## General Mechanical

Topics relate to Mechanical Enterprise, Motion, Additive Print and more

#### Mechanical contact offset

• destroy
Subscriber

Dear all,

I am trying to model 2D fluid-structure interaction of two flaps undergoing large deformation due to flowing water.

The flaps are close to eachother. I want to block some of their deformation, telling ANSYS Mechanical to not deform the body if the distance between the bodies is lower than 0.3 mm. This is done to maintain some gap for the flowing water in Fluent.

To do that, I set the frictional contact, and I added a contact offset equal 8e-4 m - where the minimum distance between the flaps at the beginning of simulation is equal about 12e-4 m.

however, it does not help - during the calculations I achieved the minimum distance between flaps equal about 2e-4 m, till the solution diverges due to excessive element distortion. I expected, that I will achieve minimum distance about defined 8e-4.

Do you have any idea why this happens? Maybe I define a distance in a wrong way...

I attatched an image showing the initial minimum distance between flaps

Kind regards

Destroy

• peteroznewman
Subscriber
Use a negative value of offset to leave a gap between the contact and target surfaces of a frictional contact when the contact elements are in the closed state.
• destroy
Subscriber
Hello again Just after posting I got two ideas:
1) Maybe I should use two times lower offset value, then the gap that I need? I mean, for example if I need a minimum gap equal 8e-4 m, maybe I shoud use offset 4e-4 m? This presumption I made, because maybe Mechanical adds two offsets, first for the Contact and second for the Target? And therefore I should use two times lower value than demanded gap?
2) I just read in Mechanical users guide:
"Offset: appears if Interface Treatment is set to Add Offset, Ramped or Add Offset, No Ramping.This property defines the contact offset value. A positive value moves the contact closer together (increase penetration/reduce gap) and a negative value moves the contact further apart."
So maybe I should use a negative value?
I added pictures of refreshed contact settings