Static Mesh Refinement

Grid Structure

The grid structure in Athena++ is completely different from Athena. Athena used a grid structure like Berger & Colella (1989), in which rectangular finer grids can be placed anywhere in the computing domain. Although the terminology about mesh refinement is not well defined, here we call this a patch-based mesh refinement. In Athena++, we use so-called oct-tree-block based mesh refinement. In this approach, the computational domain is split into small MeshBlocks, and each MeshBlock can be refined into smaller eight (in 3D; four in 2D, two in 1D) MeshBlocks self-similarly. This approach is less flexible but much simpler, therefore it is easier to implement and achieve a better performance.

Setting Up Static Mesh Refinement

No reconfiguration of the code is required for using Static Mesh Refinement. Simply, write <refinement[n]> block(s) in the input file to specify regions covered by finer resolution.

<refinement1>
x1min=-0.1
x1max= 0.1
x2min=-0.1
x2max= 0.1
x3min=-0.1
x3max= 0.1
level=2

Also do not forget to set the <meshblock> size (see Using MPI and OpenMP), otherwise the meshblock size is the same as the whole root grid. For a better flexibility (i.e., higher adaptivity, more efficient grid generation), smaller MeshBlocks are better but it is trade-off between performance and flexibility. We recommend at least 16^3 cells per MeshBlock.