• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1049-1052
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• 2006

Object of this study is to develop an Stack Silencer System for quieting abnormal noise around power plant. Abnormal noise gets resident people to feel uncomfortable. Stack Silencer System is to minimize pressure loss of exhaust gas and to maximize noise reduction effect from abnormal noise frequency band. Stack Silencer System is installation in stack and absorbing material is an aluminum foam. Reduction effect measures insertion loss of $8.2{\sim}19.4dB$ by Stack silencer installation. After Stack Silencer System installation, pressure loss of exhaust gas measured $5{\sim}9mmH_2O$.

• Journal of the Korean Magnetics Society
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• v.14 no.5
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• pp.174-179
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• 2004

Attenuation of conduction noise through microstrip line attached with the high lossy iron flakes-rubber composites has been investigated in GHz frequencies. Microstrip line was designed with characteristic impedance of 50 $\Omega$ and a length corresponding to the center frequency of 3 GHz. Iron flakes were fabricated by mechanical forging of spherical iron powders using an attrition mill. The fabricated microstrip line shows a ideal propagation characteristics of S$\sub$11/ < -60 dB and S$\sub$21/ = 0 dB. Attaching a noise absorbing sheet on the microstrip line, S$\sub$11/ increases to about -10 dB and S$\sub$21/ decreases to -20～-60 dB depending on the length of absorbing sheet. The calculated power loss is as high as 80% in the frequency range 2～8 GHz. It is suggested that the most critical material parameter is magnetic loss for the enhancement of noise attenuation.

• Journal of the Korean Magnetics Society
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• v.17 no.6
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• pp.242-245
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• 2007

Conduction noise attenuation by composite sheets of high magnetic and dielectric loss has been analyzed by using electromagnetic field simulator which employs finite element method. The simulation model consists of microstrip line with planar input/output ports and noise absorbers (magnetic composite sheets containing iron flake particles as absorbent fillers). Reflection and transmission parameters $(S_{11}\;and\;S_{21})$ and power loss are calculated as a function of frequency with variation of sheet size and thickness. The simulated value is in good agreement with measured one and it is demonstrated that the proposed simulation technique can be effectively used in the design and characterization of noise absorbing materials in the RF transmission lines.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1120-1125
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• 2001

A new concept of piezoelectric smart panels for noise reduction in wide band frequencies is proposed and their possibility is experimentally investigated. Multi-mode damping is studied by using a newly proposed tuning method. The proposed panels are based on passive shunt damping methods. This method is based on electrical impedance model and maximizing the dissipated energy at the shunt circuit. four PZT are attached on smart panel for improving performance of transmission noise reduction. 0 prove the concept of piezoelectric smart panels, an acoustic measurement experiment was performed. The smart panels exhibit a good noise reduction in middle and high frequency ranges due to the mass effects of absorbing materials or/and the air gap. The use of piezoelectric smart panel renders noise reduction at resonance frequency. Noise reduction at multiple resonance frequencies is experimentally investigaed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.125-131
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• 2000

The turbo chiller uses centrifugal compressor, which operates at about 14500 rpm. Due to the high rpm of the impeller, the noise of chiller makes one of the serious problems. The possibility of the sound reduction by using absorbing material is studied in this paper. The generated sound propagates through the duct and then radiates to the outer field. So, the use of sound absorption material inside the duct is one of the effective methods. To study the effect of location of the material, we use Boundary Element Method to analyze the sound field inside the duct system. Numerical study shows the highest sound pressure region is near the elbow of curved duct. From the analysis, it is also shown that the elbow duct is the main radiator of noise and sound absorption treatment of this duct results noise reduction of the highest noise level at BPF and high frequency region.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.883-884
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• 2012

This study deals with design and application of silencer to reduce the exhaust noise, especially at the low frequency range below 200 Hz which is main contribution for the bridge wing noise and the external noise of ships. The designed silencer is composed of side branch resonator, Helmholtz resonator and absorbing material. The resonating frequencies of resonators are set to be the firing order frequencies of the generator engine. Based on the on-board measurement result, it is verified that the designed silencer can effectively reduce the exhaust noise of generator engine.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1044-1049
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• 2007

The construction of concrete slab track system is increased because the system has advantages which are maintenance free and so on, the other side, the system has weak points such as increase of the cost of the early stage construction and noise levels. The increment of noise is due to the reflection of generated noise on the slab tracks. Therefore the acoustic-absorptive materials are considered to reduce noise level. It has been made clear that acoustic-absorptive materials are effective for reducing the wheel/rail noise on slab tracks. The important performance of the acoustic-absorptive material is absorption rates and absorption rates are verified for the considered absorber elements using acoustic duct method. In addition, the required provisons for installing acoustic-absorptive block on slab tracks are considered.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.1
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• pp.33-39
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• 2003

Interior parts of a vehicle are getting important to reduce interior noise. 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 high frequency range noise analysis of interior parts. The validity of noise analysis with SEA to interior parts has been preyed by comparing with experimental result, and the developed method with SEA has been applied in finding optimized interior parts package.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.837-842
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• 2000

Reverberation time is the well known theory and widely used in commercial apparatus to get reverberation time. However large fluctuation in low frequency region occurs in a small cabin due to superposition of a few modes. This paper investigates this phenomena in terms of modal density in frequency domain and suggests a method to get lower limit of reverberation time using the integration of the time-SPL diagram. The suggestion is confirmed by simulation and shows reasonable results to get lower limit of reverberation time and maximum absorbing power in the cabin.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.681-686
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• 1997

Foamed aluminum is well known metallic porous sound absorption material which has excellent properties of light weight and high absorbing performance. For the purpose of finding out the sound field characteristics within a simple closed cubic enclosure with foamed aluminum, analytic and experimental studies are performed. For the first time, the standing wave apparatus is used to measure absorption coefficient and impedance of the foamed aluminum. Next, the sound effects of absorption material in acoustically loaded rectangular enclosure are identified according as the foamed aluminim is to be or not.