6.1. PART 1: CONVENTIONAL MASS WEIGHTED CORRELATION 111
ISPE Test Modal Orthogonality
(NASA STD-5002 Method)
ISPE TAM to Test Modal Cross-Orthogonality
(NASA STD-5002 Method)
ISPE TAM to Test Modal Coherence (Real Test Modes)
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Test Mode
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Test Mode
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Test Mode
Figure 6.1: ISPE conventional mass weighted test-analysis correlation matrices.
liably approximated in terms of real normal modes, in spite of the facts that (a) a test article
may exhibit nonlinear behavior and (b) experimental modes are generally complex. In addition,
(c) the correlation metrics are dependent on assumed validity of the TAM mass matrix derived
from the theoretical FEM. Due to these inherent assumptions, which at times are questionable,
standardized NASA and USAF criteria are specified as goals rather than requirements.
Two test projects serve as illustrative examples for application of the widely accepted test-
analysis correlation practice. e ISS P5 modal test, conducted in 2001, demonstrates perfor-
mance of the weighted least squares correlation metrics in the presence of nonlinear test article
behavior. e more recent ISPE modal test, conducted in 2016, demonstrates performance of
the weighted least squares correlation metrics in the presence of complex test modes associated
with close modal frequency spacing.
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