• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.460-465
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• 2019

In this study, we aim to derive a solution from the structural analysis for electrical failure of single board computers for computing navigation information. By analyzing the characteristic factor, we identify that crack occur on the central processing unit board due to a certain structural problem, and that the physical effect by the crack make communication function be impossible to perform, which it causes booting error. In order to find the location of excessive stress causing the crack, structural analysis for the single board computer is done. From the structural analysis, the areas where stress concentration occurs are identified, and improvement methods changing the structures are developed. As a result, we shows that stresses are reduced entirely on the stress distribution for the improved structure. In addition, heat analysis shows that changing the structure to reduce stresses is not affect to the heat radiation, and the thermal resistance of the actual equipment is verified by measuring the temperature of the heat sink applied with the improved structure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.363-370
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• 2021

In this paper, we presented an optimized crack and flexural strength analysis of a glass-fiber reinforced polymer (GFRP) rebar, used as reinforcements for in-site railway concrete slabs. The insulation performance of a GFRP rebar has the advantage of avoiding the loss of signal current in an audio frequency (AF) track circuit. A full-scale experiment, and three-dimensional finite element simulation results were compared to validate our approaches. Parametric numerical results revealed that the diameters and arrangements of the GFRP rebar had a significant effect on the flexural strength and crack control performances of the concrete track slabs. The results of this study could serve as a benchmark for future guidelines in designing more efficient, and economical concrete slabs using the GFRP rebar.

• The Journal of Engineering Geology
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• v.21 no.1
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• pp.35-43
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• 2011

Time series analysis was applied to groundwater level, water temperature, and electrical conductivity data obtained from monitoring wells around ground-source heat pumps at Sangji University of Wonju (standing column well type) and at Jungwon University of Goesan (closed loop type), from 21 May to 12 October 2010. We found large temporal variations in the characteristics of groundwater at Wonju, but only minor variations at Goesan. These results may improve our understanding of the effects of ground-source heat pumps on the characteristics of surrounding groundwater, according to the installation method for the pumps.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.403-408
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• 2016

Lithium-ion batteries are commonly employed in hybrid electric vehicles (HEVs), and achieving high energy density in the battery has been one of the most critical issues in the automotive industry. Because liquid cooling containing antifreeze is important in automotive batteries to enable cold starts, an effective geometric configuration for high-cooling performance should be carefully investigated. Battery cooling with antifreeze has also been considered to realize successful cold starts. In this article, we theoretically investigate a specific property of an antifreeze cooling battery system, and we perform numerical modeling to satisfy the required thermal specifications. Because a typical battery system in HEVs consists of multiple stacked battery cells, the cooling performance is determined mainly by the special properties of antifreeze in the coolant passage, which dissipates heat generated from the battery cells. We propose that the required cooling performance can be realized by performing numerical simulations of different geometric configurations for battery cooling. Furthermore, we perform a theoretical analysis as a design guideline to optimize the cooling performance with minimum power consumption by the cooling pump.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.2
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• pp.85-91
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• 2016

The Positive Temperature Coefficient (PTC) is used for cabin air heating of a battery electric vehicle, which is different from conventional vehicles. Since the PTC heater consumes a large quantity of power in a parasitic manner, many valuable studies have been reported in the field of alternative heat pumps. In this study, a model for an R134a heat pump taking into account the thermal environment of the cabin was developed for a MATLAB/SIMULINK(R) platform. Component and cabin models are validated with reference values. Results show that the heat pump is more competitive for parasitic power consumption over all ambient temperature conditions. Additionally, the method of waste heat recovery to overcome disadvantages when temperatures are below zero is applied to efficiently operate the heat pump.

• Journal of IKEEE
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• v.19 no.1
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• pp.101-109
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• 2015

As the number of smartphone users grows, number of applications and the expected overall functionality in a smartphone grow simultaneously. With ever-so increasing expectations comes intense competition to squeeze in myriads of functions in a limited space that is only getting 'slimmer' by the year. In order to achieve this, companies often decrease the size of components in smartphones - battery connectors in particular. While they may fit, smaller battery connectors have their disadvantages due to the heat generated by the high current flow in the circuits. In collaborating with Korea's leading battery connector manufacturers, this research presents current issues and design concepts that should be considered when engineers design power connectors based on their electrical and thermal analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.359-366
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• 2008

A two-dimensional thermal model of proton exchange membrane fuel cell with large active area is developed to investigate the performance of fuel cell with large active area over various thermal management conditions. The core sub-models of the two-dimensional thermal model are one-dimensional agglomerate structure electrochemical reaction model, one-dimensional water transport model, and a two-dimensional heat transfer model. Prior to carrying out the simulation, this study is contributed to set up the operating temperature of the fuel cell with large active area which is a maximum temperature inside the fuel cell considering durability of membrane electrolyte. The simulation results show that the operating temperature of the fuel cell and temperature distribution inside the fuel cell can affect significantly the total net power at extreme conditions. Results also show that the parasitic losses of balance of plant component should be precisely controlled to produce the maximum system power with minimum parasitic loss of thermal management system.

• Proceedings of the KIPE Conference
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• 2010.11a
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• pp.343-344
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• 2010

화석연료의 고갈로 인하여 친환경 자동차에 대한 연구와 상용화가 급속도로 진행되면서 점점 대형 차종으로 그 범위가 넓어지고 있다. 대형 차종에 적용되는 전기동력 시스템의 MCU(Motor Control Unit), GCU(Generator Control Unit), DC/DC 컨버터 등과 같은 전장품도 그 용량이 커지면서 상용화를 위해 효율적인 측면도 많이 부각되지만 스위칭 소자, 변압기, 초크, 다이오드 등에서 동작으로 인해 열이 발생하고 제품의 구조상 밀폐된 공간에 장착이 되기 때문에 발열로 인한 동작의 신뢰성과 제품의 내구성에 큰 영향을 미치게 된다. 그중 가장 발열이 심한 IGBT(Insulated Gate Bipolar Transistor) 등과 같은 스위칭 소자에서 발생하는 열을 효과적으로 냉각시키기 위해 수냉구조가 필수적이며 동일한 조건의 수압, 유량에 보다 높은 방열특성을 가지기 위해 냉각구조에 대한 해석이 제품을 개발 전에 선행되어야 한다. 본 논문에서는 유로의 냉각핀 형상과 유로 구조에 따라 방열특성이 어떠한 차이가 있는지 시뮬레이션 프로그램을 통하여 비교하고, 모사발열체를 이용한 방열부의 냉각 성능 시험과 다이나모 환경의 최대 출력 시험을 통하여 방열 특성을 확인하였다.

• Journal of the Korean Institute of Gas
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• v.22 no.1
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• pp.1-8
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• 2018

FCV is installed with a automatic valve attached in an high pressure cylinder to control the hydrogen flow. The supply of hydrogen from the cylinder into the fuel cell stack is controlled via the on/off operation of a solenoid attached to the automatic valve. The solenoid needs to provide the necessary attraction force even at any saturation temperature caused by drive of the vehicle. In this study, the simplified prediction equations for the saturation temperature are suggested. The finite element analysis was performed by steady state technique, according to the boundary condition in order to predict the saturation temperature and attraction force. Finally, the saturation temperature was validated through comparison between the analysis results and measurement results. From the results, the measured saturation temperature $5.9^{\circ}C$ lower with respect to the analysis results. And the error of attraction force ranged from 1.0 to 2.1 N at testing conditions.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.212-216
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• 1999

SiC(3C) photodiodes (PDs) were fabricated on p-type Si(111) substrates using chemical vapor deposition (CVD) technique by pyrolyzing tetramethylsilane (TMS) with $H_{2}$ carrier gas. Electrical properties of SiC(3C) were investigated by Hall measurement and current-voltage (I-V) characteristics. SiC(3C) layers exhibited n-type conductivity. Ohmic contact was formed by thermal evaporation Al metal through a shadow-mask. The optical gain $(G_{op})$ of the SiC(3C)/Si PD was measured as a function of the incident wavelength. For the analysis of the photovoltaic detection of the Sic(3C) n/p PD, the spectral response (SR) has calculated by using the electrical parameters of the SiC(3C) layer and the geometric structure of the PD. The peak response calculated for properly chosen parameters was about 0.75 near 550 nm. We expect a good photoresponse in the SiC(3C) heterostructure for the wavelength range of 400~600 nm. The SiC(3C) photodiode can detect blue and near ultraviolet (UV) radiation.