# MATERIAL_RADIATION_MODEL

Specifies material for the P1 and discrete_ordinate radiation model.

## Type

AcuSolve Command

## Syntax

MATERIAL_RADIATION_MODEL("name") {parameters...}

## Qualifier

User-given name.

## Parameters

- absorption_coefficient (real) [=1.0 1/meter]
- Absorption of thermal radiation per unit length by the participating medium. Absorption coefficient is greater or equal to zero for the discrete_ordinate model and greater than zero for the p1_model. A value of zero means the medium is non-participating.
- scattering_coefficient (real) [= 0.0 1/meter]
- Scattering of radiation leading to further attenuation (weakening) of the incident radiation.
- phase_coefficient (real) [= 0.0]
- Linear anisotropic phase function coefficient for linear anisotropic scattering of the incident radiation. phase_coefficient range: -1 < phase_coefficient < 1. The three types of scattering are isotropic scattering (phase_coefficient = 0.0), i.e., scattering is the same in all directions; forward dominant scattering (phase_coefficient > 0) of the incident radiation, that is, more scattering in the forward direction than backward direction; and backward dominant scattering (phase_coefficient < 0). The closer the coefficient is to 1 or –1 the more dominant the scattering is in the forward or backward direction, respectively.
- refractive_index (real) [= 1.0]
- Ratio of the velocity of incident radiation propagation in a medium compared to a vacuum.

## Description

This command specifies radiation material parameters for the P1 and discrete ordinates radiation model. All media, both fluid or solid, that are participating require a MATERIAL_RADIATION_MODEL.

```
MATERIAL_MODEL( "my_participating_medium" ) {
radiation_model = "my_radiation_material"
...
}
MATERIAL_RADIATION_MODEL( "my_radiation_material" ){
absorption_coefficient = 200.0
scattering_coefficient = 0.0
phase_coefficient = 0.0
refractive_index = 1.51
}
```

If the MATERIAL_MODEL is not participating the radiation_model can simply be removed.

For a radiation material that is participating the total attenuation/loss, also termed extinction, of the incident radiative intensity is governed by the combination of absorption and scattering within the medium. The former represents absorption of intensity by the medium, while the latter is scattering of intensity onto other directions. Note for the P1 model the directional dependency is integrated out. The absorption and scattering coefficients represent a per unit length intensity loss within a participating medium.

^{-1}and a scattering coefficient of 1.0 m

^{-1}that is isotropic in all directions. Therefore, the extinction coefficient for this material is 2.0. The refractive index of the material means the velocity of incident radiation is identical to that of a vacuum. Materials, such as glass, have a higher refractive index meaning radiation propagates slower through the medium.

```
MATERIAL_RADIATION_MODEL( "Medium_HM" ) {
absorption_coefficient = 1.0
scattering_coefficient = 1.0
phase_coefficient = 0.0
refractive_index = 1.0
}
```