How to set up a transient heat transfer model with different initial part temperatures in Nastran

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Problem:

Is it possible to define a non-uniform temperature distribution for the initial temperature in a transient heat transfer analysis? 

• Specify different uniform temperatures for different parts.
• Use the temperature result from a steady or transient heat transfer analysis as the.

Causes:

The Nastran Inventor interface (Nastran In-CAD) only allows the user to specify a constant initial temperature for the entire model in a transient heat transfer analysis.

Solution:

The general process is to create the transient heat transfer analysis and replace the uniform initial temperature with the desired initial temperature profile.

1.  Apply an initial temperature load to the model (“Loads > Initial Condition > Temperature”).
2. Generate the Nastran (.nas) file. (Right-click the model tree and select “Generate Nastran File.”)
3. Edit the Nastran file to change the initial temperature from a constant value (specified by the TEMPD card) to the desired values ​​(specified by the TEMP card for each node).

• This method requires access to the Nastran Editor utility. 

Use temperatures from other heat transfer analysis

1. In Inventor Nastran (or Nastran In-CAD), confirm that “System > Default Settings > General > Prompt for solution with warnings” is enabled.
2. Run the first transient or steady-state heat transfer analysis to obtain the initial temperature distribution needed for the final transient heat transfer analysis.
3. Duplicate the analysis and change the analysis type to Linear Static.
4. Right-click a blank area of ​​the model tree and select “Generate Nastran File.
5. Click the “Save Nastran File” button on the toolbar and save it with a recognizable name.
   
6. Duplicate the original heat transfer analysis. Change the analysis type to Transient Heat Transfer.
7. Change the loads and other inputs to create the second transient heat transfer analysis. Include a dummy load of “Initial Condition > Temperature.”
8. Right-click on a blank area of ​​the model tree and select “Generate Nastran File.” 
9. Click the “Save Nastran File” button and save it with a recognizable name.
10. Start the Nastran Editor utility.
11. Open the Nastran file for the static stress analysis created in step 6.
12. Look for the TEMP commands. These provide the temperature at each node.
13. Select all TEMP lines and copy them (Ctrl+C).
14. Open the Nastran file for the transient heat transfer analysis created in step 10 in the Editor utility.
15. Display the “View > Field Marker (Narrow)” option to show the columns.
16. Find the TEMPD command which provides the fictitious initial temperature applied to the model.
17. Paste the TEMP commands copied from the stress analysis.
18. Select all TEMP commands in the transient heat transfer analysis. 
19. Use “Edit > Replace” (Ctrl+H). Replace the original number in the second column of the TEMP commands (probably “1000”) with the original number in the second column of the TEMPD command (probably “20”).
    Important notes :
    1. Include a space before and after the “Search” text, such as ” -1000- ” (where “-” indicates a space character). You don’t want to randomly search for “1000” in temperatures or node numbers and change them.
    2. In this example, “Replace with” would be ” —20- “.
       
       Column 1: TEMP command
       Column 2: ID number (originally 1000, changed to 20)
       Column 3: Node number
       Column 4: Temperature value
20. Click “Replace All” to replace the ID numbers. Make sure the pillar alignment has not changed.
21. Add a “$” to the beginning of the TEMPD command to change it to a comment.
22. Run the scan. (“Scan > Run”)
23. Review the results in the editor or return to the Inventor Nastran interface (Nastran In-CAD).
    1. In the Inventor Nastran environment, activate the transient heat transfer analysis that was created for non-uniform temperature.
    2. Click the “Load Results” button on the ribbon. Do not use the right-click > Load button in the Browser Results branch.

    3. Be aware of how your thoughts and ideas relate to each other

        

    4. Click “Results > Outline” on the ribbon to view the results as normal.

Alternative through third-party application

For large models, the time required to create the linear static analysis (steps 3 to 6) can be considerable. An alternative is to use a third-party application, such as FNO Reader (attached to the forum post ) to generate the temperature results from the initial heat transfer analysis. The temperature output can be converted into the format required for input into the Nastran file. General steps would be as follows:

1. Run the first transient or steady-state heat transfer analysis to obtain the initial temperature distribution needed for the final transient heat transfer analysis.
2. Duplicate the original heat transfer analysis. Change the analysis type to Transient Heat Transfer.
3. Change the loads and other inputs to create the final transient heat transfer analysis. Include a dummy load of “Initial Condition > Temperature.”
4. Right-click on a blank area of ​​the model tree and select “Generate Nastran File.” 
5. Click the “Save Nastran File” button on the toolbar and save it with a recognizable name.
6. Launch the Nastran Editor utility and open the transient heat transfer analysis file saved in the previous step.
7. Locate the TEMPD line and write down the number in the second column (probably “20”).
8. Add a “$” to the beginning of the TEMPD command to change it to a comment.
9. Extract the temperature results from the original heat transfer analysis to be used as the initial temperature for the final transient heat transfer analysis using a third-party application.
10. Change the output format to comma separated commands of the format “TEMP, ID, node number, temperature” where
    1. “TEMP” is the command.
    2. “ID” is the number in the second column of the TEMPD card (probably number 20) in the Nastran file of the transient heat transfer analysis.
    3. “node number” is the node number.
    4. “temperature” is the temperature calculated from the analysis performed in step 1.
11. Save the commands as a comma-separated file (CSV file).
12. Open the CSV file with Notepad.
13. Select and copy the text.

Paste the text from the Nastran file into the Nastran editor. The commands should look like this:

1. Run the scan. (“Scan > Run”)
2. Review the results in the editor or return to the Inventor Nastran interface (Nastran In-CAD).

Use different  temperatures for each piece

The process of replacing the initial temperature (TEMPD) with the desired temperature for each part (TEMP) is similar to the previous steps. The difference is how the TEMP commands are created.

• Option 1 involves performing a steady-state heat transfer analysis first to generate the temperatures for each part. The previous steps can be followed.
• Option 2 is to manually create the TEMP commands for all nodes.

Figure : Example Nastran file showing element connectivity for different idealizations.

Column 1: Element connectivity command (“A” in the image).

Column 3: Property ID (“B” in the image) corresponds to the idealization ID in Inventor Nastran. ID=2 is for Idealization 2 and ID=3 is for Idealization 3.

Remaining columns: Node numbers (“C” in the image) that define each element.

All node numbers for all elements with ID=2 should be merged together and duplicates should be removed. From that node list, TEMP commands would be created with the temperature of the elements at ID=2. The same goes for all other ID numbers that exist in the analysis.

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