• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.858-864
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• 2017

This study aims to restrain free conducting wire-type particles which are commonly and dangerously existing within DC gas-insulated transmission lines. A realistic platform of a coaxial cylindrical electrode was established by using a high-speed camera and a partial discharge (PD) monitor to observe the motion, PD, and breakdown of these particles. The probabilities of standing or bouncing, which can be affected by the length of the particles, were also quantitatively examined. The corona images of the particles were recorded, and particle-triggered PD signals were monitored and extracted. Breakdown images were also obtained. The air-gap breakdown with the particles was subjected to mechanism analysis on the basis of stream theory. Results reveal that the lifting voltage of the wire particles is almost irrelevant to their length but is proportional to the square root of their radius. Short particles correspond to high bouncing probability. The intensity and frequency of PD and the micro-discharge gap increase as the length of the particles increases. The breakdown voltage decreases as the length of the particles decreases.

• Bulletin of the Korean Chemical Society
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• 제35권6호
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• pp.1625-1632
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• 2014

A concise and efficient one-pot synthesis of chroman-2,4-dione-based HKA derivatives by three component reaction of HKAs, triethoxymethane and 4-hydroxycoumarin derivatives under solvent-free and catalyst-free conditions is described. This protocol has many advantages, in that the GAP (Group-Assistant-Purification) chemistry process is involved in this method. As a result, the experimenter can avoid cumbersome process steps such as traditional chromatography and recrystallization purifications. The desired products can be easily obtained by washing the crude products with 95% EtOH.

• Interaction and multiscale mechanics
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• 제6권1호
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• pp.15-29
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• 2013

Phononic system composed of periodical elastic structures exhibit band gap phenomenon, and all elastic wave cannot propagate within the band gap. In this article, we consider one-dimensional binary materials which are periodically arranged as a 20-layered medium instead of infinite layered system for phononic system. The layered medium with finite dimension is subjected to a uniformly distributed sinusoidal loading at the upper surface, and the bottom surface is assumed to be traction free. The transient wave propagation in the 20-layered medium is analyzed by Laplace transform technique. The analytical solutions are presented in the transform domain and the numerical Laplace inversion (Durbin's formula) is performed to obtain the transient response in time domain. The numerical results show that when a sinusoidal loading with a specific frequency within band gap is applied, stress response will be significantly decayed if the receiver is away from the source. However, when a sinusoidal force with frequency is out of band gap, the attenuation of the stress response is not obvious as that in the band gap.

• 한국음향학회지
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• 제26권1호
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• pp.32-41
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• 2007

엔지니어의 모니터링 위치가 한 지점에만 한정되어 있는 음향조정실의 기존개념을 여러 사람이 동시에 작업할 수 있는 지역적인 방식으로 개선하였다. 이를 위하여, Davis의 $LEDE^{TM}$ 방식을 도입하였고, 내부의 구조 및 흡음재료의 특성, 확산기 및 저역흡음기의 설치와 음상법 등을 활용하여 초기시간지연을 제어하였다. 따라서 여러 엔지니어들이 서로 유사한 음향특성 하에서 동시에 소리를 모니터링 할 수 있는 무반사지역을 형성시켰다. 뿐만 아니라, 음향조정실 (특히 무반사지역) 안에서 정재파, 음향초점, 컬러링, 하스효과 그리고 플러터 에코 등의 발생을 억제하거나 크게 감소시킬 수 있었다.

• 한국가시화정보학회지
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• 제18권3호
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• pp.52-60
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• 2020

When a bubble reaches a free surface, a bursting of the bubble produces a high speed jet. Despite its practical importance, significant effort has been devoted to investigate a bursting jet by a single bubble near a free surface. In the present study, we perform numerical simulations of bubbles in a tandem arrangement at Bo=0.05. The configuration of the tandem bubbles is systematically varied by changing a radius of a following bubble (RF) and the gap distance between two bubbles (L). Compared to a single bubble case, we show that the bursting bubble in the tandem arrangement accelerates, and the jet velocity increases. Moreover, we find that a critical gap distance at which the jet velocity unexpectedly changes exists in the tandem case.

• 한국전산유체공학회지
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• 제22권1호
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• pp.81-87
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• 2017

The characteristics of flow past a square cylinder submerged under the free surface have been numerically studied. An immersed boundary method was adopted for implementation of the cylinder cross-section in a Cartesian grid system. Also, a level-set method was used to capture the interface of the two fluids. The case for Reynolds number 150 was examined. At the specific Reynolds number, by varying the gap ratio(0.25, 0.40, 0.55, 0.70, 1.00, 1.50, 2.50, 5.00) the effects of the free surface on the force coefficients and Strouhal number of vortex shedding were identified. The presence of the free surface very close to the cylinder significantly affects the shedding pattern, resulting in considerable deviation of the force coefficients and Strouhal number from those of the single-phase flow. In addition, the influence of Froude number was considered in this study. By increasing Froude number(0.2-0.4), flow topology change was identified at the specific gap ratios(0.40, 0.70, 1.50, 5.00).

• 정보과학회 논문지
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• 제42권3호
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• pp.361-366
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• 2015

틈(Gap) 파싱은 완전하지 않고 틈이 있는 입력 스트링에 대한 구문 분석을 수행한다. 이런 틈 파싱에 관한 기존 연구로서 임의의 문법에 대한 단일 틈 파싱 알고리즘과 LL(1) 문법에 대한 단일 틈 파싱 알고리즘이 제안되었으며, 이들의 시간복잡도는 각각 $O(n^3)$와 $O(n^2)$이다. 본 논문에서는 확장된 PLR(1) 문법에 대한 단일 틈 파싱 알고리즘을 제안한다. 확장된 PLR(1) 문법은 LR(1) 문법의 부분 클래스이지만 LL(1) 문법보다는 휠씬 넒은 범위의 문법 클래스이다. 이 문법 클래스에 대한 단일 틈 파싱 알고리즘이 LL(1) 문법에 대한 기존에 알려진 단일 틈 파싱 알고리즘의 복잡도와 동일한 $O(n^2)$임을 보인다.

• Steel and Composite Structures
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• 제18권2호
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• pp.395-408
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• 2015

The paper considers the free vibration analysis of FGM grid systems. Up to now, very little work has been done on this type of system and the paper aspires to fill this gap. Based on the hybrid-stress finite element formulation free vibration solutions for FGM grid systems of various aspect ratios, different types of gradations functions, and support conditions are determined. The tabulation of these results, not available thus far, should be useful to designers and researchers who may use them.

• 신재생에너지
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• 제3권4호
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• pp.54-62
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• 2007

In this paper, we report the research highlight on the preparation and characterization of Indium-free $Cu_2ZnSnSe_4$ and Indium-reduced $CulnZnSe_2$ thin films in order to seek the viability of these absorber materials to be applied in thin film solar cells. The films of $Cu_2ZnSnSe_4\;and\;CulnZnSe_2$ were prepared using mixed binary chalcogenides powders. It was observed that Cu concentration was a function of substrate temperature as well as CuSe mole ratio in the target. Under an optimized condition, $Cu_2ZnSnSe_4\;and\;CulnZnSe_2$ thin films grew with strong [112]. [220/204] and [312/116] reflections. Both $Cu_2ZnSnSe_4\;and\;CulnZnSe_2$ films were found to exhibit a high absorption coefficient of $104^4cm^{-1}\;Cu_2ZnSnSe_4$ film showed a band gap of 1.5eV which closes to the optimum band gap of an ideal solar absorber for a solar cell. On the other side, an increase of optical band gap from 1.0 to 1.25eV was found to be proportional with an increase of Zn concentration in the $CulnZnSe_2$ film. All films in this study revealed a p-type semiconductor characteristic.

• Steel and Composite Structures
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• 제47권3호
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• pp.365-374
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• 2023

This paper presents a new scheme for constructing locking-free finite elements in thick and thin plates, called Discrete Shear Gap element (DSG), using multiphase material topology optimization for triangular elements of Reissner-Mindlin plates. Besides, common methods are also presented in this article, such as quadrilateral element (Q4) and reduced integration method. Moreover, when the plate gets too thin, the transverse shear-locking problem arises. To avoid that phenomenon, the stabilized discrete shear gap technique is utilized in the DSG3 system stiffness matrix formulation. The accuracy and efficiency of DSG are demonstrated by the numerical examples, and many superior properties are presented, such as being a strong competitor to the common kind of Q4 elements in the static topology optimization and its computed results are confirmed against those derived from the three-node triangular element, and other existing solutions.