Issue with use_displaced_mesh in Viscoelastic Adhesive Contact Setup

[asurovi]

I am currently working on implementing viscoelastic adhesive contact in MOOSE. To achieve this, I have considered using the BilinearMixedModeCohesiveZoneModel user object along with NormalMortarMechanicalContact constraints for defining the adhesive contact behavior. Additionally, I have chosen the GeneralizedMaxwellModel as the material model to capture the viscoelastic response.

However, after running my input file, I encountered the following error message:

*** ERROR ***
twoBlockViscoelasticAdhesiveContact.i:247.5:
The following parameter error occurred in the UserObject 'czm_uo' of type BilinearMixedModeCohesiveZoneModel.

use_displaced_mesh: 'use_displaced_mesh' must be true for the WeightedGapUserObject object

To resolve this, I attempted to set the global parameter use_displaced_mesh = true, but the issue persists.

I would appreciate any insights on how to correctly enable use_displaced_mesh in this setup or any necessary modifications to properly model viscoelastic adhesive contact.

Thank you!

[zachmprince]

Hello! I'm not familiar with contact problems or methods, but I think you need specify displacement variables for the Problem. The easiest way to do this is using GlobalParams:

[GlobalParams]
  displacements = 'disp_x disp_y disp_z'
[]

Where the number of disp_* entries should equal the dimensionality of your mesh. If you don't have variables representing displacements, you can create fake ones for now like this:

[AuxVariables]
  [disp_x]
  []
  [disp_y]
  []
  [disp_z]
  []
[]

[ttruster]

Thanks @zachmprince, that turned out to be the issue. Although use_displaced_mesh was set as a Global Parameter, this didn't fix the error because the disp_* variables weren't identified as the displacement in the Global Parameters, which meant it didn't get pasted to the Problem.

I wanted to respond to this and let @GiudGiud know, since perhaps the error message could be improved. My guess is, there is a logical test inside Problem which silently changes use_displaced_mesh to false on all objects if the displacement parameter isn't set. Might be better to check the error of the missing displacements for the Problem if use_displaced_mesh is set to true.

[GiudGiud]

I ll create an issue.
I agree the current behavior is sneaky, probably for some obscure reason dating from early moose days