Prediction of shock waves over a sound-absorbing area

Abstract

High-energy impulsive sounds from firing large weapons or demolition charges are of particular interest because the high sound pressure levels and the low-frequency content of the spectrum mean the sounds are readily heard at long distances. The rules of linear acoustics do not apply for high-energy impulsive sounds impinging on reflecting or absorbing surfaces close to the source. Reflections of blast sounds from a reflecting surface, e.g., the ground, can contribute substantially to the sound perceived at locations in communities surrounding the blast site. This paper describes predictions of blast sound-pressure waveforms, determined by the previously described Flux-Corrected-Transport computer code, and corresponding measured waveforms of blast sounds produced by charges ofC-4 explosives mounted on a pole above a 3.66-m-square gravel-filled pit. Gravel was chosen as the sound absorber because it withstands the high pressures and high temperatures that are present near such explosive sources. It is shown that the predictions agreed well with the measurements. An analytical study showed that increasing the size of the pit to a 9-m radius would yield significant additional reductions in blast sound pressures.