Nonlinear Actuator Modeling and Describing Function Analysis for Active Flutter Suppression

Active Flutter Suppression involves the movement of control surfaces at high frequencies and rates to suppress aeroelastic instability. This type of rapid motion can saturate actuators, amplifying nonlinear effects. Various modeling topologies used to represent these actuators in industry and academia are considered and evaluated for their differences in nonlinear stability of Active Flutter Suppression. Since linear analysis is typically used in flutter and control system design in industry, thousands of time domain simulations are needed to characterize these nonlinear effects. Gust and sinusoidal excitation is used to evaluate the nonlinear stability limits of a linearly stable AFS system subject to rate limiting. An analytical method to understand the impact of nonlinear rate limiting would prove useful in reducing or eliminating the need for numerical simulation in the early design phases of an AFS aircraft. Sinusoidal input describing functions have potential to predict the sinusoidal input disturbance nonlinear stability limits without the need for such simulation. A frequency domain energy integration method is used to relate sinusoidal disturbance to gust disturbance regarding their respective nonlinear stability limits. This paves the way for future work relating sinusoidal input describing functions to nonlinear gust stability limits for AeroServoElastic response and can take numerical simulation out of the workflow.