Table 1 Measured modes of azimuthing thruster in air Mode no Frequency (fi/fref) Modal damping (ȗi/ȗref) Description 1 0,636 0,1 Global mode of astern ship hull 2 0,826 0,3 1st transversal mode 3 0,906 1,7 Rotation around steering axis 4 1,000 1,0 1st longitudinal mode 5 1,182 1,1 Global mode of the ship hull 6 2,217 1,5 Vertical bending of the rotor, vertical translation of the thruster in phase 7 2,501 0,8 Vertical bending of the rotor, vertical translation of the thruster out of phase 8 3,061 1,4 Transversal bending of the rotor, rotation of the thruster around steering axis out of phase 9 4,643 1,1 First elastic mode of the thruster hull, torsion around vertical axis Fig. 5 AutoMAC for measured mode shapes 8
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