• 대한기계학회논문집B
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• 제28권9호
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• pp.1022-1031
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• 2004

The commutation errors by the filtering process in the large eddy simulation are considered. It is compared the conventional filter with the inhomogeneous filter that is devised to reduce the commutation errors. The weighting factor of the inhomogeneous filter suggested by Vasilyev is adopted. Also, using the optimizing function that estimates test filter width to eliminate the dissipations in the region excluding the vicinity of the wall, the flow patterns are analyzed. It is evaluated in simulations of the turbulent channel flow at Reynolds number of 1020, based on friction velocity and channel half height. Results show that the commutation errors can be significantly reduced by using the inhomogeneous filter and the optimized test filter width.

• 한국수산과학회지
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• 제20권4호
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• pp.370-378
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• 1987

Wave reflection control functions of mound for the foundation of composite and perforated break-waters were investigated through the theoretical considerations. The theory developed is based on a simple summation of components of reflected waves. The applicability of the theory is assured by the comparative studies of the theoretical calculation and experimental data on the sea surface elevation in front of a breakwater. It is found that the reflection is mainly controlled by depth and width of the mound. In the design of composite type perforated breakwaters, the width of perforated part of the upright section can be decreased to less than half of the conventional design width for the same reflection by using the reflection control function of mound part and the reflection can be reduced until less than $30\%$ of that in the composite breakwaters. Using the results, a design method of mounds is proposed, by which the reduction of wave reflection is assured under the given wave conditions.

• ETRI Journal
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• 제38권6호
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• pp.1135-1144
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• 2016

Fractal antenna arrays are geometry-based thinned arrays having multiband applications. The major challenge of these arrays is their large number of elements at higher expansion factors. This article presents the thinning of fractal antenna arrays while maintaining an appropriate balance between the side lobe level and beam width by using various quantized fractal distribution functions. A 2D square fractal antenna array and 3DSierpinski gasket antenna array are considered in this article to validate the proposed distribution functions. Nearly one third of the antenna elements are thinned in each successive iteration except in the case of a one-count distribution function. The proposed technique can simplify practical implementation and exhibits better performance for various parameters such as the side lobe level, side lobe angle, and half power beam width than fully populated fractal antenna arrays.

• 한국광학회지
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• 제13권4호
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• pp.319-323
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• 2002

Linewidth enhancement factor ($\alpha{-factor}$) 값이 2와 4인 두 종류의 1.55${\mu}m$ 다층양자우물(Multi-Quantum Well; MQW) 대면적 레이저 다이오드를 제작하였다. 제작된 레이저 다이오드의 far-field 측정 결과 $\alpha{-factor}$ 값이 4일 때 보다 2인 구조에서 반폭치(Full Width at Half Maximum; FWHM)와 필라멘테이션(filamentation)이 감소되었다. 주입전류의 증가에 따라 두 종류 모두 far-field의 FWHM의 증가 현상이 나타났고 이는 filament spacing이 감소하였기 때문으로 설명된다.

• 한국초전도ㆍ저온공학회논문지
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• 제5권3호
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• pp.20-22
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• 2003

Y$_2$O$_3$ films were pulsed laser deposited on cube textured Ni and Ni-W substrates to be used as a single buffer layer of YBCO coated conductor. Initial deposition of $Y_2$O$_3$ films was performed in a reducing atmosphere, and subsequent deposition was done in the base pressure of the chamber and oxygen atmosphere. The $Y_2$O$_3$ films have a strong cube texture (The full width at half maximum of the ø-scan of $Y_2$O$_3$ was 8.4 which was the same as that of metal substrate) and smooth crack-free microstructure. The biaxially textured YBCO films (The full width at half maximum of the ø-scan was 10.2) pulsed laser deposited on the $Y_2$O$_3$/metal exhibited Tc(R=0) of 86.5K and Jc of 0.7 MA/cm2 at 77K in self field, representing that the $Y_2$O$_3$ single buffer layer is an efficient diffusion barrier of Ni and thus very promising for the achievement of high-Jc YBCO coated conductor.

• Structural Engineering and Mechanics
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• 제31권6호
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• pp.679-696
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• 2009

The paper aims at analyzing the stress distribution around an underground opening that is subjected to non-symmetrical surface loading with emphasis on opening shapes with sharp corners and the stress concentrations developed at these locations. The analysis is performed utilizing the BIE method coupled with the Neumann's series. In order to implement this approach, the special recurrent relations for half plane were proven and the modified Shanks transform was incorporated to accelerate the series convergence. To demonstrate the capability of the developed approach, a horseshoe shape opening with sharp corners was investigated and the location and magnitude of the maximum hoop stress was calculated. The dependence of the maximum hoop stress location on the parameters of the surface loading (degree of asymmetry, size of loaded area) and of the opening (the opening height) was studied. It was found that the absolute magnitude of the maximum hoop stress (for all possible surface loading locations) is developed at the roof points when the opening height/width ratio is relatively large or when the pressure loading area is relatively narrow (compared to the roof arch radius), and contrarily, when the opening height/width ratio is relatively small or when the surface pressure is applied to a relatively wide area, the absolute magnitude of the maximum hoop stress is developed at the bottom sharp corner points.

• 한국진공학회지
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• 제11권2호
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• pp.97-102
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• 2002

유기금속화학기상증착방법 (metal-organic chemical vapor deposition : MOCVD)을 이용하여 실리콘 (100) 기판위엔 ZnO막을 증착하였다. 공정온도 ($250^{\circ}C$~$400^{\circ}C$)와 Ar과 $O_2$가스의 유량 비 변화에 따른 ZnO막의 특성변화를 조사하였다. 막의 결정성은 공정온도가 증가함에 따라 향상되었으며 $400^{\circ}C$에서 $0.4^{\circ}$의 반치폭(full width at half maximum : FWHM)을 얻었다. 공정온도 변화에 따른 표면 평활도(surface smoothness)변화는 결정성과 반대의 경향성을 보였다.

• Elastomers and Composites
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• 제39권4호
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• pp.281-285
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• 2004

이 연구는 열분석법을 이용하여 간단하게 자유 라디칼 중합의 활성화 에너지를 결정하는 방법을 부틸 아크릴레이트을 모델로 하여 구했다. 활성화 에너지는 Kissinger, Osawa 및 half-width법인 다수의 주사 속도법 (multiple scanning-rate method)을 이용하여 $1^{\circ}C/min,\;2^{\circ}C/min,\;5^{\circ}C/min$, 그리고 $10^{\circ}C/min$로 측정하였으며 단수 주사 속도법인 Barret 법을 이용하여 구하였다. 열분석법에 의해 구해진 중합반응의 활성화 에너지는 개시반응, 성장반응 및 종결반응의 각각의 활성화 에너지에서 계산된 전체 중합반응에서의 활성화 에너지와 가깝게 접근하였다.

• Journal of Power Electronics
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• 제17권6호
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• pp.1391-1401
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• 2017

In this paper, a secondary resonance half-bridge dc-dc converter with an inductive output filter is presented. The primary side of such a converter utilizes asymmetric pulse width modulation (APWM) to achieve zero-voltage switching (ZVS) of the switches, and clamps the voltage of the switch to the input voltage. In addition, zero current switching (ZCS) of the output diode is achieved by a half-wave rectifier circuit with a filter inductor and a resonant branch in the secondary side of the proposed converter. Thus, the switching losses and diode reverse-recovery losses are eliminated, and the performance of the converter can be improved. Furthermore, an inductive output filter exists in the converter reduce the output current ripple. The operational principle, performance analysis and design equation of this converter are given in this paper. The analysis results show that the output diode voltage stress is independent of the duty cycle, and that the voltage gain is almost linear, similar to that of the isolation Buck-type converter. Finally, a 200V~380V input, 24V/2A output experimental prototype is built to verify the theoretical analysis.

• 복식
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• 제40권
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• pp.95-107
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• 1998

The purpose of this research paper is to offer basic data for cloth design which is intended to apply appropriate shape and catacity to cloth. Followings are the analyzed result of investigation which was conducted to figure out the character of middle aged from 35 to 59 years old-women body especially in lower half of their body. 177 women took part in this investigation. 1. As a result of analyzed characters for middle aged women body shape, taking a side view of body, there are great variance in thickness coefficient which indicates the size of body. 2. According to a comparison result of early middle aged women body shape with late middle aged women body shape, the value in height items get shorter otherwise the value in thickness items get longer getting older. It means late middle aged women are relatively fat. 3. For the analysis of women body especially in lower half, 8 factors were used. They are as followings. Factor 1. Side thickness of lower half. Factor 2. Width of lower half. Factor 3. Height of lower half Factor 4. Droop of underbelly Factor 5. Salient rate of buttocks. Factor 6. Length of buttocks. Factor 7. Salient rate of underbelly. Factor 8. Droop of buttocks 4. Lower half shapes of middle aged women were divided into three groups and the character of each group are as followings. 〈Group 1〉65.0% of women who took part in this investigation have this type of body shape. They have long value in height items and thickness items. 〈Group 2〉16.4% of women who take part in this investigation were belonged to this group. The value in height items were not so different from group 1 but the thickness value are shorter than group 1. Women of group 2 have slime body shape. 〈Group 3〉18.6% of women were belonged to group 3. They show the shortest value in height items otherwise the longest value in thickness items. Therefore they are the smallest and the fattest group in this investigation.