• 한국초전도ㆍ저온공학회논문지
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• 제17권2호
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• pp.41-44
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• 2015

Critical current of high-temperature superconducting (HTS) coil is influenced by its own self magnetic field. Direction and density distribution of the magnetic field around the coil are fixed after the shape of the coil is decided. If the entire part of the HTS tape has homogeneous $I_c$ distribution characteristic, quench would be initiated in fixed location on the coil. However, the actual HTS tape has inhomogeneous $I_c$ distribution along the length. If the $I_c$ distribution of the HTS tape is known, we can expect the spot within the HTS coil that has the highest probability to initiate the quench. In this paper, $I_c$ distribution within the HTS coil under self-field effect is simulated by MATLAB. In the simulation procedure, $I_c$ distribution of the entire part of the HTS tape is assume d to follow Gaussian-distribution by central limit theorem. The HTS coil model is divided into several segments, and the critical current of each segment is calculated based on the-generalized Kim model. Single pancake model is simulated and self-field of HTS coil is calculated by Biot-Savart's law. As a result of simulation, quench-initiating spot in the actual HTS coil can be predicted statistically. And that statistical analysis can help detect or protect the quench of the HTS coil.

• 대한기계학회논문집A
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• 제39권8호
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• pp.807-812
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• 2015

리튬 전지는 에너지 밀도가 높고, 소형화 및 경량화가 가능한 이차전지로서 저장된 화학 에너지를 전기화학적 반응을 통해 전기 에너지로 변환하는 장치로 노트북, 휴대폰, 파워-툴 및 자동차 등에 널리 사용되고 있는 에너지원이다. 특히, 파워-툴이나 자동차와 같은 응용분야에서는 고율 충방전을 필요로 하는데, 본 논문에서는 리튬 전지의 고율 방전 특성에 대해서 상용 유한요소 해석 프로그램을 이용하여 전기화학 시뮬레이션을 진행하여 실험 결과와 유사한 전기화학 모델을 완성하게 되었다. 또한, 이러한 전기화학적 해석 모델을 이용하여 고율 방전용 리튬 전지의 한계 방전 전류가 63A 정도라는 것을 해석적으로 예측 할 수 있었고, 이를 바탕으로 고율 방전 시 리튬 전지의 거동에 대해서 이해할 수 있게 되었다.

• 방사성폐기물학회지
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• 제19권4호
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• pp.459-467
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• 2021

In the majority of countries, the upper limit of buffer temperature in a repository is set to below 100℃ due to the possible illitization. This smectite-to-illite transformation is expected to be detrimental to the swelling functions of the buffer. However, if the upper limit is increased while preventing illitization, the disposal density and cost-effectiveness for the repository will dramatically increase. Thus, understanding the characteristics and creating a database related to the buffer under the elevated temperature conditions is crucial. In this study, a strategy to investigate the bentonite found in Korea under the elevated temperatures from a mineral transformation and radionuclides retardation perspective was proposed. Certain long-term hydrothermal reactions generated the bentonite samples that were utilized for the investigation of their mineral transformation and radionuclide retardation characteristics. The bentonite samples are expected to be studied using in-situ synchrotron-based X-Ray Diffraction (XRD) technique to determine the smectite-to-illite transformation. Simultaneously, the 'high-temperature and high-pressure mineral alteration measurement system' based on the Diamond Anvil Cell (DAC) will control and provide the elevated temperature and pressure conditions during the measurements. The kinetic models, including the Huang and Cuadros model, are expected to predict the time and manner in which the illitization will become detrimental to the performance and safety of the repository. The sorption reactions planned for the bentonite samples to evaluate the effects on retardation will provide the information required to expand the current knowledge of repository optimization.

• 마이크로전자및패키징학회지
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• 제24권3호
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• pp.77-81
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• 2017

Pulse electroplating of Ni-P alloy was studied to fulfill the material requirement to the advanced vertical probe tip in wafer probe card. The major concerns are for the electrical conductivity and yield strength. Plating parameters such as current density, duty cycle and solution components were examined to obtain the nanocrystal structure and proper percentage of phosphorus, leading to how to control the nanocrystal grain growth and precipitation of $Ni_3P$ after heat treatment. Among the parameters, the amount of phosphorus acid was the main factor affecting on the grain size and sheet resistance, and the amount of 0.1 gram was appropriate. Since hardness in Ni-P alloy is increased by as-plated nanocrystal structure plus precipitation of $Ni_3P$, the concentration of P less than 15 at% was better choice for the grain coarsening without minus in hardness value. The following heat treatment made grain growth and dispersion of precipitates adjustable to meet the target limit of resistance of $100m{\Omega}$ and hardness number of over 1000Hv. The Ni-P alloy will be a candidate for the substitute of the conventional probe tip material.

• Steel and Composite Structures
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• 제19권1호
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• pp.173-190
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• 2015

This study presents an analytical investigation on the seismic response of a medium-rise buckling-restrained braced frame (BRBF) under the near-fault ground motions. A seven-story BRBF is designed as per the current code provisions for five different combinations of brace configurations and beam-column connections. Two types of brace configurations (i.e., Chevron and Double-X) are considered along with a combination of the moment-resisting and the non-moment-resisting beam-to-column connections for the study frame. Nonlinear dynamic analyses are carried out for all study frames for an ensemble of forty SAC near-fault ground motions. The main parameters evaluated are the interstory and residual drift response, brace displacement ductility, and plastic hinge mechanisms. Fragility curves are developed using log-normal probability density functions for all study frames considering the interstory drift ratio and residual drift ratio as the damage parameters. The average interstory drift response of BRBFs with Double-X brace configurations significantly exceeded the allowable drift limit of 2%. The maximum displacement ductility characteristics of BRBs is efficiently utilized under the seismic loading if these braces are arranged in the Double-X configurations instead of Chevron configurations in BRBFs located in the near-fault regions. However, BRBFs with the Double-X brace configurations exhibit the higher interstory drift and residual drift response under near-fault ground motions due to the formation of plastic hinges in the columns and beams at the intermediate story levels.

• 전기학회논문지
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• 제60권10호
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• pp.1846-1857
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• 2011

This paper deals with design and analysis of surface-mounted PM (SPM) motor for compressor of air-conditioning system for electric vehicle applications according to slot/pole combination. First, required torque-speed curve characteristics are determined from operating conditions of the compressor. Restricted conditions such as motor size limit and current density are also determined. And then, under same rated and restricted conditions, twelve models which have different slot/pole combinations each other are designed for various pole arc/pitch ratio using simple equations and 2-d finite element (FE) analyses. Designed models are analyzed and compared in terms of back-emf THD, cogging torque, torque ripple, power losses, efficiency, etc. On the basis of analysis results, it is found that the motor with a 6-pole PM rotor and a 27-slot stator has most outstanding performances in electromagnetic aspects. Finally, through the mechanical modal analysis and demagnetization analysis, it is concluded that the determined motor is most suitable for the compressor of air-conditioning system for electric vehicles.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.II
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• pp.1459-1461
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• 2005

Carbon nanotube -copper composite structures were fabricated using composite plating method and their field emission characteristics were investigated. Multi-walled carbon nanotubes synthesized by chemical vapor deposition were used in the present study. It was revealed that turn-on field of the structures was about 3.0 $V/{\mu}m$ at the current density of 0.1 ${\mu}A/cm^2$. We observed relatively uniform emission characteristics as well as stable emission currents. CNT-Cu composite plating method is efficient and it has no intrinsic limit on the plating area. Moreover, it gives strong adhesion between emitters and an electrode. The refore, we expect that CNT-Cu composite plating method can be applied to fabricate electron field emitters for large area FEDs and large area vacuum lighting sources.

• 센서학회지
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• 제8권4호
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• pp.308-313
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• 1999

본 논문에서는 TMAH를 이용한 비등방성 에칭기술을 이용하여 3차원의 자장의 값을 측정하기 위한 경사각 구조의 3차원 자기센서를 제작하였다. 제작된 3차원 자기센서는 비등방성 식각에 의하여 [100] 결정방향의 Si 표면에 [111] 결정방향의 경사면을 구성하여 이 경사면에 경사각 Hall 소자를 제작하였으며, 기존의 3차원 자기센서에 비하여 개선된 감도 특성을 나타내었다. 제작된 소자의 적감도는 547V/AT 이었으며 자기센서 출력의 PSD 성분의 측정에 의해 계산 되어진 최소측정 자장은 0.07G 이었다.

• 마이크로전자및패키징학회지
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• 제25권4호
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• pp.9-15
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• 2018

This paper shows the principles and characteristics of the transient liquid phase (TLP) bonding technology for power modules packaging. The power module is semiconductor parts that change and manage power entering electronic devices, and demand is increasing due to the advent of the fourth industrial revolution. Higher operation temperatures and increasing current density are important for the performance of power modules. Conventional power modules using Si chip have reached the limit of theoretical performance development. In addition, their efficiency is reduced at high temperature because of the low properties of Si. Therefore, Si is changed to silicon carbide (SiC) and gallium nitride (GaN). Various methods of bonding have been studied, like Ag sintering and Sn-Au solder, to keep up with the development of chips, one of which is TLP bonding. TLP bonding has the advantages in price and junction temperature over other technologies. In this paper, TLP bonding using various materials and methods is introduced. In addition, new TLP technologies that are combined with other technologies such as metal powder mixing and ultrasonic technology are also reviewed.

• 시스템엔지니어링학술지
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• 제17권2호
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• pp.49-60
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• 2021

The Core Protection Calculator System (CPCS) is vital for plant safety as it ensures the required Specified Acceptance Fuel Design Limit (SAFDL) are not exceeded. The CPCS generates trip signals when Departure from Nucleate Boiling Ratio (DNBR) and Local Power Density (LPD) exceeds their predetermined setpoints. These setpoints are established based on the operating margin from the analysis that produces the SAFDL values. The goal of this research is to create a simplified CPCS that optimizes operating margin for I-SMRs. Because the I-SMR is compact in design, instrumentation placement is a challenge, as it is with Ex-core detectors and RCP instrumentation. The proposed CPCS addresses the issue of power flux measurement with In-Core Instrumentation (ICI), while flow measurement is handled with differential pressure transmitters between Steam Generators (SG). Simplification of CPCS is based on a Look-Up-Table (LUT) for determining the CEA groups' position. However, simplification brings approximations that result in a loss of operational margin, which necessitates compensation. Appropriate compensation is performed based on the result of analysis. FPGAs (Field Programmable Gate Arrays) are presented as a way to compensate for the inadequacies of current systems by providing faster execution speeds and a lower Common Cause Failure rate (CCF).