Analytical modeling of the acoustic field during a Direct Field Acoustic Test.

Abstract

The acoustic field generated during a Direct Field Acoustic Test (DFAT) has been analytically modeled in two space dimensions using a properly phased distribution of propagating plane waves. Both the pure‐tone and broadband acoustic field were qualitatively and quantitatively compared to a diffuse acoustic field. The modeling indicates significant non‐uniformity of sound pressure level for an empty (no test article) DFAT, specifically a center peak and concentric maxima/minima rings. This spatial variation is due to the equivalent phase among all propagating plane waves at each frequency. Predicted spatial variation is shown to agree well with experimental measurements. The excitation of a simply supported slender beam immersed within the acoustic fields was also analytically modeled. Results indicate that mid‐span response is dependent on location and orientation of the beam relative to the center of the DFAT acoustic field. For a diffuse acoustic field, due to its spatial uniformity, mid‐span response sensitivity to location and orientation is nonexistent. Extension of the modeling to three space dimensions and numerical methods is underway.