Numerical investigation of an acoustic slow waveguide

Abstract

The effect of a cylinder of material whose sound speed is less than that of water on the radiation beam pattern of an omnidirectional sound source is investigated. Specifically a point source is placed near one end of the cylinder. The cylinder serves as an acoustic waveguide and enhances the radiation from the source in the direction of the waveguide. The waveguide is mathematically modeled by use of the surface Helmholtz integral equation together with the requirement of continuity of acoustic pressure and normal velocity on the surface common to the waveguide and surrounding water as reported by P. H. Rogers and . J. Trott [J. Acoust. Soc. Am. 56, 1111–1117 (1974)]. The integral equations are solved numerically. Calculated farfield patterns and directivity gains for waveguides of various length‐to‐diameter ratios are presented. Directivity gains greater than 14 dB together with farfield patterns having side lobes more than 10 dB down are predicted over fairly broad bandwidths for several waveguides. Experimental results were obtained and are in good agreement with the numerical results.