• International Journal of Railway
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• 제7권4호
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• pp.100-108
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• 2014

A numerical analysis method for predicting aerodynamic noise at inter-coach space of high-speed trains, validated by wind-tunnel experiments for limited speed range, is proposed. The wind-tunnel testing measurements of the train aerodynamic sound pressure level for the new generation Korean high-speed train have suggested that the inter-coach space aerodynamic noise varies approximately to the 7.7th power of the train speed. The observed high sensitivity serves as a motivation for the present investigation on elucidating the characteristics of noise emission at inter-coach space. As train speed increases, the effect of turbulent flows and vortex shedding is amplified, with concomitant increase in the aerodynamic noise. The turbulent flow field analysis demonstrates that vortex formation indeed causes generation of aerodynamic sound. For validation, numerical simulation and wind tunnel measurements are performed under identical conditions. The results show close correlation between the numerically derived and measured values, and with some adjustment, the results are found to be in good agreement. Thus validated, the numerical analysis procedure is applied to predict the aerodynamic noise level at inter-coach space. As the train gains speed, numerical simulation predicts increase in the overall aerodynamic sound emission level accompanied by an upward shift in the main frequency components of the sound. A contour mapping of the aerodynamic sound for the region enclosing the inter-coach space is presented.

• 한국소음진동공학회논문집
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• 제14권11호
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• pp.1123-1128
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• 2004

An experimental study on firing noise of K2 rifle was performed. Firing noises of K2 rifle were measured at close distance to rifle. Firing noise of K2 rifle which made in Korea, has not measured before. The measurement of firing noise at close distance is not simple, because the amplitude of firing noise is much bigger than the measuring limit of ordinary sound level meter even though it uses a signal attenuator. The measurement of firing noise at close distance is necessary for noise source positioning and for obtaining the sound power of K2 rifle. By this experimental study, the firing noise levels of K2 rifle at different positions are obtained and these data can be used to Predict the sound pressure level at any distance from muzzle of the rifle. Also these data can be used to calculate the threshold shift of gunner's ear.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.904-908
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• 2008

As the various industrial production machinery has come into being by development of industrial technology, the productivity of the basic industrial production machinery has improved and the international competitiveness of the one of Korea has strengthened. However, at the same time, noise from various industrial production machinery disturbs the quiet environment. There are 35 kinds of the noise emission machinery defined in the noise and vibration control act according to the horse power and the number of machinery. These were classified in 1992 through investigation from 1990 to 1991, and the characteristic of the noise emission machinery may be different from the past one. So we need to investigate the characteristics of the noise emitted by machinery to control it rightly. Also we need to investigate the new noise emission machinery which has come into being recently. In this survey, we measured sound intensity of 32 noise emission machinery to calculate the sound power levels of those and investigated the characteristic of the sound power level of those according to the frequency. From the survey, we found that the forging machine, concrete pipe and pile making machine, sawing machine, etc. are the noisy machinery. And the automatic packing machine, sewing machine, centrifuge, etc. are the silent machinery. Also the generator, the concrete pipe and pile making machine, the printing machine, etc. emit the low frequency noise, and the molding machine, the stone cutter, the metal cutter, etc. emit the high frequency noise. Lastly, we intented to propose the proper guide line of classifying noise emission machinery.

• 드라이브 ㆍ 컨트롤
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• 제18권1호
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• pp.1-8
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• 2021

This paper presents research on methods for the reduction of forklifts' noise level for the increased comfort and safety of its operator. A cooling fan with a high air volume flow rate installed in the forklift acts as an important design parameter which efficiently cools the heat exchanger system, helping to transfer internal heat from the engine room to the outdoors with both transmitted and diffracted opening noises. The cooling fan contributes significantly to both the forklift's emitted sound power and the operator room's noise level, thereby necessitating research on the forklift's reduction of acoustic power level and transmission. A noise analysis for various fan models with a biomimetic design based on eagle-wing geometry was conducted. In addition to the acoustic power generation, the aerodynamic performance of the cooling blade is also strongly influenced by the design of airfoil distribution, thereby requiring optimization. The cooling fans were fabricated and installed in the forklift in order to check the efficacy of the forklift engine's cooling, and the final version of the fan was measured for its ability to lower acoustic power level and cool the engine room. This study explains the aerodynamic and acoustic features of the designed fans with the use of BEM analysis and forklift test results.

• The Journal of the Acoustical Society of Korea
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• 제24권4E호
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• pp.139-143
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• 2005

The present study aims to investigate the effects of speaker location on the speech intelligibility in a classroom. In order to this, acoustic measurements were undertaken in a classroom with three different sound source locations such as center of front wall (FC), both sides of front wall (FS) and the center of ceiling (CC). SPL, RT, $D_{50}$, RASTI were measured in the 9 measurement points with same sound power level of sound source and MLS was used as the sound source signal. Also, subjective listening tests were carried out using Korean language listening materials which were recorded in an anechoic chamber. The recorded syllables were replayed and recorded again in the classroom with same sound source at three different locations and listening tests were undertaken to 20 respondents who were asked to write the correct syllables which were recorded in the classroom. The results show that higher sound intelligibility ($D_{50}$ of $47\%$, RASTI of 0.56) was obtained when sound source was located at the FS. The results also show that high sound intelligibility was obtained at the area nearby walls.

• 한국생산제조학회지
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• 제5권2호
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• pp.83-89
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• 1996

The objective of this study is to find experimentally the characteristics of the noise generated by the impinging jet on the normal plate, and also to compare the noise characteristics of the impinging jet with those of the free jet. The experiment is performed for the measurement of the noise specturm, the noise power, and the directivity for the free and impinging jets. From the experiment. it is found that the power of noises generated by the free jet as well as the impinging jet is proportional to the eighth power of the jet velocity through the circular converging nozzle, and that the noise power of the impinging jet is 15dB as high as one of the free jet when the plate distance is about within one to three times the nozzle diameter at the pressure ratio 1.39. The sound pressure level of the impinging jet depends upon the jet pressure and the plate distance. The plate distance with the maximum overall sound pressure level is increased with the jet pressure. The directivities with 1/3 octave band frequency for both the free jet and the impinging jet are greatly influenced by the convection effect.

• 한국음향학회지
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• 제39권2호
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• pp.105-112
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• 2020

발전소 소음을 저감하기 위해서는 여러 가지 설비요소의 소음원에 대해 설계단계에서부터 정확한 소음예측을 수행하고, 과도한 소음에 대해서는 효과적이고 경제적인 방음대책의 수립이 필요하다. 이에 본 논문에서는 발전소 지역 및 주변 주택지역을 포함한 소음분포 해석 가능 모델을 제안하고, 주택지역의 소음저감 방법을 수립하였다. 발전소의 주요 소음원에 대한 소음레벨의 측정을 통하여 음향파워레벨을 평가하고, 설계도면 및 지형정보를 이용하여 소음전달에 영향을 주는 지형 및 지물 등을 최대한 상세히 모델에 포함함으로써 발전소 및 주택 지역의 소음분포를 효과적으로 해석할 수 있는 모델을 수립하였다. 수립된 소음 해석 모델의 신뢰성은 주요 위치에서의 소음레벨 해석 결과와 측정 결과를 비교하여 검증하였으며, 이를 바탕으로 신규호기의 증설에 의한 인근 주택지역에서의 소음 영향도를 평가하고, 발전소의 가동 시에 소음환경기준을 만족시키는 방음벽을 제안하였다.

• 한국도로학회논문집
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• 제20권3호
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• pp.59-64
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• 2018

PURPOSES : We propose a parameter-setting-free harmony-search (PSF-HS) algorithm to determine the individual sound power levels of noise sources in the cases of industrial or road noise environment. METHODS :In terms of using methods, we use PSF-HS algorithm because the optimization parameters cannot be fixed through finding the global minimum. RESULTS:We found that the main advantage of the PSF-HS heuristic algorithm is its ability to find the best global solution of individual sound power levels through a nonlinear complex function, even though the parameters of the original harmony-search (HS) algorithm are not fixed. In an industrial and road environment, high noise exposure is harmful, and can cause nonauditory effects that endanger worker and passenger safety. This study proposes the PSF-HS algorithm for determining the PWL of an individual machine (or vehicle), which is a useful technique for industrial (or road) engineers to identify the dominant noise source in the workplace (or road field testing case). CONCLUSIONS : This study focuses on providing an efficient method to determine sound power levels (PWLs) and the dominant noise source while multiple machines (or vehicles) are operating, for comparison with the results of previous research. This paper can extend the state-of-the-art in a heuristic search algorithm to determine the individual PWLs of machines as well as loud machines (or vehicles), based on the parameter-setting-free harmony-search (PSF-HS) algorithm. This algorithm can be applied into determining the dominant noise sources of several vehicles in the cases of road cross sections and congested housing complex.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.206-211
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• 2000

Demands on a quiet environment is increasing because of noisiness and annoyance due to the extended use of noisy electronic device. Determination of sound power levels of noise sources using sound pressure in a reverberation room is usually a relevant method for devices with comparatively large volume or unevenly distributed source position. This study aims to observe the contents of ISO 3741 and analyze its changes in the revised standard ISO 3741-1999. And also aims to assess the revised ISO 1999 its effectiveness and limitations with an actual application to measure the sound power level of a refrigerator.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.525-530
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• 2013

With the increasing the importance of emotional quality of vehicle, the sound quality of systems with electric motor components has become increasingly important. Electric motors are used for windows, seats, sun roof, mirrors, steering columns, windshield wiper, climate control blowers, etc. In this paper, a study was conducted to identify sound quality factors that contribute to customer's satisfaction and preference of the window lift system. Jury test for subjective evaluation was carried out and sound quality index was developed. Averaged sound pressure level and sharpness were significant factors when glass moves down. Also, maximum loudness at stop section and averaged loudness were significant factor when glass moves up. Noise source identification was carried out for the reduced the loudness and sharpness during glass transferred section and impulsive noise at stop section, Using the source identification result, several improvement points were applied. And finally, the degree of sound quality improvement was judged using sound quality index.