1. Kratos 3D FSI Analysis Tutorial
Pooyan Dadvand
Pavel Ryzhakov
Kratos Team

2. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Partitioned FSI in Kratos
P. Dadvand, P. Ryzhakov

3. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
We have to prepair each subdomain separately
- First – structure
- Second – fluid

4. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
STRUCTURE PREPARATION

5. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
STRUCTURE PREPARATION
Load the model: open the structure part model fsi_model_str.gid
the geometry will appear
Load the problem type: Data->Problem Type: fsi_structure
Choose: Update to a new Problem Type

6. Assign the boundary conditions:
1) Zero DISPLACEMENT at the base (bottom)‏
Fsi Structure->Nodal Values->DISPLACEMENT (on surface):
D_x=0.0; V_y=0.0, V_z=0.0 (tick: is_fixed)
After assigning the DISPLACEMENT, click: Draw to check that the DISPL is assigned correctly.
The surface where the DISPLACEMENT was assigned will be coloured:

7. IS_INTERFACE
Assign the IS_INTERFACE flag, to indicate the FSI boundary:
2) IS_INTERFACE=1 on all the outer surfaces
Fsi Structure->Nodal Values->IS_INTERFACE (on surface):
(tick: is_fixed)‏
After assigning the IS_INTERFACE, click: Draw to check that the DISPL is assigned correctly.
The surface where the IS_INTERFACE was assigned will be coloured:

8. Assign the Element Type (linear 4 node tetrahedra):
2) IS_INTERFACE=1 on all the outer surfaces
Fsi Structure->Element Type->TotalLagrangian3D4N (on volume):
After assigning the TotalLagrangian3D4N, click: Draw to check that the
Element type is assigned
Element Type

9. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Mesh the geometry (Mesh->Generate Mesh)‏
and press
CALCULATE
The structure part is ready for the FSI!

10. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
FLUID PREPARATION

11. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Open GiD
Load the model: open the fluid part model fsi_model_fluid.gid
the geometry will appear
Load the problem type: Data->Problem Type: fsi_fluid
Choose: Update to a new Problem Type

12. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Assign the boundary conditions:
1) Velocity at the inlet
Fsi Fluid->Model Parts->Velocity Inlet (on surface): V_x=1.0; V_y=0.0, V_z=0.0
After assigning the velocity, click: Draw to check that the inlet velocity is assigned correctly.
The surface where the velocity was assigned will be coloured:

13. Assign the boundary conditions:
2) No-slip conditions on all the surfaces except for the inlet surface
(where inlet velicty was prescribed)
Fsi Fluid->Model Parts->NoSlipCondition (on surface)
After assigning the NoSlip, click: Draw to check that the NoSlip is assigned correctly.
The surface witn NoSlip will be coloured:

14. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Assign the boundary conditions:
3) Zero pressure at the outflow
Fsi Fluid->Nodal Values->Pressure=0 (tick: fixed)(on surface)‏
After assigning the Pressure, click: Draw to check that the Pressure is assigned correctly.
The surface with Pressure will be coloured:

15. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Assign the boundary conditions:
4) IS_INTERFACE on the surfaces representing the Structure inside of Fluid
Fsi Fluid->Nodal Values->IS_INTERFACE=0 (tick: fixed)(on surface)‏
After assigning the IS_INTERFACE, click: Draw to check that the IS_INTERFACE
is assigned correctly.

16. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Assign the ELEMENT TYPE to the Fluid Volume
5) Choose Fluid3D elements
Fsi Fluid->Elements -> Fluid3D (on VOLUME)
After assigning the Fluid3D, click: Draw to check that the Element Type is assigned correctly

17. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Finally set the Problem Parameters
Fsi Fluid->Problem Parameters
Tick the first three boxes

18. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Finally set the Problem Parameters
Fsi Fluid->Problem Parameters
Time step to be used:
Total time (not necessary)‏
Number of time steps

19. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Finally set the Problem Parameters
Fsi Fluid->Problem Parameters
Fractional Step Based solver
will be used for the fluid
Laplacian form:1
(contin. Laplacian)
Laplacian form: 2
(discr. Laplacian DM-1G)

20. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Finally set the Problem Parameters
Fsi Fluid->Problem Parameters
LOAD NOW THE STRUCTURE FILE!!!
browse: fsi_model_str.mdpa

21. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Model is ready -> Mesh the model
1) Mesh-> Unstructured->Assign Sizes on surfaces: 0.05
Choose the surfaces of the column
2) Mesh->Unstructured->Assign Sizes on volumes: 0.2
Choose the fluid volume
3) Mesh->Generate Mesh
check that the mesh at
the object is finer than the rest

22. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
Press: CALCULATE
Pre-processing is finished

23. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
To run the example:
1) copy the fsi_model_str.mdpa from /fsi_model_str.gid/ folder
into the /fsi_model_fluid.gid/ folder
2) inside the fsi_model_fluid.gid folder run:
python run_example.py

24. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
In post-processing GiD mode, load the
fsi_model_fluid.0.res.bin
Post-processing
To see the res.:
View Results->
Contour Fill->
[Var of interest], e.g.
[DISPLACEMENT]

25. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
If you would like to see the structural information, you need to change a few lines
in the run_example.py file (just in the part that is marked here!!!)
change:
fluid_model_part to
structure_model_part

26. GiD-Kratos Singapore Workshops Pre and Post Processing Techniques
In post-processing mode, load the
fsi_model_fluid.0.res.bin
Post-processing
To see the res.:
View Results->
Contour Fill->
[Var of interest], e.g.
[DISPLACEMENT]

27. Thanks… Kratos Web page: http://www.cimne.com/kratos/ Kratos Wiki
These Tutorials: