The anechoic coating capable of absorbing sound energy in low frequencies within broadband is essential to conceal underwater vehicles. However, the geometric deformation and modification of mechanical parameters under hydrostatic pressure affect the prediction of absorption performance in deep water environments. An anechoic coating embedded with tandem resonant voids is proposed in this work to achieve quasi-perfect low-frequency and broadband absorption. The analytical method based on the effective medium approach and numerical simulation are performed to estimate the effects of hydrostatic pressure on sound absorption. When additionally considering the dynamic mechanical parameters of the compressed viscoelastic medium, the original absorption humps in low frequencies are inclined to higher band, accompanied by the expanded absorption bandwidth. Then, the tandem coating specimen is measured in a water-filled impedance tube. The experimental spectra are consistent with the analytical and numerical results under various hydrostatic pressures, demonstrating the efficient absorption (α > 0.7) in broadband low frequencies via ordinary pressure. At the same time, the absorption spectrum under higher hydrostatic pressures is also verified in the tube. Consequently, this work paves the way for a broadband low-frequency underwater absorber design and provides an efficient method to characterize the low-frequency and broadband absorption from the coupled resonant coatings in deep water environments.

Metagratings offer promising opportunities for highly efficient yet anomalous wave-diffraction control characterized by scattering matrices. In this work, those degenerated states of scattering matrices, arising from elaborately induced non-Hermiticity and encoding unique scattering behaviors, are of interest. In particular, we theoretically and experimentally investigate the exotic degeneracies, exceptional points (EPs) and diabolic points (DPs) in such scattering systems. We show the distinct response strength induced by EP and DP. The extremely asymmetrical reflection occurs on the EP state in a metagrating, which exhibits a stronger reaction to disturbances and offers opportunities for microvariable detection and external perturbation monitoring. As a contrast, a stable dual-angle absorber is proposed on the DP state, which is almost unaffected by external perturbations. Our work may pave the way for extreme wave manipulation via non-Hermitian metagratings on degenerated states.

The propagation of uncertainties in structural dynamic responses, arising from variations in material properties, geometry, and boundary conditions, is of critical concern to researchers in a variety of engineering instances. Conventional methods like high-fidelity Monte Carlo simulation are computationally prohibitive, while existing surrogate models can improve efficiency at the expense of accuracy. To achieve a trade-off between accuracy and efficiency, a Physics-Informed Conditional Variational Autoencoder (PI-CVAE) model is proposed. It integrates a novel dual-branch encoder for time-frequency feature extraction, a learnable frequency-filtering decoder, and a holistic physics-informed loss function so as to enable efficient generation of dynamic responses with high accuracy and adequate physics consistency. Comprehensive numerical analysis of plate structures demonstrates that the proposed approach achieves remarkable accuracy (maximum FRF error < 0.2% and $R^2$ > 0.99) and a computational speedup of 8–11 times in comparison with conventional simulation techniques. By maintaining high accuracy while efficiently propagating uncertainties, the PI-CVAE model provides a practical framework for probabilistic vibration analysis, especially during the acoustic design phase.

In this study, we investigated toroidal shell wrinkling in free hydroforming. We specifically focused on toroidal shells with a regular hexagonal cross-section. Membrane theory was used to examine the distribution of stress and yield load in both preform and toroidal shells. The wrinkling moment was then predicted using an empirical formula of shell buckling. In addition, the wrinkling state was investigated using a general statics method, and the free hydroforming of toroidal shells was simulated using the Riks method. Subsequently, nonlinear buckling and equilibrium paths were analyzed. A toroidal preform was manufactured, and free hydroforming experiments were conducted. Overall, the experimental results confirmed the accuracy of the theoretical predictions and numerical simulations. This indicates that the prediction method used in the study was effective. We also found that wrinkling occurs during hydroforming in the inner region of toroidal shells due to compressive stress. Consequently, we improved the structure of the toroidal shells and performed analytical calculations and numerical simulations for the analysis. Our results indicate that wrinkling can be eliminated by increasing the number of segments on the inner side of toroidal preforms, thereby improving the quality of toroidal shells.

The development of pressure-resistant sound-absorbing materials is crucial for enhancing the stealth performance of underwater vehicles operating at great depths. In this paper, a pressure-resistant metastructure is proposed, and an analytical model for its acoustic impedance is derived. Through structural optimization, the low-frequency sound absorption bandwidth is further extended. The results demonstrate that the proposed metastructure achieves broadband low-frequency sound absorption based on a plate–rubber–cavity coupling resonance mechanism. Experimental validation conducted in a pressurized impedance tube shows that under hydrostatic pressures ranging from 0.5 MPa to 3 MPa, the average sound absorption coefficient between 500 Hz and 10 kHz remains above 0.8. These findings confirm the effectiveness of the proposed configuration in broadening the low-frequency absorption bandwidth while maintaining stable acoustic performance under varying hydrostatic pressures. The study provides a robust platform for the development of underwater artificial functional materials and offers a novel approach for designing noise reduction structures suitable for deep-sea environments.