31 Comparison of Multiple Mass Property Estimation Techniques on SWiFT Vestas V27 Wind Turbine Nacelles and Hubs 335 Table 31.1 Final list of inertia properties for V27 nacelles Property Nacelle # Crane Load Cell Modal Inversion 1 6804 7038 5577 2 6577 6781 5551 3 6668 7203 1 0.67 0.25 2 0.61 0.16 3 0.65 1 0.09 0.04 2 0.07 -0.08 3 0.09 1 0.06 2 0.12 3 1 2569 2 2453 1 9937 2 10876 1 9038 2 10141 Mass and Inertia Properties of V27 Nacelles Izz (kg*m2) CGz (m) Ixx (kg*m2) Iyy (kg*m2) CGx (m) CGy (m) Mass (kg) Table 31.2 Final list of inertia properties for V27 Property Hub # Load Cell Bifilar Pendulum Modal Inversion** Mass Line Inversion 1 481.7 508.1 483.7 2 474.0 CGx (m)* -0.438 -0.754 Cgy (m)* 0.015 0.105 CGz (m)* 0.005 -0.143 Ixx (kg*m2) 26.6 69.1 110.8 Iyy (kg*m2) 76.3 343.6 Izz (kg*m2) 86.2 151.6 1 Mass and Inertia Properties of V27 Hubs (Pitch Yaw Linkage Included) * Origin Defined at Front Face of Hub Rotor About the Center Using Rotor Csys ** Includes the Effective Mass of the Airbags Mass (kg) The modal inversion method and the mass-line inversion method were used to calculate the rigid body mass matrix of the hub. The resulting terms were compared to the mass obtained from the load cell and the inertia term obtained from the bifilar pendulum approach. Table 31.2 lists the various terms obtained from all of the methods used. As seen in the table, the modal inversion and mass-line inversion methods yield approximately the same mass as the load cell, to within 5 %. The CG locations are similar between both methods, but there is an observable discrepancy between the two. The inertia for the bifilar pendulum is significantly lower than either of the two methods, and the mass-line inversion is noticeably higher than the modal inversion. All four methods used to obtain the mass and inertia properties are discussed here to explain possible sources of error and to comment on their accuracy. The load cell used to measure the mass is a calibrated transducer with accuracy down to the tenth of a kilogram, so these measurements are assumed to be accurate. Use of the bifilar pendulum assumes that the two straps are equal in length and hang perfectly vertical, but since visual inspection of the straps shows that neither of these assumptions was valid, the resulting term is likely to be inaccurate. The modal inversion was shown to have a high fit between the test data and the synthesized response. The highest percent error on any of the modes was 2 %, also indicating a high level of correlation. The result for the mass is high due to the
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