Neumann boundary condition configuration

Neumann Boundary Condition Configuration in Twin Fabrica

A Neumann boundary condition specifies heat flux directly on a geometry's surface. This condition works well for modeling forced heating or cooling, laser application, or surface-based thermal loads.

This guide shows you how to configure a Neumann condition and assign it to geometrical entities in Twin Fabrica.

📝 Note: This tutorial assumes you have already created a boundary condition component. If not, please refer to the section on how to create one.

1. Select Neumann Boundary Condition Type

In your boundary condition component, select Neumann from the available types.

This lets you apply thermal input directly to external surfaces of selected entities.

2. Choose Between Heat Rate or Power Density

Define the thermal input as either:

A total heat rate (in watts), or
A surface power density (in W/m²)

Check the Enable Power Density option to use power density instead of heat rate.

The input field's unit will update based on your selection.

3. Heat Flux Spatial Distribution

Heat flux applies uniformly across selected surfaces by default.

For advanced cases, use the Power Space Distribution option to create a non-uniform distribution.

This feature allows for spatially varying heat input and will be covered in a separate tutorial.

4. Parametric Definition (Optional)

Twin Fabrica lets you define heat flux as a parametric function for time- or input-dependent behaviors like:

Pulsed heating
Periodic loading
Input-driven activation

For this tutorial, we'll use a constant value for simplicity.

5. Label the Heat Flux Input

Give your heat flux (or heat rate) parameter a descriptive label.

This label appears in the parameter list and helps track the boundary condition across simulations and calibration tasks.

Example: surface_heat_input_1

6. Enter the Nominal Value

Enter the nominal value for heat rate or power density.

This value serves as the baseline for Full Order Model simulations unless changed in parametric studies.

Make sure the value and units match your chosen input type from step 2.

7. Assign the Boundary Condition to Geometry

Use the entity tree to assign the condition to your geometry:

Both 2D and 3D geometrical entities appear in the same panel.
For 3D entities, the condition automatically applies to their external (free) surfaces.

Select the boxes to link the boundary condition to your chosen geometry.

8. Finalize the Configuration

After defining and assigning the condition:

Click SAVE to store the configuration.
The Neumann boundary condition is now ready for your simulation.

9. Verify the Assignment

To check that the boundary condition is applied correctly:

Open the Boundary Conditions section in the project navigation tree.
Select the configured Neumann condition.
Twin Fabrica will automatically highlight the assigned surfaces in the 3D viewer, showing where heat input will occur.