• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제1권2호
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• pp.119-124
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• 1997

Cloud streets were successfully simulated by numerical model (RAMS) including an isolated mountain near the coast, large sensible heat flux from the sea surface, uniform stratification and wind velocity with low Froude number (0.25) in the inflow boundary. The well developed cloud streets between a pair of convective rolls are simulated at a level of 1 km over the sea. The following five results were obtained: 1) For the formation of the pair of convective rolls, both strong static instability and a topographically induced mechanical disturbance are strongly required at the same time. 2) Strong sensible heat flux from the sea surface is the main energy source of the pair of convective rolls, and the buoyancy caused by condensation in the cloud is negligibly small. 3) The pair of convective rolls is a complex of two sub-rolls. One is the outer roll, which has a large radius, but weak circulation, and the other is the inner roll, which has a small radius, but strong circulation. The outer roll gathers a large amount of moisture by convergence in the lower marine boundary, and the inner roll transfers the convergent moisture to the upper boundary layer by strong upward motion between them. 4) The pair of inner rolls form the line-shaped cloud streets, and keep them narrow along the center-line of the domain. 5) Both by non-hydrostatic and by hydrostatic assumptions, cloud streets can be simulated. In our case, non-hydrostatic processes enhanced somewhat the formation of cloud streets. The horizontal size of the topography does not seem to be restricted to within the small scale where non-hydrostatic effects are important.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.628-635
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• 2001

Hydrodynamic behavior and response of vertical-cylindrical liquid-storage tank is considered. The equation of the liquid motion is shown by Laplace's differential equation with the fluid velocity potential. The solution of the Laplace's differential equation of the liquid motion is expressed with the modified Bessel functions. Only rigid tank is studied. The effective masses and heights for the tank contents are presented for engineering design model.

• 한국지하수토양환경학회지:지하수토양환경
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• 제9권3호
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• pp.20-26
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• 2004

2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD)로 오염된 토양의 현장 광분해 정화 과정에서 가장 중요한 이동 메커니즘인 지표에서의 증발 및 광분해에 의한 유기 용매의 이류 상방향 이동에 대한 수식화와 모델 개발을 수행하였다. 각 유체 분포에 대한 다상 유동 효과, 구동력으로서의 중력, k-S-p 관계의 정확한 묘사를 위한 van Genutchen 방정식을 포함한 유한요소법 기반의 수치 모델을 제안하였다. 실험실 규모의 비포화 토양 컬럼 내 용매 이동에 중요한 영향을 미치는 인자들을 조사하기 위하여 수행한 계산의 결과들을 제시하였다. 중력은 고투수성 토양의 유체 분포와 증발에 상당한 영향을 미쳤다. 토양의 종류 또한 증발 과정 중 유체 포화도 분포에 큰 영향을 미친다. 용매의 이류 이동량은 증발량이 증가할수록 초기 물 포화도가 감소할수록 증가하였다. 본 연구에서 수행한 시뮬레이션은 개발된 모델이 토양 환경 내에서 유기 용매의 이류 이동에 영향을 미치는 다양한 인자들의 영향을 분석하는데 유용함을 보여준다.

• 대한원격탐사학회지
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• 제29권4호
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• pp.423-441
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• 2013

이 연구에서는 MTSAT-2 적외 영상과 수증기 영상을 이용하여 2010년 9월 21일 추석 호우 사례에 대하여 대류운 생애주기의 각 단계에서 나타나는 특징을 조사하였다. 추석 호우와 관련된 최초의 구름은 20일 1630~1900 UTC에 서해 중부 지역에서 관측된 다중 세포의 하층운이다. 이 구름 가운데 일부가 1930 UTC에 산동반도 부근에서 휘도온도 $-45^{\circ}C$ 이하의 대류 세포로 발달한다. 이 때 이 지역은 수증기 영상에서 암역의 가장자리에 위치한다. 대류 세포는 동진하다가 한반도 중서부 해안 부근에서 21일 0030과 0430 UTC에 두 차례의 병합을 거쳐 급격히 발달한다. 이후 21일 0430에서 1000 UTC까지 약 6시간 동안 위성 영상에서 구름의 면적은 상대적으로 작고, 수평 이동속도는 느려졌다. 최저 휘도온도는 약 $-75{\sim}-65^{\circ}C$로 매우 낮게 유지되며, 잘 발달한 부세포가 반복적으로 형성되는 특징을 보인다. 레이더 자료에는 국지적으로 50 mm/hr 이상의 강우율을 보이는 좁은 띠 모양의 강우 밴드가 나타나고 이 밴드는 대류운의 남서쪽 가장자리에 위치한다. 그러나 수치 모델 자료의 종관 규모 역학적 강제항에는 뚜렷한 특징을 찾기 어렵다. 대류 세포의 구름 면적은 21일 1000 UTC 이후 짧은 시간에 급격한 증가를 보이고 뒤이어 소멸한다. 이러한 대류 세포의 발달과 관련된 위성 영상의 특징은 중규모 호우의 초단기 예보와 실시간 예보에 사용될 수 있을 것이다.

• 대한기계학회논문집
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• 제18권9호
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• pp.2454-2462
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• 1994

The effects of thermal stratification on the flow of a stratified fluid past a heated circular cylinder were examined in a wind tunnel. Turbulent intensities, rms values of temperature and turbulent convective heat flux distributions in the heated cylinder wake with and without thermal stratification were measured by using a hot-wire and cold-wire combination probe. A phase averaging method was also used to estimated coherent motion in the near wake. It is found that the vertical turbulent motion in the stably stratified flow case dissipates faster than that of the neutral case, i.e., vertical growth of vortical structure is suppressed under the strongly stratified condition. The coherent motion of temperature makes a large contribution like velocity coherent motion. However, the coherent motions of temperature fluctuation become very different with the change of experimental conditions, though the velocity coherent motions are quite similar in all experimental conditions.

• 설비공학논문집
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• 제9권3호
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• pp.312-322
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• 1997

The natural convective flow in a two-dimensional square enclosure with horizontal partitions is investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and two identical partitions were positioned perpendicularly at the mid-height of the right and left walls, respectively. The governing equations are solved by using the finite element method with Galerkin method. Calculations are made for different partition lengths, partition conductivites, and Rayleigh numbers based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). An oscillatory motion of the natural convective flow is affected significantly by the variation of the gap width and Rayleigh number. When the gap width is comparatively short, the heat transfer rate is raised with the increase of the thermal conductivity of partitions. However, for sufficiently large gap widths at higher Rayleigh numbers, the average Nusselt numbers of the conductive partitions are smaller than those of the adiabatic partitions.

• 설비공학논문집
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• 제17권3호
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• pp.256-261
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• 2005

The objective of the present study is to study the Soret effect of both nanoparticles and solute on the convective instabilities in binary nanofluids. A new stability criterion is obtained based on the linear stability theory. The results show that the Soret effect of solute(${\psi}_{bf}$) makes the binary nanofluids unstable significantly and the convective motion in a binary nanofluid sets in easily as the ratio of Soret coefficient of nanofluid to that of binary basefluid ${\delta}_4$ increases for ${\delta}_4$ > -1. It is also found that as an increase of the volume fraction of nanoparticles, nanofluid becomes stable but at a separation ratio of ${\psi}=-0.3$ the state of fluid changes from stable to unstable.

• 동력기계공학회지
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• 제18권1호
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• pp.14-21
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• 2014

Piezoelectric fans are thin elastic beams whose vibratory motion is actuated by means of a piezoelectric material bonded to the beam. These fans have found use as a means to enhance convective heat transfer while requiring only small amounts of power. This study presents new types of models with heat sink having air passage and investigates experimentally their heat transfer characteristics. From the comparison results for four models, the heat transfer coefficients of model 1 are approximately 44~66% higher than those of the reference model 0. The model 1 show the best overall performance about heat transfer and cooling capability. As shown in above results, it is necessary to design the heat sink with air pass for cooling of electronic devices, in order to increase the convective heat transfer coefficient of a piezoelectric fan for electronic cooling.

• 대한설비공학회지:설비저널
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• 제7권3호
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• pp.151-159
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• 1978

A heat transfer model for the case of simultaneous vibration of both the heated surface and its surrounding medium is constructed and the dimensional analysis is applied to this model in order to and the governing dimensionless Parameters in which the vibration effects the heat transfer. In the second Part of this study, an experimental investigation of the effect of vibration on natural convective heal transfer from spheres has been performed for the case of the external oscillatory motion being imposed on the heated surface which is immersed in an otherwise undisturbed air, The ranges of the experimental variables were: temperature difference 10 to $120^{\circ}C$; vibration frequency 10 to 120Hz; displacement amplitude 1.3 to 12.5mm. Three different diameter aluminum were used as the experimental models. Improvements in heat transfer due to vibration were observed, with the maximum increase being 330 Percent. A dimensionless correlation describing the measured heat transfer data is given.

• Nuclear Engineering and Technology
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• 제52권5호
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• pp.947-955
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• 2020

Predicting the sloshing motion of a coolant during a seismic assessment of a rectangular spent fuel pool is of critical concern. Linear theory, which provides a simple analytical method, has been used to predict the sloshing motion in rectangular pools and tanks. However, this theory is not suitable for the high-frequency excitation problem. In this study, the authors developed a simple analytical method for predicting the sloshing motion in a rectangular pool for a wide range of excitation frequencies. The correlation among the linear theory parameters, influencing on excitation and convective waves, and the excitation frequency is investigated. Sloshing waves in a rectangular pool with several liquid heights are predicted using the original linear theory, a modified linear theory and computational fluid dynamics analysis. The results demonstrate that the developed method can predict sloshing motion over a wide range of excitation frequencies. However, the developed method has the limitations of linear solutions since it neglects the nonlinear features of sloshing motion. Despite these limitations, the authors believe that the developed method can be useful as a simple analytical method for predicting the sloshing motion in a rectangular pool under various external excitations.