Floating periodic pontoons for broad bandgaps of water waves

The narrow attenuation bands of traditional marine structures have long been a challenge in mitigating water waves. In this paper, a metastructure (MS) composed of floating periodic pontoons is proposed for broadband water wave attenuation. The interaction of surface gravity waves with the MS is investigated using linear wave theory. The potential solutions of water waves by the MS with a finite array are developed by using the eigenfunction expansion matching method (EEMM), and the band structure of the MS is calculated by the transfer matrix method (TMM), in which the evanescent modes of waves are considered. The solution is verified against the existing numerical result for a special case. Based on the present solution, the association between Bragg resonance reflection and Bloch bandgaps is examined, the effects of pontoon geometry are analyzed, and the comparison between floating MS and bottom-mounted periodic structures is conducted. A computational fluid dynamics (CFD) model is further developed to assess the structures in practical fluid environments, and the floating MS presents excellent wave attenuation performance. The study presented here may provide a promising solution for protecting the coast and offshore structures.