37 Development of Simplified Models for Wind Turbine Blades with Application to NREL 5 MW Offshore Research Wind Turbine 397 Table 37.1 Comparison between the nominal and calibrated parameter values Section number Nominal value Calibrated value Flapwise 1 0 0.3615 2 0 0.4175 3 0 0.0407 4 0 1.9738 5 0 0.2344 6 0 0 Edgewise 1 0 0.5018 2 0 0.5339 3 0 0.0616 4 0 0.5096 5 0 0.8169 6 0 0 Torsional Entire blade 0 0.0705 Fig. 37.4 Deviation of the nominal (a) and the calibrated beam model (b) from the baseline FE model. Curves show the sum of the magnitude of accelerances and stembars indicate the location of eigenfrequencies Table 37.2 Comparison between eigenfrequencies of the nominal and updated beam models and the baseline FE model in (Hz) Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Mode 6 Mode 7 Mode 8 Nominal beam model 0.767 0.796 2.226 2.953 5.088 6.808 7.397 8.968 Updated beam model 0.574 0.732 2.087 2.633 4.580 6.179 6.853 7.873 Baseline FE model 0.577 0.727 2.136 2.622 4.526 6.229 6.822 7.906 Bottasso et al. [4] and, likewise, is attributed to the fact that the tip segment contributes the least to the rigidity of the structure. Herein, these parameters are frozen at their nominal values in the model updating procedure. The FE model calibration procedure explained in Sect. 37.4 is used to estimate the structural parameters of the parameterized beam model. The results of the FE model updating procedure are listed in Table 37.1. Figure 37.4a demonstrates a comparison between the frequency response of the nominal beam and the baseline model summed over all the sensors in the frequency interval of 0.4–8 Hz. While this figure presents a significant difference between the prediction based on the calibrated nominal beam model and the baseline model, Fig. 37.4b shows that the updating procedure converged and the predictions based on the beam and the baseline model are well aligned in terms of natural frequencies, and frequency responses in the frequency range of interest. Table 37.2 reports the eigenfrequencies of the baseline model as well as the eigenfrequencies of the nominal and calibrated beam model. The ability of the calibrated beam model to predict the low-frequency mode shapes of the baseline model is illustrated in Fig. 37.5. The degree of correlation between the mode shapes of the baseline model and the calibrated beam model is quantified using the Modal Assurance Criterion (MAC) defined by
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