Low-frequency acoustic-gravity wave emission generated by the vortex caused by a moving submerged cylinder

Abstract

Acoustic-gravity waves induced by a cylinder moving underwater are numerically calculated in this study. Based on a weak compressibility method, a boundary data immersion method (BDIM), and the acoustic-gravity wave governing equation, we derive an algorithm that calculates the acoustic-gravity waves induced by a body moving underwater. We conduct numerical calculations for two cases: a horizontal uniform moving cylinder with and without lateral oscillation. The frequency spectra of acoustic-gravity waves are calculated at different monitoring locations. Strong anisotropy phenomena are observed from the time series and frequency spectra of the velocity potential function and the dynamic pressure. At the upper and bottom boundaries, the spectrum of acoustic-gravity waves can be approximated as noise. At the left and right boundaries, in the case of a cylinder moving horizontally in a straight line, the frequency spectrum of the acoustic-gravity wave caused by vortices becomes a low-frequency line spectrum. After the cylinder is subjected to lateral oscillation, the low-frequency line spectrum becomes a combination of the low-frequency broadband spectrum and line spectrum.