Dynamic Model Verification of Large Structural Systems

Finite element models of large structural systems, such as the Space Shuttle or its major components, may contain thousands of finite elements with tens of thousands degrees of freedom. Dynamic analysis to predict structural frequencies and mode shapes is performed after transforming the mass and stiffness matrices, through a series of static reductions, to a reduced set of coordinates which still may include several hundred degrees of freedom. The objective of the present methodology is two-fold: (1) to process test data obtained from either modal survey tests, or slow sine-sweep tests, to extract a set of orthogonal modes best matching the test data while being commensurate with the dynamic model, and (2) to modify submatrices of the dynamic model mass and stiffness matrices to adjust the model to best fit the test data.

The method has been implemented using a linear statistical sequential estimator for computation on a CDC computer. Demonstration problems involving Space Shuttle Quarter-Scale vibration test data and dynamic models have been run. This paper will discuss the general methodology and experience to date.