• Title/Summary/Keyword: 저주파수 소음

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Development of silencer for low frequency exhaust noise (저주파수 배기소음 저감을 위한 소음기개발)

  • Choi, Choong-Young;Lee, Bo-Ha;Kwun, Hyuk;Eom, Jae-Kwang;HwangBo, Seung-Myun;Kim, Tae-Kyoon;Lee, Jeong-Guon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.04a
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    • pp.596-597
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    • 2011
  • 본 연구에서는 선박용 디젤엔진의 저주파수 대역 소음저감을 위해, 엔진 점화주파수 성분을 제어하고자 연장관과 헬름홀쯔 공명기, 흡음재로 구성된 소음기를 제안하고, 성능테스트를 통해 저감성능을 확인하였다. 개발된 소음기의 성능 계측결과, 저주파수 대역에서 5dB 이상의 감음성능을 확인할 수 있었다.

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Effect of Low Frequency Vibration on Human and Its Application (저주파수 진동이 인체에 미치는 영향과 응용(ISO 2631-3 내용을 중심으로))

  • 장한기
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.05a
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    • pp.823-827
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    • 2001
  • 인체에 영향을 미치는 진동을 분류하는데 가장 중요한 기준은 주파수이다. ISO의 인체진동관련 규격에서는 인체에 영향을 미치는 거동을 저주파수 운동(0.63Hz이하)과 진동(1~80Hz)으로 나누고 있다[1]. ISO 2631에서는 주파수별로 인체에 미치는 영향을 그림1과 같이 가중치로 정의하여 제시하고 있다. 저주파수 영역의 운동은 외부 거동(주로 수평방향)에 대하여 자세를 유지하기 위해 힘Tm게 되므로 물리적인 피로감을 줄 뿐만 아니라 'Motion sickness'란 증상을 유발한다.(중략)

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Time Domain Prediction and Analysis of Low Frequency Noise from Wind Turbine using Hybrid Computational Aeroacoustics (CAA) Method (복합 전산 공력음향학(CAA) 방법을 이용한 시간영역 풍력터빈 저주파수 소음 예측과 분석)

  • Lee, Gwang-Se;Cheong, Cheolung;Kim, Hyung-Taek;Joo, Won-Ho
    • The Journal of the Acoustical Society of Korea
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    • v.32 no.5
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    • pp.369-376
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    • 2013
  • Using Lowson's acoustic analogy, low frequency noise of a wind turbine (WT) is predicted in time domain and the noise sources contributing to the low frequency noise is analyzed. To compute averaged pressure distribution on blades of the WT as noise source, XFOIL is utilized. The blade source domain is divided into several segments along the span direction to compute force exerted on air surrounding the blade segments, which is used as input for noise prediction. The noise sources are decomposed into three terms of force fluctuation, acceleration and velocity terms and are analyzed to investigate each spectral contribution. Finally, predicted spectra are compared with measured low frequency noise spectrum of a wind turbine in operation. It is found that the force fluctuation component contributes strongly in low frequency range with increasing wind speed.

Study on low frequency swishing sound field by singularities in circular motion with large radius (큰 반경의 원운동을 하는 점 음원에 의한 저주파수 스위싱 음장 분석)

  • Lee, Gwang-Se;Cheong, Cheolung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2014.04a
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    • pp.90-95
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    • 2014
  • In order to investigate low frequency swishing noise of wind turbines, singularity in circular motion with large radius is introduced as a noise source model. By employing Lowson's acoustic analogy, simple exact solution is obtained. The solution shows that time histories of acoustic pressure at receiver points varied significantly according to receiver's directional location, even when the retarded time distributions are similar. However, the corresponding spectra of sound pressure for the receiver locations where the retarded time distributions are almost the same are not significantly different. It can be inferred from these results that the time-averaged sound pressure spectra which cannot take into account the detailed difference in the time-variation of wind turbine noise may not represent the sound quality of wind turbines due to its swishing.

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A Study on the Performance Improvement of Medium Speed Diesel Engine Exhaust Silencer in the Low-frequency Range Using Array Resonators (공명기 배열을 이용한 중속 디젤엔진 배기 소음기의 저주파수 대역 성능 개선 연구)

  • Kim, Young-Hyun;Joo, Won-Ho;Bae, Jong-Gug
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.19 no.7
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    • pp.693-698
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    • 2009
  • Various acoustic tests were carried out to investigate the acoustic performance of diesel engine exhaust silencers. In order to consider flow effects, the test facility was set up composed of fan, duct and silencer. Using the test facility, insertion loss tests were carried out to improve the acoustic performance in the low-frequency ranges. Through a series of tests, it was found out that the array resonators having multi-perforated holes inside the exhaust silencer, might be very effective in the low frequency range. Consequently, the hybrid-type silencer which is the combination of reflective silencer with array resonators and conventional absorptive silencer, was proposed and its high performance in the low-frequency range was also verified.

A Study on the Improvement of Acoustic Performance of Diesel Engine Exhaust Silencer in the Low-Frequency Range using Array Resonators (공명기 배열을 이용한 디젤엔진 소음기의 저주파수 대역 성능 개선 연구)

  • Lee, Tae-Kyung;Kim, Young-Hyun;Joo, Won-Ho;Bae, Jong-Gug
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.05a
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    • pp.30-35
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    • 2007
  • Various acoustic tests were carried out to investigate the acoustic performance of diesel engine exhaust silencers. In order to consider flow effects, test equipment composed of fan, duct and silencer was set up. Using the test equipment, insertion loss tests were carried out to improve the performance in the low-frequency ranges. Through a series of tests, the fact that array resonators may be effective in the low-frequency noise has been verified. Consequently, the hybrid-type silencer which is the combination of reflective silencer with array resonators and conventional absorptive silencer were proposed and its high acoustic performance in the low-frequency range has also been verified.

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Broadband Transmission Noise Reduction Performance of Smart Panels Featuring Piezoelectric Shunt Damping and Passive Characteristics (압전감쇠와 수동적 특성을 갖는 압전지능패널의 광대역 전달 소음저감성능)

  • 이중근;김재환
    • The Journal of the Acoustical Society of Korea
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    • v.21 no.2
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    • pp.150-159
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    • 2002
  • The possibility of a broadband noise reduction of piezoelectric smart panels is experimentally studied. Piezoelectric smart panel is basically a plate structure on which piezoelectric patch with shunt circuits is mounted and sound absorbing material is bonded on the surface of the structure. Sound absorbing materials can absorb the sound transmitted at mid frequency region effectively while the use of piezoelectric shunt damping can reduce the transmission at resonance frequencies of the panel structure. To be able to tune the piezoelectric shunt circuit, the measured electrical impedance model is adopted. Resonant shunt circuit composed of register and inductor in stories is considered and the circuit parameters are determined based on maximizing the dissipated energy through the circuit. The transmitted noise reduction performance of smart panels is investigated using an acoustic tunnel. The tunnel is a square crosses sectional tunnel and a loud speaker is mounted at one side of the tunnel as a sound source. Panels are mounted in the middle of the tunnel and the transmitted sound pressure across the panels is measured. Noise reduction performance of a double smart panel possessing absorbing material and air gap shows a good result at mid frequency region except the first resonance frequency. By enabling the piezoelectric shunt damping, noise reduction is achieved at the resonance frequency as well. Piezoelectric smart panels incorporating passive method and piezoelectric shunt damping are a promising technology for noise reduction in a broadband frequency.

Study on Low Frequency Swishing Sound Field by a Singularity in Circular Motion with Large Radius (큰 반경의 원운동을 하는 점 음원에 의한 저주파수 스위싱 음장 분석)

  • Lee, Gwang-Se;Cheong, Cheolung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.24 no.7
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    • pp.569-574
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    • 2014
  • In order to investigate low frequency swishing noise of wind turbines, acoustic source model using a singularity in circular motion is introduced to derive analytic solution of Lowson acoustic analogy in time domain. Results in time and frequency domains computed by the solution show apparent modulation of amplitude and frequency. The solution indicates that time histories of acoustic pressure at receiver points varied significantly according to receiver's directional location, even when the retarded time distributions are similar. However, the corresponding time-averaged spectra of sound pressure at the receiver locations where the retarded time distributions are almost same are not significantly different. It can be inferred from these results that the time-averaged sound pressure spectra which cannot take into account the detailed difference in the time-variation of wind turbine noise may not represent the sound quality of wind turbines due to its swishing. Finally, as an introduction of procedure to quantify low frequency swishing noise level, relative variation of overall sound pressure level is obtained using tonal low frequency noise model.

Refinement of Vehicle Cabin Noise by Changing Interior Trims (흡음/차음재 변경에 의한 차실 내부소음 개선)

  • 김재권
    • Proceedings of the Acoustical Society of Korea Conference
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    • 1998.06e
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    • pp.107-110
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    • 1998
  • 차량의 주요 소음원부터 실내 탑승자의 귀의 위치까지 도달되는 소음의 전달에 대한 전체적인 경로 및 주파수특성에 대한 해석은 차량의 구조-음향적인 특성이 복잡하므로 매우 어렵다. 그러나, 중-고주파수에 대한 대책에 있어서는 흡차음재가 유용함은 이미 알려진 사실이다. 차실 벽면에 사용된 흡/차음재는 소음레벨에 부분적인 기여를 함은 물론이고 음질에도 영향을 미친다. 소음 레벨에 있어서는 수백 Hz 이하의 저주파수 성분이 주요하며, 음질에는 중-고주파수 대역의 소음특성이 큰 영향을 미친다[1]. 본 논문에서는, 실험적으로 측정된 소음원의 특성을 수치해석 모델에 이용하여 소음레벨 저감과 음질개선을 위한 흡/차음재의 개선방향을 모색하였다.

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