• Journal of the Korean GEO-environmental Society
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• v.10 no.7
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• pp.117-123
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• 2009

This study is to investigate the characteristics of scour around pipeline in current and hydraulic model tests were performed. All the model test are 45 cases, which were conducted with velocities of 0.2 m/s to 0.5 m/s and pipe diameters of 45, 60, 90 mm. The developments of scour around pipeline were observed and equilibrium scour depths were recorded due to variation of pipe diameter and current velocity. According to the results, the equilibrium scour depth was proportional to current velocity and pipe diameter. The effect of diameter of pipeline on the equilibrium scour depth was bigger than current velocity. The correlations of relative scour depth and dimensionless number such as a Reynolds number, Shields number, and Froude number were analyzed. The Froude number and the relative scour depth had a high correlation of 0.900.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4B
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• pp.353-360
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• 2011

The objectives of this study were to analyzes temporal variation of local scour depth in the downstream of weir with shapes. Prediction of maximum or equilibrium scour depth was the main focus of engineers and researchers in the downstream of weir. However, it is necessary to analyzes temporal variation of local scour depth in the downstream of weir to predict real time scour depth. Experiment were performed with various weir shapes like sharp crest and inclined stepped with time variation and non-dimensional scourhole shapes, scour depths were proposed. A formula for predicting scour depths with temporal variation for weir were proposed through non-linear regression analysis. Temporal variation of scour depths could be estimated with suggested formula and 4 input data (Equilibrium scour depth, weir height, overflow depths, and water depth downstream). Suggested formula could make it possible to design a apron and bed protection economically in the downstream of a weir by considering flood duration time.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.287-292
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• 1998

The phenomena of local scour due to a current from a seadike closure gap which is protected by rock, then on to an erodible bed, have been studied. Based on the data of hydraulic model test, the scour characteristics have been investigated for the variation of maximum scour depth with time until reaching equilibrium stage and the shape of ultimate scour hole. A brief evaluation of DHL formula for the relationship between maximum scouring depth and time and a dimensionless form leading to time-scale introduced. On the basis of DHL formula, modified DHL formula denoted DHL-RDC formula is extend to the range of estimation of scour depth compared to DHL formula verified by model test.

• 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.

• Water for future
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• v.28 no.4
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• pp.147-154
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• 1995

Scour characteristics of noncohesive bed materials at the downstream of free-falling jet were analyzed through hydraulic experiments. It was assumed that the downstream had no special energy dissipators. Flow characteristics of free falling jet from rectangular section were studied, and scour characteristics with and without mounds, which were generated at the downstream of the scour hole, were comparatively analyzed for various bed materials, discharges and tailwater depths. Not only the equilibrium scour depth but also the height of mound could be expressed as a function of densimetric Froude number. Densimetric Froude number had closer relationship with the equilibrium dimensionless scour depth than other dimensionless parameters. It was suggested that the mound effects should be considered at the design stage of bed protection works.

• Journal of Korea Water Resources Association
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• v.30 no.4
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• pp.335-346
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• 1997

This study aims at examining closely the scour around a pier due to irregular water stage changes during flood. At the Sangye bridge is located lowermost downstream of the Bocheong stream in the Kum River, the IHP experimental watershed. For this purpose, we have analyzed the change of scour depths due to stage hydrographs of experimental basin by a simulation. To examine the scour phenomenon around a pier due to irregular stage change in flood, we have analyzed the change of scour depth corresponding to stage hydrograph of field watershed after verification of model channel. From this study, the following conclusions are made: First, in case of predicting the maximum scour depth around a pier with stage hydrograph in the state of steady flow, we should choose the highest stage. Second, after increasing the stage, the equilibrium scour depth became smaller than the maximum scour depth. Therefore, in case of estimating the maximum scour depth in rivers, it is recommended that we should consider additional scour depth with is reduced by infilling the sediments.

• Journal of Korea Water Resources Association
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• v.36 no.6
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• pp.893-899
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• 2003

In this study, a realtime bridge scour monitoring system was installed and operated to measure the real scour depths in relatively hard and rocky bottom. And riverbed change at before and after flood was investigated by GPR(Ground Penetrating Radar) to check the rationality of measured values. As the result of this study, it was revealed the inaccuracy of equilibrium scour depth estimation through the bridge scout equations because most of the equations do not reflect the differences of geological characteristics, evaluated the real scour depths considering both bed and flow conditions.

• Ocean Systems Engineering
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• v.2 no.4
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• pp.257-269
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• 2012

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around spherical bodies exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D nonlinear random waves, and using the regular wave formulas for scour and self-burial depths by Truelsen et al. (2005). An example calculation is provided.

• Ocean Systems Engineering
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• v.6 no.2
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• pp.161-189
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• 2016

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around a vertical pile exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (2002). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases on mild slopes are also suggested.

• Ocean Systems Engineering
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• v.7 no.3
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• pp.275-298
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• 2017

This paper provides a practical stochastic method by which the maximum equilibrium scour depth below a pipeline exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (1996). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases for random waves alone are also suggested.