• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.888-891
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• 2001

Effects of backing conditions on the impedance tube measurement are investigated experimentally, by using several pairs of generally employed end conditions. The results show that the measured values are similar for most of pairs, except the case of using an open pipe condition. In addition, the random error is investigated in the viewpoint of the variation of test conditions. The multi-termination method is suggested for minimizing such a random error.

• The Journal of the Acoustical Society of Korea
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• v.37 no.4
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• pp.223-231
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• 2018

Recently, due to various environmental problems, blast tracks in tunnel are replaced with concrete tracks, but they have more adverse effects on noise than blast tracks so that additional noise measures are needed. Among these measures, sound-absorbing blocks start to be used due to its easy and quick installation. However, the performance of sound absorption blocks need to be verified under real environmental and operational conditions. In this paper, interior noise levels in KTX train cruising in Dalseong tunnel are measured before and after the installation of sound-absorbing blocks and the measured data are analyzed and compared. Additionally, noise reduction are estimated by modeling the high speed train, the tunnel and absorption blocks. Measurement devices and methods are used according to ISO 3381 and the equivalent sound pressure levels during the cruising time inside the tunnel are computed. In addition to overall SPLs(Sound Pressure Levels), 1/3-octave-band levels are also analyzed to account for the frequency characteristics of sound absorption and equipment noise in a cabin. In addition, to consider the effects of train cruising speeds and environmental conditions on the measurements, the measured data are corrected by using those measured during the train-passing through the tunnels located before and behind the Dalseong tunnel. Analysis of measured results showed that the maximum noise reduction of 6.8 dB (A) can be achieved for the local region where the sound-absorbing blocks are installed. Finally, through the comparison of predicted 1/3-octave band SPLs for the KTX interior noise with the measurements, the understanding of noise reduction mechanism due to sound-absorbing blocks is enhanced.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.1-9
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• 2017

In this study, a test-bed system simulated a tunnel and concrete track is tested on cite and invested an allowed limit of multi-layered sound absorbing panel for reducing noise reflected on the concrete track in train tunnel considering the criteria and limitation on the theoretical back ground. The studied results are an effective evaluating system of the sound absorbing coefficient influenced fluid effects depending on the vehicle speed in the urban train tunnel and measuring not only structural behaviors of maximum displacement and acceleration of the panel but also dynamic characteristics of damping ratio and natural frequency.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.198.2-198.2
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• 2007

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.265-272
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• 1998

In this paper, the intoner noise reduction for subway railroad vehicles was studied by improving transmission loss of carbody panels and side doors, and on-line tests were conducted to examine the exterior noise levels at various running conditions. Also the transmission loss for design candidates of the carbody specimen was measured in two reverberation rooms. From the results of the tests, side door gap is the most dominant factor affecting the Interior noise level of subway railroad cars with a sliding typed side door. The next one is revealed to transmission loss of a floor panel. To improve the transmission loss of the carbody, many activities were conducted such as, treatment of resilient and sound-absorbing materials and reducing the gap of the side door by adopting a brush and rubber, etc. The estimated interior noise level for modified car which is designed with improved carbody panels is lower than original car by about 5㏈.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1109-1113
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• 2001

Interior parts of a vehicle are getting important to reduce interior noise of car. Therefore, prior analysis of cabin noise related with interior parts are necessary at first design stage. Recently, Statistical Energy Analysis(SEA) has been suggested as a possible way for meddle of high frequency range analysis with interior parts. This article introduces an example of the application of SEA to predict air born noise of cabin of car.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.1
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• pp.75-82
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• 2016

As spreading of train concrete ballast leads to the increase resounding friction noise, an porous sound absorbing block is applied in urban train tunnel as a counterparts against the friction noise. Three steps of major variables tests for an optimal mix design of the block are conducted to pursue the light weight of the block. Pilot property tests of the block for the cases of the fly-ash only as lightweight aggregates are carried satisfying KRT(Korean Rail Transit) and new KRS(Korean Railway Standards). Based on the results of pilot tests, required structural strength and admixture effects are evaluated. Additionally, typical lightweight aggregates are replaced so that lightweight and strength are improved for serviceability of poor working conditions and proper maintenance in urban train tunnel.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.139-147
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• 2017

Acoustic performance of splitter silencers was investigated by using 3-dimensional commercial software and experiments. Flow resistivity of sound absorbing material was indirectly estimated by using an impedance tube setup and a curve fitting method. In addition the acoustic impedance of perforated plate was determined by an empirical formulation. Such properties have been used as input parameters in the commercial software. The prediction for a splitter silencer with 1000 mm length was compared with the experimental result. The numerical method is then applied to identify the effects of number of splitters, length of splitters, absorptive material density, and porosity of a perforated plate on the performance of the splitter silencers. As the number and length of splitter increases, the acoustic performance significantly increases. Although the increase of density of absorptive material also increase the acoustic performance, a change in the density over a certain level hardly affect it. The increase of porosity will enhance the performance especially at higher frequencies.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.163-167
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• 2009

In this study, the acoustic properties of ceramic sound absorbing materials with different thickness and bulk density were investigated in terms of characteristic impedance, propagation constant, and absorption coefficient. The well-known two-cavity method was used for evaluating those acoustic parameter values. Also, in order to validate the experimentally measured values, the results were compared with the results obtained from Chung and Blaser's transfer function method and SWR method. The experimentally measured values of normal absorption coefficients were generally agreed well with the corresponding values from the transfer function method and the SWR method. Based on the experimental results, the following conclusions could be made. The magnitude of the absorption coefficient and the frequency range of the maximum absorption coefficient were controllable by changing the thickness and bulk density of the sound absorbing materials.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.8
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• pp.741-751
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• 2011

Vibrations caused by automobile engine are absorbed mostly by a passive-type engine mount. However, user specifications for automobile vibrations require more stringent conditions and higher standard. Hence, active-type engine mounts have been developed to cope with such specifications. In this study, the active vibration absorber which can be attached to the sub-frame of automobile is used for the suppression of vibrations caused by engine. The active vibration absorbing system consists of sensor, actuator and controller where a control algorithm is implemented using DSP. The vibration caused by engine reveals harmonic disturbances varying with engine revolution. Therefore, the control algorithm should be able to cope with harmonic disturbances. In this study, the modified higher harmonic control technique which can selectively suppress harmonic disturbance is considered. Experimental results on automobile show that the proposed active vibration absorbing system is effective in suppressing vibrations caused by engine.