A numerical study of waterborne noise propagation in air across a thin solid layer

The present paper deals with the relevant problem of prediction and understanding of physical mechanisms of noise generated in a fluid and propagated in another fluid through a thin solid interface. This is a problem of practical importance in both marine engineering and hydraulic engineering. Sound transmission through different materials involves complex wave interactions at interfaces, where impedance mismatches govern reflection and transmission processes. We first developed a numerical model able to reproduce noise propagation across sharp interfaces; it is based on a multi-domain finite-volume solution of the acoustic wave equation. The model was validated against analytical benchmarks. In addition, a dimensional framework was established to identify the key non-dimensional parameters controlling acoustic transmission across layered media. The methodology was applied to the case of waterborne noise transmitted into air through a thin solid layer, considering two types of acoustic sources, namely a monochromatic monopole at varying frequencies and a broadband signal generated by turbulent channel flow. Two materials were examined for the solid layer: one representative of steel and the other of fiberglass. Acoustic pressure fields and spectra were computed for the different case studies. The results demonstrate consistent attenuation of transmitted sound and highlight the frequency-selective behavior of the solid layers, thereby revealing the physical mechanisms governing waterborne noise transmission across heterogeneous media. Overall, the study shows that the proposed methodology, under particular conditions, is a robust and versatile tool for analyzing hydroacoustic noise in layered systems.