• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.E
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• pp.45-59
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• 1992

At downstream part of the hydraulic structures such as spiliway or drainage gate, jet flow can occur by gate opening. If stream bed is not hard or bed protection is not sufficient, scour hole will be formed due to high shear stress of the jet flow. We call this primary scour. Once the scour hole is formed, a vortex occurs in it and this vortex causes additional scour. We call this secondary scour. The primary scour proceeds to downstream together with flow direction but the secondary one proceeds to upstream direction opposite to it. If the secondary one continues and reaches to the hydraulic structure, it can undermine the bottom of hydraulic structure and this will lead to failure of structure itself. Thus, it is necessary to know the physical features of the vortex structure in a scour hole, which is the main mechanism of the secondary scour. This study deals with the characteristics of the vortex structure and its shear stress which causes the secondary scour.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.21-28
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• 2011

The primary purpose of the present study was to investigate the mechanism causing scour around a pipeline placed on the seabed in a shallow water zone. Such submarine pipelines are usually exposed to currents and waves. The present experiments made estimates for each different flow type. The scour width and depth in the equilibrium scour phase were analyzed by non-dimensional parameters. The experiment in this study considered various parameters: pipe diameters, wave periods, wave heights, and current velocities. Using the experimental results, the correlations of scour width, scour depth, and main non-dimensional parameters such as the Fr number and KC number were analyzed. In the case of steady currents, the scour hole was closely related to the bottom velocity, while the scour hole in waves showed a relatively low correlation to the bottom velocity because when exposed to waves the scour hole was restricted according to the movement distance of the water particles during a wave period. However, the scour width under a steady current was not limited because vortex shedding was well developed from having enough time and distance.

• Journal of Korea Water Resources Association
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• v.32 no.1
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• pp.41-47
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• 1999

More than 100 bridges in Korea have been annually collapsed or badly damaged by the scouring around bridge piers, particularly in the flood season. To prevent from such a tragedy, the fundamental study on the bridge scouring is required, which is essential not only to estimate the scour depth with reliability but to take it into consideration in its design. However, it is not easy to find out the physical scour mechanism since many factors on the scour are coupled with. Moreover, there exists none of the measured data sufficiently for the primary research on the bridge scour depths. In this study the field measurements are carried out to provide the fundamental data for the research and the design. Scouring depth, pier width, flow depth, and the approaching velocity and degree of pier nose are measured broadly in small and medium streams. From these measurements the present situation on bridge scours can be understood and some of important factors to affect the stability of bridges are analyzed.

• Journal of the Korean GEO-environmental Society
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• v.14 no.3
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• pp.5-11
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• 2013

The primary objective of this research is to evaluate the behavior of a bridge substructure subjected to scouring during flood. A finite element (FE) study was carried out on a substructure modeled using the standard section specified for highway bridges. The three-dimensional FE model consists of non-linear springs with tri-axial load capacities at the base in order to consider the loss of bearing capacity of the substructure by local scour phenomenon. Various time varying loading conditions and scouring patterns were considered in the analysis. The results indicate a change in the structural behavior of substructure depending on the eroded area and pattern. The outcome of this research will be useful to suggest basic design guidelines for ground sills of the bridge substructure.

• Journal of the Korean Geotechnical Society
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• v.35 no.7
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• pp.5-14
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• 2019

In this study, a prototype abutment was constructed to establish a safety assessment technique of pier and a series of non-destructive tests using impact load. The surcharge load was loaded from 0 tonf to 2.5 tonf on the prototype abutment, and maximum surcharge load was up to 25 tonf. To analyze the behavior of the piers according to the direction of impact, a total of three types of analysis were performed: the direction of the pier, the direction perpendicular to the pier, and the outer direction of the pier. The height of the impact was also tested at each top and bottom. The measuring instrument used an accelerometer to measure the acceleration response when impacted. Based on the series of experimental results, specific values were calculated according to the direction of an impact and the surcharge load using the Fast Fourier Transform (FFT). In addition, the phase difference was used to analyze the pier from the primary 1st mode to the 4th mode.

• Journal of Korea Water Resources Association
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• v.52 no.10
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• pp.743-752
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• 2019

The flow in the meandering channel is characterized by the spiral motion of secondary currents that typically cause the erosion along the outer bank. Hydraulic structures, such as spur dike and groyne, are commonly installed on the channel bottom near the outer bank to mitigate the strength of secondary currents. This study is to investigate the effects of submerged vanes installed in a $90^{\circ}$ meandering channel on the development of secondary currents through three-dimensional numerical modeling using the hybrid RANS/LES method for turbulence and the volume of fluid method, based on OpenFOAM open source toolbox, for capturing the free surface at the Froude number of 0.43. We employ the second-order-accurate finite volume methods in the space and time for the numerical modeling and compare numerical results with experimental measurements for evaluating the numerical predictions. Numerical results show that the present simulations well reproduce the experimental measurements, in terms of the time-averaged streamwise velocity and secondary velocity vector fields in the bend with submerged vanes. The computed flow fields reveal that the streamwise velocity near the bed along the outer bank at the end section of bend dramatically decrease by one third of mean velocity after the installation of vanes, which support that submerged vanes mitigate the strength of primary secondary flow and are helpful for the channel stability along the outer bank. The flow between the top of vanes and the free surface accelerates and the maximum velocity of free surface flow near the flow impingement along the outer bank increases about 20% due to the installation of submerged vanes. Numerical solutions show the formations of the horseshoe vortices at the front of vanes and the lee wakes behind the vanes, which are responsible for strong local scour around vanes. Additional study on the shapes and arrangement of vanes is required for mitigate the local scour.