90 B. Schwarz et al. Out of Phase ODSs EMA Models a b 0 2000 4000 6000 8000 2000 4000 6000 8000 S1 S2 S1 S3 S5 S7 S9 0 Expanded ODS Stimulated ODS Out of Phase ODSs FEA Models 0 2000 4000 6000 8000 1E+04 1E+04 2000 4000 6000 8000 S1 S2 S1 S3 S5 S7 S9 0 Expanded ODS Stimulated ODS Shape Participation Shape Participation Fig. 8.19 (a) EMA mode shape participation in the ODS’s. (b) FEA mode shape participation in the ODS’s Experimental vibration data always includes bothreal world boundary conditions andreal-world damping. It was shown in the first example that complex ODS data can be accurately decomposed and expanded using the normal mode shapes of the bearing blocks and base plate of a rotating machine. These normal mode shapes were derived from a relatively simple FEA model with free-free boundary conditions and no damping. Normal modes can be used to expandcomplex vibration databecause themodal participation factors used to decompose and expand the complex data are also complex valued. In the second example, normal mode shapes were used to decompose and expand real valued time waveforms. Curve fitting FEA mode shapes to this data yielded an unexpected participation of the mode shapes when two In-Phase sine wave forcing functions were applied to the top two corners of the Jim Beam structure.
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