The Material Editor is used to create additional materials not supplied with the software. There are four basic properties that are necessary to define a solid for use with Autodesk® Simulation CFD. Most of these properties can vary with temperature, pressure or scalar, in several different variation methods. These properties and methods are listed in the following table:
| Property | Variational Methods |
| Conductivity -- the same value for thermal conductivity can be used for all three directions, or each component can be different. |
Constant, Polynomial, Inverse Polynomial, Piecewise Linear. Y and Z directions also have: Same as X-Dir. |
| Density -- only needed for transient analyses. | Constant, Polynomial, Inverse Polynomial, Piecewise Linear. |
| Specific Heat -- only needed for transient analyses. | Constant, Polynomial, Inverse Polynomial, Piecewise Linear. |
| Emissivity -- useful for radiation analyses. The emissivity specified on a solid will override the value assigned to contacting fluid. | Constant, Piecewise Linear variation with temperature (useful for specrowal radiation analyses.) |
| Transmissivity -- useful for radiation analyses; see note below | Constant, Piecewise Linear variation with temperature |
| Electrical Resistivity -- only needed for Joule heating analyses. | Constant, Polynomial, Inverse Polynomial, Piecewise Linear (varies with temperature). |
| Wall Roughness -- useful for applying variable roughness height to include effects of friction | Constant. Please see section about Wall Roughness. |
Transmissivity is a measure of how much radiative energy can pass through an object. A value of 1 indicates that the object is completely transparent, and that radiative energy can pass completely through it. A value of 0 means that the object is opaque. The permissible range of Transmissivity values is between 0 and 1.
Two variation methods are available for Transmissivity: Constant and as a Piecewise Linear table varying with temperature. Transmissivity is a unitless parameter. The default value is 0.
The sum of Transmissivity and Emissivity must be less than or equal to 1.
If the sum of these two values exceeds 1, an error message will be displayed when the analysis is started.
Transmissivity can only be assigned to solids. The radiation model considers fluids to be non-participating, so it is not possible to simulate radiative heat transfer through dark or “muddy” fluids.
To simulate a Transparent object completely immersed within a fluid:
To simulate radiative heat exchange between a transparent solid and the environment, such as a window:
Surface parts cannot be used to simulate transparent media. A non-zero value of transmissivity applied to surface parts will be ignored. Likewise, non-zero values of transparency assigned to moving solids are ignored--transparency is not supported for moving solids or within rotating regions.
Note that absorption of radiation energy by transparent solids is not included in the radiation model.
The resistance per area multiplied by the length of the device. A value for resistivity is required for any solid that is heated by the Joule effect.
The relationship between resistivity and resistance is: