Fundamental acoustic modal frequency of underwater elastic rectangular open cavity

Résumé fourni par la source

With the intensification of marine development activities, underwater radiated noise has become an increasingly significant threat to the marine ecological environment. Open cavities are ubiquitous features in underwater vehicles and offshore structures, and their resonant acoustic radiation constitutes a notable source of such noise. This paper presents a comprehensive numerical investigation into the acoustic-structure coupling characteristics of an underwater elastic rectangular open cavity, with particular emphasis on the role of wall elasticity in modifying the coupled modal behavior. The study focuses on the fundamental (first-order) acoustic modal frequency, which is relevant to low-frequency underwater radiated noise and is also sensitive to the effects of elastic cavity walls. A hybrid finite element-infinite element (FEM-IFEM) framework is developed to predict acoustic modal frequencies in cavities with flexible boundaries. The model is validated against theoretical solutions, experiments, and in-air tests, with a maximum relative error of 2.19%. A parametric study further examines the effects of wall elasticity, opening geometry, and cavity depth on the first-order acoustic modal frequencies. The results reveal that wall elasticity substantially reduces the coupled modal frequencies, with the side walls exerting the most pronounced effect. For the base-elastic configuration, where only the 10-mm-thick base plate is elastic and the side walls and top plate remain rigid, the coupled modal frequency decreases from 233.0 Hz to 156.0 Hz (33.1%) as the opening area decreases from 300 × 300 mm to 100 × 100 mm. Furthermore, decreasing the opening area or increasing the cavity depth both contribute to a downward frequency shift, whereas variations in the number and shape of openings produce comparatively minor effects. Collectively, this study elucidates the intrinsic correlation between structural parameters and acoustic characteristics of elastic open cavities under acoustic-structure coupling, providing valuable theoretical guidance for the analysis, prediction, and mitigation of underwater structural vibration and radiated noise.

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