code_saturne User's Forum

Hello,
my question is about the FSI applications with internal coupling.
How can we introduce the angular parameters of the structure : the inertia moment and the torsional stiffness?
The aim is to simulate a flow around an oscillating airfoil : rotation around an elastic axis and vertical oscillations, and i use the 3.00 c_s version.
Thank you.

Hello,

You probably cannot do this using the GUI (where you only have access to a classical stiffness matrix), but you can define your own structure behavior in cs_user_fluid_structure_interaction.f90 (study and adapt the examples to your needs).

Regards,

Yvan

thank you yvan, i will try to do it.
regards.

Hello flyer,

I have been doing the same kind of analysis on bridge decks. I modified strpre.f90 and strdep.f90 in order to use the z displacement component as an inclination generalized coordinate. You can find the two functions in the code_saturne-2.3.3\src\base directory.
It is just sufficient to place them in the SRC directory of the case and the original ones will be overwritten.
My routines are modified also to allaw to define a rigid body motion around the body as I noticed that defining high viscosity around the body is not sufficient to preserve mesh quality if sharp tips are present.

Good luck and don't hesitate to contact me if you need.

Luca

Hello ;
thank you luca ,
do you mean modifying the routine called (usstr2) ?
And what about defining a rigid buddy around the structure ? I usually use a hight mesh viscosity but for large displacement I had negative volume.
good luck.

Hello flyer,

the two routines strpre.f90 and strdep.f90 can be found in the source code in the position i wrote you and it is sufficient to place them in the SRC directory to overwrite the original ones. In such subroutines the nodes of the mesh are actually displaced and the forces acting on the structure calculated so you can control the displacement as you wish. usstr2 allows access to the structures degrees of freedom but I think that you cannot redefine them there (implementing rotation and rigid zones).
In my case, I used the traslation along z as the rotational degree of freedom.

Regarding the rigid body motion I had the same problem. I defined structures on the boundary of the mesh zone I want to be rigid and then I controlled their displacements using the degrees of freedom of the real structure.
The real structure is the only one I calculate forces on and that is actually solved.
I strongly advice you to use the cs_user_module.f90 to pass data to your routines otherwise soon you will get lost in the parameters you have to change in every subroutine.

I have to admit that I still have problems. The results I obtained with Code_Saturne in the static cases are very good but when things start moving I don't have good results (compared to other codes and experimental data) but it might be a mistake in my implementation of the procedure.

If you wish and you give me your email I can send you the modified files but, as I already said, the results at the present moment are not good and I don't know the reason yet.

Luca

Hello
@Yvan and @Luca.Please help me out in my research.As I have come from Fluent to this wonderful software and plan to stay on this platform could you tell me about damping matrix and stiffness matrix more?Like where can I get how to use this.I am working on the dislacement and hence corresponding change in the fluid dynamic parameters due to the displacement in a stenosed(partially blocked) artery using ALE method.Also what does mesh viscosity mean physically?
Please help me.Thank you.

Hello,

Next time, please create a new thread rather than hijack an existing one when you have a new question (though referencing an existing one is good practice). Otherwise, this makes things confusing. Also, if the previous discussion is 8 years old, do not expect the same people to answer, as they might not still be active.

In any case, the damping and stiffness matrices are related to a "mass-spring" simple structure model, which is described in the pdf user manual. The description has not been updated much and refers to user subroutines, but the same matrices can be defined using the GUI.

Regarding the mesh viscosity, there is no physical interpretation to my knowledge. This is a numerical artifact, which will influence how far in the mesh displacements at the boundaries propagate in a given time step (and when local deformation leads to negative volumes or tangling, increasing the mesh viscosity often helps, up to a point).

Best regards,

Yvan