Analysis and Improvement of Oblique Incidence Sound Absorption Performance of Underwater Anechoic Coatings with Cavities

PurposeThis paper thoroughly investigates the oblique incidence sound absorption performance of underwater anechoic coatings with cavities. The study proposes an approach to improve the sound absorption performance under oblique incidence conditions.MethodsThe finite element method is used to analyze the sound absorption characteristics of underwater anechoic coatings. A three-dimensional FE model is established to predict the anechoic coating's absorption coefficient. The transfer matrix method is used to validate the numerical simulation under normal incidence. The oblique incidence sound absorption is validated through comparison with former research. The influences of the resonator and its geometric parameters, placement height, and material are also investigated.Results and ConclusionsThe study discovers that low-frequency absorption of underwater anechoic coatings at oblique incidence is enhanced since the global horizontal mode of the coating. Medium-high frequency absorption is diminished because of the decrease in incident sound wavelength and the increase in reflection. It is found that embedding a resonator into the coating can significantly improve the high-frequency absorption performance at oblique incidence due to the local resonance. The appropriate radius and height of the resonator can effectively enhance the UACCR's absorption performance. The absorption performance is better when the resonator is placed close to the cavity. Among the three resonator materials, steel shows a more balanced overall absorption performance than aluminum and plumbum. This study has guiding significance for designing underwater anechoic coatings and improving acoustic stealth of submarines.