Reduction of Underwater Noise Radiated by Ships: Design of Metallic Foams for Diesel Tanks

Porous materials are frequently used for noise reduction in acoustical applications with air. These types of materials lose their absorbing capacity when saturated by liquids. To reduce the underwater noise radiated by ships, metallic foams are specifically designed for acoustical dissipation when saturated by diesel, to use them as a covering in the interior of fuel tanks. The aim is to attract and dissipate noise in the fuel tanks by means of the diesel-foam viscous coupling. For this aim, analytical solutions of the reflection, absorption, and transmission coefficients have been developed. The interior covering of the tank wall with the metallic foam could produce reductions of transmitted sound to the ocean over 10 dB if the metallic foam is properly designed.