Research On Thermal-variable Stiffness Active Control Of Cylindrical Shell Based On SMA Actuator

In the development of modern aircraft,the technical index of flight velocity is being enhanced continuously,and the aerodynamic thermal coupling effect increases significantly during the flight.The temperature gradient appears in the aircraft outer structure under the aerodynamic thermal environment,leading to the local thermal stress that changes the material properties.In the same time,the elastic modulus and strength decreases under the load of high temperature.When they effect together,the stiffness of the aircraft outer structure changes.Vibration and deformation appearing subsequently lead to the uncontrollable aerodynamics and operation reverse effect.In this topic,by analyzing the stiffness variation of the aircraft outer structure under thermal load,the smart structure is employed to design a new stiffness-active-control actuator to adaptively control the variable stiffness of the aircraft under aerodynamic thermal load.In this paper,researches are conducted on the variable stiffness control of the typical aircraft outer structure under thermal load.The general contents are listed below.The smart-element mathematic model of the thin shell of revolution is developed,and the counterpart hybrid programming simulation system is built to solve the model.The dynamic model of ring shell structure is developed based on the generic shell theory.Finite difference method is employed to transform the model into smart-element matrices model containing control terms.Axial dimension added on the basis of ring shell,circumferential difference and axial difference are conducted in the cylindrical shell.Then considering the temperature effects,the smart-element model of cylindrical shell under thermal load is developed.Based on the smart-element models of ring shell and cylindrical shell,C++ and MATLAB are employed to build the hybrid programming simulation system.Cosine-distributed piezoelectric ring shell and two-ends simply supported cylindrical shell are employed as the examples to be solved respectively.After the simulations in time and frequency domain,the modal properties of the structure in controlled and uncontrolled situations are obtained.By the comparison with theoretical results,the validity of the smart element matrices model and the hybrid programming simulation system are verified.Stiffness active control actuator with shape memory alloy(SMA)is designed and optimized.Based on the constitution of the cylindrical shell smart element matrices model and the modal properties obtained by the hybrid programming simulation,the screw-type stiffness active control actuator driven by SMA is designed.Finite element simulation is employed to calculate the static properties and modal properties of the cylindrical shell in the control of the screw-type actuator with different configuration parameters.Based on the simulation results analysis,the configuration parameters of the actuator are optimized,and the optimum design of the screw-type actuator is obtained.Based on the optimum screw-type actuator,the cylindrical shell stiffness active control experiment is conducted.After the mechanical properties tests of the SMA driving source,the modal properties experiment results of the cylindrical shell stiffness active control system in different heating time are recorded and analyzed.The correctness of the theoretical cylindrical shell stiffness control model and the calculation results in this paper are proved,and the stiffness control effect of the screw-type actuator exerting to the cylindrical shell is verified.