How to use hexahedral elements and keep the shape of grains unchanged？

[smallrain1996]

In the 3D model of the -M module, how to use irregular hexahedral elements to ensure the grain shape?
In other words, I hope to use C3D8 units (for ABAUQS), but I also hope that the grain boundaries are still flat and not jagged.
Thank you very much.

[rquey]

See #98.