Use of the fast field program for predicting diffraction of sound by curved surfaces

Abstract

The fast field program (FFP) is a powerful tool for solving outdoor sound propagation problems in stratified atmospheres. It is shown here to be equally powerful for solving for the propagation of sound over curved surfaces of finite impedance. Results from scale model experiments are in excellent agreement with the FFP calculation in the deep shadow, penumbra, and bright zone behind the surface. The results are also compared with Berry and Daigle’s creeping wave series [J. Acoust. Soc. Am. 83, 2047–2058 (1988)]. The FFP calculation and creeping wave series yield identical results in the deep shadow. In the penumbra and bright zone behind the curved surface the FFP is in slightly better agreement with the data than the creeping wave series, although the differences are typically 1 dB or less which is comparable to the experimental error. The improvement is due to the more accurate sound speed profile and coordinate mapping used rather than to any differences in the computational method.