ConstantDT

Timestepper that takes a constant time step size

Description

The ConstantDT TimeStepper simply takes a constant time step size throughout the analysis, unless the solver fails to converge on an iteration.

ConstantDT begins the analysis taking the step specified by the user with the dt parameter. If the solver fails to obtain a converged solution for a given step, the executioner cuts back the step size and attempts to advance the time from the previous step using a smaller time step. The time step is cut back by multiplying the time step by 0.5.

If the solution with the cut-back time step is still unsuccessful, the time step size is repeatedly cut back until a successful solution is obtained. The user can specify a minimum time step through the dtmin parameter in the Executioner block. If the time step must be cut back below the minimum size without obtaining a solution, the problem exits with an error. If the time step is cut back using ConstantDT, that cut-back step size will be used for the remainder of the the analysis.

Example Input Syntax

[Executioner]
  type = Transient
  petsc_options_iname = '-pc_type -pc_hypre_type'
  petsc_options_value = 'hypre boomeramg'
  line_search = none
  nl_rel_tol = 1e-6
  nl_max_its = 10
  l_tol = 1e-8
  l_max_its = 50
  num_steps = 2 # 200
  nl_abs_tol = 1e-10
  nl_rel_step_tol = 1e-10
  nl_abs_step_tol = 1e-10
  [./TimeStepper]
    type = ConstantDT
    dt = 0.001
  [../]
  dtmin = .001
[]

Input Parameters

dtSize of the time step
C++ Type:double
Controllable:No
Description:Size of the time step

Required Parameters

cutback_factor_at_failure0.5Factor to apply to timestep if a time step fails to converge.
Default:0.5
C++ Type:double
Controllable:No
Description:Factor to apply to timestep if a time step fails to converge.
growth_factor2Maximum ratio of new to previous timestep sizes following a step that required the time step to be cut due to a failed solve.
Default:2
C++ Type:double
Controllable:No
Description:Maximum ratio of new to previous timestep sizes following a step that required the time step to be cut due to a failed solve.
reset_dtFalseUse when restarting a calculation to force a change in dt.
Default:False
C++ Type:bool
Controllable:No
Description:Use when restarting a calculation to force a change in dt.

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.
enableTruewhether or not to enable the time stepper
Default:True
C++ Type:bool
Controllable:Yes
Description:whether or not to enable the time stepper

Advanced Parameters

(../moose/test/tests/misc/check_error/wrong_displacement_order.i)

[Mesh]
  type = GeneratedMesh
  dim = 2
  # Mesh uses second-order elements
  elem_type = QUAD8
  displacements = 'disp_x disp_y'
  block_name = pore
  block_id = 0
[]

[Variables]
  [./temperature]
    order = SECOND
    [./InitialCondition]
      type = ConstantIC
      value = 0.0
    [../]
  [../]
[]

# We are *not* allowed to use FIRST-order displacement vars!
[AuxVariables]
  [./disp_x]
  [../]

  [./disp_y]
    [./InitialCondition]
      type = FunctionIC
      function = displ
    [../]
  [../]
[]

[Functions]
  [./displ]
    type = ParsedFunction
    expression = -1/2*x*(y-0.5)
  [../]
[]

[Kernels]
  [./diffusion]
    type = Diffusion
    variable = temperature
    use_displaced_mesh = true
  [../]
[]

[BCs]
  [./left]
    type = DirichletBC
    variable = temperature
    boundary = left
    value = 1
    use_displaced_mesh = true
  [../]
  [./right]
    type = DirichletBC
    variable = temperature
    boundary = right
    value = 0
    use_displaced_mesh = true
  [../]
[]

[Preconditioning]
  [./SMP_PJFNK]
    type = SMP
    full = true
    solve_type = PJFNK
  [../]
[]

[Executioner]
  type = Transient
  petsc_options_iname = '-pc_type -pc_hypre_type'
  petsc_options_value = 'hypre boomeramg'
  line_search = none
  nl_rel_tol = 1e-6
  nl_max_its = 10
  l_tol = 1e-8
  l_max_its = 50
  num_steps = 2 # 200
  nl_abs_tol = 1e-10
  nl_rel_step_tol = 1e-10
  nl_abs_step_tol = 1e-10
  [./TimeStepper]
    type = ConstantDT
    dt = 0.001
  [../]
  dtmin = .001
[]