MOON
=====

MOON (Multiphysics Object-Oriented Nek5000) uses the [MOOSE](http://www.mooseframework.org/) framework to implement multiphysics coupling with [Nek5000](https://nek5000.mcs.anl.gov/) CFD simulations.  The project is a collaboration between [Idaho National Laboratory](https://www.inl.gov/) and [Argonne National Laboratory](https://www.inl.gov/).


Downloading the Repo
--------------------
Cloning the MOON repository requires the `--recursive` flag, since MOOSE and libmesh are included as [Git submodules](https://git-scm.com/book/en/v2/Git-Tools-Submodules).  For example:
```
git clone --recursive https://xgitlab.cels.anl.gov/nek5000/moon.git
```
This will download and populate the src/moose and src/moose/libmesh.


Building PETSc
--------------
MOON requires PETSc, as described in the [MOOSE installation instructions](http://mooseframework.com/getting-started/).  PETSc is not distributed with MOON.  PETSc must either be compiled from source or installed as part of the MOOSE Environment package.  After installing PETSc, you must define the `$PETSC_DIR` variable in your environment.


Building libmesh
----------------
MOON also requires libmesh, as described in the [MOOSE installation instructions](http://mooseframework.com/getting-started/).  The libmesh source code is distributed with MOOSE.  It should be compiled using the following scripts:
```
$ cd moose/
$ scripts/update\_and\_rebuild\_libmesh.sh.  
```
After installing libmesh, you must define the `$LIBMESH_DIR` in your environment.


The Example Problems
--------------------

Currently, the only working example problem is "integration_example" in `moon/examples/integration_example`.  

### Building Example Problems

To configure and build each example problem, first generate the `configure` script in the top-level MOON directory:
```
$ cd moon
$ ./bootstrap
```
Then cd into the example subdirectory and simply run `configure` && `make`.  This will build the MOOSE and Nek5000 libraries, then link them to the executable driver.
```
$ cd moon/examples/integration_example`
$ ../../configure
$ make
```
The `configure` script may be run with additional options (for example, to point to a custom libmesh or MOOSE installation).  Run `./configure --help` to see a list of the available options.

### Running Example Problems

To run an example problem, it is recommended to use the convenience script `moon/examples/build_coupled_nek`.  This script will automatically setup some input files needed by Nek5000 (such as SESSION.NAME).  The script takes one command-line argument for the MOOSE configuration file, `-i <config_file>.i`.
```
$ cd moon/examples/integration_example
$ ../../scripts/build_coupled_nek.sh -i coefficient_integration.i
```

Developing Nek5000 in MOON
--------------------------
Developers may freely modify src/Nek5000 as if it were a normal part of the MOON repo.  This is because Nek5000 is included as a Git subtree (rather than a submodule).  For routine commits, pushes, and pulls to the MOON repository, no extra Git commands are necessary.

With some additional Git commands, developers may easily merge upstream changes from [https://github.com/Nek5000/Nek5000](https://github.com/Nek5000/Nek5000) into src/Nek5000.  Finally, developers may also request to merge changes from src/Nek5000 to [https://github.com/Nek5000/Nek5000](https://github.com/Nek5000/Nek5000). This [blog post](http://blogs.atlassian.com/2013/05/alternatives-to-git-submodule-git-subtree/) from Atlassian gives a brief rundown of the procedures.  


Developing MOOSE and libmesh in MOON
------------------------------------
Modifying src/moose and src/moose/libmesh require additional Git commands, since they are included as Git submodules (rather than subtrees).  Modifying either of these libraries for MOON is intended to be unnecessary.  Should the situation arise, this [chapter](https://git-scm.com/book/en/v2/Git-Tools-Submodules) from _Pro Git_ describes the procedure for making modifications to submodules.