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Steady State Dynamics

Steady State Dynamics

Steady State Dynamics

(OP)
Hy!

I am trying to model the axially vibrating rod when excited at first axial natural frequency.

First of all I ran the eigenvalue simulation to obtain eigenvalues. Te results are like

I am interested in the one at 19997 HZ.

To obtain the vibration amplitude of the TIP (the other end) at that frequency (20000Hz) I ran the steady-state response DIRECT in Abaqus. The frequency of interest is between 12000 and 27000 to get the response at wider range, to see the behaviour. The excitation is set with BC, where the amplitude of the harmonic excitation is set to 0.03 (30 micrones) in y direction. Damping is 0.05. The results (amplitude vs. excitation freq at the TIP of the rod) are shown on the Figure below;


The amplitude at 20000 Hz is right 0.12mm (120micrometers) (the results are the same as experimental). The strange thing is that the amplitude is at its lowest at that frequencies. At frequencies higher and lower from that, the amplitudes are higher. There are also two areas ( at approx. 14000Hz and 26000HZ) where the resonance occurs, although none of the computed natural frequencies are there To my understanding it should be at its biggest at 20000, because we are exciting the rod at its natural frequency.

If there is anything unclear I am more than happy to explain. If someone would be kind enough to tell me how to export the .inp file, I can also do that.

Thanks a lot!

Uroš

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