contact-convergence problem-Please help me

[Chen1]

Hello
I am modeling an underground opening. the model is composed of three rock layers, the coal layer where i made the opening. This coal is sandwitches between two strong sandstone layers .

There is a contact between the coal layer and the other two sandstone layers. the model is elastic. only 0.64 of the job was completed and i got an error message.

I used job diagnostic tool to check the model i found that the top and the bottom layers penetrate the coal layers. these are the warning messages that i got?

Displacement increment for contact is too big.

Displacement increment for contact is too big.

Excessive distortion at a total of 35 integration points in solid (continuum) elements

Excessive distortion at a total of 2 integration points in solid (continuum) elements

Excessive distortion at a total of 2 integration points in solid (continuum) elements

Displacement increment for contact is too big.

Excessive distortion at a total of 27 integration points in solid (continuum) elements

Displacement increment for contact is too big.

Excessive distortion at a total of 131 integration points in solid (continuum) elements.

please help me.

Thanks

 

[corus]

Try applying a small initial time step, add in *contact controls, automatic tolerances, and stabilize and failing that apply an initial displacement in a dummy step to push the surfaces together before removing that in the next step.

 

[Chen1]

Hello Corus, I know how to apply Contact control, however i need your help to

1- apply the stabilize and fail to apply dummy displacement to push the surface together.

2- apply the automatic stabilization.

Sorry if i ask you for more explanation, sometimes when i read the manual i can not understand, so your explanation is highly appreciated.

Thank you.

 

[Chen1]

Hello Corus, that is what i did, please let me know if i did something wrong.

I added a dummy step before the main step, i did not apply load in that step, it is just to force the surface to be in contact. Correct?

I used *contact control and enhanced mesh to overcome the distortion. the model reaches equilibrium, thank you.

However i see that the master surface penetrate the slave surface. This affect the model results, do you how can i eliminate that penetration. i tried very fine mesh, but it did not work.

Your advice is highly appreciated.
Thanks.

 

[corus]

Try and have compatible meshes between the two contact surfaces to prevent penetration, or alternatively repeat the contact definition but swapping the master and slave surfaces in the second definition.

 

[Chen1]

What is compatible mesh, Does it mean that both the master and slave should have the same element size?



I do not know how to swap the master and slave surface? could you please explain more? Thanks