Learning Forum

[matheusroverb]

Hi everyone!

I study flow-induced vibration (FIV) in cylinders and I want to simulate a moving cylinder subject to crossflow in ANSYS Fluent as a translational movement. Experimentally it is conducted with springs, having a natural frequency and a spring constant. I have already read some documents in internet, but I am still not able to do this kind of simulation. I have some questions:

1) Should I use 6 DOF option in Dynamic Mesh tab or it is better to use a UDF to represent the motion? If it works better with UDF, can you give me some ideas?

2) Could you please give a step-by-step tutorial related directly to this problem?

3) I have already tried some cases:

      3.1 I defined the cylinder wall as a rigid body and the fluid as deforming;

      3.2 With an inner-domain surrounding the cylinder, with both set as rigid body but the inner-domain with passive option enabled in 6 DOF and an outer-domain as deforming. But it hasn't worked yet.

4) Should I use overset mesh, or it isn't necessary? 

Thank you!!

[raul.raghav]

FIV or VIV on a deformable structure will require a two-way couple FSI simulation setup. If the structure is rigid and the deformation is not a crucial aspect of the investigation, you can simplify the problem by using the "Six-DOF" option in the "Dynamic Mesh" tab of Ansys Fluent. Fluent also offers the "Overset Mesh" feature which will help you set the simulation. The mass and moment of inertial properties can be defined inside the Six DOF properties tab. Alternatively, they can also be defined by an UDF. If the motion is restricted to a particular direction and if there is no rotation of the body, you can constraint the 6-DOF using the properties panel or an UDF. See the following tutorial on setting up an “One DOF Translation” using the 6 DOF properties panel:

ANSYS Fluent: Using the Six Degrees of Freedom (Six DOF) Solver 

You might also need the "Implicit Update" option in the Dynamic Mesh tab to help achieve convergence.

General advice: Start with a 2D case before moving on to the 3D case. Consider a rigid body motion before proceeding with the Six-DOF model.

[matheusroverb]

Thank you for the reply!

Yes, I am starting with a 2D case. My cylinder is set as rigid, because it has not a deformation while subject to FIV. I have just one more doubt: is it crucial to use overset mesh or can I work with just one mesh? Must I use ""Remeshing", "Layering" and so on with overset mesh? 

 

Thanks again!

[raul.raghav]

You can work with either a single mesh or create a overset mesh by setting up an overset interface between the different meshes. To understand a bit more about overset mesh and dynamic meshes, see the attached video: ANSYS Fluent: Overset Meshing and Dynamic Meshes (19.0)

[matheusroverb]

Thanks again! It seems to be working with a 2D case and with only one degree of freedom in the transversal direction.

Can this kind of simulation be done with transversal and longitudinal degrees of freedom? That is, can I enable 2 directions (X and Y) even with "One DOF Translation? 

Besides, is it possible to associate more than one Six DOF Properties to the same zone in "Dynamic Mesh Zones", that is, in the second image, can I associate two different Six DOF Properties to the zone Cylinder?

 

 

Thanks in advance!

[raul.raghav]

If you need translational motion in two directions, you can't use the one DOF. I have never tried this but I believe you can restrict rotational motion by using the 6DOF UDF and that way you have translation in the X and Y directions.

Maybe someone in the community might have some insights towards this.