Effectiveness of a nonlinear energy sink in the control of an aeroelastic system

The effectiveness of the nonlinear energy sink in controlling the limit cycle oscillations of a nonlinear aeroelastic system is assessed. The system consists of a rigid airfoil elastically mounted on linear and nonlinear springs. The coupled equations of the airfoil and sink are derived using Lagrange's equations. The nonlinear quasi-steady aerodynamics are used to model the aerodynamic loads. Parameters including the mass and placement of the passive controller are varied in order to test its efficiency in suppressing undesirable aeroelastic behavior under varying conditions. The nonlinear normal form governing the responses of the airfoil and the energy sink is derived. The contribution of the aerodynamic, structural and sink nonlinearities to the type of instability is quantified. The results show that the nonlinear energy sink has a limited impact on the system's response in terms of effectively delaying the onset of flutter, changing the type of instability or reducing the amplitude of the limit cycle oscillations.