Research On Broad Bandgaps Control Of Cylindrical Shell Mechanical Metamaterial And Vibration Isolators For Shaft And Pipe Parts

Cylindrical shells,a basic structural unit,are widely used in engineering such as agricultural machinery ships,rockets and precision instruments,while its vibration noise problem commonly exists and cannot be ignored.Mechanical metamaterial are a kind of structure composed of artificial structure,which have properties to contrary conventional mechanical properties.Phononic crystals,as a kind of Mechanical metamaterial,is of the bandgap characteristics,and can effectively control bandgap range according to the nature frequency of target.Thus the structures own great vibration isolation effect.As the matter of fact,the width of bandgaps determines the application range and effectiveness of the metamaterial vibration isolator.Hence,the metamaterial with wider bandgap has the more extensive application prospect in project design.All of this lead to the great importance of the research of wide band gap control of mechanical metamaterial and vibration isolators for cylindrical shell.In this paper,the author studied the bandgap characteristics of three kinds of cylindrical shells mechanical metamaterials and proposed two methods to widen the bandgap of longitudinal、flexural wave.;This search taking pipe parts as an example,studied practical application of cylindrical shell mechanical metamaterial in engineering.The main achievements and conclusions of this paper are listed as follows:1.Studied the control of mechanical metamaterials of two-component,three-component and microstructure cylindrical shells for longitudinal and flexural wave.The dynamic equation and Bloch period condition of cylindrical shell are derived by converting the finite period of circular direction into infinite period condition using coordinate transformation.Then the finite element numerical model is established and calculated for the dispersion curves of three kinds of cylindrical shell mechanical metamaterials.Moreover,the vibration transmission characteristics of mechanical metamaterials with finite period structure is analyzed and compared with calculated bandgaps for verifying the effectiveness of the structure.In addition,mechanism of vibration isolation is revealed by comparing the distribution of displacement fields at different frequencies outside and inside the bandgap.By adjusting the geometrical and material parameters of mechanical metamaterials cylindrical shells,the dispersion curves and transmission characteristics can be calculated.Results show that,the geometry and material parameters of mechanical metamaterials can affect the bandgap range,thus make it more flexible for actual engineering needs.2.Proposed a bandgap range of mechanical metamaterials broaden method by splicing finite period structures in a certain direction to meet the demand of broad bandgaps structures in engineering.Also,this paper analyzes the vibration transmission characteristics of three-component cylindrical shells mechanical metamaterials with splicing structure,calculates the vibration transmission characteristics of microstructural cylindrical shell mechanical metamaterial by splicing the axial and the circumferential.Results show that,the splicing technique can truly broaden the characteristics of cylindrical shell mechanical metamaterials,both in axial and circumferential direction.Meanwhile,the author establishes a theoretical model on flexural wave bandgaps in locally resonant cylindrically curved shell containing multiple periodic arrays of graded-resonators,derives the governing equations based on extended Hamilton principle,computes the bandgaps of the locally resonant cylindrical shell with attached multiple graded-resonators,and the single direction style and two-direction multiple graded-resonator style in locally resonant cylindrical shell using the plane wave expansion(PWE)method,and obtains the law of periodic arrangement of multi-stage resonators broaden bandgaps of flexural wave.Finally,the dispersion curve and vibration transmission on realistic structure of multiple graded locally resonant cylindrical shell is analyzed.Results indicated that the obtained data have a good agreement with the band gap properties predicted by the model.3.Developed a vibration isolator for shaft and pipe based on cylindrical shells mechanical metamaterials.The transmission characteristics of the three-component isolator are studied by finite element software.Thus the vibration isolation effect can be determined.Then the isolator is applied into flexible pipe to study the transmission characteristic.Results shows that,the vibration isolator can effectively control the longitudinal vibration wave in the pipe.Besides that,the three-component broadband vibration isolator is developed based on splicing technique.In addition,a microstructure cylindrical vibration isolator was developed to control the flexural wave in the pipe,and the bandgaps was verified by finite element simulation and experiment.Finally,the microstructure vibration isolator is applied to the pipe as a sleeve,and the suppression effect of the vibration isolator as a sleeve for flexural wave is analyzed.Results show that,the isolator can suppress the specified frequency flexural wave,restrain the vibration even in the structure of sleeve.For the sum up,this paper studies the propagation of elastic waves and the theory of broad bandgaps in the cylindrical shell mechanical metamaterials,provides theoretical support for the vibration isolation and noise reduction technology of cylindrical shell structures,proposes a new technique for the vibration problem of shaft and pipe.