Introduction
============

MFIX-Exa is a new massively parallel code for computing multiphase
flow in which solid particles interact with the gas surrounding them. It is
built on top of `AMReX`_, a publicly available software framework designed for
building massively parallel block-structured adaptive mesh refinement (AMR)
applications.

MFIX-Exa relies on the same fundamental physics as in MFiX but the spatial and
time discretizations differ.  Specifically,

-  Fluid velocity is defined at cell centers; pressure is defined at nodes.
-  The advection algorithm includes an intermediate MAC projection for
   face-centered advection velocities
-  Incompressibility of the fluid is imposed through the use of a projection at
   the end of the time step
-  The representation of the complex geometry includes mesh refinement around
   the fluid-solid interface, which is represented used the embedded boundary, or
   cut-cell approach
-  Parallelization via flat MPI, OpenMP, hybrid MPI/OpenMP, or MPI/MPI.
-  Porting of MFIX-Exa to GPUs is in progress.
-  Parallel I/O using AMReX native I/O or HDF5.
-  Plotfile format supported by AmrVis, VisIt, ParaView, and yt.

MFIX-Exa is being developed at NETL and LBNL as part of the U.S. Department of
Energy's `Exascale Computing Project (ECP) <https://www.exascaleproject.org/>`_.
MFIX-Exa heavily leverages `AMReX`_ which is also supported by ECP as part of
the AMReX Co-Design Center.

.. _AMReX: https://amrex-codes.github.io/
