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Euler 방정식과 Navier-Stokes 방정식을 사용한 유동장 해석 결과의 비교 연구
김문상 한국 항공대학교 항공산업기술연구소 1999 航空宇宙産業技術硏究所 硏究誌 Vol.9 No.-
Euler 방정식과 Navier-Stokes 방정식을 사용하여 유동장을 해석했을 때 사용된 지배 방정식에 따라서 해석 결과에 어떤 차이점이 발생하는지를 파악하였다. 비교 연구에 사용된 유동장 해석 코드는 입력 데이터를 사용하여 선택적으로 Euler 방정식과 Navier-Stokes 방정식을 선택할 수 있도록 구성되어 있으며 Steger-Warming의 flux vector splitting 풍상차분법을 유한체적법에 적용하여 제어 체적 경계면을 지나는 비점성 대류항의 플럭스를 계산하였고, Navier-Stokes 방정식을 사용할 경우 확산항의 플럭스는 중심차분법을 사용하여 계산하였다. 공간 정확도는 MUSCL 기법과 min-mod 플럭스 리미터를 사용하여 2차 공간 정확도가 가능하게 하였으며, 비교 검토 대상으로 마하수 0.85로 비행하는 원형 실린더 주위의 유동장과 마하수 8.0, 받음각 5˚로 비행하는 미사일탄두 형상 주위의 유동장을 선정하였고, 점성 유동장을 해석할 때 사용한 레이놀즈 수는 9.52×10??이었다. 원형 실린더의 경우 Euler 방정식을 사용하여 해석했을 때 충격파가 흐름의 하류 영역에서 형성되었으며 Navier-Stokes 방정식을 사용했을 때의 결과와 비교해 보면 유동 박리가 발생하는 지점과 박리 후 순환 영역의 크기에 차이가 있었다. 그러나 미사일 탄두 형상의 경우 는 충격파의 생성 위치 및 형상에 큰 차이점이 관찰되지 않았다. A comparative study is accomplished to figure out the differences between Euler solutions and Navier-Stokes solutions. The developed flow solver in this research can be used as either Euler solver or Navier-Stokes solver based on the flag in the input data file. The Steger-Warming's upwind finite volume method calculates the convective fluxes through the control volume surface and the diffusion fluxes in Navier-Stokes equations are calculated using a central scheme. The MUSCL and min-mod flux limiter enable the numerical solutions to keep the second order accuracy in space. Two test cases are selected : One is the flowfield analysis around a circular cylinder at Mach 0.85 and the other is the flowfield analysis around a missile shape geometry at Mach 8.0 and 5˚ angle of attack. Both test cases are run at Re=9.52×10?? in viscous flow case. A shock is formed in the downstream region of circular cylinder when the Euler equations are used. The flow separation points and circulation sizes are different between Euler solutions and Navier-Stokes solutions. However, there are not much differences in the shock forming between Euler solutions and Navier-Stokce solutions in the case of missile shape geometry.
김문상,조경래,박강,신현오,Kim, Mun-Sang,Cho, Kyung-Rae,Park, Kang,Shin, Hyun-Oh 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.8
Inspecting the dimensional accuracy of a car-body in assembly line is a very important process to assure high productivity. Now there exist two common inspecting methods in practice. One is to measure a sampled car-body with three dimensional measuring machine, and the other is to measure car-body with three dimensional measuring machine, and the other is to measure car-body in assembly line using many sensors fixed to a large jig frame. The formal method takes too long to inspect a sampled car-body of a same sort, and cannot therefore give an useful error trend for the whole production. On the other hand, the latter lacks flexibility and is very cost-intensive. By using industrial robots and sensors, an in-line Car-Body Measuring(CBM) system which ensured high flexiblity and sufficient accuracy was developed. This CBM cell operates in real production line and measures the check points by the non-contact type using camera and laser displacement sensor(LDS). This system can handle about 15 Measuring points within a cycle time of 40 seconds. A process computer controls whole process such as data acquisition file handling and data analysis. Robot arms changes in length due to ambient temperature fluctuation affecting the measuring accuracy. To compensate this error, a robot arm calibration process was developed.
김문상,김노수,김상용,Kim, Mun-Sang,Kim, No-Su,Kim, Sang-Yong 한국섬유공학회 1966 한국섬유공학회지 Vol.3 No.2
Studies were carried out on shrinkage of cotton rib knit fabrics and the following results were obtained: Wale shrinkages increase abruptly in (+) direction and course shrinkages in (-) direction beyond a certain c.p.i. limit. Effects of the immersion time and temperature to shrinkages are random and negligible. Bleaching increases considerably the shrinkages of rib knit fabrics. Area shrinkages increase linearly with c.p.i and the more complex the constructions are, the larger the increasing ratios. Increasing ratios of area shrinkage of bleached are larder than the scoured and immersed.
김문상,이재곤 한국섬유공학회 1969 한국섬유공학회지 Vol.6 No.2
In order to define the twist structure of yarn, it was assumed that the twisted yarn has a coaxial helix structure. With the assumption it was viewed that the theorical retraction approached to the experimental retraction. Also, it was shown that, even if the thickness of yarn varies, the retraction of yarn was independent on the turn per centimeter if the value of nb remains constant.