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Frequency not available in frequency response simulation

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Message 1 of 4
n1210933
520 Views, 3 Replies

Frequency not available in frequency response simulation

Hi,

 

I'm doing a frequency response analysis on a cantilevered beam.  I'm interested in the moments along the length of the beam when it is being forced at its natural frequency.  I've modelled it with beam elements and perfomed a modal analysis initially, with all the output file options checked.  I'm then doing a frequency response analysis... I've set up the damping, force amplitude, and frequency tabs as instructed in the truss tower tutorial (but with the correct values for my simulation obviously) and the simulation runs fine and gives me results (with as many load cases as there were results from the modal analysis).  However, the frequency at which the results occur is not given, saying "not available".  I know the results are in ascending order of size but the results are also not coming back with what I would expect so I was wondering if there is a way to fix this and show the frequencies.

 

Thanks

 

Pete

3 REPLIES 3
Message 2 of 4
n1210933
in reply to: n1210933

I've attached the model archive.  The simulation design scenario is what 'should' happen when the model is excited at it's first natural frequency.  The frequency response scenario is the same in every way, but even if I manually type in the natural freqency the mode shape is completely different to what I would from the modal analysis and MES simulation.

Message 3 of 4
n1210933
in reply to: n1210933

Solved it, its working fine now... I was looking at the in phase loads not the out of phase loads.

Message 4 of 4
sunj.autodesk
in reply to: n1210933

Just something might help, I checked your MES model, and it has gravity turned on. However, gravity is not included by default in the frequency response analysis, which will leads to different results when you make your comparison.

 

In the frequency response analysis, your model also has "Include Natural Frequency" option checked. You can uncheck that option and the solver will just give you the response based on your input exciting frequency. Since your input is very close to the first natural frequency of the model, you will see very large displacement response since the model exhibits "resonance".

 

You may also define multiple input exciting frequency in one analysis. Therefore, the frequency values are not displayed in results enviroment.

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