• 대기
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• 제22권1호
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• pp.1-12
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• 2012

The Atmospheric motion vectors (AMVs) derived using infrared (IR) channel imagery of geostationary satellites have been utilized widely for real-time weather analysis and data assimilation into global numerical prediction model. As the horizontal resolution of sensors on-board satellites gets higher, it becomes possible to identify atmospheric motions induced by convective clouds ($meso-{\beta}$ and $meso-{\gamma}$ scales). The National Institute of Meteorological Research (NIMR) developed the high resolution visible (HRV) AMV algorithm to detect mesoscale atmospheric motions including ageostrophic flows. To retrieve atmospheric motions smaller than $meso-{\beta}$ scale effectively, the target size is reduced and the visible channel imagery of geostationary satellite with 1 km resolution is used. For the accurate AMVs, optimal conditions are decided by investigating sensitivity of algorithm to target selection and correction method of height assignment. The results show that the optimal conditions are target size of 32 km ${\times}$ 32 km, the grid interval as same as target size, and the optimal target selection method. The HRV AMVs derived with these conditions depict more effectively tropical cyclone OMAIS than IR AMVs and the mean speed of HRV AMVs in OMAIS is slightly faster than that of IR AMVs. Optimized mesoscale AMVs are derived for 6 months (Feb. 2010-Jun. 2010) and validated with radiosonde observations, which indicates NIMR's HRV AMV algorithm can retrieve successfully mesoscale atmospheric motions.

• Computers and Concrete
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• 제9권1호
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• pp.35-50
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• 2012

The 2D representative volume element (RVE) for softening quasi-brittle materials like concrete is determined. Two alternative methods are presented to determine a size of RVE in concrete subjected to uniaxial tension by taking into account strain localization. Concrete is described as a heterogeneous three-phase material composed of aggregate, cement matrix and bond. The plane strain FE calculations of strain localization at meso-scale are carried out with an isotropic damage model with non-local softening.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.159-162
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• 2012

Combustion in a narrow space has been interested as a model of meso-scale combustors (or micro-combustors). Premixed flames have been used to overcome flame quenching in a narrow space and non-premixed flames have been used to improve flame stabilization. In this study, overall characteristics of premixed flame and non-premixed flame in narrow combustion spaces were reviewed. Various effects such as the flow velocity distribution, thermal interaction, enhanced mass diffusion were discussed and an eventual structure of the flame at the extinction limit was introduced.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 2003년도 추계학술대회 논문집
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• pp.441-442
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• 2003

복잡한 지형에서 국지적인 순환에 의한 에너지 교환은 기상변화에 중요한 역할을 담당한다. 종관장이 영향이 약하고 양호한 기상조건 하에서 대기 경계층내에서의 온도와 바람장은 국지적인 순환에 영향을 받는다(Kawamura,1979; Kuwagata et al.,1990; Winston et al.,1992). 즉 이러한 기상 조건 하에서는 중규모 순환에 의해 에너지의 수송효과가 크고 각기 수송된 에너지에 의해서 지역별로 대기 경계층내의 가열율에도 차이가 나타난다. (중략)

• Structural Engineering and Mechanics
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• 제33권4호
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• pp.429-446
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• 2009

Three-scale homogenization procedure is proposed in this paper to provide estimates of the effective thermal conductivities of porous carbon-carbon textile composites. On each scale - the level of fiber tow (micro-scale), the level of yarns (meso-scale) and the level of laminate (macro-scale) - a two step homogenization procedure based on the Mori-Tanaka averaging scheme is adopted. This involves evaluation of the effective properties first in the absence of pores. In the next step, an ellipsoidal pore is introduced into a new, generally orthotropic, matrix to make provision for the presence of crimp voids and transverse and delamination cracks resulting from the thermal transformation of a polymeric precursor into the carbon matrix. Other sources of imperfections also attributed to the manufacturing processes, including non-uniform texture of the reinforcements, are taken into consideration through the histograms of inclination angles measured along the fiber tow path together with a particular shape of the equivalent ellipsoidal inclusion proposed already in Sko ek (1998). The analysis shows that a reasonable agreement of the numerical predictions with experimental measurements can be achieved.

• Composites Research
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• 제29권1호
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• pp.33-39
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• 2016

본 논문에서는 3차원 평직 복합재료의 3-방향 섬유다발의 굴곡각에 따른 다양한 모델링을 구축하고, 제시한 모델에 대하여 등가 물성치를 예측하였다. 3차원 평직복합재료의 단위셀을 정의하고 미시역학 계산결과인 섬유다발 물성치를 사용하여 섬유다발에 굴곡각에 따라 물성치가 변화하도록 요소 물성축을 설정 후 3차원 평직 복합재료의 중시해석을 수행하였다. 계산결과 등가물성치는 참고문헌에 제시된 해석 및 실험값을 비교하여 타당성을 확보하였으며 계산결과 3-방향 섬유다발 굴곡각이 미치는 영향에 대하여 고찰하였다. 또한 초기파손 강도와 파손순서에 대해서도 조사하였다.

• 한국대기환경학회지
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• 제7권3호
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• pp.169-179
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• 1991

Atmospheric $O_3$ in the biosphere is formed under the favourable meteorological condition, when the primary pollutants, such as $NO_2, HC, CO, CH_4$, etc., react with over constituents. Observed annual average concentrations for 1989 and 1990 were 11.8 and 10.4 ppb, respectively. THe number of days measured ozone over 80 ppb in Seoul were 36 in 1989 and 39 in 1990. In general, monthly maximum values occurred in May and August. In comparison with 1 $\sim$ 2 maxima of $O_3$ distribution in large cities in other countries, it was found that there were 3 $\sim$ 4 maxima in Seoul and its suburbs. Topographic effects, resulted by wind channelling in the Han River valley and by the blocking of air pollutants in the mountain, appeared to produce multiple centres of $O_3$ maxima in Seoul. Surface $O_3$ values were low with decreasing solar radiation, when the cloudiness increased and precipitation occurred. According to 12 cases examined, 2 cases shown here, $O_3$ values exceeding 80 ppb were occurred when the Korean peninsular was under the influence of the backside airflows with high intensity of solar radiation. Occasionally, sea breezes were observed to occur in warm seasons, and the chanelling effect of the Han River valley appeared to increase the general wind (speed) to the east side of Seoul. In this meso-scale situation $O_3$ in downwind is highly correlated with precursors. The sea breeze of 2 $\sim$ 4 m $s^{-1}$ will take 3 $\sim$ 5 hours to transport photochemical precursors for 20 $\sim$ 50 km. In turn the areas of maximum $O_3$ occurrence in Seoul are in the range of meso-scale transport of air pollutants.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1733-1736
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• 2005

Many studies have been carried out to produce 3D features in the size range between $10{\mu}m\~10,000{\mu}m$, called Meso-scale. If these miniaturized systems have high relative accuracy and good volumetric utilization, it is possible to manufacture more complex and accurate shapes with various materials as well as there are advantages of reducing energy, space and resources. Due to imperfect components and misalignment in assembly, it is necessary to assess the accuracy of the miniaturized system itself to obtain high relative accuracy. Laser interferometers are widely used to measure geometric errors called as quasi-static errors. For miniaturized system, however, it is difficult to install the required accessories such as optics and the measuring range is limited because of the size of the system and also this method is very expensive. Moreover, it is impossible to measure each error component simultaneously. A new system to measure simultaneously multiple geometric errors is proposed using capacitance sensors. Each error was measured using capacitance sensors and a measurement algorithm was mathematically derived. The experiments show that the proposed measurement system can be used effectively to assess the accuracy of miniaturized system at a low cost.

• 대기
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• 제18권4호
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• pp.339-354
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• 2008

A numerical simulation of a heavy snowfall event that occurred 13 January 2008 along the Yeongdong coastal area, was performed using WRF (Weather Research and Forecasting) in order to reveal mesoscale structures and to construct a conceptual model showing the meteorological background that caused the large difference in snowfall amounts between the Yeongdong mountain area and the Yeongdong coastal area. The simulation results matched well with various observations such as corresponding 12h-accumulated observed precipitation, surface wind obscrvation, radar echoes, and satellite infrared images. The simulation and the observations showed that the scale of the event was of meso - $\beta$ and meso - $\gamma$ scale. The simulation represented well the mesoscale process causing the large difference in snowfall amounts in the two areas. First, wind flow was kept, to a certain extent, from crossing the mountains due to the blocking effect of the low Froude number (~1). The northeast flow over the adjaccnt sea tumcd northwest as it approachcd the mountains, where it was trapped, allowing so-called cold air damming. Second, a strong convergence area formed where the cold northwest flow along the Yeongdong coastal area and the relatively warm and moist northeast flow advecting toward the coast met, supporting the fonllation of a coastal front. Thus, the vertical motion was strongest over the front located near the coast, leading to the heavy snowfall there rather than in the remote mountain area.

• 한국수자원학회논문집
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• 제34권5호
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• pp.473-486
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• 2001

WGR 강우모형은 중규모 정도의 강우를 표현하기 위해 개발된 개념적인 모형으로 대기의 동역학적 특성과 강우의 통계학적 특성이 비교적 잘 반영된 모형이다(Waymire 등, 1984). 그러나 이 모형은 최대 18개의 매개변수르 가지며 모형의 구조가 강한 비선형성을 가지고 있어 매개변수 추정이 매우 어려운 문제로 남아 있다. 지금까지 각각 다른 지역의 강우에 대해 비선형 최적화 기법(non-linear programming; NLP)을 이용하여 매개변수를 추정한 예가 있으나 그 과정 자체가 매우 복잡하여 이 모형을 다른 목적으로 이용하는데 문제로 지적되고 있다. 본 연구에서는 유전자 알고리즘(genetic algorithm; GA)을 이용한 WGR 모형의 매개변수 추정법을 제시하였으며, 이를 한강유역에 적용하여 NLP에 의한 결과 (Yoo와 Kwon, 2000)와 비교하였다. 적용 결과 GA는 NLP에 비해 상대적으로 작은 SSE(sum of square error)를 나타내었고 계절의 변화에 보다 일관적인 반응을 보임을 알 수 있었다. 또한 추정된 매개변수 분석결과, 여름철의 높은 강우량은 강우 세포의 강도보다는 강우전선의 도달율과 밀접한 관계가 있는 것으로 나타났다.