CNCS Graduate Certificate Recipient

Stephen T. Trickey

Thesis Title: Global and Local Dynamics of an Aeroelastic System with a Control Surface Freeplay Nonlinearity

Ph.D. Final Defense Date:  July 20, 2000

Ph.D. Dissertation Committee:

Lawrence N. Virgin (Chair)
Earl H. Dowell
Henry S. Greenside
Laurens E. Howle
Josiah D. Knight

Abstract:

The effects of a freeplay structural nonlinearity on an aeroelastic system comprised of a 2D typical section with an approximation of Theodorsen theory aerodynamics is presented.  Particular attention is paid to the stability of a nonlinear aeroelastic response or limit cycle oscillation (LCO).  The principal contribution of this work to the field of aeroelasticity lies in the migration of experimental testing and analysis methods from the fields of system identification
and nonlinear dynamics to the arena of a nonlinear aeroelastic stability problem.  Innovations from the field of nonlinear dynamics include the use of time delay embedded coordinates to reconstruct system dynamics, the use of a Poincar\'e section to prescribe an operating point about which a linear description of the dynamics can be approximated, and the use of a basin of attraction measure to assess initial condition dependence.

Two different system identification approaches are taken to generate a linear approximation of the experimental system dynamics about the limit cycle oscillation. A large scale perturbation method using a rotating slotted cylinder gust generator and using a least squares fit of the resulting transient dynamics was shown to be a viable method to ascertain stability information to within the limitations of the experimental setup.  A small scale stochastic stability measurement technique using the natural turbulence in a low speed wind tunnel as the stochastic input and a subspace system identification method to estimate the dynamics of the system provided more repeatable and consistent results.

Also in this work is a derivation of the analytical model and a description of the experimental model. Typical global dynamic features of the aeroelastic system are presented from both numerical simulation and experiments including periodic limit cycle oscillations (LCO), quasi-periodic responses and chaotic responses.