Labyrinth quarter-wavelength tubes array for the reduction of machinery noise

Abstract

Abstract. Anthropogenic noise from navigation is a major contributor to the disturbance of the acoustic soundscape in underwater environments. The noise generated by ship’s machinery exhibits energetic tonal harmonic peaks at multiples of the rotating and firing frequency, that occur in the 20-200 Hz frequency range and difficult to control with classical soundproofing materials. Quarter wavelength tubes (QWT) can be a concrete solution since their absorption peaks are harmonic odd integers of the first resonance frequency. The main issue of QWT is their tuning length, which equals 1.43 m for a 60 Hz resonator. The problem is solved by coiling the tube into a labyrinth. Three labyrinth quarter wavelength tubes are tuned respectively at 60, 90 and 120 Hz. Samples are printed with filament 3D additive manufacturing techniques using PLA and tested with a square impedance tube designed for low-frequency measurements. Measurement results are in good agreement with analytical and numerical predictions. An array including four 60 Hz, four 90 Hz and four 120 Hz labyrinths QWTs is finally tested.