• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.8
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• pp.449-455
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• 2019

The increase in impermeable pavement from recent urbanization has resulted in an increase in surface runoff. The surface runoff has also increased the burden of the existing drainage system. This drainage system has structural limitations in that the catchment area is reduced by the waste particles transported with the surface runoff. In addition, the efficiency of the drainage system is decreased. To overcome these limitations, a new type of drainage system with a drainage layer was developed and applied. In this study, various volume porosity and permeability of the lower drainage layer were simulated using ANSYS CFX, which is a three dimensional computational fluid dynamics program. The results showed that the outlet velocity of the 35% volume porosity was faster than that of the 20% and 50% cases, and there was no relationship between the volume porosity and drainage performance. The permeability of the drainage layer can be determined from the particle size of the material, and a simulation of five conditions showed that 2 mm sand grains are most suitable for workability and usability. This study suggests appropriate values of the volume porosity and particle size of the drainage layer. This consideration can be advantageous for reducing and preventing flood damage.

• Journal of the Korea Organic Resources Recycling Association
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• v.16 no.1
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• pp.46-52
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• 2008

Oils and chlorinated solvents leaking to the subsurface are entrapped in the soil pore and these are called as nonaqueous phase liquids (NAPL). NAPL entrapped in porous media acts as a continuous source for surface and ground water contamination. This study visualized dissolution of trichloroethylene (TCE) entrapped in porous media and quantified the velocity of TCE dissolution using an image analysis technique. As the water velocity increased, the level of dissolution increased. The results imply that a TCE contaminated region having a high infiltration rate and groundwater velocity may result in severe groundwater contamination. Microscopic images of TCE entrapped in porous media showed that TCE present in the preferential flow paths was easily dissoluted into the water phase. However, TCE present in the stagnant flow region was visualized for long time. The results imply that TCE would be still present in the soil if TCE is detected in goundwater.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.388-388
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• 2021

하천에서 호안이나 교량의 교각 등은 홍수 시 주변 하상의 세굴에 의한 피해가 많이 발생한다. 하상보호를 위해서 하천 수공구조물 주변 하상에 자갈, 호박돌, 전석 등을 깔기도 한다. 이 재료들은 다공성 집단을 이루며 유수에 의한 소류력과 항력이 작용한다. 다공성 집단체 공극의 흐름에 의한 항력은 외부 흐름이 가하는 소류력에 비해 작으나 집단의 안정성에 큰 영향을 미칠 수 있다. 집단체에 작용하는 항력은 공극 내의 흐름의 유속과 항력계수를 이용하여 구할 수 있다. 본 연구에서는 다공성 매질 내 흐름에 대한 항력계수를 조사하기 위하여 수리실험을 이용하여 자갈 매질의 공극을 흐르는 물이 일으킨 항력과 동수경사를 측정하였다. 수리실험을 위한 대공극 매질은 상업용 연마 자갈을 사용하여 크기에 따라 작은 자갈(5~10mm), 중간자갈(15~25mm), 큰 자갈(25~50mm)로 구분하였다. 대표입경 D₅₀은 작은 자갈 8.0 mm, 중간 자갈 17.6 mm, 큰 자갈 32.2 mm이고, 형상계수는 각각 0.28~0.74, 0.29~0.58, 0.38~0.68의 범위였다. 자갈 매질의 공극율은 각각 0.405~0.422이었다. 매질 내의 흐름 길이는 24.2cm로 하였다. 실험결과 자갈 매질 내 흐름의 입자 레이놀즈수 Re_p에 따른 내부항력 F_D와 항력계수 C_D는 Fig. 1 및 Fig. 2와 같다. 실험에서 Re_p는 31.5~3,175.4였다. 자갈 매질의 내부항력은 Re_p가 증가하면 비선형적으로 증가하였으며 입자가 클수록 작았다. 항력계수는 작은 자갈과 중간 자갈 매질에 차이가 거의 없었으나 큰 자갈의 경우 작은 것으로 나타났다.

• Journal of Korea Water Resources Association
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• v.48 no.7
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• pp.535-543
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• 2015

Measurements of multiphase flows containing bubbles have been limited because most existing methods target one phase flows. Especially, multiphase flows with a high void ratio have been rarely successful in measurements due to the sudden change of density and thick interfaces between air and water. This study introduces two methods that are capable of measuring flow fields regardless of bubble void ratio, named bubble image velocimetry and bundle fiber optic flow meter. The calculation of the depth of field is suggested to reduce and estimate errors by perspective image velocimetry. The bundle fiber optic flow meter is designed to increase a measurement rate using many optical fibers with a thin diameter. The two methods measured bubble plumes to test reliability and the velocity measurements show good agreement. In addition a hydraulic jump, one of the multiple flows in rivers was measured to test applicability of the methods.

• Journal of Korea Water Resources Association
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• v.37 no.2
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• pp.87-96
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• 2004

The simulation results using i- V relationship of non-Darcy flow through tide embankment by Li et al.(1998) agree well to the observed data. The use of i- V relationship is applicable to the engineering practice and the correct input of porosity is necessary. The non-Darcy flow based on the pipe flow and Taylor's definition for mean hydraulics radius in rockfill material is applicable to the block and caisson materials. The correct calculation of flow through tide embankment enables the accurate calculation of velocity at final closing gap and the prediction of inner water level after tide embankment construction as well.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.286-286
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• 2011

강원도 평창군 대관령면 횡계리에 위치한 고랭지 밭 2개소를 2009년 3월부 2009년 12월까지 유출이 발생한 강우사상에 대하여 모니터링하고, 유출량을 비교하였다. 모니터링 지점 A에는 콘크리트 배수로가 설치되어있어 밭에서 발생한 강우유출수가 유입되면 빠르게 하천으로 배수되기 때문에 17.2 mm ~ 36.2 mm의 강우에도 유출이 발생하였다. 모니터링 지점 B는 콘크리트 배수로로 유입되기 전 자연(흙) 배수로가 존재하기 때문에 밭에서 발생한 강우유출수가 자연(흙)배수로로 침투되어 적은 강우에서는 유출이 발생하지 않고, 60 mm 이상의 강우에서만 유출이 발생하였다. 특히 7월 9일 발생한 강우에 의하여 모니터링 지점 B의 자연(흙) 배수로가 토사로 메워졌으며, 메워진 토사에 의해 자연(흙)배수로의 기능을 상실한 후부터 지속적으로 유출되었다. 이는 자연(흙) 배수로의 관리가 매우 중요하다는 점을 더욱 강조시키는 결과이며, 강우 발생 후 토사의 제거 등의 관리가 이루어졌다면 강우유출수와 비점오염물질의 유출이 더욱 감소하였을 것으로 판단된다. 자연(흙) 배수로는 식생에 의해 강우타격력과 유속이 작아지기 때문에 자연(흙)배수로의 공극이 막히는 현상이 줄어든다. 공극 막힘 현상이 줄어들면 토양 침투력이 보호되어 강우유출수가 저감된다. 강우유출수의 감소는 비점오염물질의 유출도 저감시킬 수 있는 것을 의미한다. 따라서 고랭지 밭 지역의 최적관리방안으로 무분별한 콘크리트 배수로의 설치보다는 자연(흙) 배수로의 유지와 관리에 초점이 맞추어져야 할 것으로 판단된다.

• Journal of Korea Water Resources Association
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• v.50 no.5
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• pp.325-334
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• 2017

In this study, the numerical investigation of the non-linear behavior of the fluid flow with physical properties, such as porosity and intrinsic permeability of a porous medium, and kinematic viscosity of a fluid, are carried out. The applied numerical model is ANSYS CFX which is the three-dimensional fluid dynamics model and this model is verified through the application of existing physical and numerical results. As a result of the verification, the results of the pressure gradient-velocity relationship and the friction coefficient-Reynolds number relationship produced from this study show relatively good agreement with those from existing physical and numerical experiments. As a result of the simulation by changing the porosity and intrinsic permeability of a porous medium and the kinematic viscosity of a fluid, the kinematic viscosity has the biggest effect on the non-linear behavior of the fluid flow in the porous medium.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1044-1048
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• 2010

해수를 이용한 세계최초의 해수수로인 송도 신도시 중앙공원 해수수로는 서해안에서 집수된 해수를 $5{\mu}m$의 공극 크기를 가지는 해수처리시설 (STF, seawater treatment facility)에 의해 여과된 뒤 2곳의 해수공급 지점에서 해수수로로 공급된다. 여과된 해수는 수로로 155L/sec의 유량으로 1.8km를 흐른 뒤 서해로 방류된다. 이러한 인공 해수수로에서는 흐름정체에 따른 수질 문제와 영양염에 의한 적조를 유발하는 조류 성장이 문제가 된다. 따라서 본 연구에서는 3차원 수치모형을 이용한 인공 해수수로내의 흐름특성 모의와 수질 모니터링의 통한 조류 생성 특성 및 장소를 비교하여 그 상관성을 분석하고자 한다. 수치모의 실험은 3차원 수치모형인 FLOW-3D를 이용하였으며, 격자망 형태는 직사각형 직각 격자가 사용되었다. 현장 모니터링을 통하여 획득한 수질 데이터와 비교 분석을 통하여 해수수로 내 해수 흐름 특성변화(유속, 와도 등)와 조류생성에 미치는 영향을 비교 분석하였다. 해수 수로내의 평균 유속은 0.01m/s 이었으며, 수로의 형상에 따라서 정체수역이 발생하였다. 이러한 정체수역은 현장 모니터링을 통하여 예측된 조류 발생 지역과 일치하였다. 이러한 흐름 특성과 조류생성과의 상관성 규명을 통하여 인공수로의 물순환 시스템 설계시 조류 생성을 억제할 수 있는 최적 관리를 위한 설계의 기초 자료를 제공할 수 있을 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.384-384
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• 2017

In this study, the numerical investigation of nonlinear flow in a porous medium was carried out. The applied numerical model is ANSYS CFX which is a three-dimensional fluid dynamic model, and the verification of this model was carried out by using the experimental data obtained from Mayer et al works(2011). The experimental and numerical results of velocity and Reynolds number-friction coefficient relationship show relatively a good agreement. Based on the experimental results, we analysed numerically the velocity and Reynolds number-friction coefficient relationship with the variation of permeability, dynamic viscosity and porosity and quantitatively the variation by applying the best curve fitting for each case.

• Journal of the Korea Organic Resources Recycling Association
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• v.20 no.3
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• pp.71-82
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• 2012

Common bulking agents in composting system include woody materials such as sawdust and woodchips. These bulking agents are mainly used for the purpose of the proper control of C/N ratio and moisture content in the composting. The topic for the effect on air permeability of bulking agents has far received relatively little attention in the composting field. This study investigated the effect of bulk density, moisture content, air-filled porosity, particle size and air flow rate on air permeability of several mixture ratios of sawdust and woodchip bulking agent. Increasing the moisture contents, the air-filled porosity was decreased and the particle size was increased for all kinds of bulking agent mixtures. Especially, with the increasing of mixing ratio of woodchip, these effects were sharply magnified. The air permeability respond to air-filled porosity was very similar to that for moisture content which was anticipated the linear relationship between air-filled porosity and moisture content. Above the region of moisture content 0.25 or 0.43(d.b.)(20 or 30% w.b.), the pressure drop decreased even though air-filled pore spaces were filling with water. Especially, to the particle size of 5 mm the pressure drop was decreased exponentially, so the air permeability was dramatically improved. By the water had the role of binding of the small particles, the macropores less resistances to air flow were created in the matrix. The effect of particle size on air permeability was much stronger than that of air-filled porosity or moisture content. And it is needed the preparing of initial particle size above 5 mm for efficient composting.