Reduction of nonlinear models for control applications

A systematic approach to the model reduction of high-fidelity fluid-structure-flight models and the subsequent flight control design for very flexible aircraft is considered. The test case is for an unmanned aerial vehicle. The full order model involves the geometrically-exact nonlinear beam equations coupled with a linear aerodynamic model. A nonlinear reduced order model is derived to reduce the computational cost and dimension of the full order nonlinear system while retaining the ability to predict nonlinear effects. The approach uses information on the eigenspectrum of the coupled system Jacobian matrix and projects the system through a series expansion onto a small basis of eigenvectors representative of the full order dynamics. The small dimension model is then used to design control laws for applications sush as load alleviation. Results are presented for an aerofoil section and an unmanned aerial vehicle model to illustrate the approach