Hybrid control of the radiated sound from a cylindrical shell with a voided soft coating

A hybrid passive-active control system composed of an array of inertial actuators is designed to attenuate sound radiation from a coated shell submerged in water. The coating embedded with cavities reduces the radiated sound from the shell over a broad frequency range. However, amplification in acoustic pressure occurs in narrow frequency bands associated with a springmass resonance of the coated shell as well as structural resonances. To address these resonances, we optimise the design of a hybrid passive-active control system composed of an array of inertial actuators tuned to different frequencies. Results show that the passive components of the inertial actuators can yield broadband reduction in the radiated sound at the shell circumferential resonances but are mostly ineffective at the spring-mass resonance. A hybrid control system in which the passive and active components are employed to target different resonances simultaneously is shown to effectively suppress the radiated sound from the coated shell.