Research On The Acoustic Absorption Characteristic Of Helmholtz Resonator Periodic Structure Based On MRF

With the increasing demand for low noise,high reliability and long life of mechanical equipment in industrial field,people have put forward higher and higher requirements for reduction technology of low frequency noise.In this paper,the low-frequency sound absorption performance of traditional noise reduction structure is difficult to achieve fast frequency conversion control.Based on the characteristics of magnetorheological fluid under the external magnetic field,the physical properties can be quickly and continuously regulated.Combined with the local resonant periodic structure,a helmholtz resonator periodic structure filled with magnetorheological fluid was designed.Through the establishment of theory model,acoustoelectric analogy theory,the transmission loss of the acoustic wave in the structure is analyzed,which proves that the structure has good low-frequency sound absorption effect,and the external magnetic field can perform frequency conversion control on it.Compared with the traditional frequency conversion method,the structure has the unique advantages of fast frequency conversion response,small volume and stable sound absorption performance.This paper mainly carried out the following aspects:First,a helmholtz resonator periodic structure filled with magnetorheological fluid was designed.According to the local resonant phononic crystal theory,the one-dimensional periodic structure formed by the arrangement of the resonator period can realize "small size control large wavelength",that is,attenuating low frequency noise with a small structural size.According to the characteristics of the elastic modulus of the magnetorheological fluid filled in the structure,the frequency conversion control of the structure can be realized by adjusting the change of the magnetic field strength.Secondly,the mathematical model that the acoustic wave propagates in the periodic structure is established.Based on Biot theory,the propagation model of acoustic wave in magnetorheological fluid was established,and the dissipation effect of magnetorheological fluid on acoustic wave was characterized.Based on acoustoelectric analogy theory,the propagation model of acoustic wave in helmholtz resonator periodic structure is established to characterize the attenuation of the acoustic wave on the macroscopic helmholtz resonator periodic structure.According to the mathematical model,the transmission loss curve of the acoustic wave is calculated.The results show that the structure has good low frequency sound absorption effect.The magnetic field strength increases from 0Oe to 4000 Oe,the band gap center frequency shifts to 394 Hz to the high frequency,which has a strong frequency regulation effect.Then,the finite element simulation calculates the sound absorption characteristics of the structure and verifies the correctness of the mathematical model.The helmholtz resonator periodic structure was simulated in the frequency domain by COMSOL software,and the transmission loss curve and sound pressure cloud chart of the acoustic wave propagating in the structure were obtained.The simulation results show that the band gap center frequency shifts to the high frequency when the magnetic field strength increases,which is in good agreement with the results obtained by the mathematical model.The deviation of the peak of transmission loss obtained by the two methods is analyzed.It is proved that the error is mainly affected by the sampling step size of the mathematical model,and the deviation is reduced when the step size is reduced.Finally,the offset of the center frequency of the band gap of the structure is calculated when the structural parameters change,and the change of the external magnetic field is compared with the frequency regulation of the structure.Using the mathematical model propagating in the structure to solve the transmission loss curve when the structural parameters such as cavity volume,neck length and cross-sectional area,lattice constant,and cross-sectional area of the connecting line are changed.The results show that the volume of the cavity and the length of the neck are reduced,and the cross-sectional area of the neck increases,the center frequency of the band gap moves to the high frequency.With the increase of the external magnetic field,the influence of the structural parameters on the center frequency of band gap increases slightly.