Acoustic propagation through surface ship wakes

Abstract

To predict acoustic propagation through a ship wake, an understanding is required of the physical properties (void fraction, spatial and temporal variation of the bubble structure, oceanic ambient dynamics, for example) of the wake, as well as an acoustic propagation model capable of handling the changes in these properties. The wakes of large surface ships contain high concentrations of air bubbles of various sizes and nonuniform distributions, which give the wake decidedly inhomogeneous acoustic properties. The extant literature contains little quantitative information. Limited material has been collected and combined with a notional hypothesis regarding the random structure to produce a physical model for some of the relevant physical properties. The model has been used as a basis for propagation calculations for this complex situation. Two methods have been employed for those calculations: range-dependent, Gaussian beam ray tracing and a 2-D parabolic equation technique, the latter having previously proven useful for turbulent atmospheric conditions. The acoustic model predictions provide a clear indication of the complexity of the problem and motivation for development of a 3-D propagation model. [Work supported by ONR Code 321 (ARL Project).]