Quarter-wavelength acoustic resonators for ship machinery noise control

• Compact quarter-wavelength resonators for reducing tonal airborne noise from ship machinery. • Noise control technology development from a technology readiness level 4 (validation in a laboratory environment), to a level 7 (prototype field testing in an operational environment). • A nearly linear relationship links the spatial density of resonators and the achieved sound attenuation. • Up to 10 dB and 6 dB reductions for airborne and underwater noise, respectively, in a simulated environment (water basin). • Up to 10 dB reduction of the airborne noise tonal components in a ship’s engine room. According to the International Maritime Organization, developing effective noise mitigation technologies has become crucial. The airborne and underwater noise generated by ship machinery poses potential risks to the health and safety of crew members working in engine rooms and disrupts marine wildlife. Attenuating the low-frequency tonal excitations that characterize the acoustic signature of systems operating in engine rooms is challenging using conventional soundproofing materials. This study proposes an original solution in the form of a structured quarter-wavelength resonator design and a hybrid configuration of resonators embedded in broadband soundproofing materials. The effectiveness of the technologies is successively assessed in laboratory conditions, in a water basin using a test platform, and finally in the engine room of a ship in operation. Laboratory tests allow for determining that the achieved sound attenuation is a nearly linear function of the spatial density of resonators. The results of tests conducted using a platform in a water basin show up to 10 dB and 6 dB reductions for airborne and underwater noise, respectively. In a real environment (a ship’s engine room), the measured reductions are still as high as 10 dB. We finally evaluate the limitations and development priorities for application in real-life situations.