• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.407-410
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• 2005

고성능 액체 로켓엔진에서 일반적으로 사용되는 기체-액체형 분사기가 장착된 연소실의 음향장을 수치적으로 해석하였다. 해당 분사기는 반파장 공명기의 역할을 할 수 있다. 다수의 공명기가 장착된 경우 연소실과 분사기간의 음향학적인 연계성으로 특이한 음향학적 특성이 관측되었다. 분사기 길이가 반파장 공명기 길이에 도달함에 따라 분사기와 연계된 새로운 음향 모드가 나타났으며, 그 음향 모드의 감쇠인자는 상당히 작았다. 따라서, 분사기의 음향감쇠 효과를 최적화 하려면 본래의 반파장 길이보다 약간 작은 길이를 갖도록 해야함을 알았다.

• 한국석유지질학회:학술대회논문집
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• 한국석유지질학회 2005년도 제12차 학술발표회 초록집
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• pp.9-16
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• 2005

The electromagnetic (light) waves are limited to penetrate the media, ie, water and sea-bottom layers, due to high energy attenuation, but acoustic (sound) waves play as the good messenger to gather the underwater target information. Therefore the acoustic methods are applied to almost of ocean equipments and technology in terms of in-water and sub-bottom surveys, Generally the sound character is controlled by its frequency. In case that the sound source is low frequency, the penetration is high and the resolution is low. On the other hand, its character is reversed at the high frequency. The common character at the both of light and sound is the energy damping according to the travel distance increase.

• 한국항공우주학회지
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• 제43권9호
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• pp.838-844
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• 2015

본 논문은 고체 로켓 모터 연소실 내의 연소과정 중 발생하는 연소 불안정 현상을 억제하는 여러 요소들 중 입자에 의한 감쇠와 유동방향 변환 감쇠에 대한 선행연구의 연구결과를 정리 분석하였다. 입자에 의한 감쇠는 연소실 내에서 발생하는 고주파 연소불안정을 억제하는데 있어 가장 효과적이며 입자의 직경과 질량 분율에 영향을 받는다. 한편 입자에 의한 감쇠에 비해 적은 감쇠량을 갖는 유동방향 변환 감쇠는 추진제의 구조에 따라 변하며, 추진제 표면에서 생성된 와도를 고려한다면 펌핑에 의한 증폭을 고려해야한다. 그러나 추진제의 형상이 원통형일 경우 유동방향 변환 감쇠와 펌핑에 의한 증폭의 크기는 같아지고 상쇄가 일어나 연소 안정성을 보다 쉽게 평가할 수 있다.

• Journal of the Korean Wood Science and Technology
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• 제34권1호
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• pp.32-39
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• 2006

본 연구는 현악기에 사용되는 현악기용 도료가 현악기의 음향성능에 미치는 영향을 조사하였다. 음향분석장치(FFT)를 이용하여 목재악기용 도료의 도막두께에 따른 음향적 성능을 평가하였다. 목재악기용으로 사용된 도료는 악기용 우레탄계 상도도료, 오일 스테인계 도료, 자외선 경화형 에폭시 도료이다. 형성된 도막의 음향적인 특성은 FFT 분석기에서 측정된 공명주파수와 댐핑값(damping factor)으로부터 동적탄성계수와 전단탄성계수를 계산하여 얻고, 밀도와의 관계와 탄성계수간의 관계를 통하여 도막의 두께에 따른 음향적인 특성을 측정하고 비교분석하여 상관관계를 조사하였다.

• 한국소음진동공학회논문집
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• 제21권4호
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• pp.357-364
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• 2011

In this study, ring-shaped acoustic resonators were proposed to be installed in a silencer to increase the acoustic performance of silencer in the low-frequency range. Evaluation of noise reduction performance of acoustic resonator arrays was carried out by measuring the random-incidence absorption coefficient. It was found that the absorption coefficient of resonator array was measured up to 1 at 125 Hz of 1/3-octave band center frequency. Insertion losses of silencers with ring-shaped acoustic resonator arrays were measured based on ISO 7235. The results were shown that the ring-shaped resonator could increase the insertion loss up to 13 dB without flow, whereas 7 dB when flow speed reached 15 m/s. As increasing the flow speed above 15 m/s, the effect of acoustic resonator decreased due to the effect of nonlinear air damping of the resonator. It was also found that the increment of pressure drop by the presence of resonator arrays was about 9 % at flow speed of 25 m/s.

• 한국소음진동공학회논문집
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• 제23권1호
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• pp.56-64
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• 2013

Turbulent boundary layer noise is already a significant contributor to sonar self noise. For developing acoustic window of sonar system to reduce self noise, a parametric study of design factors of acoustic window is presented. Distance of sensor array from acoustic window, materials of acoustic window and characteristics of damping layer are studied as design factors to influence in the characteristics of the transfer function of self noise. As the result, these design factors make change the characteristics of transfer function slightly. Among design factors the location of sensor array is most important parameter in the self noise reduction

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1120-1125
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• 2001

A new concept of piezoelectric smart panels for noise reduction in wide band frequencies is proposed and their possibility is experimentally investigated. Multi-mode damping is studied by using a newly proposed tuning method. The proposed panels are based on passive shunt damping methods. This method is based on electrical impedance model and maximizing the dissipated energy at the shunt circuit. four PZT are attached on smart panel for improving performance of transmission noise reduction. 0 prove the concept of piezoelectric smart panels, an acoustic measurement experiment was performed. The smart panels exhibit a good noise reduction in middle and high frequency ranges due to the mass effects of absorbing materials or/and the air gap. The use of piezoelectric smart panel renders noise reduction at resonance frequency. Noise reduction at multiple resonance frequencies is experimentally investigaed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.795-798
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• 2002

In this investigation, experimental attempts were made to observe and determine the variations in elastic of the PVC depending on the amounts of MBS added to the mixture, PVC/MBS, and also on the thicknesses of the specimens. An acoustic resonance technique was used for the tests in this investigation. It serves as a method to characterize properties of materials set in vibrational motions, which is initiated by low level stresses generated by externally supplied acoustic energy. Substantial variations were observed in the test results with the addition of the MBS to the PVC. It was found that the magnitudes of elastic constants decrease when MBS rubber was added in the range up to 9 phr and the shape factor effect in torsional vibration is more significant than the shape factor effect in flexural vibration.

• 한국지구과학회:학술대회논문집
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• 한국지구과학회 2005년도 추계학술발표회 논문집
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• pp.42-50
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• 2005

The electromagnetic (light) waves are limited to penetrate the media, ie, water and sea-bottom layers, due to high energy attenuation, but acoustic (sound) waves play as the good messenger to gather the underwater target information. Therefore the acoustic methods are applied to almost of ocean equipments and technology in terms of in-water and sub-bottom surveys. Generally the sound character is controlled by its frequency. In case that the sound source is low frequency, the penetration is high and the resolution is low. On the other hand, its character is reversed at the high frequency. The common character at the both of light and sound is the energy damping according to the travel distance increase.

• 한국정밀공학회지
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• 제15권6호
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• pp.48-57
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• 1998

Abrasive waterjet(AWJ)은 가공시 열에 의한 가공경화가 없기 때문에 유리, 세라믹, 타이타늄및 금속복합재료와 같은 난삭재의 가공기술로 사용이 증가되었다. Acoustic emission(AE)신호에 의한 AWJ 세라믹 drilling가공시 On-Line Monitoring의 가능성이 고찰되었다. 기계 적인 물성이 서로 상이한 3종류의 세라믹이 본 연구에서 사용되었으며, AE신호는 AWJ drilling의 깊이를 monitoring하는데 유용함을 알 수 있었고 또한 세라믹의 material removal mechanisms을 규명하였다.