ComposeTimeStepperAction

Add the composition time stepper if multiple time steppers have been created.

This action specifies the CompositionDT object when multiple time steppers are provided in the [TimeSteppers] block. If there are more than one time steppers provided, it will add a CompositionDT in the time stepper system and make the CompositionDT as the final time stepper to use in the transient simulations. An optional parameter "lower_bound" is provided to set a lower bound for the computed time step size. It can be specified with any time stepper(s) in the [TimeSteppers] block.

An example of using a growing lower bound to limit the time step size as:

[Executioner<<<{"href": "../../syntax/Executioner/index.html"}>>>]
  type = Transient
  end_time = 0.8
  solve_type = PJFNK
  petsc_options_iname = '-pc_type -pc_hypre_type'
  petsc_options_value = 'hypre boomeramg'

  [TimeSteppers<<<{"href": "../../syntax/Executioner/TimeSteppers/index.html"}>>>]
    lower_bound<<<{"description": "The maximum of these TimeSteppers will form the lower bound on the time step size. A single or multiple time steppers may be specified."}>>> = 'LogConstDT'
    [ConstDT1]
      type = ConstantDT<<<{"description": "Timestepper that takes a constant time step size", "href": "../timesteppers/ConstantDT.html"}>>>
      dt<<<{"description": "Size of the time step"}>>> = 0.2
    []

    [ConstDT2]
      type = ConstantDT<<<{"description": "Timestepper that takes a constant time step size", "href": "../timesteppers/ConstantDT.html"}>>>
      dt<<<{"description": "Size of the time step"}>>> = 0.1
    []

    [LogConstDT]
      type = LogConstantDT<<<{"description": "TimeStepper which imposes a time step constant in the logarithmic space", "href": "../timesteppers/LogConstantDT.html"}>>>
      log_dt<<<{"description": "Time step in log10(time)"}>>> = 2
      first_dt<<<{"description": "Initial time step (in absolute time)"}>>> = 0.01
    []
  []
[]
(moose/test/tests/time_steppers/time_stepper_system/lower_bound.i)

More information about Time Stepper System and CompositionDT time stepper may be found on the Time Stepper System syntax documentation.