38 R. N. Coppolino 3.8.3 Measured Data Acquisition and Measured Data Analysis (Covered in Previous Publications) Measured data acquisition, the technical discipline of highly experienced laboratory personnel, involves selection and verification and validation of excitation and response measurement resources to be used in a modal test. On the other hand, measured data analysis is a discipline that requires both (a) measured data acquisition expertise and (b) utilization of advanced mathematical tools and associated personnel (who are ideally experienced in both data acquisition and analysis). Key products of these ITAP steps are as follows: (a) Determination of linear or nonlinear modal test article behavior (nonlinear behavior is beyond the scope of this chapter). (b) Estimation of MI/MO frequency response arrays and associated coherence arrays required for experimental modal analysis. Close attention must be paid to coherence array data to establish high signal-to-noise qualities of estimated frequency response arrays and accurate experimentally determined system modes. 3.8.4 Experimental Modal Analysis (a) Estimated modes based on virtually all “digital” era experimental modal analysis algorithms are sometimes highly complex . (b) The SFD-2018 technique produces “analog” era type decoupled modal FRFs (without the burden of an excessive laboratory timeline, a unique feature of SFD-2018). (c) The SFD-2018 technique produces state-space complex experimental modes that automatically satisfy US aerospace community orthogonality standards, independent of an analytical TAM mass matrix. (d) The Aerospace Corporation’s approximate real modes (formed by the real part of “rectified” complex experimental modes) produce a mass-weighted orthogonality matrix that produces generally acceptable satisfaction of US aerospace community standards (provided the TAM mass matrix is based on an appropriately defined system dynamic model). 3.8.5 Test-Analysis Correlation The RTMA modes (formed by the real part of “rectified” complex experimental modes) produce a mass-weighted crossorthogonality matrix (correlating analytical and experimental modes) that produces generally acceptable satisfaction of US aerospace community standards (provided the TAM mass matrix is based on an appropriately defined system dynamic model) . 3.8.6 Test-Analysis Reconciliation (a) Reconciliation of the test article’s FEM with experimental modal analysis results may be accomplished on the basis of the RTMA technique and parametrically varied system dynamic modes. This is the basis for virtually all modern test-analysis reconciliation strategies. (b) In exceptional situations, for example, high modal damping and highly complex modes, it may become necessary to perform test-analysis reconciliation using complex experimental and analytical modes. It is finally noted that this chapter represents yet another step toward establishment of an improved ITAP process. Continued efforts in the academic and industry communities are absolutely encouraged.
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