Underwater vibro-acoustic performance of sandwich cylindrical shells with bidirectional re-entrant connections under hydrostatic pressure

The development of underwater pressure-resistant cylindrical shells with superior vibro-acoustic performance exhibits significant application potential for marine engineering. In this paper, a novel bidirectional re-entrant connection honeycomb (BRCH) is proposed by incorporating inclined ligament connections, which is further utilized as the honeycomb core of sandwich cylindrical shells. The directional band structures of the BRCH unit are calculated by the established dispersion dynamic model considering rotational symmetric boundary conditions. The radial vibro-acoustic transmission responses and circumferential radiated sound pressure distribution of the BRCH sandwich cylindrical shell under different hydrostatic pressures are explored. A quantitative parametric analysis using the introduced evaluation indicator is performed to reveal the effects of typical geometric parameters and hydrostatic pressure on the underwater vibro-acoustic performance. The results indicate that the calculated bandgap characteristics accounting for modal displacement polarization can accurately predict the directional longitudinal wave isolation bands. The sound insulation performance of the BRCH sandwich cylindrical shell is effectively enhanced by the attenuation of radial vibration transmission within its honeycomb core, which is driven by the directional bandgaps. The distribution of radiated sound pressure near the transmitted shell panel is differentiated at high frequencies due to the localization of the excited vibration modes. Under the internal prestress of the shell, the eigenfrequencies of vibro-acoustic transmission responses decrease as hydrostatic pressure increases, thereby leading to the shift of vibro-acoustic attenuation bands. Therefore, this work provides practical guidance for improving the vibro-acoustic performance of underwater pressure-resistant cylindrical shells with consideration of hydrostatic pressure.