Research On Electro-hydrostatic Actuator Driven By Dual Piezoelectric Stacks For Morphing Aircraft Applications

Smart material-based electro-hydrostatic actuators have the advantages of compact structure,light weight,and large output force;therefore,they have wide application prospect and important research significance in the fields of morphing aircraft and airborne hydraulic systems.In this thesis,based on the research of morphing actuators at home and abroad,an electro-hydrostatic actuator driven by dual piezoelectric stacks is developed for application in morphing aircraft,which require lightweight and compact actuators.The theoretical modeling analysis and experimental research are conducted,and furthermore,a digital prototype of the morphing aircraft is designed to analyze and verify the feasibility of the actuator in the actuation of a morphing wing.Firstly,based on the characteristics of piezoelectric stacks and the principle of nested structures,a lightweight and compact dual piezoelectric stacks compound driven actuator is designed.Furthermore,based on researches on smart material-based pumps' valves at home and abroad,a dual piezoelectric stacks-based pump and valveless electro-hydrostatic actuator is developed.The parameters of the diffuser/nozzle's are changed in order to carry out a comprehensive study of flow distribution characteristics in the valveless actuator.Secondly,as the driver of the actuator,the dual piezoelectric stacks pump directly determines the flow rate and accuracy of the actuator;therefore,the electrical-mechanical conversion output performance of the actuator is simulated and experimentally studied.Based on the asymmetric Maxwell hysteresis model and dynamics equations,the rate-dependent hysteresis model of the pump is established.The simulation results show that the established simulation model can accurately describe the output displacement of the pump.The experimental results show that the maximum displacement of the pump exceeds 40?m under the condition of stacks' maximum axial size 20 mm and input voltage 140V;the displacement attenuation is only 7.1% at 600 Hz,which shows that the output performance remains good at high frequency.Thirdly,the mechanical-hydraulic conversion process of the valveless electro-hydrostatic actuator is theoretically modeled and simulated.Through numerical analysis,it is concluded that the local hydraulic resistance of the diffuser/nozzle has a crucial influence on the performance of the actuator.The experimental results show that the maximum peak flow of the actuator is 0.386L/min,and the peak frequency is 400 Hz under the condition of a peak-to-peak input voltage of 120 V and 0.6MPa system pressure bias.Nevertheless,the load capacity of the valveless actuator is relatively low,which makes it difficult to be applied in the actuation of the morphing aircraft.In view of the above research,in order to improve the actuator's load capacity,a physical prototype of the dual piezoelectric stacks-based actuator with passive valves is developed.The experimental results show that the maximum peak flow of the actuator is 1.08L/min,the peak frequency is 400 Hz,and the load capacity can reach more than 12Kg;thus theoretically it can be used as the actuator of the morphing aircraft.Finally,by contrastively analyzing morphing schemes of various morphing aircraft and considering the performance of the actuator in this thesis,the variable aspect ratio wing is selected.The digital prototype of the variable aspect ratio wing is built using the actuator with passive valves as the driver.The feasibility of the actuator's ability to drive the morphing wing is demonstrated in simulation from the following three aspects: the torsional damping of hinges,morphing velocity,and aerodynamic load of the wing.The simulation results show that the actuator with passive valves can provide both enough power and morphing range to the morph part of the wing under certain boundary conditions.The main innovations of this thesis are: based on the principle of differential liquid resistance between diffuser and nozzle,a kind of valveless unidirectional flow distribution structure is proposed;and based on the expansion principle of piezoelectric stacks,a dual piezoelectric stacks compound actuator is proposed;furthermore,combining the nozzle/diffuser structure and the dual piezoelectric stacks compound actuator,a compact electro-hydrostatic actuator which has valves with no moving part is constructed.