Modified vibro-acoustic spectrum characteristics for underwater cylindrical shells with mechanical metastructures

Abstract

The vibro-acoustic spectrum characteristics for underwater thin-walled structures continue to attract attention. This study presents a load-bearing, wide-bandgap metastructure for modifying vibro-acoustic spectrum characteristics of a cylindrical shell. Initially, methods for calculating and evaluating the load-bearing capacity and bandgap characteristics of unit cells are established. Subsequently, an annular metastructure is configured in a cylindrical coordinate, broadening the bandgap and the range of radiated noise suppression through compound unit cells. Finally, by localized mass and reinforcement, the enhancement of macroscopic structural load-bearing capacity and the modified spectrum characteristics are achieved. This study provides a cylindrical shell in which internal vibration transmits through the flange to the shell and then generates radiated noise. The sound power of the assembly which is equipped with either the original support or the metastructures was obtained through experiments and simulations. The experimental study demonstrated a 3.1 dB noise reduction across a broad frequency range from 824 Hz to 1500 Hz, with over 50 % of the frequency characteristics significantly altered. Furthermore, the metastructure achieved a weight reduction of 2.16 kg compared with the original configuration. This study not only achieves the evaluation of the load-bearing capacity of the microscopic unit cell but also realizes the amplitude suppression and spectrum modification of radiated noise for underwater cylindrical shells.