Elastic Wave Manipulation Mechanism Of Acoustic Smart Metamaterials And Its Characteristic In Noise And Vibration Control

The control level of vibration and noise has become an important technical index to evaluate the performance of transportation,ship and aerospace equipment.With the innovation of science and technology and the upgrading of industry,the carrier equipment aims to be light-weight,integrated and intellectualized gradually.The structures of carrier equipment are more vulnerable to interference of vibration and noise.Thus,the demand for the low-frequency and broadband vibration and noise suppression techniques is increasingly urgent.Typical engineering structures such as beams,plates,membranes and shells are the basic components of various kinds of carrier equipment.It is of great significance to study and control the elastic wave propagation characteristics in these structures for vibration and noise reduction of carrier equipment.However,it is difficult for traditional sound/vibration damping or absorbing techniques to control low-frequency noise and vibration.Moreover,additional mass or volume of these traditional techniques may be too large when they work,which is difficult to meet the design requirements.Therefore,it is urgent to explore new theories,methods and technologies for structural vibration and noise reduction.In recent years,as a new type of structural materials with special physical properties,the low frequency band gap characteristics of acoustic metamaterials are expected to provide a new means for structural vibration and noise control.At the same time,the introduction of smart materials and digital control technology in acoustic metamaterials can further enrich the design of metamaterials,and the performance can be adjusted online.Thus,this kind of metamaterial can obtain extraordinary elastic wave regulation ability,which is expected to achieve better low-frequency and broadband vibration isolation and noise reduction performance than the traditional passive acoustic metamaterials.Based on the low frequency and broadband vibration and noise control requirements of typical engineering structures,this paper focus on the elastic wave propagation in acoustic smart metamaterials and the low-frequency,broadband vibration and noise control of the typical structure s.The main contributions and innovations of the paper are given as follows :(1)A kind of smart metamaterial with extraordinary sound absorption performance is realized by combining digital control and piezoelectric shunt technology.Based on the equivalent parameter theory and the finite element method,a calculation and analysis method for the acoustic absorption characteristics of this type of smart metamaterial is established.By coding the proposed digital controller,the effect of enhanced-damping and enhancedresonance can be realized.Theoretical and experimental results show that the smart metamaterial can realize multiple acoustic absorption peaks at low frequency range,and the highest acoustic absorption coefficient can reach 0.97.(2)A kind of ultra-thin membrane-type smart metamaterial with low frequency and broadband sound insulation performance is proposed.The mechanism analysis shows that the negative effective bending stiffness is the internal mechanism of the extraordinary sound insulation performance of the smart metamaterial.The theoretical and experimental results show that the bandwidth of sound insulation of the membrane-type acoustic metamaterials can be significantly expanded by introducing the multimodal-resonance enhanced control strategy,and the bandwidth can be expanded by more than one time compared with that of the acoustic metamaterials using multi-mode resonant shunt-circuit.(3)The abnormal nonlinear phenomenon that the nonlinear strength is inversely proportional to the structural variation is found,and the concept of inversed nonlinearity is proposed,which improves the theoretical framework of nonlinear vibration.The smart metamaterial with inversed nonlinear is realized by introducing digital control technology.The theoretical analysis,simulation and experimental results show that the vibration suppression bandwidth of the smart metamaterial under small amplitude excitation are much larger than those under large amplitude excitation.(4)Based on a feedforward control scheme containing single-sensor and double-actuators,a kind of a smart metamaterial is implemented.The theoretical and experimental results show that with the help of a time-modulated control strategy,the proposed metamaterial can independently and continuously control the amplitude,phase and frequency of elastic wave.In addition,we also found that the proposed smart metamaterial has chirality,which can break the reciprocity a nd realize the asymmetric transmission of elastic waves,providing a new nonHermitian system implementation for the regulation of elastic waves.In conclusion,this thesis deeply investigates the elastic wave propagation mechanism and regulation methods in smart metamaterials based on digital control technology.A quantity of design techniques of digital controller and smart metamaterials are proposed.A series of new methods and characteristics of elastic wave propagations were discovered,analyzed and verified firstly.This work preliminarily realizes the noise and vibration control of the structure by using smart metamaterials.The research results provide important technical and theoretical basis for the field of smart metamaterials and provide new technical solutions for vibration and noise reduction in structures.