Dynamic Aeroservoelastic Response with Nonlinear Structural Elements

Abstract

Linear structural dynamics, unsteady aerodynamics, control system, and actuator models are combined for linear aeroservoelastic equations of motion that are augmented with nonlinear feedback loops based on the increased-order modeling approach. Although the linear equations are formulated in the frequency domain for best combined efficiency, accuracy, and robustness in industrial environment, the nonlinear feedback loops are modeled in the time domain to provide maximal flexibility in adding nonlinear effects in all the involved disciplines. The linear equations are solved first to provide a baseline response to deterministic or stochastic gusts, maneuver commands, or direct-force excitations using fast Fourier transform techniques. Nonlinear effects are then added in a time-marching process that modifies the linear solution using convolution integrals. The numerical process was used in the Dynresp code that was recently developed as a framework for industrial applications and research in the area of nonlinear structural dynamics. The procedure is outlined with emphasis on structural nonlinearities using a fictitious-mass technique. The numerical example exhibits limit-cycle oscillations due to actuator nonlinearities.