• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1991.06a
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• pp.63-69
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• 1991

프로팅링저어널베어링은 저어널과 슬리브 사이에 자유롭게 움직일 수 있는 링을 삽입하여 이중의 유막이 형성되도록 한 것이다. 프로팅링저어널베어링은 이중의 유막을 가짐으로 인해 유량이 많이 필요하여 열적 특성이 좋고 마찰손실이 작으며 외축유막의 진동감쇠작용을 기대할 수 있으나, 링에 의해 내외축유막이 분리되어 있으므로 내축유막에 윤활제를 공급하는 것이 쉽지 않은 문제점이 있다. 동베어링에 대한 윤활제의 공급방법으로는 축을 통한 공급을 고려하지 않을 경우 다음과 같은 두가지를 생각할 수 있다. 첫째, 링에 내외축유막을 연결하는 급유구를 뚫어 외축유막으로 공급된 윤활제의 일부가 급유구를 통해 내축유막으로도 공급되도록 하는 방법 둘째, 축방향의 일단에서 내외축유막에 직접 가압급유하는 방법 이 가운데 둘째 방법은 축방향의 일단이 윤활제에 완전히 잠겨 있도록 밀봉하여야 하는 번거로움이 있으므로 잘 사용되지 않고 첫째 방법을 사용하는 것이 일반적이다. 첫째 방법에서도 링내외면에 원주방향급유홈을 파면 내외축유막으로의 윤활제공급이 보다 더 원활히 이루어 질 수 있을 것으로 기대되는데, 본논문에서는 이와 같이 원주방향급유홈이 있는 베어링을 원주방향급유홈 프로팅링저어널베어링이라 부르기도 하고, 이에 대하여 해석하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2205-2215
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• 1992

The stability of the flexible rotor mounted on circumferentially grooved floating ring journal bearings was investigated theoretically and experimentally. The floating ring journal bearing was analyzed by using JFO reformation boundary condition. The flexible shaft was analyzed by the finite element method based on Rayleigh beam theory. It was found that the measured ring speed agrees well with the theoretical results. The instability of the system due to not only the outer film but also the inner film of the bearing could be predicted by the theory which allows negative vapor pressure. The tendency that reducing the supply pressure of lubricant stabilizes the system was observed both experimentally and theoretically.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.260-268
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• 2001

Wake structures behind two circular cylinders with different groove configurations(U and V-shape) have been investigated experimentally. The results were compared with those for the smooth cylinder having the same diameter D. The drag force, mean velocity and turbulent intensity profiles of wake behind the cylinders were measured with varying the Reynolds number in the range of Re(sub)D=8,000∼14,000. As a result, the U-shaped groove was found to reduce the drag up to 18.6%, but the V-shaped groove reduced drag force only 2.5% compared with the smooth cylinder. As the Reynolds number increases, the vortex shedding frequency becomes a little larger than that of the smooth cylinder. The visualized flow using the smoke-wire and particle tracing methods shows the flow structure qualitatively.

• Tribology and Lubricants
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• v.12 no.2
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• pp.41-47
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• 1996

고속에서 작동하는 공기동압 스핀들을 개발하기 위해 축방향 하중을 포함하여 설계와 관련된 문제들을 살펴보았다. 협곡이론에 근거한 지배방정식을 사용하였고, 차분법을 사용하여 해석하였다. 설계인자인 홈의 형상, 홈의 각도, 회전수, 그리고 편심량 등을 사용하여 축방향과 원주방향의 압력분포를 수치해석적으로 구하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.263-269
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• 2003

Magnetic flux leakage (MFL) signals were used for corrosion inspection of buried oil and gas pipeline. 3D finite element analysis was used to examine the effects of far and near-side pit depth and tensile stress on MFL signals. Anisotropci materials were used, and the effects of simulated tensile stress on MFL were investigated. The axial and radial MFL signals depended on far and near-side single pit depth and on the bulk stress, but the circumferential MFL signal did not depend on them. The axial and radial MFL signals increased with increasing pit depth and the bulk stress, but the circumferential MFL signal was scarcely changed.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1460-1465
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• 2004

Flow patterns around a rotating circular cylinder having square dimpled surface were visualized by the hydrogen bubble technique at velocity ratios from a=0 to 4.8 and Reynolds number of $Re=1.0{\times}10^{4}$. The wake region of the cylinder was reduced as the velocity ratios increase and was smaller than that of the smooth cylinder without dimples at the same velocity ratio. The hydrodynamic characteristics on the cylinder was investigated by measuring of lift and drag at velocity ratios from a=0 to 4.1 and Reynolds number from $Re=1.2{\times}10^{4}$ to $Re=2.0{\times}10^{4}$. As the velocity ratios increase, the average lift and drag coefficients were increased and at the same velocity ratio, the average lift was larger but the average drag was smaller than that of the smooth cylinder.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.508-513
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• 2000

An experimental investigation has been carried out for two circular cylinders having different groove configurations(U and V-shape). The results were compared with those for the smooth circular cylinder. The drag force, mean velocity and turbulent intensity profiles of wake behind the cylinders were measured with varying the Reynolds number $Re=8000{\sim}14,000$ based on the cylinder diameter. As a results, the U-groove circular cylinder was found to be most effective riblet shape with reducing the drag up to 21%. As the Reynolds number increases, the vortex shedding frequency of the grooved cylinders becomes a little larger, compared to the smooth cylinder. The flow visualization using the smoke-wire technique was also carried out to see the flow structure qualitatively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.241-244
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• 2003

Recently, IETF Mobile IP WG focus on security problem issues in Mobile IPv6 and provide appropriate protocol to solve them. These include the protections of Binding Updates both to home agents and correspondent nodes, prefix discovery messages and transporting data packets. In Mobile IPv6, control traffics between home agents and mobile nodes uses IPsec to avoid that mobile nodes and correspondent nodes may be vulnerable to attacks. It is used, however, Return Routability procedure for correspondent node to assure that the right mobile node is sending the messages. In this paper, we propose method of IPser processing to protect messages between home agents and mobile nodes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.851-856
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• 2012

Automotive turbochargers have become common in gasoline engines as well as diesel engines. They are excellent devices to effectively increase fuel efficiency and power of the engines, but they unfortunately cause several noise problems. The noises are classified into mechanical noises induced from movement of a rotating shaft and aerodynamic noises by air flow in turbochargers. The mechanical noises are whine and howling noises, and the aerodynamic noises are BPF (blade-passing frequency), pulsation, surge, some special frequency noises. These noises are bothering passengers because their levels are higher or their frequencies are clearly separated from engine or vehicle noises. The noise investigated in this paper is a BPF noise induced by compressor wheels, whose frequency is the multiplication of the number of compressor wheel blades and its rotational speed. The noise is strongly dependent upon the geometry of wheels and the number of blades. This study tried to apply a groove close to the inlet side of compressor wheels in order to reduce the BPF noise. The groove has successfully reduced the noise of narrow band frequency of a turbocharger. It shows that the groove could reduce the wide band frequency noise, the compressor BPF noise with a best shape of the groove.

• Tribology and Lubricants
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• v.7 no.2
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• pp.75-84
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• 1991

The static and dynamic performances of a floating ring journal bearing with central circumferential grooves at the inner and outer films are obtained numerically with isothermal lubrication theory. Elrod algorithm implementing Jakobsson-Floberg-Olsson cavitation boundary condition is adopted to predict cavitation regions in the inner and outer films more accurately than conventional analyses using half Sommerfeld or Reynolds conditions. The pressure drop in the circumferential groove of the inner film due to the rotation of the journal and ring is taken into account. It is shown that the lubricant supply pressure has significant influence on the load capacity and dynamic coefficients of the bearing. When the supply pressure is low and the journal speed is high, the pressure drop results in severe starvation of lubricant in the inner film and varies the overall performance of the bearing remarkably.