Mantle convection

Underworld can precondition a Stokes solve with geometric multigrid built from a real hierarchy of meshes, rather than with the algebraic multigrid it falls back to. What the difference is, how to build a mesh that has a hierarchy, and when the choice is worth making.

There are three ways to put resolution where a calculation needs it: rebuild the mesh, subdivide it, or move its nodes. The third conserves the node budget and leaves the connectivity, the parallel partition and the multigrid hierarchy untouched — nothing is created or destroyed, only relocated. How that redistribution works in Underworld3, what it is worth in numbers, and where its ceiling is.

CITCOM is a geodynamics modelling code based on the finite element method that is designed for planetary evolution modelling where large spatial variations and strong non-linearities occur in the material properties.