Hybrid honeycomb structure for enhanced broadband underwater sound absorption

A hybrid honeycomb structure (HHS) with energy dissipation enhancement effect is proposed for broadband underwater sound absorption. The HHS is constructed using hexagonal honeycomb structure with embedded metal rings of different size and filled with viscoelastic rubber. A theoretical model is developed to study the sound absorption performance of the HHS by applying the transfer matrix method, and a finite element model is also developed to validate the theoretical model. The innovative introduction of metal rings concentrates rubber vibrations near the ring edges and within conical regions formed by the ring holes and the longitudinal waves in the rubber are converted into transverse waves, these vibrations increase the friction within the rubber at the rubber-metal interface, which significantly increases the friction loss at the rubber-metal interface, thus increasing the dissipation of acoustic energy. Compared to the homogeneous rubber layer and the rubber-filled honeycomb wall structure, the average increase in energy dissipation is 238 % and 181 %, respectively. The results of the energy dissipation distribution of the HHS confirm that the energy dissipation is mainly concentrated in the conical region, indicating a significant energy dissipation enhancement effect. By designing the structural parameters of the rings, the shape of the conical region can be changed, thereby achieving the regulation of energy dissipation enhancement effect. In addition, the key structural and material parameters of the hybrid honeycomb structure are optimized using the particle swarm optimization algorithm, resulting in a broadband sound absorption performance with an average sound absorption coefficient of 0.96 in the range of 1-10 kHz. This work proposes a new design concept and provides valuable guidance for the development of underwater sound absorption structures.