Boundary Conditions

Boundary conditions are used to prescribe values of basic solution variables. In the case of heat transfer analysis temperature is the basic solution variable. The Thermal Analysis workbench supports the definition of temperature boundary conditions.

Creating Temperature Boundary Conditions: Defines the time history of temperature degrees of freedom on a geometry selection.

You apply environmental actions, such as boundary conditions, to supports (geometrical features) on your model. The supports that are available include points/vertices, curves/edges, surfaces/faces, or volumes/parts. In addition, point, line, or surface groups that were created from a mesh part are also valid supports. You can either select the support and then set the boundary condition specifications or set the boundary condition specifications and then select the support. Table 10–1 summarizes the supports to which each type of boundary condition can be applied.

Table 10–1 Supports for boundary conditions.

Boundary Condition	Point, Vertex, or Point Group	Curve, Edge, or Line Group	Surface, Face, or Surface Group
Temperature

Creating Temperature Boundary Conditions

Temperature boundary conditions constrain selected temperature degrees of freedom to a prescribed temperature history.

You can apply temperature boundary conditions only in heat transfer steps.

The magnitude of a temperature boundary condition can vary with time during a step according to an amplitude definition (see Amplitudes for more information on defining amplitudes).

You can prescribe the time variation of the magnitude of a temperature boundary condition in a user subroutine, which is sometimes preferable when the time history of the magnitude is complex. You can also apply knowledgeware techniques to control the value of a temperature boundary condition (for more information, see Applying Knowledgeware).

You can import temperature data into a temperature boundary condition from an Excel (.xls*) spreadsheet or a text (.txt) file. The imported temperature data must satisfy the following criteria:

The data must be arranged in four columns in the following order: X–coordinate, Y–coordinate, Z–coordinate, and temperature value.
The data must include a header row in which the dimensional data is provided in parentheses. Temperature data can be provided without dimensions. The following sample header row provides one example of proper header row syntax:

X(mm) Y(mm) Z(mm) Temperature()

The actual temperature values created from imported data will be the product of the dimensionless temperature values multiplied by the value you provide for the Magnitude of the temperature. For example, if your imported data specifies a dimensionless value of 10 at the location (0,0,0) and you specify a value of 20Kdeg for the temperature boundary condition object, the temperature at that location will be 200K for the analysis.

Temperature boundary conditions can be applied to point/vertex, curve/edge, or surface/face supports or to a point, line, or surface.

Note: For static analyses, make sure you define sufficient boundary conditions to allow for a unique solution.

This task shows you how to create a temperature boundary condition on geometry.

Click the Temperature Boundary Condition icon .

The Temperature BC dialog box appears, and a Temperature object appears in the specification tree under the Boundary Conditions objects set for the current step.
You can change the identifier of the boundary condition by editing the Name field.
Select the geometry support (a point, an edge, or a surface). Any selectable geometry is highlighted when you pass the cursor over it. You can select several supports to apply the boundary condition to all supports simultaneously. You can also select an appropriate group.

The Supports field is updated to reflect your selection.
Enter a value for the temperature Magnitude.
Right-click on the Magnitude field to add knowledgeware controls (for more information, see Applying Knowledgeware).
To import and incorporate temperature mappings into the boundary condition object, perform the following steps:
1. Toggle on Data mapping, then click the ... button.
  
  The Data Mapping dialog box opens.
2. Click Browse, then select the Excel (.xls*) file or text (.txt) file from which you want to import temperature data.
  
  Once you select a file, you can display the imported data in tabular form in the Imported Table dialog box by clicking Show.
3. If desired, toggle on Display Bounding Box to display a three-dimensional box incorporating the minimum and maximum values from the imported table. The bounding box enables you to confirm that the support you select lies completely within the space dictated by the imported data; if a portion of the support is outside this box, an error will be returned during the analysis.
4. Click OK to close the Data Mapping dialog box.
Click More to access additional temperature boundary condition options.
1. Toggle on Selected amplitude, and select an amplitude from the specification tree to define a nondefault time variation for the temperature boundary condition.
  
  If you do not specify an amplitude, the solver applies the reference magnitude based on the Default load variation with time option that you selected when you created the step. The solver either applies the reference magnitude linearly over the step (Ramp) or applies it immediately at the beginning of the step and subsequently holds it constant (Instantaneous).
2. Toggle on Apply user subroutine to define a nonuniform variation of the temperature boundary condition magnitude throughout the step in user subroutine DISP. For more information, see Using User Subroutines.
3. The propagation status shows the following:
  - Whether the boundary condition was Created in this step or Propagated into this step.
  - Whether the boundary condition is Active or Inactive.
Click OK in the Temperature BC dialog box.

Symbols representing the constrained degrees of freedom are displayed on the geometry.