• The Journal of the Acoustical Society of Korea
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• v.27 no.1
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• pp.33-39
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• 2008

Void fraction of air bubble in the seagrass bed by photosynthesis was estimated with sound speed dispersion. A field experiment was conducted at Seagrasss bed of which bottom type is sandy mud and 120 kHz CW waveform was transmitted to obtain backscattered signals from seagrass bed. The differences of the arrival time of received signal from seagrass bed were observed between day and night. The diurnal variation of arrival time was caused by sound speed dispersion of air bubble generated by photosynthesis of seagrass.

• The Journal of the Acoustical Society of Korea
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• v.27 no.3E
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• pp.69-76
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• 2008

Measurements of bubble size and distribution in the surface layer of the sea, wind speed, and variation of ocean environments were made continually over a four-day period in an experiment conducted in the South Sea of Korea during 17-20 September 2007. Theoretical background of bubble population model indicates that bubble population is a function of the depth, range and wind speed and bubble effects on sound speed shows that sound speed varies with frequency. Observational evidence exhibited that the middle size bubble population fit the model very well, however, smaller ones can not follow the model probably due to their short lifetime. Meanwhile, there is also a hysteresis effect of void fraction. Observational evidence also indicates that strong changes in sound speed are produced by the presence of swarms of micro bubbles especially from 7 kHz to 50 kHz, and calculation results are consistent with the measured data in the high frequency band, but inconsistent in the low frequency band. Based on the measurements of the sound speed and high frequency transmission configuration in the bubble layer, we present an estimation of underwater acoustic channel capacity in the bubble layer.

• Journal of Institute of Convergence Technology
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• v.1 no.2
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• pp.25-28
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• 2011

Void fraction has been measured for the gas-liquid cocurrent slug flow in 8mm vertical acrylic tube using an optical method. Bubble speed, length and period could be measured with the two sets of laser-infrared sensor modules mounted 25mm apart alongside the tube, which were designed to detect variation of light intensities with a time delay when two parallel laser beams were refracted successively by a passing bubble. It was found that the results were in good agreement with the previous studies in the literature suggesting that the method used in this study were sound and accurate.

• Journal of computational fluids engineering
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• v.19 no.3
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• pp.91-97
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• 2014

A high resolution numerical method aimed at solving cavitating flow was proposed and applied to gas-liquid two-phase shock tube problem with arbitrary void fraction. The present method with compressibility effects employs a finite-difference 4th-order Runge-Kutta method and Roe's flux difference splitting approximation with the MUSCL TVD scheme. The Jacobian matrix from the inviscid flux of constitute equation is diagonalized analytically and the speed of sound for the two-phase media is derived by eigenvalues. So that the present method is appropriate for the extension of high order upwind schemes based on the characteristic theory. By this method, a Riemann problem for Euler equations of one dimensional shock tube was computed. Numerical results of high speed flow phenomena such as detailed observations of shock and expansion wave propagations through the gas-liquid two-phase media and some data related to computational efficiency are made. Comparisons of predicted results and solutions at isothermal condition are provided and discussed.