Design and laboratory validation of multistructured acoustic resonators for the attenuation of airborne machinery noise in ships

Ship machinery generates significant noise levels, mainly including energetic and low-frequency tonal components, posing two issues. The first is linked to potential health and safety problems related to onboard noise, mainly for the crew working in the engine room. The second concern is that the underwater noise generated by machinery can harm marine life. Conventional sound-absorbing materials are hardly efficient in mitigating low-frequency tonal components. This study introduces multistructured acoustic resonators for machinery noise attenuation. These resonators are based on either Helmholtz resonators, labyrinthine quarter wavelength tubes, or spiral quarter wavelength tubes embedded into a broadband soundproofing material. Design elements are provided for each resonator type, and their effectiveness in reducing machinery noise is evaluated using numerical simulations and tests primarily conducted using a low-frequency impedance tube and a reverberant room. The subsequent validation steps and perspectives are finally summarized. • Mitigation technologies for reducing airborne noise from ship machinery. • Enhanced sound absorption of low-frequency tonal excitation. • Laboratory validation using the reverberant and impedance tube methods. • Numerical modeling using periodic unit cell model of a hybrid configuration.