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.
Abstract:Using the idea of phononic crystals, the ship hydraulic pipeline isolator is designed to be a one-dimensional periodic structure which is composed of metal and rubber. The vibration of ship hydraulic pipeline can be controlled by the band gaps properties of the isolator. The band structure and FRF of the isolator is calculated by the transfer matrix method and finite element method, respectively. The influence of material properties, lattice constant and fineness ratio to the frequency ranges and the width of the band gaps is also be considered, and the best structure parameters are obtained. By combing the numerically calculations and experimental measurements, the results indicate that the isolator has longitudinal vibration band gaps at low frequencies form 600 Hz to 10 000 Hz, and the isolator could control the vibration of ship hydraulic system transferring form pipeline to ship hull structures effectively. The research provides a new technical way for vibration control of ship hydraulic pipeline.
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