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김옥현,이희복,이민기,홍정희,곽용운,Kim, Ock-Hyun,Lee, Hee-Bok,Lee, Min-Ki,Hong, Jeong-Hui,Kwak, Yong-Woon 한국생산제조학회 2010 한국생산제조학회지 Vol.10 No.6
Magnetic fluid seal is characterized by its simple design, low friction and being dustless. Those advantages are deduced from the fact that the sealing element is not a solid such as rubber or plastic but it is a fluid. Those are critical for application to a rotating shaft which is inserted into a vacuum chamber where high level of vacuum and cleanness are required. For the reason the magnetic fluid seal has become a standard for vacuum chambers for semiconductor and LCD processing. It should be noted that its sealing performance is sensitive to temperature. If necessary, water cooling should be considered. Thus anticipation of the temperature distribution of the magnetic fluid seal is important before applying it. In this paper an FEM analysis of the heat transfer has been executed and compared with experimental results. An overall convective heat transfer coefficient has been adopted for the analysis, which results in satisfactory consistency of the theoretical and experimental results.
김옥현 ( Ock Hyun Kim ) 충북대학교 산업과학기술연구소 2016 산업과학기술연구 논문집 Vol.30 No.2
Suppression of vibrations of a car is important for driving safety and comfort. To suppress the vibrations, suspension systems are provided for most of cars. The suspensions have been concerned with only the up-down motion(vertical motion) of cars and the back-forth motion of cars has been ignored. Actually the back-forth motion would be ignored when a car is running. But just after a car stops with deceleration, the back-forth motion is activated and the driver feels more discomfort by the back-forth motion because of its higher frequency. In this study a vibrational model of a car has been suggested to consider the back-forth motion and the model parameters have been estimated by some experiments. Vibrational motions of a car when it stops with some constant decelerations have been simulated. Through the study it is verified that when a car stops with deceleration the back-forth motion occurs much larger than other up-down motion, which may raise necessity of a suspension device to suppress the back-forth motion.
김옥현 ( Ock Hyun Kim ),이규호 ( Kyu Ho Lee ) 충북대학교 산업과학기술연구소 2011 산업과학기술연구 논문집 Vol.25 No.2
This paper contributes to design of a static air bearing. Performance of the air bearing is characterized by its load capacity and consumed air flow rate. Performance of the air bearing has been estimated theoreticallyby a numerical analysis based on the Reynolds equation. For the numerical analysis finite difference formulation of the Reynolds equation has been provided. A prototype air bearing has been designed and fabricated. Its performance of load capacity has been tested and compared with the numerical solutions. The result matches well with each other, which convinces that the numerical approach can be used as an efficient tool to anticipate air bearing performances. Effects of design parameters on the bearing performance have been analyzed by Taguchi’s experimental methods. It is shown that the clearance is the most influential parameter and the next is the number of holes.
김옥현(Ock Hyun Kim) 한국기계가공학회 2009 한국기계가공학회지 Vol.8 No.1
Magneto-Rheological(MR) fluid composes of a base fluid and ferromagnetic particles less than tens of micrometer size dispersed in the fluid. It is called as a smart material because its rheological properties are changable by a magnetic field. Its important applications are active devices such as controllable dampers and controllable clutches. The merit of those products is that their functional characteristics are controllable such that they enable active control strategies. This paper proposes an idea for machine tool applications of the MR fluid clutch as a safety device for power transmission. FEM has been used for magnetic field analyses and the results are compared with some former experiments. Some design syntheses of the MR clutches are suggested and hopefully considered that it may be an effective safety device for power transmission of machine tools.
김옥현(Ock-Hyun Kim),이민기(Min-Ki Lee) 한국기계가공학회 2011 한국기계가공학회지 Vol.10 No.2
Magnetic seal uses a magnetic fluid to seal a gap between a rotating shaft and housing. It is distinguished from other kinds of seals from the fact that solid contact does not occur in the seal. This implies that it is free from solid rubbing thus dustless and provides a clean circumstance. That is the reason why the magnetic seal is used exclusively for most of vacuum chambers in semiconductor process where dustless clean circumstance is critical. A magnetic seal has been developed of which design parameters are determined based on published data, and an air pressure test has been done to examine its sealing capability. Effects of some design parameters have been studied through FEM analysis. The results show some notable aspects of design parameters and provide suggestions for developing the seals. Regarding the sealing capacity of the magnetic seal the factor to match the theoretical value with the actual one was found to be 0.4~0.7, which means still there is some discrepancy between theory and actual.
김옥현 ( Ock Hyun Kim ),문사현 ( Sa Hyun Moon ) 충북대학교 산업과학기술연구소 2012 산업과학기술연구 논문집 Vol.26 No.2
This paper presents a study for developing a shock absorber of which the orifice is being changed according to the oil pressure. The orifice is widen when the oil pressure is high and becomes narrow when it is low, thus the damping force is less sensitive to the velocity than the case of a shock absorber with a fixed orifice. It is well known that the damping force can be written as C ·ua. For fluid film damping the force is proportional to velocity, i.e., a: = 1, and for orifice damping it is proportional to the square of velocity i.e., a = 2. The shock absorber proposed in this paper should show different relationships between the damping force and velocity because the orifice is being changed according to the induced oil pressure. Theoretical and Experimental study have been done to verify the damping characteristics of the shock absorber. Effect of some major design parameters of the shock absorber has been also examined to relate the design parameters to the damping characteristics.