• Journal of Korea Foundry Society
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• v.31 no.3
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• pp.145-151
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• 2011

Metallic foam has been known as a functional material which can be used for absorption properties of energy and sound. The unique characteristics of Al foam of mechanical, acoustic, thermal properties depend on density, cell size distribution and cell size, and these characteristics expected to apply industry field. Al-Zn-Mg-Cu alloy foams was fabricated by following process; firstly melting the Al alloy, thickening process of addition of Ca granule to increased of viscosity, foaming process of addition of titanium hydride powder to make the pores, holding in the furnace to form of cooling down to the room temperature. Metal foams with various porosity level were manufactured by change the foaming temperature. Compressive strength of the Al alloy foams was 2 times higher at 88% porosity and 1.2 times higher at 92% porosity than pure Al foams. It's sound and vibration absorption coefficient were higher than pure Al foams and with increasing porosity.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.3
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• pp.214-223
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• 2004

This study aim to find an appropriate window for classrooms to provide proper sound insulation against aircraft noise and to achieve this goal, measurements were taken of the sound insulation performance of windows with various thicknesses of inner air space and sound absorption materials in the inner air spaces. As a result of this study the improvement of the sound insulation performance of windows(single, double and triple window) was shown through the analysis and the measuring of windows with these characteristics. These results may be applied to the manufacture of window frames and provide basic data for the improvement of the sound insulation performance of windows.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.710-717
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• 2003

This study aim to find an appropriate window for class rooms to provide proper sound insulation against aircraft noise and to achieve this, measurements were taken of the sound insulation performance of windows with varying thicknesses of inner air space and sound absorption materials in the inner air spaces. As a result of (his study the improvement of the sound insulation performance of windows(single , double and triple window) has been shown through the analysis and the measuring of windows with these characteristics. These results may be applied to the manufacture of window frames and provide data lot the improvement of the sound insulation performance of windows.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.219-223
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• 2003

For the noise reduction measures in a construction field or near the traffic line receiver is often the most economic measure in order to exclude the propagated sound. The dimension of the barrier is decided by the noise and construction design, and the constructive quality of a soundproof panel shall be secured in accordance with KS F4770 to guarantee the safety of sound barriers. In this paper the problems included in the KS F4770-1 that is the regulation for the metallic sound barrier of the absorption type are identified and it is suggested what to be corrected or improved. Through a series of the analyses, conclusions were reached that it is required to improve test methods in KS F4770-1 as well as to break down test loads for building more cost-effective sound barrier.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.125-131
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• 2000

The turbo chiller uses centrifugal compressor, which operates at about 14500 rpm. Due to the high rpm of the impeller, the noise of chiller makes one of the serious problems. The possibility of the sound reduction by using absorbing material is studied in this paper. The generated sound propagates through the duct and then radiates to the outer field. So, the use of sound absorption material inside the duct is one of the effective methods. To study the effect of location of the material, we use Boundary Element Method to analyze the sound field inside the duct system. Numerical study shows the highest sound pressure region is near the elbow of curved duct. From the analysis, it is also shown that the elbow duct is the main radiator of noise and sound absorption treatment of this duct results noise reduction of the highest noise level at BPF and high frequency region.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.10
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• pp.960-967
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• 2010

The sound field can be classified to the direct, diffract and reverberant sound field. If the sound absorption material in a room is not applied sufficiently, the reverberant sound field increases and the sound pressure in a room also increases when the sound source exists in a room. Therefore, the reverberation time should be controled in order to reduce the reverberant sound as well as sound pressure level in a room. Even though the reverberation time is specified and researched widely in architectural engineering, it is rarely performed in a marine engineering. Therefore, in this research, the reverberation time in a navel vessel is researched related to the noise reduction in a cabin.

• KIEAE Journal
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• v.1 no.2
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• pp.47-54
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• 2001

Single sound absorbers such as porous materials, panels, and Helmholts resonators have limited performance with some extents of frequency region. For example, porous materials do not attenuate low frequency sounds, while panels do not absorb high frequency sounds. Composite absorption structure with coverings, porous materials, and air gaps are an alternative for wide band sound absorption. Slits, panels, perforated panels are those materials for coverings, glass wool, mineral wool, polyester, and polyurethane are frequently used porous materials. Air gap between the porous material and background surface is one of major factors which governs the absorption characteristics of composite absorption structures, especially in the low frequency area. Calculations and measurements show that the absorption coefficients of composite absorption structure, in mid and low frequency bands, are getting higher with increased air gaps. Perforated panels rather than slits and panels are good coverings with higher number as far as absorption coefficient is concerned. Perforated panels with porous materials and 37 cm of air gaps in background have high absorption coefficients for all frequency bands, above 0.7 to 1.0. All measurements are performed in reverberation chamber, Mokpo National University, according to ISO 354 and ISO 3382.

• Journal of the Korean Wood Science and Technology
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• v.36 no.3
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• pp.9-16
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• 2008

Ribbed birch (Betula costata Trautv.), Japanese larch (Larix kaempferi (Lamb.) Carr.), and tulip tree (Liriodendron tulipifera L.), were used as experimental specimens to measure the sound absorption coefficient with various resonator types, regular resonator (Type-R), eccentric resonator (Type-E), aligned resonator (Type-A), and screwed resonator (Type-S). Resonators consisted of the simple perforation by hand drilling. Sound absorption performances of the resonators installed perforations were better than those of untreated specimens. They were varied with the resonator's type and wood species. Increased area by a wood screw gave no significant change on the sound absorption.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.879-884
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• 2003

This paper is to experimentally investigate the effect of the through-flow and grazing-flow on the absorption performance of a perforated plate system. The experiment is performed through the systematic change of the through-flow velocity, grazing-flow velocity, incident sound pressure level, and the geometrical parameters such as the porosity and hole diameter. From the experimental results, it is found that for the nonlinear relationship between the acoustic resistance and incident sound pressure level there is no influence of the through-flow on the absorption performance, but fur the linear relationship between them there is a strong dependence of the absorption performance on the through-flow velocity. It is also shown that the absorption performance is controllable by changing the porosity and hole-diameter in size.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.163-167
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• 2003

This paper is to experimentally investigate the effect of the through-flow on the absorption performance of a perforated plate system. The experiment is performed through the systematic change of the through-flow velocity, incident sound pressure level, and the geometrical parameters such as the porosity and hole diameter. From the experimental results, it is found that fur the nonlinear relationship between the acoustic resistance and incident sound pressure level there is no influence of the through-flow on the absorption performance, but for the linear relationship between them there is a strong dependence of the absorption performance on the through-flow velocity. It is also shown that the absorption performance is controllable by changing the porosity and hole-diameter in size.