Masters Theses

Date of Award

12-1994

Degree Type

Thesis

Degree Name

Master of Science

Major

Engineering Science

Major Professor

T.G. Carley

Committee Members

J.F. Wasserman, G.S. Jordan

Abstract

A statistically generated weighting function for a second order polynomial curve fit of residual functions has been developed. The residual flexibility test method, from which a residual function is generated, is a procedure for modal testing large structures in an exter- nal constraint free environment to measure the effects of higher order modes and interface stiffness. This test method is applicable to structures with distinct degree of freedom inter- faces to other system components. A theoretical residual function in the displacement/force domain has the characteristics of a relatively flat line in the lower frequencies and a slight upward curvature in the higher frequency range. In the test residual function, the above mentioned characteristics can be seen in the data, but due to the present limitations in the modal parameter evaluation (natural frequencies and mode shapes) of test data, the resid- ual function has regions of ragged data. A second order polynomial curve fit is required to obtain the residual flexibility term. A weighting function of the data is generated by examining the variances between neighboring data points. From a weighted second order polynomial curve fit, an accurate residual flexibility value can be obtained. The residual flexibility value and free-free modes from testing are used to improve a mathematical model of the structure. The residual flexibility modal test method is applied to a straight beam with a trunnion appendage and a space shuttle payload pallet simulator.

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