Research On Structural Of Position And Attitude Adjusting System Based On Stewart Platform In Wind Tunnel Test

Wind tunnel test plays an important role in aircraft design process.However,the high unidirectionality of wind tunnel flow field determines the aircraft have to adjust the multiposition frequently to complete the real-time simulation during flight process.Therefore,position and attitude adjusting system of aircraft model has a great effect on the accuracy and stability of wind tunnel test data.It not only requires that the position and attitude adjustment system has the high stiffness of the overall structure,but also have the feature of the high precision,good controllability and good decoupling.With reference to the existing wind tunnel test position and attitude adjustment system,this paper proposes a wind tunnel test experimental position and attitude adjustment system based on six degrees of freedom Stewart platform.The basic configuration of the system is determined,Kinematic inversion for the system is carried out.Based on the kinematic subproject projection,the kinematic Jacobi matrix of the system was deduced.The velocity of the end-effectors slider and acceleration response in the wind tunnel test is simulated,combines with Matlab to the numerical calculation and draws the slider speed and acceleration curve during the pose adjustment process,summarizes the kinematic performance of the system.Based on the Lagrange method,the dynamic model of the system is deduced.Combine the duality of the kinematic Jacobi matrix with the force Jacobi matrix,the variation of the system driving force is deduced.The numerical calculation is carried out with Matlab.The variation curves of system dynamics are drawn,and the dynamic performance of system is summarized.Based on Hooke's law and principle of virtual work,deduce the stiffness matrix of the system under full states with the combination of the system Jacobi matrix.In the wind tunnel test,choose five key locations to simply the model of system structure respectively under the key position.Import the ANSYS Workbench to build the entity-beam element model for static analysis,get the stiffness value of the six-dimensional load,and compose the complete stiffness matrix in this position.Finally,import the stiffness matrix into Matlab for eigenvalue decomposition to find out the weak stiffness direction and stiffness value under this position,and provide the reference to the evaluation of the overall stiffness and the loading during the test.For the uncertainty of the loading during the wind tunnel test,make the model analysis for the system and identify the vibration frequency band of the safety and danger.Firstly,simply the model to the aircraft model and import into the finite element for modal analysis.Sum up the six modes under the five key positions and analyze the danger of excitation frequency in this position.Finally,summarize the risk and safety frequency of the whole system and provide the theoretic basis to the loading during the wind tunnel test to avoid the resonance during the test,and also have the certain guidance meaning for the wind tunnel test.