Learning Forum

[FabricioMorais]

Hello,

I'm wondering to understand how does workbench process the frictionless contact on a Modal Analysis.

I do know that the Modal Analysis is a linear analysis and only take in consideration linear contacts, any non linear contact is ignored (according to the help "3.1. Uses for Modal Analysis"), however I do have a situation where I have lots of covers bolted to a more rigid body along the extremities and the faces of both are touching each other. That will not allow some of the displacements.

If I run that model considering NO Face-To-Face contacts, I have very low natural frequencies but none of them are actually real. So I decided using frictionless contact. The results were 3 times better, the displacements shown were very close to what I expect on the reality. But..... How did it run a nonlinear contact on the Modal Analysis???? Does it convert the contacts into Bonded???

Well I did that test, I converted all frictionless contacts into bonded and run again. The results were again even better than with frictionless contacts, though not real, I know!

So again my question is, How does Workbench run Frictionless face contact on a Modal Analysis? Can I even trust the results???

 

Thanks!

Fabricio Morais

[peteroznewman]

Hello Fabricio,

Don't trust an FEA result, do verification and validation.

Modal is a linear analysis, so only linear contacts are allowed, which are Bonded and No Separation.  All nonlinear contacts such as Frictional and Frictionless are automatically converted to a linear contact according to the table below which came from some training material.

I spent 15 minutes searching for a table like this in the ANSYS Help and could not find it. Maybe someone from ANSYS can find it for us.

Kind regards,
Peter