### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 5pSA8. Prediction of scattering cross sections using averaged models.

**Douglas M. Photiadis
**

**
David Hughes
**

**
**
*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.