## Report of a behavior in FSI

Numerical methods and mathematical models of Elmer
hamed
Posts: 110
Joined: 12 Oct 2009, 18:28

### Report of a behavior in FSI

Dear Elmer
Consider the following two sets of boundary conditions defined in sif file for FSI problem:
1-

Code: Select all

``````! Internal FSI (Beam) Boundary
Boundary Condition 3
Target Boundaries = 17
Velocity 1 = 0.0
Velocity 2 = 0.0
FSI BC = True
Calculate Fluidic Force = True
Mesh Update 1 = Equals Displacement 1
Mesh Update 2 = Equals Displacement 2
End

! Internal Fixed Boundary
Boundary Condition 6
Target Boundaries = 20
Velocity 1 = 0.0
Velocity 2 = 0.0
Displacement 1 = 0.0
Displacement 2 = 0.0
Calculate Fluidic Force = True
Mesh Update 1 = 0.0
Mesh Update 2 = 0.0
End
``````
2-

Code: Select all

``````! Internal FSI (Beam) Boundary
Boundary Condition 3
Target Boundaries = 17
Velocity 1 = 0.0
Velocity 2 = 0.0
FSI BC = True
Mesh Update 1 = Equals Displacement 1
Mesh Update 2 = Equals Displacement 2
End

! Internal Fixed Boundary
Boundary Condition 6
Target Boundaries = 20
Velocity 1 = 0.0
Velocity 2 = 0.0
Displacement 1 = 0.0
Displacement 2 = 0.0
Mesh Update 1 = 0.0
Mesh Update 2 = 0.0
End

! Fluidic Force Calculation Boundary
Boundary Condition 7
Target Boundaries = 17 20
Calculate Fluidic Force = True
End
``````
In the second case the elastic solid (beam) behaves as if all of its DOFs are completely fixed and it doesn’t deform at all.
Of course it’s not a problem or bug. Maybe you were aware of it or set it intentionally this way. Anyway, it is something that I have experienced with Elmer and I here feedback it.
Regards, Hamed