Why the flexible body deflection is dependent on the number of modes? I believe I already have sufficient number of modes in my MNF.

I have a flexible shaft in my model by importing an MNF file. I have found the deflection of the shaft (simply supported) is dependent to the number of modes. Only a radial load is applied to the shaft center and I need to confirm the shaft center displacement with classical formulations. I already have 14 modes and I doubled it to 28 and the results changed. Why does this dependency happen? The 60mm diameter shaft spins at a low speed 100 rpm

0 Jesper Slattengren over 2 years ago

Well, clearly you don't have enough modes.

This is a part of model tuning that is often forgotten or ignored. But you are doing the right thing, increase number of modes until your results converges. Remember that the interface modes adds six modes each. Often very high frequent, but smeared out among all modes through the Craig-Bampton process.

All too often I see models with over a dozen interface modes, but only a handful modes are active. That rarely gives a converged behavior.
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0 Abbas Shafiee over 2 years ago

Ok. Thanks @Jesper Slattengren . With the 14 modes I got the correct answer but I doubled the number of modes and results changed and did not make sense. Sure I continue to increase the number of modes till I get a converged solution.

Thanks for the help!
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