Assigning Thermal Materials

When choosing a material for a thermal analysis, you will see a different set of materials and material properties compared to a circuit, electromagnetics, or structural analysis. Instead of properties such as Electrical Conductivity and Relative Permittivity, the physical properties of interest for thermal analyses are the Thermal Conductivity, Mass Density, Specific Heat, Thermal Material Type (Solid or Fluid), and Dynamic Viscosity (fluids only). Materials with at least the first of these five properties defined will appear in the Select Definition dialog box, where you choose the default material or assign an object material.

Only the Thermal Conductivity is needed for Steady-State Thermal solutions (other thermal material properties can be zero). For Transient Thermal solutions, non-zero Mass Density and Specific Heat values are also required. When defining materials for a steady-state solution, it is best to include the mass density and specific heat values when available, even though they are not required. Doing so ensures that the same materials will also be suitable for a transient analysis if the solution type is later changed, avoiding a transient solution error.

Anisotropic Properties

Materials for thermal solutions can have simple isotropic properties (that is, behaving quantitatively the same way in every direction), or anisotropic properties (exhibiting different behavior in three orthogonal directions). Specifically, the Thermal Conductivity can differ in each of three orthogonal directions. These directions are defined by the Orientation property of each object that uses the material (indicating a global or user-defined coordinate system).

All predefined library materials are of the simple (isotropic) type. You must define your own custom material to use anisotropic properties.

See the Defining Anisotropic Tensors topic for more information.

Temperature-Dependent Properties

Thermal materials can also have temperature-dependent properties. Specifically, the Thermal Conductivity, Mass Density, and Specific Heat can vary as a function of temperature.

Additionally, the Dynamic Viscosity of fluids can vary as a function of temperature. This property is used in the calculation of the equivalent thermal conductivity for rotating fluid boundaries.

Note:

If your design will experience temperatures below 0° C, you must define the thermal modifiers for all applicable properties using manually defined dataset tables. General expressions (linear, quadratic, conditional, and so on) are automatically converted to tables for the solver, and these automatically generated tables only contain temperature datapoints in the range of 0–1000° C.

All predefined library materials are of the non-temperature-dependent type. You must define your own custom materials to use temperature-dependent properties.

See the Specifying Thermal Modifiers topic for more information.

Default Material and Applicable Libraries

The default material for thermal analyses is air. Thermal materials can be solid, liquid, or gaseous, with the Fluid material type representing both liquids and gases. All 3D elements are treated as solids, but the dynamic viscosity and other properties of fluid materials are used to estimate the equivalent thermal conductivity within the gap of rotating machine simulations.

The following libraries contain materials suitable for Thermal solutions:

Note:

The Specific Heat of the materials is not required because this property is only applicable to transient thermal analyses (that is, those in the time domain). A steady-state solution provides the temperatures and heat flux results that exist once a steady-state condition (or thermal equilibrium) is achieved. However, the time it takes to achieve thermal equilibrium is not determined.

Material Selection

To set the default material for all objects you subsequently create:

  1. At the far right end of the Draw ribbon tab, choose Select from the Default material drop-down menu.

    2. The Select Definition dialog box appears.

  2. In the Libraries list, ensure that one or more of the previously listed suitable libraries are selected, or a user library with thermal material properties. Click the ellipsis button ( ... ) to the right of the Libraries list to access a pop-up dialog box in which you can select which libraries to include in the Materials list:

    3. Alternatively, select the Select all libraries option:

  3. Optionally, type a portion of the material name in the Search by Name text box. The list will automatically scroll as needed and the first material matching the search string will be selected. If you scroll the selected material off screen, click Search to quickly bring the searched material back into view.
  4. Select the desired material, if present.
  5. Optionally, to define your own material properties, click Add Material.

    6. The View / Edit Material dialog box appears:

  6. Optionally, if you are adding a gas or liquid material, choose Fluid from the Material Type drop-down menu in the Value column.
  7. Optionally, to specify anisotropic Thermal Conductivity values (when the conductivity varies in the three global directions), select Anisotropic from the Type drop-down menu. Otherwise, the Simple option is for isotropic properties (when the conductivity is the same in every direction).
  8. Optionally, if you want to define temperature-dependent material properties, follow the instructions in the Specifying Thermal Modifiers topic.
  9. If editing properties, or defining a new material, specify the desired Material Name, Thermal Conductivity, Mass Density, Specific Heat, and Dynamic Viscosity values.

    10. The following material validation rules apply:

    • Simple (isotropic) materials:
      • Thermal Conductivity (λ) must be greater than zero: (λ > 0)
      • For Transient Thermal solutions, Mass Density and Specific Heat must both be greater than zero.
    • Anisotropic materials:
      • Thermal Conductivity (λ) must be greater than zero in all three directions: [for λ, T(1,1) > 0, T(2,2) > 0, and T(3,3) > 0]

        • For Thermal Conductivity, T(1,1), T(2,2) and T(3,3) respectively correspond to λx, λy, and λz (the conductivity in the three axis directions, whether the coordinate system is global or user-defined).

    The following image shows an example of the properties for an Anisotropic material:

  10. Optionally, select the Use Material Appearance option and specify the desired Color and Transparency attributes.
  11. Optionally, click Validate Material to check for errors in the specified properties.

    12. If the properties pass the validation check, a green check mark appears to the right of the Validate Material button. Otherwise, a red X appears, and a pop-up message provides the error details.

  12. Click OK to close the View / Edit Material dialog box.
  13. Click OK to close the Select Definition dialog box.

To assign a different material to a selected solid object:

  1. Select the object to which you want to assign a material.
  2. Use one of the following five methods of accessing the Select Definition dialog box:
    • On the Draw ribbon tab, click Material.
    • Using the menu bar, click Modeler > Assign Material.
    • Right-click in the Modeler window and choose Assign Material from the shortcut menu.
    • In the Attribute tab of the docked Properties window, choose Edit from the Material Value drop-down menu.
    • If the Properties dialog box appears automatically when you create an object, select the Attribute tab. Then, choose Edit from the Material Value drop-down menu.
  3. Complete steps 2 through 6 of the previous procedure.

To add, remove, or edit materials:

  1. Use one of the following two methods of accessing the Edit Libraries dialog box:
    • Using the menu bar, click Tools > Edit Libraries > Materials.
    • Under Definitions in the Project Manager, right-click Materials and choose Edit Library from the shortcut menu.
  2. Select the desired material library from the Libraries list, or select Show all libraries.
  3. Select an existing material or click Add Material to define a new one.
  4. Optionally, you can click the following buttons once you've selected one or more existing materials:
    • View / Edit Materials: To change the name or properties.
      • Note:

      When you change the properties of a SysLibrary material, a new Project library material is created.

    • Clone Material(s): Make copies of the selected materials as a starting point for defining new ones.
    • Remove Material(s): Remove the selected materials from the library.
      • Note:

      You cannot remove predefined SysLibrary materials. You can only delete materials that you've added to the project library or a user library (and only if the material is not being used in the current design).

  5. After making the desired changes, click OK to close the View / Edit Material and/or Edit Library dialog boxes.