Research On Design And Complex Response Of Wing-based Aeroelastic Vibration Power-Source System

In order to supply power for the wireless sensor devices,developing new energy harvesting technology has become a topical issue of the intelligent society.The flow-induced vibration energy harvesting is a new energy harvesting technology which is usable and important.As a typical flow-induced vibration phenomenon,the aeroelastic flutter provides a key choice for the power-source design of energy harvesting and gets more and more attention.In this dissertation,the mechanical-mathematical models of the wing-based aeroelastic vibration power-source and energy harvesting systems are built up.Beginning with the point that energy can be harvested from different structural branches,an external store is introduced to design and optimize the dynamic characteristics of the systems.Several nonlinearities,like the freeplay,are used to enlarge the operating flow speed range(OFSR)of the systems.The nonlinear flutter analysis method and the equivalent method by isolating the store are developed to conduct the design and analyses of the performances of the power-sources and energy harvesting systems efficiently.The influences of the type of the Hopf bifurcation,the type of the limit cycle oscillation(LCO)and the flutter mode on the system performances are summarized.The complicated dynamic behaviors and their mechanisms are revealed on the power-source systems.Instructive suggestions are thereby provided on the system design.Starting from the local design,an airfoil-based electromagnetic aeroelastic harvester driven by the pitch and a store-based piezoelectric harvester are firstly built up.They are used to evaluate the effects of the type of LCO and the flutter mode on the harvesting performances from the perspective of energy conversion.In order to study the moderating effect of the store on the power design,a power-source is subsequently developed based on the airfoil-store.Finally,a power-source named deformable wing-store is proposed and used to investigate the impact of the flutter mode change and the freeplay nonlinearity in the store stiffness on the nonlinear behaviors and performances.The main contents and achievements are as follows:(1)The preload freeplay nonlinearity is introduced to the airfoil-based energy harvester.With the nonlinear flutter analysis and the frequency response function,the effects of the type of the Hopf bifurcation and the type of the LCO on the EHFSR and the output power are discussed.The combination mode of the subcritical Hopf bifurcation and the single stable LCO is shown to be better for the higher performance.The bistable LCO always means the subcritical Hopf bifurcation.Compared to the plunge stiffness and the position of the elastic axis,the center of mass,greatly changing the slope of the flutter boundary,has the significant impact on the EHFSR.The output power much depends on the electromagnetic parameters and the flow speed,but not sensitive to the center of mass.(2)The store-based energy harvester is developed by isolating the store subsystem and using the forced vibration modeling method.The forced excitations acting on the store are derived from the aeroelastic responses.Analyses of the forced dynamics and the energy harvesting are conducted.The formulations of the harvested power and efficiency on the forced frequency are approximately presented when there is no freeplay in the store stiffness.The higher harvested efficiency is revealed from the lower frequency response.When the aeroelastic response changes from the perodic-1 motion to the quasi-periodic one by the generation of a high frequency branch,the dual frequency excitation acted on the store are produced and the high frequency branch makes the harvested performance decrease significantly.The larger the ratio of the high frequency branch,the lower the performance.If the freeplay is included in the store stiffness,many harmonic,multi-stable and chaotic motions are generated in the region away from resonance.In the multi-stable motion,the lower the peak frequency,the higher the power and the efficiency.(3)Four nonlinearities,including the freeplay stiffness in the store,the cubic stiffness in pitch,the motion inertia and the aerodynamic force,are considered in the power-source of airfoil-store.Through analyzing the response,bifurcation,the fluid energy absorption and the percentage of store energy with respect to the total ones,it is shown: among the bistable motion induced by the freeplay,the larger one of the airfoil benefits to the higher efficiency absorption of the fluid energy;the larger(smaller)one of the store makes most system energy included in the store(airfoil)such that installing the transducer on the store(airfoil)benefits to the better harvesting performance.Moreover,the crisis should be avoided for which makes the general laws of the fluid energy absorption and vibration energy supply destroyed,while the nonlinear dynamic behaviors such as the period doubling and period windows do not.(4)Nonlinearities produced by the geometry,motion inertia and aerodynamic force are included in the deformable wing-store.An improved method is proposed to make the computation of the ONERA model more efficient and accurate.The period-1 motions resulting from different flutter modes,the second Hopf bifurcation and the quasi-periodic motion related to the second flutter of the corresponding linear system are commented,respectively,along with their impacts on the store energy and its percentage.The calculation results indicate that most system energy concentrates in the store(wing)due to low(high)frequency flutter,and the store energy is larger in the low frequency case than that in the high frequency one,such that installing the transducer on the store(wing)is better.Farther,the second Hopf bifurcation and the quasi-periodic motion make the system energy distribution change significantly,which is bad for harvesting energy from the wing and the store and should be avoided.(5)In view of the property that the equivalent stiffness of the freeplay nonlinearity covering all values to the zero,the freeplay is introduced to the store stiffness to enlarge the EHFSR of the power-source based on the deformable wing-store.The freeplay and the other nonlinearities are observed to dominate the responses in two approximate independent EHFSRs.The design on the enlargement behaviors of the EHFSR and on the type of LCO is therefore accomplished by the nonlinear flutter analysis.The EHFSR is enlarged in the direction of the lower flow speed by the freeplay if there is lower flutter critical flow speed on the corresponding flutter boundary.Additionally,if the store stiffness is greater than its critical static divergence value,and there is only one flutter branch in the effective flutter boundary,or the store stiffness is smaller than its critical one,then the system energy distribution ratio is almost same to the results without freeplay,which benefits to the transducer design.However,if the store stiffness is greater than its critical one,and the effective flutter boundary consists of two flutter branches,then the bistable motions with different frequencies are induced and dominated by the freeplay.Among the bistable motion,the high frequency one makes most system energy concentrated in the store,which is opposite to the other results and can be used to transduce energy from the store in the high frequency flutter case.