• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1402-1410
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• 1995

An influence coefficient method with an optimal correction balancing algorithm is developed for balancing a high-speed flexible rotor system. Conventional flexible balancing algorithms such as least square and weighted least square algorithms may not satisfy allowable residual vibration levels in certain speed ranges, while the optimal correction balancing method can be more effective in controlling vibration levels in a target speed. Related analyses were reviewed and applied to a test rig to show the effectiveness of the optimal correction balancing method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2205-2215
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• 1992

The stability of the flexible rotor mounted on circumferentially grooved floating ring journal bearings was investigated theoretically and experimentally. The floating ring journal bearing was analyzed by using JFO reformation boundary condition. The flexible shaft was analyzed by the finite element method based on Rayleigh beam theory. It was found that the measured ring speed agrees well with the theoretical results. The instability of the system due to not only the outer film but also the inner film of the bearing could be predicted by the theory which allows negative vapor pressure. The tendency that reducing the supply pressure of lubricant stabilizes the system was observed both experimentally and theoretically.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.409-418
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• 1988

Steam turbines, gas turbines, multistage centrifugal compressors are operated over the range of the first critical speed. In these rotors flexible rotor balancing technique is necessary. In such balancing, influence coefficients are measured by rotating a rotor with trial weight. But for the large rotor, the measurement of influence coefficient takes much time and it reduces the cost efficiency. In this paper the new influence coefficient with rotation of rotor is proposed. First the theoretical background of the method is presented and it is applied to the simple flexible rotor model. Then the experiments are performed and the results of presented method are compared with those of analytical method. By using the obtained influence coefficient, balancing of the flexible rotor is performed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.280-283
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• 2005

This study performed by a previous research for the applying expert system to active vibration control algorithm. In order to increase productivity and efficiency, high-speed rotating machines become popular these days. They are likely to vibrate and cause machine failure even though they have small unbalance. Therefore, a high-speed rotating machine needs a balancing technique. ISO 11342 classifies flexible rotors in accordance with their balancing requirements and establishes methods of assessment of residual unbalance. But, even if they finished balancing work, they have harmful effect vibration under the high-speed rotating environment. This vibration effect is very small, but it must be removed for the improvement of the rotor's spin accuracy. This paper introduces a new active control method that remove the exciting force by a phase control. For this method, the high-speed rotating rotor was reconstructed by a flexible rotor model. The forces which excite the rotating system suppose cyclic forces, we obtain the responses by numerical method. And then through the pattern analysis about the vibraton responses, the controler generate the control force with the reverse phase and similar magnitude. This paper suggest an phase control method and shows how to improve the rotating vibration accuracy of the flexible rotor dynamics system using phase control method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.258-263
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• 2009

This paper describes an analysis of the stability and performance of a large-capacity flywheel energy storage system (FESS) supported by active magnetic bearings. We designed and manufactured the system that can store up to 5kWh of usable energy at the maximum speed of 18,000 rpm. In order to analyze the stability of the systems accurately, we derived a rigid body rotor model, flexible rotor model using finite-element method, and a reduced-order model using modal truncation. The rotor model is combined with those of active magnetic bearings, amplifiers, and position sensors, resulting in a system simulation model. This simulation model is validated against experimental measurements. The stability of the system is checked from the pole locations of the closed-loop transfer functions. We also investigated the sensitivity function to quantify the robustness of the systems to the disturbances such as mass imbalance and sensor noises.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.425-426
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• 2006

This study proposes a new simulation method of high speed rotor system with the dynamic model using multi body dynamic analysis tool and with a new phase modulating technique as a system control algorithm. A dynamic model of high speed rotor system was built by, ADAMS, commercial multi body dynamic program. The phase modulating technique is a new control algorithm for a rotor system. This algorithm can control system using an adaptive proportional gain and an adaptive phase which are obtained from periodical input signal. To make control system, a ADAMS model and component parameters and phase controller was composed by Matlab Simulink And simulate it.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.6
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• pp.167-174
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• 2013

High speed rotor systems with magnetic bearings have been the subject of much research in recent years due to the potential for active vibration control. In this thesis, optimal design was conducted for an 8-pole heteropolar magnetic bearing used in the flexible rotor of a turbo blower. In connection with bearing stiffness, this optimal design process was conducted using a genetic algorithm(GA), which is based on natural selection and genetics. The maximum stiffness of the magnetic bearing-rotor was found by considering the critical speeds of the flexible rotor. As a result, the magnetic bearings were optimized to have maximum stiffness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.736-742
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• 2008

This paper proposes new searching algorithm for the optimal PD gains of flexible rotor supported by active magnetic bearings. Under the assumption of linearized bearing parameters with respect to PD gains, the performance index in quadratic form is defined and steepest descent method is adopted for determining local minimum. Moreover, the eigenpair sensitivity concept is utilized to evaluate the sensitivity of performance index. To evaluate the effectiveness of suggested algorithm, the finite element model is constructed and its reduced model is retained in modal domain. Given starting gains, the optimal gains are successfully found and the control performance is demonstrated by simulation to show the efficiency of the proposed method.

• Journal of Power System Engineering
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• v.7 no.3
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• pp.48-53
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• 2003

This paper deals with the control of a horizontally placed flexible rotor levitated by electromagnets in a multi-input/multi-output (MIMO) active magnetic bearing(AMB) system. AMB is a kind of novel high performance bearing which can suspend the rotor by magnetic force. Its contact-free manner between the rotor and stator results in it being able to operate under much higher speed than conventional rolling bearings with relatively low power losses, as well as being environmental-friendly technology for AMB system having no wear and no lubrication requirements. In this MIMO AMB system, the rotor is a complex mechanical system, it not only has rigid body characteristics such as translational and slope motion but also bends as a flexible body. Reduced order nominal model is computed by consideration of the first 3 mode shapes of rotor dynamics. Then, the $H_{\infty}$ control strategy is applied to get robust controller. Such robustness of the control system as the ability of disturbance rejection and modeling error is guaranteed by using $H_{\infty}$ control strategy. Simulation results show the validation of the designed control system and the modeling method to the rotor.

• Tribology and Lubricants
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• v.16 no.3
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• pp.157-165
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• 2000

A discharge free Electro-Rheological Squeeze Film Damper (ER-SFD) with predetermined-clearances at leakage ends can inherently eliminate electric discharge problems while still supplying stable leakage control. Test results show that the damping force of the slotted-ring ER-SFD is mainly affected by electric voltage, oil supply pressure, position of the damper and ratio of effective surface area of slotted-rings. As the supply voltage is larger, the amplitudes of both slotted ER-SFD and rotor are decreased at first and second critical speeds. The influence of the oil supply pressure and the effective surface area ratio was shown mainly near the first critical speed. The effective surface area ratio of slotted-rings influences the reduction of flexible rotor vibration. As a result, experimental results confirm that the slotted-ring ER-SFD satisfactorily controls the flexible rotor vibration, while eliminates the inherent electric discharge problems in conventional ER-SFDs.