### ASA 126th Meeting Denver 1993 October 4-8

## 5aNS7. Finite element and finite difference models for the fast-field
program in outdoor sound propagation.

**Kenneth E. Gilbert
Scott D. Hansen
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*Appl. Res. Lab. and the Graduate Program in Acoust., Penn State Univ., P.
O. Box 30, State College, PA 16804
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The so-called ``fast-field program'' (FFP) has become a popular method for
predicting sound pressure levels in outdoor sound propagation. The method
requires the solution of a one-dimensional Green's function equation. The usual
approach in outdoor sound propagation has been to obtain the solution in terms
of sinusoids or special functions. Here, a simple direct method is demonstrated
that uses either finite elements or finite differences in much the same way as
does the parabolic equation method. The finite element method presented here is
adapted from a range-dependent FFP model developed for underwater acoustics [K.
E. Gilbert and R. B. Evans, in Ocean Seismo-Acoustics, edited by T. Akal and J.
M. Berkson (Plenum, New York, 1986)]. The finite element FFP has been used
successfully for propagation problems in atmospheric acoustics for several
years. The finite difference approach, which has been developed only recently,
is more straightforward than finite elements but equally accurate. We compare
the FFP solutions in terms of speed and accuracy using several existing
benchmark problems as test cases.