topic Modal Frequency Response Example Help in Inventor Nastran Forum

Modal Frequency Response Example Help

pzachNKATE — Tue, 24 Nov 2020 18:54:56 GMT

Version: Nastran 2021, Modal Frequency Response

I am following the tutorial outlined here: https://knowledge.autodesk.com/support/inventor-nastran/getting-started/caas/CloudHelp/cloudhelp/2020/ENU/NINCAD-Tutorials/files/GUID-12006DFC-688C-4D4C-98BD-71042D6B1AF4-htm.html

As you can tell from the image below, response is not as expected.

Re: Modal Frequency Response Example Help

John_Holtz — Tue, 24 Nov 2020 19:04:43 GMT

Hi @pzachNKATE

I agree that your results are not correct. I think you missed step 2, but I do not know on which page you missed step 2. 😉 (I am joking. No one can determine what you did differently without having your model. Please attach the .ipt file to the forum.)

Also, did you review the warnings and errors in the log file? There might be a warning that explains what is wrong in the analysis. (See How to locate the log, output, and Nastran file.)

Re: Modal Frequency Response Example Help

pzachNKATE — Tue, 24 Nov 2020 19:20:11 GMT

John,

Thank you for the quick reply. ipt is attached. Yes, there is one error:

WARNING E5052: EXCESSIVE ERROR MEASURE DETECTED FOR ONE OR MORE MODES

Thanks,

Peter

Re: Modal Frequency Response Example Help

John_Holtz — Tue, 24 Nov 2020 22:25:46 GMT

Hi Peter,

You applied a force to a node that is fully constrained. Therefore, there is no load in the analysis, and the results are zero.

You should have changed the load type to an enforced motion and applied an acceleration of 1 in/sec^2. The enforced motion moves the constraint, and the constraint moves the model. (Wow, the problem was with step 2. I guessed correctly!)