Research On Dynamic Behavior And Energy Harvesting Structure Optimization Of Laminates

With the development of various low power electronic components,it has become a research hotspot to obtain sustainable energy and capture signals from low-frequency hydropower by means of environmental and low cost devices in field automatic monitoring such as ocean.Piezoelectric laminate which owns the characteristics of high sensitivity and good durability,is wildly used in both sensors and energy harvesting sturctures as main component in general monitoring systems.Howerver,in the complex hydrodynamic environment,the dynamic behavior of monitoring systems is depended on the fluid-structure interaction and low-frequency vibration environment.Therefor,the research on dynamic behavior and energy harvesting structure optimization of laminates has its theoretical and practical significance.In this paper,the dynamic equation of piezoelectric laminate was theoretically deduced.Analytical,semi-analytical and finite element methods were proposed to study the dynamic response and fluid-structure coupling problems of piezoelectric laminates.Furthermore,a lowfrequency piezoelectric energy harvesting structure was proposed based on the theoretical research,and it performance is verified by numerical and experimental tests.The main research achievements of this paper are as follows:(1).Based on Reissner's theory of thick plate,the energy equation was established based on the variational theory and the constitutive equation of piezoelectric materials,and the state space matrix equation on dynamic response of piezoelectric laminates was deduced.By Fourier transform,differential quadrature method and Laplace transform,the state space equation was analyzed through time and space variables.According to the contiuity of the interlayers in the state space method,a response solving system was established by the modified numerical Laplace inverse transformation.And the dynamic response of the piezoelectric laminates under different boundary conditions was calculated.Meanwhile,a finite element simulation is carried out and the results are compared with thoese obtained by the semi-analytical method.(2).A semi-analytical model of piezoelectric laminates subjected to underwater impact was established under Talyor fluid-structure interaction.A case study of the impact load from underwater blasting was proposed to obtain the dynamic response of piezoelectric laminates under different support boundaried and fluid boundaries by state space method.In terms of the four response vectors of displacement,stress,electric potential and electric displacement,the influence of underwater impact load on piezoelectric lamintes was investigate.The results were also compared to the finite element simulation case.(3).The approximate formulas of natural vibration frequency and response current were derived based on Euler-Bernoulli beam hypothesis and energy harvesting cantilever beam,thus the influence of geometric variables on energy harvesting frequency and efficiency is discussed.A nonlinear low-frequency energy harvesting structure was designed.And the resonant frequency and mode shape of the structure are analyzed by finite element simulation.Referring to the distributions of the surface charge,the piezoelectric layer was optimized on the harvesting efficiency of the structure.At the same time,the influence of load resistance is analyzed to get the optimal resistance value.In the control group with different grometric configurations,the spiral rotation angle of group ? and ? can harvest the highest energy efficiency,and the reduction of structure width can bring down the first natural frequency.(4).Performance of the piezoelectric energy harvesting structure was further investigated by experimental study.A packaging process was improved for the piezoelectric layer and the laminating of whole structure.Then control groups were tested and analyzed by the excitation system and data acquisition instruments.According to different geometrical configurations and materials,the low-frequency nonlinear piezoelectric energy harvesting device could be designed for the three demands of optimum working frequency,lower damping and better energy harvesting efficiency.It was found that the brass material has lower natural vibration frequency,damping and higher harvesting energy power than the galvanized steel.Finite slement simulation with different excitation accelerations was established,in order to compare with the existing litratures,which shows that the proposed energy harvesting structure in this paper has higher harvesting energy power under low frequency and low amplitude excitation.