本研究以實驗方法探討單一水滴降落鹽水面時氣泡產生的過程及噪音之特性，並探討不同鹽度對氣泡振動阻尼的影響。實驗分為兩部分，第一部份之實驗是利用數位式高速照相機拍攝水滴降落鹽水面時氣泡形成之過程；另一部份則是以水中收音器量測水滴降落鹽水面時產生之噪音，並用Gabor transform將時域訊號轉換成時間–頻率域，得知訊號之頻率特性。此外，藉由分析噪音之訊號，可得氣泡振動之阻尼係數。實驗結果顯示水滴撞擊鹽水面產生氣泡的類型與清水的情形相似，主要有三種類型。但是氣泡在鹽水中會有分裂的現象，氣泡會由一顆分裂成兩顆或更多顆，而且其生成機制也比清水的情形複雜。當鹽水的鹽度較小時，實驗所得氣泡振動之阻尼係數與理論值相當接近。而當鹽度增加到海水的鹽度時，實驗所得氣泡振動之阻尼係數與理論值相差較大。主要原因為鹽水中氣泡的起始形狀不是球形，會因氣泡表面的形狀振動造成額外的能量損失。因此若加上形狀振動所造成的阻尼，會使得阻尼係數的理論值與實驗值較為接近。

　　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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