3 Using Hybrid Modal Substructuring with a Complex Transmission Simulator to Model an Electrodynamic Shaker 31 Fig. 3.10 TS test vs FEM—(Top) natural frequency, and (Bottom) MAC plot Curve fitting for the experimental data was done using the Algorithm of Mode Isolation (AMI) [10, 11]. This program successively fits and subtracts single DOF modal models from the experimental data until all significant peaks have been eliminated. Natural frequencies, damping ratios and mass normalized modeshapes are computed and gathered from the AMI output data. To validate the FEMs, the natural frequencies and modeshapes of each were compared to their experimental counterparts. For the TS, or the half cube isolated on foam, the comparisons are shown above in Fig. 3.10. In the top portion, the composite FRF of all the test points is given as the blue curve. The black vertical lines represent the FEM natural frequencies. There is very good agreement through 5000 Hz. The lower portion displays a Modal Assurance Criterion (MAC) plot, comparing the test and FEM modeshapes. A value closer to 1, or a color closer to black in the plot, indicates that the modes are similar in shape. This then shows that the first 29 test modes very closely correspond to FEM modes. These are the same modes whose frequencies corresponded closely in the upper plot.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==