Sound propagation in range‐degendent double ducts

Abstract

In a companion paper, M. A. Pedersen et al. (Abstract Q4) discuss sound propagation in range‐independent double ducts. Here we examine the effects of range dependence on the interchange of energy between adjacent acoustic ducts associated with a pair of resonant normal modes. The basic interchange mechanism is reviewed and the interchange distance (i.e., distance required to transfer acoustic energy from one duct to the other) is related to profile parameters. Calculations for a partial field (two modes) and a complete field (all modes) will be shown. Comparisons are then made between the exact solution (normal modes) and the approximate solution (parabolic equation) which will be used for range‐dependent calculations. Propagation loss curves and sound intensity contours will be given for two realistic cases of range dependence. It is shown that moderate range dependence does not destroy the fundamental resonance transfer of energy between ducts, but it does cause significant variation of the interchange range. [Work supported by ONR code 425AC.]