• Proceedings of the Technology Innovation Conference
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• 1997.07a
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• pp.266-285
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• 1997

This paper addresses a methodology for monitoring the first phase('92-'94) progress and its strategic implication of Highly Advanced National R&D Program(HAN or G7 project) in Korea. The conceptual framework and its strategic thrust of the interim evaluation, which is the main focus of this paper, was designed both by reviewing related literature and by analyzing the unique characteristics of the HAN Program. Actual monitoring or interim evaluation was initiated by the G7 Planning and Evaluation Committee, which was established for advising, directing, and monitoring the HAN Program, with the help of large number of experts from various industries, universities, and research institutes. The monitoring results had been reported to the related ministries and project coordinating agencies. According to the suggestion made by the G7 Planning and Evaluation Committee, several projects were suffered structural changes and one was dropped.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.10a
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• pp.202-206
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• 1996

An experimental study of the characteristics of the repulsiveytype magnetic bearing using high Tc superconductor is presented. In field cooling superconductor has the position-stability due to a flux pinning effect and the strong damping due to hysterisis, while in zero field cooling it has the only strong repulsive force due to Meissner effect. Lift force in superconducting levitation has a hysterisis characteristics, and it is the dissipation of energy, the mechanism of damping. As the relative linear velocity between a magnet and a superconductor increases, the area of the hysterisis loop becomes smaller. It means the decrease of damping. In field cooling, the static stiffness is very nonlinear in smaller than initial gap, but almost linear in larger than initial gap.

• Tribology and Lubricants
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• v.14 no.4
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• pp.100-107
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• 1998

A new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performance of a hydrodynamic journal bearing. This concept features a wave in bearing surface. Not only straight but also twisted wave journal bearing are investigated numerically. The performances of straight and twisted bearings are compared to a plain journal bearing over a wide range of eccentricity. The bearing load and stability characteristics are dependent on the geometric parameters such as the number of waves, the amplitude and the start point of the wave relative to the applied load direction. The wave journal bearing, especially for the twisted one, offers better stability than the plain journal bearing under all eccentricity and load orientation.

• Tribology and Lubricants
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• v.16 no.2
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• pp.106-113
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• 2000

Effects of surface roughness on bearing performances are investigated numerically in this study, especially for the parallel thrust bearing. Although mating surfaces are parallel and separated by thin fluid film, the pressure distribution is formed due to asperities. Model surface is generated numerically with given autocorrelation function and some surface profile parameters. Then the average Reynolds equation is applied to predict the effects of surface roughness between hydrodynamic and mixed lubrication regimes. In this equation, flow factors are defined as correction terms to smooth out high frequency surface roughness. The correlation length is proposed to get the minimum load for the parallel thrust bearing for various sliding conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.3
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• pp.206-213
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• 2002

In this paper, the flow characteristics of an axial fan spraying isothermal compact jet in a confined space were investigated by the experimental methods, the numerical method, and the free jet theory According to the results, the numerical result and the experimental result are agreed well qualitatively and different quantitatively within $\pm1.0%$ for the centerline velocity, the entrainment ratio, and the maximum throw. However, the free jet theory can reasonably predict the centerline velocity except the entrainment ratio and the maximum throw. In other words, the entrainment ratio and the maximum throw by 1.he free jet theory are hard to estimate the characteristics of jet because of restriction of c confined space.

• Tribology and Lubricants
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• v.13 no.4
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• pp.1-9
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• 1997

ER clutch is a device using ER fluid, so called "intelligent material" and is a power transmission system controlled with electric field strength. In this paper(Part III), the behavior of ER clutch under proper conditions was investigated experimentally and compared to theoretical analyses developed from Part I, II. Considering the optimum design concept proposed from Part I, the concentric cylinder type of ER clutch was designed and the experimental apparatus for the performance test was constructed. The comparisons made indicated that the power transmission model of ER clutch and the temperature rise model of ER fluid developed from Part I, II were acceptable for engineering design calculations.culations.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.122-128
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• 1997

초전도체의 임계온도를 높이는 연구들이 수행되어 임계온도가 액체질소의 비등점(77K)보다 높은 산화물 고온 초전도체가 1986년에 발견되었고, 최근에는 $10^4A/cm^2$이상의 임계전류밀도를 갖는 덩어리형 고온 초전도체가 용융공정을 통해 개발되었으며, 산화물 고온 초전도체 $YBa_2 Cu_3 O_{7-y}$은 산소 조성이 7에 가까우며 임계온도가 95K로서 현재 가장 많이 사용되고 있다. 응용 분야로서는 수송분야, 의료분야, 전력분야, 그리고 기초과학분야등이 있고, 향후 상온 초전도체의 출현으로 인한 응용범위의 확대는 획기적일 것으로 예측되어 진다. 이중에 10$^{-8}$이하의 마찰계수를 갖는 초전도 마그네틱 베어링을 플라이휠 같은 에너지 저장장치에 적용시키는 연구가 국내외적으로 진행되고 있다. 여러 선진국에서는 용융공정된 초전도체를 이용하여 실험단계적인 플라이휠의 설계, 제작 및 성능실험을 진행중이거나 완성하였고, 제2단계 목표로서 실용화를 위한 대규모 플라이휠의 설계와 제작에 대한 연구가 진행중이다.

• Tribology and Lubricants
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• v.11 no.1
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• pp.20-26
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• 1995

Most magnetic bearings are based on the attractive force between the magnets and ferrous materials. One of the disadvantages of such attractive type magnetic bearings is the instability so that an active control device is necessary to operate bearing successfully. In this study a repulsive type magnetic bearing is analyzed which uses eddy current as a force source. The load capacities are analyzed for the various gap sizes, the rotor velocities and the frequencies of current supplied to electromagnet. Analytic Results show that as the gap size decreases, the levitation and drag forces increase, while the number of poles increasqs, the drag force decreases in the higher linear velocity region. Experimental results show that as the gap size decreases the levitation and the drag force increase, and as the velocity of rotor increases, the drag is larger than the levitation force up to certain velocity. But after that, the levitation is larger than the drag force. As the frequency of the current increases the levitation and drag decreases while the thickness of rotor gets thicker the forces decrease because of increase in eddy current loss.

• Tribology and Lubricants
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• v.13 no.4
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• pp.26-32
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• 1997

The heat generation of the angular contact and the deep groove ball bearing is studied experimentally and numerically. The temperature variation of the inner and outer races and the temperature increase distribution are measured for the shaft rotational speeds, preloads, viscosities of the lubricant and lubrication methods. The measured temperature distributions are used as the input data of the numerical simulation to estimate the heat generation rate at the bearing. The temperatures of the inner and outer race increase more rapidly and approach faster to their steady values as the rotational speed increases. The optimal viscosity of the oil to minimize the heat generation is 8~10 cSt at 4$0^{\circ}C$ when the oil-air lubrication method is adopted. The heat generation of the bearing increases with the rotational speed and depends more on the lubrication method than on the preload variation.

• Tribology and Lubricants
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• v.16 no.4
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• pp.259-265
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• 2000

Pump which is the fundamental device in the hydraulic system affects on overall system performance to a great deal. Such problems as leakage and solid friction loss become important in field applications, especially for the case of operation under high pressure and at high speed. So the research on this kind of subjects is necessary to improve the performance of hydraulic devices. A high pressure radial piston pump is analyzed here, which has a stationary cylinder block. It pumps hydraulic fluid by letting camring push a piston in a cylinder. Fluid leaks between the piston and cylinder so that it deteriorates the pump efficiency. Furthermore, the piston happens to touch the cylinder wall to increase the friction loss and wear. In this research, by means of FDA, volumetric, mechanical and overall efficiencies are observed by varying several design parameters and operation conditions. Design values or their trends are presented to improve these effciencies.