• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.701-702
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• 2011

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.676-677
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• 2013

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.555-556
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• 2007

• Journal of the KSME
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• v.28 no.6
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• pp.556-562
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• 1988

기계나 구조물의 수명을 결정하는 마멸은 물체간의 접촉으로 인한 것이고 마멸을 줄이기 위해 윤활이 발달되어 왔다. 여러 형태의 마멸을 해석하기 위해서 접촉역학의 이해는 필수적이라 할 수 있다. 하중과 운동 조건에 의한 다양한 접촉문제를 일반적으로 다루기 위해 접촉면을 중심 으로 한 접근 방법을 소개하였으며, 접촉문제의 특이성을 보이기 위해 마찰접촉문제 해석을 위한 한기법을 간단히 기술하였다. 고속 볼 베어링의 특성 해석과 접촉형상 최적설계를 통하여 광 범위한 접촉 역학의 적용의 일부를 소개하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.427-435
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• 1999

In the field of shape optimum design, much efforts are needed in regridding method and shape design sensitivity analysis. In this paper, Bezier curve is used to make the boundary of a structure and the improved direct differentiation method is used to calculate the shape design sensitivity. To regrid the finite element model, modified displacement field is presented in this paper. The modified displacement field makes more fine grid at large curvature. The purpose of this paper is to obtain the optimum shape of a cantilever with weight and a 3-dimensional journal bearing cap.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.2
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• pp.7-13
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• 2011

Turbine journal bearings are designed to support the weight of the rotors on a hydrodynamic oil film and to provide dynamic stability to the rotor system. The life time of journal bearings is infinite theoretically because the journal bearings are separated from the shaft journal by oil film. But poor design, assembly, operation and maintenance can cause problems to the journal bearings. The FMEA(Failure Mode and Effects Analysis) results of the journal bearings show that frequent maintenance of the journal bearings can cause failures and reduction of the bearing life. Therefore, the maintenance periods and history of the journal bearings with the bearing FMEA results are reviewed in order to establish the optimized maintenance period of the journal bearing for the nuclear power plants. Consequently it is necessary to maintain a best condition of lubrication system, reject time-based maintenance and perform the condition-based maintenance of journal bearings in order to maintain optimum condition of the journal bearing.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.199-206
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• 2002

This paper describes a reliability characteristics of an air foil journal bearing for high speed turbomachinery at room temperature. To verify the reliability of air foil journal bearing, lift-off characteristics, load carrying capacity, and 10,000 cycle start-stop test were performed with motor driven test rig. Lift-off test shows the relationship between the rotating speed of the shaft and the frictional torque with bearing surface. About load carrying capacity, the tested air foil journal bearing produced a load capacity of 500N at an operating speed of 15,000rpm, which is compared with results of numerical analysis and empirical coefficients. Finally, The trends in change of start torque, stop torque, and bearing temperature were shown during 10,000 cycle start-stop test of an air foil journal bearing. from the results of this work, an air foil bearing will be done well, as a supported bearing for high speed turbo-compressor.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1016-1021
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• 2004

The need for developing a mathematical model for pad-pivot friction in tilting pad proceeding bearings has been well-recognized, since previous experimental work about the performances of the bearings hypothesized that the friction in the bearings is closely related to their performances. Especially, the sliding friction between pad and pivot in the ball and socket type of the bearings can influence the performance of the bearing. We propose a mathematical model for pad-pivot friction in the ball and socket type, which considers the geometrics of the pad and pivot of the bearings, by assuming the sliding friction in the ball and socket bearing as Coulomb friction. By utilizing the proposed model for pad-pivot friction, we show the analysis of Reynolds equation and energy equation, which explain the thermo-hydrodynamic characteristics of tilting pad proceeding bearings, by taking into account the turbulence and inlet pressure building as well. The results of the study show that the performance of titling-pad proceeding bearings can be greatly influenced by the pad-pivot friction. In particular, we have shown that the analysis of the pad-pivot friction is useful to explain the static proceeding loci and the dynamic characteristics of the ball and socket type of the bearings. Furthermore, for a given operating condition, we can obtain various equilibrium states which satisfy the static equilibrium conditions, by considering the pad-pivot friction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.4
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• pp.344-351
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• 2004

Tilling pad journal bearings have been widely used to support the rotors of the high rotating machinery such as steam and gas turbines owing to their inherent dynamic stability characteristics. However, serious bearing problems such as fatigue damage in the upper unloaded pad, the break of locking pins and the wear of pinholes etc. by pad fluttering are frequently taken place in the actual steam turbines. The purpose of this paper is to investigate the mechanism of pad fluttering and to suggest the useful design guideline(application of preload, m) for the purpose of preventing bearing problems by pad fluttering in a tilting pad journal bearing. It is estimated that upper pad is easy to flutter because the film shape of the upper pad is diverged by moment acting on pivot point. This paper suggests that effective preload range(m $\geq$ 0.5) in order to be statically loaded pad under all operating conditions. Also, design modified bearing is suggested for the adjustment in actual steam turbines. And bearing and rotor dynamic analysis are performed to identify bearing characteristics and to verify the reliability of rotor-bearing system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.4
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• pp.247-257
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• 2003

This paper presents an analytical method to Investigate the stability of a hydrodynamic journal bearing with rotating herringbone grooves. The dynamic coefficients of the hydrodynamic Journal bearing are calculated using the FEM and the perturbation method. The linear equations of motion can be represented as a parametrically excited system because the dynamic coefficients have time-varying components due to the rotating grooves, even in the steady state. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving Hill's infinite determinant of these algebraic equations. The validity of this research is proved by the comparison of the stability chart with the time response of the whirl radius obtained from the equations of motion. This research shows that the instability of the hydrodynamic journal bearing with rotating herringbone grooves increases with increasing eccentricity and with decreasing groove number, which play the major roles in increasing the average and variation of stiffness coefficients, respectively. It also shows that a high rotational speed is another source of instability by increasing the stiffness coefficients without changing the damping coefficients.