• 한국생산제조학회지
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• 제23권1호
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• pp.56-63
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• 2014

This paper provides a comprehensive study on the Sommerfeld phenomena in an asymmetric rotor with a nonideal power supply. An analytical approach is employed by deriving the equations of motion in a nondimensional form. The system parameters, including the asymmetry, external and internal damping, and motor power, are chosen to find their effects on the characteristics of the Sommerfeld phenomena and critical behavior around resonance. Results show that the rotor asymmetry suppresses the Sommerfeld phenomena and helps pass through resonance if the asymmetry is small. However, it is observed that the opposite effects exist in case of a large asymmetry. It is also found that the effects of external damping on the Sommerfeld phenomena are similar to those of the asymmetry, whereas internal damping has less effects than external damping and the asymmetry. By performing numerical simulations, four types of critical behavior are identified from the viewpoints of the stability and the passage through resonance.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권12호
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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).

• 조명전기설비학회논문지
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• 제15권6호
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• pp.8-14
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• 2001

메탈핼라이드램프는 고효율, 고연색성이며 집광능력이 좋다. 그러나 메탈핼라이드 램프의 단점은 아크튜브내에서 음향공명현상이 발생되는 것으로 알려져 있다. 이러한 음향공명은 점등상태의 불안정과 기체의 심한 파동을 일으킨다. 심한 파동과 불안정한 점등으로 아크가 소멸되는 부위는 전압이 상승되고, 방전관내벽에 근접된 아크는 국부의 과열로 튜브를 금가게한다. 이 연구의 목적은 펄스스타트 메탈핼라이드램프 MH200[W]의 아크튜브내에서 음향공명을 감소시키는 것이다. 음향공명현상을 감소시키기 위하여 전자식안정기가 84.6[kHz]에서 94.2[kHz] 대역내에 있는 89[kHz]의 단독주파수인 정현고주파를 램프에 공급하기 위하여 설계되었다. 실험결과 고효율 펄스스타트 MH200[W] 램프의 방전관내에 음향공명 현상이 없었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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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.

• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1245-1249
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• 2017

Recently, unusual transformer failures have been reported in 25kV power systems connected with a VCB and transformer. In this study, performance of the protection system, dielectric strength of the transformers, characteristics of switching surges and resonance phenomena were analysed and assessed. All investigations regarding the insulation breakdown of the transformers were carried out by simulations, laboratory tests, factory tests and on-site measurements in order to thoroughly investigate the root causes. Furthermore, experimental methods for investigating the resonance phenomenon were derived and tests were conducted applying the derived method to recreate the phenomenon in the transformer. It is found that resonance between the transformer and switching surge generated by closing a VCB can initiate the breakdown of internal windings of a transformer.

• 한국자기학회지
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• 제5권5호
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• pp.800-804
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• 1995

The complex permeability dispersions and the microwave absorbing phenomena are investigated in ferrite microwave absorber. The complex permeability of NiZn ferrite, NiZnCo ferrite, and Y-type hexagonal ferrite were measured in 200MHz-14GHz range. Two types of resonances, the domain wall and the spin rotational resonance, were observed. With a ferrite particle with a diameter of about $1\;\mu\textrm{m}$, only spin rotational resonance were observed. The theoretical matching frequency is determined by plotting the measured complex permeability locus on the impedance matching solution map. One or two impedance matching phenomena are observed in the ferrite absorbers according to their complex permeability loci on the impedance matching solution map. The first matching frequency, found in the ferrite-rubber composites, which was higher than that of spin rotational resonance, increased with spin rotational resonance frequency.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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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.

• Investigative Magnetic Resonance Imaging
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• 제1권1호
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• pp.79-85
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• 1997

Fast spin echo imaging utilizes multiple spin echoes to encode multiple k-space lines instead of multiple $T_2-weighted$ images. As results, intensities in k-space data are varying according to T2 decay, which generates Gibb's artifact in the reconstructed image. The echo time for e encoding dc block determines contrast, as is specified by the effective echo time, however, all location of other echoes to different k-space frequency blocks in fast spin echo imaging is not f fully investigated. In this study, symmetric arrangement of multiple echoes in k-space is investigated to reduce Gibb's artifact. Design of filters based on the measurement of multiple e echo intensities is also proposed in two stage manner, i.e., equalization and filtering. From s simulation and experiment, it was observed that Gibb's phenomena were substantially reduced b by the proposed methods.

• Journal of the Optical Society of Korea
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• 제5권3호
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• pp.110-116
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• 2001

Recently observed dark resonance phenomena is solids are reviewed and discussed for potential applications to high-resolution coherence spectroscopy. in an inhomogeneously broadened system, a new type of high-resolution spectroscopy based on electromagnetically induced transparency is demonstrated.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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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.