Abstract

Sound absorption coatings for underwater noise control applications are generally manufactured using a soft viscoelastic material with an impedance match to the surrounding water. The multi-functional capabilities of a coating include its ability to absorb water-borne sound waves as well as reduce the transmission of sound from a vibrating hull to the surrounding water. Inclusions embedded within the soft material results in wave scattering at frequencies around the resonance frequency of the inclusions, which facilitates the conversion of longitudinal waves into shear waves. This phenomenon results in the strong attenuation of sound within the coating due to high shear damping and low shear modulus compared to the bulk modulus for soft rubber-like materials. Inclusions are typically cavities which exhibit monopole resonance associated with pulsating motion or hard scatterers which exhibit dipole resonance associated with translational motion. Multiple wave scattering also occurs between inclusions in proximity, further enhancing sound dissipation within the coating. This presentation provides an overview of our approaches to predict the acoustic performance of sound absorption coatings for maritime applications and the physical mechanisms governing their acoustic performance.