Change Number of Iterations

[Anonymous]

I have been working on running calculations for a small(ish) structural platform. I have been playing around with it for a few days, learning to use Nastran as I go. When my analysis is solving, it has been doing 5 iterations. I have run 10-20 analysis with 5 iterations, then at some point it started doing 30. The issue is that this takes significantly longer. Can this be adjusted manually or does Nastran automatically run until it gets an acceptable forecast? Please see the attached image:

[KubliJ · Accepted solution]

Hi @Anonymous 

The iterations are due to separation contact. My best guess without seeing your model is that the slower solving model has more contact, or relies more on contact for static stability. Separation contact is a guess and check process, meaning that it has to test to see if the contact is enacted or if the parts are separating and contact is not needed. More complexity means more contact to guess and check.

Thanks,

James

[Anonymous]

I was able to fix the issue by deleting all automatically created contacts and place all of the contacts manually.

However, it was a large model so I missed some stuff and the solver created an error at the end as a result. I found a few more issues, fixed them, then ran again... another error at the end. I tried doing my contacts with different picks (just had a feeling it may be the issue) and it ran without error.

It is frustrating to run the solver for 45m to find out that there is an issue with the contacts... is there any way to pre-test the contacts? In the modeling environment you can drag parts around to see how your constraints are working, is there any equivalent in the Nastran In-CAD environment?

[john]

I think this is 90 percent of peoples issues with Autodesk Nastran i am hoping they can develop an environment where this is possible the current environment set up is ok for small assemblies but when you are dealing with in my case sometimes up to 800 contacts it is all to easy to miss something. 

[kim.martin]

this is a helpfull video to check contacts: https://www.youtube.com/watch?v=RxDSnI5CtwU