• Journal of Korea Water Resources Association
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• v.50 no.2
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• pp.89-97
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• 2017

Turbulent flow structure in the high amplitude meandering channel is complex due to secondary recirculation with helicoidal motions and shear layers formed by flow separation from the curved sidewall. In this work, the secondary flow and the superelevation of the water surface produced in the high-amplitude Kinoshita channel are reproduced by the unsteady Reynolds-averaged Navier-Stokes (RANS) computations using the VOF technique for resolving the variation of water surface elevation and three statistical turbulence models ($k-{\varepsilon}$, RNG $k-{\varepsilon}$, $k-{\omega}$ SST). The numerical results computed by a second-order accurate finite volume method are compared with an existing experimental measurement. Among applied turbulence models, $k-{\omega}$ SST model relatively well predicts overall distribution of the secondary recirculation in the Kinoshita channel, while all three models yield similar prediction of water superelevation transverse slope. The secondary recirculation driven by the radial acceleration in the upstream bend affects the flow structure in the downstream bend, which yields a pair of counter-rotating vortices at the bend apex. This complex flow pattern is reasonably well reproduced by the $k-{\omega}$ SST model. Both $k-{\varepsilon}$ based models fail to predict the clockwise-rotating vortex between a pair of counter-rotating vortices which was observed in the experiment. Regardless of applied turbulence models, the present computations using the VOF method appear to well reproduce the superelevation of water surface through the meandering channel.

• Journal of Korea Water Resources Association
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• v.38 no.7 s.156
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• pp.545-554
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• 2005

The detailed interdisciplinary surveys were conducted on the pattern of habitat use of dominant fishes during the spawning and adult stage. The hydraulic parameters of the depth and velocity, discharge, substrate cover streams, and distribution of fish in the Yeonggang, WiCheon, HoeCheon, GeochangwiCheon, CheongdoCheon, DanjangCheon (the Nakdong River Basin) were measured. The Habitat Suitability Criteria was developed for the two fish species (Zacco Platypus and Zacco Temmincki) and life stages(spawning and adult), habitat conditions (depth, velocity and covet). The Physical Habitat Simulation of the Instream Flow Incremental Methodology was applied to calculate for optimal flow and the ecological flow recommendation was proposed by choosing the largest one in the optimal flow. The ecological flow recommendation was $5.0\;m^3/s{\sim}10.0\;m^3/s$ (e.g., $6.5\;m^3/s$ in the NaeseongCheon). Also, the ecological flow recommendations were compared with the existing ecological flow and flow duration analysis.

• Journal of the Korean Geotechnical Society
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• v.28 no.4
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• pp.101-113
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• 2012

The degradation of a tunnel drainage system leads to increases in pore water pressure around the tunnel and the lining stress, which results in affecting the tunnel stability. In the present study of the Namsan 3th tunnel, more than 30 year old tunnel, the effects of the drainage performance reduction due to drain hole clogging on the tunnel lining stability were investigated by examining pore water pressure distribution around the tunnel and the lining stresses through numerical analysis. Groundwater flow modeling on the Mt. Namsan region was done first and 3D seepage and coupled stress-pore water pressure finite element analysis were performed on the tunnel using the results of the groundwater flow modeling. The pore water pressure distribution and the tunnel lining stresses could be predicted using a drain hole outflow data measured in the tunnel site. This analysis method may be used to evaluate the current stability of old tunnels for which in most cases field investigations and related information are not readily available.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.312-315
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• 2008

The flow structure behind circular and elliptical type rings embedded in a cross-flow was investigated experimentally using two-frame particle image velocimetry (PIV). The experiments were performed in a circulating water channel with a test section of 0.35m height ${\times}$ 0.3m width ${\times}$ 1.1m length. PIV measurements were carried out with varying the Reynolds number in the range of 4.5 ${\times}$ $10^2$ - 4.5 ${\times}$ $10^3$. In the present study, turbulent flow structures in the stream-wise direction and span-wise direction were investigated. The mean velocity field distribution was obtained by statistical-averaging instantaneous velocity fields. The spatial distributions of turbulent statistics such as turbulent intensities and turbulent kinetic energy were also investigated.

• International Journal of Automotive Technology
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• v.5 no.1
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• pp.17-22
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• 2004

An experimental investigation was conducted to study the characteristics of turbulent swirling flow in an axisymmetric annuli. The swirl angle measurements were performed using a flow visualization technique using smoke and dye liquid for Re=60,000-80,000. Using the two-dimensional Particle Image Velocimetry method, this study found the time-mean velocity distribution and turbulence intensity in water with swirl for Re=20,000, 30,000, and 40,000 along longitudinal sections. There were neutral points for equal axial velocity at y/(R-r)=0.7-0.75, and the highest axial velocity was recorded near y/(R-r)=0.9. Negative axial velocity was observed near the convex tube along X/(D-d)=3.0-18.0 for Re=20,000.

• Journal of Soil and Groundwater Environment
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• v.20 no.3
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• pp.41-50
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• 2015

Hydrogeologic environment of the Mega City such as Seoul, suffers from rapid changes caused by urbanization, construction of underground subway or buildings, and contaminant loading by diverse anthropogenic activities. Understanding the present condition of groundwater environment and water budget is necessary to prevent natural and manmade disasters and to prepare for sustainable water resource management of urban environment. In this study, regional groundwater flow and water budget status of Seoul was analyzed using numerical simulation. Modeling result indicated that groundwater level distribution of Seoul generally followed the topography, but the significant decreases in groundwater level were observed around the subway network. Steady-state water balance analysis showed groundwater recharge by rainfall and leakage from the water supply network was about 550,495 m³/day. Surface water inflow and baseflow rate via Han River and major streams accounted for 799,689 m³/day and 1,103,906 m³/day, respectively. Groundwater usage was 60,945 m³/day, and the total groundwater leakage along the subway lines amounted to 114,746 m³/day. Modeling results revealed that the subway could decrease net groundwater baseflow by 40%. Our study result demonstrated that the subway system can have a significant influence on the groundwater environment of Seoul.

• Journal of the Korean Geotechnical Society
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• v.26 no.11
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• pp.5-15
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• 2010

Debris flow is defined as water mixture flow with wide range of large size soil particles such as rock, gravel and sand. Localized heavy rain, derived from abnormal weather, results in the debris flow which generally occurs in summer, especially during and after rainy season and typhoon. This study focuses on the characteristics of impact force of the debris flow with different gravels and gravel mixtures by model experiment. Based on measured experiment results, it is found that the impact force derived by debris flow is mot proportional to the amount of dry material mixture, but depends on the particle size distribution of the debris flow.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.87-90
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• 2003

In this paper, flow characteristics of plasma flow in a micro-tube were investigated experimentally using Micro-PIV. For comparision, the experiments were repeated for DI-water instead of plasma. Both velocity profiles of Plasma and DI-water are well agreed with the theoretical velocity distribution of newtonian fluid. We also carried out generating plasma-in-oil droplet formation at a Y-junction microchannel. In order to clarify the hydrodynamic aspects involved in plasma droplet formation. Rhodamin B were mixed with plasma only for visualization of plasma droplet.

• Journal of Korea Water Resources Association
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• v.52 no.4
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• pp.291-300
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• 2019

If pipes are damaged in a water distribution network (WDN), adjacent valves are closed to isolate the pipes for repair. Due to the closed valves, parts of WDN are isolated from water supply sources. The isolated area is divided into Intended Isolation Area (IIA) and Unintended Isolation Area (UIA). The IIA occurs by intention to isolate the damaged pipe, while UIA is unintentionally disconnected from the sources due to IIA. Thus, the extension of isolated area and suspended flows are mainly affected by number and location of installed valves in WDN. In this study, optimization models were developed to determine optimal valve locations in WDN. In a single-objective model, total water supply suspension is minimized, while a multi-objective model intends to simultaneously minimize the suspended flow and valve installation cost. Optimal valve placement results obtained from both models were compared and analyzed using a sample application network.

• Journal of Korea Water Resources Association
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• v.37 no.11
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• pp.915-927
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• 2004

The purpose of this paper is to estimate the instream flow of the South Han River Basin to ensure an adequate supply of suitable quality of water for preservation and enhancement of aquatic ecosystems. Proposed methods is Physical Habitant Simulation System of Instream Flow Incremental Methodology. Accurate estimation on a water depth and a velocity distribution was acquired by applying a two dimensional hydrodynamic model for a simulation of a hydraulic parameter necessary for the habitat evaluation to be used in a physical habitat simulation system. The Habitat Suitability Criteria with the application of univariate curve on zacco platypus as a representative fish was able to be established by conducting a field investigation. The establishment of a hydrological materialistic balance between upper and lower streams was confirmed by conducting a simulation simultaneously together with a mainstream section, which was excluded from the considered sections for the inhabitation evaluation of fish.