• 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.

• 한국화재소방학회논문지
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• 제22권1호
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• pp.16-23
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• 2008

본 연구에서는 도로터널에서의 화재발생 시 최적의 방재시스템을 구축하기 위하여 실제 터널의 축소모형을 대상으로 제트팬의 위치 및 운전방식에 따른 연기의 유동 및 교란을 가시화함으로서 연기의 전파특성을 고찰하여 제트팬 운전방식의 타당성을 연기의 농도 분포에 의하여 검토하였다. 실험 결과로 화원으로부터 상류방향으로 근접한 제트팬 운전 시에는 연기의 역류를 방지하기위하여 화원과 제트팬의 거리는 최소 50 m이상 이격시켜야 한다. 반면에 화원으로부터 하류방향으로 근접한 제트팬 운전 시에는 모든 조건에 대하여 연기의 편류가 발생하지 않으나 하류방향으로 흐르는 연기의 성층화에 영향을 주기 때문에 사용이 불가능하다.

• 한국태양에너지학회 논문집
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• 제29권2호
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• pp.31-38
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• 2009

This study was conducted to forecast inner water temperature strata change by extracting deep water from a dam. For the methodology, the scope wherein the balance between the volume of low-temperature water intake through the virtual water intake opening as installed within the stored water area and the volume of water intake from the surrounding area is not destroyed was calculated through the CFD simulation technique using the computational fluid dynamics(CFD) interpretation method. This study suggested a supplementary method(diffuser) to avoid destroying the water temperature strata, and the effect was reviewed. In case of intake of the same volume, when the velocity of flow of water intake is reduced by increasing the pipe diameter, the destruction of water temperature strata can be minimized. When the area(height) where the intake of water is possible is low, a diffuser for interrupting the vertical direction inflow should be installed to secure favorable water intake conditions in case of water intake on the upper part. This study showed that there was no problem if the intake-enabled, low-temperature area was secured approximately 10m from the bottom when the scope that does not destroy the water temperature strata in case of water intake was forecast using the regression formula.

• Ocean and Polar Research
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• 제44권1호
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• pp.1-11
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• 2022

Hypoxia can affect water-atmosphere methane flux by controlling the production and consumption processes of methane in coastal areas. Seasonal methane concentration and fluxes were quantified to evaluate the effects of seasonal hypoxia in Dangdong Bay (Gyeongsangnamdo, Jinhae Bay, South Korea). Sediment-water methane flux increased more than 300 times during hypoxia (normoxia and hypoxia each 6, 1900 µmol m^-2 d^-1), and water-atmospheric methane flux and bottom methane concentration increased about 2, 10 times (normoxia and hypoxia each 190, 420 µmol m^-2 d^-1; normoxia and hypoxia each 22, 230 nM). Shoaling of anaerobic decomposition of organic matter in the sediments during the hypoxia (August) was confirmed by the change of the depth at which the maximum hydrogen sulfide concentration was detected. Shoaling shortens the distance between the water column and methanogenesis section to facilitate the inflow of organic matter, which can lead to an increase in methane production. In addition, since the transport distance of the generated methane to the water column is shortened, consumption of methane will be reduced. The combination of increased production and reduced consumption could increase sediment-aqueous methane flux and dissolved methane, which is thought to result in an increase in water-atmospheric methane flux. We could not observe the emission of methane accumulated during the hypoxia due to stratification, so it is possible that the estimated methane flux to the atmosphere was underestimated. In this study, the increase in methane flux in the coastal area due to hypoxia was confirmed, and the necessity of future methane production studies according to oxygen conditions in various coastal areas was demonstratedshown in the future.

• 한국수소및신에너지학회논문집
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• 제34권2호
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• pp.155-161
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• 2023

Recently, a study on alternative and renewable energy is being conducted due to energy depletion and environmental problems. In particular, a hydrogen has the advantage of converting and storing the remaining energy into water-electrolyzed hydrogen through renewable energy generation. In general, due to reasons such as insulation problems, a study on high-pressure hydrogen storage tanks and related parts has recently been conducted. However, in the case of liquid hydrogen, the volume can be reduced by about 800 times or more compared to high-pressure hydrogen gas, so the study on this is needed as a technology that can increase energy density. In this study, the evaporation characteristics were analyzed under fixed heat flux conditions for liquid hydrogen storage tanks and the change in thermal stratification according to sloshing was analyzed. The heat flux condition was fixed at 250 W/m² and the horizontal resonance frequency of the primary mode was applied to the storage tank. As a result, it was confirmed that the thermal stratification phenomenon decreased compared to the case where the slashing was not present due to forced convection when the slashing was present.

• 한국환경과학회지
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• 제24권5호
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• pp.647-655
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• 2015

In this study, to targeting Songpa of Seoul, were analyzed the effect on the noise mitigation in roadside buffer green spaces. Noise of Songpa Street buffer green space was determined to be higher during the day than at night. In addition, it was most of 60 db or more. However, the noise reduction function of the buffer green was not greatly affected by time. In the case of noise reduction rate, during the day time it was the order of the mounding type (18.14%)> plain type (5.73%)> slope type (4.08%), And, in the case of night time, it was the order of the mounding type (11.29%)> slope type (10.22%)> plain type (4.42%). Noise reduction rate, all of the daytime, was the highest in the mounding type. As a result of the factors on the amount of reduction of noise, More physical structure is mounding type, green structure is the stratification of green space, and the number of individuals is large, the higher the tree planting density, it is determined that the noise reduction effect is high. Also, factors affecting the noise reduction effect of the day and night were different.

• 한국항공운항학회지
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• 제30권2호
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• pp.44-54
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• 2022

An empirical analysis was conducted on the workload of helicopter pilots flying in high-risk flight environments such as ground obstacles and weather effects at low altitudes. To evaluate the workload, an independent sample t-test was performed using the NASA-TLX evaluation method most suitable for the aviation field, and the workload score was calculated by applying the analytical stratification method (AHP) to compare and analyze private and commercial pilots. There is a significant difference in mean between private and commercial pilots and the result of work load was obtained over 70%. This paper studied the 'surprise and startle effect' on the helicopter field for the first time. In the future, it is intended to contribute to the safe operation of helicopters by presenting a method for effective safety management by utilizing it in the field of education and training for helicopter pilots and providing basic data for preventing accidents caused by human error.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권3호
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• pp.101-107
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• 2007

Indoor air quality becomes of a concern recently in view of human health. This study investigates the air diffusion performance and the air change efficiency of a classroom, when outdoor air is introduced in two different ways in addition to the heating/cooling operation of a ceiling-mounted heat pump. A CFD analysis has been performed to investigate the effect of the discharge angle of the air jets from the heat pump for both parallel and series types of outdoor air system. It is observed that the series type creates more uniform indoor environment compared to the parallel type in general. It can be concluded the discharge angle should not be larger than 40o for the parallel type, in order not to generate thermal stratification in the room.

• 한국양식학회지
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• 제14권1호
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• pp.43-50
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• 2001

To study the effect of paddle wheel on water circulation, velocity components were measured in shrimp ponds both along the longitudinal direction from a single paddle wheel and at 25 grid points of two ponds, which have mean water depth of 1.2m and aspect ratio (length/width) 1.05 and 0.68, respectively. An analysis of factors related to water quality and circulation showed that I) a single paddle wheel has an effective distance of 33m for de-stratification, 16m for particulate suspension and 25m for removal of organic material, dispersion of DO and prevention of bed sediment disturbance and ii) with doubling the number of paddle wheels at the pond corners, the flow speed increased by 13% over the ponds, while it reduced by 8.5% around the pond centres. Contrary to expectation, increasing the number of paddle wheel did not generate strong circulation around the pond centre and improve water quality.

• Journal of Ginseng Research
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• 제6권1호
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• pp.56-66
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• 1982

The effects of various dehiscent application such as dehiscent materials (big chaffs, vermiculite etc.), growth regulators and agricultural chemicals (plant protector.) on stimulation of dehiscence and shortening of dehiscent period were investigated Results obtained were as follows : 1. The moisture content of endosperm and seed coat at 10 day after dehiscent application amounts between 40% and 50%. 2. Endosperm diameter was increased with time of stratification, and the embryo growth showed in linear function, 3. Non-dehiscent seed showed also normally development of embryo, and the property of dehiscence dependent from physico-chemical nature of ginseng seed coat. 4. The best dehiscent materials were big chaffs and followed vermiculite, sand and sand with big chaffs. 5. The effect of dehiscence of ginseng seed showed higher activity in fungi than in bacteria in general. 6. Agricultural chemicals ( plant Protector) reduced the dehiscent rate of ginseng seed 7. The best timing of dehiscent treatment was between August 1 and August 10 but the smaller amount of dehiscent rate after August 10 dehiscent appllication indicated that big chaffs and growth regulator treatment may be controlled shortening of dehiscent period of ginseng seed.