• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.8
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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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.254-257
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• 2010

Acoustic design parameters of a Helmholtz resonator are studied experimentally and numerically for acoustic stability in a model acoustic tube. Acoustic damping is quantified by the amplitude of the fluid velocity in mass-spring-damper system. The length of an orifice, the volume of a cavity, and the diameters of an orifice and a cavity in the resonator are selected as design parameters for tuning of the resonator. It is found that acoustic damping capacity is increased by shorter orifice and longer cavity in the resonator. As the ratio of the orifice diameter to the cavity diameter increases in the resonator, the damping capacity decreases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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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.

• Journal of KSNVE
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• v.4 no.2
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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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.121-124
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• 2014

Many of research on noise reduction techniques have been progressed for the improvement of noise environment in subway train. There are many way to noise reduction techniques in the tunnel, but it has been reported as an alternative to attach sound absorption material on tunnel wall. For this reason sound absorption material has been studied for application of tunnel. The objective of this study is to investigate design parameters on a Helmholtz resonator with built-in sound absorption panel for the reduction of the tunnel noise in the subway. Sound absorption panel composed of the perforated panel with sub-millimeter holes and the airspace backed a rigid wall or between panels. The experiment is performed through the change of number of perforated panel, cross sectional area and the depth of airspace of the sound absorption panel under the normal incidence sound.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.964-968
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• 2007

A helmholtz resonator has been widely used for the purpose of suppressing low frequency noises propagated from various heat and fluid machineries. However, the resonator has demerits that the absorption bandwidth at resonance frequency is very small and a large cavity is necessary. In order to overcome these problems, in this paper, a resonator with perforated panels at the neck and/or in the cavity is proposed. The absorption performances of resonators are measured by two-microphone method and are estimated by transfer matrix method. The experimentally measured values of normal absorption coefficients are agreed well with the corresponding values from the transfer matrix method. By introducing perforated panels at the neck of a resonator, it is shown that the absorption performances and bandwidth have a significant improvement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.2
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• pp.167-175
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• 2013

The wave propagation characteristics of an acoustic metamaterial composed of periodically repeated one-dimensional Helmholtz resonator array was investigated considering the effects of dimensional changes of the resonator geometry on the transmission coefficient and band gap. The effective impedance and transmission coefficient of the acoustic metamaterials are obtained based on the acoustic transmission line method. The designed acoustic metamaterials exhibit band gaps and negative bulk modulus that are non-existent properties in the nature. The band gap of the acoustic metamaterial is strongly dependent on the geometry parameters of Helmholtz resonators and lattice spacing. Also, a new type of metamaterial that is periodically constructed with two different resonators was designed to open the local resonance band gap without change of Bragg scattering.

• Journal of KSNVE
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• v.8 no.6
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• pp.1113-1120
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• 1998

For an analysis of some Helmholtz resonators, it is likely to be more appropriate to consider acoustic field within cavity than just the 1-DOF analogous model. However, a design method that considers increased parameters than the lumped model. is not a trivial process due to the trade-off effect among the parameters. In this paper. the genetic algorithm. one of the optimization technique that rapidly converges to global fittest solution and robust convergence. is applied to the design process of Helmholtz resonators. Results show that the genetic algorithm can be successfully and efficiently used to find the resonant frequencies for both lumped model and distributed model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.8
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• pp.752-758
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• 2013

The effect of external leakage on the acoustic performance of Helmholtz resonators is experimentally and numerically investigated. The transmission loss of the Helmholtz resonator with a circular perforated hole is measured by using an impedance tube setup. The experimental results are then compared with one-dimensional analytical and three-dimensional numerical results. As the size of the hole increases, the peak of the transmission loss shifts to higher frequency, especially for the holes on the cavity. While the transmission loss is almost independent of the location of the hole on the cavity, the impact of the hole location on the neck on the transmission loss is not negligible. The results show that one-dimensional analytical method can predict the overall trends, whereas three-dimensional numerical method is necessary for more accurate predictions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.966-972
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• 2010

Damping characteristics of a Helmholtz resonator to passively control the combustion instability were investigated by linear acoustic analysis and atmospheric acoustic tests. Its orifice length and diameter were selected as the design parameters and supplied SPL(sound pressure level) effect on damping characteristics were investigated. Damping capacity is improved by decreasing the orifice length as well as by increasing the orifice diameter. Also, the results showed that the damping capacity of the resonator decreased nonlinearly about above 110 dB and instabilities in the nonlinear region were more effectively suppressed by increasing the orifice diameter.