• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.282-287
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• 2001

The test facility has been manufactured to predict the dynamic insertion loss and the pressure drop for ducted silencers based on ISO 7235. The qualification test of the test facility is necessary for determining the dynamic insertion loss and the pressure drop of the test silencer, and is surveyed the reflection coefficient for an anechoic termination, the velocity profile near the upstream connection to the test silencer, the reduction of the system silencer and the limiting insertion loss due to the flanking sound transmission along the duct walls.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.4
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• pp.232-238
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• 2012

In this study, the noise mapping simulation is executed to design an effective barrier reducing noise levels of a school site. The geographical features of the ambient site and the school buildings are modelled in detail in order to consider sound propagation, deflection, and absorption phenomena etc. The main sound source, sound power level of expressway, is estimated on the basis of measured noise levels at several points of the site. The noise mapping simulation is performed by using ENPro, environmental noise prediction program based on ISO 9613 to analysis the effectiveness of noise barrier. Consequently, the noise barrier is designed to meet an environmental noise standard and satisfy low cost and safety conditions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.606-611
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• 2000

It has been noted that the low frequency absorption coefficient of a porous sample placed in a standing wave tube is affected by the nature of the sample's edge constraint. The edge constraint has the effect of stiffening the solid phase of the sample, which itself can be strongly coupled to the material's fluid phase, and hence the incident sound field, by viscous means at low frequencies. In recent work it has also been shown that such a circumferential constraint causes the low frequency transmission loss of a layer of fibrous material to approach a finite low frequency limit that is proportional to the flow resistance of the layer and which is substantially higher than that of an unconstrained sample of the same material. However, it was also found that the benefit of the circumferential edge constraint was reduced in a transitional frequency range by a shearing resonance of the sample. Here it will be shown that the effect of that resonance can be mitigated or eliminated by adding additional axial and radial constraints running through the sample. It will also be shown that the constraint effect can be modeled closely by using a finite element procedure based on the Biot poroelastic theory. Implications for low frequency barrier design are also discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.587-593
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• 2000

The background noise and transmission loss of wall were measured on site for the multiplex cinema. The results from the simulation analysis was compared with the measurements from the site for different frequencies to review the acoustical parameters, and the analysis results in the relatively small error. Therefore, it is concluded that the reliable estimation can be made once accurate data such as sound source and sound absorption coefficient of interior material is utilized during the simulation process. However, the calibration is necessary for the test room with the small room volume.

• Journal of KSNVE
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• v.9 no.6
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• pp.1218-1226
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• 1999

In this paper, the extended Biot's semilinear model was developed. Combining the extended Biot model with the dynamic equation yields the nonlinear wave equation in poproelastic sound absorbing materials. Both perturbation and matching techniques are used to find solutions for nonlinear wave equations. By comparing results between linear and nonlinear wave solutions, characteristics of nonlinear waves in poroelastic sound abosrbing materials have been studied. Nonlinear waves were found to be attenuated faster than the linear ones. A maximum amplitude of the nonlinear wave occurred near its surface boundaries and decay quickly with distance from the surface. It has also been found that, if the amplitudes of linear waves are known at the surface boundaries, those of nonlinear ones can be determined. This will be the basis of finding effects of nonlinearity on the absorption coefficient and the transmission loss.

• Computers and Concrete
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• v.33 no.5
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• pp.621-630
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• 2024

This study presents novel electromagnetic wave-based methods for evaluating the integrity of cement-based structures using time domain reflectometry (TDR). Two cement-based plates with embedded rebars are prepared under sound and defective conditions. TDR tests are carried out using transmission lines with various numbers of artificial joints, and electromagnetic waves are measured to assess the integrity of the plates. The experimental results show that the travel time of electromagnetic waves is consistently longer in sound plates than in defective ones, and an increase in the reflection coefficients is observed in the defect zone of the defective plates. Electromagnetic wave velocities are higher in the defective plates, especially when connectors are present in the transmission line. A novel approach based on the area of the reflection coefficient provides larger areas in the defective plates, and the attenuation effect of the electromagnetic waves induces a difference in the areas of the reflection coefficient between the two defect conditions. An alternative method using the centroid of the defect zone slightly overestimates the location of the defect zone. The length of the defect zone is estimated using the defect ratio and wave velocities of cement, air, and plate. The length of the defect zone can also be calculated using the travel times within the plate, total measured length of the plate, and wave velocities in the cement and air. Therefore, the electromagnetic wave-based methods proposed in this study may be useful for estimating the location and length of defect zones by considering attenuation effects.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.500-505
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• 2005

This paper introduces an experimental study for the noise characteristics and reduction of a ventilating fan system. For the purpose of noise reduction of it, an absorptive duct silencer filled with a glass fiber has been conventionally utilized. However, a glass fiber has some disadvantages like hygiene and secondary pollution problems. In order to overcome these problems, in this paper, a perforated duct silencer has been applied to the ventilating fan system. For the designing of a perforated duct silencer, the transmission losses for various perforated panel systems are measured and compared with their sound absorption performances.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.3
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• pp.161-169
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• 1999

In order to investigate the validity of acoustic tomography for current measurement, an experiment of reciprocal sound transmission was conducted in April, 1997 in the southern water of Koje island. This experiment was attempted as a preliminary field study on coastal ocean acoustic tomography for construction of real-time current observation system. Examining the physical oceanography environments, the current data obtained by travel time difference of reciprocal sound wave was compared with the data of Acoustic Doppler Current Profiler (ADCP). The result shows the correlation coefficient of 0.943, very good relation between the two data, and therefore the ocean acoustic tomography could be a useful method for current measurement in the coastal area.

• The Journal of the Acoustical Society of Korea
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• v.27 no.2
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• pp.92-101
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• 2008

To dissolve the multi-layered model problems, and to complement 2-layered model's simplicity, assumed fluid-fluid-solid 3-layered model. Generally it is known that if the sediment thickness is more than 10 wavelength, the half space's influence to the in-water acoustic field could be disregarded. By tracking the maximum correlation coefficient of calculated results and experimental ones we confirmed that the requirement could be more realized. To calculate the maximum correlation coefficient we used single sensor transmission loss. On the assumption that the sediment sound velocity was 1813 m/s and frequency range 50 kHz to 120 kHz, the conversion condition was from 2.5 to 7.7 wavelength.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.372-375
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• 2006

건설 공사장에서 발생하는 건설장비의 소음을 저감하여 공사장 인근 지역의 생활환경에 미치는 소음영향을 최소화할 수 있도록 건설업체에서는 최대한의 노력으로 가설방음벽을 설치 운영하고 있으나, 설치된 가설방음벽의 효과분석 및 운영방법에 대한 검토가 부족하여 효율적인 소음저감대책으로서의 가설방음벽 운영이 어려운 실정이다. 따라서, 본 연구에서는 가설방음벽의 기초데이터의 확보와 소음해석을 통한 효율적인 운영방안을 제시하며, 설치기준에 관한 방안을 제시하고자 한다.