Sound propagation through a complex bubble-filled medium using a parabolic equation method

A 2D parabolic equation (PE) code is used to predict sound propagation through a complex bubble field. The wake of a surface ship is the basis of the bubble distribution that is modeled as a simplistic geometric structure. Propeller motion and ship hydrodynamics create a dynamic field and the modeled simplistic structure is an estimation of this field as a ‘‘snapshot’’ in time. The complex features of the bubble field impact the sound field by variations in the sound velocity, density, and attenuation—all contributing loss mechanisms from the ship wake. A PE is used so that the environment can be changed to follow the spatial variation of the wake. Predictions are made for two different representations of the wake at three time frames, or distances from the source ship. For each location, the distribution of the bubbles is significantly different. Propagation is predicted for three pathways through the wake: down the wake (toward or away from the ship), across the wake (perpendicular to), and diagonally across the wake. [Work supported by ONR.]