• Journal of KSNVE
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• v.11 no.2
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• pp.323-328
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• 2001

The paper describes a theoretical study on the flexural vibration of an elastic rectangular plate with periodically nonuniform material properties. The approximate solution of the natural frequency and mode shape has been obtained using the perturbation technique for sinusoidal modulation of the flexural rigidity and mass density. It has been shown that distributed modes exist in the plate which Is a two-dimensional model of the flat panel speaker.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1138-1143
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• 2001

The paper deals with a theoretical study on the radial vibration of cylindrical piezoelectric transducers. The differential equations of piezoelectric radial motion have been derived in terms of the radial displacement and electrical potential. Applying mechanical and electrical boundary conditions has yielded the characteristic equations of natural vibration. Numerical results of the fundamental natural frequency have been compared with experimental observations for the transducers of several sizes, and have shown a good agreement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.6
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• pp.535-541
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• 2012

The three-down one-up method which is commonly used in the field of psychophysics is employed in this study that is to reveal how much magnitude of vibration makes discomfort in passenger vehicle on idle condition. Thirteen taxi drivers were invited for subject of the experiment where they evaluated the controlled vibrations on rigid seat in terms of idle vibration on passenger vehicle at frequency range from 15 Hz to 40 Hz. As the result, vibration of 100~105 dB is marginal range to make discomfort on passenger seat. Frequency dependency of the discomfort was found at the frequency range, which is the higher frequency the lower discomfort with the same magnitude of vibration. The frequency dependency found here was compared with ISO 2631-1 that is more sensitive at the frequency range.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.11
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• pp.840-846
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• 2002

The vibrational system of this study is consisted of a cantilever pipe conveying fluid, the moving masses upon it and an attached tip mass. The equation of motion is derived by using Lagrange equation. The influences of the velocity and the number of moving masses and the velocities of fluid flow in the pipe have been studied on the natural frequency of a cantilever pipe by numerical method. As the size and number of a moving mass increases, the natural frequency of cantilever pipe conveying fluid is decreased. When the first a moving mass Is located at the end of cantilever pipe, the increasing of the distance of moving masses make the natural frequency increase at first and third mode, but the frequency of second mode is decreased. The variation of natural frequency of the system is decreased due to increase of the number of a moving mass. The number and distance of moving masses effect more on the frequency of higher mode of vibration.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.594-603
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• 2018

Recently, according to the development of measurement techniques, it has become possible to take complicated and time-consuming field measurements in a simple and convenient manner. In this background, this study estimated the tension of cables under ambient vibration using minimized measurement and signal processing. The VBDM using video-only by low-cost equipment was used as a minimized measurement. An estimation of the natural frequency using the mirror frequency concept was also proposed to solve the shortage of frequency band in this case. Furthermore, the FDD method was adopted for a natural frequency estimation in the ambient vibration related to field application. Experimental studies using a cable-stayed bridge model were carried out to examine the properties of the mirror frequency and the applicability of FDD with the proposed minimized system. The results showed that FDD for ambient vibration also works properly in an estimation of the natural frequency using the minimized system. In addition, the mirror frequency concept can allow a high natural frequency estimation even in a distorted signal by low-speed recording, which can overcome the limit of the minimized system. Overall, the proposed minimized system can be effective for the tension estimations of a cable under ambient vibration.

• Journal of KSNVE
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• v.6 no.3
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• pp.341-347
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• 1996

Vibration analysis is one of the most powerful tools available for the detection and isolation of incipient faults in mechanical systems. The methods of vibration analysis in use today and under continuous study are broad band vibration monitoring, time domain analysis, and frequency domain analysis. In recent years, great interest has been generated concerning the use of time- frequency repesentation and its application for a machinery diagnostics and condition monitoring system. The objective of the study described in this paper was to develop a new diagnostic tool for the rotating machinery. This paper introduces a new time frequency representation. Directional Winger-Ville Distribution, which analyese the time-frequency structure of the rotating machinery vibration.

• Korean Journal of Materials Research
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• v.2 no.3
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• pp.220-227
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• 1992

Electrorheological(ER) fluid's storage shear modulus(G') and loss factor(${\eta}$) have been directly measured using small amplitude forced oscillating rheometer as a function of oscillating frequency, strain amplitude and applied electric field. Two types of experiment were performed , (a) frequency sweep and (b) amplitude sweep. Two kinds of sample were employed for this experiment ; cornstarch particles in corn oil and zeolite particles in silicone oil. The storage shear modulus was a strong function of driving frequency. Generally, the modulus increased with driving frequency. On the other hand, the loss factor was not well behaved as storage modulus, but as the driving frequency increases the loss factor slightly decreases was the trend of the material's characteristics. Also the modulus was a strong function of strain amplitude. Generally, modulus decreased with increasing strain, but loss factor increases slightly with increasing strain amplitude. For G', cornstarch in corn oil ER fluid has higher values than zeolite based fluid as we increased applied electric field. On the other hand, zeolite based fluid has higher values for ${\eta}$. There is a reasonable agreement between theoretical calculation and experiment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.3
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• pp.1749-1755
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• 2014

Technique for analyzing a pile installed by vibrohammer was developed and parametric studies were executed in order to evaluate reliability of the developed technique. Comparing the accelerations obtained from parametric studies of varying eccentric moment and frequency, it can be seen that magnitude of maximum acceleration was proportional to the eccentric moment and square of frequency. It can also be seen that amplitude of displacement was roughly proportional to the eccentric moment but has nothing to do with the frequency. It can be said that all of the analysis results reflect characteristics of behavior of a pile in case of free vibration. Comparing the dynamic load transfer curves, maximum dynamic unit toe resistance was constant regardless of the eccentric moment and the frequency and it can be seen that dynamic unit skin friction was affected by the eccentric moment not by frequency. Comparing all of the analysis results, it can be said that the developed technique is reliable.

• Explosives and Blasting
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• v.29 no.2
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• pp.51-58
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• 2011

Frequency is a very important factor in discussing the effect on facilities such as precision instruments and therefore, in evaluating the effect of blasting vibration, it is necessary to identity information on frequency in addition to maximum amplitude of vibration. This study collected rock samples in gneiss area to perform an indoor rock test and to identify frequency of blasting vibration according to priming location, performed of single hole test blasting. Then the study decided dominant frequency through FFT and analysed changes according to priming locations. Consequently frequency range according to priming location is indicated top priming is distributed high range, bottom priming is distributed high range, middle priming is distributed evenly range. Frequency trend according to priming location is indicated distance increase with frequency discrease in top priming, distance increase with frequency increase in bottom priming.

• Tunnel and Underground Space
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• v.12 no.3
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• pp.210-219
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• 2002

In the ground vibration due to demolition blasting vibration and impact vibration of collapsed structure are separated. In this paper, model structures were collapsed by blasting with different charge locations. Ground vibrations were measured and separated as blasting and impact vibrations by waveform and dominant frequency. Vibration characteristics of different charge locations were examined.