• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.8
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• pp.24-32
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• 2005

Micro-source units having power ratings in thousands of watts can provide power quality with higher reliability and efficiency than the conventional large scale units. Since these units are small and easy to install, they are clustered with loads creating micro-grid services to customer sites such as office buildings, industrial parks and homes. Micro-sources adopt voltage source inverter to ensure the power quality of sensitive loads. This paper deals with the connection of micro-sources into the system grid EMTDC modeling of the grid connected micro-sources at the power frequency range are proposed and the characteristics of the control system parameters are investigated. Simulation results show that the micro-grid system with two micro-sources has good dynamic characteristics.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.2
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• pp.87-100
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• 2006

A kinematically constrained microplane constitutive model is developed for intact granite. The model is verified by fitting the experimented data of Westerly granite and Bonnet granite. Using the model with the standard finite element method, the behavior of the intact granite subjected blasting impact is studied. What is studied includes the attenuation of the blasting waves, the size of the fractured zone and the effect of the charge condition to avoid overbreak of the rock mass. The model developed captures the energy loss due to the inelastic behavior and the microcracking of granite during blasting very well. The attenuation of the blasting waves calculated based on the model is much more than that based on the linear-elastic constitutive law. The size of damaged (or fractured) zone is calculated directly from the principal strain as blasting impact is spreading, not like in the case with the linear elasticity model.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.821-827
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• 2014

In this study, an experimental study was performed to predict the two-phase frictional pressure drop of FC-72 in parallel micro-channels. The parallel micro-channels consist of 15 channels with depth 0.2 mm, width 0.45 mm and length 60 mm. And tests were performed in the ranges of mass fluxes from 152.2 to $584.2kg/m^2s$ and heat fluxes from 7.5 to $28.3kW/m^2$. The experimental data was compared and analyzed with existing correlations to predict the pressure drop. The existing methods to predict the pressure drop used the homogeneous model and the separated model. In this study, the new correlation was proposed by modified existing correlation using the separated model, and the new correlation predicted consequently with the experimental data within MAE of 9.6%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.823-829
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• 2014

In the present study, simple models were proposed to predict the capillary-driven flow length in a surfactant-added poly(dimethylsiloxane) (PDMS) rectangular microchannel. Owing to the hydrophobic nature of PDMS, it is difficult to transport water in a conventional PDMS microchannel by means of the capillary force alone. To overcome this problem, microchannels with a hydrophilic surface were fabricated using surfactant-added PDMS. By measuring the contact angle change on the surfactant-added PDMS surface, the behavior was investigated to establish a simple model. In order to predict the filling length induced by the capillary force, the Washburn equation was modified in the present study. From the investigation, it was found that the initial rate-of-change of the contact angle affected the filling length. Simple models were developed for three representative cases, and these can be useful tools in designing microfluidic manufacturing techniques including MIcroMolding In Capillaries (MIMIC).

• Journal of the Korean Institute of Telematics and Electronics
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• v.22 no.2
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• pp.66-74
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• 1985

An idea is presented in this paper that control panel be implemented with a ${\mu}$-processor instead of interrupt based logic circuits. To prove that the idea is reasonable, a ${\mu}$-computer controlled traffic light control system is chosen as a model, and its control panel is imple-mented witll a f-processor. The result is that the microprocessor-based control panel performs its function very well.

• Composites Research
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• v.25 no.4
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• pp.117-125
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• 2012

Warpage of the film insert molded (FIM) part is caused by an asymmetric residual stress distribution. Asymmetric residual stress and temperature distribution is generated by the retarded heat transfer in the perpendicular direction to the attached film surface. Since warpage was not prevented by controlling injection molding conditions, glass fiber (GF) filled composites were employed as substrates for film insert molding to minimize the warpage. Distribution of short GFs was evaluated by using micro-CT equipment. Proper models for micro mechanics, anisotropic thermal expansion coefficients, and closure approximation should be selected in order to calculate fiber orientation tensor and warpage of the FIM part with the composite substrate. After six kinds of micro mechanics models, three models of the thermal expansion coefficient and five models of the closure approximation had been considered, the Mori-Tanaka model, the Rosen and Hashin model, and the third orthotropic closure approximation were selected in this study. The numerically predicted results on fiber orientation tensor and warpage were in good agreement with experimental results and effects of GF reinforcement on warpage of the FIM composite specimen were identified by the numerical results.

• Journal of the Korean Geotechnical Society
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• v.22 no.2
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• pp.41-53
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• 2006

The brittle materials like rocks show complicated strain-softening behavior after the peak which is hard to model using the classical constitutive models based on the relation between strain and stress tensors. A kinematically constrained three-dimensional microplane constitutive model is developed for granite. The model is verified by fitting the experimented data of Westerly granite and Bonnet granite. The triaxial behavior of granite is well reproduced by the model as well as the uniaxial behavior. We studied the development of the fracture zone in granite during blasting impact using the model with the standard finite element method. All the results obtained from the microplane model developed are compared to those from the linear elasticity model which is commonly used in many researches and practices. It is found that the nonlinearity of rocks sigificantly affects the results of analysis.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.183-190
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• 2013

In this paper, we propose an improved anisotropic diffusion model for micro-crack detection in heterogeneously textured surface of polycrystalline solar wafers. Due to the nature of the image sensor, the gray-level of the diagonal micro-crack is non-uniform. Thus, the conventional algorithms can't fully detect diagonal micro-cracks when the number of iteration is not enough. However, the increasing of the iteration number leads to increase computation time and detects micro-crack thicker than the original micro-crack. In order to overcome this drawback, we use the gradient of north, south, east, and west directions as well as extended directions. To calculate the diffusion coefficients, we compare the gradients of conventional directions and extended directions and apply the larger gradient values to the coefficient function. This is because the proposed method reflects the information of diagonal micro-crack. Comparing to Tsai et al.'s and Ko and Rheem's, the proposed algorithm shows superior efficiency in detecting the diagonal micro-cracks with less iterations in the images of polycrystalline solar wafers. In addition, it also shows that the thickness of segmented micro-crack is similar to the orignal micro-crack.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.108-109
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• 2014

본 논문에서는 배터리, 양방향 DC-DC 컨버터, 그리고 브러시레스 직류 전동기로 구성되는 마이크로 터빈 구동 시스템의 제어 방식에 대해 소개한다. 브러시레스 직류 전동기 구동용 인버터의 직류링크 전압이 가변되기 때문에 기존의 소신호 모델 기반으로는 양방향 DC-DC 컨버터의 과도 응답 제어 성능이 저하되는 문제점이 있다. 본 논문에서는 평균 모델을 이용하여 양방향 DC-DC 컨버터를 제어함으로써 과도 응답 제어 성능을 개선하였고, PAM 방식 제어를 이용하여 브러시레스 직류 전동기의 고속 센서리스 운전을 구현하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.116-118
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• 2011

일반적으로 나노입자의 크기는 나노복합체의 역학적 특성에 상당한 영향을 미친다. 이에 본 연구에서는 나노입자 크기를 고려한 나노복합체 재료 구성모델 (Kim et al., 2011)을 소개하고자 한다. Kim et al. (2011)에 의해서 나노입자 크기효과를 위한 Size-dependent Eshelby tensor가 미세역학 모델에 적용되었으며, 나노스케일 해석과 함께 다양한 수치해석을 수행하였다. 특히, 본 연구에서는 이를 활용하여 $SiO_2$/Epoxy 나노복합체의 역학적 특성을 예측해 보았다.