138 7. RECONCILIATION OF FINITE ELEMENT MODELS AND MODAL TEST DATA
Table 7.3: Summary of FEM parameters adjusted for reconciliation
TSS02
Update ValueOriginal ValueDescriptionParameter Update Value Update Value % Change% Change% Change
TSS04 TSS17
Table 7.4: ISS P5 data sets TSS2, TSS4, and TSS17 test to updated FEM NASA-STD-5002
compliance status
TSS02
Mode Post-Test (Hz) ∆F (%)Test (Hz) COR (%) Post-Test (Hz) ∆F (%)Test (Hz) COR (%) Post-Test (Hz) ∆F (%)Test (Hz) COR (%)Freq (Hz)
Pre-Test
Comments
Satisfies NASA STD-5002 Modal Frequency
and On-Diagonal Cross-Orthogonality Goals
Satisfies NASA STD-5002 Modal Frequency
and On-Diagonal Cross-Orthogonality Goals
Frequency Band associated with Reduced
MI/MO Coherence (Strong Nonlinearity)
TSS04 TSS17
7.2.5 ILLUSTRATIVE EXAMPLE: ISPE MODAL TEST
While ISPE FEM-test reconciliation activities have been the responsibility of NASA/MSFC,
it is of interest here to engage in an independent hypothetical exercise that employs RMA sen-
sitivity and modal cost function (norm) minimization methodology tools. A hypothetical pair
of single parameter mass and stiffness sensitivity matrices, which are “rigged” to effect perfect
test-analysis correlation (ISPE modes in the 0–65 Hz band) for a unit value of the sensitivity
parameter, p, are defined. While the ISPE modes estimated with SFD-2018 are complex, the
target test modes for the present exercise are the real parts of those modes.
Migration of ISPE modal frequencies, presented in Figure 7.8, illustrates the capability of
RMA to track substantial modal frequency changes associated with large parametric variation
(as previously noted in Figure 7.1). Large modal frequency variations with “cross-overs” cannot
be adequately tracked through the use of exact and approximate modal derivatives.
Results of Monte Carlo based minimization of the single-parameter-based modal cost
function search analysis, and a summary of ISPE original TAM, reconciled TAM, and SFD-
2018 test modal frequencies, respectively, are summarized are illustrated in Figure 7.9.
Displays of SFD-2018 test mode orthogonality, TAM-test mode cross-orthogonality, and
TAM-test modal coherence, for the original and reconciled TAMs are illustrated in Figure 7.10.
Please note that the above ISPE model correlation and reconciliation exercise represents
an idealized hypothetical process. Official ISPE model correlation and reconciliation results,
performed by NASA/MSFC, are not presented in this book.