APPLY BOUNDARY CONDTION ON INTERNAL FACE

[孙翔]

Hi, I want to model injecting heat fluid into a tiny fracture which is inside a block. The fracture is modeled as an interface which is an internal face shared by two hex elements. Is it possible for us to apply the Dirichlet boundary condition on the interface? If not, how should I do it?  

Best,

Xiang

[Bruno Turcksin]

Xiang,

You cannot apply a boundary condition on an internal face. You need to use the AffineConstraint class to impose the constraints yourself. This is what we use internally to apply Dirichlet boundary condition.

Best,

Bruno

[Daniel Arndt]

Xiang,

Adding to Bruno's response: If the interface you want to apply Dirichlet boundary conditions to stays the same through the whole simulation, then treating the corresponding faces as disjoint while creating your mesh might be a better option.

Setting constraints yourself requires you to know how the degrees of freedom map to function values (which depends on the finite element you are using). FE_Q elements are nodal, though, so you can simply constrain the degrees of freedom to the desired function value at the corresponding support points.

Best,

Daniel

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[孙翔]

Hi, Bruno,

Thank you very much. Does the AffineConstraint force the value at the specified DOF? I need to how the node numbers map to the DOF, right? 

Best,

Xiang

[孙翔]

Hi, Daniel,

Thank you very much. So, if I want to disjoint the faces, how should I do using dealII or I need to disjoint them manually? If I manually disjoint them, should I duplicate the joint nodes and assign them with the new number, then assemble the adjacent element with the duplicated nodes? I am not sure if Grid_in can read it. 

Best,

Xiang

[孙翔]

Hi, Daniel,

Thank you very much. So, if I want to disjoint the faces, how should I do using dealII or I need to disjoint them manually? If I manually disjoint them, should I duplicate the joint nodes and assign them with the new number, then assemble the adjacent element with the duplicated nodes? Please see the attached figure. I am not sure if Grid_in can read it. 

Best,

Xiang

On Monday, 12 October 2020 at 11:09:31 UTC-7 d.arnd...@gmail.com wrote:

[Bruno Turcksin]

Xiang,

Here is an example on how to do it:
https://github.com/geodynamics/aspect/blob/master/cookbooks/prescribed_velocity/prescribed_velocity.cc#L297-L303
As you can see, you need to know which dof you need to constrain

Best,

Bruno

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[Daniel Arndt]

Xiang,

deal.II doesn't have functionality to create separate cells sharing a face but only to join them. Hence, whatever input you provide to Triangulation::create_triangulation() must have these faces already. GridIn should work for that if the faces are disjoint in the input file.

Best,

Daniel

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[孙翔]

Hi, Bruno,

Thanks a lot. We will have a try based on the example you gave us. 

Best,

Xiang

[孙翔]

Hi, Daniel,

I see. Thank you very much. So, I think our method may be available as long as it can separate the face.  

Best,

Xiang