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

Y. F. Hwang

Carderock Div., Naval Surface Warfare Ctr., Bethesda, MD 20084-5000

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.]