10 An Experimental Modal Channel Reduction Procedure Using a Pareto Chart 105 Fig. 10.4 Pareto chart for the laser vibrometer test Table 10.1 Data used to create the Pareto chart Location AvgRMS %of total Cum% Node 7 0.1382 42 42 Node 6 0.0640 19 61 Node 5 0.0412 13 74 Node 8 0.0239 7 81 Node 9 0.0201 6 87 Node 10 0.0120 4 91 Node 11 0.0080 2 93 Node 4 0.0065 2 95 Node 1 0.0057 2 97 Node 2 0.0053 2 99 Node 3 0.0046 1 100 Total 0.3294 10.5 Modal Testing A modal analysis was performed to investigate the validity of the sensor location identification method, to illustrate the different sensor set results (Step 7). Four tests were performed with different levels of instrumentation. These tests included a base test with sensors placed at each measurement location from the laser vibrometer test, a test corresponding to the 95 % Pareto level, one corresponding to 90 % and one corresponding to 75 %. The accelerometer locations for each of the tests can be seen in Fig. 10.5. All of the accelerometers were mounted to measure acceleration in the Z direction except for the ones on the vertical stabilizer, which were mounted to measure in the Y direction. The final step (Step 8) was to conduct a complete modal analysis of the structure. The aircraft was excited at several different locations, all in the Z direction, that are identified by the red dots in Fig. 10.6 and a load cell was attached in line with the shaker’s stinger to measure input force. The accelerometers and excitation devices were routed through a National Instruments data acquisition board that was connected directly to a computer. Data capture and analysis was performed using ModalVIEW, software designed specifically for modal testing and analysis. The natural frequencies presented are the average of eight tests. These eight tests are comprised of two tests at each of the four excitation locations. The measurement type was set to FRF-EMA in ModalVIEW for an experimental modal analysis. The sampling rate was left at the default of 1651.61 Hz with the resolution set to 0.1 Hz. The shaker was activated so that the Super Hauler
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