Studies On Piezoelectric Energy Harvesting Of Nonlinear Aeroelastic System

With the rapid development of Micro-Electro-Mechanical System(MEMS)and micro-integrated circuit,small-sized low-power electronic devices are widely used in sensor networks,wireless transmission,wearable or implanted devices,etc.However,the power supply of these large-scale used electronic devices is the main limitation that restricts their service life.Replacing or recharging the batteries which are embedded in devices or located in remote area requires expensive economic costs,and there would also exist risks of safety.In the past twenty years,the concept of harvesting energy from ambient sources,such as solar,wind flow and mechanical vibration,for the purpose of eliminating the need of batteries and realizing self-powering of low-power devises has becoming a multidisciplinary research hotspot.It has important academic research significance and engineering application prospects.In this thesis,based on flutter response,and by using piezoelectric transducer with high energy density and stable power generation performance,the studies on nonlinear aeroelastic-piezoelectric energy harvesting is carried out to provide theoretical guidance of the energy harvesting system.The main work and innovations are summarized as follows:(1)By employing the typical section airfoil as host structure,a novel nonlinear magnetic-coupled aeroelastic-piezoelectric energy harvester is proposed to harvest energy from wind flow.Based on the Hamilton’s variational principle of continuous system,piezoelectric constitutive equation,the Kirchhoff’s law of electricity,and considering the geometric nonlinear effect of large deformation of structure,the dynamic governing equations of the energy harvester are established and its performance evaluation index is defined.A semi-analytical and semi-numerical method is derived for modal analysis of a piezoelectric cantilever beam with variable cross-section.Therefore,a reduced-order theoretical modal is deduced by using the modal superposition method,which is used to analyze the dynamic behavior of the system and to predict the energy harvesting performance.According to the empirical model of magnetic force and the stability theory of equilibrium,the static bifurcation characteristics of the energy harvester with respect to the changing of magnetic force is qualitatively discussed,which proves the existence of mono-stable configuration and bi-stable configuration of the harvester.Therefore,the nonlinear magnetic-coupled mono-stable aeroelastic-piezoelectric energy harvester(NMAEH)and the nonlinear magnetic-coupled bi-stable aeroelastic-piezoelectric energy harvester(NMBAEH)are designed,respectively.(2)Based on the Theodorsen’s unsteady aerodynamic theory,the flutter characteristics of the NMAEH is theoretically investigated.The influence of system parameters on flutter characteristics is analyzed,and the regulation mechanism of nonlinear magnetic force on flutter speed of the harvester is obtained.Theoretical simulation and wind tunnel experimental results show that the NMAEH exhibits supercritical flutter behavior as the wind speed increases,which suggests that the harvester could start to generate electrical power beyond its linear flutter speed.Resonant frequency tuning method is employed to soften the equivalent linear stiffness of the piezoelectric beam through attractive magnetic force.Therefore,the NMAEH can undergo flutter limit cycle oscillation(LCO)at a quite low wind speed of 1 m/s.Compared with a non-magnetic-coupled traditional aeroelastic-piezoelectric energy harvester(AEH),the usable wind speed range for energy harvesting is greatly broadened,meanwhile,the energy harvesting performance is enhanced by 75% within the tested wind speed range.(3)A prototype of the NMBAEH is developed and fabricated using the repulsive magnetic force subjected onto the tip of the piezoelectric beam to generate the bi-stable configuration.The Dipole-Dipole magnetic theory is introduced to model the nonlinear magnetic force.Therefore,according to static bifurcation property,the separation distance between external and internal magnets is obtained when achieving bi-stability.The influences of separation distance on dynamic behavior and energy harvesting performance of the NMBAEH are theoretically investigated and experimentally validated.The results depict that the NMBAEH can snap-through between bi-stable potential wells and exhibit the subcritical flutter characteristics which is different from the NMAEH.Therefore,the cut-in wind speed for flutter LCO extends significantly to low speed range.Meanwhile,the bi-stable equilibriums enlarge the vibration amplitude which leads to the beneficial improvement for energy harvesting performance compared with the NMAEH.It is found that the output power increases with the decreasing of magnets separation distance.However,as the result of the deepening bi-stable potential barriers,the inter-wells vibration is restricted and the flutter cut-in speed increases.As for the optimal separation distance,the usable wind speed range is extended by 34 % and the energy harvesting performance is more than doubled.In addition,it is found that regulating the depth of bi-stable potential barriers through structural variable-potential-well technique can effectively resolve the limitation that the wind speed range and the output power cannot be increased simultaneously,which further enhances the energy harvesting performance of the NMBAEH.(4)A simple and efficiet hysteresis model is proposed to predict the hysteretic property of piezoelectric transducers.From the phenomenology point of view,the hysteresis modeling approach establishes the butterfly-shaped derivative relationship between input and output of the piezoelectric transducers through a hysteresis elementary operator with hysteresis switching unit.Although the hysteresis model has only two parameters,it is able to predict both the unipolar and bipolar hysteresis responses accurately,and can be easily developed and promoted into practical application.Based on the proposed hysteresis model,the hysteresis nonlinearity is difined to quantify the degree of hysteresis property.The influence of piezoelectric hysteresis on the energy harvesting performance of the traditional AEH is studied.The results show that the piezoelelctric hysteresis directly affects the electromechanical coupling coefficient of the harvester.Therefore,when a certain degree of hysteresis nonlinearity exists in piezoelectric transducers,it is benifit to enhance the output power.However,due to the deformation-dependent property,the benefitial hysteresis nonlinearity changes with the variation of wind speed,and excessive hysteresis reduces energy harvesting performance.