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김영민(Y. M. Kim),신영재(Y. J. Shin),이응숙(E. S. Lee),김동우(D. W. Kim),이동주(D. J. LEE) 한국정밀공학회 2004 한국정밀공학회 학술발표대회 논문집 Vol.2004 No.10월
A new, commercially available polishing process called magnetorheological finishing is used to polish and figure precision optics. To understand and model this process correctly it is important to determine the mechanical properties of the fluid under the influence of the magnetic field. Magnetorheological (MR) fluids are commonly modeled as Bingham fluids, so one of the essential properties to measure is the yield stress. Since MR fluids are inherently anisotropic, the yield stress will depend on the mutual orientation of the magnetic field and the direction of deformation. The relative orientation of the field and deformation in polishing does not coincide with common rheological setups, so a new rheometer has been designed and tested. This new magnetorheometer design has been shown to give correct stresses during calibration experiments using Newtonian fluids with a known viscosity. The measured stress has also been shown to have a magnitude consistent with published finite element approximations for magnetic fluids. The design of the instrument was complicated because of the requirements imposed upon the magnetic field, and the difficulty in satisfying the no slip boundary condition. Our results show the importance of having a homogeneous field in the test region during measurements. The solutions to these problems and discussion of the measurements on nonmagnetic and magnetic fluids are given.
와이어프레임 기반의 3차원 형상제시기의 실시간 SMA 제어
김영민(Y. M. Kim),추용주(Y. J. Chu),송재복(J. B. Song) 한국정밀공학회 2006 한국정밀공학회 학술발표대회 논문집 Vol.2006 No.5월
We developed wire frame drive unit based on SMA for the 3D Shape display. Our basic concept is wire frame combination connected with a chain form which can create various shapes and it compared with pin array mechanism which is not able to display mushroom shape. It imitates antagonist mechanism of human musculoskeletal system, we create similar motion using repair-relaxation mechanism and locking mechanism by SMA. Therefore, in this paper, we propose SMA control solution for actuating repair-relaxation mechanism and locking mechanism. In our control system, we use optical sensor and quantitative angle between wire frames for closed loop control. And we supply amplified current for SMA by circuit composed of transistor and apply PWM signal to circuit for efficient control. So, wire frame drive unit enable diversity angle control based on sensor data. And then combination of wire frame drive units will create various objects.
점화플러그 중심전극의 극성이 전극마모 및 천연가스 엔진성능에 미치는 영향
김영민(Y.M.Kim),이장희(J.H.Lee),이춘희(C.H.Lee),신동성(D.S.Shin),정익재(I.J.Chung) 한국자동차공학회 1998 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1998 No.11_1
In the present work, a durability test has been performed to investigate the effects of different polarities of plug central electrode on the electrode wear with gasoline engine which electronic characteristics of spark plug is similar to natural gas engine. And a series of experiments have been performed to investigate the effects of different polarities on the ignition pattern and the performance of natuarl gas engine in lean regions.<br/> The results show that electrode wear of positive central polarity is much less than conventional negative polarity and different central polarities have very little effects on the engine performance such as lean limit and IMEP in lean regions.<br/>
김영민(Y.M.Kim),이장희(J.H.Lee),이춘희(C.H.Lee),신동성(D.S.Shin),정익재(I.J.Chung) 한국자동차공학회 1997 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1997 No.11_1
Natural gas is an attractive fuel in view of abundant resources and low emission. So in order to meet stricter cmission regulation on smoke and particulate matter from Diesel engine with lower CO₂ emission. natural gas has been applicated to heavy duty Diesel engine.<br/> This study describes the contents of the conversion of Diesel engine to spark ignited engine and effect of ignition timing. air fuel ratio and injection timing. For ease of experimental variable applications. IIL six cylinder engine was converted to experimental single cylinder engine.<br/>
[가솔린엔진] 연소가시화를 통한 HD 천연가스엔진의 연소특성 연구
김영민(Y.M. Kim),이장희(J.H. Lee),이진호(J.H. Lee),신동성(D.S. Shin),정익재(I.J. Chung) 한국자동차공학회 1999 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
At present study a IIL DI diesel engine was converted to a single-cylinder spark ignited CNG engine allowing optical access through an extended piston The fuel system also was converted to deliver CNG by injection into the intake ports and the cylinder head was modified to install a spark plug. The combustion characteristics of the engine were analysed by using direct imaging of the propagating flame with simultaneous measurement of in-cylinder pressure The effect of injection timing on the combustion in lean region is remarkable and intake-synchronous injection results in favorable combustion