• Journal of KSNVE
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• v.7 no.5
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• pp.797-801
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• 1997

This paper raises issues in testing the absorption coefficients of sound-absorptive samples using the standing wave apparatus according to the Korean standard of KS F 2814. The standard code does not consider any effect of air-damping which is significant in testing relatively low sound-absorptive samples. This limitation has been shown to yield much variation of sound absorption coefficients for recent samples tests whose coefficients are less than 10%. An improved method of calculating the sound absorption coefficients is proposed in this work and its effectiveness in real test is also illustrated. Finally, the guideline for the modification of our national standard code KS F 2814 is proposed.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.135-139
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• 2002

In this study, the experimental open-tube and close-tube thermoacoustic apparatuses were built. In order to determine the optimum length of resonant tube and the optimum length of stack, the resonant characteristics of thermoacoustic apparatuses were investigated, The length of resonant tube varies from 400mm to 850mm. The experimental frequency varies from 100Hz to 1000Hz. In case of the second and third harmonics, the maximum temperature difference of open-tube thermoacoustic apparatus is 53$^{\circ}C$ (resonator length: 400mm) and the maximum temperature difference of closed-tube thermoacoustic apparatus is 51$^{\circ}C$ (resonator length: 500mm). In the open-tube thermoacoustic apparatus, the peak efficiency point is about 2%, 55%, 69% in the resonant tube and in the closed-tube thermoacoustic apparatus, the peak efficiency point is about 2%, 41%, 50% in the resonant tube.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.617-624
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• 2011

The two-dimensional sloshing problem in a rigid rectangular tank with a free surface is considered. The flow is generated by a container in harmonic motion in time along the horizontal axis, i.e., a container excited by u=Asin($2{\pi}ft$) where u denotes the container velocity imposed externally, A is the amplitude of the oscillation velocity, and f is the frequency of oscillation. Experimental apparatus is arranged to investigate the large-amplitude sloshing flows in off-resonant conditions, where the large amplitude means that A~O(1), and the distance, S, is comparable to the breadth, L, of the container, i.e., L/S~O(1). Comprehensive particle image velocimetry (PIV) data are obtained, which show that the flow physics of the nonlinear off-resonant sloshing problem can be characterized into three peculiar free surface motions: standing-wave motions similar to those of linear sloshing, a run-up phenomenon along the vertical sidewall at the moment of turn-over of the container, and gradually propagating bore motion from the sidewall to the interior fluid region, like a hydraulic jump.