TimeStepper System

The method calculates the size of the time steps using either the [TimeStepper] block or the [TimeSteppers] block. The [TimeStepper] block takes only one time stepper while [TimeSteppers] block keeps the features of [TimeStepper] and also supports the composed time step size with multiple time steps inputs.

warning

This page and the [TimeStepper] block will be deprecated soon in the future.

When more than one time steppers are provided, the time stepper system will add a Composition TimeStepper as the final time stepper of the transient simulation. The Composition TimeStepper takes all input time steppers except the ones used for "lower_bound" and compute the minimum time step size within "lower_bound" as the output time step size. There are a number of types of TimeStepper available. They control the time stepping in different ways, including using fixed time stepping, time stepping based on a function, or adaptive time stepping.

The time stepper system is controllable via Controls block. The user can turn on/off the time steppers to control the usage of time steppers like make time stepper(s) only active at certain time period.

Example input syntax

[Executioner<<<{"href": "../index.html"}>>>]
  type = Transient
  end_time = 0.8
  solve_type = PJFNK
  petsc_options_iname = '-pc_type -pc_hypre_type'
  petsc_options_value = 'hypre boomeramg'
  # Use as many different time steppers as we could to test the compositionDT,
  # SolutionTimeAdaptiveDT give slightly different dt per run, set rel_err = 1e-2
  # to ensure the test won't fail due to the small difference in the high-digit.
  [TimeSteppers<<<{"href": "../TimeSteppers/index.html"}>>>]
    [ConstDT1]
      type = ConstantDT<<<{"description": "Timestepper that takes a constant time step size", "href": "../../../source/timesteppers/ConstantDT.html"}>>>
      dt<<<{"description": "Size of the time step"}>>> = 0.2
    []

    [FunctionDT]
      type = FunctionDT<<<{"description": "Timestepper whose steps vary over time according to a user-defined function", "href": "../../../source/timesteppers/FunctionDT.html"}>>>
      function<<<{"description": "The name of the time-dependent function that prescribes the time step size."}>>> = dts
    []

    [LogConstDT]
      type = LogConstantDT<<<{"description": "TimeStepper which imposes a time step constant in the logarithmic space", "href": "../../../source/timesteppers/LogConstantDT.html"}>>>
      log_dt<<<{"description": "Time step in log10(time)"}>>> = 0.2
      first_dt<<<{"description": "Initial time step (in absolute time)"}>>> = 0.1
    []

    [IterationAdapDT]
      type = IterationAdaptiveDT<<<{"description": "Adjust the timestep based on the number of iterations", "href": "../../../source/timesteppers/IterationAdaptiveDT.html"}>>>
      dt<<<{"description": "The default timestep size between solves"}>>> = 0.5
    []

    [Timesequence]
      type = TimeSequenceStepper<<<{"description": "Solves the Transient problem at a sequence of given time points.", "href": "../../../source/timesteppers/TimeSequenceStepper.html"}>>>
      time_sequence<<<{"description": "The values of t"}>>> = '0  0.25 0.3 0.5 0.8'
    []

    [PPDT]
      type = PostprocessorDT<<<{"description": "Computes timestep based on a Postprocessor value.", "href": "../../../source/timesteppers/PostprocessorDT.html"}>>>
      postprocessor<<<{"description": "The name of the postprocessor that computes the dt"}>>> = PostDT
      dt<<<{"description": "Initial value of dt"}>>> = 0.1
    []
  []
[]

[Executioner<<<{"href": "../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": "../TimeSteppers/index.html"}>>>]
    [ConstDT1]
      type = ConstantDT<<<{"description": "Timestepper that takes a constant time step size", "href": "../../../source/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": "../../../source/timesteppers/ConstantDT.html"}>>>
      dt<<<{"description": "Size of the time step"}>>> = 0.1
    []
  []
[]

[Controls<<<{"href": "../../Controls/index.html"}>>>]
  [c1]
    type = TimePeriod<<<{"description": "Control the enabled/disabled state of objects with time.", "href": "../../../source/controls/TimePeriod.html"}>>>
    enable_objects<<<{"description": "A list of object tags to enable."}>>> = 'TimeStepper::ConstDT1'
    disable_objects<<<{"description": "A list of object tags to disable."}>>> = 'TimeStepper::ConstDT2'
    start_time<<<{"description": "The time at which the objects are to be enabled/disabled."}>>> = '0.3'
    end_time<<<{"description": "The time at which the objects are to be enable/disabled."}>>> = '0.8'
  []
[]

Available Objects

Moose App
AB2PredictorCorrectorImplements second order Adams-Bashforth method for timestep calculation.
CSVTimeSequenceStepperSolves the Transient problem at a sequence of given time points read in a file.
CompositionDTThe time stepper takes all the other time steppers as input and returns the minimum time step size.
ConstantDTTimestepper that takes a constant time step size
ExodusTimeSequenceStepperSolves the Transient problem at a sequence of time points taken from a specified exodus file.
FixedPointIterationAdaptiveDTComputes time step size based on a target number of fixed point iterations
FunctionDTTimestepper whose steps vary over time according to a user-defined function
IterationAdaptiveDTAdjust the timestep based on the number of iterations
LogConstantDTTimeStepper which imposes a time step constant in the logarithmic space
PostprocessorDTComputes timestep based on a Postprocessor value.
SolutionTimeAdaptiveDTCompute simulation timestep based on actual solution time.
TimeSequenceFromTimesSolves the Transient problem at a sequence of time points taken from a specified Times object.
TimeSequenceStepperSolves the Transient problem at a sequence of given time points.

Available Actions

Moose App
AddTimeStepperActionAdd a TimeStepper object to the simulation.

Input Parameters

active__all__ If specified only the blocks named will be visited and made active
Default:__all__
C++ Type:std::vector<std::string>
Controllable:No
Description:If specified only the blocks named will be visited and made active
inactiveIf specified blocks matching these identifiers will be skipped.
C++ Type:std::vector<std::string>
Controllable:No
Description:If specified blocks matching these identifiers will be skipped.

Optional Parameters

control_tagsAdds user-defined labels for accessing object parameters via control logic.
C++ Type:std::vector<std::string>
Controllable:No
Description:Adds user-defined labels for accessing object parameters via control logic.

Advanced Parameters

(moose/test/tests/time_steppers/time_stepper_system/multiple_timesteppers.i)

[Mesh]
  type = GeneratedMesh
  dim = 2
  nx = 10
  ny = 10
[]

[Variables]
  [u]
  []
[]

[Kernels]
  [diff]
    type = CoefDiffusion
    variable = u
    coef = 0.1
  []
  [time]
    type = TimeDerivative
    variable = u
  []
[]

[Functions]
  [dts]
    type = PiecewiseLinear
    x = '0   0.85 2'
    y = '0.2 0.15  0.2'
  []
[]

[BCs]
  [left]
    type = DirichletBC
    variable = u
    boundary = left
    value = 0
  []
  [right]
    type = DirichletBC
    variable = u
    boundary = right
    value = 1
  []
[]

[Executioner]
  type = Transient
  end_time = 0.8
  solve_type = PJFNK
  petsc_options_iname = '-pc_type -pc_hypre_type'
  petsc_options_value = 'hypre boomeramg'
  # Use as many different time steppers as we could to test the compositionDT,
  # SolutionTimeAdaptiveDT give slightly different dt per run, set rel_err = 1e-2
  # to ensure the test won't fail due to the small difference in the high-digit.
  [TimeSteppers]
    [ConstDT1]
      type = ConstantDT
      dt = 0.2
    []

    [FunctionDT]
      type = FunctionDT
      function = dts
    []

    [LogConstDT]
      type = LogConstantDT
      log_dt = 0.2
      first_dt = 0.1
    []

    [IterationAdapDT]
      type = IterationAdaptiveDT
      dt = 0.5
    []

    [Timesequence]
      type = TimeSequenceStepper
      time_sequence  = '0  0.25 0.3 0.5 0.8'
    []

    [PPDT]
      type = PostprocessorDT
      postprocessor = PostDT
      dt = 0.1
    []
  []
[]

[Postprocessors]
  [timestep]
    type = TimePostprocessor
    execute_on = 'timestep_end'
  []

  [PostDT]
    type = ElementAverageValue
    variable = u
    execute_on = 'initial timestep_end'
  []
[]

[Outputs]
  csv = true
  file_base='multiple_timesteppers'
[]

(moose/test/tests/time_steppers/time_stepper_system/active_timesteppers.i)

[Mesh]
  type = GeneratedMesh
  dim = 2
  nx = 10
  ny = 10
[]

[Variables]
  [u]
  []
[]

[Kernels]
  [diff]
    type = CoefDiffusion
    variable = u
    coef = 0.1
  []
  [time]
    type = TimeDerivative
    variable = u
  []
[]

[BCs]
  [left]
    type = DirichletBC
    variable = u
    boundary = left
    value = 0
  []
  [right]
    type = DirichletBC
    variable = u
    boundary = right
    value = 1
  []
[]

[Executioner]
  type = Transient
  end_time = 0.8
  solve_type = PJFNK
  petsc_options_iname = '-pc_type -pc_hypre_type'
  petsc_options_value = 'hypre boomeramg'

  [TimeSteppers]
    [ConstDT1]
      type = ConstantDT
      dt = 0.2
    []

    [ConstDT2]
      type = ConstantDT
      dt = 0.1
    []
  []
[]

[Controls]
  [c1]
    type = TimePeriod
    enable_objects = 'TimeStepper::ConstDT1'
    disable_objects = 'TimeStepper::ConstDT2'
    start_time = '0.3'
    end_time = '0.8'
  []
[]

[Postprocessors]
  [timestep]
    type = TimePostprocessor
    execute_on = 'timestep_end'
  []
[]

[Outputs]
  csv = true
  file_base='active_timesteppers'
[]