Master Thesis Defense

Camden Abrams

(Faculty advisor: Professor Cristina Riso)

Output-Based Limit-Cycle Oscillation Prediction in Aeroelastic Systems with Multiple Structural Nonlinearities and Noise

Thursday, July 9

3:00 p.m.

Montgomery Knight, 317

Abstract:

Current trends in aircraft design are increasingly moving towards lightweight and unconventional configurations for higher energy efficiency. In these concepts, flutter is a critical design concern that must be addressed early in the development phase while accounting for disparate sources of nonlinear behavior. Traditional methods for flutter prediction are typically either based on linear assumptions or are computationally expensive and inefficient for iterative design or optimization. A recently proposed method for predicting limit-cycle oscillations (LCOs) induced by freeplay nonlinearity offers a potential solution to this problem. The method uses output-data from free-decay time histories prior to the onset of instability to estimate recovery rates to equilibrium following perturbations, which are then used to simultaneously estimate both flutter and limit-cycle oscillation boundaries.

This thesis explores three questions to advance the proposed method: How do different forms of structural nonlinearity affect the accuracy of LCO prediction? What level of signal noise can the method tolerate before accuracy critically degrades? Can LCOs due to freeplay be accurately predicted and characterized for models with more complex dynamics? To answer these questions, several studies are performed. First, the method is applied to cases of polynomial stiffness and combined freeplay-polynomial nonlinearity in a two-degree-of-freedom propeller-nacelle model and the results are compared with alternative methods. Then, predictions are performed for increasing levels of simulated noise. Finally, an additional four-degree-of-freedom propeller-nacelle-wing model with various forms of freeplay nonlinearity is considered.

The contributions of this thesis have the potential to improve the prediction of LCOs in the development phase of nonlinear aeroelastic systems.

Committee:

Dr. Cristina Riso (advisor), School of Aerospace Engineering
Dr. Graeme Kennedy, School of Aerospace Engineering
Dr. Keegan Moore, School of Aerospace Engineering