Infrastructure changes, data structures definition, and mesh-level changes to support CSG-based output mesh from MOOSE mesh input file

[shikhar413]

Motivation

In an attempt to create a system that can create a Constructive Solid Geometry (CSG)-based mesh output, a number of changes are proposed to the existing mesh generator system.. The following steps are considered to enable this functionality

• Creation of csg_only action, triggered by --csg-only command line option
• Definition of CSGBase object, similar to MeshBase, that stores all data related to the output CSG object
• Definition of generateCSG for specific mesh generators found in RGMB, Reactor module, and MOOSE framework.

Design

Add a new command line --csg-only option that triggers an action that is responsible for generating the CSG output mesh. Any mesh generator that supports the generateCSG function should be able to be used in conjunction with the --csg-only option. Currently, the output from running --csg-only will most likely be a JSON output file. A hook can be enabled for the csg_only action with downstream codes to

Impact

Ability to generate Exodus meshes and CSG-based meshes within the same input file. This feature would be useful for codes that interface with MOOSE and Monte Carlo codes, such as Cardinal and Shift/Titan.

[YaqiWang]

Are you going to use mesh meta data to generate CSG or CSG will be another mesh format describing all elements, etc.?

[shikhar413]

The idea is to have a low-level representation of the mesh using internal representation for cells, surfaces, and universes, which will be the most generalizable to be able to interface with MC codes. For certain mesh generators, we will also have a metadata-based representation of the CSG mesh as well, as this is better suited for creating Shift-based geometry input files. This metadata-based representation will represent engineering units such as pins, assemblies, core etc. instead of their constituent cells and surfaces