Table 5 Natural modes during operation in water FE-model, in water Experimental in water Difference FE-model - Experimental in water FE-model Diff. in air – in water Experimen tal Diff. in air – in water No Description frequency (fi/fref) frequency (fi/fref) (FE – Exp) (%) (in water – in air) (%) (in water – in air) (%) 1 Rotation around steering axis 0,277 0,279 -0,9 -69,7 -69,2 2 1st Transversal mode 0,724 0,707 2,4 -13,5 -14,3 3 1st Longitudinal mode 0,940 0,953 -1,4 -4,6 -4,7 4 Vertical bending of the rotor, vertical translation of the thruster in phase 1,806 1,920 -5,9 -17,1 -13,4 5 Vertical bending of the rotor, vertical translation of the thruster out of phase 2,098 - - -16,9 - 6 Transversal bending of the rotor, rotation of the thruster around steering axis out of phase 2,498 2,186 14,3 -15,3 -28,6 Fig. 13 First longitudinal mode shape in water. Pressure in the acoustic medium is presented as colors Fig. 14 Vertical bending mode of the rotor coupled with vertical translation of the thruster in phase 16
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