Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Aeronautics and Astronautics

First Advisor

Brad S. Liebst, PhD


The research focused on the development of a new method to identify damaged structural elements from a large flexible space structure on-orbit, using limited measured modal data. Limited measured modal data is loosely defined as measured data containing only a few modal frequencies and less than 10% of the total structural degrees-of-freedom. This effort was decomposed into four specific tasks. The first is the identification of partial modal properties from measured data of the nominal space structure. Second, the finite element model must be adjusted to match the measured nominal partial data. The third task is an analysis of the extent to which structural damage can be localized to individual structural elements using the measured data. In conjunction with this task is the determination of where to best place the limited number of sensors on the structure. Lastly, the identification of structural damage must be performed using the limited measured modal data from a damaged space structure. Identification of the modal parameters was accomplished using the Eigensystem Realization Algorithm, a time domain based method, adopted for use with averaged measured frequency response functions. Model tuning was performed using the Automated Structural Optimization Software package, adapted for model tuning. The method minimizes a cost function based on the mismatch between the measured and analytical eigenstructure. The minimization is solved using the eigenvalue and eigen-vector sensitivities at each iteration step. The determination of prioritized sensor locations and damage localization is performed using the eigenvalue and eigenvector sensitivities.

AFIT Designator


DTIC Accession Number



See also, a selection of Dr. Cobb's publications as an AFIT Faculty member.