### ASA 124th Meeting New Orleans 1992 October

## 4pSA6. Nonlinear panel response and acoustic radiation from plane-wave
excitation.

**A. Frendi
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*Analytical Services and Materials, Inc.
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**L. Maestrello
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*NASA-Langley Res. Ctr., M.S. 463, Hampton, VA 23665-5225
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**A. Bayliss
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*Northwestern Univ.
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The generation and propagation of nonlinear sound waves radiated from a
flexible panel excited by an acoustic source at a near resonant frequency were
considered. The panel response is coupled to the radiation field of the
surrounding fluid in a fully consistent manner. For each time step, the panel
response is calculated by solving the nonlinear plate equation with the
pressure difference across the panel as a source term. The pressure near the
panel is computed by solving the nonlinear Euler equations with a boundary
condition on the normal velocity obtained from the plate equation. The Euler
equations also yield the near- and far-field radiation due to the panel
vibration. The results show that nonlinearity tends to arise by formation of
subharmonics as the amplitude of the excitation increases. There are small
windows of excitation amplitude for which apparently chaotic behavior is
obtained. The far-field directivity pattern is highly directional with a marked
reduction in acoustic energy emitted normal to the pattern. The relative
high-frequency content of the radiated pressure increases as the far field is
approached. As the amplitude of excitation is increased, the effect of the
coupling to the acoustic fluid is to delay the development of nonlinearities on
the structure.