254 R.A. Perez et al. Fig. 23.4 PSD of panel center point response, DIC vs. ROM Fig. 23.5 Panel top-surface and frame with DIC speckled pattern for the case with no shock impingement Spottswood et al. [4] observed that the panel vibration has an effect in the flow near-field. This can be seen in Fig. 23.8, which shows the PSD of the pressure data at the panel quarter, middle, and three-quarter points. The effect of the panel vibration can be observed by the peaks in the PSD at frequencies that match the frequencies of the dominant peaks in the panel response. The exact physical mechanism leading to those peaks has not been determined yet. Next, pressure data obtained for the same nominal flow conditions, but with a rigid specimen instead of the compliant panel, was used. Shown in Fig. 23.9 is the updated PSD of the panel center point response. There is a clear decrease in the response level when compared to the results obtained using the pressure data for the compliant panel. However, the level of the predicted response is still higher than the test data. As discussed by Hollkamp et al. [13] coupling between the structure and acoustics can lead to additional damping. Next, the damping of modes 1, 3, and 8 was increased. Shown in Fig. 23.10 is the PSD of the panel center response obtained with the updated damping matrix. The resulting damping ratios as well as the original ones are shown in Table 23.3. Shown in Fig. 23.10 is the PSD of the response at the center point of the panel. The prediction of the ROM with updated damping agrees well with the test data. As it was mentioned in the Introduction, quantification of the measurement error in the PSP data will be performed in the upcoming wind tunnel tests. This will help clarify if extra damping required to improve the ROM predictions is necessary or if measurement error in the PSP is leading to a higher pressure than the one actually seen by the panel in the test.
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