Abstract: Raindrops produce sound underwater by two known mechanisms: a relatively low energy impact sound and a much stronger bubble sound when a bubble is trapped during the drop splash. Although the bubble sound dominates when it occurs, in other circumstances the impact sound is important. The impact sound has been studied in the laboratory using single drops falling at terminal velocity and with numerical simulation. In both instances, it is convenient to monitor the pressure field in the immediate vicinity of the drop impact. This 'near-field' pressure contains acoustic and nonacoustic components. The acoustic components include an impulsive acoustic water hammer and internal resonances of the water drop itself. The nonacoustic component of the pressure field is part of the hydrodynamic establishment of the splash flow and should not be interpreted as acoustic energy. The two components have been separated in order to identify the far-field acoustic propagation.
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