12 Feasibility Study of SDAS Instrumentation’s Ability to Identify Mobile. . . 115 Fig. 12.20 FRFs using All Forces as References vs FRFs using Subset of Least Correlated Forces as References, CT Speed 2 Table 12.1 Summary of parameter variation CTspeed Damping 1 2 3 4 5 1% X X X X X 3% X X X X X 5% X X X X X Broadband noise (1% damping) 1 2 3 4 5 30 ugrms X 100 ugrms X 200 ugrms X Table 12.2 Percentage of target modes extracted CTspeed Damping 1 2 3 4 5 1% 93% 93% 93% 89% 93% 3% 75% 89% 75% 79% 82% 5% 36% 46% 43% 36% 39% Broadband noise (1% damping) 1 2 3 4 5 30 ugrms 61% 100 ugrms 43% 200 ugrms 43% Table 12.2 shows the percentage of the 28 target modes in this study that were automatically or very clearly selected from a stability diagram/CMIF. With no sensor/ambient background noise present, the highest number of target modes could be identified for CT speed 2. With no sensor/ambient background noise present, the first three target modes, which were the most challenging modes to extract cleanly in all data sets, were most easily identified for CT speed 5. As expected, increasing modal damping and the sensor/ambient background noise levels make identification of the target modes more difficult. In the case of sensor/ambient background noise however, the addition of any level significantly reduces the ability to identify target modes. This study did not run the combined highest levels of noise and highest levels of damping in the same case. This was primarily because it was perceived by the analyst that this would generate the unrealistic case where no target modes could be extracted. In reality, the noise levels and damping levels vary from frequency to frequency and as such, it is likely that some modes will not be extracted because of a high of combination of noise level and damping while others will be extracted. Detailed accounts of all the results are presented in the upcoming paragraphs. Speed Parameter Sensitivity Varying the CT speed did not have a significant impact on the overall ability to extract modal parameters in this simulation. CT speed variations primarily impacted identification of the first three target modes. In the stability diagrams shown in Fig. 12.21 for CT Speed 1 and CT Speed 5 with 1% modal damping level and no sensor/ambient background noise, there
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