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밑에서 일정하게 가열되는 유체층의 안정성 : 점근해 Asymptotic Analysis
김장주,최창균 한국화학공학회 1980 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.18 No.5
대류가 일어나지 않는 상태에서 전도에 의한 비정상적인 온도분포를 유효 열깊이와 밑면의 온도를 이용하여 모사하고 이를 이용하여 간편하게 적용될 수 있는 점근해법을 제시하고 이를 이용하여 최초 정지상태에 있는 수평면상의 유체에 대한 안정성을 해석하였다. Prandtl수가 큰 경우 열 disturbance는 유효 열 깊이내에 한정된다는 것을 확인할 수 있었고 온도 분포의 비선형 정도가 큰 경우 점근해법은 안정성 해석 뿐만 아니라 자연대류의 시작시간을 구하는데 잘 적용되었다. The extended Rayleigh-Be´nard problem, where an unperturbed temperature profile is nonlinear and time-dependent, was examined by linear stability theory. The unperturbed temperature profile induced by constant heat flux from below was approximated, using a bottom temperature and penetration distance. Applying this modified temperature profile to the present system, the asymptotic power-series method was developed and the onset of natural convection was analyzed. It was found that this analysis is well applied to the transient system with the Rayleigh number larger than 10⁴. It is evident that for large Prandtl numbers temperature disturbances are confined within the effective thermal depth.
2대의 CCD 카메라를 이용한 새로운 3차원 형상 측정법
김장주,정국영 대한치과기공학회 2002 대한치과기공학회지 Vol.24 No.1
Accurate acquisition of surface geometries such as machined surfaces, biological surfaces, and deformed partshave been very important technique in scientific study and engineering, expecially for system design,manufacturing and inspection. Two camera method is relatively simple with an acceptable accuracy. In this paper,a new method is studied to acquire 3D geometric data of the small object such as a die in stone model. When thedevices, cameras, laser beam and object are in a perfect plane, the calculation becomes very simple with less error.But this paper shows that arbitrarily positioned system can also be used to obtain 3D data.
도재금속구조물을 위한 Ni-Cr계 비귀금속합금의 주조성에 관한 연구
김장주 광주보건대학 1997 論文集 Vol.22 No.-
The purpose of this study is to evaluate the castability of Ni-Cr nonprecious alloys for the porcelain metal framework. Two different Ni-Cr alloys were cast in two kind of phosphate bonded investments at the burnout temperatures of 1400℉, 1500℉ and 1600℉ respectively and the mesh patterns of the cast bodies were measured with magnifier in each case. The results are as follows : 1. The highest castability of the alloy can be obtained with Rexillium Ⅲ cast in the Hi-Temp investment at 1600℉ and the lowest castability is resulted with the Vera bond alloy cast in the Uno-vest at 1400℉. 2. The alloys of Vera bond and Rexillium Ⅲ reveals the highest castability when cast in Hi-Temp investment at temperature of 1600℉ and the castability drops as the temperature drops. 3. The castability of Vera bond and Rexillium Ⅲ alloys when cast in the Uno-vest investment also reveals the highest at 1600℉ and castability drops as the temperature drops.