3 A Somewhat Comprehensive Critique of Experimental Modal Analysis 33 Table 3.2 Mass-weighted self-orthogonality (absolute values) of SFD-2018 complex experimental modes Table 3.3 Mass-weighted self-orthogonality (absolute values) of SFD-2018 “Rectified, Real” experimental modes . [COR21] =[ϕV2]∗ [M] [ϕV1] (Cross-orthogonality, [ϕV1] & [ϕV2] =unit mass normalized complex or real modes) (3.32b ) Employing the modified definition for self-orthogonality, the mass-weighted (using the ISPE TAM mass matrix) selforthogonality of the SFD-2018 “credible” complex experimental modes (previously summarized in Table 3.1) is provided in Table 3.2. It is interesting to note that the predominantly real experimental modes (colored in light blue) satisfy US aerospace community orthogonality criteria [1, 2], that is, off-diagonal term magnitudes ≤ 10% . Employing the real part of rectified SFD-2018 modes, following a practice adopted by several US aerospace organizations for “real test mode” approximation (RTMA) [3], the orthogonality matrix (originally complex mode) terms exhibit closer compliance with respect to orthogonality criteria, as shown in Table 3.3. Finally, orthogonality of linear least-squares refitted (real) SFD-2018 modes, computed according to Eqs. 3.26 and 3.27, a common practice in many experimental modal analysis applications, regardless of particular modal estimation technique [15], is provided in Table 3.4.
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