Design and Manufacturing solutions through Digital Prototyping and Interoperability

Simulation | Contact Surface Selection Beware

There are a few methods of identifying surface contact pairs in Autodesk Simulation Mechanical 2013 (formerly Algor). These include automatic creation during the model import, and manual selection of each contact. The Automatic method is my favorite, which allows Simulation to find every surface that is in contact during the import.

Autodesk Simulation Mechanical Surface Contacts

In this example, I’ve used both Part – Part and Surface – Surface contact types. I found numerous surfaces that were NOT being evaluated in the analysis.

Multiple Surface Contact Sets

There are a few other methods that can be used, including two that I want to point out:

  • Part to Part contact
  • Surface Selection Group contact

Both of these greatly reduce the user’s time in telling the analysis process where (and how) the contacts exist. When these exist in the analysis scenario, Mechanical must make the specific surface contact itself, comparing each set of surfaces at run-time.

How are these run-time surface contacts then catalogued? They aren’t; they are tossed out after the analysis is performed, and yes, recreated during each subsequent analysis run.

Did Mechanical make an accurate determination during the analysis? Who knows.

The Good News

These methods of creating contact pairs is wonderfully simple, and allow the user to work with the software in a more natural manner, simply stating that ‘some surface on this part will contact some surface on that part, and when they do, they will be sliding’.

The Bad News

The problem is that if you ask mechanical to make those determinations:

  • It may make determinations improperly
  • It WILL take substantially more time, and require more processing power

Furthermore, there is always the possibility that the surfaces that you thought would contact, will not, and subsequently are not even paired in the analysis, creating erroneous results..

Use When Appropriate

Take the time to identify each contact pair when and where reasonable. There are times where it’s just better to leave that to Mechanical, and there are times and places where you could define things accurately without too much labor. Completing these yourself will:

  • Reduce each analysis run-time
  • Permit inspection of the contact
  • Ensure that each contact is generated properly

Give it a try and let us know

Try a mid-sized assembly, employing specific surface – surface contacts in one scenario, and general part – part contacts in the other. Compare the analysis time, and let us know what you find.