Nonlinear Aeroelastic System Identification And Limit Cycle Oscillation Analysis

Due to complex and unknown mechanism of a non-linearness, it is effective to build up a nonlinear aeroelastic model based on the flight testing data. The nonlinear aeroelastic model is identified by block-oriented model identification method using the testing data, based on the input or output data of the aeroelastic system. Meanwhile, the problem of the nonlinear aeroelastic system respond is studied. First, the assumption of the nonlinear of the nonlinear aeroelastic system is the function of the input or ouput of the system. The formula of the nonlinear aeroelastic system is derived in the type of block-oriented, and a block-oriented identification frame of the nonlinear aeroelastic system is established. The process of the noniterative identification of Hammerstein model, Wiener model and Feedback Block-Oriented model are derived in detail. Meanwhile, it presents how to construct the orthonormal base functions using the information of the prior poles.The nonlinear operator and the linear time invariant systems of Hammerstein model, Wiener model and Feedback Block-Oriented model are expressed by the polynominal function of the input or output and by the orthonormal base functions using the information of the prior poles, respectly. The parameters are estimated using least square estimation (LSE) and singular value decomposition (SVD). Effective are the methods proved by the nonlinear airfoil and the nonlinear wing cases.Finally, the problem of a nonlinear aeroelastic system respond is studied. The flutter speed and frequency of the corresponding linear model of a nonlinear aeroelastic system is analysed by the V ? gmethod. The range of speed where a limit-cycle oscillation occurs in the initial condition is studied. The relation of the amplitudes and the frequencies of the limit-cycle oscillation of the nonlinear airfoil and the velocities of the limit-cycle oscillation are studied.