• 해양환경안전학회지
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• 제21권4호
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• pp.372-380
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• 2015

인공용승구조물 설치 전 후 주변해역의 하계 물리환경특성을 조사하였다. 구조물 설치 전(2002년)의 수온구조는 수심 30m에 강한 성층이 형성되었다. 한편 구조물 설치 3~4년 후(2012, 2013년)의 수온구조는 조류방향에 따라 구조물에 의한 성층의 형성수심 및 세기가 변화하였다. 이와 같은 현상은 구조물에 의한 연직류의 효과로 하계 강한 성층에 의해 저층에 분포하는 저수온수가 상승류에 의해 부상하여 성층분포에 영향을 미친 것으로 판단한다. 또한 구조물 설치 이후 연직류의 분포를 보면, 구조물 중심으로 국지적인 상승류 및 하강류가 혼재하여 나타났다. 즉 연직류는 조류방향에 따라 시 공간적인 변화를 보이면서 흐름이 진행하는 방향의 구조물 후면부에서 형성하는 상승류에 의해 성층이 약화되는 현상을 볼 수 있다. 또한 구조물에 의해 발생하는 연직류는 보다 넓은 해역으로 확장하여 발생한다. 본 연구해역에 설치한 인공용승구조물에 의해 발생하는 국지적인 용승은 한국 남동해안에 나타나는 연안 용승에 비해 유량이 100배 이상 크게 나타났다. 이와 같이 구조물에 의해 발생하는 상승류는 하계 저층에 존재하는 고농도의 영양염을 표층으로 상승시켜 주변해역의 기초생산량을 증가 시키는 역할을 가능하게 한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.723-728
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• 2001

Wind flow perturbations, recirculations and turbulence generated by buildings often dominate air pollutant distributions around buildings. This paper describes dispersion of contaminants in the vicinity of a building by solving the concentration equation based on previously simulated wind flow field. Turbulence closure is achieved by using the standard k-e two-equation model. The paper shows application of the CIP method for solving a species concentration equation of contaminant gas around a rectangular building for two different sources under conditions of neutral atmospheric stratification. Results have been compared to the experimental data and the previous numerical results by hybrid scheme. The computational results of concentration profiles by the CIP method agree well with experimental data.

• 한국전산유체공학회지
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• 제6권4호
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• pp.1-7
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• 2001

Wind flow perturbations, recirculations and turbulence generated by buildings often dominate air pollutant distributions around buildings. This paper describes dispersion of contaminants in the vicinity of a building by solving the concentration equation based on previously simulated wind flow field. Turbulence closure is achieved by using the standard k-ε two-equation model. The paper shows application of the CIP method for solving a species concentration equation of contaminant gas around a rectangular building for two different sources under conditions of neutral atmospheric stratification. Results have been compared to the experimental data and the previous numerical results by hybrid scheme. The computational results of concentration profiles by the CIP method agree well with experimental data.

• 대한기계학회논문집
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• 제18권12호
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• pp.3297-3304
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• 1994

Experimental investigation have been made to study the double-diffusive nature of convection of an initially stratified salt-water solution heated from below in a cylindrical cavity. The objective is to examine the process of mixed-layer formation, the flow phenomena, the heat transfer characteristics, and temperature and concentration distribution according to the changes in the effective Rayleigh number based on the reference height which represents the relation of temperature and concentration gradient. The types of initially formed flow pattern are categorized in three regimes depending on the effective Rayleigh number ; stagnant flow regime, single mixed-layer flow regime and successively formed multiple mixed-layer flow regime. The temperature and concentration profiles are both uniform in each layer due to convective mixing in the layered flow regime, but both linear in stagnant flow regime and single mixed-layer flow regime. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly. The layers expand by diffusion of concentration through the interface along with its random fluctuation.

• 해양환경안전학회지
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• 제5권2호
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• pp.57-65
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• 1999

The in situ observations and the seawater analyses were conducted at all seasons from July 1996 to April 1999 for the purpose of describing the characteristics of seasonal variations of water quality in Mokpo harbour, Korea. Vertical stratification started to be formed in water column in spring, developed in summer and disappeared in fall. In summer, vertical density distribution of water column was found to be in stable structure with lower temperature and higher salinity of bottom water, and the vertical mixing of water between surface and bottom layers was restricted. In winter, however, surface water was found to be similar to bottom water in temperature and salinity, and water column was in unstable structure and in well-mixed condition between surface and bottom waters. The saturation percentage of dissolved oxygen(DO) in bottom water of inner part of Mokpo harbour at all seasons was shown to be decreased to the third grade or under the third grade of Korean standards of seawater quality. In particular, dissolved oxygen was oversaturated in surface water and undersaturated in bottom water in summer, due to stratification and organic pollution. The difference of DO concentration between surface and bottom waters was found to be greater in spring and summer than in fall and winter, due to stratification and photosynthesis of phytoplankton. The concentrations of chemical oxygen demand(COD) over the entire waters of Mokpo harbour were found to fluctuate from below the third grade to the first grade of Korean standards through all seasons and COD concentrations of same seasons were shown to be different year after year. In particular, in view of COD, the annual average seawater quality of Mokpo harbour was evaluated to be in third grade of Korean standards, due to organic pollution. The average COD of surface water was greater than that of bottom water in spring and summer, due to the autochthonous COD caused by production of phytoplankton in surface waters, while the average COD of surface water was similar to that of bottom water in fall and winter, due to the vertical mixing of water between surface and bottom layers.

• Ocean and Polar Research
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• 제23권4호
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• pp.401-410
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• 2001

Global climate change will alter many such properties of the Southern Ocean as temperature, circulation, stratification, and sea-ice extent. Such changes are likely to influence the species composition and activity of Antarctic marine microorganisms (protists and bacteria) which playa major role in deter-mining the concentration of atmospheric $CO_2$ and producing precursors of cloud condensation nuclei. Direct impacts of climate change on Antarctic marine microorganisms have been determined for very few species. Increasing water temperature would be expected to result in a southward spread of pelagic cyanobacteria, coccolithophorids and others. Growth rates of many species would be expected to increase slightly but nutrient limitation, especially micronutrients, is likely to result in a negligible increase in biomass. The extent of habitats would be reduced for those organisms presently living close to the upper limit of their thermal tolerance. Increased UVB irradiance is likely to favour the growth of those organisms tolerant of UVB and may change the trophic structure of marine communities. Indirect effects, especially those as a consequence of a diminution of the amount of sea-ice and increased upper ocean stratification, are predicted to lead to a change in species composition and impacts on both trophodynamics and vertical carbon flux.

• Asian Journal of Atmospheric Environment
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• 제12권1호
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• pp.47-58
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• 2018

The aim of this work is to investigate the effect of atmospheric stability on near-field pollutant dispersion from rooftop emissions of a single cubic building using computational fluid dynamics (CFD). This paper used the shear stress transport (here after SST) k-${\omega}$ model for predicting the flow and pollutant dispersion around an isolated cubic building. CFD simulations were performed with two emission rates and six atmospheric stability conditions. The results of the simulations were compared with the data from wind tunnel experiments and the result of simulations obtained by previous studies in neutral atmospheric condition. The results indicate that the reattachment length on the roof ($X_R$) obtained by computations show good agreement with the experimental results. However, the reattachment length of the rooftop of the building ($X_F$) is greatly overestimated compared to the findings of wind tunnel test. The result also shows that the general distribution of dimensionless concentration given by SST k-${\omega}$ at the side and leeward wall surfaces is similar to that of the experiment. In unstable conditions, the length of the rooftop cavity was decreased. In stable conditions, the horizontal velocity in the lower part around the building was increased and the vertical velocity around the building was decreased. Stratification increased the horizontal cavity length and width near surface and unstable stratification decreased the horizontal cavity length and width near surface. Maintained stability increases the lateral spread of the plume on the leeward surface. The concentration levels close to the ground's surface under stable conditions were higher than under unstable and neutral conditions.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1422-1436
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• 1997

Numerical investigations were conducted to study the convective phenomena of an initially stably stratified salt water solution with lateral heating in a uniformly rotating annulus. The method of investigation is the finite difference analysis of the basic conservation equation for an axisymmetric, unsteady, double-diffusive convection and calculation is made for R $a_{\eta}$=2*10$^{5}$ and Ta=10$^{7}$ ~ 2.5*10$^{8}$ . Formation of layered flow structure, merging process of layers, the corresponding temperature and concentration distributions, Nu variation with time are examined. Numerical results show that in each layer, the temperature profile looks 'S'-shaped and the concentration profile is uniform due to the convective mixing. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly. As the effect of the rotation increases, the generation of rolls at hot wall, the formation and merging of layers are delayed. The average Nu shows the trend of conduction heat transferees the effect of the rotation increases.n increases.

• 한국해양학회지:바다
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• 제8권2호
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• pp.177-186
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• 2003

하계 진동만 저층수의 저산소화에 미치는 성층 및 바람의 효과를 고려한 수평 및연직 유동성분의 영향을 조사하여 내만역에서의 빈산소수괴 형성기구를 밝혔다. 진동만에서 수온, 염분, 용존산소 및 풍향, 풍속은 1998년 3월부터 1999년 2월 사이에 조사하였다 저층수에서 5 이하의 낮은 용존산소농도가 5월에서 9월에 걸쳐 존재하였으며, 표층수의 고온·저염화에 따라 강한 약층이 형성되어 연직기울기는 매우 크게 나타난 하계(7∼8월)에 3 이하의 극히 낮은 용존산소농도가 출현하였다. 이와 같은 저농도의 용존산소는 특히 만 안쪽 정점에서 춘계(5∼6월)에도 관찰되었다. 또한, 하계(8∼9월)에 5 이하의 낮은 용존산소농도를 가지는 저층수가 약 4∼6 m 수층까지 표층쪽으로 부상하는 특징적인 현상이 나타났다 여름철 진동만에서 바람의 효과를 고려한 잔차류의 연직성분을 살펴보면, 이 지역에서 우세한 북풍이나 서풍계열의 바람에 의해서 만 바깥쪽을 하강류역이, 만 안쪽은 상승류역이 발생한다. 또한, 하강류역인 만 바깥쪽에서 만 안쪽으로 향하는 저층류가 발달하였는데, 이것은 표층으로부터 침강된 유기물질의 만 안쪽으로의 유입을 초래할 수 있을 것으로 기대된다. 한편 말 안쪽에서 나타나는 상승류의 존재가 만 안쪽에서 형성된 저층의 빈산소수를 표층 근처까지 부상하게 하는 역할을 하는 것으로 보인다.

• 환경영향평가
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• 제3권2호
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• pp.33-45
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• 1994

Water quality of Chongju and Daejeon Water Intake Tower Region, embayments in Daechong Reservoir was found to be worse than that of main lake after analysis of water which were sampled during April, July, October in 1993. Concentration of COD and SS at those two water intake tower sites were 2.8-5.6 mg/l and 2.2-3.2 mg/l, higher than that of main lake. T-N concentration of those two sites was 1.1-1.9 mg/l similar to that of main lake, and T-P concentration of those two sites was 0.14-0.18 mg/l, higher than that of main lake. This study used water quality model of embayment which can analyse pollutant loads from stream and surrounding land use, advection, decay, and diffusion transport between embayment and main lake. The model can predict water quality of embayment according to the change of pollutant load, water elevation of embayment, quantity of water intake in order to suggest water quality management. This study suggests embayment water quality management alternatives, 1) construction of waste water treatment facilities at embayment and main lake for the decrease of pollutant loading, 2) water intake at main lake less polluted or eutrophicated than embayment, and 3) outflow elevation selection for polluted hypolimnion water outflow during stratification.