On fluid-structure interactions of a cloaked submerged spherical shell
Abstract
Backscattering from a cloaked submerged spherical shell is analyzed
in the low, mid, and high frequency regimes. Complex poles of the scattered
pressure amplitudes using Cauchy residue theory are evaluated in
an effort to explain dominant features of the scattered pressure and how
they are affected by the introduction of a cloak. The methodology used
is similar to that performed by Sammelmann and Hackman in a series of
papers written on scattering from an uncloaked spherical shell in the
early 1990s. In general, it is found that cloaking has the effect of diminishing
the amplitude and shifting tonal backscatter responses. Extreme
changes of normal and tangential fluid phase velocities at the fluid-solid
interface when cloaking is employed leads to elimination of the "mid-frequency
enhancement" near the coincidence frequency for even
modestly effective cloaks, while reduction of the "high-frequency
enhancement" resulting from the "thickness quasi-resonance" near the
cutoff frequency of the symmetric (SB 2) mode require more effective
cloaking, but can be practically eliminated by employing a cloak that
creates tangential acoustic velocities in excess of the SB 2 mode phase
speed near cutoff.
Rights
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