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It is well-known that many species of owl have the unique ability to fly silently, which can be attributed to their distinctive and special feather adaptations. Inspired by the owls, researchers attempted to reduce the aerodynamic noise of aircraft and other structures by learning their noise reduction features from different viewpoints and then using the gained knowledge to develop a number of innovative noise reduction solutions. Although fruitful results have been achieved in the bio-inspired aerodynamic noise control, as far as the authors know, comparatively little work has been done to summarize the main findings and progresses in this area. In this bibliographic survey, we systematically review the progresses and trends of the bio-inspired aerodynamic noise control, including the macroscopic and microscopic morphological characteristics of the owl wing feathers, the noise measurements on both flying birds in the field and prepared wings in the wind tunnel, as well as theoretical, numerical and experimental studies that explored the feasibility, parameter influence, aerodynamic effects and underlying mechanisms of the four main bio-inspired noise reduction techniques, i.e., leading edge serrations, trailing edge serrations, fringe-type trailing edge extensions and porous material inspired noise reduction. Finally, we also give some suggestions for future work.

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This paper investigates the suppression of vibration and noise radiation in a flexible raft system through the use of periodic structure theory. A floating raft isolation system is constructed. The transfer matrix method, the finite element method and periodic structure theory are combined to calculate the dynamic response of the system and the dispersion relations of the periodic structure. The effects of substructure resonances on vibration and noise radiation are analyzed. Next, the periodic isolation structure is used to suppress the vibration and noise radiation in the floating raft system. The isolation performance of the combination of periodic structures and continuous isolators are investigated. Additionally, the influences of the parameters of the floating raft system on vibration and noise are discussed. The numerical results demonstrate that vibration and noise are significantly suppressed in stop bands and are not worsened in pass bands.