• Wind and Structures
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• 제32권5호
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• pp.453-469
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• 2021

Snow accumulation on the road frequently induces a big traffic problem in the cold snowy region. Accurate prediction on snow distribution is fundamental for solving drifting snow disasters on roads. The present study adopts the transient method to simulate the wind-induced snow distribution on embankment based on the mixture multiphase model and dynamic mesh technique. The simulation and field measurement are compared to confirm the applicability of the simulation. Furthermore, the process of snow accumulation is revealed. The effects of friction velocity and snow concentration on snow accumulation are analyzed to clarify its mechanism. The results show that the simulation agrees well with the field measurement in trends. Moreover, the snow accumulation on the embankment can be approximately divided into three stages with time, the snow firstly deposited on the windward side, then, accumulation occurs on the leeward side which induced by the wake vortex, finally, the snow distribution reaches an equilibrium state with the slope of approximately 7°. The friction velocity and duration have a significant influence on the snow accumulation, and the vortex scale directly affected the snow deposition range on the embankment leeward side.

• 한국농공학회지
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• 제39권4호
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• pp.64-74
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• 1997

The purpose of this study is to analyze hydraulic characteristics of surface irrigation in a paddy field of direct seeding culture. Field experiment was performed in the paddy field of ridge direct dry seeding. Simulation by a numerical model was also accomplished with the data obtained from the field experiment. The model was developed by one dimensional zero-inertia equation and finite difference method. From the result of the field observation, the furrows of the experimental field were found to have various geometric characteristics. Advance distance and time were measured both in the field and by the model simulation for various furrow lengths and irrigation discharges. Roughness coefficients of each furrow were also estimated by the model.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마연구회
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• pp.57-60
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• 2003

This paper explained electric field distribution's characteristics of dielectric pellets with a shape of ball to voltage. When discharge gap of electrode and input voltage are each 20[mm], 10000[V], the electric field simulation results of dielectric pellets with a shape of ball with relative dielectric constant of several kind measured stronger electric field near electric pellets with a shape of ball of ${\phi}5$[mm] than $1{\phi}$[mm] and $3.33{\phi}$[mm] at atmosphere. And the maximum electric field of dielectric pellets with a shape of ball over ${\phi}5$[mm] increased about 5[%] to maximum electric field of electric pellets with a shape of ball ${\phi}5$[mm]. And the result of simulation, when relative dielectric constant of dielectric pellets with a shape of ball is 100, it measured about 90[%] of maximum electric field of dielectric pellets with a shape of ball with relative dielectric constant over 1000.

• Journal of Magnetics
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• 제22권2호
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• pp.326-332
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• 2017

The effects of exposure to an extremely low-frequency magnetic field (25 Hz 20G) on animal cells have been studied. In some reports, stimulation was performed for fixed frequency and variations in magnitude; however, animal-cell experiments have established that both parameters play an important role. The present work undertook the modeling, simulation, and development of a uniform-magnetic-field generation system with variable frequency and stimulation intensity (0-60 Hz, 1-25G) for experimentation with cell cultures in situ. The results showed a coefficient of variation less than 1 % of the magnetic-field dispersion at the working volume, which is consistent with the corresponding simulation results demonstrating a uniform magnetic field. On the other hand, long-term tests during the characterization process indicated that increments of only $0.4^{\circ}C$ in the working volume temperature will not be an interfering factor when experiments are carried out in in situ cell cultures.

• 멤브레인
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• 제27권4호
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• pp.358-366
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• 2017

연료전지용 전해질막의 성능에 있어서 가장 중요한 요소는 수소이온이 전해질막 내부에 형성된 수화채널을 따라서 얼마나 빨리 전달될 수 있느냐이다. 여기에는 수화채널의 모폴로지 및 수소이온의 확산도 등이 매우 중요한 요소가 되는데, 이를 규명하기 위하여 다양한 분자동역학 전산모사 연구가 진행되고 있다. 분자동역학 계산에 있어서 각 원자의 움직임 및 상호작용을 미리 변수화 시켜 놓은 force-field는 필수 요소 중 하나로서, 본 연구에서는 이러한 force-field의 종류가 전해질막 전산모사에 미치는 영향을 분석하기 위하여, 다양한 force-field를 이용하여 연료전지용 전해질막의 수소이온 확산도를 계산하였다. 이 과정에서 non-bonding interaction을 결정하는 전하 값이 수화채널 모폴로지 형성에 매우 중요한 역할을 한다는 것이 밝혀졌으며, COMPASS force-field가 가장 정확한 수소이온 확산도 값을 얻음으로써 연료전지용 전해질막의 전산모사에 있어서 가장 적절한 force-field일 것으로 판단된다. 이러한 force-field의 적절한 선정은 최종 분자 구조 뿐만 아니라 수소이온 확산도에도 큰 영향을 주는 것을 알 수 있었으며, 연료전지용 전해질막 전산모사 수행 시에는 이러한 부분을 충분히 감안하여 force-field를 선택하여야 할 것이다.

• 천문학회보
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• 제35권2호
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• pp.49.2-49.2
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• 2010

In order to understand the configuration of magnetic field producing a solar penumbral microjet that was recently discovered by Hinode, we performed a magnetohydrodynamic simulation reproducing a dynamic process of how that configuration is formed in a modeled solar penumbral region. A horizontal magnetic flux tube representing a penumbral filament is placed in a stratified atmosphere containing the background magnetic field that is directed in a relatively vertical direction. Between the flux tube and the background field there forms the intermediate region in which the magnetic field has a transitional configuration, and the simulation shows that in the intermediate region magnetic reconnection occurs to produce a clear jet- like structure as suggested by observations. The result that a continuous distribution of magnetic field in three-dimensional space gives birth to the intermediate region producing a jet presents a new view about the mechanism of a penumbral microjet, compared to a simplistic view that two field lines, one of which represents a penumbral filament and the other the background field, interact together to produce a jet. We also discuss the role of the intermediate region in protecting the structure of a penumbral filament subject to microjets.

• 대한토목학회논문집
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• 제26권2A호
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• pp.383-390
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• 2006

본 연구에서는 급수전개를 이용한 추계론적 유한요소해석법의 개선을 위한 등가몬테카를로 추계장함수를 제안하고 1차 Taylor전개를 이용한 추계론적 유한요소해석법인 가중적분법에 적용하였다. 일반적으로 1차 Taylor전개를 이용하는 수치해석법에서의 응답변화도는 고려하고 있는 추계장의 분산계수에 대하여 선형거동을 보인다. 그러나 몬테카를로 해석의 경우 추계장 분산계수에 대하여 비선형 거동을 나타낸다. 이는 급수전개법의 1차 Taylor전개에 따른 선형특성에 기인한다. 따라서, 가중적분법에서 사용되는 Taylor전개된 변위벡터와 몬테카를로 해석에서의 변위벡터를 비교하고 이들 두 변위벡터 사이에 상호 불일치 하는 점을 고찰하여 몬테카를로 해석에서의 변위벡터와 등가의 변위벡터를 구성하고 이를 가중적분법에 적용하였다. 제안한 등가몬테카를로 추계장은 본래의 추계장 함수에 대한 고차함수로 주어진다. 평면구조에 대한 수치해석을 통하여 제안한 등가몬테카를로 추계장을 이용한 정식화의 타당성을 고찰하였다 새로운 정식화는 기존의 l차 가중적분법을 위한 정식화 과정과 유사하게 수행할 수 있었다.

• 한국재난관리표준학회지
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• 제4권1호
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• pp.29-37
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• 2011

최근 고성토 도로건설 구간에서 거주민들이 고성토 도로가 생활환경에 영향과 경제적인 피해를 최소화 해 줄 것을 요구하는 민원이 급격하게 증가하는 실정이다. 본 연구에서는 고성토 도로와 교량이 건설되는 도로구간을 연구 대상지역으로 선정하고, 3차원 미기후모델 'Envi-met'을 이용하여 도로의 건설 전과 후에 온도장과 바람장의 변화에 대한 수치해석을 수행하였다. 그 결과를 요약하면 다음과 같다. 바람장의 분석 결과, 고성토 구간의 도로가 기류의 흐름 방해하여 바람장의 급격한 변화를 나타내었으며, 대부분 분석공간에서 풍속의 감소를 나타내었다. 그러나 교량 구간의 도로는 풍향에 미치는 영향이 크지 않았고, 풍속의 감소에 미치는 영향도 상대적으로 낮게 나타났다. 온도장의 분석 결과, 고성토 도로가 기류의 유동과 혼합을 방해하여 분석공간의 내부에서 미세한 온도의 변화가 나타났다. 이러한 결과는 도로건설 사업에서 수치모사의 이용이 미기후 변화와 교통사고 등과 같은 재난 가능성을 최소화하는데 필요한 유용한 정보를 제공할 수 있음을 나타내었다.

• Journal of Mechanical Science and Technology
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• 제19권3호
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• pp.913-923
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• 2005

The dynamic mixed model (DMM) combined with a box filter of Zang et. al. (1993) has been generalized for passive scalar transport and applied to large eddy simulation of turbulent channel flows with Prandtl number up to 10. Results from a priori test showed that DMM is capable of predicting both subgrid-scale (SGS) scalar flux and dissipation rather accurately for the Prandtl numbers considered. This would suggest that the favorable feature of DMM, originally developed for the velocity field, works equally well for scalar transport problem. The validity of the DMM has also been tested a posteriori. The results of the large eddy simulation showed that DMM is superior to the dynamic Smagorinsky model in the prediction of scalar field and the model performance of DMM depends to a lesser degree on the ratio of test to grid filter widths, unlike in the a priori test.

• 전기전자학회논문지
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• 제5권2호
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• pp.121-127
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• 2001

Actual system apparatuses are necessary in order to verify the efficiency and stability of photovoltaic(PV) generation systems considering the size of solar panel, the sort of converter type, and the load conditions and so on. Moreover, it is hardly possible to compare a certain MPPT control scheme with others under the exactly same weather and load conditions as well. For the purpose of solving above mentioned difficulties in a laboratory basis, a transient simulation of PV generation system using real field weather conditions is indispensable. A straightforward simulation scheme with cost effective hardware structures under real weather conditions is proposed in this paper using EMTDC type of transient analysis simulators. Firstly, a solar cell has been modeled with VI characteristic equations, and then the real field data of weather conditions are interfaced to the EMTDC through Fortran program interface method. As a result, the stability and the efficiency analysis of PV generation systems according to various hardware structures and MPPT controls are easily possible under the exactly same weather conditions.