11 Use of Continuous Scanning LDV for Diagnostics 135 80 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 Frequency [Hz] Correlation [%] 270 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 Fig. 11.10 Degree of correlation between averaged sum of the sidebands with and without noise The proposed simulations suggest that the spectral sidebands of the calculated ODS show changes from its undamaged configuration. So, mapping the evolution of such changes could provide useful insight on the health state of structures under diagnosis. However, the number of cases studied in here is still too small for generalizing conclusions. Nevertheless, the correlation of the sidebands can offer an advantage in terms of quasi real-time diagnostic. This is possible thanks to the continuous scanning which can provide both spatial and temporal information. Finally, this technology could be implemented in several applications but more vigorously, for example, in the assessment of bolted structures. Future works will need to consider additional damage cases, different boundary conditions and also experimental validation for one of the test cases simulated. 11.3 Conclusions This short paper wished to demonstrate the capacity of continuous scanning as diagnostic tool. The CSLDV is often used in modal analysis thanks to its high resolution ODS. However, that requires data processing which for cases of quasi real-time assessment would not be suitable. The same applies to the standard stepped scanning method where the ODS recovery can be even lengthier. This paper showed that the sole use of ODS spectral sidebands is sufficient for monitoring the health state of a structure, whose surface can be continuously scanned and monitored by the laser beam. The work was based on numerical simulation of the LDV output signal from structures which were artificially modified by reducing the thickness of some elements. Levels of damage severity were considered and those showed clear alteration of the sidebands. Similar output was achieved by adding noise to the simulated time signals. Future works will try to address more complicated test cases and experimental validation.
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