Experimental verification of ultra-broadband vibration reduction of underwater vehicle pressure-resisting shells using acoustic black holes

The aim of this paper is to design acoustic black hole structures for underwater pressure-resistant shells (PRSs), including single- and double-leaf structures, which are applied to the inner and outer PRS surfaces. The mean square velocity and displacement modes on the shell surface indicate that surface vibrations above the cutoff frequency can be effectively attenuated. Three sets of experiments are designed, i.e., PRS under white noise point excitation and underwater vehicle motor under no-load and load conditions. The data acquired at key measuring points reveal that the vibration acceleration on the shell surface has a significant attenuation effect in most of the frequency bands from 0.001 to 25 kHz, with a maximum attenuation of up to two orders of magnitude. It is particularly effective in suppressing strong vibrations at the switching frequency of underwater vehicle motors. The paper conclusions of this study can be directly applied to vibration and noise reduction systems for underwater equipment. Moreover, they offer another insights for developing potential broadband vibration and noise reduction structures.