| Vibration and noise problems widely exist in the fields of mechanical,aerospace,vehicle and traffic,marine and civil engineering.In particular,with the use of lightweight composite materials in various engineering structures,vibration and noise problems of composite structures have already received extensive attention.How to effectively control harmful vibration and noise has become one of the key problems that need to be solved in the development of science and technology.This puts forward higher requirements for vibration and noise reduction technology of structures.The frequency band gap characteristics of phononic crystals and acoustic metamaterials can be used to suppress the propagation of vibration and noise excitations within the band gap frequency range,which provides a novel idea for vibration and noise reduction of engineering structures.Based on the concepts of phononic crystals and acoustic metamaterials,this dissertation designs the band gap characteristics of beam-type structures in engineering by means of designing material properties,changing structural configurations,integrating piezoelectric materials,etc.,in order to suppress the propagation of harmful vibration in such structures.In addition,the adaptive method is used to identify the vibration signal of the beam structure,and the harmful vibration amplitude of the beam structure can be directly controlled by the actuation force exerted by piezoelectric materials.Thus,a closed-loop adaptive active vibration control model is established and applied to the vibration control of composite sandwich beam structures.The specific research works of this dissertation are given as follows:Based on the first order shear deformation beam theory,the dynamic model of the functionally graded frame structure is established,and the free and forced vibration characteristics of functionally graded frame structures are studied.By designing the material composition distribution of functionally graded beam members,the functionally graded frame structures with different dynamic characteristics and frequency band gap characteristics are obtained,which can meet different vibration reduction requirements.On this basis,the active controller is designed by periodically placing piezoelectric patches on the functionally graded frame structure and adopting the displacement feedback control strategy.Based on Euler beam theory,the dynamic model of piezoelectric functionally graded frame structure is established.By designing the material composition distribution of the functionally graded beam members and adjusting the feedback control gain,the active and passive vibration control of piezoelectric functionally graded frame structures are realized by utilizing the band gap characteristics.A piezoelectric metamaterial pipe is constructed by periodically placing piezoelectric patches on the pipe structure of a fluid-conveying pipe system and connecting the external shunting circuits on the piezoelectric patches.Based on Timoshenko and Euler beam theories,a dynamic model of the metamaterial pipe is established.It is found that the metamaterial pipe can generate the electromechanical locally resonant band gap for low-frequency vibration reduction.By coupling with the Bragg scattering band gap,the broadband vibration reduction of the fluid-conveying pipe is realized.Furthermore,a hybrid resonant metamaterial fluid-filled pipe is proposed by combining the electromechanical local resonators and the mechanical local resonators.Based on Timoshenko and Rayleigh beam theories,the dynamic model of the hybrid resonant metamaterial pipe is established.Based on the idea of multi-frequency local resonators,the ultra-wideband vibration reduction of fluid-filled pipe is realized by reasonably designing the mechanical locally resonant band gap and utilizing the controllable property of the electromechanical locally resonant band gap.By periodically attaching macro-fiber composite piezoelectric patches to a functionally graded sandwich beam and connecting external shunting circuits on the piezoelectric patches,a functionally graded sandwich metamaterial beam structure is constructed.Based on Euler beam theory,a dynamic model of functionally graded sandwich metamaterial beam is established.The research results show that the metamaterial beam possesses lowand medium-frequency Bragg scattering band gaps and electromechanical locally resonant band gap that can be adjusted at low-and medium-frequency.By adjusting the shunting circuit parameters,the coupling between the electromechanical locally resonant band gap and the low-and medium-frequency Bragg scattering band gaps is realized.In that way,the frequency range of the low-and medium-frequency band gap is effectively widened,and the broadband vibration reduction of the functionally graded sandwich metamaterial beam is realized.In addition,the effects of gradient index,thickness ratio and the length of piezoelectric patch on the band gap characteristics of functionally graded sandwich metamaterial beams are analyzed.In order to control the low-frequency vibration of the lightweight lattice sandwich structure,a class of lattice sandwich metamaterial beam structure is constructed and studied by using the beam-type mechanical local resonators to open the low-frequency band gap.Based on Timoshenko beam theory,a dynamic analysis model is established,and the amplitude-frequency responses of the lattice sandwich metamaterial beam are calculated.The frequency response experiment is carried out,and the correctness of the analysis model is verified.By calculating the vibration transmission property of lattice sandwich metamaterial beam structure with different configurations,the influence of the configuration of sandwich structures on the low-frequency mechanical locally resonant band gap is discussed.The influence of different parameters of the resonant beam and mass block on the mechanical locally resonant band gap is further studied.It is found that the desired band gap location and width can be obtained by changing the length of resonant beam and the weight of mass block.In addition,the coupling and widening of the mechanical locally resonant band gap are realized by using dual-frequency mechanical local resonators and reasonably designing their parameters,which can be applied to the low-frequency broadband vibration reduction of lattice sandwich beam structures.A closed-loop adaptive active vibration control of piezoelectric cantilever system is established by attaching macro-fiber composite piezoelectric patches to the composite sandwich beam as exciter,sensor and actuator,respectively.The low-frequency vibration control of the composite sandwich beam is studied.The free and forced vibration characteristics of the piezoelectric cantilever system are calculated using the improved theoretical model and the finite element model,and the adaptive vibration control of the piezoelectric cantilever system is carried out in time domain.Through the adaptive vibration control experiment,the effectiveness of the adaptive vibration control method is verified.The influence of adaptive control parameters on vibration amplitude and convergence time is further studied.The vibration control effects under complex multi-frequency excitations and different excitation voltage amplitudes are analyzed.The relations among the excitation voltage,sensing voltage and actuation voltage amplitudes are discussed. |
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