• Journal of KSNVE
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• v.6 no.5
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• pp.635-644
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• 1996

In this paper, Allard's modelling method which employs the method of acoustic transfer matrix(ATM) is applied to yield more precise results in the analysis of porous sound absorbing material. The method of ATM, based on Biot's theory, is known to play an important role in the estimation of the sound absorption when a sound projects onto the material. In the case of a single layered porous sound absorbing material, the surface impedance and the absorption coefficient by using the method of ATM are estimated. With the variation of the material properties, sound absorption characteristics and analyzed. Transmission Loss in a combination of the porous sound absorbing material with a thin plate is predicted.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.182-186
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• 2000

The porous woven hose is recently considered as an effective element of automotive intake systems. In order to predict the acoustic performance of an intake system with a porous woven hose, the information on the acoustic wall impedance is required. In this article, a measurement technique that is valid over the low frequency range and without mean flow condition is presented. The measurement is performed in a cylindrical chamber with a concentric layout of the sample and the resistance is estimated from measured reactance and transmission loss data. It is observed that the measured transmission loss for a porous woven hose with an arbitrary length agrees well with the predicted one that uses the estimated impedance for a small sample length.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.795-800
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• 2008

The sound transmission loss is a key index to evaluate the acoustic performance of a car-body structure at the high frequency range. From this paper, a new validation method for in-situ sound transmission loss is proposed. First, in-situ sound transmission loss is measured by using PU intensity probe on the condition of complete vehicle. Second, validation test, which is consisted of internal, external and total frequency response function test, is performed by using volume acceleration source and microphones. Then, these test results are compared to validate the accuracy of in-situ sound transmission loss. Finally, the test result of in-site method is compared with results of two reverberant room test method and SEA analytical method. The reliability of in-situ method is confirmed by these procedures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.861-864
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• 2006

In general, 4-pole parameter and three-point method are used for predicting transmission loss which is one of characteristics of Muffler using CAE tools. However, these mehtods show different results from experiment when the flow effects are presented in practical model. In this parer, to overcome these problems, both Fluent and.Sysnoise are used to analyze the performance of extended inlet/outlet muffler including flow effects with varying flow velocity at inlet of duct. Flow fields and quadrupole source is calculated by Fluent. And Sysnoise is used to analyze acoustic performances of muffler with quadrupole source data extracted from Fluent. Finally, the variation of transmission loss is estimated according to various inlet flow velocity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.687-689
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• 2014

This paper deals with the optimal muffler model by using acoustic analysis and CFD(computational fluid dynamics) analysis. The complicated muffler model could be better noise reduction performance. However, it could be worse affected to back-pressure performance by pressure drop in working fluid. High back-pressure is caused to low system efficiency. Therefore, it is important for the muffler design to consider the pressure drop. The muffler models are changed their partition plate position. Acoustic power transmission loss(TL) and pressure drop of working fluid are calculated by using computational analysis and used to build database for finding their trends. The optimal muffler model in user-interested frequency range could be selected by analyzing this database.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.69-72
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• 2007

In this paper, we describe the analysis of interior noise for tilting train that is being developed in Korea. Tilting train is made of composite material to reduce the car body's weight and attached a self-steering system on bogie to improve curving performance. However, the acoustic performance (Transmission Loss) of such material is worse than the materials of conventional train, such as aluminum, steel and so on. Therefore, we measure the transmission loss of side wall / floor of tiling train and predict the interior noise for tilting train using its measuring results

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.249-256
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• 1998

Design target values of transmission loss in a high-speed train wall are suggested by calculating the difference between interior and exterior noise levels of it. Exterior noise level distribution on the boundary of train wall is calculated by Sysnoise, with sound source input prepared by experiments. Two kinds of exterior sound sources are considered, the rolling noise of train wheels on the rail and the aerodynamic noise from the pantograph. Interior noise level is provided by high-speed design target. Transmission loss characteristics according to the frequency band are examined.

• The Journal of the Acoustical Society of Korea
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• v.43 no.3
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• pp.261-269
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• 2024

In this paper, the acoustic performance of an absorptive silencer was enhanced by optimizing an arrangement of multi-layered absorbing materials. The acoustic performance of the silencer was evaluated through transmission loss, and finite element method-based numerical analysis program was employed to calculate the transmission loss. Polyurethane, a porous elastic material frequently used in absorptive silencers, was employed as the absorbing material. The Biot-Allard model was applied, assuming that air is filled inside the polyurethane. By setting the frequency range of interest up to the 2 kHz and the acoustic performance affecting properties of the absorbing materials were investigated when it was composed as a single layer. And the acoustic performance of the silencers with the single and multi-layered absorbing materials was compared with each other based on polyurethane material properties. Subsequently, the arrangement of the absorbing materials was optimized by applying the Nelder-Mead method. The results demonstrated that the average transmission loss improved compared to the single-layered absorptive silencer.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2
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• pp.62-72
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• 1995

The acoustic characteristics of perforated tube muffler are studied in terms of non-dimensional wavenumber ka and admittance-ratio AZ. This study includes not only the case of perforated tubes having uniform hole distribution along the length but also the case of having non-uniform hole distributions. The acoustic hole impedance and transmission loss of perforated tube of which has various hole distributions were measured. The experimental results demonstrated that the transmission loss of perforated tube is a function of non-dimensional wave number ka and admittance-ratio AZ. The transmission loss of perforated tube muffler is predicted by the numerical method which is based on Sullivans and compared with the experimental ones.

• The Journal of the Acoustical Society of Korea
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• v.21 no.8
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• pp.679-685
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• 2002

Low-frequency mono-static reverberation model for shallow-water environment is presented. It is necessary to develop the transmission loss model to calculate the sub-bottom interaction because the ray-based transmission loss model is difficult to compute the pressure accurately which penetrates the bottom medium. In this paper reverberation level is calculated using the RAM (Range dependent Acoustic Model) to augment the multi-path expansion model because it does not estimate transmission loss accurately in shallow water. The signals generated by the L-HYREV and the GSM are compared with the observed signals and it is showed that the L-HYREV model provides a closer fit to the observed signals than those obtained using the GSM.