• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.253-257
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• 2010

최근 들어 이상 강우 현상으로 인한 기록적인 집중 강우와 더불어 토지 이용 변화로 인해 탁수의 발생 빈도가 증가하고 있다. 강우 유출로 유입한 탁수는 저수지 내 장기간 체류하면서 하류 하천의 수질 및 수생태계 뿐만 아니라 저수지 내부의 영양단계에도 많은 영향을 준다. 특히, 성층화된 저수지의 경우 높은 영양염류 농도를 포함한 탁수는 밀도류 거동 특성을 보이면서 수평 및 수직 혼합 과정을 거치면서 국부적인 부영양화 현상과 조류의 수화 현상의 원인이 되고 있다. 따라서 대형 저수지의 수질관리에 있어 하천 유입 탁수의 밀도류 해석, 저수지의 수온 성층 구조 변화, 부유입자의 동력학적 해석이 중요한 요소로 부각되어 왔다. 본 연구에서는 소양호를 연구 대상 지역으로 선정하여 2005년과 2007년 수문 사상을 바탕으로 2차원 횡방향 수치 모형을 구축하였다. 수치모형을 통해 수온 성층 구조의 재현성을 확인하였으며, 다양한 탁수 거동 모형을 구축하여 적용성을 평가하였다. 유입수의 SS(Suspended Solid)를 단일 입경으로 가정한 TM-1 모형, SS의 입경분포에 따라 3개의 그룹(SSi)으로 구분한 TM-2 모형, 3개 그룹을 포함하면서 저수지내 탁수 장기화로 인한 탁수 저감 효과를 1차 반응상수로 매개 변수화(유기물 함량($a_0$) ${\times}$ 분해속도(${\lambda}_a$))하여 수정된 지배방정식을 적용한 TM-3 모형을 사용하였다. 각각의 탁수 거동 모형은 2005년과 2007년 수문 조건에서 수온 성층 구조를 잘 재현하였다. TM-1 모형과 TM-2 모형을 비교해보면, 탁수 중심축의 최고 탁도에 대한 예측 성능은 TM-2 모형이 우수한 결과를 나타냈었다. 하지만, 장기 탁수 모의 시 저수지 수중 잔류 SS가 지속적으로 높게 나타나 중층 탁도를 과대평가하는 경향을 보였다. TM-3 모형이 TM-2 모형에 비해 수심별 탁도 분포에 대한 중심축 탁도가 저평가되는 경향을 보였지만 저수지 내 잔류 탁도에 대한 영향 부분에서는 개선된 결과를 나타내었다. 본 연구 결과는 저수지 탁수 밀도류 해석 및 운영 시스템에 활용 될 수 있으며, 선택 취수 설비 등의 수리 구조물의 영향 평가에 활용할 수 있다.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11b
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• pp.241-244
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• 2003

2000년에 발생한 12호 태풍(Prapiroon)에 의한 성층 호수의 식물플랑크톤 군집 변화양상을 주암호의 복교지점에서 2000년 8월 30일부터 9월 29일 까지 조사하였다. 프라피룬은 복교지점에서 초속 40m의 강풍을 동반하였는데, 이 물리력은 성층으로 인해 불연속적 층을 형성하고 있던 수괴 전체를 혼합시켰다. 수체의 혼합은 격리로 인해 이질적 환경과 생물조성을 이루고 있던 층간의 혼합을 유도하여 식물플랑크톤의 우점 분류군, 종조성, 우점종을 교체시키는 요인으로 작용한 것으로 추측되었다. 식물플랑크톤의 우점 분류군은 태풍 이전의 규조류에서 녹조류로 교체되었고, 후에 남조류로 교체되었다. 우점종은 태풍 이전에는 Melosira granulata였으나 태풍 이후에는 Scenedesmus spp.와 Staurastrum sp.가 우점하는 것으로 나타났다. 개체수의 밀도는 태풍에 의한 변화가 크지 않았다. 태풍에 의해 파괴되었던 성층은 태풍 이후 재성층화 되기 시작하여 6일째엔 안정된 성층이 관찰되었다. Secchi depth는 태풍에 의해 많이 감소하였으나 수체가 안정화되면서 다시 증가하는 양상을 나타냈다. 결론적으로 태풍은 여름의 성층으로 분리된 수괴를 혼합시킬 수 있는 물리력을 가져 수서 생태계 내 생물의 동태에 영향을 미칠 수 있음을 알 수 있다.

• Journal of Environmental Science International
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• v.7 no.2
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• pp.223-232
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• 1998

The spatial characteristics of stratification In Deukryang Bay were studded using observed data and analytical models. From the description of the density structure and its the potential energy anomaly (PEA) from observed data along longitudinal direction (from the mouth to head of the bays, we found that the stratification Intensity could be changed strongly by density current effect during the spring-neap tidal cycle, and depth variation. To find out density current effect for the formation of the stratification In detail, we Implemented a diagnostic approach by using the modified analytical model including density current, tidal current, surface heating and wind stirring. The model allowed for the observed similarities for the whole domain in the bay and increased tidal mixing efficiency value s up to 0.006-0.007 as compared to the results without density current effect. We found that the density current effect was also an important key factor In determining the formation of the spatial distribution of stratification.

• Korean Journal of Ecology and Environment
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• v.38 no.1 s.110
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• pp.105-117
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• 2005

During the period of heavy rain from 2002 to 2004, the characteristics of the inflow, temporal and spatial fluctuations of high turbid water according to thermal stratification were studied on the Andong Reservoir which is the largest artificial lake in the Nakdong River basin, Korea. Thermal stratification was formed in June. Its structure determined to the pathway of inflowing turbid water and has affected by the transportation of high turbid water. Regardless of the time and amount of inflow, the high turbid water showed the shape of underflow at the riverine zone, separated from the bottom at the transition zone and moved to the lacustrine zone with the shape of density current. The plunging point depended on the time and amount of inflow. The distributions of thermal stratification and DO concentrations were changed by inflowing discharge. Two thermoclines and minimum DO layers were found out existing at metalimnion in a specific time, respectively. The layer of high turbid water which formed with the thickness of 20 m at the maximum below the depth of 15 m moved toward dam. Not settled to the bottom, the newly formed layer was discharged through the intake-outlet and dispersed into all layers by the circulation in the fall.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.85-92
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• 2001

중력이 작용하는 압축성유체를 고려함에 있어, 밀도성층 뿐만 아니라 엔트로피 성층의 고려도 중요하다. 본 연구에서 압축성격자볼츠만 유체모델을 이용한 차분계산법을 이용하여 2차원 채널에서 성층류의 전형적인 형상인 선택취수현상을 시뮬레이션 하였으며, 본 모델의 유효성을 확인하였다. 또한 비점성, 비압축성유체의 선택취수흐름과의 차이에 관해서 압축성의 관점에서 고찰하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.6
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• pp.419-423
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• 2015

The flowing caused by artificial upwelling structure occurs ascending water flowing and vortex of rear side. In this moment, plentiful nutrient in the bottom water moves to the surface of the water and makes those plankton and fishing ecology promoted so that the fishing productivity can be enhanced. In this study, the changes of the upwelling flowing is included in consideration of the conditions of stratification by using CFD. In the conclusion, the closer upwelling effect is from the artificial upwelling structure, the better effectiveness comes out. Regardless of the conditions of stratification, only the upwelling feature from the bottom to the surface was shown up. But considering the conditions of stratification, the repeated flowing feature between upwelling and downwelling was verified.

• Journal of Korea Water Resources Association
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• v.37 no.3
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• pp.219-231
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• 2004

The use of air diffuser system to ameliorate the reservoir by breaking stratification is now widespread. This study focuses on the hydrodynamic behavior of bubble plumes, which is the major mechanism of destratification and their combined effect of adjacent plumes on destratification efficiency. By introducing 2-phase Computational Fluid Dynamics(CFD) technique, we could suggest the optimal diffuser spacing having optimal destratification efficiency by simply analyzing the complex destratification procedures varying with the seasonal stratification intensity and bubble flow rate. Lab experiments were also carried out to verify CFD model in thermally stratified fresh water which quite differs from former researches using salts. This study showed that the mixing efficiency strongly depends on the spacing of neighboring plumes. When diffuser spacing is lower than 1.5 times the depth, the combined effect is stronger; as Plume Number(PN) is increased, the efficiency is strongly affected by spacing. If the distance is shorter than the depth of water, the efficiency increases linearly in proportion to PN. Otherwise, the efficiency increases non-linearly. These findings suggest that the combined effect should be more quantitatively taken into consideration for design and operation of air-diffuser destratification system, and recommend that the optimal destratification efficiency will be when plume number is 1000 and the spacing between neighboring diffusers is 1.5 times the depth.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.155-168
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• 2011

Coastal boundary current flows along the eastern boundary of the Yellow Sea and its speed was about 0.l m/s during the summer 2007. In order to find major factors that affect the coastal boundary current in the eastern Yellow Sea, three-dimensional numerical model experiments were performed. The model simulation results were validated against hydrographic and current meter data in the eastern Yellow Sea. The eastern boundary current flows along the bottom front over the upper part of slopping bottom. Strength and position of the current were affected by tides, winds, local river discharge, and solar radiation. Tidal stirring and surface wind mixing were major factors that control the summertime boundary currents along the bottom front. Tidal stirring was essential to generate the bottom temperature front and boundary current. Wind mixing made the boundary current wider and augmented its north-ward transport. Buoyancy forcing from the freshwater input and solar radiation also affected the boundary current but their contributions were minor. Strong (weak) tidal mixing during spring (neap) tides made the northward transport larger (smaller) in the numerical simulations. But offshore position of the eastern boundary current's major axis was not apparently changed by the spring-neap cycle in the mid-eastern Yellow Sea due to strong summer stratification. The mean position of coastal boundary current varied due to variations in the level of wind mixing.

• Water for future
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• v.25 no.2
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• pp.99-110
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• 1992

A problem of outlet salinity from a stratified fluid with a well developed interface thickness consisting of an upper and lower layer differing slightly in density is considered. Three kinds of apparatus were used for the experimental test and salinity differences between inlet layer and outlet discharge were estimated by the functional relationship using the dimensionless values. For the critical incipient condition of withdrawal of upper layer, Densimetric Froude number is correlated by the inlet diameter and depth ratio in the tank.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1909-1914
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• 2004

An immersed boundary method for simulation of density-stratified flows is developed and applied to computation of viscous flows over two-dimensional obstacles in a bounded domain under stable density stratification. Density sources/sinks are introduced on the body surface. Two obstacle shapes are used, a vertical barrier and a smooth cosine-shaped hill; weak stratification, defined by $K=ND/{\pi}U{\leq}1$, where U, N, and D are the upstream velocity, buoyancy frequency, and domain height, respectively, is considered. The results are consistent with other authors' calculations, and shed light on computation of density-stratified flows in complex geometries.