• Wind and Structures
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• 제4권1호
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• pp.31-44
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• 2001

Mean concentrations of ammonia gas released as a tracer from an isolated low-rise building have been measured and predicted. Predictions were calculated using computational fluid dynamics (CFD) and two dispersion models: a diffusion model and a Lagrangian particle tracking technique. Explicit account was taken of the natural variation of wind direction by a technique based on the weighted summation of individual steady state wind direction results according to the probability density function of the wind direction. The results indicated that at distances >3 building heights downstream the weighted predictions from either model are satisfactory but that in the near wake the diffusion model is less successful. Weighted solutions give significantly improved predictions over unweighted results. Lack of plume spread is identified as the main cause of inaccuracies in predictions and this is linked to inadequate resolution of flow features and mixing in the CFD model. Further work on non-steady state simulation of wake flows for dispersion studies is recommended.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.27-34
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• 2006

In this paper, a recently proposed parallel hybrid particle-continuum (DSMC-NS) scheme employing 3D unstructured grid for solving steady-state gas flows involving continuum and rarefied regions is described [1]. Substitution of a density-based NS solver to a pressure-based one that greatly enhances the capability of the proposed hybrid scheme and several practical experiences of implementation learned from the development and verifications are highlighted. At the end, we present some simulation results of a realistic RCS nozzle plume, which is considered very challenging using either a continuum or particle solver alone, to demonstrate the capability of the proposed hybrid DSMC-NS method.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.302-305
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• 2007

During the CareBeijing campaign in September 2006, Imaging Differential Optical Absorption Spectroscopy (IDOAS) measurements were made over the city of Beijing, China using a spatial resolution of 146 pixels horizontally and 61 pixels vertically, each with a field of view of $0.133^{\circ}$ and $0.072^{\circ}$ in the horizontal and vertical directions, respectively. Using Fraunhofer reference spectra (FRS) for the evaluation of data for two consecutive days, the diurnal variation of $NO_2$ distributions was determined from data measured every single hour from 08:00 until 16:00 on September 9 and 10. Both days presented a fairly clear sky with high visibility. The setup allowed detailed images of the low surface $NO_2$ distribution over Beijing. Images with less than a 30-min temporal resolution showed variation of plume dispersal in both horizontal and vertical directions. An in-situ measurement was also conducted. Results from both instruments are interpreted by considering local emission sources and wind conditions.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.30-33
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• 2007

고고도에서의 노즐 플룸 해석에 가장 일반적으로 사용되는 CFD 기법은 DSMC 방법이다. 본 논문에서는 DSMC 방법으로 만들어진 러시아 ITAM 연구소의 SMILE 코드를 사용하여 Rothe 마이크로노즐 내부유동을 시뮬레이션 하였다. 또한, SMILE 코드 결과의 유효성(신뢰성)을 확보하기 위하여 레이놀즈 수에 따른 노즐 내부 centerline의 온도를 Rothe의 실험치와 비교하여 검증하였다.

• Bulletin of the Korean Chemical Society
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• 제34권5호
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• pp.1361-1365
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• 2013

The smallest ketenimine and hydrogen cyanide N-methylide ($CH_2CNH$ and $CH_2NCH$) are provided from the argon/acetonitrile matrix samples exposed to radiation from laser ablation of transition-metals. New infrared bands are observed in addition to better determination of the vibrational characteristics for the previously reported bands, and the $^{13}C$ substituted isotopomers ($^{13}{CH_2}^{13}CNH$ and $^{13}CH_2N^{13}CH$) are also generated. Density functional frequency calculations and the D and $^{13}C$ isotopic shifts substantiate the vibrational assignments. $CH_2CNH$ is probably produced through single-step conversion of $CH_3CN$, whereas $CH_2NCH$ through two-step conversion via 2H-azirine. Inter-conversions between these two products evidently do not occur during photolysis and annealing.

• 한국항해항만학회지
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• 제28권10호
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• pp.947-953
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• 2004

연안에서 대규모 항만개발이 단계적으로 진행되고 항만 부근역에서의 인구가 더욱 더 증가되면서 항만의 오폐수 및 도시하수의 처리방안에 대한 문제가 관심을 끌고 있다. 오폐수를 1차 또는 2차 처리한 후 수중 방류관을 통해 해안이나 심해 또는 그 중간지점에서 방류하는데, 오폐수가 방류되면 주변 해수를 연행하여 플룸, 제트 또는 부양성 제트의 형태로 해수면까지 상승하면서 크게 희석된다. 본 연구는 효율적인 해양방류시스템의 설계시 간과되어온 계절적, 공간적인 해수온도의 변화에 따른 플룸의 거동 및 희석 특성에의 영향을 다루고자 한다. 방류수의 수온 뿐 아니라 방류지점의 계절적 주변수의 온도변화를 고려하여 CORMIX-GI을 적용하였다. 결과를 방류수의 혼합역 특성을 평가하는데 사용시에는 주의하여야 한다. 이 연구가 방류관의 효율적 운영, 바람직한 방류관의 설계, 수질보호, 발전소의 온배수 방류문제 등에 도움이 되기를 바란다.

• International Journal of Automotive Technology
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• 제5권3호
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• pp.155-164
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• 2004

The direct injection gasoline spray-wall interaction was characterized inside a heated pressurized chamber using various visualization techniques, including high-speed laser-sheet macroscopic and microscopic movies up to 25,000 frames per second, shadowgraph, and double-spark particle image velocimetry. Two hollow cone high-pressure swirl injectors having different cone angles were used to inject gasoline onto a heated plate at two different impingement angles. Based on the visualization results, the overall transient spray impingement structure, fuel film formation, and preliminary droplet size and velocity were analyzed. The results show that upward spray vortex inside the spray is more obvious at elevated temperature condition, particularly for the wide-cone-angle injector, due to the vaporization of small droplets and decreased air density. Film build-up on the surface is clearly observed at both ambient and elevated temperature, especially for narrow cone spray. Vapor phase appears at both ambient and elevated temperature conditions, particularly in the toroidal vortex and impingement plume. More rapid impingement and faster horizontal spread after impingement are observed for elevated temperature conditions. Droplet rebounding and film break-up are clearly observed. Post-impingement droplets are significantly smaller than pre-impingement droplets with a more horizontal velocity component regardless of the wall temperature and impingement angle condition.

• 한국농공학회지
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• 제40권2호
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• pp.112-122
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• 1998

Measurement of electrical resistivity in soils has been used for many years with purpose of estimating in situ porosity or density. Recently electrical resistivity has also been used as an indicator of soil contaimination. This paper presents the result of laboratory experiment to investigate the resistivity variation in contaminated sandy soils. The results can be used with the Cone Penetrometer Test (CPT) result to analyse ground condition. In the experiment, the water content and leachate concentration of soils were controlled by groundwater and leachate, and then the resistivity measurement was made with 'STING-R1' by Advanced Geosciences Inc. In the case of using groundwater, the resistivity was in the range of over 1000${\omega}{\cdot}m$, but in the case of using polluted water by leachate, the resistivity decreased significantly down to 10~ 100${\omega}{\cdot}m$ for the same moisture content. Also the resistivity varied according to the degree of saturatrion. Therefore, if soil is contaminated by leachate, the CPT with electrical resistivity sensor might be used to investigate the contamination status and plume migration. But exact component of leachate and the pollutant concentration are still hard to identify.

• 천문학회지
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• 제37권4호
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• pp.257-259
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• 2004

We compare the results of the surveys of starless cores performed with CS (2-1) and (3-2) lines to study inward motions in the cores. The velocity shifts of the CS(3-2) and (2-1) lines with respect to $N_2H^+$ are found to correlate well with each other and to have similar number distributions, implying that, in many cores, systematic inward motions of gaseous material may occur over a range of density of at least a factor ${\~}$4. Fits of the CS spectra to a 2-layer radiative transfer model in ten infall candidates suggest that the median effective line-of-sight speed of the inward-moving gas is ${\~}0.07 km\;s^{-l}$ for CS (3-2) and ${\~} 0.04 km\;s^{-l}$ for CS(2-1). Considering that the optical depth obtained from the fits is usually smaller in CS(3-2) than in (2-1) line, this may indicate that CS(3-2) usually traces inner, denser gas with greater inward motions than CS(2-1) implying that many of the infall candidates have faster infall toward the center. However, this conclusion may not be representative of all starless core infall candidates, due to the statistically small number analyzed here. Further line observations will be useful to test this conclusion.

• Nuclear Engineering and Technology
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• 제41권7호
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• pp.953-968
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• 2009

It is important to accurately predict the temperature and density distributions in large stratified enclosures both for design optimization and accident analysis. Current reactor system analysis codes only provide lumped-volume based models that can give very approximate results. Previous scaling analysis has shown that stratified mixing processes in large stably stratified enclosures can be described using one-dimensional differential equations, with the vertical transport by jets modeled using integral techniques. This allows very large reductions in computational effort compared to three-dimensional CFD simulation. The BMIX++ (Berkeley mechanistic MIXing code in C++) code was developed to implement such ideas. This paper summarizes major models for the BMIX++ code, presents the two-plume mixing experiment simulation as one validation example, and describes the codes' application to the liquid salt buffer pool system in the AHTR (Advanced High Temperature Reactor) design. Three design options have been simulated and they exhibit significantly different stratification patterns. One of design options shows the mildest thermal stratification and is identified as the best design option. This application shows that the BMIX++ code has capability to provide the reactor designers with insights to understand complex mixing behavior with mechanistic methods. Similar analysis is possible for liquid-metal cooled reactors.