Dynamic Mesh problem, can't avoid negative cell volume detected
I would like to ask you some help because I have been stuck for a few weeks with a simulation.
I have this geometry; it is half of the top of a hemispherical piston. The green walls correspond to the piston, so they move in the simulation.
I mesh this geometry with a tetrahedral mesh and create named selections. When I go to Fluent I make sure that the boundary conditions are correct (symmetry, walls and interior). Then I add the compiled UDF with the movement of the piston (sinusoidal movement) and I go to the dynamic mesh section. In the mesh methods I enable smoothing (spring constant factor=0 because I do not want the boundary to get deformed) and remeshing (where I enable local cell, local face and I use defaults in the parameters). After this, I create the dynamic mesh zones:
- Piston walls as rigid body with UDF motion and the interior cell height in meshing options.
- For the exterior walls I do not create a dynamic mesh zone
- Interior and symmetry as deforming with smoothing/remeshing and their respective zone parameters.
In the display zone motion, I check that the movement is correct and finally I go to preview mesh motion where I always get the “negative cell volume detected” error.
I have already tried many combinations creating individual selections, changing and trying different dynamic mesh zones with rigid body, deforming and stationary, trying different mesh method settings, … And I do not know what else I can try.
When I refine the mesh or change the time step to a lower one, I only came to the conclusion that the error will be delayed but will appear, it always does.
I have discard changing something in the udf motion because I have tried the same udf with other geometry using hexahedral mesh and layering and the simulation goes perfect. Also in the udf I have "udf.h", "dynamesh_tools.h" and "unsteady.h" included.
I have found that with a Cell Register I can see where the negative volume is created but I can´t create the Field Variable (it is locked in grey) or at least I don’t know how to use it.
Could you give me any advide or some help?
Thanks for your attention.