*********************************
**Default Material Species Type**
*********************************

::

	Default Material Species Type = {species_type_string}

-----------------------
**Description / Usage**
-----------------------

This optional parameter sets the form of the species variable type within *Goma*. Valid
options for {species_type_string} are given below by the *SPECIES_** names (along
with a description and variable (prefix) name:

=========================== ======================== =============
**SPECIES_MASS_FRACTION**   Mass Fractions           *Yk_*
**SPECIES_MOLE_FRACTION**   Mole Fractions           *Xk_*
**SPECIES_VOL_FRACTION**    Volume Fractions         *Vk_*
**SPECIES_DENSITY**         Species Densities        *Dk_*
**SPECIES_CONCENTRATION**   Species Concentration    *Ck_*
**SPECIES_UNDEFINED_FORM**  Undefined form           *Y*
=========================== ======================== =============

The default is to assume **SPECIES_UNDEFINED_FORM**. Please refer to the
Technical Discussion for important details.

------------
**Examples**
------------

Following is a sample card:
::

   Default Material Species type = SPECIES_MASS_FRACTION

-------------------------
**Technical Discussion**
-------------------------

For nondilute systems the *SPECIES_* quantities above are not just simply
interchangeable via a multiplicative constant. Their values are distinct, and their
interrelationship evaluated via a potentially nontrivial equation of state. Prior to the
implementation of this card/capability, *Goma* hadn’t handled many nondilute cases,
and where it had, this issue was finessed by special casing property evaluations.

This card both sets the type of the species variables and establishes a convention for the
units of equations within *Goma*. For settings of **SPECIES_MASS_FRACTION** and
**SPECIES_DENSITY_FRACTION**, equations generally have a mass unit attached to
them. Equations have concentration units attached to them for settings of
**SPECIES_MOLE_FRACTION**, **SPECIES_VOL_FRACTION**, and
**SPECIES_CONCENTRATION**. For example, given a setting of
**SPECIES_MASS_FRACTION**, each volumetric term in the species conservation
equation has units of mass per time, i.e., the time derivative term is written as

.. figure:: /figures/257_goma_physics.png
	:align: center
	:width: 90%

For a setting of **SPECIES_MOLE_FRACTION**, each volumetric term would have
units of moles per time, i.e., the time derivative term is written out as

.. figure:: /figures/258_goma_physics.png
	:align: center
	:width: 90%

All this is necessary in order to handle cases where the total density or total
concentration of a phase is spatially variable. In that case, it can’t just be divided out as in earlier versions of *Goma* but must be included in the conservation equations, and therefore the units of the conservation equation must reflect this.

The species variable type affects the units and thus values of quantities returned from
certain boundary conditions. For example, the **IS_EQUIL_PSEUDORXN** boundary
condition returns units of moles per time per :math:`length^2` if the species variable type is defined to be **SPECIES_CONCENTRATION**, but will multiply by molecular
weights and thus return units of mass per time per :math:`length^2` if the species variable type is defined to be **SPECIES_MASS_FRACTION**. This change conforms to the expected units of the overall species conservation equation for the two values of the species variable type variable used as examples above.

The last column in the table above contains a three letter string. This string is used as a prefix for the name of the species variable in the EXODUS output file. If no names are
specified in the material file and Chemkin is not used (which provides names for the
species variables itself), then integers are used for names. For example, the first species unknown in *Goma* problem employing Mass Fractions as the independent species
variables will be called **Yk_1**. If Chemkin is used in the same problem and the first
chemkin species is named **H2O**, then the name in the EXODUS output file will be
**Yk_H2O**. If a *Goma* problem is solved with no specification of the type of the species
variable, then the first unknown in the EXODUS file will be named **Y1**.

Additionally, some boundary conditions and inputs from the material file section will
set the species variable type on their own without the benefit of this card, if the species variable type is the default undefined form. Some internal checks are done; if an
inconsistency is caught, *Goma* will abort with an informative error message.




..
	TODO - Lines 57 and 64 contain pictures that need to be changed into the equations.