A cylindrical shell comprising multifunctional metamaterial cores with ultra-low frequency vibroacoustic reduction and mechanical performances

Abstract

Abstract Deep-sea submersible is an important part of oceanic equipment, where special operating environment must require the outer material to have multifunctional properties such as load-bearing, buckling, and vibroacoustic suppression. Here, we proposed a novel metamaterial with excellent mechanical and ultra-low frequency vibroacoustic characteristics as a core material for cylindrical shells used in deep-sea submersibles. Compared to honeycomb materials, the proposed metamaterial utilized the design principles of local resonance theory, incorporating a subwavelength structure periodically embedded within the porous honeycomb structure. This configuration was expected to result in superior static and dynamic properties. Then, we systematically discussed the mechanical and vibroacoustic performance of sandwich cylindrical shells with metamaterial cores, characterized by positive or negative Poisson's ratios, to explore their potential for engineering applications in submerged pressure-resistant structures. The respective unit cells were designed to have equivalent load-bearing capabilities, and simulations were conducted to analyze the physical characteristics related to pressure resistance, buckling, and wave reduction. The results indicated that, compared to conventional honeycomb structures, the metamaterials based on PMMA could safely withstand hydrostatic pressures of nearly 7 MPa, resulting in nearly a twofold increase in structural strength. Additionally, the proposed metamaterials could open bandgaps in an ultra-low frequency range (with the normalized frequency Ω as low as 0.013) and an ultra-wide frequency range (with the bandwidth ratio as high as 83.50%), attributable to the coupling effect of traveling waves and subwavelength units. It is worth noting that the robustness and hydrostatic pressure insensitivity of the metamaterial were demonstrated in the studied hydrostatic pressure range of 0.1 MPa to 5 MPa. This work verified the feasibility of coupling the design between local resonance theory and porous structures, and provided guidance for the multifunctional design of sandwich cylindrical shells.