108 A. Mario Puhwein et al. (a) (b) Fig. 5 Visual representations of mode shapes at a) 270, 4 Hz form “front” direction b) 140, 7 Hz from “top” direction free end. The bearing housing on the right-hand side also shows a rotational movement around its mounting. Fig. 5b) shows a mode shape at 140, 7 Hz with a damping ratio 0, 92%. The 3D animation clearly shows that the flexible plate exhibits a torsional mode. This is clarified by the movement of the attachment parts, in particular by the counter-movements of the bearing housing and the motor. In both the “front” and “top” measurements, the discs with the composite cover are excited by an impact from the automatic modal hammer onto the support steel disc. Fig. 6 presents the MAC matrices (see equation 2) determined for the measurements shown in Fig. 4 and 5, comparing the modes of the respective measurements. The matrix in Fig. 6a) shows the results of the “front” direction measurement, where it can be observed that the modes at 41.7 Hz and 270.4 Hz exhibit a similarity of approximately 40%. This can be attributed to the tilting motion of the bearing housing around the plate in both modes. In the “top” direction measurement, mode similarities are also present, which were confirmed through detailed analyses of the mode animations. Notably, the modes at 42.7Hz and140.7Hz, as well as at 89.7Hz and229.0Hz, show a similarity of 55%and45%. These similarities were again traced back to the pronounced movements of the bearing housing. (a) (b) Fig. 6 MAC matrix for the respective measurement to compare the modes with one another for a) ‘front’ direction b) ‘top’ direction
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