Learning Forum

[fares abbara]

Hello,

I am working on a FSI model of fluid flow in a bifurcating tube with added cyclic loading on the outer surface of the tube. I have simulated the model without added load and it ran smoothly. Before applying the full cyclic load, i fugred i should test how the tube would react to a normal load. When i ran the simulation with the following loading condition i ran into an error that states "update dynamic mesh failed. negative cell volume detected". I have tried several things to resolve the issue:

1- Decreasing the time step size.

2- Decreasing element size in fluid and solid domain.

3- Mesh refinement for the tube model.

4- Adding a meshing method to the fluid mesh (Hex Dominant).

5- Inflation at the walls of the fluid domain.

The last thing i tried was reducing the load. Although that worked, the deformation of the tube at that point was very small that it did not affect the fluid domain.

I have attached a picture of the results obtained from the FSI run without loading, a picture of the load position and value that worked, pictures of the meshing conditions i applied for the no-load run. the tube is of a hyper elastic material.

[RM]

Hi 

Ensure that mesh quality is good (orthogonal quality > 0.1).

This error might be due to failure of dynamic mesh. You can modify the inputs to the dynamic mesh, refer 11.6. Using Dynamic Meshes (ansys.com) 

Please refer 42.11. Troubleshooting Two-Way Coupled Analysis Problems (ansys.com) for more info.

Hope this helps!

[fares abbara]

Hello,

thank you for your reply. However, i might not be able to access the links you provided as they take me to the cutomer portal. I have a free student account.

Regards,

[RM]

Please check out Using Help with links (ansys.com) this thread on how to access the help. 

[peteroznewman]

 

Do not use Hex Dominant meshing method on a fluid mesh!  This method is intended for Structural models only. The reason is the Hex Dominant method creates poorly shaped elements on the inside of the volume in order to get nice Hex elements on the outside boundary. Structural analysis can cope with poorly shaped elements inside the volume, CFD analysis can’t cope with poorly shaped elements inside the volume.