166 M. Piraccini et al. 1.2 1F 1 0.8 0.6 0.4 0.2 0 0 1000 2000 3000 4000 5000 6000 Frequency [Hz] Discrete Fourier transform:0°-1F-int3 ⏐DFT⏐ 7000 8000 9000 Fig. 15.18 Frequency spectrum shows no nonlinearities. Decay intensity 3 10 8 6 4 2 0 0.5 1.5 2.5 Displacement [mm] Damping ratio from logarithmic decrement:0°-1F 10−3 Damping ratio 3.5 4.5 1 2 3 4 5 Fig. 15.19 Damping ratio linearly increases with increasing vibration amplitude 0.1 0.05 1.6 1.8 2 2.2 Time [s] Decay:0°-1T-int3 Displacement [mm] 2.4 2.6 2.8 −0.05 −0.1 0 Fig. 15.20 Velocity decay of the unidirectional blade vibrating at first flexural mode. Decay intensity 4
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