• Plant Journal
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• v.8 no.3
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• pp.49-54
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• 2012

In this study, the way how we can find the defects of motor windings in advance will be discussed. The magnetic flux spectrum in the high frequency region of the large motor was analyzed based on the actual fault practices related with motor windings. In case of defective motor relative amplitude ratio of the stator slot frequency to its sideband was very high compared to that of healthy motor. And the defective signal related with motor windings was indicated in advance in the magnetic flux spectrum prior to over 1 month before failure. Considering this aspect it can be estimated that magnetic flux spectrum in the high frequency region has the excellent predictive diagnostic capability.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.44-48
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• 2000

Several parameters to represent the characteristics of the observed at the domestic networks from several earthquakes occurred in the Korean Peninsula. Parameters to fit most the multiple Fourier amplitude spectra of the observed accelerations are estimated. This study adopts the stochastic ground motion model referred to the BLWN mode in which the energy is distributed randomly over the duration of the source and which has proven to be very effective in modeling a wide range of ground motion observations. The stochastic ground motion model employed here uses an omega-squared ({{{{ omega ^2 }}) Brune source model with a single corner frequency and a constant stress drop,. The {{{{ omega ^2 }} source model has become a seismological standard because of its simplicity an ability to predict spectral amplitudes and shapes over an extremely broad ranges of magnitudes distances and from the inversion show very unstable based on the fact of high values of mean/median. These results may imply that more observed data and more precise site classification including accurate preparation analysis of data such as more accurate scaling from counts to kine are needed for more stable are effective inversion of Fourier amplitude spectrum of the observed ground motions.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.401-406
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• 1999

In relation to a non-destructive evaluation of irradiation damages of micro-structure interstitial, void and dislocation, the changes in the hysteresis loop, Barkhausen noise amplitude and the harmonics frequency due to a neutron irradiation were measured and evaluated. The Mn-Mo-Ni low alloy steel of RPV was irradiated to a neutron fluence of $2.3\times10^{19}\;n/cm^2\;(E\geq1\;MeV)\;at\;288^{\circ}C$. The saturation magnetization of neutron irradiated metal did not change. The neutron irradiation caused the coercivity to increase, whereas susceptibility to decrease. The amplitude of Barkhausen noise parameters associated with the domain wall motion were decreased by a neutron irradiation. The spectrum of Barkhausen noise is analysed with an applied frequency of 4 Hz and 8 Hz, sampling time of $50\;{\mu}sec\;and\;20\;{\mu}sec$. The harmonic frequency shows 4 Hz, 8 Hz, 12 Hz; and 16 Hz reflected from an unirradiated specimen. On the contrary, the harmonic frequency disappeared on the irradiated specimen.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1533-1542
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• 2003

In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40. vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90$^{\circ}$ the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.

• Tribology and Lubricants
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• v.33 no.4
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• pp.141-147
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• 2017

The vibration data of bearings are very useful for monitoring and determining the condition of the bearings. The defect frequencies of ball bearings have been used for monitoring there condition. However, it is not easy to verify the defect frequencies as the wear progress. Therefore there is a need for an easy method to monitor the damages of bearings in real-time and to observe the variations in vibration characteristics as the wear progress. In this study, a bearing test equipment is constructed to diagnose the damage of bearings. The friction coefficient and vibration data are measured by using a torque sensor and an acceleration sensor, and the correlation between the measured data is analyzed to diagnose the condition of the bearing. We reached the following conclusions from the results. When the ball surface, inner and outer rings of a ball bearing are damaged, the friction coefficient increases to over 0.02 with an adhesion on the surface. Moreover this damage occurs more quickly with an increase in the number of revolutions. In the vibration characteristics, the amplitude of vibration wave appears high with an increase in the friction coefficient. In the high frequency range between 1000 and 2000 Hz, a wide range of frequency components with high amplitude occurs continuously irrespective of the number of revolutions.

• The KSFM Journal of Fluid Machinery
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• v.6 no.3 s.20
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• pp.51-57
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• 2003

Characteristics of the high frequency pulsatile flow have been investigated experimentally to understand the flow phenomena in the hydraulic system. One axis fatigue test bed, which is widely used for automobile field test, is used. Four pressure transducers, an amplifier and a A/D convertor are used to obtain the high frequency pulsatile pressure waveform in hydraulic system. The characteristics of frequency are analyzed by power spectrum method. According to the variations of pump input pressure and actuator acceleration frequency, the pressure is measured with or without an accumulator. The amplitude of pressure with accumulator is very lower than those without accumulator due to absorbing function of accumulator. As the frequency of actuator acceleration is increased, the effect of accumulator become very important to decrease the amplitude of pulsatile pressure waveform with high frequencies.

• Progress in Medical Physics
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• v.9 no.1
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• pp.23-28
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• 1998

We measured the flow at peripheral blood vessel of finger dorsum surface using noninvasive LDF(Laser Doppler Flowmeter). We investigated the flow properties between the normal and the diabetic with the Amplitude Spectral Densities of FFT analysis. We classified the diabetic as four groups of negative neuropathy, positive neuropathy, hyperthyroid and hypothyroid. And tested the neuropathic and thyroid effects of peripheral blood flow. As the results, the diabetic, the positive neuropathic and the hypothyroid respectively showed the abnormal blood flow properties on the contrary of the normal flow of negative neuropathic and hyperthyroid.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.12 no.4
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• pp.386-398
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• 1987

This paper is proposed the Suboptimal PAWM(Pulse Amplitude Width Modulation) for minimize harmonic effects generated by switching operation of PWM Inverter. This strategy determine one switching pattern at a fixed point(fundamental) voltage u1=1.2) which THD(Total Harmonic Distortion) are minimized in the suboptimal PWM strategy, and controls only frequency in the inverter while voltage control is carried out by DC Chopper in the DC Link. This strategy is applied at VSD(Variable Speed Drive) of Three phase induction moter, and acoustic noise of motor, line to line voltage and current of inverter, current harmonic spectrum was estimated and also compared with other switching strategy. From the results, the validity of this strategy can be verified.

• Journal of the Korean Vacuum Society
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• v.21 no.6
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• pp.322-327
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• 2012

The strain effects of ZnSe epilayer on ZnSe/GaAs heterojunction structure grown by molecular beam epitaxy have been investigated by using electroreflectance (ER) spectroscopy. The ER measurements were performed as a function of modulation voltage, dc bias voltage, and temperature. From the room temperature ER spectrum, we observed a heavy-hole (HH: 2.609 eV) and light-hole (LH: 2.628 eV) transitions due to a compressive strain. With increasing the bias voltage, the amplitude of HH transition signal decreased and the amplitude of LH transition signal was almost the same. From the temperature dependence of ER spectra, we have studied the interaction between the strain and the thermal expansion coefficient.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.5
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• pp.43-49
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• 2000

In this paper, a new control method is presented to reduce acoustic resonance phenomena of metal halide lamps with electronic ballasts. A behavior of frequency controlled resonant inverter is analyzed and the transfer function is obtained. An integrator as a current controller for ballast is employed. By using both a disturbance of the lamp power and spread spectrum effects for reducing acoustic resonance, an amplitude modulation is done by using the current controller with 200[Hz] sinusoidal wave. Arc stabilities of MH 250[W] lamps are studied with changing the modulation index. Experiments with two MH 250[W] lamps, made by different manufacturers, showed the validity of the proposed method.