Problems with circular shapes in FSI simulations
 

Hello,

I am working on a impact model of the human head. Skull, Cerebrospinal fluid (CSF) and the human brain.
First I made a very simple model without the brain. Just a simple square filled with the CSF. There is a force applied (starts at 3e-5 seconds ends at 9e-5 seconds ) at the front of the square which represents the impact.
BUT when I model the brain in this square (see it as a circle in a square, around the square is the CSF) the simulation stops always at the timestep when the force will come up.

I tried all different kind of meshes and it didn't help. Maybe the problem is the density of the brain and the fluid, because they are almost simular??

end time = 3e-3
time step = 3e-5

Hope someone can help me.

Kezman

UPDATE: error text
 

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| CFX encountered the error: Read. Fatal error occurred when reque- |
| sting Total Mesh Displacement for Boundary 1. |
| |
| |
| |
| |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| cplg_SendCommand failed to send the command: ERROR -- CFX encount- |
| ered the error: Read. Fatal error occurred when requesting Total |
| Mesh Displacement for Boundary 1. |
| |
| |
| |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Stopped in routine cplg_SendCommand |
| |
| |
| |
| |
| |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| An error has occurred in cfx5solve: |
| |
| The ANSYS CFX solver exited with return code 1. No results file |
| has been created. |
+--------------------------------------------------------------------+

End of solution stage.

+--------------------------------------------------------------------+
| The following transient and backup files written by the ANSYS CFX |
| solver have been saved in the directory |
| /scratch/ronald/square_withBrain/square_withBrain_CSF_003: |
| |
| 1_CS.trn, 0_CS.trn |
+--------------------------------------------------------------------+


+--------------------------------------------------------------------+
| An error has occurred in cfx5solve: |
| |
| ANSYS Solver terminated with return code 256 |
+--------------------------------------------------------------------+

Could it be that the CSF domain gets squeezed so thin the mesh goes to zero thickness (or inverts)? You should output the mesh at several time steps to get a feel for how the mesh is moving.

You may also be able to do this using the immersed grid feature in V12.

I am modeling head with 3 parts: skull, CSF and Brain
The two-way FSI example in ANSYS tutorial only mentions
1 solid parts and one Fluid part.
When I define two interface between solid and fluid
1 for Skull-CSF and one for CSF- Brain
I get error that the solver can not get the total mesh displacement for
CSF-Brain interface.
Do you have any idea what the problem can be?
Thanks