• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.11
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• pp.747-752
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• 2015

Underwater radiated noise is an important characteristic in the naval weapon systems. It is difficult to measure the radiation efficiency of underwater vehicle, such as UUV(unmanned underwater vehicle) and underwater weapons in real operation environment. In this study, acoustic radiation efficiency of a circular cylindrical structure is measured in the laboratory-water tank. The radiation efficiency is compared with the numerical results and it is found that they are in a good agreement. Therefore, the measurement method can be applied effectively for predicting the underwater radiation noise and effectiveness of radiation reduction means.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.1
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• pp.19-25
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• 2003

As a test specimen. an aluminum extruded panel with a dimension of 640 mm$\times$740 mm$\times$40mm is considered. This plate has 9 mm thickness if mass is concerned. Based on the FEM modeling in rigidity. the specimen turns out to be 32 mm and 12 mm thickness In isotropic steel plate. Also, the characteristics of transmission loss on the honeycomb structure have been examined experimentally with reverberation chamber. A honeycomb structure follows mass law in above 800 Hz. In order to improve the noise transmission effect in lower frequency, extra damping treatment is suggested. As a conclusion. the examined honeycomb structure Is designed to Improve the bending rigidity, not for the noise reduction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1071-1076
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• 2002

The purpose of this paper is to examine sound absorption characteristics of sintered Al(aluminum) plate. Comparison between experiment and theoretical analysts by using empirical formula are made. Based on comparison. it is found that Voronina model gives more reasonable explanation for sound absorption characteristics of sintered Al plates. Effect of air gap with varying the thickness of plates are also investigated, which concludes that the air gap generally increase absorption but for too thick thickness of Al plates. Al plates with air gap shows 0.85∼0.9 of NRC(Noise Reduction Coefficient) measured in reverberation room. which is comparable to glass wool. Comparison between normal and random Incident absorption shows that random incident absorption is higher than normal incident absorption.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.276-277
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• 2012

This study was carried out in the laboratory of the reverberation. A total of six specimens were fabricated depending on the thickness and strength. Floor impact sound insulation performance was measured in 1/3 octave band center frequency. The results of this study are as follows. Although some differences in the frequency band, the result of evaluating the weight impact sound blocking performance as the thickness increases, the floor impact sound insulation performance is improved. In addition, to increase the strength of the slab, even if the block impact sound performance is improved.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.425-430
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• 2000

This paper describes the effect of the pad stiffness on the noise reduction of impact noise isolation pads of a floor. And also a new semi-experimental method for measuring the impact noise isolation capability of a pad is introduced. The impact noise isolation pads made of wire-mesh, urethane-chip and foam rubber are used for measuring the stiffness, the vibrational insulation performance and the impact noise isolation capability. The correlation between the stiffness and impact noise isolation capability of pads is theoretically reviewed, and confirmed from the experimental results. For measuring the impact noise isolation capability of only an isolation pad, a semi-experimental method proposed in this study is more effective than the reverberation room method.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.653-660
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• 2008

The purpose of this study is to analyze the optimal mix design of the sound absorption material that is made from perlite and various binder systems for noise barrier wall. The polymer cement slurry which is made from two types of polymer dispersions, and silicone type inorganic material are used as binder. The test specimens are prepared with various polymer cement ratios, binder ratios, and tested for strengths, freezing and thawing and sound absorption performance by the tube and the reverberation room methods. From the test results, the difference of sound absorption coefficient by the tube method is a little recognized, however, noise reduction coefficient (NRC) of test specimens bound by the polymer cement slurry is in the ranges of 0.48 to 0.51. They are a little higher than those bound by cement only, and are lower values than recommended value of 0.7 by the Ministry of Environment. However, the sound absorption coefficient of test specimens at low frequency range of 250 to 500 Hz by reverberation room method shows very high values as 0.84 to 1.00, and 0.57 to 0.77 at the high frequency. The test specimens with polymer cement slurry binder have a good balance between performance and cost, and have proper properties in strengths, freezing and thawing resistance as sound absorption material for noise barrier wall. It is apparent that the good sound absorption material can be produced according to the optimum mix design that is recommended from this study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.622-625
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• 2006

This study is a fundamental investigation for standardization of the heavy-weight floor impact measuring method by the impact ball. The distribution chrematistics of floor impact sound level and reverberation time in a receiving room of the testing building for floor impact sound were measured with variations of number and arrangement of the sound-absorbing materials. Total 8 cases were investigated. The distribution of the floor impact sound level($L_{i,\;Fmax}$) was measured at 30 points with same intervals. The absorption coefficient of the room is 0.10 in case of installation of 6 absorbing materials and 0.02 in case of non-installation. The distribution shape of the impact sound pressure level was similar to the result of the bang machine driving at the measured frequency range. However, the overall reduction of the impact sound level investigated in the 125 to 500 Hz shows that the sound absorption characteristics of the receiving room actually affects the result of the heavy-weight impact measurement.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.568-571
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• 2004

This research estimated the physical. mechanical characteristic and the character of sound absorption according to target void ratio of porous concrete and the mixing ratio of recycled aggregate for the valid utilization of recycled aggregate using waste concrete and sound reduction out of a road, a railway, a residential street, and a downtown area. As a result of the test, compressive strength tended to be a radical strength fall when target void ratio was $25\%$ and contents of recycled aggregate exceeded over $50\%$. Also, the character of sound absorption of porous concrete which used recycled aggregate using waste concrete was the most excellent when target void ratio was $25\%$, and the influence by contents of recycled aggregate was trivial. Therefore, when the strength and the character of sound absorption of porous concrete are considered, it is proved valid that proper target void ratio was $25\%$ and contents of recycled aggregate using waste concrete was $50\%$ or so.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.2
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• pp.96-105
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• 1992

The objective of this paper is to study experimentally on the noise characteristics of supersonic jet from multihole orifice in the range of jet pressure from $at_g$ to $at_g$ in the reverberation room. At first, the single orifice jets are investigated for various hole diameter from 3.8mm to 10mm. Through the noise spectrum, the turbulent mixing noise and the shock associated noise is analyzed. The noise for confined jets into a tube of diameter 30mm or 90mm with length 2m is investigated in comparision with that for the free jets. The sound power level is measured and compared with thoretical models for free jet. At second, multihole orifice jets are investigated to study the effect of multijet on noise reduction. The spectrum and power level of multijets are measured and compared with single jets. The multi-jets in a confined pipe are also investigated. It is found that the noise spectrum is significantly altered by increasing the number of jet with decrease in jet diameter and also by confining the jet into tube.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.367-370
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• 2005

This paper investigated the sound characteristics in an apartment complex. The field measurement was conducted in order to examine the acoustical characteristics of the apartment complex in situ. As a result, it shows that there are around 3 sec. reverberation time and the additional sound reinforcements at the area of high height due to the surrounded buildings. Thus, 1:50 Scale model measurement and Raynoise computer simulation were carried out with insertion of the parapet and the canopy on the balcony. In case of a single building, the parapet was effective to reduce noise level at low floor levels, and the canopy was effective to reduce noise level at high floor levels. But it also shows that both the parapet and the canopy were not effective to reduce noise level at middle floor levels. In case of an apartment complex, the canopy was less effective to reduce noise level at each floor in comparison with case of the single building.