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Mecway
FEA
Sanity Check on Contacts / Grounding Technique
Hi,
I have recently found a very interesting technique to check and improve the contacts performance in the model.
-It helps to find disconnected areas.
-It shows the need to address geometry at some areas.
-It can help to decide which contact will perform better in case we have some option to choose.
-It helps to identify nonsense vibrational modes.
And finally, is an excellent method to warranty our vibrating analysis and modes are right.
The method is new to me, so any comment is welcome in case I miss something.
The method is called Grounding check and focus on the first six free-free vibration modes of our model.( Rigid Body modes).
The quality of these six modes together with the Strain energy density associated with each mode can tell us if the contacts are properly set.
Ideally the first six modes should have a frequency (Hz) below 1e-3 together with marginal Strain Energy Density. Hot spots will tell us areas where an adjustment can be made. Ideally as the first six modes are Rigid body modes (Rigid=0 strain) , the Strain energy density should be zero there.
I have prepared the formula for the Strain energy in case someone wants to use the internal solver and Victor is facilitating its extraction in ccx too.
It’s impressive how this method helped me to clean up the model and how the different contact options converge in performance once the contact areas and stiffness are addressed.
As an example, last contact option (NL_Contact+PERTURBATION) shows an unusual high Strain energy and high modes deviates from the rest. (I think that’s because this contact allows separation ). The hot spots shows where the contact could be improved and that maybe it is not the best option in that specific area.
@Victor
-I think I have mostly convinced myself that those weird modes come from wrong modeling and contact set ups.
-The option with NL_CONTACT+PERTURBATION extracts two modes not properly sorted. (295Hz- 287Hz). The EIGENVALUE is missing in the *DAT FILE.
Attached an abstract of modes extraction comparing different contact techniques and the model I have used to do the testing.
Please excuse me the simplicity of the terminology used in the “Plane”. It could have been a box, but this looks more appealing to me.
Regards
I have recently found a very interesting technique to check and improve the contacts performance in the model.
-It helps to find disconnected areas.
-It shows the need to address geometry at some areas.
-It can help to decide which contact will perform better in case we have some option to choose.
-It helps to identify nonsense vibrational modes.
And finally, is an excellent method to warranty our vibrating analysis and modes are right.
The method is new to me, so any comment is welcome in case I miss something.
The method is called Grounding check and focus on the first six free-free vibration modes of our model.( Rigid Body modes).
The quality of these six modes together with the Strain energy density associated with each mode can tell us if the contacts are properly set.
Ideally the first six modes should have a frequency (Hz) below 1e-3 together with marginal Strain Energy Density. Hot spots will tell us areas where an adjustment can be made. Ideally as the first six modes are Rigid body modes (Rigid=0 strain) , the Strain energy density should be zero there.
I have prepared the formula for the Strain energy in case someone wants to use the internal solver and Victor is facilitating its extraction in ccx too.
It’s impressive how this method helped me to clean up the model and how the different contact options converge in performance once the contact areas and stiffness are addressed.
As an example, last contact option (NL_Contact+PERTURBATION) shows an unusual high Strain energy and high modes deviates from the rest. (I think that’s because this contact allows separation ). The hot spots shows where the contact could be improved and that maybe it is not the best option in that specific area.
@Victor
-I think I have mostly convinced myself that those weird modes come from wrong modeling and contact set ups.
-The option with NL_CONTACT+PERTURBATION extracts two modes not properly sorted. (295Hz- 287Hz). The EIGENVALUE is missing in the *DAT FILE.
Attached an abstract of modes extraction comparing different contact techniques and the model I have used to do the testing.
Please excuse me the simplicity of the terminology used in the “Plane”. It could have been a box, but this looks more appealing to me.
Regards
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Comments
**! NL Contact +Perturbation clearly need some attention as now mode 1 and 2 shows sorted wrong which could be potential problem.