• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.411-414
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• 2002

The CHFG(Critical Heat Flux in Cap) test results have been evaluated to quantify the critical powers in hemispherical narrow gaps and Park's correlation has been verified. For verification of the Park's correlation, the critical powers in hemispherical narrow gaps have been measured using water at a pressure of 0.1-0.3 WPa for the hemispherical gap thickness of 1.0mm, and the heated top diameter of 238mm The measured critical powers were compared with Park's and Monde's correlation. As a results, the Park's correlation was most accurate of other correlations, however, estimated the critical powers somewhat larger than measured ones. So, it was suggested that the diameter factor in Park's correlation should be revised.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2006년도 High Temperature Superconductivity Vol.XVI
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• pp.81-81
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• 2006

• 마이크로전자및패키징학회지
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• 제7권2호
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• pp.13-19
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• 2000

금속간 화합물의 두께와 솔더와 금속간 화합물의 계면 거칠기가 Cu pad위의 BGA솔더 조인트의 전단강도에 미치는 영향을 Sn (0. 1.5, 2.5wt.% Cu)와 Sn-40Pb (0, 0.5wt.% Cu) 솔더를 사용하여 알아보았다. 각각의 조성의 솔더를 사용하여 솔더링 반응을 1, 2 ,4분 동안 한 후 전단강도를 측정하였다. Sn솔더에 Cu 첨가는 초기 금속간 화합물의 두께를 증가시키는 결과를 가져오는 반면 Sn-40Pb 솔더의 경우에는 주로 금속간 화합물/솔더의 계면거칠기의 감소를 가져오게 된다. 최대 전단 강도값을 나타내는 금속간 화합물의 임계두께는 솔더의 물질에 따라 변하게 되는데, 본 실험에서는 Sn-Cu솔더의 경우에는 ~2.3 $\mu\textrm{m}$, Sn-Pb-Cu에서는 ~ 1.2 $\mu\textrm{m}$ 정도로 측정되었다. 금속간 화합물의 임계두께는 금속간 화합물/솔더의 계면이 더욱 거칠어질수록 증가하는 것으로 나타났다. 이는 파단면 관찰에서 나타난 초기의 솔더내에서의 파괴가 금속간 화합물이 임계두께 이상으로 성장함에 금속간 화합물/솔더의 계면으로 이동하는 결과와 일치한다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2002년도 춘계공동학술발표회요약집
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• pp.103-103
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• 2002

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1775-1780
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• 2003

A hybrid finite element analysis was used to analyze the influence of ring gear rim thickness and spline number on the static properties of an epicyclic gear system with manufacturing errors. Both of these parameters affected the bearing force and critical stress. The effect of changes in the rim thickness on the load sharing between the gears depended on the type of manufacturing error. Ring flexibility improved the load sharing between planetary gears only in systems with planet tooth thickness or planet tangential errors; for other types of error, ring flexibility worsened the load sharing. To improve load sharing, rim thickness and spline number should be controlled within a specific range. The effect of the ring gear boundary condition was more apparent in a system with errors than in a normal system.

• 한국항공운항학회지
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• 제23권4호
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• pp.1-5
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• 2015

In this work, a study was conducted to investigate the effect of diaphragm thickness on the regression rate of the hybrid rocket motor. To observe the flow pattern and the recirculation zone, visualizations of combustion chambers with different diaphragm thickness (5mm, 10mm) were performed. It was found that the case with 5 mm thickness had a larger recirculation zone and therefore, had a higher regression rate than the case with 10mm thickness due to the increased residence time and heat transfer toward the fuel surface. Finally, it was concluded that the thickness of diaphragm can be a critical parameter for the enhancement of the regression rate.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.252-255
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• 2009

The roll gap set-up in the finishing mill is one of the most important technologies in the hot plate rolling process. As the target thickness can be obtained by the correct set-up of the roll gap, improving the roll gap set-up technology is very critical for plate thickness accuracy. The main cause of thickness variation in hot plate mills is the non-uniform temperature distribution along the length of the slab. The objective of this study is to adjust the roll gap set-up for the thickness accuracy of plate in hot rolling process considering top-end temperature drop. Therefore this study has concentrated on determining the correct amounts of roll gap to compensate thickness variation due to top-end temperature drop. The off-line simulation of compensated roil gap significantly decreases top-end thickness variation.

• Structural Engineering and Mechanics
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• 제14권6호
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• pp.661-677
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• 2002

The subject of this investigation is to study the buckling of cross-ply laminated orthotropic cylindrical thin shells with variable elasticity moduli and densities in the thickness direction, under external pressure, which is a power function of time. The dynamic stability and compatibility equations are obtained first. These equations are subsequently reduced to a system of time dependent differential equations with variable coefficients by using Galerkin's method. Finally, the critical dynamic and static loads, the corresponding wave numbers, the dynamic factors, critical time and critical impulse are found analytically by applying a modified form of the Ritz type variational method. The dynamic behavior of cross-ply laminated cylindrical shells is investigated with: a) lamina that present variations in the elasticity moduli and densities, b) different numbers and ordering of layers, and c) external pressures which vary with different powers of time. It is concluded that all these factors contribute to appreciable effects on the critical parameters of the problem in question.

• Advances in concrete construction
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• 제9권1호
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• pp.103-113
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• 2020

This paper deal with the critical fluid velocity response of nanocomposite pipe conveying fluid based on numerical method. The pressure of fluid is obtained based on perturbation method. The motion equations are derived based on classical shell theory, energy method and Hamilton's principle. The shell is reinforced by nanoparticles and the distribution of them are functionally graded (FG). The mixture rule is applied for obtaining the equivalent material properties of the structure. Differential quadrature method (DQM) is utilized for solution of the motion equations in order to obtain the critical fluid velocity. The effects of different parameters such asCNT nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios and internal fluid are presented on the critical fluid velocity response structure. The results show that with increasing the CNT nanoparticles, the critical fluid velocity is increased. In addition, FGX distribution of nanoparticles is the best choice for reinforcement.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2001년도 추계학술대회 논문집
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• pp.534-539
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• 2001

This paper presents the critical speed analysis of geogrid-reinforced rail roadbeds on soft soil. A rail roadbed on soft ground must be designed to avoid intolerable stress in the underlying soil and to give sufficient support for the rail system. At high speeds, the deformation of rail systems will gain dynamic amplification, and reach excessive values as a certain speed, here termed critical speed is approached. The elastic Winkler foundation model was used to predict the critical speed of geogrid-reinforced rail roadbeds on soft soil and the model properties were determined by the in-situ cyclic plate load test. Based on the parametric study of elastic beam on Winkler foundation model, the critical speed increase with the increase of the flexural risidity of subgrade EI and the stiffness coefficient of Winkler foundation k. From the in-situ cyclic load tests and analysis of elastic beam on Winkler foundation model, the critical speed increase with increase in number of reinforced layer and non-dimensional value for depth of first geogrid layers and the thickness of reinforced rail roadbed u/d.