• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.84-92
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• 2005

This work presents the feasibility of shunt damping far vibration suppression of the rotating HDD disk-spindle system using piezoelectric bimorph. A target vibration mode which significantly restricts the recording density increment of the drive is determined through modal analysis and a piezoelectric bimorph is designed to suppress unwanted vibration. After deriving the two-dimensional generalized electromechanical coupling coefficient of the shunted drive, the shunt damping of the system is predicted by simulating the displacement transmissibility using the coefficient. In addition, optimal design process using sensitivity analysis is undertaken in order to improve the shunt damping of the system. The effectiveness of the proposed methodology is verified through experimental implementation by observing the vibration characteristics of the rotating disk-spindle system in frequency domain.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.8
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• pp.651-657
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• 2003

A new mechanical-electrical hybrid passive damping treatment is proposed to improve the performance of structural vibration control. The proposed hybrid passive damping system consists of a constrained layer damping treatment and a shunt circuit. In a passive mechanical constrained layer damping, a viscoelastic material damping layer is used to control the structural vibration modes in high frequency range. The passive electrical damping is designed for targeting the nitration amplitude in the low frequency range. The governing equations of motion are derived through the Hamilton's principle. The obtained mathematical model Is validated experimentally. The presented theoretical and experimental techniques provide invaluable tools for controlling the multiple modes of a vibrating structure over a wide frequency band.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1190-1193
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• 2004

The purpose of this study is to evaluate the possibility of identifying joint damping property through commercially available isokinetic ergometer (BIODEX). The proposed method is to estimate the damping torque of the knee joint from the difference between the external joint torque for maintaining isokinetic movement and the gravity torque of the lower leg. The damping torque was estimated at various joint angular velocities, from which the damping property would be derived. Measurement setup was composed of the BIODEX system with an external force sensor and Labview system. Matlab was used in the analysis of the damping property. The experimental result showed that the small variation in angular velocity due to acceleration and deceleration of the crank arm resulted in greater change of inertial torque than the damping torque, so that the estimation of damping property from the isokinetic movement is difficult.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.7
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• pp.913-917
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• 2013

During the restoration process of primary restorative transmission system, some over voltages may happen due to nonlinear interaction between unloaded transformers and transmission systems. These over voltages caused by harmonic resonance can be suppressed by inserting damping loads before energizing transformers. But it is very difficult to predict the occurrence possibility of harmonic resonance and complex simulation must be repeated to estimate the sufficient damping loads. This paper presents a damping loads prediction system to prevent harmonic resonance. Detailed analysis of the relationship between harmonic resonance and the amount of damping loads is discussed. The prediction system is developed using a curve fitting and a neural network based on this relationship. A curve fitting used a Gaussian function based on non-linear least square method and multi-layer back-propagation neural network is applied. The system is applied to primary restorative transmission lines in korean power system and the result showed satisfactory performance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.86-91
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• 1996

In this study, the modal analysis is adopted for the investigation of vibratory characteristics of a rolling stock. A governing equation for this system is deverived on a condition that the rolling stock is in proportional viscous damping and proportional hysteretic damping. By applying this method a computational modal analysis software is developed. The validity and reliability of this method is verified by comparing the results for the above case and with those of a system having proportional viscous damping and a system having general viscous damping. A system that has non-linearity, an error from the calculation may occur in the analysis. In this case, we applied the piecewise linear method to estimate the modal parameters.

• KIEE International Transactions on Power Engineering
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• v.4A no.4
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• pp.178-191
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• 2004

This paper presents a new approach to HVDC system control for damping subsynchronous oscillation (SSO) involving HVDC converters and turbine generator shaft systems. This requires a novel eigenvalue analysis (NEA) program, derivation of HVDC system modeling considering steady-state conditions and dynamic conditions in the combined AC/DC system, and an appropriate control scheme. The method suggested makes possible the design of a subsynchronous oscillation damping controller (SODC) to provide positive damping torque for the range of torsional modes in combined AC/DC systems. There are three steps involved in the design of a SODC； first the worst torsional mode is determined using the NEA program, next the SODC parameters are designed for the range of that torsional mode, and then finally an off-line simultaneous time domain program such as PSCAD/EMTDC is used to verify the parameters of the SODC. The suggested SODC design method is applied to two AC/DC systems, and its practicality is verified using the PSCAD/EMTDC simulation program.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.680-685
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• 2006

This paper describes the aeroelastic stability test of the small-scaled 'Next-Generation Blade(NRSB)' with NRSH (Next-Generation Hub System) and HCTH hingeless hub system in hover and forward flight conditions. Excitation tests of rotor system installed in GSRTS(General Small-scale Rotor Test System) at KARI(Korea Aerospace Research Institute) were tarried out to get lead-lag damping ratio of blades with flexures as hub flexure. MBA(Moving Block Analysis) technique was used for the estimation of lead-lag damping ratio. First, NRSB-1F blades with HCTH hub system, Then NRSB-1F with NRSH hub system were tested. Second, NRSB-2F blades with NRSH hub system were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Non-rotating natural frequencies, non-rotating damping ratios and rotating natural frequencies were showed similar level fir each cases. Estimated damping ratios of NRSB-1F, NRSB-2F with HCTH and NRSH were above 0.5%, and damping ratio increased by collective pitch angle increasement. Furthermore damping ratios of NRSB-2F were higher than damping ratios of NRSB-1F in high pitch angle. It was confirmed that the blade design for noise reduction would give observable improvement in aeroelastic stability compared to paddle blade and NRSB-1F design.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.8 s.113
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• pp.848-856
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• 2006

This paper describes the aeroelastic stability test of the small-scaled 'Next-generation Blade(NRSB)' with NRSH (next-generation hub system) and HCTH hingeless hub system in hover and forward flight conditions. Excitation tests of rotor system installed in GSRTS (general small-scale rotor test system) at KARI (Korea Aerospace Research Institute) were carried out to get lead-lag damping ratio of blades with flexures as hub flexure. MBA(moving block analysis) technique was used for the estimation of lead-lag damping ratio. First, NRSB-1F blades with HCTH hub system, then NRSB- 1F with NRSH hub system were tested. Second, NRSB-2F blades with NRSH hub system were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Non-rotating natural frequencies, non-rotating damping ratios and rotating natural frequencies were showed similar level for each cases. Estimated damping ratios of NRSB-1F, NRSB-2F with HCTH and NRSH were above 0.5%, and damping ratio increased by collective pitch angle increasement. Furthermore damping ratios of NRSB-2F were higher than damping ratios of NRSB-1F in high Pitch angle. It was confirmed that the blade design for noise reduction would give observable improvement in aeroelastic stability compared to paddle blade and NRSB-1F design.

• Fibers and Polymers
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• v.4 no.2
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• pp.49-53
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• 2003

Polyurethane (PU) layer and copolymer consisted of the different molecular weights (1000 and 2000 g/mol) of poly(propylene glycol) (PPG) were prepared. The damping and mechanical properties of these materials were compared with PU 1000 made by PPG having the molecular weight of 1000 g/mol. The optimum composition of PU2000 used for PU layer and copolymer was diphenylmethane diioscynate (MDI)/propylene glycol (PPG)/butanediol (BD) (1/0.3/0.7) based on the damping and mechanical properties. The damping peak of PU copolymer was higher than those of PU layer and PUI 1000 in low temperature range (-30- $10^{\circ}C$). For application in noise reduction, the transmission loss of the mechanical vibration through solid structure was measured. PU layer and copolymer were used as a damping layer. The transmission loss of PU copolymer was more effective than those of PU layer and PU 1000 in the experimental frequency range.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.8
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• pp.1963-1970
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• 1993

A simple technique to decouple the modal equations of motion of a linear nonclassically damped system is to neglect the off-diagonal elements of the modal damping matrix. This is called the decoupling approximation. It has generally been conceived that smallness of off-diagonal elements relative to the diagonal ones would validate its use. In this study, the relationship between elements of the modal damping matrix and the error arising from the decoupling approximation is explored. It is shown that the enhanced diagonal dominance of the modal damping matrix need not diminish the error. In fact, the error may even increase. Moreover, the error is found to be strongly dependent on the exitation. Therefore, within the practical range of engineering applications, diagonal dominance of the modal damping matrix would not be sufficient to supress the effect of modal coupling.