• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.342.1-342
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• 2002

In this work, the dynamic characteristics of an oil-lubricated, short SFD with a central feeding groove are derived based on a theoretical analysis considering the effect of a groove. The validity of the analysis is investigated experimentally using an Active Magnetic Bearing (AMB) system as an exciter. For the theoretical solution, the fluid film forces of a grooved SFD are analytically derived so that the dynamic coefficients of a SFD are expressed in terms of its design parameters. (omitted)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.400.1-400
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• 2002

This paper presents an optimum design of rotor-bearing system using a hybrid method to compute the solutions of optimization problem. The present hybrid algorithm, namely Enhanced Artificial Life Algorithm(EALA), is a synthesis of an artificial life algorithm(ALA) and the random tabu search(R-tabu) method. We applied EALA to the optimum design of rotor-shaft system supported by the floating ring journal bearings. (omitted)

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.746-753
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• 2006

This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings. The Reynolds equations and their perturbation equations are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between bearings. The Reynolds boundary condition is used in the numerical analysis to simulate the cavitation phenomena. The dynamic coefficients of the proposed method are compared with those of the numerical differentiation of the loads with respect to finite displacements and velocities of bearing center. It shows that the proposed method is more accurate and efficient than the differentiation method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.172-177
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• 2001

This paper proposes an adaptive feedforward controller (AFC) based on LMS for periodic disturbance rejection in active magnetic bearing system. The proposed controller does not alter the stability and robustness of the existing AMB system. It is shown that the control delay due to the eddy current as well as runout and unbalance can be identified and compensated using the estimated displacement from the measured magnetic flux. The simulation results confirm that the proposed scheme successfully identifies and compensates for the runout, unbalance and eddy current effect, leading to a high-precision magnetic bearing system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.439-448
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• 2004

Magnetic bearing is an attractive device in precision engineering field because of its non-contacting nature and controllability of its dynamic characteristics. This paper provides a method of designing a sliding mode control for an active magnetic hearing(AMB) system which is used to support the elevation axis of a target tracking sight instead of mechanical bearings to eliminate the effect of mechanical friction. In such system, the axis should be levitated and supported within a predetermined air gap while AMB is excited by base motion. Experimental results showed that the sliding mode control is effective in disturbance rejection than conventional PID-control without any additive measurements.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.247-251
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• 2001

Nowadays, base isolation systems such as lead-rubber bearing, elastomer bearing and sliding bearing have been installed to the various structures to prevent the disaster from seismic. The performance of base isolation system have been well proved by model-scale experiments and numerical analysis. However. the seismic response data measured at real large base-isolated structures is still insufficient. This paper presents a seismic monitoring system, acquiring real-time acceleration signals up to 32 channels, displaying time history and spectrum of the signals, storing the acquired data at a PC hard disk, and replaying the saved data. Moreover, the system can be operated without any limitation for monitoring period by automatic management of stored data file. The developed system has been installed at a real base-isolated building using lead-rubber bearings and we expect its seismic response data with ground motion signal can be well licquired in case of earthquake occurrence.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1102-1107
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• 2000

The signals that can be obtained from a rotating machine often convey the information of machine. For example, if the machine under investigation has faults, then we can measure the signal which has a pulse train, embedded in noise. Therefore the ability to detect the fault signal in noise determines the degree of diagnosis level of rotating machine. In this paper, minimum variance cepstrum (MV cepstrum), which can easily detect impulse in noise, has been applied to detect the type of faults of ball bearing system. To test the performance of this technique, experiment has been performed for ball bearing elements that have man made faults. Results show that minimum variance cepstrum can easily detect the periodicity due to faults.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1051-1057
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• 2000

A projected 100 kW APU gas turbine rotor-bearing system has a main outer shaft, which is composed of some numbers of segmented sections for manufacturing and assembly conveniences. For a secure assembly of the segmented sections a tie shaft or inner shaft is installed inside of the outer shaft and a tensional axial preload of 50,000 N is provided to it. In this paper it is intended to set-up a sound modeling method of the APU rotor system, and particularly, the influences of the tie shaft on the rotordynamic characteristics of the entire APU gas turbine rotor-bearing system are investigated. Analysis results show that as a conservative design practice the inner tie shaft should be actively modeled in the rotordynamic analysis of the APU rotor-bearing system, and its effects on the dynamic behaviors of the outer shaft should be thoroughly design-reviewed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.160-166
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• 1999

Nonlinear characteristics of the hydrodynamic journal bearing with circumferentially groove are analyzed numerically considering cavitation region, when an external sinusoidal shock is given to the system. The oil film force is obtained by solving the finite width universal Reynolds equation at each time step. Frequency response function and journal orbit obtained from both linear and nonlinear bearing simulations are compared with each other. The vibration response of the journal is different from the expectation obtained from the linear analysis as increase the vibration amplitude of external disturbance. Therefore, the linear theory is not adequate, and the nonlinear calculation such as used in this research is needed to design safety rotor systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.1076-1082
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• 2003

As functional requirement of massive digital information storage devices are on a trend for the higher data transfer rate and lower cost, many different technical efforts are being tested and implemented in the industry. FDB(Fluid Dynamic Soaring) is one of the major breakthroughs in rotor design in terms of TMR budget. Although FDB analysis based on Reynolds' equation is well established and popularly being used for DB design especially for the estimation of bearing stiffness, there are obvious limitations in the approach due to the inherent assumptions. A generalized analysis tool employing the full Navier-Stokes equation and the energy balance is to be beneficial for detailed FDB design In this publication, an efficient geometry modeling method is presented that provides fully integrated inputs for general FVM/FDM codes. By virtue of the flexibility of the presented method, many different detailed FDB design and analysis are carried over with ease.