• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.109-114
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• 2004

Measurement of noise is not only to know the information of acoustic pressure but to assess human response for noise. Provided that want to find human response for transportation noise, we will have to reproduce the measured noise. The method of reproduction is largely divided into monaural and binaural reproduction techniques. Human fundamentally hears sound through both ears, which is binaural hearing. And binaural technique includes the more information of physical phenomena like acoustical reflection and deflection. So, binaural reproduction is more suitable for assessment of the psychoacoustical and physiological response for transportation noise exposures.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.200-207
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• 1999

The purpose of this research is to setup the design procedure of low noise rolling stocks. Noise sources are identified at a field test, and the contribution of noise sources to each part of car interior is ensured by sound intensity measurement technique. Added material to each section of the carbody makes it possible to identify absorption or reflection performance of each part to the anterior random noise. Such experimental tests to the exterior noise intruding through the floor represent that the best countermeasure on the floor is to implement reflecting material which can properly interfere noise. Design procedure of low noise rolling stocks is set through several experiments.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.1
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• pp.101-108
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• 2019

In this study, the hole-cavity resonance technology and the micro pore stainless chip sintering technology were fused to develop silencers with excellent noise attenuation performance even at fluid pressures exceeding 30 bar for the first time at home and abroad. As a result of this study, the noise attenuation performance was greatly improved as reflection, loss, and resonance were made to occur thousands of times simultaneously when fluids pass through the sintered micro pore stainless steel chip sound absorber. The noise of the gas emitted from the bomb without the silencer was shown to be 125dB. And noise test conducted after installation of the silencer showed the noise of 67dB. Given the study results, the amount of noise was greatly reduced in the sintered silencer.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.513-518
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• 2017

Groundroll is a coherent noise showing dispersive behavior in land seismic-reflection records and its rejection has been a stubborn problem in data processing because they severely degrade the continuities and resolution of reflection signals. Conventional processing schemes of attenuating noises are the kind of frequency filtering (i.e., bandpass and f-k) that uses the Fourier transform (FT) along the entire trace in the time domain. To suppress them in this study, 1D wavelet filtering (WT) that can control time-varying frequency properties is tested and performed in the land-based synthetic and field seismic data. The results are compared to the ones from conventional filtering techniques in terms of continuities and resolution of reflection events. This filtering technique enhanced the reflection events by effectively eliminating the dispersive groundroll and random noises with control of time-scale function on wavelet domain.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.6 s.99
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• pp.738-748
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• 2005

The ship radiated noise level fluctuates by the difference of interference and reverberation according to measurement methods and environmental conditions. These phenomena cause error of the source level estimation even in the same environment conditions. This paper describes a quantitative analysis and a reduction method for an error value to the source level estimation in spatial and temporal interference environment. The design criteria of the radiated noise measurement array composed of omni-directional hydrophones and the source level accuracy in the deep water range are given. The source level accuracy in the shallow water range is also derived based on the statistical model of the multiple reflection paths. The results are verified using the water tank experiment and the sea trial.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.1203-1209
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• 2001

Identification of noise sources, their locations and strengths, have been taken great attention. The method that can identify noise sources normally assumes that noise sources are located at a free field. However, the sound in a reverberant field consists of that coming directly from the source plus sound reflected or scattered by the walls or objects in the field. In contrast to the exterior sound field, reflections are added to sound field. Therefore, we have to consider the reverberation effect on the source identification method. The main objective of this paper is to identify noise source in the reverberant field. At fist, we try to identify noise sources in a rigid wall enclosure using the spherical beamforming method. In many case of practical interest, the wall has an admittance so that complex reflection process occurred. In this paper, we assumed the complex reverberant field in the enclosure to be the sum of plane waves with random incidence and magnitude. Then the effects of reverberant field at interior source identification have been studied theoretically as well as experimentally

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.338.2-338
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• 2002

Passengers in automobile or train are exposed to a worse noise environment when they are in the tunnel than in the open field. This is due to a relatively higher space density of sound energy by multiple reflection phenomenon of noise generated by operation of transportaton vehicles from tunnel wall compared to open field. In this study, noise characteristics of subway train running through a tunnel were investigated at straight/cruved track and tunnel type(semi circula/box). (omitted)

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.438-443
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• 2007

In the recent railway construction, the concrete slab track is highlighted as the maintenance-free track and the main stream is moving from ballasted track to concrete slab track. However, in spite of many merits of concrete slab track, the higher noise generated from the concrete slab track is a troublesome question to solve and, by this reason, many studies on noise reduction of concrete slab track are carried out. The railway noise can be classified into the reflection noise emitted from wheel/rail contact and the structure-borne noise transmitted through railway structures. In this presentation, we would like to introduce an example of the successful reduction of structure-borne noise at track retrofitting to maintenance-free concrete slab track in elevated Changdong Station which was built with ballasted track on Rahmen structure.

• Journal of KSNVE
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• v.4 no.2
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• pp.187-198
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• 1994

This study is to describe the effects of the duct termination conditions conditions upon the active noise attenuation system. The adaptive filtering algorithm using FIR filter is implemented for duct noise attenuation. To avoid the instability caused by the acoustic feedback, two methods are considered. One is to use a compensating FIR filter. The other is to utilize uni-directional detecting microphone and uni-directional control speaker. Experimental results show that the reflections of sound from duct terminations greatly reduce the performance of ANC system. The directionality of detecting microphone and control speaker is a major factor to decide ANC performance. When there are some reflections from both duct terminations, the noise attenuation using finite FIR filter is not enough to model the duct plant. Especially, the reflection from the upstream termination reduces the noise attenuation in the frequencies related to the distance between control speaker and upstream termination. The performance of the noise attenuation is found to be largely enhanced by using uni-directional coupler, both on detecting microphone and control speaker, even if the duct system has an arbitrary termination conditions.

• International Journal of Highway Engineering
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• v.17 no.5
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• pp.19-24
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• 2015

PURPOSES : The noise, which is typically generated by fast moving vehicles, can be intercepted by installing a noise barrier with a soundproof panel. However, reflections from the panels cause secondary noise, and hence lower the effectiveness of the panels. In this study, the reduction of reflection noise by considering the shape, especially zigzag one, of the soundproof panel have been evaluated. METHODS : The simulation model used in this study was Nord2000, which simulates real-road situations effectively. Based on the simulation results, the joining angle of $133^{\circ}$ with the pattern width (a) equal to 2 m and the projection height (b) equal to 0.5 m was adapted in the zigzag shape as the best profit designing factors. RESULTS: The measuring results at middle height, 15 m showed reduction at all points except the point with average -1.6 dB. At a greater height of 30 m, 2 points showed reduction. A real-sized facility was constructed to investigate the reflected sound from a zigzag shaped panel up to the height of 5 m. CONCLUSIONS: The reduction effects were detected in all the receive points in the range of 2-6 m distances and 1-5 m heights comparing the plane panel. Compared to plane panel, the noises are reduced at an average of 2.4 dBA.