Oscillating microbubbles created by water drops falling on fresh and salt water : amplitude, damping and the effects of temperature and salinity.
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Authors
Scofield, Christopher D.
Subjects
Advisors
Medwin, Herman
Nystuen, Jeffrey A.
Date of Issue
1992-06
Date
Publisher
Monterey, California. Naval Postgraduate School
Language
en_US
Abstract
Recent studies of underwater sound produced by raindrops
have identified trapped bubbles as the principle sound source.
Two mechanisms have been described, one for small drops (Type
I) and one for large drops (Type II). A study of sound
produced by large raindrops (Jacobus, 1991) showed that the
underwater sound radiated by the raindrops is 45 % less in
salt water (salinity, 35 ppt) than in fresh water. The same
studies also showed that bubbles radiate more energy as the
magnitude of the temperature difference between the drop and
surface increases. These findings are examined in more detail using the
pressure decay curve of both large and small raindrops. Using
small raindrops it is shown that bubbles in salt water have a
larger damping constant and smaller initial peak pressures
than bubbles in fresh water. Reviewing data from Jacobus
(1991) for large raindrops, increasing the absolute
temperature difference between the drop and bubble showed
little effect on the damping constant, but did increase peak
pressure. Since the sound energy radiated by a bubble is
directly proportional to the peak pressure squared and
inversely proportional to the damping constant, the energy
radiated by bubbles from raindrops increases with absolute temperature difference and decreases with salinity.
Type
Thesis
Description
Series/Report No
Department
Engineering Acoustics
Organization
Naval Postgraduate School
Identifiers
NPS Report Number
Sponsors
Funder
Format
64 p.;28 cm.
Citation
Distribution Statement
Approved for public release; distribution is unlimited.