• Journal of Korean Society on Water Environment
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• v.30 no.4
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• pp.394-402
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• 2014

High-voltage dielectric discharges are an emerging technique in environmental pollutant degradation, which are characterized by the production of hydroxyl radicals as the primary degradation species. The initiation and propagation of the electrical discharges depends on several physical, chemical, and electrical parameters such as 1st and 2nd voltage of power, gas supply, conductivity and pH. These parameters also influence the physical and chemical characteristics of the discharges, including the production of reactive species such as OH, $H_2O_2$ and $O_3$. The experimental results showed that the optimum 1st voltage and oxygen flow rate for RNO (N-Dimethyl-4-nitrosoaniline, indicator of the generation of OH radical) degradation were 160 V (2nd voltage of is 15 kV) and 4 L/min, respectively. As the 2nd voltage (4 kV to 15 kV) was increase, RNO degradation was increased and, generated $H_2O_2$ and $O_3$ concentration were increased. The conductivity of the solution was not influencing the RNO degradation, $H_2O_2$ and $O_3$ generation. The pH effect on RNO degradation was not high. However, the lower pH and the conductivity, the higher $H_2O_2$ and $O_3$ generation were observed.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.1 no.1
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• pp.35-43
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• 1997

Handling the emergency problems such as Chemobyl accident require real time prediction of pollutants dispersion. One-point real time sounding at pollutant source and simple model including turbulent-radiation process are very important to predict dispersion at real time. The stability categories obtained by one-dimensional numerical model (including PBL dynamics and radiative process) are good agreement with observational data (Golder, 1972). Therefore, the meteorological parameters (thermal, moisture and momentum fluxes; sensible and latent heat; Monin-Obukhov length and bulk Richardson number; vertical diffusion coefficient and TKE; mixing height) calculated by this model will be useful to understand the structure of stable boundary layer and to handling the emergency problems such as dangerous gasses accident. Especially, this simple model has strong merit for practical dispersion models which require turbulence process but does not takes long time to real predictions. According to the results of this model, the urban area has stronger vertical dispersion and weaker horizontal dispersion than rural area during daytime in summer season. The maximum stability class of urban area and rural area are 'A' and 'B' at 14 LST, respectively. After 20 LST, both urban and rural area have weak vertical dispersion, but they have strong horizontal dispersion. Generally, the urban area have larger radius of horizontal dispersion than rural area. Considering the resolution and time consuming problems of three dimensional grid model, one-dimensional model with one-point real sounding have strong merit for practical dispersion model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.254-257
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• 2017

As a part of the development of aircraft gas turbines, combustion performance tests have been conducted in the single combustor sector. The effects of change in the amount of air supplied to the main combustion zone to the performance of the combustor, such as a pollutant emission, a liner temperature distribution and an exit temperature patterns, were studied. Emissions of CO and NOx increased with the main air-ratio and exit temperature pattern was improved. When changing the pattern of the dilution holes, it was shown that the temperature patterns on the exit plane of the combustor and the surface of liner changed depending on the main flame structure and mixing with diluent air. These observations will be applied to combustor liner designs to improve combustor durability and emissions reduction performance.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.11
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• pp.1168-1179
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• 2006

The validity of an unsteady two-dimensional(2-D) numerical hydrodynamic and pollutant dispersion model(2DNHPDM) was evaluated using the data obtained from I-sa streams in Sooncheon, Chonnam, during rain-fall run-off. Field observations was conducted for 35 hours during the 10 hours rainfall event on 7th May 2005. The water level, 2-D velocity, flow field, and COD at seven points selected along the river were measured at intervals of one hour. The model was applied to describe two-dimensional movement of dissolved pollutants in meandering non-uniform river. Major physical processes affecting the lateral and horizontal mixing of the river flow were simulated. The model was proved effective in describing the hydrodynamics and dispersion of the river pollutants from its major tributaries as well as non-point sources.

• Advances in aircraft and spacecraft science
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• v.3 no.3
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• pp.243-257
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• 2016

The increase of air traffic volume has brought an increasing amount of issues related to carbon and NOx emissions and noise pollution. Aircraft manufacturers are concentrating their efforts to develop technologies to increase aircraft efficiency and consequently to reduce pollutant discharge and noise emission. Ultra High By-Pass Ratio engine concepts provide reduction of fuel consumption and noise emission thanks to a decrease of the jet velocity exhausting from the engine nozzles. In order to keep same thrust, mass flow and therefore section of fan/nacelle diameter should be increased to compensate velocity reduction. Such feature will lead to close-coupled architectures for engine installation under the wing. A strong jet-wing interaction resulting in a change of turbulent mixing in the aeroacoustic field as well as noise enhancement due to reflection phenomena are therefore expected. On the other hand, pressure fluctuations on the wing as well as on the fuselage represent the forcing loads, which stress panels causing vibrations. Some of these vibrations are re-emitted in the aeroacoustic field as vibration noise, some of them are transmitted in the cockpit as interior noise. In the present work, the interaction between a jet and wing or fuselage is reproduced by a flat surface tangential to an incompressible jet at different radial distances from the nozzle axis. The change in the aerodynamic field due to the presence of the rigid plate was studied by hot wire anemometric measurements, which provided a characterization of mean and fluctuating velocity fields in the jet plume. Pressure fluctuations acting on the flat plate were studied by cavity-mounted microphones which provided point-wise measurements in stream-wise and spanwise directions. Statistical description of velocity and wall pressure fields are determined in terms of Fourier-domain quantities. Scaling laws for pressure auto-spectra and coherence functions are also presented.

• Journal of Korean Society on Water Environment
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• v.27 no.1
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• pp.73-87
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• 2011

An abnormal mono-specific bloom of the cyanobacterium Microcystis aeruginosa had developed at a specific location (transitional zone, monitoring station of Hoenam) in Daecheong Reservoir from middle of July to early August, 2001. The maximum cell counts during the peak bloom reached 1,477,500 cells/mL, which was more than 6~10 times greater than those at other monitoring sites. The hypothesis of this study is that the timing and location of the algal bloom was highly correlated with the local environmental niche that was controled by physical processes such as hydrodynamic mixing and pollutant transport in the reservoir. A three-dimensional, coupled hydrodynamic and ecological model, ELCOM-CAEDYM, was applied to the period of development and subsequent decline of the bloom. The model was calibrated against observed water temperature profiles and water quality variables for different locations, and applied to reproduce the algal bloom event and justify the limiting factor that controled the Microcystis bloom at R3. The simulation results supported the hypothesis that the phosphorus loading induced from a contaminated tributary during several runoff events are closely related to the rapid growth of Microcystis during the period of bloom. Also the physical environments of the reservoir such as a strong thermal stratification and weak wind velocity conditions provided competitive advantage to Microcystis given its light adaptation capability. The results show how the ELCOM-CAEDYM captures the complex interactions between the hydrodynamic and biogeochemical processes, and the local environmental niche that is preferable for cyanobacterial species growth.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.88-88
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• 2020

수심평균 2차원 혼합모형은 하천환경에서 다양한 용존성 오염물질의 혼합현상을 모의하기 위해 널리 활용되어왔다. 2차원 혼합모형에서 분산계수는 하천의 전단 흐름에 의해 야기되는 오염물질의 퍼짐 현상을 표현하는 중요한 인자로서 작용하기 때문에 정교한 오염물질 혼합거동을 모의하기 위해서는 적합한 분산계수를 산정하는 것이 필수적이다. 분산계수를 실험적으로 산정하는 방법으로는 크게 모멘트법과 추적법으로 나뉘며, 비정상상태의 혼합거동에 대해 종방향 및 횡방향 분산계수를 동시에 산정할 수 있는 방법은 추적법 계열의 2차원 유관추적법(2D STRP)이 유일하다. 본 연구에서는 하천에 유입된 오염물질의 2차원 혼합해석을 위한 수치모형을 개발하였으며, 개발된 모형의 수치해를 바탕으로 다양한 Peclet 수의 범위에 대해 기존연구에서 제시된 2D STRP의 적용범위 및 성능을 정량적으로 분석하였다. 분석된 정보를 바탕으로 기존 2D STRP의 한계를 극복하기 위한 개선된 2차원 유관추적법(2D STRP-i)을 개발하고, 사행하천을 모형화한 실규모 하천실험시설에서 검증하였다. 기존 2D STRP의 성능평가 결과, Peclet 수가 낮은 조건일수록 농도분포의 예측 정확도가 감소하는 경향을 보였으며, 하안 경계에 도달하는 농도가 증가할수록 부정확한 결과를 초래하는 것으로 나타났다. 본 연구에서는 기존 2D STRP의 한계를 보완하여 더욱 정확한 분산계수를 산정하고자 하안 경계면 조건을 고려한 2차원 유관추적법(2D STRP-i)을 개발하였다. 2D STRP-i는 직교-곡선좌표계 기반의 2차원 이송-분산 방정식을 바탕으로 횡방향 유속분포 및 하안 경계조건을 고려할 수 있도록 개선되었다. 2D STRP-i는 공간적으로 상이한 이송효과 및 하안경계 조건을 적절히 반영함으로써 농도분포의 예측 정확도를 개선 시키는 것으로 평가되었으며, 하안경계면에서 농도가 증가하는 구간에서 기존 2D STRP의 결과와 비교하여 더욱 정확한 농도분포 및 분산계수를 제공하는 것으로 밝혀졌다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.20-20
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• 2021

하천에서 유해화학물질 유출사고로 인하여 오염물질이 유입되었을 경우, 이에 대응하기 위하여 오염운의 도달시간과 농도를 예측하는 것은 매우 중요하다. 종방향의 혼합거동이 중요한 넓은 범위의 하천을 대상으로 오염물질의 이송을 예측하기 위하여 일반적으로 1차원 Fickian 모형을 사용한다. 그러나 실제 하천에서 오염물질의 농도를 측정하였을 경우, 대부분의 농도분포는 오염물질의 저장대효과로 인하여 긴 tail 부분을 갖는 왜곡된 분포를 갖게 된다. 이러한 저장대 효과는 여러 하천내의 다양한 불규칙성으로부터 발생하나, 국내 하천에 많은 보가 설치되어 있음에도 불구하고 하천 내부에 설치된 수리구조물에 의하여 발생하는 인공적인 저장대 효과에 관한 연구가 미흡한 실정이다. 따라서 본 연구에서는 실내 수리실험과 수치 모의를 통하여 노치가 존재하는 보주변에서의 흐름 특성과 오염 물질의 이송 특성을 규명하고, 이를 통해 보의 지형 및 수리적 인자가 저장대 메커니즘에 미치는 영향을 분석하였다. 수리 실험을 통한 넓은 범위에서의 수평방향 흐름장과 농도장을 측정하기 위하여 본 연구에서는 광역 계측방법인 Large Scale Particle-Image-Velocimetry (LSPIV) 기법과 Planar-Concentration-Analysis (PCA) 기법을 각각 유속과 농도 측정을 위해 적용하였다. 더 많은 보의 지형 및 수리적 조건에 따른 저장대 메커니즘을 분석하기 위하여 3차원 Reynolds-averaged Navier-Stokes (RANS) 모형을 통해 모의조건을 확장 적용하였다. 측정 및 모의 결과를 바탕으로 노치가 존재하는 보의 지형 및 수리적 인자가 저장대 메커니즘에 미치는 영향을 분석하였다. 저장대 영역 면적의 크기는 노치사이의 간격이 증가할수록 증가하였으며 노치의 높이의 경우에는 크게 민감하지 않은 경향을 나타냈다. 추적물질의 체류 시간은 노치사이의 간격과 보의 높이가 증가할수록, 유량이 감소할수록 증가하여 질량교환계수 값이 감소하는 경향을 나타냈다. 프루드 수와 레이놀드 수 모두 질량교환계수와 양의 상관 관계를 나타냈으나 저장대 영역의 면적의 크기와는 낮은 관계성을 나타냈다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2B
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• pp.161-170
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• 2006

A tracer test technique using a radioisotope was proposed to investigate pollutant mixing characteristics in rivers. The main advantages of radioisotope as a tracer in field tests are that it can be detected easily, and that its detection range is quite large. Also, using the radioisotope, the amount sorbed by the bed material and the biota may be a minimum. Field tracer tests were conducted at seven different sites in natural rivers with various meandering pattern. Based on the acquired data, the behavior of the tracer cloud in the intermediate-field was examined two-dimensionally, and dispersion coefficients were calculated using several evaluation methods. Results revealed that the tracer cloud was transported skewed to the outer bank and dispersion coefficients in bends were larger than those in straight reaches.

• Korean Journal of Environmental Agriculture
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• v.34 no.2
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• pp.91-97
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• 2015

BACKGROUND: Earthworms are essential detritus feeders that play a vital role in the process of decomposition of organic matter and soil metabolism. The complex process of partial breakdown of organic matter and mixing with mucous and gut microbial flora in the form of earthworm cast results in the reduction of the toxicity. This study focused on the change of cast amount and pollutant contents before and after the eating of the organic waste and upland soil with the two species of earthworm. METHODS AND RESULTS: The two species of earthworms were compared to the cast production. In the upland soil material, the daily amount of worm's cast was 1.42 g in E. andrei and 0.40 g in A. agrestis. In the organic waste material, the cast of E. andrei was 0.78~0.83 g and the cast of A. agrestis. have not been collected because all earthworms died after the treatment. The heavy metals treated in the upland soil were evaluated the impact of the worm excretion. With the E. andrei, the cast production was decreased 0.1~0.8 times in zinc, 0.2~0.5 times in copper, and 0.1~0.7 times in cadmium compared to the control treatment according to the levels of concentration. With A. agrestis, the cast amount was decreased 0.3~1.1 times in zinc, 0.2~0.3 times in copper, and 0.1~2.1 times in cadmium, respectively. The changes of pollutant contents before and after the eating of the organic wastes with E. andrei were studied. In the treatment of the Alcohol Fermentation Processing Sludge and the Fruit Juice Processing Sludge, heavy metal content of the cast was increased 0.7~53.3% compared to the sludge materials. PAHs contents were decreased 50.1% in the cast of the Alcohol Fermentation Processing Sludge and 36.6% in the cast of the Fruit Juice Processing Sludge, respectively. CONCLUSION: In conclusion, although the A. agrestis was bigger than E. andrei in size and weight, the cast amount of A. agrestis was small. The two species of earthworm was less excretion with high concentration of heavy metals. While the heavy metals such as zinc, copper, and cadmium were considerably accumulated in the cast, the total compounds, PAHs were fairly decomposed. There results would provide us for restoring contaminated soil and cleaning organic wastes.