• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.785-790
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• 2000

The resonant frequency of a gas-filled cylindrical Helmholtz resonator in a liquid is obtained analytically. The equation of motion of the resonator is derived by using the condition of equilibrium of forces acting on the mass in the neck of the resonator. The reaction force on the upper side of the cylinder due to the acceleration of external fluid and sound radiation is obtained by using the analytical results for the baffled circular-piston problem. From the frequency response function of the resonator, a formula to predict the resonant frequency of the resonator is derived. It is shown that the resonant frequency of the Helmholtz resonator significantly decreases due to the cushioning effect of gas inside the cavity. Therefore, when a pressure transducer is to be installed in a pin-hole type mounting method, much care should be paid to remove the gas from the cavity.

• 대한기계학회논문집A
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• 제28권2호
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• pp.118-124
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• 2004

The objective of the paper is to demonstrate the noise reduction characteristics of an air-gap resonator, which is composed of an air gap and a partition sheet. By means of installing the air-gap resonator in an enclosed cavity, acoustic resonance can be effectively suppressed using a small space. In particular, it is revealed from a simple, one-dimensional model that the air-gap resonator serves as the Helmholtz resonator that generally absorbs acoustic resonance energy at its resonance frequency. As a result, the air-8ap resonator also has a resonance frequency, which can be predicted with a simple frequency equation derived in the paper. Finally, verification experiments show that the air-gap resonator can be effectively designed by predicting a reasonable gap thickness using the simple frequency-equation.

• 한국소음진동공학회논문집
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• 제22권8호
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• pp.756-762
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• 2012

A method of the low-frequency noise reduction in an enclosure by using an array of Helmholtz resonator is presented. An integral form of equation, which represents the acoustical coupling between the internal sound field and the resonator array, is formulated so that the boundary element method can be applied to solve the coupling problem. It is shown that the resonator array on the surface of the enclosure can be regarded as impedance patches on the boundary element. Experiments on a simple enclosure acoustically coupled with an array of resonators are conducted to verify the method. The predicted noise reduction by the boundary element method shows good agreement with the measured one. The effects of the resistance of resonators as well as the number of resonators on the noise reduction are demonstrated. As a practical example, the presented method is applied to the payload fairing of a space launcher with resonator arrays. It is demonstrated that the resistance of resonators affects significantly the required number of resonators to achieve a desired noise reduction.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.873-876
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• 2011

본 연구에서는 열적 구배를 갖는 열음향 진동 환경에 Helmholtz resonator를 적용하여 연소 불안정 연구를 수행하고자 하였다. 열음향 불안정 환경은 DC power supplier를 이용한 전기적 방법으로 정량적인 열량을 공급하고 blower를 이용하여 유량을 제어하는, 특정한 공진 주파수를 갖는 수평형 Rijke tube로 구현하였다. 열음향 불환경 환경 하에서 얻어진 Helmholtz resonator 의 감쇠특성을 상온 실험 자료와 비교/분석하여 열음향 불안정 환경에서의 Helmholtz resonator의 감쇠특성을 확인하기 위한 예비 연구를 수행하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.107-110
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• 2009

연소불안정현상은 주로 음향파와 열방출률 섭동간의 상호작용에 의해 발생한다고 알려져 있다. 이러한 현상은 헬름홀츠 공진기와 같은 수동제어기를 사용하여 감소시킬 수 있다. 그러나 헬름홀츠 공진기는 일반적으로 좁은 주파수대역에 대해서만 효과가 있는 단점을 가진다. 따라서 본 연구에서는 다양한 작동 범위에서 효과를 가질 수 있도록 피스톤을 사용하여 헬름홀츠 공진기의 부피를 변화시켜가며 연소불안정현상에 적용하였다. 그 결과 피스톤을 최적위치에 동조시킴으로써 연소 불안정 모드의 진폭을 감소시킬 수 있었다. 또한 이러한 결과를 바탕으로 능동적으로 동조되는 수동제어방식의 가능성에 대해서 알아보고자 한다.

• 한국소음진동공학회논문집
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• 제19권6호
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• pp.634-640
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• 2009

Helmholtz resonator has been used, especially in intake and exhaust systems of vehicles, due to its good noise reduction characteristics at low frequencies. Many approaches have been developed to predict the acoustic behavior of the resonator with the assumption that there is no leakage from the resonator. However, its behavior may be affected by leakage which may exist in manufacturing processes or on purpose. This study investigates the effect of leakage on the noise reduction characteristics of Helmholtz resonator with two practical examples. One is a resonator with a gap between baffle and housing of the resonator and the other one is a resonator with two drain holes on the baffle. The measured transmission loss shows that the resonance frequencies are considerably shifted to higher frequency due to the leakage. The Boundary Element Method was applied to predict the transmission loss of the Helmholtz resonator with drain holes. The comparison between the measured and predicted transmission loss shows that the acoustic impedance of the holes is essential for accurate predictions of the transmission loss.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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• pp.153-156
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• 2003

스월 인젝터의 분무특성을 변화시키는 기하학적인 변수인 백홀은 스월 인젝터의 내부유동이나 음향학적인 특성에도 큰 영향을 주게 된다. 백홀이 연소불안정 제거를 위하여 연소실에 부가적으로 부착하는 음향공(Acoustic cavity)과 유사한 역할을 할 수 있는지 알아보기 위하여 백홀을 Helmholtz resonator나 Quarter-wave resonator로 해석하였다. 그 결과 백홀을 가지는 스월 인젝터는 연소실내의 파동과 상쇄될 수 있는 고유주파수를 가지게 될 수 있었다. 또한 이를 위한 설계식을 제시하였다.

• 한국소음진동공학회논문집
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• 제14권10호
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• pp.975-982
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• 2004

Helmholtz resonator is used to reduce noise of the narrow frequency band. It has high transmission loss at its resonance frequency. The silencer that combines many resonators could control broadband noise at low frequency. To convey this rather simple idea, serial and parallel arrangement of resonators have been tested to obtain high transmission loss characteristics in the band of which are selects. Theoretical and experimental results explain these characteristics in the absence of mean flow. The change of acoustic characteristics by the resonance frequencies and resonators arrangement are explained by using the equivalent Impedance analysis that is defined in this paper. It shows that the transmission loss has a maximum value when the separation distance between each resonator is λ/4 of its wavelength.

• 소음진동
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• 제4권2호
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• pp.209-219
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• 1994

Classical method calculates the resonance frequency of Helmholtz resonator by postulating that there is a moving mass in neck and a stiffness which expresses the compressibility of cavity. This has been widely accepted as reasonable to determine the resonant frequency, provided that the wave length of interest is longer that any length scale of resonater. Nevertheless, it has been often recognized that this classical method sometimes does not well predict the resonant frequency. This paper decribes the way in which the dynamics of resonator very often does care about the detail geometries of resonator; location of the neck, diameter ratio of the neck to that of cavitty, length of resonator compared with that of neck, etc. This rather unexpected observations have been proved theoretically; 3 dimensional analysis of acoustic wave equation, as well as experimentally by comparing the resonant frequencies, transmission loss, and insertion loss of resonator.

• The Journal of the Acoustical Society of Korea
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• 제21권2E호
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• pp.81-90
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• 2002

Single absorbing materials and Helmholtz resonators have limited absorption characteristics over limited frequency ranges due to their structures and properties. Porous materials are highly absorptive for mid and high frequency ranges, while they have little sound absorption for low frequency sounds. Helmholtz resonators are generally used to absorb sound energy for a specified frequency range. Hence they have limited capability in controlling the overall acoustic properties of a space. Not much has been known about useful finishing materials which have enough rigidity and absorption over broad frequency range, in spite of wide demands from acoustic designers and consultants. The present work measured and analyzed absorption characteristics of a slit absorber by varying surface materials, depths of air gap, dimensions of slat and slit widths. It was found that the narrower the slit width, the larger the absorptions over the wide frequency ranges and the pattern was dependent on the presence of porous material. Narrower slat's width tend to increase the slit absorber's absorption more or less. Absorption coefficients at low frequency ranges were dramatically improved (from 0.23 to 0.56) by increasing air gap when porous materials were present.