You are invited to the

Daniel Guggenheim School of Aerospace Engineering

Brown Bag Lunch

featuring research presentations by

Hanif S. Hoseini

Advisor: Dr. Dewey Hodges

and

Johnny Worthy

Advisor:  Dr. Marcus Holzinger

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Hanif S. Hoseini:

“Aeroelastic Stability Analysis of Damaged HALE Aircraft Wings”

Abstract:  Nonlinear aeroelastic analysis of damaged High-Altitude-Long-Endurance aircraft composite wings is considered. The structural model consists of full three-dimensional finite elements continuum model for the damaged area, which is a small localized area of the wing, and a geometrically exact one-dimensional displacement-based finite elements beam model for the undamaged part of the wing. The solid and the beam parts are then rigorously combined using a transformation between the joined nodes of the two models at their intersection. The transformation is derived using the recovery equations of variational asymptotic beam model and employed to eliminate the six degrees-of-freedom of the single joined node of the beam. The validity and efficiency of the method is demonstrated using test cases involving cracks and delaminations in the solid part. It is shown that although the accuracy remains virtually the same between the full three-dimensional model and the joined one-dimensional/three-dimensional model, the computational cost is considerably lower for the latter. Finite-state induced flow theory of Peters is exploited as the unsteady aerodynamic model to compute aerodynamic forces and moments acting on the wing. Combining the structural and aerodynamic models, a dynamic nonlinear aeroelastic element is developed for the time simulation of the dynamic responses of composite high aspect-ratio wings. The model can be conveniently used for analyzing flutter characteristics and time responses to external excitations, as well as synthesizing passive and active flutter suppression control systems. Numerical results verifying the validity of the method are presented and the results are discussed.

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Johnny Worthy:

“Dempster-Shafer Theory Applied to Admissible Regions”

Abstract:  The admissible region approach is often used a bootstrap method to initialize a Bayesian state estimation scheme for too-short-arc measurements. However, there are ambiguities in how prior probabilities are assigned for states in the admissible region. Several approaches have proposed methods to assign prior probabilities, however there are inconsistencies in how the prior probabilities can be manipulated. The application of Dempster-Shafer evidential reasoning theory to the admissible region problem can avoid these ambiguities by eliminating the need to make any assumptions on the prior probabilities.  Dempster-Shafer theory also enables the testing of the validity of the assumptions used to construct the admissible region. This paper introduces Dempster-Shafer theory and formulates the admissible region in terms of plausibility and belief which reduce to traditional Bayesian probability once there is sufficient information in the system.

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About the Brown Bag...

Held every other Friday at noon while classes are in session, the Brown Bag Lunch is an AE tradition in which select graduate and undergraduate students present their research findings before an audience of their peers and mentors.  Lunch is provided.  If a research presentation is required for your program or major, talk to your advisor about signing up for a Brown Bag Lunch.  Approval must be obtained before you can be scheduled.  Scheduling is done through Michelle Hall.