8 Characterization of Torsional Vibrations: Torsional-Order Based Modal Analysis 87 Table 8.2 Comparison of modal parameters: FS and LMS virtual.lab Fixed sampling LMS virtual.lab Natural Damping Natural Damping frequency ratio frequency ratio Order 1 18.32 Hz 1.90 % 18.27 Hz 1.64 % 51.26 Hz 3.36 % 51.23 Hz 3.36 % 74.00 Hz 2.28 % 74.04 Hz 2.30 % Order 2 18.28 Hz 1.91 % 51.28 Hz 3.35 % 73.99 Hz 2.30 % Order 3 18.00 Hz 1.97 % 51.21 Hz 3.30 % 73.94 Hz 2.28 % 20 40 60 80 100 120 10−4 10−2 100 102 20 40 60 80 100 120 −π 0 π Frequency [Hz] Phase [rad] Fig. 8.10 Multi-orders algorithm:comparison between measured and resampled orders 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s ss s s s s ss s s s s s s s s s s s s s s s v v v v v v v v v v v v v v v s s s s v v v v v v v o o o o o o f [Hz] Number of poles, n Fig. 8.11 Multi-orders algorithm: stabilization diagram This example can be used for validating the Multi-orders algorithm. Figure 8.10 shows the same order for different measurement channels before and after the resampling step. It confirms that the resampling step has been performed in the correct manner. Figure 8.11 shows the stabilization diagram obtained after having applied the multi-orders algorithm. The three main resonances are very well identified with a perfect match with the LMS Virtual.Lab natural frequencies and damping ratios, as shown in Table 8.3.
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