diff --git a/docs/source/InputsProblemDefinition.rst b/docs/source/InputsProblemDefinition.rst
index 3f29f797f4cda6d2dab8da8d17d74745a8b51eb9..d3304926ae69d598a44b1921ff8602bb038a8a3e 100644
--- a/docs/source/InputsProblemDefinition.rst
+++ b/docs/source/InputsProblemDefinition.rst
@@ -48,7 +48,7 @@ The following inputs must be preceded by "mfix."
+----------------------+-------------------------------------------------------------------------+----------+-----------+
| po_no_par_out | Let particles exit (default) or bounce-back at pressure outflows | Int | 0 |
+----------------------+-------------------------------------------------------------------------+----------+-----------+
-| gravity | Gravity vector (e.g., mfix.gravity = -9.81 0.0 0.0) [requried] | Reals | None |
+| gravity | Gravity vector (e.g., mfix.gravity = -9.81 0.0 0.0) [required] | Reals | None |
+----------------------+-------------------------------------------------------------------------+----------+-----------+
@@ -85,20 +85,246 @@ To specify multiple mass inflows (e.g., define a jet and uniform background flow
xlo.zhi = 0.75
-The following inputs must be preceded by "fluid."
+## Fluid model settings ##
+
+Enabling the fluid solver and specifying fluid model options.
+----------------------+-------------------------------------------------------------------------+----------+-----------+
| | Description | Type | Default |
+======================+=========================================================================+==========+===========+
-| solve | Flag to enable (1) or disable (0) the fluid solver [required] | Int | None |
+| fluid.solve | Specified name of the fluid or None to disable the fluid solver. The | String | None |
+| | name assigned to the fluid solver is used to specify fluid inputs. | | |
++----------------------+-------------------------------------------------------------------------+----------+-----------+
+
+
+The following inputs must be preceded by the given to the fluid solver e.g., "fluid."
+----------------------+-------------------------------------------------------------------------+----------+-----------+
-| density_model | Specify which density model to use for fluid [requried] | String | None |
+| | Description | Type | Default |
++======================+=========================================================================+==========+===========+
+| density | Specify which density model to use for fluid [required] | String | None |
| | "constant" -- constant density | | |
+----------------------+-------------------------------------------------------------------------+----------+-----------+
-| constant_density | Value of constant fluid density [required if density_model= "constant" | Real | None |
+| density.constant | Value of constant fluid density [required if density_model= "constant" | Real | None |
+----------------------+-------------------------------------------------------------------------+----------+-----------+
-| viscosity_model | Specify which viscosity model to use for fluid [requried] | String | None |
+| viscosity | Specify which viscosity model to use for fluid [required] | String | None |
| | "constant" -- constant viscosity | | |
+----------------------+-------------------------------------------------------------------------+----------+-----------+
-| constant_viscosity | Value of constant fluid viscosity [required if viscosity_model="constant"| Real | None |
+| viscosity.constant | Value of constant fluid viscosity [required if viscosity_model="constant"| Real | None |
+----------------------+-------------------------------------------------------------------------+----------+-----------+
+
+Below is an example for specifying fluid solver model options.
+
+.. code-block:: none
+
+ fluid.solve = myfluid
+
+ myfluid.density = constant
+ myfluid.density.constant = 1.0
+
+ myfluid.viscosity = constant
+ myfluid.viscosity.constant = 1.8e-5
+
+
+
+## DEM model settings ##
+
+
+Enabling the DEM solver and specifying model options.
+
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| | Description | Type | Default |
++=========================+=========================================================================+==========+===========+
+| dem.solve | Specified name(s) of the DEM types or None to disable the DEM solver. | String | None |
+| | The user defined names are used to specify DEM model inputs. | | |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| dem.friction_coeff.pp | Friction coefficient :: particle to particle collisions [required] | Real | None |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| dem.friction_coeff.pw | Friction coefficient :: particle to wall collisions [required] | Real | None |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| dem.spring_const.pp | Normal spring constant :: particle to particle collisions [required] | Real | None |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| dem.spring_const.pw | Normal spring constant :: particle to wall collisions [required] | Real | None |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| dem.spring_tang_fac.pp | Tangential-to-normal spring constant factor :: particle to particle | Real | None |
+| | collisions [required] | | |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| dem.spring_tang_fac.pw | Tangential-to-normal spring constant factor :: particle to wall | Real | None |
+| | collisions [required] | | |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| dem.damping_tang_fac.pp | Factor relating the tangential damping coefficient to the normal | Real | None |
+| | damping coefficient :: particle to particle collisions [required] | | |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| dem.damping_tang_fac.pw | Factor relating the tangential damping coefficient to the normal | Real | None |
+| | damping coefficient :: particle to wall collisions [required] | | |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+
+The following inputs use the DEM type names specified using the `dem.solve` input to define restitution coefficients and
+are proceeded with `dem.restitution_coeff`. These must be defined for all solid-solid and solid-wall combinations.
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| | Description | Type | Default |
++=========================+=========================================================================+==========+===========+
+| [solid0].[solid1] | Specifies the restitution coefficient between solid0 and solid1. Here | Real | None |
+| | the order is not important and could be defined as [solid1].[solid0] | | |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+| [solid0].wall | Specifies the restitution coefficient between solid0 and the wall. | Real | None |
+| | Order is not important and this could be defined as wall.[solid0] | | |
++-------------------------+-------------------------------------------------------------------------+----------+-----------+
+
+Below is an example for specifying the inputs for two DEM solids.
+
+.. code-block:: none
+
+ dem.solve = sand char
+
+ dem.friction_coeff.pp = 0.25
+ dem.friction_coeff.pw = 0.15
+
+ dem.spring_const.pp = 100.0
+ dem.spring_const.pw = 100.0
+
+ dem.spring_tang_fac.pp = 0.2857
+ dem.spring_tang_fac.pw = 0.2857
+
+ dem.damping_tang_fac.pp = 0.5
+ dem.damping_tang_fac.pw = 0.5
+
+ dem.restitution_coeff.sand.sand = 0.85
+ dem.restitution_coeff.sand.char = 0.88
+ dem.restitution_coeff.char.char = 0.90
+
+ dem.restitution_coeff.sand.wall = 0.85
+ dem.restitution_coeff.char.wall = 0.89
+
+
+## Region definitions ##
+
+Regions are used to define sections of the domain. They may be either boxes, planes or points. They are used in building initial condition regions.
+
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| | Description | Type | Default |
++=====================+=======================================================================+=============+===========+
+| mfix.regions | Names given to regions. | String | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| regions.[region].lo | Low corner of physical region (physical not index space) | Reals | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| regions.[region].hi | High corner of physical region (physical not index space) | Reals | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+
+Below is an example for specifying two regions.
+
+.. code-block:: none
+
+ mfix.regions = full-domain riser
+
+ regions.full-domain.lo = 0.0000 0.0000 0.0000
+ regions.full-domain.hi = 3.7584 0.2784 0.2784
+
+ regions.riser.lo = 0.0000 0.0000 0.0000
+ regions.riser.hi = 0.1000 0.2784 0.2784
+
+
+
+## Initial Conditions ##
+
+Initial conditions are build from defined regions. The input names are built using the prefix `ic.`, the name of the
+region to apply the IC, and the name of the phase (e.g., `myfuild`).
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| | Description | Type | Default |
++=====================+=======================================================================+=============+===========+
+| ic.regions | Regions used to define initial conditions. | String | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+
+For a fluid phase, the following inputs can be defined.
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| | Description | Type | Default |
++=====================+=======================================================================+=============+===========+
+| volfrac | Volume fraction [required] | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| pressure | Fluid pressure | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| temperature | Fluid temperature | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| velocity | Velocity components | Reals | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+
+
+The name of the DEM phases to be defined in the IC region and the packing must be defined.
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| | Description | Type | Default |
++=====================+=======================================================================+=============+===========+
+| ic.[region].solids | List of solids | Strings | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| ic.[region].packing | Specifies how auto-generated particles are placed in the IC region: | String | None |
+| | * hcp - Hex-centered packing | | |
+| | * random | | |
+| | * pseudo_random | | |
+| | * oneper -- one particle per cell | | |
+| | * eightper -- eight particles per cell | | |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+
+For each solid, the following inputs may be defined.
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| | Description | Type | Default |
++=====================+=======================================================================+=============+===========+
+| volfrac | Volume fraction | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| temperature | Fluid temperature | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| velocity | Velocity components | Reals | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| diameter | Method to specify particle diameter in the IC region. This is | String | None |
+| | only used for auto-generated particles. | | |
+| | * constant -- specified constant | | |
+| | * uniform -- uniform distribution | | |
+| | * normal -- normal distribution | | |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| diameter.constant | Value of specified constant particle density | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| diameter.mean | Distribution mean | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| diameter.std | Distribution standard deviation | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| diameter.min | Minimum diameter to clip distribution | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| diameter.max | Maximum diameter to clip distribution | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| density | Method to specify particle density in the IC region. This is | String | None |
+| | only used for auto-generated particles. | | |
+| | * constant -- specified constant | | |
+| | * uniform -- uniform distribution | | |
+| | * normal -- normal distribution | | |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| density.constant | Value of specified constant particle density | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| density.mean | Distribution mean | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| density.std | Distribution standard deviation | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| density.min | Minimum density to clip distribution | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+| density.max | Maximum density to clip distribution | Real | None |
++---------------------+-----------------------------------------------------------------------+-------------+-----------+
+
+
+Below is an example for specifying an initial condition for a fluid (fluid) and one DEM solid (solid0).
+
+.. code-block:: none
+
+ ic.regions = bed
+
+ ic.bed.fluid.volfrac = 0.725
+
+ ic.bed.fluid.velocity = 0.015 0.00 0.00
+
+ ic.bed.solids = solid0
+ ic.bed.packing = pseudo_random
+
+ ic.bed.solid0.volfrac = 0.275
+
+ ic.bed.solid0.velocity = 0.00 0.00 0.00
+
+ ic.bed.solid0.diameter = constant
+ ic.bed.solid0.diameter.constant = 100.0e-6
+
+ ic.bed.solid0.density = constant
+ ic.bed.solid0.density.constant = 1000.0