• 한국음향학회지
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• 제36권5호
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• pp.305-313
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• 2017

본 논문은 강체 덕트 내에 고정된 얇은 탄성 판의 흡음을 해석적으로 구하는 방법을 다루었다. 판의 개수는 1개 또는 2개이며 각각의 판은 미세천공(micro-perforation)을 포함할 수도 있다. 판의 진동과 덕트 내부 음장을 모드 함수의 무한 급수의 합으로 전개하였다. 평면파 가정하에서 저주파수 대역의 근사식을 판의 처음 몇 개의 모드만 고려하여 유도하였다. 미세천공이 없는 판의 흡음율은 공진주파수에서 피크를 보이는데 공진주파수는 판과 캐비티의 상호작용으로 인하여 캐비티 간격이 변하면 공진주파수도 변함을 알 수 있었다. 미세천공판의 경우 천공율이 흡음율에 가장 큰 영향을 미치는 요소임을 확인하였는데, 천공율이 몇 퍼센트에 이르면, 흡음율은 거의 판의 진동에 영향을 받지 않는다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.196-199
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• 2005

Flow traveling over a cavity opening forms a vortex due to unstable shear layer and induces an aerodynamic pressure excitation from the diffusion of the vortex convecting out of the trailing edge of the opening. The interaction between the excitation force and the cavity response sustains resonance in the resonator(cavity) and locked-in vortex shedding at the leading edge of the opening. The aerodynamic excitation force can be described from the diffusion of the vortex over the trailing edge and the level of its diffusivity is related to the strength of vorticity seeded at the loading edge. In this study, the control scheme of the internal pressure oscillation was proposed from regulating the vorticity at the leading edge by use of an oscillating spoiler. It was found that the relative motion between the spoiler and the air mass at the cavity opening influenced vorticity strength and the control was achieved by direct feedback of the cavity pressure fluctuation to the actuator.

• 한국소음진동공학회논문집
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• 제27권1호
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• pp.94-99
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• 2017

Breaking the rigid connection between the two faces of the wall can significantly improve the sound transmission loss of the wall. This is usually achieved by resiliently mounting the gypsum board on one of the two faces of the wall using resilient channel. Resilient channel with less stiffness than that of air cavity could move the resonance frequency of the light-weight wall. So we can get higher sound transmission loss at low frequencies for light-weight wall using resilient channel. It's sound transmission loss is 17 dB higher than that of single stud wall, and 5 dB higher than that of double stud wall.

• 한국음향학회지
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• 제35권4호
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• pp.288-294
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• 2016

타이어와 휠가드 사이의 공간은 타이어 패턴음의 전달경로가 된다. 본 논문에서는 타이어-휠가드 공간에서 발생하는 음향현상을 음장모드 분석과 휠 가드 표면에서 음압분포 가시화를 통해 규명하였다. 타이어 패턴음 저감을 위해 음향학적 댐퍼 역할을 수행하는 캐비티를 휠가드 표면상에 적용하였다. 실내소음은 2 dB(A) 감소하였는데, 본 연구에서 다룬 소음저감방법은 완성차 단계에서 원가/중량의 증가없이 실내음질을 개선하는 효과적인 방안이 될 것이라고 판단된다.

• 설비공학논문집
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• 제28권6호
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• pp.224-231
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• 2016

When aiming to reduce the low frequency noise of a subway guest room through sound absorbing treatment methods inside the wall of a tunnel the resonator is often more effective than a porous sound absorbing material. Therefore, the perforated panel type resonator embedded with a perforated panel is proposed. The perforated panel is installed in the neck, which is then extended into the resonator cavity so that it can ensure useful volume. The absorption performance of the perforated panel type of resonator is obtained by acoustic analysis and experiment. The analytical results are in good agreement with the experimental results. In the case of multiple perforated panel type resonators, as the number of perforated panels increase, the 1st resonance frequency is moved to a low frequency band and sound absorption bandwidth is extended on the whole. In order to obtain excellent absorption performance, the impedance matching between multi-panels should be considered. When the perforated panel in the resonator is combined with a porous material, the absorption performance is highly enhanced in the anti-resonance and high frequency range. In case of the resonator inserted with perforated panels of 2, the 2nd resonance frequency is shifted to a low frequency band in proportion to the distance between perforated panels.

• Journal of the Optical Society of Korea
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• 제18권3호
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• pp.261-273
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• 2014

In this paper, metal insulator metal (MIM) plasmonic slot cavity narrow band-pass filters (NBPFs) are studied. The metal and dielectric of the structures are silver (Ag) and air, respectively. To improve the quality factor and attenuation range, two novel NBPFs based on tapered structures and double cavity systems are proposed and numerically analyzed by using the two-dimensional (2-D) finite difference time domain (FDTD) method. The impact of different parameters on the transmission spectrum is scrutinized. We have shown that increasing the cavities' lengths increases the resonance wavelength in a linear relationship, and also increases the quality factor, and simultaneously the attenuation of the wave transmitted through the cavities. Furthermore, increasing the slope of tapers of the input and output waveguides decreases attenuation of the wave transmitted through the waveguide, but simultaneously decreases the quality factor, hence there should be a trade-off between loss and quality factor. However, the idea of adding tapers to the waveguides' discontinuities of the simple structure helps us to improve the device total performance, such as quality factor for the single cavity and attenuation range for the double cavity. According to the proposed NBPFs, two, three, and four-port power splitters functioning at 1320 nm and novel ultra-compact two-wavelength and triple-wavelength demultiplexers in the range of 1300-1550 nm are proposed and the impacts of different parameters on their performances are numerically investigated. The idea of using tapered waveguides at the structure discontinuities facilitates the design of ultra-compact demultiplexers and splitters.

• 동력기계공학회지
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• 제3권3호
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• pp.60-69
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• 1999

The noise and vibration sources of rotary compressor for room air-conditioner are pressure pulsation of compression process, cavity resonance of inner space, structural radiation noise of shell and impact noise of discharge valve. Among them, pressure pulsation is very important noise and vibration source. Because it transferred various kinds of noise and vibration like as mentioned above. In this reason, muffler and resonator are used in order to absorb and remove these noises. But an analytical prediction using acoustic analysis does not coincident with the experimental result. The difference between analysis and actual state is due to the assumption of analysis. This paper covered with new concept of muffler design based on the turbulence kinetic energy of flow by using CFD. From this analysis, it is possible to decide the best position of discharge port of muffler. Therefore $2{\sim}3dB$ noise reduction effect is acquired in rotary compressor of 5000 BTU grade. Also new approach of resonator design is suggested. From this study, the characteristics of resonator and surge hole (a kind of resonator without pipe length) are identified. The former is useful for pure tone noise (narrow frequency band), and the latter is effective for broad frequency band. This paper shows that it is very available to use 3 dimensional analysis of resonator in order to predict more exact tuning frequency. The result is proved by a lot of experiments. From combination of fluid analysis and acoustic analysis, up stream position is effective location of resonator concerning turbulence motion of fluid.

• 대한후두음성언어의학회지
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• 제4권1호
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• pp.24-32
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• 1991

Cleft palate or velopharyngeal incompetence shows many disorders and disabilities affecting speech transmission. including distortion. substitution. and the nasalization of the vowels. The nasalized vowels are produced primarily by lowering of the velum. resulting in opening a side passage for the air flow through the nasal cavity. These abnormal movements give rise to complex modification of the physical property of the sound or in the sound spectrum. The authors employed Sonagraph$^{\circledR}$ as a sound analyzer in order to ascertain the features which characterize the nasalization of vowels. Twenty healthy Korean male adult voluteers were analyzed in artificial conditions of anterior and posterior nasal obstruction. and velo-pharyngeal incompetence. The results were as follows : 1) Fundamental frequency was not changed by nasal obstruction or velopharyngeal incompetence. 2) There was no significant difference of the formant intensity between normal and nasal vowels. 3) In VPI, a decrease of the frequency of $F_2$ was observed in /e/ and /i/ vowels(p<0.001). 4) In VPI, the $F_2$ was frequently missed in /o/ and /u/ vowels. 5) In the consonant spectra of VPI, the 'release burst' was usually not observed.

• 한국연소학회지
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• 제1권1호
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• pp.51-55
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• 1996

An experimental investigation has been made with the objective of studying the limits of equivalence ratio on mixing enhancement in a tone excited jet flame. The jet is pulsed by means of a loudspeaker-driven cavity and rich flames(${\phi}>1.5$) are used. The excitation frequency is chosen for the resonant frequency identified as a pipe resonance due to acoustic excitation. Methane, propane and butane are used to examine the effect of mixture property on the limit of equivalence ratio. Mixing is always enhanced in a methane/air flame as the excitation intensity increases. Constant lower limits of equivalence ratio for mixing enhancement are present in cases of propane/air and butane/air flames irrespective of mean mixture velocities. The equivalence ratio limits are also found to be related to the flame instability ; the lower Le, the higher the limit of equivalence ratio. Under the equivalence ratio limits, cellular flames are generated as the excitation intensity increases. The amplitude of oscillating velocity for generating a cellular flame in the equivalence ratio limit is proportional to a mean mixture velocity irrespective of fuels.

• 한국방사선학회논문지
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• 제13권7호
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• pp.1025-1033
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• 2019

뇌 질환과 두경부 검사에서 전산화단층촬영의 선속 경화현상이 없는 자기공명영상이 조직의 높은 대조도와 우수한 분해능의 영상을 획득하는 검사 방법으로 인식되고 있지만 구강 내 금속 이식물이 있는 경우는 자화율 인공물(magnetic susceptibility artifact)이 발생되어 영상 진단에 장해 요소가 된다. 따라서 본 연구는 자기공명영상에서 치아 임플란트와 보철에 의한 인공물 감소 방안을 강구하고자 한다. 자기공명영상에서 임플란트에 의한 인공물 발생은 GE 기법에서 TE가 짧을수록 신호 크기가 증가하였고, 물의 온도 변화에서는 일관성이 없게 나타났다. SE 기법에서도 공기보다 물의 신호 크기가 전반적으로 높았지만, 신호대 잡음비는 공기와 온도에 의한 차이가 없었다. EPI 기법에서는 공기보다 물이 있을 때 정량적, 정성적으로 인공물이 적게 발생한 영상을 얻을 수 있었고, 특히 물 온도 20°와 30°에서 신호 대 잡음비가 가장 높게 측정되었다. 결론적으로 EPI 기법에서 물 온도 20°와 30°의 물주머니를 이용하여 뇌 확산강조영상을 획득하면 임플란트와 보철물에 의한 자화율인공물이 감소되어 보다 진단적 가치가 있는 영상을 획득할 수 있을 것으로 사료된다.