Sound propagation characteristics of a metamaterials-type periodic pipe and its low-frequency broadband control

Control of low-frequency noise for piping system of ships is an urgently task that needs to be solved during the design and fabrication for new ships. Introducing the theory of acoustic metamaterials (AMs) into the structure design of pipe system of ships, a 1D periodic pipe structure with low-frequency band gaps (BGs) is constructed. Calculation methods for tile acoustic BGs and the coefficients of transmission waves are developed to conduct the investigation. Calculational results show that the Bragg and locally resonant (LR) BGs are simultaneously existed in the periodic pipe. Within these two two BGs, acoustic wave propagation in the system will be stopped. Further, these two types of BGs could be coupled under certainly condition, such that a broader BG is generated. Moreover, the coupling condition for Bragg and LR BGs could be exactly formulated. Utilizing the character of coupled BG and the low-frequency design, the propagation of acoustic wave can be manipulated in desired low frequency range, thus rendering the control of low-frequency noise in a broad range feasible.