• Journal of Korean Society of Forest Science
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• v.84 no.4
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• pp.409-414
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• 1995

This study was carried out for the analysis and comparison about the noise diminution effects by the height, width and density of Euonymus japonica wall, the distance of sound source, the distance of sound receiver, the height of sound source, and the height of sound receiver. The results obtained were summarized as follows; 1. After the establishment of tree wall, the volume of noise diminution measured 6.8dB and the effects of noise diminution measured heigher than before by 10.6% and t-value was significant at the 1% level 2. In simple correlation between the effects of noise diminution and variables, the density of tree wall was found as the most significant factor, and the last were found in the order of the distance of sound receiver, the width of tree wall, and the distance of sound source. 3. In partial correlation coefficients the effects of noise diminution and variables, the density of tree wall (r=-0.959) was found as the most significant factor, and the last were found in order of the distance of sound receiver (r=-0.906) and the width of tree wall (r=-0.753). 4. The estimated equation to measure the effects of noise diminution according to variables (the height of tree wall, the width of tree wall, the density of tree wall, the distance of sound source, the distance of sound receiver, the height of sound source, and the height of sound receiver) was $Y=69.520-1.672X_1-1.656X_2-0.066X_3-0.248X_4-3.134X_5-0.222X_6-0.343X_7$, and the coefficient of determination of this estimated equation was highly found as 0.950. 5. In semi-partial correlation coefficient the effects of noise diminution were found in the order of the density of tree wall, the distance of sound receiver, the width of tree wall, and the height of tree wall from the highest to the lowest. Therefore, it was considered that the density of tree wall, the distance of sound receiver, the width of tree wall and the distance of sound source should be controlled effectively to increase the effects of noise diminution by Euonymus japonica wall.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.857-860
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• 2006

It is important to diminish noise source of an electric motor used in appliances. We studied on the noise reduction of BLDC motor to drive a fan. Especially, this study was focused on detent torque caused by interaction between a permanent magnet of rotor and groove in stator. This source and rotating system brought about a resonance. This paper showed that the higher harmonic component of this torque had a main factor to lessen noise. So, we had designed new magnets with shape like a peanut and pseudo-sinusoidal flux density for low-noise BLDC motor in refrigerator.

• Environmental Engineering Research
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• v.20 no.4
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• pp.383-391
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• 2015

Transparent type noise barrier is a desirable facility since it provides a secure view to drivers and passengers. However, reflection from this type of barrier could annoy dwellers on the sides of the road. To reduce reflection noise by transparent type barrier, modification can be made to the shapes on the front side and hence get effects by distortion of sound transmission. To achieve this, we have conducted simulation by which the effects of patterned screens of noise barrier on high-ways were investigated. The reduction effects of reflected sounds were evaluated for swelling, swelling with curved, rectangular and V-shaped screen type barriers, compared to the planar panel. The emitting noise was generated by 6-lane road and the patterned noise barriers had shown the reduction effects, especially in swelling and swelling with curved type for middle height dwellers, and the V-shaped screen type for higher elevation dweller. The swelling-type showed a decrease of 0.7~1.2 dB, performing the best diminution effect among the tested noise barriers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.3 s.258
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• pp.217-224
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• 2007

A numerical analysis for a silencer with three baffles of 120mm tank gun has been performed. The Reynolds-Averaged Wavier-Stokes equations with Baldwin-Lomax turbulence model were employed to compute unsteady, compressible flow inside the tank gun and the silencer. An axisymmetric computational domain was constructed by using 12 multi block chimera grids. The resolution of flow field is observed by depicting calculated pressure and muzzle brake force. The peak blast pressure and noise through the silencer reduced approximately 99% and 41dB in comparison to the tank gun without the silencer at near filed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.2 s.95
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• pp.161-168
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• 2005

The absorbing material is mostly used to changing the acoustic energy to the heat energy in the passive control, and that consists of the porous media. That controls an air borne noise while the stiffened plates, damping material and additional mass control a structure borne noise. The additional mass can decrease the sound by mass effect and shift of natural frequency, and damping material can decrease the sound by damping effect. The passive acoustic control using these kinds of control materials has an advantage that is possible to control the acoustic in the wide frequency band and the whole space at a price as compared with the active control using the various electronic circuit and actuator. But the space efficiency decreased and the control ability isn't up to the active control. So it is necessary to maximize the control ability in the specific frequency to raise the capacity of passive control minimizing the diminution of space efficiency such an active control. Therefore, the characteristics of control materials and the optimum layout of control materials that attached to the boundary of structure-acoustic coupled cavity were studied using sequential optimization on this study.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.3
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• pp.217-224
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• 2007

The present work addresses an experimental study on sound attenuation characteristics of silencer by live firing test. When a gun fires, there exists excessive noise which propagates as a form of blast wave. As muzzle energy of the weapon systems increases, the level of impulsive noise also increases. It is well known that the impulsive noise from a gun gives a serious damage to human bodies and structures. The adverse effects of impulsive sound also cause both social and military problems. So it is very important to study the characteristics of the impulsive sound attenuation. The live firing test is performed to evaluate the effect of four different silencers. The test result is compared with the case of bare muzzle which is not installed the silencer. The frequency characteristics are also analyzed to investigate the diminution of sound pressure level. The results of this study will be helpful to the designing silencer for large caliber weapon systems.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1345-1351
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• 2013

Variable iron loss as function of current phase angle of Interior Permanent Magnet Synchronous Motor(IPMSM) was calculated through Curve Fitting Method(CFM). Also, a magnetic flux density distribution of iron core according to current phase angle was analyzed, and an iron loss calculation was performed including harmonic distortion. The experiment was performed by production of non-magnetizing model for the separation of mechanical loss, and the iron loss was calculated by the measurement of input using power analyzer and output power using dynamometer. Some error was generated between experimental results and calculation value, but an iron loss diminution according to current phase angle followed a same pattern. So, errors were generated by measurement, vibration, noise, harmonic distortion loss, etc.

• Journal of the Korean Professional Engineers Association
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• v.25 no.1
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• pp.11-14
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• 1992

얼마전까지만 해도 우리나라는 조용한 아침의 나라, 동방예의지국이라 예찬되어 왔으며, 아름다운 산하는 금수강산이라 불리어져 왔다. 비록 창호지 한장으로 바른 창문이었지만 소음공해같은 것은 결코 느끼지 않고 살았으며, 창호지를 통하여 전달되는 첫새벽의 닭우는 소리는 소음이라기 보다는 장부의 단잠을 깨워주는 자연음으로서의 낭만이 있었다. 그러나, 이젠 사정이 크게 달라졌다. 지난 40년 동안에 우리나라 경제가 고도성장을 이룩함으로써 우선 국민생활은 풍요로와 겼으나 대소 공장과 사업장 및 교통혼잡으로부터 The아져 나온 각종 오염물질이 엄청나게 증가하여 호흡하는 공기와 마시는 물, 곡물이 자양되는 토양은 병들어 가고 있을 뿐만 아니라 옛날에는 생각지도 못했던 온갖 소음ㆍ진통으로 우리는 포장되어 살아가고 있다 해도 과언이 아니다. $\ulcorner$소음진동규제법$\lrcorner$에 소음이란 기계ㆍ기구ㆍ시설 기타 물체의 사용으로 인하여 발생한 강한 소리라 정의하고 있다. 말할 것도 없이 이는 인위적으로 발생되는 시끄러운 소리를 의미하며, 이러한 소음을 다소나마 피하기 위해 창문을 알루미늄샤시 유리창으로 바꾸어 커텐을 치고, 출입문을 두중한 원목 도어로 교체 해도 다양해지고 강해진 소음공해를 막기는 어려운 세상이 되 었다. 이로 인하여 우리는 생활의 안정을 위협 받게 되었으며, 학업과 생업에 크고 작은 장해를 받으며 살아가고 있는 것이 오늘의 현실이다. 정부ㆍ기업ㆍ국민 각자가 쾌적한 환경을 보전하고자 하는 확고한 의지와 배경이 없다면 후손들에게도 대물림 될 것임에 틀림없으며, 특히 이러한 현상은 도회지에서 더욱 심화될 것임은 명약관화하다 하겠다.