• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.12
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• pp.622-626
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• 2001

HID(high intensity discharge)lamps are high pressure mercury lamp, high pressure sodium lamp and metalhalide lamp. metalhalide lamp among these lamps has considered to be one of the most effective artificial light sources and this lamp has good efficiency, good color rendition and good focusing capability, But the shortcorning of metalhalide lamp is known as acoustic resonance phenomena in the discharge tube when lighted by electronic ballast and then acoustic resonance cause various problems such as the arc instability, light output fluctuations. In this paper, to reduce the acoustic resonence phenomena, the electronic ballast was designed by three methods for high frequency operation wish frequency-modulated sinusodial waves in acoustic resonance frequency band. These frequency-modulated methods are resonance frequency and resonance frequency, resonance frequency and non-resonance frequency non-resonance frequency and non-resonance frequency Experiment results could't show the Presence of acoustic resonance visually and it proved that the resonance-generating conditions can be avoided by continuously changing the two operating frequencies in acoustic resonance band (20.59kHz∼94.2kHz).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.178-183
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• 2004

This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a large fossil power plant. The phenomena of acoustic resonance may arise when the vortex shedding frequency coincides with the acoustic natural frequency. In this system dominant frequency of vibration and noise was 37.5Hz. The $3^{rd}$ acoustic natural frequency calculated was 37.2 Hz. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}20%$, acoustic resonance could occur. If system is the state of acoustic resonance, vibration and noise become large. In order to prevent acoustic resonance, anti-noise baffle should be installed in the tube bank. In the case of installing baffle, we should consider the number of baffle and the effect of acoustic mode due to baffle extension length. To do this, we did acoustic mode analysis. After installing anti-noise baffle, acoustic resonance was disappeared and vibration magnitude and noise level was reduced dramatically.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.98-103
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• 2003

This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a HRSG. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At this tube bank, dominant frequencies of vibration in this system were 43.5, 67.5㎐. The 3$\^$rd/ acoustic natural frequency calculated was 68.5㎐. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}$20%, acoustic resonance could occur. In this system, in order to prevent acoustic resonance, acoustic baffle was installed in the tube bank before operating. But acoustic resonance occurred. So, we evaluate the effect of acoustic mode due to baffle extension length. After investigating, we did revise acoustic baffle to eliminate acoustic resonance effectively.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.6
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• pp.8-14
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• 2001

MetalHalid lamps have good efficiency, good color rendition and good focusing capability. But the shortcoming of metalhalid lamps is blown as acoustic resonance phenomena in the arc tube. Such acoustic resonance produce annoying fluctuations in the intensity and distribution of the emitted light, they can raise the voltage to the point where the arc is extinguished and they can move the arc close enough to the wall to cause local overheating and tube cracking. The objective of this research is to reduce acoustic resonance in the arc tube of the Pulse Start MetaIHaide lamp(MH200[W]). To reduce the acoustic resonance phenomena the electronic ballast was designed for high frequency operation with the constant frequency sinusoidal wave of 89[kHz] in the 84.6[kHz]∼94.2[kHz] range. Experimental results show that the acoustic resonance phenomena are not in the arc tube of Pulse Start MetalHalide lamp (MH200[W]) .

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.101-106
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• 2011

In the present paper, the phenomena of abnormal noise and vibration due to acoustic resonance of CFBC(Circulating Fluidized Bed Combustion) boiler was presented. The acoustic resonance which occurred in the gas path of CFBC boiler system was caused by coincidence of vortex shedding frequency of tube bank and acoustic natural frequency of duct and hopper. And, the phenomena of beating arose from the interference of two closed resonant waves at 66.4Hz and 70.8Hz. There are two control methods for acoustic resonance in this system. The first method is to change the vortex shedding frequency from the structural alterations on the tube bank. And the second method is to change the acoustic natural frequency of the gas path with the installation of anti-noise baffles. The second one which is relatively easy to apply, was adapted in this study. As a result, the noise and vibration level have been decreased by 41dB and 94% at 66.4Hz, respectively. And the improvement of noise and vibration at 70.8Hz was identified by sensory evaluation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.150-155
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• 2000

This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a power plant. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At the resonance, the value of vibration in this system was 595 ${\mu}m$, p-p and the sound pressure level was maximum 103 dBA. And the resonance frequency was found to be 35 Hz. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}20%$, acoustic resonance is possible. In this system, the difference of these frequencies was 1.8%. We can evaluate the possibility of acoustic resonance by using damping parameter. We did eliminate acoustic resonance by installing baffle in tube bank. After installing baffle, the level of vibration and noise was reduced dramatically.

• The Journal of the Acoustical Society of Korea
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• v.30 no.5
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• pp.249-254
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• 2011

Inquiring activities on the acoustic phenomena have been carried out by using a sound card installed in a personal computer. A sound card is cheaper and more accessible to the students than the precision equipment such as a function generator or an oscilloscope. The students record the sounds from various acoustic phenomena to the sound card. Then they analyze the frequency spectrums of that sounds by using a program. Inquired phenomena include beat by two tuning forks, sound from Rijke tube, pouring sound, breaking of a wine glass and pop-up sound of a wine bottle. Through these activities students perform quantitative analysis of various phenomena due to superposition, resonance and standing wave.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.385-393
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• 2013

In this paper, the mechanism identification and the avoidance measures on the phenomena of transient acoustic vibration amplified at the water-supply piping system to regulate the steam temperature of the boiler reheater in 500MW class supercritical power plant are presented. The pressure pulsation waves induced by the impeller passing of two feed-water pumps with five blades are coincident with the local acoustic modes of boiler reheater water-supply piping system. There are the phenomena amplified at the peaks of 5X, 10X, 15X and 20X in spectrums of piping vibration, sound pressure, and the feed-water's pressure pulsation waves. The shut-off device is installed in the piping system for the interception of pressure pulsation waves transmitted from two feed-water pumps and the modified design change of the piping layout is applied for the acoustic resonance avoidance. The acoustic natural frequencies are separated from the harmonics of pressure pulsation waves induced by the pump impellers passing through the design change of the span length. The acoustic vibration is gone by resonance avoidance measures. As a result, more than 20 dBA reduction is achieved from 100 dBA to 80 dBA.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.470-475
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• 2012

The downstream piping system of the water supply system in a supercritical power plant is affected by the fluctuation pressure waves induced by accessing to the acoustic modes of the piping systems with the rotation and impeller passing pulsations of the feed water pump. There are the phenomena amplified at the same time in the range of 415 ~ 455Hz, 830 ~ 910Hz, 1245 ~ 1365Hz and 1660 ~ 1820Hz on the spectrums of the vibration, the sound pressure, and the pressure fluctuation waves.

• Journal of Power System Engineering
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• v.3 no.2
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• pp.26-33
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• 1999

Pressure pulsation Inside the discharge and suction cavity of rotary and scroll compressor are often a major source of objectionable noise and vibration. The key factor of these noise and vibration is due to the cavity resonance. It is not only necessary to understanding the characteristics of pulsation in order to reduce the excitation force of gas to the cavity but also to verifying the phenomena of cavity resonance. For the purpose of these understandings, measurement and simulation of cavity resonance can lead to a better understandings how they occur and be very important to identify the ways to reduce the noise efficiently. In this paper, modeling of the cavity(internal acoustics inside the shell) is discussed and simulated using FEM. Results from the simulation are compared with those measurement in experiments. In describing of cavity mode by experiments, it is very important to specify the exact conditions under which they are measured. Finally, this paper shows the one example of reduced cavity resonance in the compressor.