Biomedical Engineering Reference
In-Depth Information
Figure 11 shows a typical FRF (top curve) and coherence (bottom curve) from the
measurement. Each measurement point in Table 1 resulted in one FRF. A peak at a certain
frequency means large vibration at that frequency, which indicates a mode at that
frequency. If the FRF at a particular point shows a valley or low response at a modal
frequency, it is indicating that the point is a node (point of no motion) of the corresponding
mode shape. Using those rules, the mode shapes at any resonant frequency could be
visually determined. A modal analysis program uses mathematical algorithms to compute
the natural frequency, damping and mode shapes from the FRFs. It was used to analyze
data from this test, but may not be necessary if the tester can figure out the modes by careful
visual examination of the FRFs.
Fig. 22. An FRF (top) and coherence (bottom) obtained without a local stiffener on the
surface of the melon.
