Analytical Services and Materials, Inc.
NASA-Langley Res. Ctr., M.S. 463, Hampton, VA 23665-5225
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.