• 한국소음진동공학회논문집
• /
• 제25권11호
• /
• pp.747-752
• /
• 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.

• 한국소음진동공학회논문집
• /
• 제13권1호
• /
• pp.19-25
• /
• 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.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 춘계학술대회논문집
• /
• pp.1071-1076
• /
• 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.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2012년도 추계학술대회 논문집
• /
• pp.276-277
• /
• 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.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 추계학술대회논문집
• /
• pp.425-430
• /
• 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.

• 콘크리트학회논문집
• /
• 제20권5호
• /
• pp.653-660
• /
• 2008

본 연구는 펄라이트를 이용한 흡음재료의 흡음성능을 개선시키기 위한 최적배합에 대한 분석을 실시하였다. 결합재로서 폴리머 시멘트 슬러리와 무기질 결합재를 사용하여 흡음재료를 각종 배합조건에 따라 제작하여, 강도, 동결 융해 저항성, 그리고 흡음성능에 대하여 실험을 실시하였다. 실험 결과, 관내법에 의한 흠음재의 흠음계수는 배합에 따라 약간의 차이가 있으나 폴리머 디스퍼션을 결합재로 사용한 경우 흡음재의 감음계수 (NRC)는 $0.48{\sim}0.51$로 시멘트만 결합재로 사용한 경우에 비해 약간 크게 나타났으나, 방음벽의 환경부 고시 기준에서의 흡음재로서 감음계수 0.70에 비하면 낮은 수치이다. 그러나 잔향실법에 의한 흡음용 패널의 저주파수 영역($250\;Hz{\sim}500\;Hz$)에서 흡음계수가 $0.84{\sim}1.00$로 매우 높게 나타났으며, 고주파 영역에서도 $0.57{\sim}0.77$ 정도로 비교적 높은 흡음률을 나타내 감음계수가 0.77로 높게 나타났다. 폴리머 디스퍼션을 결합재로 사용한 흡음재는 압축강도, 휨강도 및 동결융해 저항성 등에서 방음벽 재료로서 적당한 성능을 발휘하였으며, 성능과 가격면에서 밸런스를 확보할 수 있는 배합을 도출할 수 있었다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2006년도 추계학술대회논문집
• /
• pp.622-625
• /
• 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.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
• /
• pp.568-571
• /
• 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.

• 설비공학논문집
• /
• 제4권2호
• /
• pp.96-105
• /
• 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.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 추계학술대회논문집
• /
• pp.367-370
• /
• 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.