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中国物理学会期刊

暗声学超材料型充液管道的低频消声特性

CSTR: 32037.14.aps.68.20190311

Characteristics of low-frequency noise elimination in a fluid-filled pipe of dark acoustic metamaterial type

CSTR: 32037.14.aps.68.20190311
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  • 充液管道低频声的有效吸收和消减一直是一个颇具挑战性的难题. 受声学超材料理论启发, 本文设计了一种沿管道轴向方向等距布置小体积声学短管的充液周期管道系统. 该管道系统可以诱发声波传播超宽低频带隙的产生, 使得声波在带隙频率范围内传播将被显著衰减, 乃至无法透射, 近乎被完全吸收, 称为暗声学超材料型充液管道. 进一步, 揭示了暗声学超材料型充液管道中声传播带隙的产生机理、参数影响规律, 研究了该波导管对低频噪声的降噪特性, 初步探讨了工程实际可实现的暗声学超材料型充液管道的结构实现形式. 研究成果有望为管道低频噪声控制提供一条新的技术途径.

     

    The suppression and absorption of low-frequency noise for a fluid-filled pipe system has become a challenging task. Inspired by the properties of acoustic metamaterials, we construct a fluid-filled periodic pipe system, consisting of small-size short acoustic pipes mounted on a fluid-filled main pipe system equidistantly along the axial direction of main pipe. The short acoustic pipe is filled with fluid and gas, and the fluid section is connected to the main pipe that is filled with the same liquid. In such a periodic pipe system, an ultra-low frequency and ultra-broad band gap of acoustic waves can be generated, making the acoustic waves transmitting in the pipe system effectively attenuated within the band gap frequency range. Since the attenuation effects of the band gap on the low-frequency sound are so strong (the acoustic waves almost cannot be transmitted through the pipe system) that the periodic pipe system is referred to as a dark acoustic metamaterial (DAM)-type fluid-filled pipe system. The formation mechanism of the first band gap can be ascribed to the co-resonance of the short acoustic pipe array in the piping system, and this band gap is categorized as resonant-type BG (RBG). The contribution of short acoustic pipes is to introduce a low-frequency and large impedances spatially into the system, whereupon the transmitting waves will experience a tempestuously resonance in the pipe. As a result, the transmission of acoustic waves within the RBG is stopped. The second band gap in a higher frequency range is classified as Bragg-type band gap (BBG), since it is induced by the effects of interference between the incident, the reflected and the transmitted acoustic waves existing in the periodic units. The interference effect on the suppression of wave transmission is strengthened by the ceaselessly repeating uniform cells. The lattice constant change can bring in a modulation effects on both the BBG and the upper band edge of RBG. Increasing the volume of gas chamber in the short acoustic pipe will result in a shift of lower band edge of RBG towards the low-frequency range but has no action on the upper band edge; similarly, the augment of the liquid volume of the short acoustic pipe also lowers the band edges of RBG, however, bandwidth of the RBG will be reduced. A membrane may be used to physically separate the gas from the fluid in the short acoustic pipe, rendering the design more feasible to be realized in practical engineering. The installation of membrane will not change the low-frequency band gap properties of the DAM pipe. The obtained results show that the proposed design in this study may provide a new way to solve the defiant problem of noise control in the low frequency range for fluid piping systems.

     

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