Analysis On Characteristics Of Periodic Meta-structure With Lateral Local Resonance In Low Frequency Range

When the machine is running,vibration and noise accompanies.Noise is a threat to the cosy environment for the residents and the concealment and safety for specific vehicles.And vibration may damage the buildings and bridges,and affect the stability of equipments installed on the aircrafts.Specifically,waves in low frequency range,with longer wavelengths,is difficult to be manipulated in practical engineering,while artificial periodic structures capble to prohibit the wave propagation in low frequency range attracts lots of attention.In terms of the problem of vibration suppression in low frequency range,this thisis proposed such two kinds of spacialy periodical meta-structure and periodically resonant meta-structure to investigate the characteristics of band gap and transmission to provide guidance for noise and vibration control.And tests of vibration suppression of meta-beam are conducted.Based on the Jeruslam phononic crystal and multi-mass-in-mass acoustic metamaterial,an S shaped spacialy periodical meta-structure and a multi-band-gap hybrid periodical resonance meta-structure are presented.Finite element model of the S shaped meta-structure is established and results show that under the circumstance of the same structural parameters,S shaped produced a 200 Hz lower band gap than the Jeruslam phononic crystal due to the cavity resonance.Meanwhile,the improved multi-band-gap hybrid periodical resonance meta-structure can generate lower and wider band gaps for the resonance of outer and inner resonators,which shows better potential in vibration suppression.Moreover,this thesis proposed a spindle shaped spacially periodical meta-structure and constructed a metastructure with lateral local resonace inserted.Theoretical and numerical models are elstablished,and corresponding results are calculated.It is demonstrated that the spindle shaped spacially periodical meta-structure can generate low-frequency band gap,and the elastic waves attenuate dramatically.Futhermore,model of the metastructure with lateral local resonace inserted is built and simulative results revel that the metastructure generates multiple band gaps in low frequency range and waves attenuates exponentially.And within the band gaps,the closer to the natural frequency,the faster the waves attenuates.The meta-beam and meta-plate with lateral local resonance is presented in this theis to implement the meta-structre in practical engineering.When resonance of the lateral local resonance happens,inertia force from the vertical resonator and lateral resonators via a four-link mechanism counteracts the shear excited by the flexural waves in the base beam and plate,and multiple band gaps in low frequency range are yielded.In the meantime,simulation results indicate that within the band gaps,the farther distance away from the excitation source,the lower the vibration response and the power flow.Furthurmore,the attenuation speed of the power flow within the band gap is faster than that out side of the band gap,which verifies the suppression performance of the meta-beam and meta-plate.Sound transmission loss of the meta-plate with lateral local resonance is investigated with the exsistence of the external flow.Within the band gaps,the sound transmission loss is higher than that of the isotropic plate.Simultaneously,study on the rules of the transmission loss with various Mach number,incident angle,damping is worked on.Eventually,experiments of distributive mass of the spring on power flow and vibration suppression performance of the meta-beam with lateral local resonance is conducted.Simulation and tests results show that distributive mass of the spring induces multiple anti-resonances,which results in much higher mechanical impedance and power flow.Experiments of the vibration suppression characteristics of the meta-beam with lateral local resonance indicate that multiple band gaps can be found under 100 Hz,within which the vibration response is much lower than those of the isotropic beam and structural beam.The metastructure shows better characteristics of vibration suppression.Meanwhile,it is theoretically and experimentally verified that the gap width in low frequency range can be broadened by reasonably increasing the number of resonators.And a complex meta-beam is constructed with two kinds of lateral local resonance,and multiple band gaps are tested.Experiments of the meta-beam with lateral local resonance validate the correctness of the theoretical model and shows prosperous potential in practical engineering.