Learning Forum

[kh_d]

Hello,

I am trying to do substructuring with different sets of MDOFs. When I select the minimum possible nodes for Master DOFs everything is fine, although there is an average of 15% change in modal analysis results. So, I am selecting more nodes every time to see if I can improve the results. Now, I want to select all the nodes as MDOFs in the super element, GEN phase runs with some warnings, I have similar warnings in the USE phase as well, but it aborts the simulation and the files are lost.

Do you have any idea why this is happening? Or how I can reduce the deviation between the complete model and the one with a super element?

Thank you very much for your time and help. I highly appreciate it.

[Chandra Sekaran]

You mentioned a 15% difference in results. I am assuming you are talking about the use pass where you are using the superelement with other elements in a modal analysis. Can you confirm?
Are you using CMS method in the superelement generation pass? With CMS method the reduced matrices do not depend so much on master DOF selection and should not show 15% difference in the use pass.

[Chandra Sekaran]

You may want to increase the number of modes in the CMSOPT,FIX,nmode command in the generation pass.

[kh_d]

Hello Thank you very much for your response.
For now, I am trying substructuring. Yes, the 15% deviation corresponds to the use pass with modal analysis when in gen pass I have the minimum number of DOFs.
I also have a rather high deviation in the static analysis as well when I am using substructuring with the minimum number of MDOfs.
Do you know that using D command in gen or use pass may affect the results this much? I am now applying D command in the use pass for super and non-super elements. I tried using it for super element in gen pass, but although it shows the constraints, later in results the DOFs are not constrained.
I will try using CMS for modal analysis as well later, but it is not applicable to static analysis, right?

Sorry for the many questions, and thank you very much in advance for your time and help.
Best regards