Stochastic Optimization of Nonlinear Energy Sinks for Nonlinear Aeroelasticity

Abstract

Nonlinear Energy Sinks (NESs) are found to be promising for mitigating vibrations passively. The focus of this thesis is to investigate the mitigation of limit cycle oscillations (LCOs) in wings using these NESs. For this purpose, a NES attached to a two degree-of-freedom airfoil with nonlinear stiffness in pitch and heave is modeled. Depending on the nonlinear properties of the airfoil, it is shown to exhibit super- or sub-critical LCOs. To mitigate these LCOs, a NES is designed based on a stochastic optimization approach. This optimization approach is capable of accounting for various sources of uncertainties, including initial and loading conditions. The optimization approach is also tailored to handle potential discontinuities in the response of the airfoil. The non-smoothness of the response can be either due to sub-critical LCOs or due to the activation of the NES. Several stochastic optimization problems with the objective of maximizing the mean reduction of LCOs are presented in this work.