Broadband bandgap and shock vibration properties of acoustic metamaterial fluid-filled pipes

This paper describes the design of an acoustic metamaterial fluid-filled pipe with periodically variable materials. The aim of this design is to improve the broadband vibration attenuation frequency range of fluid-filled pipes by combining the mechanism of local resonance (LR) and Bragg scattering bandgaps (BGs). The vibration bandgap (BG) of the pipe is investigated using the transfer matrix method. It is demonstrated that the coupling of LR and Bragg scattering BGs produces a remarkable improvement in effective bandwidth. Additionally, the external shock excitation effect on pipe vibration is calculated using the finite element method. This indicates that the strongest interaction between the LR and Bragg BG is achieved when the LR is located in the center of the softer material. However, this strong coupling effect may cause some degeneration in the Bragg BG. Moreover, in practical applications, the position of the LR BG should be determined according to the vibration BG requirements. Experimental samples are prepared, and an experimental test and verification procedure is conducted. The positions and widths of the BG and the shock vibration properties measured during the experiment agree well with the theoretical results. This research provides a technical and theoretical basis for the attenuation design of vibration reduction systems for fluid-filled pipes that may be subjected to explosive loads.