• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1601-1606
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• 2004

In this paper, the unsteady behavior of the viscous flow field past an impulsively started elliptic cylinder is studied numerically. In order to analyze flow field, we introduce vortex particle method. The vorticity transport equation is solved by fractional step algorithm which splits into convection term and diffusion term. The convection term is calculated with Biot-Savart law, the no-through boundary condition is employed on solid boundaries. The diffusion term is modified based on the scheme of particle strength exchange. The particle redistributed scheme for general geometry is adapted. The flows around an elliptic cylinder are investigated for various attack angles at Reynolds number 200. The comparison between numerical results of present study and experimental data shows good agreements.

• 대한기계학회논문집B
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• 제28권7호
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• pp.809-817
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• 2004

In this paper, the unsteady behavior of the viscous flow field past an impulsively started elliptic cylinder is studied numerically. In order to analyze flow field, we introduce vortex particle method. The vorticity transport equation is solved by fractional step algorithm which splits into convection term and diffusion term. The convection term is calculated with Biot-Savart law, the no-through boundary condition is employed on solid boundaries. The diffusion term is modified based on the scheme of particle strength exchange. The particle redistributed scheme for general geometry is adapted. The flows around an elliptic cylinder are investigated for various attack angles at Reynolds number 200. The comparison between numerical results of present study and experimental data shows good agreements.

• 대기
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• 제20권2호
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• pp.161-172
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• 2010

In an effort to investigate the characteristics of synoptic meteorological conditions in association with long-range transport of haze phenomena occurred over Korea, we statistically classified characteristics of haze events into two types of haze: stagnant case and long-range transport case, based on the synoptic meteorological parameters, and analyze comparatively the characteristics of synoptic meteorological conditions for each case. The results showed that the occurrence frequency of stagnant case accounts for 64.5%, showing superiority of stagnant haze cases over the long-range transport case which occupies only 35.5% among total 67 cases for the period from 2000 to 2007. This result indicates that haze phenomena occurred over Korea has influenced by not only the emission in Korea by itself but long range transport effects originating from China inland. The synoptic condition on 850hPa level showed that, when stagnant case occurred, Korean peninsula was located under the effects of negative vorticity with the significantly weak wind speed and stable atmospheric condition. In contrast, long-range transport case shows positive vorticity and relatively strong wind speed over 850hPa level, especially with the location of high pressure system over the area of southwestern China. This location of high pressure system implies to induce the westerlies or northwesteries consistently due to its pressure gradient by itself. Also other comparative studies haze days (vs.) Asian dust days are carried out, and we found out that the patterns of long-range transport of haze phenomena in Korea shows similar to Asian dust case but the static stability condition indicates more stabilized atmospheric condition than dust phenomena.

• 대기
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• 제20권4호
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• pp.399-414
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• 2010

Sand and dust storm in East Asia, so called Asian dust, is a seasonal meteorological phenomenon. Mostly in spring, dust particles blown into atmosphere in the arid area over northern China desert and Manchuria are transported to East Asia by prevailing flows. An Asian dust event occurred on 6-8 May 2007 is chosen to investigate how sensitive the Asian dust transport forecast to the initial condition uncertainties and to interpret the characteristics of sensitivity structures from the viewpoint of dynamics and predictability. To investigate the forecast sensitivities to the initial condition, adjoint sensitivities that calculate gradient of the forecast aspect (i.e., response function) with respect to the initial condition are used. The forecast aspects relevant to Asian dust transports are dry energy forecast error and lower tropospheric pressure forecast error. The results show that the sensitive regions for the dry energy forecast error and the lower tropospheric pressure forecast error are initially located in the vicinity of the trough and then propagate eastward as the surface low system moves eastward. The vertical structures of the adjoint sensitivities for the dry energy forecast error are upshear tilted structures, which are typical adjoint sensitivity structures for extratropical cyclones. Energy distribution of singular vectors also show very similar structures with the adjoint sensitivities for the dry energy forecast error. The adjoint sensitivities of the lower tropospheric pressure forecast error with respect to the relative vorticity show that the accurate forecast of the trough (or relative vorticity) location and intensity is essential to have better forecasts of the Asian dust event. Forecast error for the atmospheric circulation during the dust event is reduced 62.8% by extracting properly weighted adjoint sensitivity perturbations from the initial state. Linearity assumption holds generally well for this case. Dynamics of the Asian dust transport is closely associated with predictability of it, and the improvement in the overall forecast by the adjoint sensitivity perturbations implies that adjoint sensitivities would be beneficial in improving the forecast of Asian dust events.

• 대한토목학회논문집
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• 제13권2호
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• pp.267-277
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• 1993

본 논문에서는 유한요소법을 2차원 난류경계층에 적용하였으며, 점성유체의 시간의존 비압축성 운동을 시간과 압력장(場)에서 Navier-Stokes방정식과 vorticity방정식을 이용하여 정식 화하였다. 수치계산방법은 Galerkin방법에 기초하였으며, 난류 경계층의 eddy kinematic viscosity에 대해서는 Prandtl의 혼합거리이론을 도입하였다. 난류 경계층에서 파동에 의한 임의 저면에서 저질의 이동을 수치계산하였다. 유한 요소법에 의해 얻어진 결과는 진동흐름에 의한 경계층과 파동에 의한 경계층에서의 특성의 차이를 분명히 하였다.

• 한국환경과학회지
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• 제11권2호
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• pp.111-120
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• 2002

Asian dust(or yellow sand) occurs mainly in spring and occasionally in winter in east Asia, when the weather conditions are under an upper trough/cut-off low and surface high/low pressure system during blocking episode days associated with the stationary patterns of the upper level jet stream. The transport mechanism for Asian dust during the blocking episode days in spring 2001 was analyzed using the TOMS aerosol index and meteorological mesoscale model 5(MM5). Based on the E vector, an extension of an Eliassen-Palm flux, the blocking episode days were found to be associated with the development of an upper cut-off low and surface cyclones. Concurrently, the occurrence of dust storms was also determined by strong cold advection at the rear of a jet streak, which exhibited a maximum wind speed within the upper jet stream. As such, the transport mechanism for Asian dust from China was due to advection of the isentropic potential vorticity(IPV) and isentropic surfaces associated with tropopause folding. The transport heights for Asian dust during the blocking episode days were found to be associated with the distribution of the isentropes below the IPV At the same time, lee waves propagated by topography affected the downward motion and blocking of Asian dust in China. The Asian dust transported from the dust source regions was deposited by fallout and rain-out with a reinforcing frontogenesis within a surface cyclone, as determined from satellite images using TOMS and GMS5. Accordingly, these results emphasize the importance of forecasting jet streaks, the IPV, and isentropes with geopotential heights in east Asia.

• 대한토목학회논문집
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• 제7권1호
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• pp.11-22
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• 1987

흐름수역(水域)에서 연직상향으로 방류되는 평면부력(平面浮力)?의 거동이 연속방정식(連續方程式), 운동량방정식(運動量方程式) 및 추적물수송식(追跡物輸送式)의 기본방정식을 수치적(數値的)으로 풀음으로서 해석(解析)된다. 난류확산(亂流擴散)에는 Prandtl의 혼합거리이론(混合距離理論)을 도입한 난류수송모형(亂流輸送模型)이 이용된다. 수치해과정(數値解過程)은 기본방정식을 유함수(流凾數)(stream function)식(式)과 골도수송(滑度輸送)(vorticity transport)식을(式) 이용하여 변환(變換)한 후, ?방류속도(放流速度), ?방류구폭(放流口幅) 등(等)으로 표현되는 변수(變數)와 흐름을 지배(支配)하는 무차원매개변수(無次元媒介變數)를 도입하여 무차원화(無次元化)하고 successive under-relaxation을 이용하여 Gauss-Seidal 반복법(反復法)으로 해를(解) 구(求)하는 것이다. 수치실험(數値實驗)은 방류(放流)Froude수(數)가 4~32, 방류속도(放流速度)와 가로흐름속도와의 비로(比) 정의되는 속도비가 8~15 의 범위의 흐름영역(領域)에서 수행되었다. 부력(浮力)?으로 인한 주변(周邊)흐름수역(水域)의 속도변화(速度變化), 온도상승(溫度上昇)범위, 흐름상태 및 골도(滑度)가 조사되었으며, ?의 경로에 대한 속도비와 방류밀도Froude 수의 영향이 또한 조사되었다. ?중심선의 속도, 온도변화, 국부밀도(局部密度)Froude 수(數)의 변화가 계산되며 퍼짐율(spreading rate)과 확산비(擴散比)(dispersion ratio)가 방류밀도(放流密度)Froude 수, 국부밀도(局部密度)Froude 수(數) 및 속도비(速度比)의 항(項)으로 해석되었다. 또한 속도와 온도분포를 상사(相似)(similarity)로 나타낼 수 있음이 밝혀졌으며, Gaussian 분포(分布)를 이용한 적분형해석(積分型解析)(integral type analysis)이 가능한 것으로 사료된다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.78-85
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• 2011

The Vortex-In-Cell(VIC) method combined with panel method is applied to the analysis of incompressible unsteady viscous flow. The dynamics of resulting flow is governed by the vorticity transport equation in Lagrangian form with vortex particle representation of the flow field. A regular grid which is independent to the shape of a body is used for numerical evaluation based on immersed boundary technique. With an introduction of this approach, the development and validation of the VIC method is presented with some computational results for incompressible viscous flow around two or three dimensional bodies such as wing section, sphere, finite wing and marine propeller.

• 한국전산유체공학회지
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• 제12권1호
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• pp.9-15
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• 2007

A three dimensional numerical model to predict the flow and transport of mixtures and also the electrochemical reactions in polymer electrolyte membrane (PEM) fuel cells is developed. The numerical computation is base on vorticity- velocity method. Governing equations for the flow and transport of mixtures are coupled with the equations for electrochemical reactions and are solved simultaneously including production and condensation of vapor. Fuel cell performance predicted by this calculation is compared with the experimental results and resonable agreements are achieved.

• 한국가시화정보학회지
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• 제13권1호
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• pp.21-25
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• 2015

Three-dimensional vortex structures in the corner region of translating normal plates are visualized experimentally with defocusing digital particle image velocimetry. Vortex formation processes for three plates with corner angle $60^{\circ}$, $90^{\circ}$, and $120^{\circ}$ are compared in order to study the effect of corner shape on vortex formation. In all cases, the self-induction of the starting vortex and its interaction with the potential flow induced by the moving plate cause the vortex to change its form dynamically after the plate starts to translate. While the vortex near a corner follows the plate in the low corner angle of $60^{\circ}$, the vortex separates early from the plate and its forward motion becomes slow in the high corner angle of $120^{\circ}$. It is also found that the starting vortex can transport inward at the corner, which depends on the corner angle.