Investigation On The Dynamics And Sound Insulation Of Sandwich Structures With Lattice Truss Core

With the large-scale and high-speed development of structures such as aerospace,high-speed trains and submarine ships,their power devices are increasingly moving toward light and heavy loads.Structural vibration and noise caused by engine excitation and high-speed airflow impact waiting to be solved.Due to its light weight,high strength and other multifunctional properties,composite sandwich structures have been widely used in various engineering fields.Therefore,it is of great practical significance to study how to improve the vibration and noise reduction capabilities of composite structures.This paper analyzes the dynamics and noise insulation characteristics of different types of composite beam and plate structures,which not only provides theoretical guidance,but also uses simulations and experiments to complete the validation of the theoretical results..The main contents of this dissertation are as follows:The sound transmission characteristics of hourglass lattice core sandwich plate was studied.The Reissner sandwich plate theory was used to establish the vibraacoustic coupling theoretical model of the lattice sandwich plate,and the sound transmission loss of the sandwich plate under the plane wave incident and diffuse sound fields were calculated respectively.Compared with the existing literature and finite element analysis,the correctness of the theoretical model is verified.The influence of geometry parameters on the sound insulation performance of sandwich plate is analyzed.In addition,by selecting different material combinations,the better sound insulation effect is achieved.The dynamic characteristics of the double-layer hourglass lattice core sandwich beam and its active and passive control are studied.A dynamic model was established using the Hamilton principle and the assumed modes method.The natural frequencies were calculated and compared with the finite element method.The consistency of the comparison results verifies the correctness of the analytical model established in this paper.In addition,the velocity feedback control method is used to verify the effectiveness of piezoelectric materials in actively suppressing the vibration of doublelayer sandwich beam,and the idea of nonlinear energy sink(NES)is used to passively control the vibration response of sandwich beam structures.The dynamic and energy harvesting characteristics of the hourglass lattice truss core sandwich beam prepared by 3D printing technology is studied theoretically and experimentally.The equation of motion of the sandwich beam is established using the Hamilton principle and the homogenization model,and the natural frequencies are calculated.Comparison with published literature and finite element analysis results verifies the correctness of the theoretical model.The design of the 3D printed sandwich beam structure was completed through design optimization,and the dynamics and energy harvesting experiments of the cantilever sandwich beam structure were completed for the first time.The idea of substitution method is summarized and further applied to continuous and nonlinear systems to reduce the degree of freedom of the system.The effectiveness of the substitution method is proved by frequency analysis of the discrete spring-mass system and continuous Timoshenko beam and composite structures.The dynamic analysis of the gyroscope system represented by the rotating structure and orbital periodic structure further proves the correctness of the substitution method.The key to the idea of the substitution method is to study the functional relationship between all degrees of freedom of systems,which has wide application value.The transfer matrix method(TMM)was used to study the band structure of flexural waves in the metamaterial sandwich beam(MSB)with hourglass truss core.The hourglass truss structure with lumped mass is equivalent to the local oscillator.Then a metamaterial dual-beam(MDB)model is established to describe the MSB model,and it is proved that the MDB model is equivalent to the classic metamaterial beam(CMB)model under basic excitation.The finite element method is used to study the MSB model directly.The method determines that the MSB can be represented by CMB through transmission analysis and band structure analysis.Subsequently,parametric studies were conducted to explore the effects of material and structural parameters on the band structure of MSB.The spectral element method is used to study the dynamic response of corrugated plane rigid frame structure.Based on the Timoshenko beam theory modeling and the finite element assembling theory,the dynamic stiffness matrix of the overall structure is obtained.The frequency domain response of the structure under dynamic load is analyzed and the bandgap position is determined.The influence of boundary conditions on the Bragg bandgap is studied.