110 H. R. Kramer et al. Fig. 2 The modal assurance criterion scores (experimental to experimental) for the three test stand configurations: (a) undamped, (b) damped, (c) stiffened, (d) undamped vs damped When damping is applied to a system, a single mode can be split into two, lower amplitude modes. Each of the two resultant modes exhibit part of the behavior of the original mode shape. In Figure 2d mode splitting was observed between the undamped and damped configurations. Specifically, modes 3, 4, 5, 8, and 9 of the undamped configuration appear to have split, corresponding to the main diagonal of Figure 2d being stretched along the X-axis. Visual inspection of the extracted mode shapes were consistent with this finding, providing an explanation for five of the six additional modes. The last additional mode, mode 15 of the damped configuration, had very low similarity with any nearby modes. Aside from mode splitting, spontaneous addition of a mode is another potential result of changing the dynamics of a structure (such as adding damping). From this analysis, it can be concluded that the dynamics of the test stand shifted by a measurable amount due to the changes we made. Transmissibility Analysis The modal data from our impact tests were useful for identifying dynamic changes between test stand configurations. However, the relative motion between points on the structure was also of interest. One metric that can be useful for understanding relative motion between DOFs is transmissibility. Transmissibility (TR) can be derived using several methods, leading to slightly different interpretations. To avoid ambiguity, a brief review of how we calculated transmissibility is described.
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