• Tribology and Lubricants
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• 제15권4호
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• pp.304-313
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• 1999

High-speed rotors set a lot of high vibration and stability problems especially when the speed of rotation is going through the first or the second critical speed. The aim of this paper is to investigate the possibility of an active control of a rigid rotor with squeeze film damper which has a good configuration of easily controlled end seal clearances and/or adjustment of a feed pressure. A theoretical method is presented and some numerical results are compared with test measurements. Both results show that the vibration or bit sizes are decreased when the end seal gap decreases with constant supply pressure, and when the supply oil pressure increases with constant seal gap. The experimental results show also a pleasing similarity on both orbit sizes and their decrement ratio compared with theoretical analysis. The possibility of an active control with the squeeze film damper was verified by adjusting the seal gap and the supply pressure.

• Tribology and Lubricants
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• 제33권3호
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• pp.112-118
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• 2017

Tilting pad journal bearings(TPJBs) are widely used for high speed rotating machinery owing to their rotordynamic stability and thermal management feature. With increase in the rotating speed of such machinery, an increasingly important aspect of TPJB design is the prediction of their thermal behaviors. Researchers have conducted detailed investigations in the last two decades, which provided design tools for the TPJBs. Based on these previous studies, this paper presents a thermohydrodynamic(THD) analysis model for TPJBs. To calculate pressure distribution, we solve the generalized Reynolds equation and to predict the lubricant temperature, we solve the 3D energy equation. We employ the oil mixing theory to calculate pad inlet temperature; further, to consider heat conduction via the pad, we solve the heat conduction equation for the pads. We assume the shaft temperature as the averaged oil film temperature and apply natural convection boundary conditions to the pad side and back surfaces. To validate the analysis model, we compare the predicted pad temperatures with those from previous research. The results show good agreement with previous research. In addition, we conduct parametric studies on a TPJB which was used in a gas turbine simulator system. The predicted results show that film temperature largely depends on the rotating speed and oil supply condition.

• Tribology and Lubricants
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• 제34권3호
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• pp.75-83
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• 2018

Microturbomachinery (< 250 kW) using gas foil bearings can function without oil lubricants, simplify rotor-bearing systems, and demonstrate excellent rotordynamic stability at high speeds. State-of-the-art technologies generally use bump foil bearings or leaf foil bearings due to the specific advantages of each of the two types. Although these two types of bearings have been studied extensively, there are very few studies on leaf-bump foil bearings, which are a combination of the two aforementioned bearings. In this work, we illustrate a simple mathematical model of the leaf-bump foil bearing with leaf foils supported on bumps, and predict its static and dynamic performances. The analysis uses the simple elastic model for bumps that was previously developed and verified using experimental data, adds a leaf foil model, and solves the Reynolds equation for isothermal, isoviscous, and ideal gas fluid flow. The model predicts that the drag torques of the leaf-bump foil bearings are not affected significantly by static load and bearing clearance. Due to the preload effect of the leaf foils, rotor spinning, even under null static load, generates significant hydrodynamic pressure with its peak near the trailing edge of each leaf foil. A parametric study reveals that, while the journal eccentricity and minimum film thickness decrease, the drag torque, direct stiffness, and direct damping increase with increasing bump stiffness. The journal attitude angle and cross-coupled stiffness remain nearly constant with increasing bump stiffness. Interestingly, they are significantly smaller compared to the corresponding values obtained for bump foil bearings, thus, implying favorable rotor stability performance.

• Composites Research
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• 제19권6호
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• pp.8-15
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• 2006

본 연구에서는 대형 LCD 패널 제조용 복합재 롤러에 대한 3차원 회전체 동역학 해석을 수행하였다. 전산해석은 로터시스템의 회전에 의한 자이로스코픽 영향을 고려한 일반적인 유한요소법에 근거하고 있다. 본 연구에서는 유럽의 범용 상용 유한요소해석 프로그램인 SAMCEF를 활용하였으며 이는 전문적인 로터해석 모듈을 포함하고 있다. 전산해석 기법의 검증을 위해 베어링 지지된 2중 회전축 로터 모델에 대한 해석 및 비교결과를 제시하였다. 설계된 복합재 롤러 모델에 대한 상세 유한요소 모델을 구축하였으며, 중력 효과를 고려한 전산해석을 통하여 실제 운용환경에서의 진동특성을 고찰하였다. 이의 결과로 다른 회전조건에 대한 로터 안정성 선도 및 불평형 응답에 대한 결과들을 제시하였다.

• Tribology and Lubricants
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• 제31권6호
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• pp.302-307
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• 2015

The use of turbocharger in internal combustion engines has increased as it is a key components for improving system efficiency without increasing engine size. Because of increasing demand, many studies have evaluated rotordynamic performance so as to increase rotation speed. This paper presents a linear and nonlinear analysis model for a turbocharger rotor supported by a floating ring bearing. We constructed rotor model by using the finite element method and approximated bearings as being infinitely short. In the linear model, we considered fluid film force as stiffness and damping element. In nonlinear analysis, calculation of the fluid film force involved solving the time dependent Reynolds equation. We verified the developed model by comparing the results to those of previous research. The analysis results show that there are four unstable modes, which are rigid body modes combining ring and rotor motion. As the rotating speed increases, the logarithmic decrement shows that certain unstable modes goes into the stable area or the stable mode goes into the unstable area. These unstable modes appear as sub-synchronous vibrations in nonlinear analysis. In nonlinear analysis frequency jump phenomenon demonstrated in several experimental studies appears. The analysis results also showed that frequency jump phenomenon occurs when the vibration mode changes and the sequence of unstable mode matches the linear analysis result. However, the natural frequency predicted using linear analysis differs from those obtained using nonlinear analysis.

• 대한기계학회논문집A
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• 제39권10호
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• pp.1029-1037
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• 2015

최근 회전 시스템의 고속화 경향에 따라 회전체 동역학적 안정성의 중요성이 부각되었다. 고속회전 시스템에 적용되는 가스베어링의 동특성을 규명하는 것은 회전체의 거동을 예측하는데 상당히 중요하다. 본 연구에서는 대표적인 가스베어링인 가스포일베어링의 범프 구조에 대하여 가진실험을 수행하고 가진 주파수에 따른 동특성을 측정하였다. 실험 결과, 범프 구조의 강성은 주파수에 따라 증가하였고 감쇠는 감소하였다. 또한, 가압 조건에서의 동특성은 범프 구조의 동특성 보다 낮은 값을 가졌다. 본 실험을 통해 범프 구조의 주파수 의존 동특성의 경향을 파악하였으며 가스포일베어링의 동특성에 윤활막이 미치는 영향에 대해 확인하였다. 또한 두 가지 동특성 계산 방법을 제시하여 실험결과를 통해 효과 적인 동특성 계산 방법에 대해 비교 고찰하고 범프 구조와 윤활막의 동특성을 비교 하였다.