34 A Comparison of Different Boundary Condition Correction Methods 325 301/320 104 101 131 (a) (b) (c) 331/315 302/322 304/319 332/312 Y Z X Y Z X Y Z X 307 303/321 333/309 330/305 Fig. 34.2 TDMs showing (a) the measurement DOFs of the full model, and select node numbers for the (b) full model and (c) baseplate Fig. 34.3 DP FRFs for vertical impacts at the four corners of the baseplate the data collection, special attention was paid to ensuring the quality of the antiresonances of the baseplate drive point (DP) FRFs. Figure 34.3 shows the consistency of the antiresonances of the DP FRFs for the four corners of the TA. Figure 34.4 shows the complex mode indicator function (CMIF) of all references and responses. The higher-order curves of the CMIF appearing to show multiple closely spaced modes near the primary bending modes of the structure are actually small shifts in frequency of the first two modes associated with the roving impact hammer. Twenty-three free-free modes of the TA were extracted from three different curve fits over different frequency ranges to capture sufficient higher-frequency modes for subsequent use in different BCCMs. Table 34.1 summarizes the predicted FEM free-free, FEM FB, and measured free-free test modal frequencies for the target modes (green) and additional modes (orange). The FEM was not updated with the free-free mode shapes before the FB modes were predicted. Figure 34.5 shows plots of the measured free-free target mode shapes.
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