• 소음진동
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• 제3권1호
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• pp.47-55
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• 1993

In order to maintain comfortable life environment around railroad site, noise from train itself, and to train & rail interaction, and the vibration transmitted through the ground should be controlled to the extent of permissible level. In order to achieve this, the basic railroad noise & vibration data such as magnitude and frequency characteristics of them are necessary to establish the counterplan for railroad noise & vibration. In this study, we measured and analysed the characteristics of time variation, frequency, direction and distance attenuation of noise and vibration of the railroad between Seoul and Pusan.

• 한국공작기계학회논문집
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• 제11권3호
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• pp.33-38
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• 2002

This paper deals with pressure ripple attenuation far separated-type Hydrostatic Transmission (HST) consisting ova variable axial piston pump connected in an open loop to a fried displacement axial piston motor. Pressure ripples in HST is major source of vibration which can lead to fatigue failure of components and cause noise. In order to reduce the pressure ripple, an annular tube tripe hydraulic filter is proposed to attenuate pressure ripples with the high frequencies components to achieve better noise reduction in HST. The basic principle of a hydraulic filter is allied to propagation of pressure wave, reflection, absorption in cross section of discontinuity and resonance in the hydraulic pipeline. It is experimentally shown that the hydraulic filter attenuates about 30∼40dB of pressure ripple with high frequencies. These results will assist in modeling and design of noise reduction in hydraulic control systems, and provide a means of designing a quieter HST.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1999년도 추계학술대회 논문집
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• pp.479-486
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• 1999

The noises generated from the air-conditioning duct are known to strongly affect the indoor-noises of high speed trains. The acoustic characteristics of an air-conditioning duct should depend on the geometry and shape of the duct. The structural material for Korean high speed train is supposed to be changed from Steel, which was used for TGV, to Aluminum in order to reduce the total train weight. Accordingly, the shape and layout of the air-conditioning duct of Korean high speed train will be different from that of TGV. Thus, this paper introduces a analytical method to predict the noise attenuation through the air-conditioning duct, based on the ISO 7235. In this method, the whole duct is divided into several pieces and the noise attenuations predicted for each duct piece are integrated to get the noise attenuation for the whole duct system. The validity of the method introduced herein is discussed through some numerical tests.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.23-32
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• 2000

The purpose of this study is to identify the dynamic characteristics of a motor-die in washing machine and provide quantitative design information needed for the reduction of radiated sound from the motor-die. To perform the design analysis, dynamic characteristics are identified by motor-die modeling and the availability of model is verified by experimental modal analysis. Numerical approach using MSC/NASTRAN and SYSNOISE predicted sound attenuation effects according to the change of design parameters, such as thickness, concentrated mass and rib. The numerical results due to the rib attachment showed the significant noise attenuation effects over 15dB in the frequency range of 450-700Hz.

• 한국해양공학회지
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• 제26권3호
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• pp.13-19
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• 2012

Recently, as the importance of the interior noise in a ship cabin has risen, ship builders have becomeconcerned about the use of noise reduction panels to reduce cabin noise. The results of previous researches have been based on analytical and experimental methods using simple sandwich panels. However, panel structures are becoming more complex to improve the transmission loss. Thus, researches that analyze the transmission loss of a panel are reaching the limit of study. This paper reports on research that was performed to determine the sound transmission characteristics of multi-complex panels applicable to high value-added vessels. It presents comparisons between analytical methods and experimental results by using a mini-reverberant chamber with components of sound attenuation panels, including the core and surface materials. The sound transmission loss of multi-complex panels are also analyzed in terms of the influences of the inside perforate plates and air gap thickness on the attenuation. Finally, the multi-complex panel with the highest noise attenuation is proposed based on the analysis results and experimental results in mini-reverberant chamber, which wereverified using a real-size reverberant chamber.

• 대한전자공학회논문지TC
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• 제48권5호
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• pp.40-45
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• 2011

본 논문에서는 광대역 지중 전력선 통신 모뎀 및 네트워크 기술개발을 위하여 실제측정을 통해 지중 전력선 통신채널의 특성을 해석하였다. 지중 배전선로의 길이 및 구조물에 따른 지중 배전선로의 광대역 전력선 통신채널의 감쇠 량을 측정하기 위해 신호발생기, 스펙트럼 분석기, 비접촉식 커플러 등을 이용하여 채널 측정 시스템을 구성하였다. 실증시험을 위해 시험선로 내 단일 선로로서 가장 긴 고압 선로 두 곳을 선택하고, 그 채널상의 노이즈 특성 및 신호감쇠 레벨을 측정하였다. 측정결과 통신성능을 매우 떨어뜨릴 수 있는 임펄스 노이즈가 존재하는 것을 확인하였으며, 장거리 선로의 경우 선로 길이에 의한 고주파 감쇠가 나타나는 것으로 확인하였다.

• Journal of Magnetics
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• 제12권1호
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• pp.21-26
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• 2007

Si-based electromagnetic noise suppressors on coplanar waveguide transmission lines incorporated with a $SiO_2$ dielectric layer and a nanogranular Co-Fe-Al-O magnetic thin film are reported. Unlike glass-based devices, large signal attenuation is observed even in the bare structure without coating the magnetic thin film. Much larger signal attenuation is achieved in fully integrated devices. The transmission scattering parameter ($S_{21}$) is as small as -90 dB at 20 GHz at the following device dimensions; the thicknesses of the $SiO_2$ and Co-Fe-Al-O thin films are 0.1 $\mu$m and 1 $\mu$m, respectively, the length of the transmission line is 15 mm, and the width of the magnetic thin film is 2000 $\mu$m. In all cases, the reflection scattering parameter ($S_{11}$) is below -10 dB over the whole frequency band. Additional distributed capacitance formed by the Cu transmission line/$SiO_2$/Si substrate is responsible for these characteristics. It is considered that the present noise suppressors based on the Si substrate are a first important step to the realization of MMIC noise suppressors.

• 한국인터넷방송통신학회논문지
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• 제16권2호
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• pp.113-122
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• 2016

본 연구에서는, 웨이블릿 노이즈 감쇠에 고속 푸리에 역 변환을 포함하는 방법을 제안한다. 위너 필터링에 인자를 채용하여 역 필터링을 나타내고, 최적의 계수는 전체 평균 제곱 오차를 최소화하도록 선택된다. 위너 필터를 적용하기 위해, 손상된 그림에서 원 화상의 파워 스펙트럼을 계산한다. 위너 필터링은 역 필터링 처리를 포함하기 때문에 블링 필터가 반전되지 않을 때 노이즈는 확장한다. 큰 노이즈를 제거하려면 최고의 웨이블릿 임계값을 사용하여 노이즈를 제거하는 것이다. 웨이블릿 노이즈 감쇠 단계는 역 필터링 및 웨이블릿 기능으로 노이즈 감소로 구성된다. 실험결과는 전체 재생 성능 이상의 다른 방법을 능가하지는 않았다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.196-202
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• 1997

A reinforced hydraulic hoses,caiied a resonator hoses,with fixible metal tube are commonly used in automotive power steering hydraulic systems to attenuate and eliminate the objectionable fluid borne noise(pressure ripple) or vibration produced by a pump or steering gear. To achieve better nose attenuation in automotile vehicles, the investigations on propagation and attenuation characteristics of fluid borne pressure ripple in power steering hydraulic ciruit are required. So, this paper descibes a mathematical model of hydraulic hoses to support design the power steering hydraulic circuit and analyze the attenuation characteristics of flow and pressure ripples. The model is based on the transfer matrix approach. The experimental results show that the pulsation attenuation characteristics of hydraulic house is remarkably affected by the flexible metal tube inserted coaxially inside a hydraulic hose with a finite length as well as viscoelastic properties of house wall. It is also shown that the predicted results bymodel proposed here agree well with the measured results over a wide frequency range. These results will assist in the modeling and design of hydraulic hoses, and hear, should provide a means for designing a quieter automotive power steering hydraulic systems.

• Safety and Health at Work
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• 제12권2호
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• pp.184-191
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• 2021

Background: Hearing protection devices (HPDs) are often used in the workplace to prevent hearing damage caused by noise. However, a factor that can lead to hearing loss in the workplace is improper HPD fitting, and the previous literature has shown that instructing workers on how to properly insert their HPDs can make a significant difference in the degree of attenuation. Methods: Two studies were completed on a total of 33 Hydro One workers. A FitCheck Solo field attenuation estimation system was used to measure the personal attenuation rating (PAR) before and after providing one-on-one fitting instructions. In addition, external ear canal diameters were measured, and a questionnaire with items related to frequency of use, confidence, and discomfort was administered. Results: Training led to an improvement in HPD attenuation, particularly for participants with poorer PARs before training. The questionnaire results indicated that much HPD discomfort is caused by heat, humidity, and communication difficulties. External ear canal asymmetry did not appear to significantly influence the measured PAR. Conclusion: In accordance with the previous literature, our studies suggest that one-on-one instruction is an effective training method for HPD use. Addressing discomfort issues from heat, humidity, and communication issues could help to improve the use of HPDs in the workplace. Further research into the effects of canal asymmetry on the PAR is needed.