====== Radiative Material ======

<note important>
This Documentation refers to Metafor version >= 3593.
for more informations on changes see [[https://gitlab.uliege.be/am-dept/MN2L/oo_meta/-/merge_requests/167|MR !167]] for technical informations). 

for a Metafor version < 3593, please refers to this [[radiation_pre3593|page]].
</note>

===== RadiativeMaterial =====     

The ''RadiativeMaterial'' is implemented to take into account the heat exchange between the boundary of a mesh and the surrounding atmosphere (at uniform Temperature) without taking into account any view factor or self exchange between mesh.

The heatFlux (W/m²) is equal to 
$flux = -\sigma \epsilon (T^4-T_{amb}^4)$
with : 
  * $\sigma$ : the Stefan-Boltzmann Constant (5.67 × 10-8 W/m²K4)
  * $\epsilon$ : relative emissivity parameter (1)
  * $T$ : temperature at the integration point (K) 
  * $T_{amb}$ : Room temperature (K)

It is designed to work with ''Tm(2)Boundary2D(/3D)Element''. By default, the surrounding model has to be defined in Kelvin, but defining the parameter ''RAY_CELSIUS'' to ''True'' allows using it in a Celsius defined test.


  mat = materset.define(no, RadiativeMaterial )
  mat.put(param1, value1)
  mat.depend(param1, fct1, Lock1)) #optional


where
|''param1''| name of the property associated to the element (for example ''RAY_EMISSIVITY'')  |
|''value1''| value of the corresponding property  |
|''fct1''  | function which characterizes the dependency of the property (optional: no fct if no dependency) |
|''Lock1'' | [[doc:user:general:locks|Lock]] which defines the dependency variable of the property (compulsory if there is a dependency) |


=== Parameters ===
^   Name                                          ^     Description       ^  Dependency ^
| ''BOLTZMANN_CST'' | Stefan-Boltzmann Constant (required to set units)\\ =  $ 5.67e^{-8}  W/m^2K^4 $\\ =  $ 5.67e^{-11}  mW/mm^2K^4$|  Set  |
| ''RAY_EMISSIVITY''| Relative emissivity between two gray bodies (solid / room)\\ $\epsilon = \frac{\epsilon_1 * \epsilon_2}{\epsilon_1 + \epsilon_2 - \epsilon_1 * \epsilon_2}$    |  time  | 
| ''RAY_TEMP_AMB''  | Room temperature (K)  |  time  |
| ''RAY_CELSIUS''   | flag to chose Themperature unit system of the test (default : Kevin => False)     |  -  |