How can I get or calculate the gradient of the surface normal？

[Always-kimi]

Check these boxes if you have followed the posting rules.

• Q&A Navier Stokes is the most appropriate category for my question
• I have consulted the posting Guidelines on the Discussions front page
• I have searched the Discussions forum and my question has not been asked before
• I have searched the MOOSE website and the documentation does not answer my question
• I have formatted my post following the posting guidelines (avoid screenshots if possible, triple back quotes before/after pasted text, etc)

Question

Hi there,

Does anyone know how to calculate the gradient of the surface normal? In my application, I consider the surface tension force and it need to calculate the surface curvature. According the equation it is equal to the gradient of the surface normal.
However, I browsed the framework source file only found the _normals and _ad_normals.

Additional information

No response

[GiudGiud]

@lindsayad did you have a surface tension term in the melt pool?

[lindsayad]

Yes, but it's only computed through a correlation with the temperature. @Always-kimi we do compute curvatures in libMesh and in MOOSE assembly. You can retrieve curvatures with automatic differentiation (AD) information, via _assembly.adCurvatures(). We do also have an Assembly member for curvatures without AD, but we strangely don't have an API for it. It could be easily added

[Always-kimi]

Thank you very much! I found it.