Study On Vibration And Noise Reduction Characteristics Of Combined Phononic Crystal Plate In Low-frequency

Phononic crystal(PC)is a kind of artificial periodic composite material,which is composed of hard scatterers periodically distributed in a matrix with low mass density.It is the most important characteristic to be able to produce the complete bandgaps that limits elastic wave transmission.This makes it possible to control the propagation of elastic wave manually.In the field of low-frequency noise control,plate-like locally resonant PCs have attracted wide attention of researchers because of their sub-wavelength thickness and low surface density.This work mainly discusses the generation of low frequency bandgaps of plate-type PC and how to realize vibration reduction and noise reduction by used PC plate.We designed the two-dimensional practical PC plate with low frequency BG.The BG characteristics of the model are calculated by the finite element method and the formation mechanism of BG is studied and geometrical optimization of PCs structure was carried out carefully.From the perspective of practical application,the problem that PCs plates are difficult to be widely used is solved.In addition,due to the frequency range of the PC plate structure,it is still difficult to fully cover the frequency range of the low-frequency vibration and noise control.PCs combination system is introduced,by combining the new PC plate with other types of PCs plates,we study the coupling mechanism of BG and try to get the wider BG.First,a two-dimensional practical PCs plate is designed,which is composed of cross-like beams embedded in silicone rubber plate with periodic holes.The band structure,transmission loss spectrum and displacement filed are calculated.At the same time,the acoustic displacement field at the edge of the BG is analyzed,the mechanism of BG generation is clarified,and the influence of parameter change on the BGs is also discussed in detail.In addition,considering the application value of the model,the structure of large-size combined sealing plate is further studied and described.Results show that in contrast the traditional PC plates with two-dimensional single cylindrical and double cylindrical,the novel PC plate has the wider first BGs and better vibration damping characteristics.The generation of the BG is due to the out-of-plane torsional vibration of the cross-like beams.This torsional mode is obviously different from the traditional structure,which is more conducive to the opening of low frequency BG.Equally important,the bandgaps mainly depend on the matching degree of material and the geometry parameters of periodic hole,while the bandgaps are not quite sensitive to the the thickness of plate.The design of new PC plate is beneficial to its processing and application.Two sealing plate models with good stability and ductility are proposed,which can be applied to plane and surface respectively.This study provides a theoretical reference for the practical engineering application of PCs plate.In order to obtain a wider low-frequency bandgap,starting from the idea of PC combination system,the designed PC plate and two traditional PC plates are combined and studied the coupling mechanism of the BG.Results show that the range of a single BG has not been widened,but multiple complete BGs have appeared and the range of BGs has increased.After structural combination,the coupling of BG has a great relationship with the symmetry of the structure.The lower the symmetry,the smaller the number of complete BGs,and the other way around is different.After the phonon crystal plate is combined,the single frequency band in the band gap is mainly generated by the bending vibration of the scatterers at the joint of the combined structure.And finally,by adding circular periodic holes and adjusting the lattice constant,the band gap characteristics of the combined phononic crystal plate are optimized,and the optimal band structure is obtained.The research content of this dissertation can provide a reliable basis for the development of lightweight and porous practical vibration and sound insulation materials.And the research of the combined PC plate system provides a new idea and theoretical basis for the plate structure to obtain a fuller range of BG.