| With the continuous development of rail transit system,the problem of vibration and noise has gradually become the core problem of restricting the green,environmental protection and sustainable development of the urban rail system.Most of the traditional vibration reduction and noise reduction measures focus on taking measures for medium and high frequency vibration and noise inside the train,but there are few effective measures for the medium and low frequency vibration and noise problems.This is because medium and low frequency noise has long-wave characteristics,and the energy decays slowly during the propagation process while medium and low frequency noise is not easy to be isolated.Under the requirements of high-speed performance of rail trains,lightweight of the whole vehicle,and complex road conditions,the low-noise design of the trains is difficult to meet the requirements of low-frequency noise-reduction performance.Therefore,this thesis designs a spindle-type local resonator acoustic metamaterial board based on the acoustic metamaterial design concept of “local resonance principle” to solve the medium and low frequency vibration and noise of trains.By studying the intrinsic bandgap properties of the spindle-type local resonator acoustic metamaterial and the sound insulation properties of the metamaterial plate,the sound-insulation effect of the combination with the train body floor structure was analyzed.The main research work and conclusions of this thesis are as follows:(1)Based on the line test,through the vibration and noise test inside and outside of the city EMU and the identification of the sound source inside the car,analysis of the noise transmission path in the car is made.Combined with the analysis of the vibration and noise spectrum diagram,the results show that the main contribution frequency band of the radiated sound of the car body floor is in the frequency band of 100～400 Hz.These make reference for the design of metamaterials in following section.(2)Through finite element simulation,we found that the formation of the band gap of the spindle-type local resonant acoustic metamaterial depends on the effect of the local resonance mode of the spindle-type local resonator on the substrate plate.The band gap is generated by the mutual coupling between the motion of the substrate plate and the local resonance unit.Then,we investigated the influence of Matrix Parameters and Local Resonator parameters on the Band Gap Characteristics of Acoustic Metamaterials.Optimizing the structure and material parameters further widen the band gap making band gap to 108～386 Hz.(3)By comparing the sound insulation properties of the finite-structure acoustic metamaterial plate and the traditional plate,it is found that compared with the same size substrate plate and the same quality substrate plate.The sound transmission loss of the finitestructure acoustic metamaterial plate in the mid-low frequency band is increased by about 20 d B.There is basically no difference in the sound transmission loss in the low frequency range below 100 Hz.And at 400～700 Hz,which is slightly larger than the band gap,the sound transmission loss is reduced by 15 d B.For 700～2000 Hz,which is much larger than the band gap,the sound transmission loss was compared with the same size base plate and the same quality base plate,and there is basically no difference.Based on this difference in sound insulation properties,we investigated the effects of multi-local resonator design,periodic arrangement size,and periodic arrangement pattern on sound insulation properties.(4)Combining the spindle-shaped acoustic metamaterial with the composite floor,the combination of aluminum profile of the floor structure with the interior panel of the floor structure was considered,respectively.Firstly,calculating the sound insulation characteristics,and the results show that the aluminum profile-metamaterial plate structure is suitable for the case where the main frequency of the interior noise is slightly smaller than the design bandgap.The interior panel-metamaterial panel structure is suitable for the case where the main frequency of the interior noise is slightly larger than the design bandgap;but compared with the combination with aluminum profiles. |
