The nonlinear propagation of acoustic noise

Abstract
This paper is concerned with the nonlinear propagation of high-intensity acoustic noise. The noise source is assumed to have a smooth, Gaussian output. The medium in which the noise propagates is assumed lossless. The noise spectrum given by Rudenko & Soluyan (1977) is found to be incorrect at arbitrary distance from the source, owing to the presence of shocks. However, for small ranges, where shocks are not too frequent, it is shown to be valid at the lower frequency ranges. At high frequencies, how­ever, the noise spectrum is substantially different. The correction to the Rudenko & Soluyan spectrum at all frequencies for small ranges is derived. This correction has a universal functional form, which is calculated numerically. If the noise is so smooth that the source spectrum is exponentially decaying at high frequencies in the range of interest, then the complete spectrum has a similarity form at these high frequencies. The resulting spectrum describes the transition from the ω-3 form of Rudenko & Soluyan to the ω-2 form typical of a waveform containing shocks.

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