| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系碩博士班 === 92 === The bubble formation and underwater sound produced by a single water drop impacting on the saline water was investigated experimentally in this study. A CCD camera was set up to photograph the drop impact and the process of bubble formation. Underwater sound was received using a hydrophone connected to a charge amplifier and a data-acquisition system for capturing the main characteristics of the sound. The time-series of the underwater sound was transformed into the time-frequency domain using the Gabor transform. The damping constants were then determined from the measured bubble sound. The experimental results show that bubble types generated by the water drops impacting on the saline water are similar to those of the fresh water. There are three main types of bubble formation. When the salinity of the saline water is small, the experimental damping coefficients are in good agreement with the theoretical values. However, as the salinity of the saline water is increased to be that of the seawater, the deviation between the theoretical and experimental damping constants becomes apparent. This is due to that in the saline water the initial shape of the bubble is non-spherical. The associated shape oscillation of the bubble induces extra energy loss. If the damping constant due to the shape oscillation is included, then the experimental damping constants compare favorable with the theoretical values.
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