• 한국환경과학회지
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• 제23권7호
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• pp.1223-1232
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• 2014

Density currents have been easily observed in environmental flows, for instance turbidity currents and pollutant plumes in the oceans and rivers. In this study, we explored the propagation dynamics of density currents using the FLOW-3D computational fluid dynamics code. The renormalization group (RNG) $k-{\varepsilon}$ scheme, a turbulence numerical technique, is employed in a Reynold-averaged Navier-Stokes framework (RANS). The numerical simulations focused on two different types of intrusive density flows: (1) propagating into a two-layer ambient fluid; (2) propagating into a linearly stratified fluid. In the study of intrusive density flows into a two-layer ambient fluid, intrusive speeds were compared with laboratory experiments and analytical solutions. The numerical model shows good quantitative agreement for predicting propagation speed of the density currents. We also numerically reproduced the effect of the ratio of current depth to the overall depth of fluid. The numerical model provided excellent agreement with the analytical values. It was also clearly demonstrated that RNG $k-{\varepsilon}$ scheme within RANS framework is able to accurately simulate the dynamics of density currents. Simulations intruding into a continuously stratified fluid with the various buoyancy frequencies are carried out. These simulations demonstrate that three different propagation patterns can be developed according to the value of $h_n/H$ : (1) underflows developed with $h_n/H=0$ ; (2) overflows developed when $h_n/H=1$ ; (3) intrusive interflow occurred with the condition of 0 < $h_n/H$ < 1.

• 환경생물
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• 제34권2호
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• pp.73-78
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• 2016

Bhutanese forests have been well preserved and can sequester the atmospheric carbon (C). In spite of its importance, understanding Bhutanese forest C dynamics was very limited due to the lack of available data. However, forest C model can simulate forest C dynamics with comparatively limited data and references. In this study, we aimed to simulate Bhutanese forest C dynamics at 6 plots with the Forest Biomass and Dead organic matter Carbon (FBDC) model, which can simulate forest C cycles with small amount of input data. The total forest C stock ($Mg\;C\;ha^{-1}$) ranged from 118.35 to 200.04 with an average of 168.41. The C stocks ($Mg\;C\;ha^{-1}$) in biomass, litter, dead wood, and mineral soil were 3.40-88.13, 4.24-24.95, 1.99-20.31, 91.45-97.90, respectively. On average, the biomass, litter, dead wood, and mineral soil accounted for 36.0, 5.5, 2.5, and 56.0% of the total C stocks, respectively. Although our modeling approach was applied at a small pilot scale, it exhibited a potential to report Bhutanese forest C inventory with reliable methodology. In order to report the national forest C inventory, field work for major tree species and forest types in Bhutan are required.

• 환경정책연구
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• 제2권1호
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• pp.1-29
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• 2003

This paper examines the dynamics of environmental policy development in Korea by reviewing some of the ways on how the policy windows have been opened. There are a lot of theoretical arguments about the major factors influencing policy development or changes. Many scholars have believed that severe pollution accidents or salient environmental episodes might have been the main motivation of environmental policy development. This line of argument seems valid, especially with the water pollution control policy in Korea. Water pollution control programs had rapidly expanded along with the series of water pollution accidents in the tap water sources from the late 1980s to mid-1990s. However, regarding other major env. issues, various other factors have played more important roles in the development of the relevant policies. In case of air pollution control policy international sport events such as, 1986 Asian Games, 1988 Summer Olympics, and 2002 World Cup Competition, have contributed for the development. The municipal solid waste management policy partly owed its development to the introduction of local autonomy system in the mid-1990s. Even the foreign currency crisis occurring in December 1997 helped the policy paradigm shift from rigid supply-oriented to soft demand-oriented approaches. After closely looking at the dynamics of environmental policy development in Korea, this paper tries to identify the logical background of the observed outcomes.

• 한국항만학회지
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• 제14권3호
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• pp.353-360
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• 2000

In this study a drift prediction model based on fluid dynamics theory is introduced. The essential effects of environmental loads and target characteristics are taken into account from a fluid dynamics point of view. The governing equations of motion are derived from Netwon's law of dynamics. In the mathematical formulation only three degrees of freedom(surge, sway, yaw) of the drifting object are assumed and the environmental loads considered are the forces and moments by wind and current. A computer algorithm for this model is implemented to obtain the numerical result in the time domain. The preliminary tests for model verification are conducted and the results are compared with the field experiment data as well as leeway formula suggested from the field test data.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2000년도 추계학술대회논문집
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• pp.63-71
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• 2000

In this study a drift prediction model based on fluid dynamics theory is introduced. The essential effects of environmental loads and target characteristics are taken into account from a fluid dynamics point of view. The governing equations of motion are derived from Newton's law of dynamics. In the mathematical formulation only three degrees of freedom(surge, sway, yaw) of the drifting object are assumed and the environmental loads considered are the forces and moments by wind and current. A computer algorithm for this model is implemented to obtain the numerical result in the time domain. The preliminary tests for model verification are conducted and the results are compared with the field experiment data as well as leeway formula suggested from the field test data.

• 환경생물
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• 제25권2호
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• pp.158-167
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• 2007

내설악 전나무림 현황을 조사하고 이를 통하여 산림 생태계 이해방식을 비판적으로 고찰하였다. 조사는 1996년부터 2006년까지 수행된 것으로 일종의 중간보고서로 작성하였다. 임분의 수직구조 위주로 조사하였으며 비록 내설악 전나무림에 한정된 것이기는 하나 고전 천이론 보다는 Stand dynamic이 산림생태계를 설명하는데 적합하다는 것을 확인할 수 있었다.

• 한국환경과학회지
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• 제27권10호
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• pp.901-906
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• 2018

Water and oxygen are two of the most essential molecules for many species on earth. Their unique properties have been studied in many areas of science. In this study, the interaction of water and oxygen molecules was observed at the nano-scale. Using molecular dynamics, a water droplet with 30,968 water molecules was simulated. Then, 501 oxygen molecules were introduced into the domain. A few oxygen molecules were attracted to the surface of the water droplet due to van der Waals forces, and some oxygen molecules actually entered the water droplet. These interactions were visualized and quantified at four temperatures ranging from 280 to 370 K. It was found that at high temperatures, there was a higher possibility of the oxygen molecules penetrating the water droplet than that at lower temperatures. However, at lower temperatures, oxygen molecules were more likely to be found interacting at the surface of the water droplet than at high temperatures.

• 환경생물
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• 제23권2호
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• pp.93-97
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• 2005

Zooplankton dynamics were investigated based on samples collected monthly during the period between November 1998 and October 1999 at 15 stations in Gwangyang and Sachon Bay. Zooplankters were quantitatively collected with horizontal towing through the surface and oblique hauling from the bottom to surface at each station, simultaneously. A total of 88 taxa of zooplankton were distributed and 60 taxa were identified to species. Copepods showed the prosperity in species number of 52 species. Number of taxa occurred in samples hauled obliquely always showed $2\~5$ more species than those captured in the surface except for stations near the Namhae bridge. In waters near Namhae bridge, fast current seemed to mix waters vertically. Seasonally these differences were more distinct in the spring and summer than those in other seasons possibly due to the stratification in warmer seasons. In quantitative aspects, differences between two layers seemed to be obscure. Spatial and temporal variations in species diversity of copepods showed more prosperity in pelagic realm than those in the surface. Our collection carrying out in day time might be one of the important reason to cause these differences in zooplankton dynamics between two layers.

• 한국산업보건학회지
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• 제8권2호
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• pp.163-177
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• 1998

Computational Fluid Dynamics(CFD) was applied to predict air flow around the hoods : circular hoods, square hoods, and push-pull hoods. A commercially available CFD software, CFD-ACE(Ver. 4.0), was tested, which is based on the finite volume method using the ${\kappa}-{\varepsilon}$ turbulence model. Numerical results were compared with the experimental, analytical and numerical results from other studies. CFD solutions showed an excellent agreement with the previous experimental and numerical results. It is promising that CFD techniques could be applied on the variety of complex problems in the industrial ventilation engineering.

• 한국습지학회지
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• 제21권2호
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• pp.132-139
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• 2019

식생과 지하수위 사이의 양방향 상호 작용은 습지 식생의 동역학에 많은 영향을 미친다. 본 연구에서는 지하수위에 의해 영향을 받는 습지 식생의 비선형 동역학이 분석된다. 지하수위에 대한 영향은 습지 식생의 지배방정식에서 손실 항으로 설명되며, 지하수위 변화에 따라서 습지 식생이 어떻게 서로 다른 두 개의 안정적인 상태로 수렴될 가능성이 있게 되는지를 살펴보게 된다. 이러한 개념적 접근법으로부터 지하수위 변화에 따라 현재 습지에 존재하는 식생이 소멸되어 다른 식생 종으로 안정화되는 대변환에 대한 취약성이 분석된다.