P929
Hi,
The message you’re getting:
“74 mailles mal orientées”
means that some shell elements in group Exc_1_R have inconsistent normal directions. When applying pressure on shells, the solver uses the element normal to determine the pressure direction — so if normals are flipped, pressure will act inward on some elements and outward on others.
For irregular geometries, you don’t need to manually define all normal vectors. The correct approach is to fix the mesh orientation, not the pressure definition.
Recommended Solution
Use MODI_MAILLAGE with ORIE_NORM_COQUE to automatically reorient all shell elements consistently.
Example:
MODI_MAILLAGE(
MAILLAGE = mesh,
ORIE_NORM_COQUE = _F(
GROUP_MA = 'Exc_1_R',
),
)
- If necessary, you can specify a reference vector using VECTEUR to enforce a global orientation direction, but usually this isn’t required if the surface is continuous.
For Irregular Surfaces
For arbitrarily shaped areas:
Pressure loads in Code_Aster are applied normal to each shell element locally.
You do not need to calculate normals manually.
As long as shell normals are consistently oriented, pressure will behave correctly regardless of geometry complexity.
The real issue here is mesh consistency, not the irregular shape.
Quick Check
Before applying pressure:
Visualize element normals (if your pre/post tool allows it).
Ensure they all point in the same physical direction.
If some are flipped, correct them via mesh orientation tools before solving.
Once the mesh normals are consistent, applying:
PRES_REP = _F(GROUP_MA='Exc_1_R', PRES=...)
will work properly even for highly irregular geometries.
Hope this helps clarify the issue.
