• 대한기계학회논문집A
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• 제29권10호
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• pp.1416-1429
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• 2005

In order to meet the increasing competitive pressures coupled with higher demands for component quality, whirling machines have been at the cutting edge of the automobile industry for more than 25 years. The hard whirling process can save on machining time and operation elimination. Hard whirling is done dry, without coolant. The chips carry away nearly all of the heat during cutting, leaving the workpiece cool and minimizing any thermal geometry variations. The surface finish and profile accuracy are close to grinding quality. Whirling machines usually consist of four major parts; 1) loading system that requires the necessary axial speeds, 2) head stock that needs high precision clamping and positioning system at the chuck and tailstock, 3) whirling unit that demands the high cutting speeds and cutting power fer cutting deep thread profiles and 4) unloading system that requires an easy workpiece unloading. Also, capabilities of the whirling machine can be improved by attaching a vision system to the machine. Most of whirling machines in Korean automobile industry are imported from the Leistritz company, Germany and the Hasegawa company, Japan. Tn this paper, a basic research will be performed to improve and enhance the existing whirling machines. Finally, a new Korean whirling machine will be proposed and developed.

• 한국유체기계학회 논문집
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• 제20권2호
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• pp.53-62
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• 2017

In this paper, the effect of oil conditions in rotor dynamic behaviors of a FFRB (Fully-Floating Ring Bearing) is investigated. Through the characteristic of a FFRB has two films, it has several advantages such as less friction loss and better stability over a wide speed range. However, it is difficult to supply a oil to the inner film. Thus, turbocharger makers have been paid significant attention to the lubrication of a FFRB because of its importance. This work focuses on the influence of oil inlet pressure and temperature. The methodologies of computational simulation and experimental test were used to estimate the rotor dynamic behaviors. In experimental test, the single-scroll turbocharger for the 1.4L diesel engine was used. The results show that the oil inlet pressure and temperature will place considerable influence on the rotor response. Oil conditions affect RSR (Ring Speed Ratio) which is cause of sub-synchronous vibrations, which also cause of oil whirling and whip even a critical speed. At higher speed range, the phenomenon of self-excited vibrations which is cause of instability of fluid whirl is investigated through the orbit shapes that consist of small orbit and large amplitude orbit. It is shown that some performance of a FFRB can be controlled by the conditions of oil supply. Finally, it was revealed that the oil induced operating conditions will strongly affect the turbocharger rotor dynamics behaviors.

• International Journal of Fluid Machinery and Systems
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• 제9권3호
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• pp.194-204
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• 2016

Floating ring seals offer an opportunity to reduce leakage flows significantly in rotating machinery. Accordingly, they have been applied successfully to rotating machinery within the last several decades. For rocket turbopump applications, fundamental behavior and design philosophy have been revealed. However, further work is needed to explore the rotordynamic characteristics associated with rotor vibrations. In this study, rotordynamic forces for floating ring seals under rotor's whirling motions are calculated to elucidate rotordynamic characteristics. Comparisons between numerical simulation results and experiments demonstrated in our previous report are carried out. The three-dimensional Reynolds equation is solved by the finite-difference method to calculate hydrodynamic pressure distributions and the leakage flow rate. The entrance loss at the upstream inlet of the seal ring is calculated to estimate the Lomakin effect. The friction force at the secondary seal surface is also considered. Numerical simulation results showed that the rotordynamic forces of this type of floating ring seal are determined mainly by the friction force at the secondary seal surface. The seal ring is positioned almost concentrically relative to the rotor by the Lomakin effect. Numerical simulations agree quite well with the experimental results.