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홍단비,안오성 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.11
본 논문에서는 항공우주 구조물 설계를 효율적으로 수행할 수 있는 다중레벨 최적화기법을 소개하였다. 복잡한 항공우주 구조물을 설계하는 경우 많은 설계변수를 다루어야 하는 특성상 거대한 수학적 문제로 정식화되고, 이러한 큰 수학적 문제를 직접 풀기 위해서는 많은 계산자원 및 계산시간이 필요하고, 수렴성이 좋지 않은 등 많은 문제점이 있다. 따라서 큰 규모의 전역레벨 문제를 상대적으로 풀기 용이한 여러 개의 작은 국부레벨의 문제로 나누어 푸는 다중레벨 최적화기법은 상기의 문제점을 해결하기에 적합한 장점을 가지고 있다. This paper shows a multi-level optimization in order to perform efficiently the structural design for aerospace structure. The feature of structural design with a complex layout leads to a huge-sized mathematical problem with a great deal of design variables accordingly. In order to solve such a large-scale problem, enormous computational resources are required because the amount of computational resources and time required is proportional to the size of numerical problem in question. Furthermore, the direct solution of a large-scale problem would frequently bring about the performance problem such as a poor convergence. Hence, the multi-level optimization approach is adequate to solving such a large-scale problem efficiently, where the original problem in the global level can be divided into a set of smaller problems in the local level to be more easily solved.
원주형(圓柱型) 장애물의 위치변화에 따른 이차원 난류 열전달 특성 변화의 측정실험
최영돈,홍오성 고려대학교 공학기술연구소 1987 고려대학교 생산기술연구소 생기연논문집 Vol.23 No.1
The effects of cylindrical blockages in unsymmetrical position in the rectangular duct on the velocity profiles and heat transfer coefficients were examined experimentally. Duct was made with having the cross section of the ratio between width and height of 5.8:1 in order to simulate 2-dimensional channel flows at its center line. Cylindrical blockage was located at the position where the flow was fully developed and constant heat flux was supplied from the upper and lower wails after blockage. Blockages increase the heat transfer coefficients of the wall toward which blockage shifted,. up to 5 diameters downstream, on the other hand they reduce the heat transfer coefficients of the wall in opposite side.
최우형,오성한,이충재,임종국,정봉섭,홍혁진 대한척추신경외과학회 2012 Neurospine Vol.9 No.3
Objective: Osteoporotic compression fracture is an increasing issue in this community and its diagnosis depends on the magnetic resonance images (MRI). Although T1- and T2-weighted images (T1WI and T2WI) have high sensitivity and specificity, the fat suppression technique gives more clear delineation of this abnormalities. Accordingly, we re-evaluated its exact sensitivity and specificity for the imaging diagnosis of osteoporotic compression fractures in our cases. For additional information about the osteoporotic compression fractures, we evaluate the fracture lines, fluid sign and adjacent discs change on the MRI. Methods: Retrospectively, total 85 patients who had been diagnosed with acute osteoporotic compression fracture were enrolled. They all had been underwent MRI including T1WI, T2WI and T2- Spectral Adiabatic Inversion Recovery (SPAIR) sequence. Results: In this study, the incidence of high signal intensity on T2-SPAIR image was very high (0.9917). The fluid sign was seen in 56.7% on the SPAIR image. The fracture lines were more observed on the T2WI than T1WI (p=0.0062). The adjacent discs change on T2WI and T2-SPAIR image were higher than T1WI (p<0.001). Conclusion: For the acute osteoporotic compression fracture, T2-SPAIR image is the most specific sequence of the all sequences. The fluid sign is another suggestive finding when considered other studies. T2WI is more useful to find the fracture line than T1WI. Abnormal signal intensity on the adjacent discs may provide additional information for the acute osteoporotic compression fractures. Objective: Osteoporotic compression fracture is an increasing issue in this community and its diagnosis depends on the magnetic resonance images (MRI). Although T1- and T2-weighted images (T1WI and T2WI) have high sensitivity and specificity, the fat suppression technique gives more clear delineation of this abnormalities. Accordingly, we re-evaluated its exact sensitivity and specificity for the imaging diagnosis of osteoporotic compression fractures in our cases. For additional information about the osteoporotic compression fractures, we evaluate the fracture lines, fluid sign and adjacent discs change on the MRI. Methods: Retrospectively, total 85 patients who had been diagnosed with acute osteoporotic compression fracture were enrolled. They all had been underwent MRI including T1WI, T2WI and T2- Spectral Adiabatic Inversion Recovery (SPAIR) sequence. Results: In this study, the incidence of high signal intensity on T2-SPAIR image was very high (0.9917). The fluid sign was seen in 56.7% on the SPAIR image. The fracture lines were more observed on the T2WI than T1WI (p=0.0062). The adjacent discs change on T2WI and T2-SPAIR image were higher than T1WI (p<0.001). Conclusion: For the acute osteoporotic compression fracture, T2-SPAIR image is the most specific sequence of the all sequences. The fluid sign is another suggestive finding when considered other studies. T2WI is more useful to find the fracture line than T1WI. Abnormal signal intensity on the adjacent discs may provide additional information for the acute osteoporotic compression fractures.