An impact with a calibrated modal hammer was made at the top-right corner at Location 1 in Figure 6 of the Upright structure. The displacement data was collected at the same 8 target locations shown in Figure 6. The displacement responses at 7 out of the 8 recorded locations were used to expand to 3112 finite element nodes using the expansion process. To identify the number of mode shapes required in the expansion process, an (Fast Fourier Transform) FFT was performed on a response measurement made at top-right corner of the Upright (one of the 8 measured locations). This location was chosen because all modes excited can be observed at that location. The results of the FFT are shown in top portion of Figure 7. The displacement response was collected for 4 seconds using 200 frames per second cameras that is, at 200Hz sample rate. So a maximum of 100Hz frequency data could be captured using DIC as seen in top portion of Figure 7. The bottom portion of the Figure 7 shows a typical frequency response of BU collected using Laser Doppler Vibrometer (LDV). The FFT collected using LDV gives a better interpretation of the higher modes of the BU. The two out-of-plane modes, at 26 Hz and 78 Hz are mainly excited by the impact as seen from Figure 7. As seen from previous studies [1- 5], the expansion process should at least contain those modes excited by the forcing function for proper expansion. The first five modes of the Upright (which include the two out-of-plane modes excited by the impact) are used in this case for expansion purposes. Figure 7: Details of the excitation force and response of the structure. 207
RkJQdWJsaXNoZXIy MTMzNzEzMQ==