# Surface Integral Output

Surface Integral Output computes surface integrals of custom user variables on selected surfaces and can optionally report moving statistics over time.

# Available Options

Option Description Applicable
Output fields Custom user variables to integrate over the assigned surfaces always
Statistics function Optional moving statistic applied to the integrated values always
Moving window size Window size for moving statistics (in output data points) when Statistics function is not None
Start step Step at which to start statistics calculation when Statistics function is not None
Assigned surfaces Surfaces used for the integral always

# Detailed Descriptions

# Output fields

The custom user variables to integrate over the selected surfaces.

  • Required (at least one field must be selected)
  • Allowed fields: Custom user variables only
  • Example: PressureForce, HingeTorqueZ

Note: Surface Integral Output only accepts custom user variables. Define them in Variable Settings (Custom variables tab).

# Statistics function

Optional moving statistic applied to the integrated values. When set to None, raw integral values are reported.

  • Default: None
  • Options:
    • None - No statistics processing
    • Mean - Moving average
    • Min - Minimum in the window
    • Max - Maximum in the window
    • Standard deviation - Sample standard deviation (Bessel's correction)
    • Deviation - Range (maximum minus minimum) in the window

# Moving window size

The number of output data points used in the moving statistics window.

  • Default: 10
  • Minimum value: 2

Note: For steady simulations, the solver typically outputs a data point every 10 pseudo steps. For unsteady simulations, it outputs every physical step.

# Start step

The number of steps to skip before statistics calculation begins.

  • Default: 0

Note: For steady simulations, this value is rounded up to the nearest multiple of 10 (based on output cadence).

# Assigned surfaces

The surfaces on which the integral is computed.

  • Required: Yes (at least one surface must be selected)
  • Supported surface types:
    • Simulation surfaces (mesh boundaries)
    • Imported sample surfaces

Notes:

  • Import sample surfaces in the Entities browser before selecting them. See Sample Surfaces.
  • Do not mix simulation surfaces and imported sample surfaces in a single Surface Integral Output. Create separate outputs if you need both.

# Use Cases

Surface Integral Output is useful for:

  • Computing hinge torques, forces, or moments defined as custom variables
  • Integrating heat flux or other derived quantities over selected surfaces
  • Monitoring integrated quantities with moving statistics during transient simulations

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