Title page for ETD etd-09202005-090955
|Type of Document
||Improved approaches to the indirect force determination problems via experimental modal analysis
|Wicks, Alfred L.
|Hendricks, Scott L.
|Mitchell, Larry D.
|Mitchiner, Reginald G.
|Robertshaw, Harry H.
|Date of Defense
Solving the inverse problem, finding the applied forces knowing the system characteristics
and the response, has been a difficult problem in structural dynamics. Insufficient
accuracy in the system identification and uncorrelated content in the response
exacerbate the ill-conditioned nature of the indirect-force-determination problem.
Numerical techniques for performing the force determination are exploited and
compared. The characteristics of the force determination problems are investigated
through least squares solution procedures and numerical examples. The credibility
of the estimated forces are studied in the numerical examples using the correlations
of the matrix condition number and the mode contribution factor with the resulting
The focus of this research is the improved estimation of the applied forces. The
two important factors in reducing the force determination error are accurate system
identification and improved conditioning of the system matrix. A variety of techniques
are examined to reduce the system identification error and control the response measurement
uncertainty. The use of rotational or curvature degrees of freedom as an
alternative to the translational degrees of freedom for the response measurements
and for the structural dynamics model yields a quite differently conditioned system
matrix. The choice of a particular degrees of freedom is shown to depend on the
frequency contents of the applied forces.
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