Convert existing gmsh mesh from first- to second-order elements?

Question

Is there a way to take an existing gmsh .msh file, and convert it to second-order elements? Specifically, I'm trying to go from 8-point hexahedra (hex8) to 20-point hexahedra (hex20). Ideally, I'd like a command-line solution. I tried this:

gmsh -o output.msh -format msh2 input.msh -order 2 -0

But it doesn't seem to work - I still get hex8 elements in the output. Is there a way to do this, or does the order need to be set when the mesh is first generated? I do need to maintain the gmsh version 2 format (unfortunately).

Answer 1

You should ask this on gmsh list. The gmsh developer answers questions.

Searching online suggests an answer

http://geuz.org/pipermail/gmsh/2020/013631.html

Create a geo file like this

Merge "input.msh";
SetOrder 2;
Save "output.msh";

and run it in Gmsh.