• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1034-1039
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• 2000

In turbo-machines operated at high speeds through gear speed increasers a precise coupled analysis of lateral and torsional vibrations is required to achieve highly reliable designs with low vibration and low noise levels, where the vibration coupling is due to the gear pair mesh stiffness. In this paper, applying the generalized coupled lateral-torsional finite element model of a gear pair element, has been analyzed a coupled lateral-torsional vibration of the prototype 800 RT turbo-chiller rotor-bearing system with a bull-pinion gear speed increaser. Results have shown that the coupled torsional natural frequencies have decreased due to the coupling effect of lateral vibration and particularly, the 2nd torsional natural frequency and its mode shape have had big changes. However, changes of lateral vibration characteristics have been noticed only at high lateral whirl natural frequencies above 15,000 rpm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.29-35
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• 1997

This research presented a frequency analysis method to analyze NRRO in a computer hard disk drive. RRO was proved to be the harmonics of rotational frequency. The frequency components of NRRO is the subtraction of the harmonics from TIR in frequency domain, so that NRRO in time domain can be obtained by Fourier inverse transformation of NRRO in frequency domain. This method can make the experiments simple without the index signal indispensable to time domain analysis. This research also shows that NRRO is caused by the defect frequencies of ball bearing. Even though the excitation force of ball bearing is independent of the rotational speed, the amplitude of NRRO is magnified near the resonance frequencies of the spindle motor. NRRO in axial direction is almost twice bigger than that in radial direction, because the spindle motor has smaller stiffness in axial direction.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.3-6
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• 2000

The magnetic bearing system are intrinsically unstable, and need the feedback control of electromagnetic forces with measured displacements. So the controller design plays an important role in constructing high performance magnetic bearing system. In case of magnetic bearing system, the order of identified model is high because of unknown dynamics included in closed loop systems - such as sensor dynamics, actuator dynamics - and non-linearity of magnetic bearings itself. In this paper the identification and robust control of flexible rotor supported by magnetic bearing are discussed. We measure and identify overall system that contains not only flexible rotor model but also magnetic bearing and time delay. The structured and unstructured uncertainties are modeled that cover variations of natural frequencies, uncertainties in sensor and actuator gains and unmodeled dynamics. And desired performances are specified with several weighting function. Using augmented system that includes identified model, uncertainties, and weighting functions, μ-synthesis is applied to flexible rotor supported with magnetic bearing. The flexible rotor was spin up over the first flexible critical speed.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1955-1962
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• 2017

Induction motors are a workhorse for the industry. The condition monitoring and fault analysis are the main concern for the engineers. The bearing is one of the vital segment of the induction machine and the condition of the whole machine is decided based on the condition of the bearing. In the present paper, the vibration signal of the bearing has been used for the analysis. The first line of action is to perform a statistical analysis of the vibration signal which gives trends in signal. To get the location of a fault in the bearing the second action is to develop an index based on Wavelet Packet Transform node energy named as Bearing Damage Index (BDI). Further, Teager-Kaiser Energy Operator (TKEO) has been calculated from higher index value to get the envelope and finally Power Spectral Density (PSD) has been applied to identify the fault frequencies. A performance index has also been developed to compare the usefulness of the proposed method with other existing methods. The result shows that the strong amplitude of fault characteristics and its side bands help to decide the type of fault present in the recorded signal obtained from the bearing.

• Journal of Magnetics
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• v.18 no.4
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• pp.443-453
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• 2013

Maglev wind turbine generator (MWTG) technology has been widely studied due to its low loss, low maintenance cost, and high reliability. However, the dynamics of the magnetic bearing system differ fromthe those of the traditional mechanical bearing system. A horizontal axial MWTG supported with a permanent magnetic bearing is designed in this research and the radial forces and the natural frequencies of the rotor system are studied. The results show that the generatorhas a cyclical magnetic forceand an unreasonable bearing stiffness may mean that the rotor system needs to work in the resonance region; the bearing stiffness is the key factor to avoid this problem. This is the main rule of the bearing stiffness design in the MWTG, and this rule can also be used in other maglev permanent magnet motors.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.5 s.182
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• pp.128-136
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• 2006

To predict the noise and vibration characteristics of induction motor system, it is necessary to develop the mathematical model including all the mechanical elements such as shaft, blower, rotor, fan, bearing, case and mounting parts. Coupling effect between case-mount system and rotor- shaft system including shaft, blower, rotor, fan and bearing is examined. Impact exciting experimentation was done in order to verify vibration model of the induction motor system. From experimental results, we can appreciate that the natural frequencies of induction motor system are in good agrements with analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1026-1031
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• 2001

In this paper. the dynamic characteristics of a super high-speed tilting-pad air bearing(TPGB) used in a turbo expander with high expansion ratio are analyzed. The dynamic behavior and stability of a rotary system supported by two journal air bearings are investigated numerically. The transient response of the shaft is obtained by simultaneously solving the equation of motion of the shaft and the dynamic Reynolds equation. The stiffness and damping coefficients of the bearing are calculated from the loading coefficients of the bearing are calculated from the loading capacity. shaft velocity and displacement by using a curve fitting method. The natural frequencies of the 1st and 2nd rigid modes can be calculated from these coefficients. The theoretical method of a rigid rotor system is verified by experimentsut.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1439-1444
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• 2005

Induction motors are the most commonly used electrical drives because they are rugged, mechanically simple, adaptable to widely different operating conditions, and simple to control. The most common faults in squirrel-cage induction motors are bearing, stator and rotor faults. Surveys conducted by the IEEE and EPRI show that the most common fault in induction motor is bearing failure (${\sim}$40% of failure). Thence, this paper addresses experimental results for diagnosing faults with different rolling element bearing damage via motor current spectral analysis. Rolling element bearings generally consist of two rings, an inner and outer, between which a set of balls or rollers rotate in raceways. We set the experimental test bed to detect the rolling-element bearing misalignment of 3 type induction motors with normal condition bearing system, shaft deflection system by external force and a hole drilled through the outer race of the shaft end bearing of the four pole test motor. This paper takes the initial step of investigating the efficacy of current monitoring for bearing fault detection by incipient bearing failure. The failure modes are reviewed and the characteristics of bearing frequency associated with the physical construction of the bearings are defined. The effects on the stator current spectrum are described and related frequencies are also determined. This is an important result in the formulation of a fault detection scheme that monitors the stator currents. We utilized the FFT, Wavelet analysis and averaging signal pattern by inner product tool to analyze stator current components. The test results clearly illustrate that the stator signature can be used to identify the presence of a bearing fault.

• Toxicological Research
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• v.6 no.1
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• pp.21-28
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• 1990

This study was undertaken to evaluate the immune responses to sheep red blood cell (SRBC) and potential anti-tumor effect of Bacillus Calmette-Guerin (BCG) in the mice bearing rumor induced by DMBA. The frequencies of tumor appearances were 62% in DMBA-treated mice and 14% in DMBA and BCG-treated group, respectively. Cellular immune response such as delayed-type hypersensitivity (DTH) to SRBCs, natural killer (NK) cell activity and antigen-binding cell (ABC) assay were decreased apparently in the tumor bearing mice compared to the normal controls. Humoral immune responses such as hemagglutinin (HA) and hemolysin (HE) were noted to be reduced in the tumor bearing mice, but the spleen index increased in tumor bearing mice. All the immunological parameters in the DMBA and BCG-group appeared to be higher than those of only DMBA-treated group. These results indicated that DMBA-induced tumor suppressed host immune responses. Also, they imply the idea that BCG enhanced the immune responses of tumor-bearing host and antitumor effects.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.1022-1027
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• 2002

This paper describes the fluttering characteristics of the upper pad in a tilting pad journal bearing(6-pad, LOP type) using a steam turbine. In order to investigate the phenomena of the upper pad fluttering experimentally, the absolute vibration of the upper pads the relative vibration between bearing and shaft and the circumferential distribution of the film thickness are measured under the different values of supply oil flow rate, shaft speed and bearing load. It can be known that the fluttering mechanism of the upper pads has a tendency of the self-excited vibration from the study of fluttering frequencies and amplitudes with the change of shaft speed. furthermore, it is observed that the incipient upper pad fluttering velocity is increased by the increase of oil supply flow rate and fluttering amplitude of the upper pads is increased by the decrease of the oil flow rate and by the increase of the bearing load.