# Embedded Boundaries

MFIX-Exa uses AMReX’s Embedded Boundaries to represent container walls. This allows MFIX-Exa to simulate a wide range of shapes and boundary conditions using constructive solid geometry. MFIX-Exa also has the capability of locally refining the computational meshes near walls.

Contents:

- Constructing Embedded Boundaries in MFIX-Exa
  - EB Specification
    - Native AMReX functions
    - CSG File Format
    - Planar Walls
    - STL File Format
  - How MFIX-Exa Constructs the EB Geometry
  - MFIX-Exa’s EB Data Structures
  - A note about constructing EB Levels
- Local Mesh Refinement at Walls
  - MFIX-Exa Initialization Process
- The Level-Set Function
  - Special Cases Involving Level-Sets