Douglas M. Photiadis
Naval Res. Lab., Washington, DC 20375-5350
The presence of internal structure can greatly alter the acoustic behavior of elastic structures. Even in relatively simple systems, it is necessary to employ approximate models, effectively averaging out unwanted detail. Some phenomenological aspects can be easily obtained in this way provided the ``base'' structure is not too complicated. For example, the locus of peaks in the scattering cross section as a function of frequency and angle can often be predicted in a deterministic manner, but estimating the actual scattering levels requires more sophisticated modeling. One approach to this modeling problem is to employ a ``fuzzy'' structures paradigm in which a Neumann series involving the random aspects of the internal structure is averaged. A more sophisticated approach involves directly constructing and approximating equations for the desired averages; employing the Dyson and Bethe-Salpeter equations of random media theory. These techniques have been applied to predict the scattering cross section from an irregular ribbed structure. The results will be discussed and compared.