• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.870-873
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• 2003

This research is about the sound attenuation in the duct with lining sound absorbing material in it. Many previous researches assumed the property of lining material as locally-reacting. As the thickness of lining material thickens or the upper limit of the interested frequency range goes higher, there is a growing tendency for the experiment results to deviate from the theoretical results based on the locally reacting assumption. In this paper, the acoustic performance of the two-dimensional dissipative silencer with the propagation of sound in the absorbent was derived theoretically and calculated. The effect of increase of sound absorbing material is also considered. These results are compared from the previous results with using the locally-reacting property of sound absorbing material.

• Journal of KSNVE
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• v.7 no.3
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• pp.401-409
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• 1997

This study observed the meterological influence on the excess attenuation with various flow resistivities. The flow resistivity is simulated up to 30, 000 cgs rayls. There is no significant differences among results from spherical wave analysis for excess attenuation, from plane wave analysis, and from locally reacting analysis. This is validated only when the flow resistivity is more than 100 cgs rayls. For the determination of effective flow resistivity of ground by measuring the excess attenuation experimentally, it is highly recommended that the distance between source and receiver is about 2.5m, and that the height of them is 0.3-0.4 m in case that they have the same height. Under this proposed conditions, the flow resistivity of 6-month-passed asphalt ground is estimated to 5, 000 cgs rayls by comparing the measured excess attenuation with the calculated.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2E
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• pp.37-42
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• 1995

The polar parabolic equation method (Polar PE) which introduces a series of "cascaded" boundary fitting coordinates into the parabolic equation method has been verified as a good numerical method for atmospheric sound propagation over a curved surface and hills. Polar PE is applied here to underwater sound propagation over a sea mountain assuming locally reacting boundary sea bottom and pressure release water surface for the boundary conditions. Calculations are presented for underwater propagation over a 450 m high sea mountain. Feasibility of Polar PE application for underwater sound propagation over a smooth mountain is discussed.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.209-219
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• 2006

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Different shock tube fill pressures have various inflow conditions. $15^{\circ}$ inclined hydrogen fuel injection is located before the cavity. Oblique shock is generated at the trailing edge of the cavity and reflects off the top and bottom wall. For non-reacting flow, static pressures in low equivalence ratio are similar to those in no fuel injection. As equivalence ratio is increased, static pressures are increased in the duct. In the similar equivalence ratio, static pressures are increased when total enthalpy is decreased. For reacting flow, the flame is occurred near the cavity. The combustion is weak locally in the middle of the duct. The up and down pressure distribution in the duct means that the supersonic combustion is generated.

• Journal of the Korean Society of Combustion
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• v.12 no.1
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• pp.21-27
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• 2007

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Different shock tube fill pressures have various inflow conditions. $15^{\circ}$ inclined hydrogen fuel injection is located before the cavity. Oblique shock is generated at the trailing edge of the cavity and reflects off the top and bottom wall. For non-reacting flow, static pressures in low equivalence ratio are similar to those in no fuel injection. As equivalence ratio is increased, static pressures are increased in the duct. In the similar equivalence ratio, static pressures are increased when total enthalpy is decreased. For reacting flow, the flame is occurred near the cavity. The combustion is weak locally in the middle of the duct. The up and down pressure distribution in the duct means that the supersonic combustion is generated.

• Journal of KSNVE
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• v.9 no.2
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• pp.302-309
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• 1999

In this paper, a circular lined-duct is modeled by using an axisymmetric foam finite element, which is based on elastic porous material theory of Biot. For various thicknesses of three kinds of lining materials, finite element predictions are compared with measurement results and Morse's analytical results. While the analytical model has larger error as the lining becomes thicker, results of the present model have a good agreement with experimental results for all the thicknesses considered here. It has also been found that constraining the axial motion on the circumferential surface of the lining enhances sound attenuation at low freqneucies.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.370.1-370
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• 2002

A method using beamforming has been developed to measure absorption coefncient of oblique incidence. MUSIC(Multiple Signal Classification) method detects the angle of incidence and reflection. And beamforming method separates the incident and reflected wave. And spatial smoothing technique is used to reduce the coherence between the incident and reflected wave. The test material were modeled as a locally reacting surface. Numerical and experiment results are performed to verify the performance of proposed method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.699-704
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• 2002

A method using beamforming algorithm has been developed to measure oblique incidence reflection coefficients of sound absorption materials. MUSIC(Multiple Signal Classification) method detects the angles of incidence and reflection. By separating the incident and reflected waves using beamforming method, the reflection coefficient is calculated. Spatial smoothing technique is also used to reduce the coherence between the incident and reflected waves. The test materials were modeled as a locally reacting surface. Numerical and experiment results are performed to verify the acuracy of proposed method.

• Journal of KSNVE
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• v.8 no.3
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• pp.435-440
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• 1998

The main objective of this study is to estimate location and strength of sound sources distributed on the surface of an enclosure. Acoustic holography method has been used to identify the sources in an interior sound field. However, it can not completely distinguish between the direct sound field from sources and the reflections from surfaces. The method just reconstructs the entire sound field based on the sound pressure at the finite number of measurement points. In this stduy, a method which estimates only the active sources by using measurements of field pressure and surface admittance is proposed. An in-situ technique to estimate the general boundary condition is also proposed by using acoustic holography, assuming the surfaces are locally reacting.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.143-146
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• 2004

This study is aimed to numerically evaluate a sound absorption performance of periodically folded barriers. Based on the formulation for sound absorption of a locally reacting surface in a periodic arrangement, variations of the sound absorption with parameters such as the folded width and depth are investigated. In comparison with the sound absorption of a conventional barrier with a flat surface, it is found that the periodically folded barriers can achieve a higher sound absorption especially in the low frequency range.