scholarly journals Local Scour Near Flexible Flow Deflectors

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 153 ◽  
Author(s):  
Liquan Xie ◽  
Yehui Zhu ◽  
Huang Li ◽  
Yan-hong Li ◽  
Yuanping Yang ◽  
...  
Keyword(s):  
Flow Field ◽  
Turbulent Energy ◽  
Local Scour ◽  
Scour Depth ◽  
Engineering Structures ◽  
Local Flow ◽  
Horseshoe Vortices ◽  
Bed Scour ◽  
Flow Deflector ◽  
Prone Posture

Rigid flow deflectors are usually used on water flow beds to protect engineering structures such as breakwater in coasts and to regulate flow routes in open channels. To reduce its side-effects, i.e., local scour at the toe of deflectors, a flexible flow deflector is proposed, and the corresponding local scour was investigated in this study. A flume experiment was conducted to investigate local scour. To show the advantage of flexible deflectors, a control experimental test was also conducted using a traditional rigid deflector under the same blockage area configuration and the same flow conditions. The flow field near the flexible deflector was also measured to reveal the local flow field. The results show that the bed-scour develops near the toe edges of both flexible and rigid deflectors, but the maximum and averaged scour depths for the flexible deflector are smaller. This advantage of flexible deflector in scour depth is mainly caused by its prone posture, which induces the upward stretching and enlarging horizontally rotating vortex and the upward shifted vertically rotating vortex. The former dissipates more turbulent energy and the latter results in smaller bed shear stress, which lead to smaller scour depth directly. In addition, the up- and down-swaying movement of the flexible deflector can also assistant to dissipate more turbulent energy, thereby damping the intense of the horseshoe vortices and thus weakening scour depth as well. The results of this study provide an elementary understanding on the mechanisms of a flexible flow structure and an alternative deflector-device to reduce scour depth.

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

2018 ◽  
Vol 40 ◽  
pp. 03038 ◽  
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.

scholarly journals Numerical Simulation of the Influence of Spur Dikes Spacing on Local Scour and Flow

2019 ◽  
Vol 9 (11) ◽  
pp. 2306
Author(s):  
Jian Ning ◽  
Guodong Li ◽  
Shanshan Li
Keyword(s):  
Shear Stress ◽  
Pearson Correlation ◽  
Fixed Bed ◽  
Maximum Velocity ◽  
Turbulent Energy ◽  
Local Scour ◽  
Shielding Effect ◽  
Scour Depth ◽  
Spur Dike ◽  
Spur Dikes

The spacing of spur dikes is an important consideration for the layout of spur dike channels. This study focuses on the local scour morphology and flow field characteristics of spur dikes with different spacings. The results show that the maximum scour depth is generally found in the vicinity of the first spur dike head. With the increase of the spacing of spur dikes, the shielding effect of the first spur dike is weakened. The maximum velocity in the main flow zone is twice that of the approach flow velocity in the fixed bed. But it is approximately the same as the incoming velocity in equilibrium scouring. The maximum turbulent energy appears to be mainly located in the backflow area of the fourth spur dike in the fixed bed, while the maximum value appears at the second spur dike head in the movable bed. Further, the shear stress decreases as scouring develops. Pearson correlation analysis was carried out between scour depth and shear stress. The analysis results are significantly correlated, indicating that the bed shear stress plays a prominent role in the scouring process. These discoveries can serve as a guide to determine the most reasonable spacing of spur dikes.

Equilibrium Profile of Current-Induced Scour Around Submarine Pipelines

2006 ◽  
Author(s):  
Mir Emad Mousavi ◽  
Abbas Yeganeh Bakhtiary ◽  
Nastaran Enshaei
Keyword(s):  
Flow Field ◽  
Granular Materials ◽  
Human Activities ◽  
Numerical Models ◽  
Experimental Investigations ◽  
Scour Depth ◽  
Total Width ◽  
Local Flow ◽  
Equilibrium Profile ◽  
Bed Roughness

Submarine pipelines installed on seabed disturb the local flow field and bring imbalance in local sediment transport that leads to scouring. Local scouring can leave the pipeline unsupported in significant distances. The free spans of the pipeline are susceptible to damages arising from environmental forces or human activities. This paper presents results of experimental investigations on the equilibrium profile of the local scouring around the pipe due to unidirectional current. New equations are proposed for the prediction of the scour depth and width before installation of the pipe. It is evident from the experimental results that the equilibrium depth of the current-induced scour is a function of pipe diameter and Shields number. Also scour width at upstream and downstream of the pipe and the total width of the scour are investigated. The results are simplified in the form of diagrams for prediction of the scour depth/width in practice based on flow velocity, bed roughness condition and size of the granular materials. The results can be used either for the design purposes or for the calibration of numerical models. One of the results of this work is that the scour width at downstream of the pipe is about 2.5 times of the width at upstream.

Experimental Investigation of Local Scour Around a Submerged Vertical Circular Cylinder in Steady Currents

2009 ◽  
Author(s):  
Ming Zhao ◽  
Liang Cheng ◽  
Zhipeng Zang
Keyword(s):  
Experimental Investigation ◽  
Circular Cylinder ◽  
Laboratory Experiments ◽  
Three Dimensional ◽  
Development Rate ◽  
Local Scour ◽  
Scour Depth ◽  
Sediment Size ◽  
Seabed Topography ◽  
Bed Scour

Local scour around a submerged vertical circular cylinder in steady currents was studied by laboratory experiments. The experiments were conducted under live-bed scour conditions. Only one median sediment size of d50 = 0.40 mm was used in the experiments with a uniformity parameter of d85/d15 = 1.42. In some of the tests, time-developments of scour depth at the stagnation point of the cylinder were measured using the conductivity scour probes. Three-dimensional (3D) seabed topography around each model cylinder was measured using a laser profiler developed at University of Western Australia. The experimental results showed that the scour depth increased with an increase in cylinder height. The development rate of scour depth increases if Shields parameter increases.

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.

Estimation of maximum local scour depth around submerged spur-dike

2016 ◽  
pp. 193-199
Author(s):  
S.Y. Hao ◽  
Y.F. Xia ◽  
H. Xu
Keyword(s):  
Local Scour ◽  
Scour Depth ◽  
Spur Dike

scholarly journals Nose-Angle Bridge Piers as Alternative Countermeasures for Local Scour Reduction

2018 ◽  
Vol 13 (2) ◽  
pp. 110-120 ◽  
Author(s):  
Ibtesam Abudallah Habib ◽  
Wan Hanna Melini Wan Mohtar ◽  
Atef Elsaiad ◽  
Ahmed El-Shafie
Keyword(s):  
Froude Number ◽  
Local Scour ◽  
Bridge Piers ◽  
Scour Depth ◽  
Skew Angle ◽  
Flow Angle ◽  
Sediment Size ◽  
Low Froude Number ◽  
Skew Angles ◽  
Depth Reduction

This study investigates the performance nose-angle piers as countermeasures for local scour reduction around piers. Four nose angles were studied, i.e., 90°, 70°, 60° and 45° and tested in a laboratory. The sediment size was fixed at 0.39 mm whereas the flow angle of attack (or skew angle) was varied at four angles, i.e., skew angles, i.e., 0°, 10°, 20° and 30°. Scour reduction was clear when decreasing nose angles and reached maximum when the nose angle is 45°. Increasing the flow velocity and skew angle was subsequently increasing the scour profile, both in vertical and transversal directions. However, the efficiency of nose angle piers was only high at low Froude number less than 0.40 where higher Froude number gives minimal changes in the maximum scour depth reduction. At a higher skew angle, although showed promising maximum scour depth reduction, the increasing pier projected width resulted in the increase of transversal lengths.

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