• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.331-337
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• 2013

Acoustic Emission technique is widely applied to develop the early fault detection system, and the problem about a signal processing method for AE signal is mainly focused on. In the signal processing method, envelope analysis is a useful method to evaluate the bearing problems and Wavelet transform is a powerful method to detect faults occurred on rotating machinery. However, exact method for AE signal is not developed yet. Therefore, in this paper two methods which are Hilbert transform and DET for feature extraction. In addition, we evaluate the classification performance with varying the parameter from 2 to 15 for feature selection DET, 0.01 to 1.0 for the RBF kernel function of SVR, and the proposed algorithm achieved 94% classification accuracy with the parameter of the RBF 0.08, 12 feature selection.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.805-809
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• 2001

This paper is presented to determine the optimal parameters of squeeze film damper using an enhanced genetic algorithm (EGA). The damper design parameters are the radius, length and radial clearance of the damper. The objective function is minimization of a transmitted load between bearing and foundation at the operating and critical speeds of a flexible rotor. The present algorithm was the synthesis of a genetic algorithm with simplex method for a local concentrate search. This hybrid algorithm is not only faster than the standard genetic algorithm, but also gives a more accurate solution and can find both the global and local optimum solution. The numerical example is presented that illustrated the effectiveness of enhanced genetic algorithm for the optimal design of the squeeze film damper for reducing transmitted load.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1010-1014
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• 2001

A severe strip vibration in continuous galvanizing line facilities of the steel companies has sometimes occurred due to the exceeding wearing of the roll bush and bearing. This vibration brings on the lack of uniform coating thickness in steel plate. As a result, the total maintenance and product costs in this factory are increased by the shortage of operation time for the replacement of bush, bearings and these components. In this study, the vibration characteristics of this strip are investigated by the FEM using ANSYS. Also the vibration measurement of strip and its structure performed by the laser Doppler vibrometer(LDV) and accelerometers are compared to theoretical analysis results.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.277-280
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• 2006

Using yaw system, Wind turbine can face the wind to make it's electricity generating maximum and to make it's fatigue load minimum. So, in wind turbine design process, selecting optimum yaw system is very important work. In this paper, the yaw moments on yaw bearing, yaw drive and yaw brake were calculated. and From the result, the duty cycle was obtained. At last, using this duty cycle, optimum yaw system is selected.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.175-181
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• 1996

The magnetic levitation system is utilized in the magnetic bearing of high-speed rotor because of little friction, no lubrication, no noise and so on. The magnetic levitation system need the feedback controller for the stabilization of system, and gap sensors are usually used to measure the gap. The use of sensor is troublesome such as sensor trouble, discord between the measurement point and the control point etc. This paper presents the design of robust stabilizing controller by H$_{\infty}$ control theory using the sensorless method proposed already by authors in the magnetic levitation system. And we investigated both the validity of the designed controller and the usefulness of the sensorless method proposed by authors of magnetic levitation system through results of actual experiment..

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.314-317
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• 2005

There are many benefits such as increased areal density, reduced power consumption, applied smaller size and improved shock resistance in Load/Unload(L/UL) mechanism. It has been the key technology of developing small form factor hard disk drive used in portable digital devices. The main objectives of L/UL are no slider-disk contact and faster L/UL process. For realizing those, we must consider many design parameters in L/UL systems. In this paper, we focus on the effects of ramp profile. We can investigate dynamic characteristics of suspension tap and slider on ramp during unloading process experimentally. In special, we examine the effects of vortical velocities, ramp slopes and disk vibrations. As the result of these experiments, we propose design criteria of advanced ramp profile for good unloading performance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.838-843
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• 2001

Internal damping plays an important role in some rotor dynamic systems with the use of various materials for shafts, for example, composite material. However, although the effects of internal damping have been investigated for a couple of decades, there are several different internal damping models in use, none of which are accepted as the most reliable model. The purpose of this paper is to compare the results of dynamic analysis of rotor systems with several different internal damping models. The exact dynamic element method is used to formulate and analyze the problem. The simulation results provided in this paper may be useful for the dynamic analysis of high rotor systems subject to significant internal damping.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.586-591
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• 2001

Dynamic analysis using impulse responses is formulated to estimate effect of slider rail shape on dynamic responses. Impulse responses are obtained on numerical nonlinear model including rigid motion of slider and fluid motion of air bearing under the slider. Dynamic characteristics of slider motion are evaluated by utilizing the decay ratio of impulse responses and modal frequencies from frequency response functions. The dynamic characteristics of the developed NFR(Near Field Recording) slider are checked by comparing those of HDD sider(Nutcracker). Also, sensitivities of slider position conditions and rotation speed on the dynamic characteristics are investigated. The researches show that the utilized method is a good indicator of designing the better slider.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.739-744
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• 2001

In order to investigate the stability of magneto-rheological fluid based squeeze film damper (MR-SFD), its negative stiffness effect, which arises from magnetization of MR-SFD, is identified theoretically and experimentally. The analytical model of MR-SFD includes the magnetic circuit as well as the displacement stiffness associated with the squeeze mode of MRF. Extensive experiments are carried out to measure the magnetic attraction forces generated in the MR-SFD, with the excitation frequency and the eccentricity of the journal varied, which are controlled by an active magnetic bearing. The simulation and experimental results are found to be in good agreement. It is concluded that the negative stiffness effect dominates only in the low frequency region because its effect diminishes in the high frequency region due to the eddy-current loss.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.662-665
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• 2004

In this paper, based on shaking table test results on a seismically isolated bridge model, an inelastic numerical model is refined by using Bouc-Wen model representing the hysteretic behavior of isolators. Seismic responses of isolated bridges are numerically investigated varying with relative stiffness ratios, which is a ratio of the effective stiffness of isolator to the lateral stiffness of bridge pier. From the results, it is found that an adequate range of relative stiffness ratio could be defined for seismic design of isolated bridges without considering the flexibility of piers.