Rongfu Mao

Distributed vibration mitigation by distributed absorbers suppresses line-spectrum vibrations within a defined bandwidth through the installation of absorbers with different tuned frequencies along the structure. Based on a cantilever-beam–discrete-mass system, this work proposes a simple cantilever-beam distributed absorber design. It investigates how the cantilever’s geometric parameters, the magnitude of the lumped mass, and its location influence the system’s natural frequencies to achieve tuning of the absorber frequencies; on this basis, a pair of immersed porous disks is introduced. By adjusting the inter-disk angle, the porosity changes are induced, thereby modulating the contact area between the disks and the liquid inside the housing to realize tunable damping of the absorber. In practical applications, the number of distributed absorbers and the corresponding optimal design parameters are first determined; subsequently, several cantilever-beam absorbers are integrated and mounted on a common fixed boundary, and the parameters of each independent cantilever-beam absorber are adjusted to their optimum values.

Active control is a highly effective method for mitigating low-frequency noise transmission. To address the coupling effect and practical implementation challenges associated with conventional active control methods, a specific strategy for active control of noise transmission is developed. By leveraging an intuitive representation of transmitted sound power through force radiation modes, the control forces are designed such that the total excitation force vector becomes orthogonal to each dominant force radiation mode. Detailed theoretical development and case studies are presented. The research results indicate that decoupled control of transmitted sound power corresponding to each force radiation mode can be achieved, and excellent control outcomes can be obtained in both oblique incident and diffuse field applications. Further investigations reveal that the noise transmission can be effectively reduced, while the total vibration attenuation on the plate may not be assured, which depends on the relationship that exists between dominant force radiation modes and corresponding structural modes.