NONLINEAR EFFECTS IN LONG RANGE PROPAGATION

The Nonlinear Progressive Wave Equation (NPE) [McDonald and Kuperman, 1987] computer code was coupled with a linear normal mode code in order to study propagation from a high intensity source in either shallow or deep water. Simulations using the coupled NPE/linear code are used to study both harmonic (high frequency) and parametric (low frequency) generation and propagation in shallow or deep water with long-range propagation paths. Included in the modeling are both shock dissipation and linear attenuation. The results of these studies are presented. OBJECTIVE Linear acoustic propagation in a waveguide has been studied extensively theoretically, numerically and experimentally. In case of a large underwater explosion, nonlinear processes affect the properties of the acoustic wave. One can expect to characterize and localize nuclear underwater explosions by examining spectrograms, which would show this specific nonlinear behavior [Kuperman et al, 2001; D’Spain et al 2000; Gerstoft, 1999]. The aim of this paper is to highlight the nonlinear phenomena of acoustical propagation such as the nonlinear steepening and shock dissipation. The nonlinear scar in a pulse propagated over long ranges is discussed. Work on this topic has also been carried out by B. Ed McDonald [2002]