• 한국환경과학회지
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• 제3권1호
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• pp.39-47
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• 1994

Dispersion characteristics of air pollutants in the mountainous coastal area are investigated in considering with the mesoscale local circulations using a two dimensional numerical model with two kinds of topograpy of 500m and 300m. In the model, land-sea breezes and mountain-valley wind are mainly considered under the condition of the absence of large scale prevailing flow in the circulation analysis, and the pollutants dispersion is traced by the Lagrangian methods. According to the results, the wind velocity is affected by topography and is stronger in the case of 500m height mountain than that of 300m, the Pollutants that source is near the coast transported over the mountain and dispersed to behind inland area. It is classified that the topography change control affects the wind velocity and the circulations. The pollutants that source is different transported and concentrated to behind inland and/or diffused to the sea area by the combination of the wind system with topographic changes. The results can be applied to the air pollution control with the arrangement design of industrial area and the planning of coastal developments.

• 한국대기환경학회지
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• 제23권2호
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• pp.214-224
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• 2007

A three-dimensional computational fluid dynamics (CFD) model with the renormalization group (RNG) $k-{\varepsilon}$ turbulence model is used to examine the effects of difference in building height on flow and pollutant dispersion in asymmetric street canyons. Three numerical experiments with different street canyons formed by two isolated buildings are performed. In the experiment with equal building height, a portal vortex is formed in the street canyon and a typical recirculation zone is formed behind the downwind building. In the experiment with the downwind building being higher than the upwind building, the ambient flow comes into the street canyon at the front of the downwind building and incoming flow diverges strongly in the street canyon. Hence, pollutants released therein are strongly dispersed through the lateral sides of the street canyon. In the experiment with the upwind building being higher than the downwind building, a large recirculation zone is formed behind the upwind building, which is disturbed by the downwind building. Pollutants are weakly dispersed from the street canyon and the residue concentration ratio is largest among the three experiments. This study shows that the difference in upwind and downwind building height significantly influences flow and pollutant dispersion in and around the street canyon.

• Asian Journal of Atmospheric Environment
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• 제11권3호
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• pp.153-164
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• 2017

Odor dispersion around a cubic building from rooftop odor emissions was investigated using computational fluid dynamics (CFD). The Shear Stress Transport (here after SST) $k-{\omega}$ model in FLUENT CFD code was used to simulate the flow and odor dispersion around a cubic building. The CFD simulations were performed for three different configurations of cubic buildings comprised of one building, two buildings or three buildings. Five test emission rates were assumed as 1000 OU/s, 2000 OU/s, 3000 OU/s, 4000 OU/s and 5000 OU/s, respectively. Experimental data from wind tunnels obtained by previous studies are used to validate the numerical result of an isolated cubic building. The simulated flow and concentration results of neutral stability condition were compared with the wind tunnel experiments. The profile of streamline velocity and concentration simulation results show a reasonable level of agreement with wind tunnel data. In case of a two-building configuration, the result of emission rate 1000 OU/s illustrates the same plume behavior as a one-building configuration. However, the plume tends to the cover rooftop surface and windward facet of a downstream building as the emission rate increases. In case of a three-building configuration, low emission rates (<4000 OU/s) form a similar plume zone to that of a two-building configuration. However, the addition of a third building, with an emission rate of 5000 OU/s, creates a much greater odorous plume zone on the surface of second building in comparison with a two-building configuration.

• 한국응용과학기술학회지
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• 제30권3호
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• pp.540-550
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• 2013

Various efforts have been explored to save the cost in many industrial fields. In order to recover the residual thermal energy from the flue gas, an extreme high efficiency heat exchanger is planning to install at a power plant. The gas temperature will be reduced to $40^{\circ}C$ from $115^{\circ}C$. Thus gas buoyancy decreases, and dispersion of nitrogen oxides is expected to deteriorate as increasing relative humidity. In this study, the conversion of nitrogen monoxide to nitrogen dioxide and dispersion regime are investigated through computational modeling. Nitrogen dioxide which indicates 0.1 ppm at 85 m from the ground could be propagated to 620 m at $115^{\circ}C$ of the flue gas, whilst when cooled down to $40^{\circ}C$, it expands up to 750 m. The ground level influence area showed more expansion of dispersion, approximately to 930 m.

• 대기
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• 제21권1호
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• pp.95-108
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• 2011

The effects of an apartment complex on flow and pollutant dispersion in an urban area are numerically investigated using a computational fluid dynamics (CFD) model. The CFD model is based on the Reynolds-averaged Navier-Stokes equations and includes the renormalization group k-${\varepsilon}$ turbulence model. The geographic information system (GIS) data is used as an input data of the CFD model. Eight numerical simulations are carried out for different inflow directions and, for each inflow direction, the effects of an apartment complex are investigated, comparing the characteristics of flow and dispersion before and after construction of the apartment complex in detail. The observation data of automatic weather system (AWS) is analyzed. The windrose analysis shows that the wind speed and direction after the construction of the complex are quite different from those before the construction. The construction of the apartment complex resulted in the decrease in wind speed at the downwind region. It is also shown that the wind speed increased partially inside the apartment complex due to the channeling effect to satisfy the mass continuity. On the whole, the wind speed decreased at the downwind region due to the drag effect by the apartment complex. As a result, the passive pollutant concentration increased (decreased) near the downwind region of (within) the apartment complex compared with that before the construction.

• 대한토목학회논문집
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• 제7권4호
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• pp.147-157
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• 1987

대류 분산 모형의 유한 차분 방법으로 양해법, Bresler방법, 음해법, upstream차분법과 Chaudhari방법등을 선택하여 각 차분법들의 특성을 규명하고 수치실험을 통하여 이들의 효율적인 사용 방안을 제시하였다. 비교 분석 결과 Chaudhari방법은 수치 분산 현상에 가장 둔감한 반면 조건부 안정이고, Bresler방법은 overshooting에 민감한 반면 무조건 안정이라는 특성이 있다. 분산이 지배적인 흐름에서는 양해법이 가장 정확하고, 대류가 지배적인 흐름에서는 Chaudhari방법이 가장 정확하다. 계산 시간(CPU)은 양해법 또는 Chaudhari방법이 비슷하게 가장 작고 Bresler방법이 항상 가장 크다.

• Journal of the Optical Society of Korea
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• 제17권5호
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• pp.433-440
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• 2013

We present an experimental and numerical study of spectral profiles of effective group indices of hydrogenated amorphous silicon (a-Si:H) waveguides and of their chromatic-dispersion effect on the four-wave-mixing (FWM) signal generation. The a-Si:H waveguides of 220-nm thickness and three different widths of 400, 450 and 500 nm were fabricated by using the conventional CMOS device processes on a $2-{\mu}m$ thick $SiO_2$ bottom layer deposited on 8-inch Si wafers. Mach-Zehnder interferometers (MZIs) were formed with the a-Si:H waveguides, and used for precise measurement of the effective group indices and thus for determination of the spectral profile of the waveguides' chromatic dispersion. The wavelength ranges for the FWM-signal generation were about 45, 75 and 55 nm for the 400-, 450- and 500-nm-wide waveguides, respectively, at the pump wavelength of 1532 nm. A widest wavelength range for the efficient FWM process was observed with the 450-nm-wide waveguide having a zero-dispersion near the pump wavelength.

• 지구물리와물리탐사
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• 제3권2호
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• pp.39-47
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• 2000

복잡한 지층구조에 대한 파동방정식의 해를 유한 차분법을 이용하여 구하는것은 많은 컴퓨터 계산시간과 기억 용량이 필요하다. 컴퓨터 계산시간과 기억용량은 최소 파장당 격자수를 줄이므로써 감소 시킬 수 있지만 수치분산으로 인해 정확도가 떨어지게 마련이다. 본 연구에서는 정확도를 유지하면서 파장당 격자수를 줄이는 방법으로 이용되고 있는 가중평균법을 최대 169점 까지 확장하여 주파수 영역에서 음향파동방정식의 해를 유한차분법으로 구할 때 최소 격자수를 구하기 위한 격자분석을 실시하였다. 지금까지 수치오차가 정확도 $1\%$내에 존재하기 위해서는 일반적인 5점을 이용하는 경우 파장당 격자수가 13개 이상이 필요하고, 9점의 경우 9개, 25점에서는 3개, 49점에서는 2.7개 이상이 필요하였다. 본 연구에서 정확도를 유지하기 위한 최소격자수를 결정하기 위해 실시된 격자분석 결과 81점에서는 2.5개 121점에서는 2.3개 그리고 169점에서는 오차 한계를 벗어나 가중평균 계수를 구할 수 없었으며 격자수를 2개까지 줄일 수 없음을 알 수 있었다. 또한 격자분석을 통해 가중평균에 적용되는 격자수가 증가할수록 정확도는 증가하지만 차분식 자체가 증가하여 매우 복잡하게 된다.

• 한국환경과학회지
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• 제11권9호
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• pp.897-905
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• 2002

A three-dimensional photochemical air pollution model considered advection, dispersion, photochemical reactions, and precipitation processes was developed. The calculated results of meteorological observation clearly exhibited geographical effects of Gwangyang Bay, in which land and sea breezes, mount-valley winds and local circular winds occurred. The observed results of daytime NOx concentrations were slightly higher than the calculated NOx concentrations in Yosu industrial complex, Gwangyang iron mill, and container yard. Eventually, the calculated NOx results generally agreed well with the observed ones.

• 한국콘텐츠학회논문지
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• 제7권1호
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• pp.124-130
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• 2007

네모 동축선은 동축선과 도파관을 연결하는 대표적인 천이구조이다. 또한 TEM 셀은 DUT의 EMC 측정을 위해 광범위하게 사용되는 소자이다. 네모 동축선과 TEM 셀의 동작을 정확히 예측하기 위해서는 네모 동축선과 TEM 셀의 분산관계 해석이 필수적이다. 본 논문에서는 TEM 모드에 대한 분석을 기반으로 고차 모드인 TE와 TM 모드에 대한 분산관계를 단순하면서도 정확한 방법을 이용해 유도한다. 모드정합법과 그린 함수를 이용하여 네모 동축선과 TEM 셀의 분산관계를 해석적으로 정확히 다룬다. 이를 위해 네모 동축선의 구조를 4개의 L블록으로 나누고 중첩의 원리를 사용하여 전체 전자장 표현식을 쉽게 구한다. 분산관계 수렴성을 파악하기 위해 수치해석을 행하고 FDTD 결과와 비교한다.