Creating Film Conditions

Film conditions represent heat flux on a surface due to convection. The governing equation for this heat flux is

where

is the heat flux across the surface,

is the film coefficient,

is the temperature at this point on the surface, and

is a reference sink temperature value.

Film conditions can be applied only in heat transfer steps.

By default, the sink temperature varies linearly with time throughout the step from its value at the end of the previous step (ramp function), while the film coefficient is applied immediately and remains constant throughout the step. Nondefault time variations can be defined for the sink temperature and/or the film coefficient by referring to amplitude definitions (see Amplitudes for more information on defining amplitudes).

You can prescribe the time variation of the magnitude of the film coefficient in a user subroutine, which is sometimes preferable when the time history of the magnitude is complex.

You can import reference sink temperature and film coefficent data into a film condition definition from a Microsoft Excel spreadsheet (.xls*) or a text file (.txt). The imported data must satisfy the following criteria:

The data must be arranged in five columns in the following order: X–coordinate, Y–coordinate, Z–coordinate, reference sink temperature, and film coefficient.
The data must include a header row in which the dimensional data are provided in parentheses.Abaqus for CATIA V5 disregards dimensional data, if provided for reference sink temperature data and film coefficients. The following sample header row provides one example of proper header row syntax:
X(mm) Y(mm) Z(mm) Sink Temperature() Film Coefficient()

If you toggle on Use temperature-dependent data and specify reference sink temperature and film coefficient values in the Film Condition dialog box, all imported film coefficient data are disregarded and the data specified in the dialog box are used instead. Imported sink temperature data are still included in the analysis.

Film conditions can be applied to surface or face supports or to a surface group.

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

Click the Film Condition icon .
The Film Condition dialog box appears, and a Film Condition object appears in the specification tree under the Loads objects set for the current step.
You can change the identifier of the load by editing the Name field.
Select the geometry support (a surface). Any selectable geometry is highlighted when you pass the cursor over it. You can select several supports to apply the load to all supports simultaneously. You can also select a surface group.
The Supports field is updated to reflect your selection. A temporary symbol will appear at the supports to indicate zero values until you apply a nonzero load.
Specify the film coefficient, h. By default, the film coefficient is assumed to be a function of surface temperature.
1. Enter the film coefficient versus temperature values in the data table.
2. To add or delete table rows, click Add or Delete below the data table.
3. To read the film coefficient data from a text file, click the Folder icon , and select an ASCII text file that contains columns of numerical data separated by commas, tabs, or spaces.
4. Toggle off Use temperature-dependent data if the film coefficient does not vary with temperature, and enter only a single film coefficient value in the data table.
Enter a value for the Reference sink temperature, .
To import and incorporate mappings for sink temperature and film coefficients into the film condition definition, perform the following steps:
1. Toggle on Data mapping, then click the ... button.
  The Data Mapping dialog box appears.
2. Click Browse, then select the spreadsheet or text 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 film condition options.
1. Toggle on Selected amplitude, and select an amplitude from the specification tree to define a nondefault variation for the Sink Temperature vs Time.
  If you do not specify an amplitude, Abaqus applies the reference sink temperature based on the Default load variation with time option that you selected when you created the step. Abaqus 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).
  See About Prescribed Conditions in the Abaqus Prescribed Conditions Guide for more information.
2. Toggle on Selected amplitude, and select an amplitude from the specification tree to define a nondefault variation for the Film Coefficient vs Time.
  If you do not specify an amplitude, Abaqus applies the reference film coefficient immediately at the beginning of the step and subsequently holds it constant (Instantaneous). See About Prescribed Conditions in the Abaqus Prescribed Conditions Guide for more information.
3. Toggle on Apply user subroutine to define a nonuniform film coefficient as a function of position, time, temperature, etc. in user subroutine FILM. For more information, see Using User Subroutines and FILM in the Abaqus User Subroutines Guide.
Right-click on the Reference sink temperature field to add knowledgeware controls (for more information, see Applying Knowledgeware).
Click OK in the Film Condition dialog box.
Symbols representing the applied film condition are displayed on the geometry.