• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.652-657
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• 2000

In this paper, Firstly, it is shown that the high vibration source of piping system is the pulsation transmission of pipe line element, such as, orifice plate, valves and the control valve is a broad band source and the branch wall and the cavity have vortex frequency. Secondly, in order to decrese the high vibration of piping system, some practical Friction damper with high damping have been developed and its effectiveness is investigated as installing it at piping system practically.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.1
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• pp.3-9
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• 2003

In an apartment building, the impact sound from upstairs has been regarded as a main source of noise causing discontentment among occupants. To set the optimum design for sound insulation. it is nesessary to suggest the useful tools or technique that predict the floor impact sound. The purpose of this study is to investigate the applicability of the theory of sound radiation. We measured the vibration acceleration levels on the interior structures and predicted the sound pressure level of the room by using them. The result show that the predicted value, in general, were in good agreement with the measured values within 5∼10% in error rate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.135-140
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• 2013

This paper deals with noise reduction on a light source driving board in a projector. We analyze causes of noise/vibration in the circuit with the present increasing use of LD and LED driving boards. The main source of noise is the MLCC in the driving board. Our aim is to investigate how the mechanical arrangement of the circuit elements affects noise reduction. The result of our experiment shows that noise can be reduced by symmetrical arrangement and slots in PCB. This result is expected to facilitate a variety of applications for manufactures without a need to change circuit elements.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.2
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• pp.126-131
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• 2003

This study is concerned with the reduction of noise radiation by an industrial fan unit. First, spectral decomposition method is used to decompose the spectrogram obtained in experiments into source function and noise transfer function, and then major noise generation sources are investigated. Among the noise sources involved in the fan unit. this article is focused on the noise source due to vibration of panels of the unit housing. It is shown here that noise radiation associated with the panel vibration can be as significant in some frequency ranges as that associated with other noise sources such as aeroacoustic fan noise.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1515-1526
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• 2019

Ear-piercing high-frequency noise from electromagnetic vibrations in motors has become unacceptable in sensitive environments, due to the application of pulse width modulation (PWM) and in consideration of switching losses. This paper proposed a synchronous periodic frequency modulation (SPFM) method based on the interleaving technique for paralleled three-phase voltage source inverters (VSIs) to eliminate PWM vibration noise. The proposed SPFM technique is able to effectively remove unpleasant high-frequency vibration noise as well as acoustic noise more effectively than the conventional periodic carrier frequency modulation (PCFM) and interleaving technique. It completely eliminates the vibration noise near odd-order carrier frequencies and reduces the PWM vibration noise near even-order carrier frequencies depending on the switching frequency variation range. Furthermore, the SPFM method is simple to implement and does not employ additional circuits in the drive system. Finally, the effectiveness of the proposed method has been confirmed by detailed experimental results.

• Geomechanics and Engineering
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• v.13 no.2
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• pp.269-284
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• 2017

A new technique is proposed to obtain more effective screening efficiency against the ground vibration using intermittent geofoam (IF) in-filled trench. The numerical analysis is performed by employing two-dimensional finite element method under dynamic condition. Vertically oscillated strip foundation is considered as the vibration source. In presence of the ground vibration, the vertical displacements at different locations (pick-up points) along the ground surface are captured to determine the amplitude reduction factor (ARF), which helps to assess the efficiency of the vibration screening technique. The efficiency of IF over continuous geofoam (CF) in-filled vibration barriers is assessed by varying the geofoam density, the location of trench and the frequency of excitation. The results from this study indicate that a significant reduction in ARF can be achieved by using intermittent geofoam as compared to continuous geofoam. Further, it is noticed that the efficiency of IF increases with an increase in the frequency of the vibrating source. These encouraging results put forward the potential of utilising intermittent geofoam as a vibration screening material.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.5 s.98
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• pp.604-611
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• 2005

The relationship between floor impact sound and vibration has been studied by field measurements, and the vibration modal characteristics have been analyzed. Vibration levels impacted by a standard heavy-weight impact source have been predicted according to the main design parameters using finite element method. Experimental results show that the dominant frequencies of the heavy impact sounds range below 100 Hz and that they are coincident with natural frequencies of the concrete slab. In addition, simple 2-dimensional finite element models are proposed to substitute 2 types of 3-dimensional models of complicated floor structural slabs those by The analytical result shows that the natural frequencies from first to fifth mode well correspond to those by experiments with an error of less than $12\%$, and acceleration peak value iscoincident with an error of less than $2\%$. Using the finite element model. vibration levels areestimated according to the design Parameters, slab thickness, compressive strength, and as a result, the thickness is revealed as effective to increase natural frequencies by $20\~30\%$ and to reduce the vibration level by 3$\~$4 dB per 30 mm of extra thickness.

• Structural Engineering and Mechanics
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• v.28 no.6
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• pp.677-694
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• 2008

A vibration power minimization model is developed, based on the mobility matrix method, for a vibration isolation system consisting of a vibrating source placed on an elastic support structure through multiple resilient mounts. This model is applied to investigate the design optimization of an X-Y motion stage-based vibration isolation system used in semiconductor wire-bonding equipment. By varying the stiffness coefficients of the resilient mounts while constraining the dynamic displacement amplitudes of the X-Y motion stage, the total power flow from the X-Y motion stage (the vibrating source) to the equipment table (the elastic support structure) is minimized at each frequency interval in the concerned frequency range for different stiffnesses of the equipment table. The results show that when the equipment table is relatively flexible, the optimal design based on the proposed vibration power inimization model gives significantly little power flow than that obtained using a conventional vibration force minimization model at some critical frequencies. When the equipment table is rigid enough, both models provide almost the same predictions on the total power flow.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.463-468
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• 2007

The abnormal sound of generator frame is analyzed by a acceleration signal. The spike-like time signal is major characteristics of impacting force. The distributional map of vibration level is one of visualization method. With map, noise source was easily detected. After de_assembly of generator, loose part of internal component is the source of impact force by mechanical movement of stator inherently. In contact condition of part with clearance, the level of impact signal is different at each revolution and impact signal did not happens periodically.

• Journal of Radiation Protection and Research
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• v.32 no.1
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• pp.35-44
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• 2007

Sealed sources have to conducted the tests be done according to the classification requirements for their typical usages in accordance with the relevant domestic notice standard and ISO 2919. After each test, the source shall be examined visually for loss of integrity and pass an appropriate leakage test. Tests to class a sealed source are temperature, external pressure, impact, vibration and puncture test. The environmental test conditions for tests with class numbers are arranged in increasing order of severity. In this study, the apparatus of tests, except the vibration test, were developed and applied to three kinds of sealed source. The conditions of the tests to class a sealed source were stated and the difference between the domestic notice standard and ISO 2919 were considered. And apparatus of the tests were made. Using developed apparatus we conducted the tests for $^{192}Ir$ brachytherapy sealed source and two kinds of sealed source for industrial radiography. $^{192}Ir$ brachytherapy sealed source is classified by temperature class 5, external pressure class 3, impact class 2 and vibration and puncture class 1. Two kinds of sealed source for industrial radiography are classified by temperature class 4, external pressure class 2, impact and puncture class 5 and vibration class 1. After the tests, Liquid nitrogen bubble test and vacuum bubble test were done to evaluate the safety of the sealed sources.