Kenneth E. Gilbert Scott D. Hansen
Appl. Res. Lab. and the Graduate Program in Acoust., Penn State Univ., P. O. Box 30, State College, PA 16804
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.