• Tribology and Lubricants
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• v.30 no.1
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• pp.64-70
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• 2014

This paper presents a numerical model for investigating the structural dynamics response of a rigid rotor supported on deep-groove ball bearings. The numerical model was used to investigate the influence of race waviness on the dynamic characteristics of a rotor ball bearing system, which is very important from a design viewpoint. The forth-order Runge-Kutta numerical integration technique was applied to determine the time displacement response, Poincare map, and frequency spectra. The analysis demonstrated that the model can be used as a tool for predicting the nonlinear dynamic behavior of a rotor ball bearing system under different operating conditions. The results of this study may help further understanding of the nonlinear dynamics of a rotor bearing system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.255-260
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• 1998

A detailed rotordynamic design analysis is performed with a turbo-chiller compressor rotor-bearing system. A pinion is machined into a compressor shaft and the pinion is driven by a bull gear to a rated speed of 14,600 rpm. Utilizing a finite element method each bearing loads are calculated considering various gear loadings as well as the rotor weight itself. A Partial bearing and a 3-Lobe bearing are designed as the compressor impeller out-board bearing and in-board bearing, respectively. Finally a complex rotordynamic analysis of the compressor rotor-bearing system is carried out to evaluate the system whirl natural frequencies, stabilities, and unbalance responses.

• Tribology and Lubricants
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• v.11 no.2
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• pp.56-62
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• 1995

The anisotropic pressure distribution of the hydrodynamic bearing may generate the unstable vibration phenomenon over a certain speed. These vibrations, known as whirl, whip or rotor instability, cannot be sustained over a wide range of rotational spees. Besides these vibrations not only perturb the normal operation of a rotating machine, but may also cause serious damage to the machinery system. And, it is really impossible to change one parameter without changing others, or difficult to fabricate the modified non-circular type bearing, with all the other cures used just now, In this study, hybrid bearing with magnetic exciter is designed for stability improvement of hydrodynamic bearing rotor system without changing mechanical parameters. For stability study, eigenvalue study of the bearing-rotor system is executed by finite element method and results of analyses and experiments show the possibilities of the stability improvement of the hydrodynamic bearing system by using the electricmagnetic force.

• Journal of KSNVE
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• v.6 no.1
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• pp.71-82
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• 1996

The finite element analysis for rotor bearing systems has been an essential tool for design, identification, and diagnosis of rotating machinery. Among others, the unbalance response analysis is fundamental in the vibration analysis of rotor bearing systems because rotating unbalance is recognized as a common sourve of vibration in rotating machinery. However there still remains a problem in the aspect of computational efficiency for unbalance response analysis of large rotor bearing systems. Gyroscopic terms and local bearing parameters in rotor bearing systems often make matters worse in unbalance response computation due to the complicated dynamic properties such as rotational speed dependency and/or anisotropy. The present paper proposes an efficient method for unbalance responses of multi-span rotor bearing systems. An improved substructure synthesis scheme is introduced which makes it possible to compute unbalance responses of the system by coupling unbalance responses of substructures that are of self adjoint problem with small order matrices. The present paper also suggests a scheme to easily deal with gyroscopic tems and local, coupling or bearing parameters. The proposed method causes no errors even though the computational effort is reduced drastically. The present method is demonstrated through three test examples.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.1
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• pp.175-181
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• 2012

This paper presents a novel dynamic vibration absorber (DVA) to suppress the unbalance response of flexible rotor-bearing systems. The DVA unit consists of two DVAs, an adapter to place the DVAs and an adapter frame to locate the adapter. The essential feature of the proposed DVA unit is to place itself on any desirable location of the shaft without disassembling the rotor-bearing system under consideration. A simulation with a 3D element based commercial rotor dynamic software is made to test the possibility of the proposed DVA on the suppression of unbalance response in rotor-bearing systems. Experiments are performed to validate the proposed DVA unit. The simulation and experiments show that the proposed DVA unit is very effective to suppress the unbalance response in rotor-bearing system at designated rotational speeds of interest.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.2
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• pp.40-46
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• 2004

Magnetic bearing has been adopted to support a rotor by electromagnetic force without mechanical contact and lubrication process. The recent growth of magnetic bearing applications in many industrial fields requires more accurate design of bearing-rotor system. Due to external forces and uncertainties of magnetic bearing system the actual performance and stability my be worse than it is designed. This paper describes the governing equations of rotor magnetic bearing systems and/or the designing of robust controller via standard $H_{\infty}$ control problem. The system stability and response characteristics are studied by simulations and verified with experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.283-289
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• 1997

A 500Wh class high-speed Flywheel Energy Storage System (FESS) driven by a built-in BLDC motor/generator has been designed, which runs from 30000 to 60000rpm nominally. Due to the motor/generator inside, the flywheel rotor made of composites supported by PM/EM hybrid bearing system has a shape of bell or pendulum and thus requires accurate rotordynamic analyses and prediction of its dynamic behavior to secure the operating reliability. Rotordaynamic analyses of the flywheel rotor-bearing system revealed that the bell shaped rotor has two conical rigid-body modes in the system operating range and the first conical mode, of which nodal point lies in the radial EM bearing position, can adversely affect the dynamic response of the rotor at the corresponding critical speed. To eliminate the possibility of wild behavior of the rotor, two guide bearings are adopted at the upper end of the rotor and motor/generator. It was also revealed that the EM bearing stiffness of 0.5~1.0E+6 N/m and damping of 2000 Ns/m are favorable for smooth operation of the system around the 2nd critical speed.

• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.9-18
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• 1997

This paper is a study on the dynamic characteristics of truncated cone type squeeze film damper(SFD) bearing and rotor system. This model can alter the radial oil film gap which Is Important to the performance of rotor-bearing system and manufactured easily to change the shape concept of traditional circular type SFD bearing. In theoretical analysis, the oil film pressure distribution, the oil film force, the film damping coefficient and the eccentricity ratio, etc. were induced with regard to the film inertia effect. The film damping coefficients and optimum design parameters are calculated. When unbalance parameter U is greater than 0.2, the nonlinear vibration such as "Jump" phenomena appears in the vicinity of rotor critical speed. At this time, the increases of bearing parameter U, journal distance S, Reynolds number Re can control this unstable vibration. The experimental results show that SFD hearing and rotor system which are designed according to the design parameters in the stable region are operated stably in rotational speed 9,600rpm without nonsynchronous behavior.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.04a
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• pp.101-106
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• 1993

A new rotor control scheme, the isotropic control of anisotropic rotor bearing system in complex state space, is proposed, which utilizes the concepts on the eigenstructure of the isotropic rotor system. Then the control scheme is applied to an active magnetic bearing system and the control performance is investigated in relation to control energy, transient response, and unbalance response. In particular, it is shown that the proposed method is efficient for control of unbalance response.

• The KSFM Journal of Fluid Machinery
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• v.16 no.3
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• pp.18-25
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• 2013

Recently the requirement of long-term mobile energy source for mobile robot or small-sized unmanned vehicle is highly increased, and the micro turbine generator(MTG) which is known to have high energy and power density is under development. MTG is designed to have air foil bearing and high speed rotor of which operating speed is 400,000rpm. In the development stage of high speed rotor and bearing, stability analysis for the full operational speed range is essential and the dynamic coefficients such as stiffness and damping coefficients of bearing depending on the rotational speed are required for that. Although perturbation method is usually used to identify the dynamic coefficients, it's not easy to give the perturbation to the high speed rotating rotor. In this study, we present the dynamic coefficients measurement system for air foil bearing which consists of electromagnets, gap sensors, high speed motor and controller. This measurement system can exert the sine sweep force to the rotor-bearing, measure the displacement of rotor and get FRF(Frequency response function) of rotor-bearing. The least square estimation method is applied to identify the dynamic coefficients of bearing from the measured frequency response at the different rpm and the identified dynamic coefficients for the wide rotational speed range are presented.