• 한국항공우주학회지
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• 제34권7호
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• pp.79-88
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• 2006

본 논문에서는 대와동모사를 이용하여 모형 가스터빈 연소기에서 난류 예혼합연소의 선회 유동구조와 화염특성이 검토되었다. 비정상 화염 거동을 모사하기 위하여 G-방정식 화염편 모델이 적용되었다. 결과로서, 입구 선회수 증가에 따른 코너 및 중앙 재순환 유동이 뚜렷한 차이를 보이며, 화염의 길이도 점차 감소됨을 확인 할 수 있었다. 또한 강선회 조건에서 역화현상의 원인이 확인되었다. 정확한 비정상 화염거동의 모사를 위하여, 연소실 내 음향파 거동의 예측성능이 우선적으로 검토되었으며, 스텝 모서리 근처에서 생성된 와동이 화염면 변동에 가장 큰 영향을 주고 있음을 알 수 있었다. 마지막으로 비정상 화염-와동 상호작용에 대한 해석을 통해 선회와 음향파의 전개로부터 생성된 와동의 진동이 화염면 및 열발생의 변동과 밀접하게 관련되어짐을 체계적으로 규명하였다.

• 한국방재학회 논문집
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• 제11권3호
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• pp.165-174
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• 2011

본 연구의 목적은 하천의 홍수저감을 목적으로 설치하는 하천변 저류지의 홍수저감특성을 분석하기 위한 모형의 개발에 있다. 하천에 홍수가 발생하였을 경우에 하천변 저류지는 하천의 홍수첨두 일부를 분담하는 기능을 갖으며, 이는 제방의 일부를 낮춘 월류제를 통한 범람으로 가능하게 되며, 또한 범람된 물은 저류지 내에서 저류 하게 된다. 이러한 저류지가 갖는 홍수저감특성은 하천 홍수위, 월류제 제원(높이, 위치, 길이 등), 저류지의 수리거동 등에 의해 좌우되게 되므로, 본 연구에서는 이러한 일련의 물의 거동을 재현하기 위해서 1차원 하천부정류 모델, 월류제 상의 월류량 산정 모델 및 제내지 홍수범람 모델을 연계한 통합모형을 개발 하였다. 이상에서 개발된 연계 모형을 가상하도 및 실제하도에 적용하여 월류제가 갖는 기하적 특성이 홍수경감에 미치는 영향에 대해 분석하였으며, 이를 통해 향후 개선하여야 할 시사점에 대해 기술하였다.

• 수산해양교육연구
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• 제27권5호
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• pp.1303-1309
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• 2015

The behavior and flow characteristics of the floating wave energy converter were analyzed by using CFD in this study. The average significant wave height was confirmed as 0.5~2.0m from the Korean coastal sea area. This study was carried out by selecting a range of 1.0~1.6m in the wave height to simulate the operations of realistic wave energy converter system. The principle of a piston wave maker was applied in order to produce periodic wave. The behavior of the wave energy converter and the state of the wave overtopping according to the generated periodic wave were confirmed through the unsteady three-dimensional flow analysis. It was found that the wave overtopping rate according to the generated periodic wave was in range of the 11.6~30.0 kg/s.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1998-2004
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• 2003

Numerical study were performed to analyze for fire safety in railway tunnel with forced ventilation vents. For the condition of train fires with heat release rate of 30 MW, unsteady three dimensional analysis were carried out to investigate the effects of smoke movements, the heat transfer and $CO_2$ concentrations and in double track tunnel with two vents. Among three operation modes of forced ventilations at two vents, the exhaust-exhaust mode of the vent represents the best performance for the evacuation of passengers to avoid the fire.

• 한국인쇄학회지
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• 제28권2호
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• pp.45-56
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• 2010

The computer simulation is presented of gravure ink transferring behavior and penetration to the paper when an gravure roller is used to transfer a printing ink onto a substrate. The three dimensional unsteady ink motion is simulated by Polyflow package software and experimented by IGT gravure printing test machine. The simulation is performed where the flow domain is bounded above by a stress free surface and bounded below by a moving substrate. Specific predictions are made for particular pattern of cells and substrates. Cell size and ink rheological properties are found to be the principal determination of transferring behavior. Simulation is currently restricted to the flow domain beneath the receding meniscus. Both Newtonian and shear thinning inks are considered.

• 소음진동
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• 제4권2호
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• pp.221-230
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• 1994

This paper deals with the dynamic stability and the nonlinear behavior of a check valve system. The nonlinear equations of motion of fluid-valve interation model are derived, which are composed of the unsteady Bernoulli's equation included the jet flow mechanism and equation of motion of a check valve formulated by one degree of freedom. Also, the derived equations of motion are nondimensionalized. According to the change of the nondimensional parameters, the stabilities of the system are analyzed, and the nonlinear interaction responses of the check valve and the passing flow rate are obtained. As the results, the stability charts are constructed for the variation of nondimensional parameters. It is shown that self-excited vibrations exist in a check valve system. And also the Hopf bifurcation and the periodic doubling are found. The presented theoretical model of a check valve system can be utilized to the design and operation of a piping system with the check valve.

• 대한기계학회논문집B
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• 제28권7호
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• pp.771-779
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• 2004

Unsteady behavior of the early wake in the viscous flow field past an impulsively started semicircular cylinder is studied numerically. In this paper, we propose the hybrid diffusion scheme to simulate dynamic characteristics of wake such as a fishtail-like flapping and an alternate vortex-shedding more accurately. This diffusion scheme based on particle strength exchange is mixed with the stochastic nature of random walk method. Also, the viscous splitting algorithm which calculates convective and diffusion terms successively is applied in order to handle random walk method effectively. Consequently, the early behavior of wake due to the breakdown of symmetrical vortici balance is more practically simulated with the vortex particle method.

• 에너지공학
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• 제26권4호
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• pp.67-73
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• 2017

미세조류를 바이오 연료로 전환하여 이용하기 위해서는 미세조류의 배양, 응집 수거, 바이오 지질 추출, 에너지 전환 등 여러 공정을 거친다. 각 부분 공정 마다 필요한 비용이 발생하며 이러한 비용을 합산하여 미세조류의 에너지화로의 생산 단가가 만들어진다. 미세조류의 생산비용은 기존의 바이오 연료에 비하여 아직 높은 수준이다. 각 공정에서 생산 비용을 저감하는 것이 미세조류의 바이오 연료로서 가격 경쟁력을 높이는 것이다. 미세조류의 응집 수거는 미세조류가 물과 유사한 밀도로 물에서 분리하기가 어려운 물질이기 때문에 저비용으로 미세조류를 응집하고 수거하는 기술이 필요하다. 미세조류의 응집과 수거를 위해 초음파를 이용하는 공정은 기존 공정에 비하여 환경 위해 요소가 거의 없으며 저비용 고효율의 공정으로써 연구가 필요한 분야이다. 본 연구는 미세조류를 응집 수거하는 방법으로 초음파를 조사할 때 일어나는 유동과 미세조류 거동에 대한 메카니즘을 수치해석을 통해 규명하고자 수행 하였다. 이를 위해 미세조류가 포함된 유체를 배관에 흐를 때 초음파 압력장에서 미세조류가 응집이 일어나는 현상을 비정상상태 유동해석으로 시간 변화에 따라 속도, 압력, 미세조류의 농도 변화를 관찰하여 초음파를 이용한 미세조류 응집에 대한 최적 설계의 토대를 정립하는 것을 목적으로 수행하였다.

• 한국분무공학회지
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• 제1권2호
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• pp.16-23
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• 1996

In case of a high-speed D.I. diesel engine. the injected fuel spray is unavoidable that the impinging on the wall of piston cavity and in this case the geometry of piston cavity has a great influence on the atomization structure and air flow fields. In the field of combustion and in many other spray applications, there are clear evidence of correlation between spray structure and emission of pollutants. Ordinary, the combustion chamber of driving engine have unsteady turbulent flow be attendant on such as the change of temperature, velocity and pressure. So the analysis of spray behavior is difficult. In this study, a single spray was impinged on each cavity wall at indicated angle in a quiescent atmosphere at room temperature and pressure, as being the simplest case, and 3 types of piston cavity such as Dish, Toroidal and Re-entrant type was tested for analyzing the influence of cavity geometry. And hot wire probe was used for analyze non-steady flow characteristics of impinging spray, and to investigate the behavior of spray, the aspects of concentration c(t), standard deviation $\sigma(t)$ and variation factor (v.f.) was measured with the lapse of time.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.365-368
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• 2002

The design of industrial arc plasma systems is still largely based on trial and error although the situation is rapidly improving because of the available computational power at a cost which is still fast coming down. The desire to predict the behavior of arc plasma system, thus reducing the development cost, has been the motivation of arc research. To interrupt fault current, the most enormous duty of a circuit breaker, is achieved by separating two contacts in a interruption medium, $SF_{6}$ gas or air etc., and arc plasma is inevitably established between the contacts. The arc must be controlled and interrupted at an appropriate current zero. In order to analyze arc behavior in $SF_{6}$ gas circuit breakers, a numerical calculation method combined with flow field and electromagnetic field has been developed. The method has been applied to model arc generated in the Aachen nozzle and compared the results with the experimental results. Next, we have simulated the unsteady flow characteristics to be induced by arcing of AC cycle, and conformed that the method can predict arc behavior in account of thermal transport to $SF_{6}$ gas around the arc, such as increase of arc voltage near current zero and dependency of arc radius on arc current to maintain constant arc current density.