1 Nonlinear Modeling and Vibration Characterization of MAV Flapping Wings

Flapping-wing dynamics of MAVs is a complex nonlinear fluid-structure interaction problem that is difficult to analyze using conventional aeroelasticity analysis. This paper presents a fully nonlinear finite element modeling and analysis method for simulation of large-amplitude flapping motion of micro air vehicle wings. The MAV wing is modeled using fully nonlinear beam and membrane elements based on geometrically exact total-Lagrangian beam and membrane theories, and the unsteady aerodynamic loads are estimated using the modified strip theory of DeLaurier with improvements of Han. Direct numerical transient analysis is performed using the Newmark-β method, and the resulted nonlinear wing flapping motion is characterized using time-frequency signal processing techniques based on Hilbert-Huang transform and a newly developed three-point frequency tracking method. Moreover, in-flight dynamic wing deformations are experimentally measured using an 8-camera real-time digital motion analysis system. Numerical and experimental results indicate that flapping-wing dynamics is very complicated and is mainly dominated by the unsteady aerodynamic loads. Hence, a reverse design process by first optimizing the time-varying aerodynamic loads with assumed time-varying wing geometries is recommended. I