### ASA 127th Meeting M.I.T. 1994 June 6-10

## 1aSA14. Acoustic scattering from doubly reinforced elastic plates.

**Angela K. Karali
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*Dept. of Eng., Penn State Univ., 147 Shenango Ave., Sharon, PA 16146
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**Sabih I. Hayek
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*Penn State Univ., University Park, PA 16802
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Almost all known structures are designed for low weight and high strength.
For metal structures and especially aircrafts and underwater vehicles this
means reinforcements in the form of ribs. This paper presents the development
of analytic models that can be used in predicting the acoustic scattered field
from such structures, assuming that the geometry is that of an elastic plate of
infinite dimensions reinforced with a periodic double array of ribs. The plate
is in contact with a homogeneous and isotropic acoustic fluid on one side only.
Mindlin's plate theory is used in modeling the plate and this allows the
evaluation of the nonspecular scattered field, generated at the reinforcements,
at frequencies below and above the coincidence frequency of the plate. The
reinforcements are assumed to exert both forces and moments on the plate and
they are included in the mathematical model through their transverse and
rotational impedances. A Fourier transform technique is used to evaluate the
nonspecularly reflected field due to the periodic double array of ribs.
Analytic solutions are obtained and implemented numerically for frequencies
ranging from 1 to 15 times the classical coincidence frequency of the plate.