Damage location and model refinement for large flexible space structures using a sensitivity-based eigenstructure assignment method.

Abstract

The complexity and size of the next generation of spacecraft, along with the exceedingly high performance and pointing accuracy requirements, mandate that the load carrying capability of the structures by maintained at all times. This work describes a systematic method by which large structures, such as the Space Station Freedom, can be examined periodically to evaluate the integrity of the load carrying structures and determine the location and magnitude of damage to the structure if such damage exists. The Eigenstructure Assignment Damage Location method is developed and successfully demonstrated using modal data from a comprehensive set of tests on a hybrid scaled Space Station truss. The algorithm computes the distance between the measured eigenvectors and a subspace that is spanned by the columns of the damaged structure's system matrix. Damage is located when this distance is zero (for exact data). Once the damage has been located, a simple calculation provides the magnitude of the damage. The method has several unique features, including the ability to easily include loss of mass as well as the ability to filter noise from the measured data. The Model Sensitivity parameter, a scalar measure of each eigenpair's sensitivity to damage in a particular truss member, was developed to assist in pre-test determination of the ability to detect damage in different critical members. The modal strain energy distribution and the Modal Assurance Criterion are also shown to be useful indicators of the ability to detect damage.