# Stopping criterion

Stopping criterion provides a mechanism to automatically terminate a simulation when a monitored field reaches a certain value. This is achieved by tracking the deviation of the field over a moving window of iterations. When the deviation falls below a defined tolerance, the simulation is considered converged and stops.

# Available Parameters

Parameter Description
Output type The type of output to be monitored (e.g., Probe, Surface Integral).
(Output name) The name of a specific, pre-defined output instance. This field appears after selecting an Output type.
Output field The specific scalar field within the selected output to monitor for convergence.
Tolerance The threshold for the moving deviation of the monitored field.
Change window The number of iterations over which to calculate the moving deviation of the monitored field.

# Detailed Descriptions

# Output type

Specifies the category of output that contains the field to be monitored.

  • Default: None
  • Options:
    • Probe
    • Surface probe

Notes:

  • The chosen output type must be configured in output section of the simulation setup.
  • This determines which specific outputs are available in the next dropdown.

# Output name

Selects a specific, named output instance of the chosen "Output type" to monitor.

  • Default: None

Notes:

  • You must define an output (e.g., a ProbeOutput or SurfaceIntegralOutput) before it can be selected here.
  • The list of available names is filtered based on the selected Output type.

# Output field

Field within the selected output whose convergence will be tracked.

  • Default: None
  • Example: Cl, Pressure, MyVelocityVariable

Note:

  • The selected field must be one of the output_fields defined in the selected output instance.

# Tolerance

Convergence threshold. The simulation stops when the moving deviation of the Output field is less than this value.

  • Default: 0.01
  • Example: 1e-4

Notes:

  • This value is non-dimensional if the monitored field is a string-defined default field (e.g., 'Cl').
  • If using a UserVariable for the output field, the dimensions of the tolerance must match the dimensions of the field.

# Change window

The number of data points used for the moving window to calculate the deviation of the monitored field.

  • Default: 10
  • Example: 20

Notes:

  • The value must be an integer greater than or equal to 2.
  • A larger window provides a more stable measure of convergence but may react slower to changes.

🐍 Python Example Usage

 
import flow360 as fl

fl.Fluid(
    stopping_criterion=[
        stop_on_lift_convergence = fl.Criterion(
            name="StopOnLift",
            monitor_output=fl.SurfaceIntegralOutput(
                name="wing_forces",
                entities=[surface_mesh['wing']],
                output_fields=['Cf', 'Cl', 'Cd']
            ),
            monitor_field='Cl',
            tolerance=1e-5,
            criterion_change_window=50
        )
    ],
    ...
)

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