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

## 3pSAa6. Higher-order mode acoustic radiation from fluid-loaded,
multi-layer composite plate.

**M. Kim
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Y. F. Hwang
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*Carderock Div., Naval Surface Warfare Ctr., Bethesda, MD 20084-5000
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One of the outstanding features of the composite plate is that one can
reduce the longitudinal wave (the first symmetrical mode) speed significantly
at higher frequencies by intelligently arranging the various layers of elastic
and viscoelastic materials. In such cases, however, the higher-order modes
shift to a lower frequency region as compared to those of a single-layer
elastic plate. Consequently, those higher-order modes may now become
susceptible to an excitation band. An exact mathematical formalism was
developed to calculate the acoustic radiation of a fluid-loaded, multi-layer
composite plate subjected to a harmonic excitation. The formal solution is
developed using the classical integral transform technique incorporated with
the multilayer elasticity theory. The formalism was validated with the solution
of a fluid-loaded, infinite, single-layer elastic plate. Numerical results are
then presented for the far-field directivity pressure pattern of various plate
configurations subjected to normal- and tangential-line forces. The pressure
pattern and in-vacuo dispersion curve of the plate are used to explain
radiating mechanisms and evaluate the acoustic significance of the higher-order
modes. In addition, the effects of fluid-loading and damping on higher-order
supersonic waves are also discussed. [Work supported by ONR.]