Abstract
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.
Highlights
Control of low frequency noise transmission, the low frequency noise that exists in the fluid-filled pipe systems of ships, has been a thorny problem for many researchers.[1,2,3] The fluid medium inside the pipe is an excellent carrier for sound transmission
This study presents a periodic waveguide consisting of an array of expansionary mufflers installed axially on a pipe to provide low frequency noise control in the fluid-filled pipe systems of ships
The introduction of a muffler array to the pipe system gives rise to innumerable reflected, transmitted, and incident waves at the muffler installation nodes, which results in interference over some frequency range between every two anechoic nodes
Summary
Control of low frequency noise transmission, the low frequency noise that exists in the fluid-filled pipe systems of ships, has been a thorny problem for many researchers.[1,2,3] The fluid medium inside the pipe is an excellent carrier for sound transmission. This causes the low frequency noise transmitted in water-filled pipe systems to have many undesirable features, such as a long transmission distance and a distinct characteristic spectrum. The results and analysis presented in this study may help to guide the achievement of low frequency and broad acoustic band gaps in waveguide systems to solve the complex problem of noise control in piping systems
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