# MATERIAL_MODEL

Specifies a material model by collecting specific models.

## Type

AcuSolve Command

## Syntax

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

## Qualifier

User-given name.

## Parameters

- type (enumerated) [=fluid]
- Type of the material model.
- fluid
- Fluid material model.
- solid
- Solid material model.

- density_model or dens (string) [no default]
- User-given name of the density model. This is a required parameter. Density is used in the fluid, solid, and shell element sets.
- specific_heat_model or cp (string) [=none]
- User-given name of the specific heat at constant pressure model. This parameter is needed for solving the temperature equation in the fluid, solid, and shell element sets. If none, no specific heat model is provided.
- viscosity_model or visc (string) [=none]
- User-given name of the viscosity model. This parameter is needed for solving the flow equations in the fluid element sets. If none, no viscosity model is provided.
- conductivity_model or cond (string) [=none]
- User-given name of the thermal conductivity model. This parameter is needed for solving the temperature equation in the fluid, solid, and shell element sets. If none, no conductivity model is provided.
- vapor_phase_model (string) [=none]
- User-given name of the vapor-phase model. This parameter is used exclusively for solving the single-phase nucleate boiling. This material model represents the vapor state of the current material and whose properties are used in the evaluation of the heat transfer due to boiling. It is important to note that for single-phase nucleate boiling, the material model for the vapor phase requires the latent heat and latent heat temperature entries. Used when nucleate_boiling is set to on to the wall type. If none, no vapor phase model is provided.
- surface_tension_model (string) [=none]
- User-given name of the surface tension model. This parameter is needed for solving the single-phase nucleate boiling. Used when nucleate_boiling is set to on to the wall type. If none, no surface tension model is provided.
- diffusivity_1_model or diff_1 (string) [=none]
- diffusivity_2_model or diff_2 (string) [=none]
- diffusivity_3_model or diff_3 (string) [=none]
- diffusivity_4_model or diff_4 (string) [=none]
- diffusivity_5_model or diff_5 (string) [=none]
- diffusivity_6_model or diff_6 (string) [=none]
- diffusivity_7_model or diff_7 (string) [=none]
- diffusivity_8_model or diff_8 (string) [=none]
- diffusivity_9_model or diff_9(string) [=none]
- User-given name of the diffusivity model for the corresponding species transport equation. This parameter is needed for solving the corresponding species transport equation in the fluid element sets. If none, no diffusivity model for the corresponding species is provided.
- porosity_model or poros (string) [=none]
- User-given name of the porosity model. This model may be used for solving the flow equations in the fluid element sets. If none, no porosity modeling is provided.
- viscoelastic_model (string) [=none]
- User-given name of the viscoelastic model. This model may be used for solving the flow equations in the fluid element sets. If none, no viscoelastic modeling is provided.
- radiation_model (string) [=none]
- User-given name of the material radiation model. This model may be used for solving the P1 and discrete ordinates radiation equations in the fluid or solid element sets that are participating. Used with MATERIAL_RADIATION_MODEL. If none, no MATERIAL_RADIATION_MODEL is provided and the medium does not participate in radiative heat transfer.

## Description

This command specifies a material model.

MATERIAL_MODEL commands collect

- DENSITY_MODEL
- SPECIFIC_HEAT_MODEL
- VISCOSITY_MODEL
- CONDUCTIVITY_MODEL
- DIFFUSIVITY_MODEL
- POROSITY_MODEL
- VISCOELASTIC_MODEL
- MATERIAL_RADIATION_MODEL

```
DENSITY_MODEL( "my density model" ) { ... }
SPECIFIC_HEAT_MODEL( "my specific heat model" ) { ... }
VISCOSITY_MODEL( "my viscosity model" ) { ... }
CONDUCTIVITY_MODEL( "my conductivity model" ) { ... }
DIFFUSIVITY_MODEL( "my diffusivity model 1" ) { ... }
DIFFUSIVITY_MODEL( "my diffusivity model 2" ) { ... }
POROSITY_MODEL( "my porosity model" ) { ... }
VISCOELASTIC_MODEL( "my viscoelastic model" ) { ... }
MATERIAL_RADIATION_MODEL( "my radiation model" ) { ... }
MATERIAL_MODEL( "my material model" ) {
density_model = "my density model"
specific_heat_model = "my specific heat model"
viscosity_model = "my viscosity model"
conductivity_model = "my conductivity model"
diffusivity_1_model = "my diffusivity model 1"
diffusivity_2_model = "my diffusivity model 1"
diffusivity_3_model = "my diffusivity model 2"
porosity_model = "my porosity model"
viscoelastic_model = "my viscoelastic model"
radiation_model = “my radiation model”
}
ELEMENT_SET( "fluid elements" ) {
material_model = "my material model"
...
}
```

Every ELEMENT_SET command of medium fluid or solid must reference a MATERIAL_MODEL command. ELEMENT_SET commands of medium shell must reference an array of MATERIAL_MODEL commands, one for each layer. The same material model may be shared by any number of element sets or shell layers. All material models not referenced are ignored.

A material model must contain all the necessary parts associated with the equations being solved in the problem. These equations are defined by the EQUATION command.

Must Include | When Solving For |
---|---|

density_model | any equation |

viscosity_model | flow and turbulence |

specific_heat_model | temperature |

conductivity_model | temperature |

diffusivity_1_model | species 1 |

diffusivity_2_model | species 2 |

diffusivity_3_model | species 3 |

diffusivity_4_model | species 4 |

diffusivity_5_model | species 5 |

diffusivity_6_model | species 6 |

diffusivity_7_model | species 7 |

diffusivity_8_model | species 8 |

diffusivity_9_model | species 9 |

viscoelastic_model | viscoelasticity |

radiation_model | P1 or discrete ordinates radiation |

In addition, the porosity_model may be added for the flow equations. In general, you should always include the viscosity_model even if the flow equations are not being solved. Some models, such as the conductivity model with a constant Prandtl number, may require the viscosity.

Since only the energy and mesh displacement equations are defined in the solid and shell element sets, the corresponding material models need only the density_model, specific_heat_model, and conductivity_model parameters.

`medium = design`

). Any number of element sets of other
medium types may still be used in the
simulation.```
ELEMENT_SET( "Design" ) {
…
medium = design
material_model = "fluid_medium"
design_material_model = "poros_solid_medium"
design_variables_field = "topology"
…
}
```

```
MATERIAL_MODEL( "fluid_medium" ) {
type = fluid
density_model = "air"
viscosity_model = "air"
porosity_model = "none"
}
DENSITY_MODEL( "air" ) {
…
}
VISCOSITY_MODEL( "air" ) {
…
}
POROSITY_MODEL( "air" ) {
type = none
}
MATERIAL_MODEL( "poros_solid_medium" ) {
type = fluid
density_model = "air"
viscosity_model = "air"
porosity_model = "poros"
}
DENSITY_MODEL( "air" ) {
}
VISCOSITY_MODEL( "air" ) {
}
POROSITY_MODEL( "poros" ) {
type = "constant"
porosity = 1.0
forchheimer_coefficient = 0.0
darcy_coefficient = 1.e5
}
```