes of the present experimental study showed that the non-dimensional maximum equilibrium scour depth increases with critical velocity ratio (U/Uca), water depth-armour particle ratio (h/da), Froude number for sediment mixture (Frsm), water depth-spur dike length ratio (h/l), and decreases with increase in armour particle-spur dike length ratio (da/l). The maximum scour depth is proportional to dimensionless parameters of U/Uca, h/da, Frsm, h/l, but the scour depth is inverse proportional to da/l. Scour around spur dike in a sand–gravel mixture is mainly influenced by the property of the sediment mixture. The scour increases with decrease in non-uniformity of the sediment mixture. A non-linear empirical equation is proposed to estimate the maximum scour depth at an upstream nose of rectangular spur dike with a maximum error of 15%. The sensitivity analysis indicates that the maximum non-dimensional equilibrium scour depth depends on Frsm, followed by the secondary sensible parameters da/l, h/l, and h/da.

Download Full-text

Scour depth prediction at the base of longitudinal walls: a combined experimental, numerical, and field study

Environmental Fluid Mechanics ◽

10.1007/s10652-019-09704-x ◽

2019 ◽

Vol 20 (2) ◽

pp. 459-478 ◽

Cited By ~ 3

Author(s):

A. Khosronejad ◽

P. Diplas ◽

D. Angelidis ◽

Z. Zhang ◽

N. Heydari ◽

...

Keyword(s):

Field Study ◽

Scour Depth ◽

Depth Prediction

Download Full-text

Viscosity effects on local scour around vertical structures in clear-water conditions

E3S Web of Conferences ◽

10.1051/e3sconf/20184003038 ◽

2018 ◽

Vol 40 ◽

pp. 03038 ◽

Cited By ~ 1

Author(s):

Costantino Manes ◽

Francesco Coscarella ◽

Ashley Rogers ◽

Roberto Gaudio

Keyword(s):

Local Scour ◽

Hydraulic Structures ◽

Scour Depth ◽

Foundation Design ◽

Viscous Forces ◽

Erosion Rates ◽

Sediment Removal ◽

Viscosity Effects ◽

Horseshoe Vortices ◽

Equilibrium Scour Depth

Local scour represents the erosion process that occurs at the base of hydraulic structures overlying sediment beds. Horseshoe vortices forming at the bed-structure junction are the main responsible for sediment removal and dictate erosion rates as well as the maximum erosion depth resulting from a significant flow event. In steady-flow conditions this is often referred to as the equilibrium scour depth, which, for many hydraulic structures, represents a key parameter for foundation-design and risk-assessment purposes. The equilibrium scour depth has been investigated for decades and many predictive formulae have been developed following the classical empirical approach, whereby numerous experimental datasets are used to isolate and identify the influence of non-dimensional groups emerging from dimensional analysis. Within this context, the influence of obstacle Reynolds numbers, and consequently of viscous forces, has always been neglected because of the large Re values normally encountered in engineering and laboratory conditions. The present paper demonstrates that this assumption is largely incorrect especially for beds made of sand or finer material. The theoretical analysis presented in Manes and Brocchini ([1]) is herein extended to include viscosity effects and investigate their importance on equilibrium scour depths forming around obstacles resembling bridge piers.

Download Full-text