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우성형 중성자 수송방정식을 이용한 광첨두현상 감소 및 제거
盧泰元 弘益大學校 科學技術硏究所 1996 科學技術硏究論文集 Vol.7 No.1
The discrete-ordinates and the piecewise constant approximations are applied to both the first-order Boltzmann and the second-order even-parity transport equations. The result is that the mitigation of ray effects is only achieved by so called the 'angularly smearing effect' of the piecewise constant method, in which new angular quadratures are generated by integrating the angle variables over the specified region. In order sense, the newly generated angular quadratures turn out to decrease the contribution of cross-derivative terms in the even-parity equation. This result can be interpreted as the entire elimination of ray effect is possible in the simplified even-parity equation which has no cross-derivative terms. For more valid conclusion, the rotational invariance of the simplified even-parity equation should be studied.
盧泰元 弘益大學校 科學技術硏究所 1999 科學技術硏究論文集 Vol.10 No.1
In this study, the polynomial expansion nodal method is applied to both the simplified even-parity transport equation and its accelerating equation. The result confirms the stability of the method and its accelerating efficiency. We again find that the elliptic nature of the simplified even-parity equation enhances the robustness of the algorithm.
노태원,J.-G. Yoon,B. S. Kang,J. D. Kim,S. Seo,Y. K. Lee,Y. S. Park 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
If ferroelectric random access memory is to become one of major non-volatile memories, the problems in conjunction with existing CMOS integration should be resolved. One of the problems is hydrogen-induced degradation, which occurs during the dielectric layer deposition or the forming gas annealing. We investigated the degradation mechanisms in widely used materials, such as SrBi2Ta2O9, Pb(Zr,Ti)O3 (PZT), and newly discovered (Bi,La)4Ti3O12 (BLT) lms. We found that these materials have dierent hydrogen-induced degradation mechanisms: The degradation of the Bi-layered BLT and SBT should be due to the chemical decomposition of weak Bi-O bond, but that of PZT is most likely come from trapped defects charges.
축소 확대 노즐의 열전달 해석을 위한 열전달 계수 계산 및 검증
노태원,노태성,이형진,이현섭,유필훈 한국추진공학회 2022 한국추진공학회지 Vol.26 No.2
The heat transfer coefficient on the wall, which is used as a boundary condition in the thermal analysis of general contract-divergent supersonic nozzles, affects the thermal analysis accuracy of the entire nozzle. Accordingly, many methods of deriving a heat transfer coefficient have been proposed. In this study, the accuracy of each method was compared. For this purpose, the heat transfer coefficients were calculated through theoretical-based analogy methods, semi-empirical equations, and CFD simulations for the previously performed heat transfer experiment with an isothermal wall and compared with the experimental results. The results show that the Prandtl-Taylor analogy methods and the CFD results with the k-ω SST turbulence model were in good agreement with the experimental results. Furthermore, the Modified Bartz empirical formula showed an overall over-prediction tendency. 일반적인 축소 확대형 초음속 노즐에 대한 열해석에서 경계조건으로 사용되는 벽면의 열전달 계수는 노즐 전체의 열해석 정확도에 영향을 미친다. 이에 많은 열전달계수 도출 방법이 제안되어 왔으며, 본 연구에서는 각각의 기법들을 실제 실험 조건에서 열전달 계수를 계산하고 비교하고자 하였다. 이를 위해 기 수행된 벽면 등온 노즐의 열전달실험에 대해 이론 기반의 analogy 기법과 반경험식, 유체전산해석을 통해 열전달 계수를 도출하고 실험결과와 비교하였다. 해석 결과는 반경험식들은 전반적으로 다른 방법에 비해 대류 열전달 계수를 과도하게 예측하고, Prandtl-Taylor analogy 기법과 k-ω SST 모델을 적용한 전산해석 결과가 실험결과와 비교적 잘 일치하는 경향성을 보였다.