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차정훈(Jeong-Hoon Cha),김문언(Moon-Uhn Kim),박승오(Seung-O Park) 한국항공우주학회 2006 韓國航空宇宙學會誌 Vol.34 No.1
포물형안정방정식을 이용한 2차원 벽면제트의 선형안정성해석을 수행하였다. 벽면제트 유동은 노즐의 출구근방을 제외하고 경계층근사가 매우 잘 성립하며, 국소상사성의 도입으로 기본유동의 유동방향속도성분은 출구에서의 레이놀즈수에 무관하게 된다. PSE를 사용해 얻은 벽면제트의 안정성특성은 이전의 실험결과들과 좋은 일치를 보임을 알 수 있었다. Linear stability analysis of 2-dimensional wall jet is conducted by using parabolized stability equation (PSE). Wall jet is found to be modelled well by boundary layer approximation except for the neighborhood of the nozzle exit, and the introduction of local similarity variable makes the streamwise basic flow Reynolds number independent. Stability characteristics of the wall jet obtained by PSE analysis are shown to be in good agreement with previous experimental results.
층류 예혼합 곡면 화염의 국부 안정성에 관한 기본적 연구
이대근(Dae Keun Lee),김문언(Moon-Uhn Kim),신현동(Hyun Dong Shin) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Firstly in this paper, the local flow field of weakly curved flames spatially standing in a uniform flow is asymptotically examined. The weakly curved flame means that its radius of curvature at a point of our concern is much larger than characteristic length of unstable flame wrinkles, which is also much larger than flame thickness. In this case, the local flow field near the flame front can be decomposed into an uniform flow, a constant-vorticity flow and a counter flow. Secondly in this paper, the local stability of each flow field obtained as above is reviewed and examined. The flame structure is resolved by a large activation energy asymptotics and a long wave approximation. The coupling between hydrodynamics and diffusion processes is included and near-unity Lewis number is assumed. From these analyses, the local stability of curved flames that we are already known is qualitatively described and a suggestion on the works to do is proposed.
김응삼,한기호,조영호,김문언,Kim, Eung-Sam,Han, Ki-Ho,Cho, Young-Ho,Kim, Moon-Uhn 대한전기학회 2001 전기학회논문지C Vol.49 No.5
In this paper, we present theoretical and experimental study on the viscous damping of the on-substrate torsional micromirrors, oscillating near the silicon substrates. In this theoretical study, we develop theoretical models and test structures for the viscous damping of the on-substrate torsional micromirrors. From a finite element analysis, we estimate the theoretical damping coefficients of the torsional micromirrors. From a finite element analysis, we estimate the theoretical damping coefficients of the torsional micromirrors, fabricated by the surface-micromaching process. From the electrostatic test of the fabricated devices, frequency-dependent rotationalvelocity of the micromirrors has been measured at the atmospheric pressure using devices, frequency-dependent rotational velocity of the micromirrors has been measured at the atmospheric pressure using the Mach-Zehnder interferometer system. Experimental damping coefficients have been extracted from the least square fit of the measured rotational velocity within the filter bandwidth of 150 kHz. We have compared the theoretical values and the experimental results on the dynamic performance of the micromirrors. The theoretical analysis overstimates the resonant frequency in the amount of 15%, while underestimating the viscous damping in the factors of 10%.
Computation of the Slow Viscous Flow about a Circular Arc
추정호(Jeong-ho Chu),김문언(Moon-Uhn Kim),최도형(Do Hyung Choi) 한국전산유체공학회 1997 한국전산유체공학회 학술대회논문집 Vol.1997 No.-
와도-유량함수를 이용하여 원호 주위를 흐르는 점성류를 레이놀즈 수 30까지 계산하였다. 점점 주위에서 발산하는 와도를 원호의 곡률 특성을 잘 표현하는 국소점근식을 이용하여 해석적으로 처리하였다. 그리고, 물체로부터 멀리 떨어진 곳에서는 물체가 받는 힘과 관련이 있는 Oseen 유동을 이용한 경계조건을 사용하였다. 이러한 해석해와 수치해의 접합으로 여러 입사각의 유동에 대한 원호 주위에서 박리를 보다 안정적이고 효율적으로 고찰하였다.