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ensure accuracy. Twenty-First Symposium on NAVAL HYDRODYNAMICS
The second term under the integral sign is due to pressure
fluctuations which may be caused by flow or structural
vibrations. Dimensional analysis yields: This dependence on the
sixth power of the flow is characteristic of dipoles on a
compact scale. However, even at the low Mach numbers prevailing
in underwater acoustics, sources are not always compact and
consequently a different speed dependence will apply. Generally,
the flow is not affected by structural vibrations since the
amplitudes are much smaller than the characteristic length
scales of the fluid. An exception is the well-known phenomenon
of propeller “singing” where blade vibrations tend to increase
the coherence of a periodically shed vortex wake which, in turn,
feeds more energy into the structure. At mo