• 한국환경과학회지
• /
• 제1권1호
• /
• pp.35-43
• /
• 1992

Handling the emergency problems such as Chemobyl accident require real time prediction of pollutants dispersion. One-point real time sounding at pollutant source and simple model including turbulent-radiation process are very important to predict dispersion at real time. The stability categories obtained by one-dimensional numerical model (including PBL dynamics and radiative process) are good agreement with observational data (Golder, 1972). Therefore, the meteorological parameters (thermal, moisture and momentum fluxes; sensible and latent heat; Monin-Obukhov length and bulk Richardson number; vertical diffusion coefficient and TKE; mixing height) calculated by this model will be useful to understand the structure of stable boundary layer and to handling the emergency problems such as dangerous gasses accident. Especially, this simple model has strong merit for practical dispersion models which require turbulence process but does not takes long time to real predictions. According to the results of this model, the urban area has stronger vertical dispersion and weaker horizontal dispersion than rural area during daytime in summer season. The maximum stability class of urban area and rural area are "A" and "B" at 14 LST, respectively. After 20 LST, both urban and rural area have weak vertical dispersion, but they have strong horizontal dispersion. Generally, the urban area have larger radius of horizontal dispersion than rural area. Considering the resolution and time consuming problems of three dimensional grid model, one-dimensional model with one-point real sounding have strong merit for practical dispersion model.al dispersion model.

• 전기학회논문지
• /
• 제58권10호
• /
• pp.2011-2015
• /
• 2009

In an insulating dielectric liquid such as transformer oil, space charge injection and propagation were analyzed under the Fowler-Nordheim and Richardson-Dushman's thermal emission charge injection conditions for blade-plane electrodes stressed by a step voltage. The governing equations were composed of all five equations such as the Poisson's equation for electric fields, three continuity equations for electrons, negative, and positive ions, and energy balanced equation for temperature distributions. The governing equations for each carrier, the continuity equations, belong to the hyperbolic-type PDE of which the solution has a step change at the space charge front resulting in numerical instabilities. To decrease these instabilities, the governing equations were solved simultaneously by the Finite Element Method (FEM) employing the artificial diffusion scheme as a stabilization technique. Additionally, the terminal current was calculated by using the generalized energy method which is based on the Poynting's theorem, and represents more reliable and stable approach for evaluating discharge current. To verify the proposed method, the discharge phenomena were successfully applied to the blade~plane electrodes, where the radius of blade cap was $50{\mu}m$.

• 한국연소학회지
• /
• 제16권2호
• /
• pp.23-32
• /
• 2011

To investigate cell formation in hydrocarbon/hydrogen/carbon monoxide-air premixed flames, the outward propagation and cellular instabilities were experimentally studied in a constant pressure combustion chamber at room temperature and elevated pressures. Unstretched laminar burning velocities and Markstein lengths of the mixtures were obtained by analyzing high-speed schlieren images. In this study, hydrodynamic and diffusional- thermal instabilities were evaluated to examine their effects on flame instabilities. The experimentally-measured unstretched laminar burning velocities were compared to numerical predictions using the PREMIX code. Effective Lewis numbers of premixed flames with methane addition decreased for all of the cases; meanwhile, effective Lewis numbers with propane addition increased for lean and stoichiometric conditions and increased for rich and stoichiometric cases for hydrogen-enriched flames. With the addition of propane, the propensity for cell formation significantly was diminished, whereas cellular instabilities for hydrogen-enriched flames were promoted. However, similar behavior of cellularity was obtained with the addition of methane to the reactant mixtures.

• 한국항공우주학회지
• /
• 제34권2호
• /
• pp.1-10
• /
• 2006

본 연구에서는 수치적 방법을 이용하여 타원형 익형의 공력특성에 대한 연구를 수행하였다. 타원형 익형의 경우 현재까지 널리 사용되어진 NACA 계열 익형들에 비하여 작은 앞전 곡률반경을 가진다. 또한 NACA 계열 익형들과는 달리 앞전과 같은 곡률반경을 가지는 뒷전 형상을 가지며, 익형의 최대 두께가 시위의 1/2지점에 존재한다. 타원형 익형의 경우 이러한 형상적인 특징들에 의하여 NACA 계열 익형들과는 다른 공력특성을 나타내는데, 본 연구에서는 같은 최대 두께를 가지는 NACA 계열 익형과 타원형 익형의 다양한 유동조건에서의 공력특성에 대한 수치해석 결과의 비교를 통하여 타원형 익형의 공력특성에 대하여 살펴보았다. 또한 타원형 익형의 두께변화에 따른 공력특성의 변화 역시 함께 고려하였다.

• 한국군사과학기술학회지
• /
• 제13권5호
• /
• pp.717-724
• /
• 2010

The initial trajectory of a spheroid configuration bobbin for precision guidance has been investigated by analyzing its aerodynamic load and six-degree-of-freedom motion. The effects of changes in the spheroidal head configuration, flow angle and lateral center-of-gravity offset are numerically studied using the commercial software "FLUENT". A wind tunnel test is also conducted to validate the numerical scheme and to examine effect of the Reynolds number on the flow around the bobbin. It is shown that the size of the separation bubble formed on the surface decreases significantly when the Reynolds number is varied between 110,000 and 140,000. At a zero flow angle, an oblate spheroidal head shows relatively moderate rotation while a prolate spheroidal head shows rapid rotation. The bobbin with a spherical head shape has little effect on the flow direction; however, the oblate bobbin is sensitive to the flow angle. The roll motion of the bobbin is greatly influenced by the lateral center-of-gravity offset and maximum dispersion is observed at half of the radius.

• 한국산학기술학회논문지
• /
• 제10권7호
• /
• pp.1453-1458
• /
• 2009

본 논문은 중공을 가진 판재 두 매를 결합하기 위하여 중공 주위를 따라 기존 레이저 용접법 대신 기계적 프레스 결합법을 적용하는 것에 관한 연구이다. 이를 통해 레이저 용접을 적용했을 때 불가피하게 발생하는 열 변형을 효과적으로 없앨 수 있다. 유한요소해석을 통하여 중공형 판재를 기계적으로 결합시킬 수 있는 금형 설계 방법을 제안하였다. 기계적 결합력을 최대화시키는 데 관련 있는 다섯 가지 설계인자를 선택하여 다꾸치 실험법을 적용한 결과 성형 깊이와 펀치모서리 반경이 가장 크게 영향을 미치는 인자로 나타났다.

• 한국지하수토양환경학회지:지하수토양환경
• /
• 제6권3호
• /
• pp.43-52
• /
• 2001

쓰레기 매립지에 개설된 수많은 포집정으로부터 매립가스를 포집하여 연결된 배관망을 통해 처리계통까지 지속적이고 안정적으로 수송시키는 일은 매우 중요하다. 이러한 매립가스의 안정적인 포집 및 수송은 매립지의 유체유동특성, 가스생성량, 배관망내 침출수 수분점유 상황, 배관망의 구조 및 사양 등에 따라 그 성공여부가 결정된다. 이에 따라 본 연구에서는 오래된 쓰레기 매립지에 생성된 매립가스의 포집 및 수송 메커니즘을 포집정과 지상 배관망 단계별로 분석하였고, 최종적으로 매립지 압력강하의 최소화에 따른 가스막힌 밀집구역이 발생되지 않도록 송풍기의 흡입력을 최적으로 운용하는 방법을 제안하였다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 춘계학술대회 논문집
• /
• pp.101-105
• /
• 2005

Hemming process, composed of flanging, pre-hemming and main hemming, is the last one of a series of forming processes conducted on the automotive panels, having a great influence on the outward appearance of them. The hem quality can be quantitatively defined by the hemming defects including turn-down, warp and roll-in. However, it is difficult to evaluate and predict the hem quality through the experimental measurement or the numerical calculation since the size of defects is very small. This study is focused on how to simulate in the finite element analysis (FEA) the same conditions as in the experiment. The FEA result on turn-down, that was obtained from a finite element model including the spring element linked to the flanging pad, had a good correlation with the experimental data. It was found that the radius of curvature of the flange deeply affects the final hem quality and therefore high rigidity of forming tools and tight assembling tolerance are highly recommended. An over-stroke of the main hemming punch is also proposed to reduce the turn-down.

• 한국소음진동공학회논문집
• /
• 제21권7호
• /
• pp.599-608
• /
• 2011

FPS(friction pendulum system) is an isolation system which is possible to isolate structures from earthquake by pendulum characteristic. Natural frequencies of the structures could be determined by designing the radius of curvature of FPS. Thus, response vibration could be reduced by changing natural frequency of structures from FPS. But effective periods of recorded seismic wave were various and estimation of earthquake characteristic could be difficult. If effective periods of seismic wave correspond to natural frequency of structures with FPS, resonance can be occurred. Therefore, CFPBS(cone-type friction pendulum bearing system) was developed for controlling the acceleration and displacement of structure by the slope of friction surfaces. Structural natural frequency with CFPBS can be changed according to position of ball on the friction surface which was designed cone-type. Therefore, superstructures on CFPBS could be isolated from earthquake. In this study, seismic performance of CFPBS was evaluated by numerical analysis and shaking table test.

• 대한기계학회논문집B
• /
• 제28권11호
• /
• pp.1332-1338
• /
• 2004

This paper presents the response surface optimization method using three-dimensional Navier-Stokes analysis to optimize the shape of a forward-curved blades centrifugal fan. For numerical analysis, Reynolds-averaged Navier-Stokes equations with k-$\varepsilon$ turbulence model are discretized with finite volume approximations. In order to reduce huge computing time due to a large number of blades in forward-curved blades centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models. Three geometric variables, i.e., location of cut off, radius of cut off, and width of impeller, and one operating variable, i.e., flow rate, were selected as design variables. As a main result of the optimization, the efficiency was successfully improved. And, optimum design flow rate was found by using flow rate as one of design variables. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.