• Fibers and Polymers
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• 제6권2호
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• pp.131-138
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• 2005

A theoretical model is proposed in order to investigate rheological behavior of bubble suspension with large deformation. Theoretical constitutive equations for dilute bubble suspensions are derived by applying a deformation theory of ellipsoidal droplet [1] to a phenomenological suspension theory [2]. The rate of deformation tensor within the bubble and the time evolution of interface tensor are predicted by applying the proposed constitutive equations, which have two free fitting parameters. The transient and steady rheological properties of dilute bubble suspensions are studied for several capillary numbers (Ca) under simple shear flow and uniaxial elongational flow fields. The retraction force of the bubble caused by the interfacial tension increases as bubbles undergo deformation. The transient and steady relative viscosity decreases as Ca increases. The normal stress difference (NSD) under the simple shear has the largest value when Ca is around 1 and the ratio Of the first NSD to the second NSD has the value of 3/4 for large Ca but 2 for small Ca. In the uniaxial elongational flow, the elongational viscosity is three times as large as the shear viscosity like the Newtonian fluid.

• 한국지반환경공학회 논문집
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• 제4권1호
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• pp.59-66
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• 2003

건설공사에서 발생하는 환경문제에 대한 관심이 고조되는 가운데 기성 말뚝을 항타하는 과정에서 유발되는 소음, 진동문제를 해결하기 위해 저소음, 저진동 공법인 매입말뚝공법이 많이 적용되고 있다. 국내에서는 매입말뚝공법으로 SIP공법이 주로 사용되고 있다. 그러나 아직까지 SIP공법에 관한 합리적인 지지력 산정식이 제시되어있지 못한 실정이다. 이에 대해 본 연구에서는 SIP 말뚝의 주면저항력 특성을 고찰하여 이러한 문제점들을 개선, 보완하기 위하여 다양한 조건에서 SIP말뚝 주면과 지반사이의 경계면에 대하여 직접전단 시험을 실시하였다. 시험 결과를 토대로 통일분류상 SM, SC 지반에서의 SIP말뚝 주면저항력 특성을 고찰하고 해당 지반에서 주면저항력 산정식을 제시하였다. 또한, 말뚝 경계요소의 저항력에 대한 새로운 비선형 수치 모델식과 계수산정식을 제안하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.759-760
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• 2006

In this paper proposed to Neural network PI self-tuning direct controller using Error back propagation algorithm. Proposed controller applies to speed controller and current controller. Also, this built up the interface environment to drive it simply and exactly in any kind of reference, environment fluent and parameter transaction of BLDC motor. Neural network PI self-tuning simulator using Visual C++ and Matlab Simulation is organized to construct this environment. Built-u-p interface has it's own purpose that even the user who don't have the accurate knowledge of neural network can embody operation characteristic rapidly and easily.

• 소성∙가공
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• 제18권1호
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• pp.45-51
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• 2009

Shape memory alloy has been used to improve the tensile strength of composite by the occurrence of compressive residual stress in matrix using its shape memory effect. In order to fabricate shape memory alloy composite, TiNi alloy fiber and Al2024 sheets were used as reinforcing material and matrix, respectively. In this study, TiNi/Al2024 shape memory alloy composite was made by using hot press method. In order to investigate bonding condition between TiNi reinforcement and Al matrix, the micro-structure of interface was observed by using optical microscope and diffusion layer of interface was measured by using Electron Probe Micro Analyser. And the mechanical properties of composite with three parameters(volume fraction of fiber, cold rolling amount and test temperature) were obtained by tensile test. The most optimum bonding condition for fabrication the TiNi/Al2024 composite material was obtained as holding for 30min. under the pressure of 60MPa at 793K. The strength of composite material increased considerably with the volume fraction of fiber up to 7.0%. And the tensile strength of this composite increased with the reduction ratio and it also depends on the volume fraction of fiber.

• Journal of Welding and Joining
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• 제35권2호
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• pp.13-22
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• 2017

In laser full penetration welding process, full penetration hole(FPH) is formed as a result of force balance between the vapor pressure and the surface tension of the surrounding molten metal. In this work, a three-dimensional numerical model based on a conserved-mass level-set method is developed to simulate the transport phenomena during laser full penetration welding process, including full penetration keyhole dynamics. Ray trancing model is applied to simulate multi-reflection phenomena in the keyhole wall. The ghost fluid method and continuum method are used to deal with liquid/vapor interface and solid/liquid interface. The effects of processing parameters including laser power and scanning speed on the resultant full penetration hole diameter, laser energy distribution and energy absorption efficiency are studied. The model is validated against experimental results. The diameter of full penetration hole calculated by the simulation model agrees well with the coaxial images captured during laser welding of thin stainless steel plates. Numerical simulation results show that increase of laser power and decrease of welding speed can enlarge the full penetration hole, which decreases laser energy efficiency.

• 제어로봇시스템학회논문지
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• 제14권2호
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• pp.205-211
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• 2008

This paper describes the method aimed at establishing the equipment measuring the parameter of Cable Network by Best proper Cable Modem and PDA through RS232 interface. In this paper, we propose our creative experimental configuration and develope the Cable Modem (DOCSIS 2.0) superior more performing than the referred Cable Modem (DOCSIS 1.0, 1.1) and the measuring equipment of HFC network compositing of Cable Modem and PDA through RS232 interface. This equipment analyzes Upstream (U/S) and Downstream (D/S) Signal quality and generates the signal of Upstream by CW signal. The paper also provides the experimental results to check the Best Proper Cable Modem and the displayed screen for parameters for SNR, BER and the demodulated IQ diagram of 256QAM through LCD of PDA. Henceforth, it'll be possible to support a variety of the functions for E-mail, Internet, the speed test of WEB connection and the transmission of the measured result real time by PDA.

• 한국진공학회지
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• 제10권1호
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• pp.72-80
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• 2001

본 논문에서는 ELA(excimer laser annealing) 및 SMC(silicide mediated crystallization) 공정으로 제작된 다결정 실리콘 TFT-LCD(Thin Film Transistor-Liquid Crystal Display) 화소의 전기적 특성을 Spice회로 시뮬레이션을 통해 비교 분석하였다. 복잡한 TFT-LCD 어레이 (array) 회로의 전기적 특성 분석을 위하여 GUI(Graphic User Interface) 방식으로 손쉽게 복잡한 회로를 구성할 수 있는 PSpice에 AIM-Spice의 다결정 실리콘 박막 트랜지스터 소자 모델을 이식하고, AIM-Spice의 변수 추출법을 개선 체계화하였으며 ELA 및 SMC공정으로 각기 제작된 다결정 실리콘 박막트랜지스터에 적용하여 단위 화소 및 라인 RC 지연을 고려한 화소 특성을 비교 분석하였다. 비교 결과 ELA 다결정 실리콘 박막 트랜지스터 소자가 SMC에 비해 TFT-LCD의 화소 충전 시간 및 킥백(kickback) 전압 특성이 모두 우수하게 나타남을 확인하였다.

• 콘크리트학회논문집
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• 제14권4호
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• pp.474-482
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• 2002

본 연구의 목적은 섬유의 부착시험을 통하여 섬유의 파괴없이 최대 인발저항을 가지고 시멘트 모체 내에서 완전한 정착작용을하는 구조용 합성섬유의 최적형상과 최적형상함수를 도출하는데 있다. 7가지 다른 형상의 구조용 합성섬유를 조사하였고 부착시험을 수행하였다. 부착시험의 변수는 7가지의 다른 형상이고, 2종류의 시멘트 모르타르의 배합이다. 부착시험 결과, 7가지 다른 형상중 crimped type이 계면인성(인발에너지)와 인발하중에서 가장 우수한 성능을 보였다. Crimped type을 기본으로 하여 섬유의 주기와 높이를 바꾸어 부착시험을 실시한 결과 최적형상함수, D= $b^{{\alpha}ο{\alpha}}$ $h^{λ{\beta}}$ 를 도출하였다.

• Journal of Power Electronics
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• 제14권5호
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• pp.1069-1078
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• 2014

This study presents the design and implementation of a web-based remote laboratory for a multi-mode single-leg power converter, which is a topic in advanced power electronics course. The proposed laboratory includes an experimental test rig with a multi-mode single-leg power converter and its driver circuits, a measurement board, a control platform, and a LabVIEW-based user interface program that is operated in the server computer. Given that the proposed web-based remote laboratory is based on client/server architecture, the experimental test rig can be controlled by a client computer with Internet connection and a standard web browser. Although the multi-mode single-leg power converter can work at four different modes (main boost, buck-boost, boost-boost, and battery boost modes), only the buck-boost mode is used in the experiment because of page limit. Users can choose the control structure, control parameters, and reference values, as well as obtain graphical results from the user interface software. Consequently, the feedbacks received from students who conducted remote laboratory studies indicate that the proposed laboratory is a useful tool for both remote and traditional education.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1646-1648
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• 2000

This paper investigated structural and electrical properties of $Y_{2}O_3$ as a buffer layer of sin91r transistor FRAM (ferroelectric RAM). $Y_{2}O_3$ buffer layers were deposited at a low substrate temperature below 400$^{\circ}C$ and then RTA (rapid thermal anneal) treated. Investigated parameters are substrate temperature, $O_2$ partial pressure, post- annealing temperature, and suppression of interfacial $SiO_2$ layer generation. for a well-fabricated sample, we achieved that leakage current density ($J_{leak}$) in the order of $10^{-7}A/cm2$, breakdown electric field ($E_{br}$) about 2 MV/cm for $Y_{2}O_3$ film. Capacitance versus voltage analysis illustrated dielectric constants of 7.47. We successfully achieved an interface state density of $Y_{2}O_3$/Si as low as $8.72{\times}10^{10}cm^{-2}eV^{-1}$. The low interface states were obtained from very low lattice mismatch less than 1.75%.