| The distribution and application of pipeline system are gradually expanding with the development of modern industrial production and vehicle equipment.In the process of ventilation and transportation of gas and liquid,the low-and medium-frequency noise is generally generated due to the flow and collision of media.Noise spreads everywhere along the pipeline path,which has serious influence on the work and life of surrounding personnel.Due to the characteristics of changeable,long wavelength,strong penetration and difficult attenuation,the low-and medium-frequency noise of pipeline is difficult to solve in the actual noise attenuation process.Helmholtz resonator has been paid more attention and developed in the field of noise suppression because of its advantages such as tailored noise suppression and subwavelength size.However,due to its strong frequency selectivity,it leads to the problem of the narrow bandwidth of noise attenuation,and it is difficult to adapt to the complex and changeable environment of low-and medium-frequency noise.The tunable strategy is expected to solve this problem,by changing the size of structure and the properties of material to reach the adjustable of frequency band of noise attenuation of Helmholtz resonator.However,it is still a great challenge to precisely control the performance of noise attenuation.In recent years,the research of origami structure has been developed rapidly.Among them,accordion origami has the characteristics of reversible and large deformation,which can create conditions for the changes of shape and size of the noise attenuation structure,and further realize the tunable performance.Based on this,a novel origami-based acoustic structure(OBAS)with tunable and broad bandwidth sound-eliminating capacities is proposed by incorporating an accordion origami with single degree of freedom extension into Helmholtz resonator as the main structure,and then we develop a pneumatic control method to adjust its characteristics of noise suppression.The transmission loss was used to characterize the characteristics of noise suppression.The noise attenuation performance of the proposed OBAS is studied by combining theory,finite element simulation and experiment,and then analyze the physical mechanism behind it.The proposed OBAS has the comprehensive properties of tunability,broad bandwidth noise attenuation and subwavelength scale.The periodic structure is designed,which use the OBAS as a cell,to further explore the characteristics of sound-eliminating.Due to the application of pneumatic control method,the periodic structure has various case of structural heights,and has a wider noise attenuation range and more complex performances of noise suppression than the OBAS.The main work of this paper is as follows:(1)An accordion origami tube(AOT)with reversible large deformation is designed.Taking the AOT as an example,the pneumatic control method is studied to adjust the AOT’s structural height.Based on the rigid origami idea,the 3D topology structure of accordion origami is designed and fabricated,and its stiffness characteristics are studied by the quasi-static compression test with the help of the electronic tensile testing machine.On this basis,the pneumatic control method is introduced to establish the mechanical model of the relationship between air pressure and the structure height of the AOT,and the correctness of the model is verified by experiments.The proposed AOT can realize the precise adjustment of structure height under pneumatic control,which provides conditions for the subsequent control of the frequency band of noise attenuation of the OBAS.(2)Based on the research of AOT and pneumatic control,combined with Helmholtz resonance muffler,a novel origami-based acoustic metamaterial with tunable and broad bandwidth sound-eliminating capacities is proposed.The frequency band above 10 d B transmission loss is defined as the effective frequency band of noise elimination,and its bandwidth is defined as the effective bandwidth,and the ratio of structure to acoustic wave length is the structural wavelength ratio.The transmission loss of the OBAS is calculated based on the transfer matrix method,and the acoustic model is established by COMSOL finite element simulation software to study the characteristics of the sound field and calculate the transmission loss.Then,utilize the measurement system of acoustic impedance tube based on the double load method to verify the correctness of the theory and acoustic model.On this basis,it can be found that the physical mechanism of noise elimination is mainly determined by the impedance mismatch caused by local resonance through studying the characteristics of sound field and understanding the physical mechanism of noise elimination.Finally,the influence of geometric parameters on transmission loss is analyzed to further expand the range of noise elimination.The results show that by utilizing pneumatic control method to chang the height of the AOT,the effective frequency band of noise elimination is changed,i.e.(269,757)Hz can be moved to(574,1138)Hz,which moves by 113%.Compared with the traditional Helmholtz resonant muffler,the OBAS has the comprehensive performance of ttunability,broad bandwidth noise attenuation and subwavelength scale in the low-and medium-frequency.In addition,the OBAS also has other excellent features,such as programmability,real-time control of the characteristics of noise suppression,etc.(3)Using the OBAS as a cell,A periodic silence structure(PSS)are designed and its noise attenuation characteristics are studied.Due to the introduction of the pneumatic control method,the structural height of each cell can have a variety of combinations.Take the combination of the same structural height and ladder structural height of a finite number of cells for example,the noise attenuation characteristics are studied.Using Bloch theory and transfer matrix method to calculate the band structure and transmission loss of the PSS,respectively.It can be found that the band structure of the PSS has the band gap of local resonance and Bragg reflection,which greatly broadens the effective bandwidth of noise elimination.Then,the band structure model and acoustic model are established by COMSOL finite element simulation to verify the correctness of the theory.According to the characteristics of sound field,the PSS with the ladder structural height of a finite number of cells has more complex acoustic phenomena,such as sound waves of different frequencies will stop propagating forward at different positions of the PSS and energy will accumulate around here.This is a phenomenon of spatial frequency division and wave energy enhancement,indicating that the PSS with the ladder structural height has the rainbow trapping effect.Tthese two combinations of structural heights have different the effective frequency band of noise elimination and acoustic phenomena,which also indicates that the PSS has a variety of structural height combinations by the pneumatic control method,obtaining more abundant the characteristics of noise elimination.And further adjust its ability of noise attenuation,showing strong tunable and programmable capabilities.It provides a new idea for the design of noise attenuation structure in the fields of pipeline noise control and other engineering. |
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