• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.683-689
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• 2006

The sound absorption materials have been used to enhance the performance of a noise barrier and improve the room acoustics. In this study, 6 products of sound absorption materials generally used in Korea were chosen, and their absorption performance was tested in various conditions, that is, it was measured while changing thickness, density and air-gap in their back, and measured with or without facing on their face.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.340-341
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• 2010

A computational study to capture the flow around a floor mounted greenhouse shaped HAWT model was performed using the commercial software PowerFLOW 4.2b. The simulation kernel of this software is based on the numerical scheme known as the Lattice Boltzmann Method (LBM), combined with an RNG turbulence model. Simulations were performed at 60 and 140 km/h free stream air speeds. Selective results from these computational simulations are presented to show the capability of this numerical approach to predict the aerodynamics and aeroacoustics characteristics of the 3-D flow field around the HAWT model.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2004.11a
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• pp.343-348
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• 2004

Since its foundation of Won-Buddhism in 1916 there established around 500 Temple-Halls in both domestic and overseas areas, and it is a native religion that currently on its development of edification activities. As for Won-Buddhism which being under rapid development likely as such going, together with its expansion of the religious influence, there required more broader spaced grand sanctum at where the large-scaled religious events are able to perform. According to this, Balcony-styled plane form is on increasing trend from the internal plane form of Won Buddhism Sanctum. On such viewpoint, this study hereby intends to grasp the character of room acoustics through on-the-spot survey about the objects of 3 Won Buddhism Sanctums which equipped with mutually different characters of the balconies already built, and willing to furnish the fundamental material which enables to improve acoustic capability when design Won Buddhism Sanctum equipped with balcony in the future.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.622-625
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• 2008

While the research for flow over a circular cylinder has been actively carried out up to the present, it has been known that the flow has not been clarified even now. Various complex flow and aero-acoustic characteristics exist around a circular cylinder such as flow separation, wake and pressure wave propagation. In this paper, research was carried out for wake flow and aeroacoustics over a circular cylinders by using high order, high resolution techniques that are used in two dimensional aero- acoustic analysis. OpenMP parallel processing method was used. For the numerical result, the periodic characteristic of Strouhal Number due to vortex shedding was comparatively analyzed with other experiment values and two dimensional numerical results.

• The Journal of the Acoustical Society of Korea
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• v.19 no.1
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• pp.48-53
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• 2000

To analyze a room reverberation, many objective parameters have been suggested as measures of subjective perception in concert hall acoustics. However, it is difficult to understand the relationship among the individual parameters and to have a whole image of them. In this paper five primary objective parameters were selected and a reverberation model based on them was established by the reverberation decay curve. The proposed model was interpreted geometrically in terms of subjective characteristics. And finally we discuss the usefulness and the limitation of the model when it is applied to the analysis and.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.673-678
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• 2014

In a compressor, highly impulsive pressure fluctuations induced by a reciprocating piston and valves cause noise and vibration to be so critical issues that low noise requirement always challenges engineers developing it. A muffler is frequently used for reducing these impulsive noise components, but has adverse effects on compressor's performance due to additional pressure drop and heat transfer of refrigerant when it pass through the muffler. In this study, compressible full 3-dimensional CFD simulations are performed to investigate both of flow and acoustic performances of a muffler in use for compressors. On a basis of the analysis results, a parametric study using design factors introduced to improve flow and acoustic performances of the existing muffler is carried out. Finally, improved designs are suggested to confirm the current results.

• KIEAE Journal
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• v.7 no.3
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• pp.63-70
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• 2007

It is known that early reflections, their energy and delay times after the arrival of direct sound are important factors for speech intelligibility. In this basis, acoustical parameters like D50 and C80 had been proposed and are widely used for assessing the listening condition of rooms. These parameters are focused on the fraction of the early energy to the total, regardless of the spatial characteristics of the early reflections. This means that all the early reflections, arrived in certain time boundary. from front, behind, down and upside have the same impact on speech intelligibility. From the questionable simplicity, the influence of the direction of early reflections on speech intelligibility is examined in this study. A computer simulation speech intelligibility test, conducted for 22 university students, found that the reflection of vertical direction with method of the Paired comparison also the preference of 0.746 degree was visible an increase.

• The Journal of the Acoustical Society of Korea
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• v.1 no.1
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• pp.19-26
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• 1982

n optimization technique is adapted to determine the stage enclosure configuration preferred by performers. The merit function which quantifies the ease of ensemble among the performers is derived from a set of qualitative conditions recommended by researchers of hall acoustics. The ray path tracing technique based on the modified method of images is used to analyze acoustical characteristics at any locations of performers in stage enclosure. The gradient search technique is employed to find the geometric parameters which maximmize the merit function. As an example, optimum stage enclosure configuration of the trio chamber music is obtained using the computer program developed. The developed technique can be used in the design of concert hall stage and also in forming a special enclosure with movable reflecting surfaces.

• International Journal of Railway
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• v.4 no.1
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• pp.19-27
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• 2011

Many studies for improving the railway vehicle's performance and comfort such as speed, weight and noise are currently in progress. Improving the structural characteristics of the vehicle for greater noise insulation is considered important for reducing disturbance due to noise, but measuring transmission loss entails large costs. This study explores an alternative method for estimating and measuring the railway vehicle's transmission loss that involves on applying the numerical analysis coupled with scaled reverberation chamber measurement. The transmission loss measurement using scaled reverberation chamber was performed after the compensation value was found through 1mm thickness(1t) specimen. For numerical analysis, a commercially available acoustics solver VA ONE was used. The proposed method is found to lead to transmission loss measurement comparable to the measurements based on large-scale reverberation chamber. Thus, it can be argued that a reliable method has been developed for measuring railway vehicle's transmission loss.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.824-833
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• 1991

본 연구에서는 차체구조계의 진동모드 변수와 차실음향계의 음향모드변수들이 어떻게 관련되어 차실소음을 결정하는 가를 밝혔다. 그 결과, 수치해석 결과의 효용 성을 높이고 실내소음 평가방법을 체계화 시킬 수 있었으며, 효과적인 소음저감을 위 한 유용한 자료를 얻을 수가 있었다. 한편, 이제까지의 차실소음의 응답해석에서 가 장 큰 오차의 발생요인은 차체의 구조진동 모드데이타인데, 본 연구에서는 유한요소해 석 대신 모드시험 결과를 이용함으써, 유한요소 모델리이 어려운 경우의 소음 해석의 신뢰도를 높일수가 있었다.