Suppression of low frequency sound transmission in fluid-filled pipe systems through installation of an anechoic node array

To provide low frequency noise control in the fluid-filled pipe systems of ships, a periodic waveguide made of an array of expansionary mufflers (referred to as anechoic nodes) installed axially on a pipe is proposed. Broad and low frequency acoustic band gaps can be generated with this periodic pipe system from the destructive interference of reflected, transmitted, and incident waves at the muffler installation nodes, and will be reinforced over some desired low frequency ranges. Within the band gaps, the transmission of acoustic noise inside the internal media of the periodic pipe system will be effectively attenuated. Key parameters for modulating the central frequency, bandwidth, and attenuation coefficient of the band gaps include the lattice constant, expansion ratio, and muffler length, and these factors are investigated following analysis of the formation mechanism of the band gaps. The results obtained in this study suggest that the introduction of a muffler array to form a periodic structure in the piping system can suppress the propagation of acoustic waves with longer wavelengths, thus achieving control of lower frequency pipe noises.