PostprocessorDT

Computes timestep based on a Postprocessor value.

The postprocessor can be computing a global metric, like the Courant Friedrich Levy criterion with the CFLTimeStepSize or the LevelSetCFLCondition postprocessor. In those cases, the postprocessor computes the maximum value of the timestep that should ensure stability. Variations in numerical schemes may impact the accuracy of this postprocessor, so the PostprocessorDT allows for a scaling factor and an offset to modify the time step.

If the application using the PostprocessorDT is a sub-app, its time step may also be received through a MultiAppPostprocessorTransfer using a Receiver postprocessor.

Example input syntax

In this example, we set the time step to be the maximum value allowable under a CFL criterion for a fluid flow simulation in a shock tube.

[./TimeStepper]
  type = PostprocessorDT
  postprocessor = cfl_dt
[../]

[Postprocessors]
  [./cfl_dt]
    type = ADCFLTimeStepSize
    c_names = 'sound_speed'
    vel_names = 'speed'
  [../]
[]

Input Parameters

postprocessorThe name of the postprocessor that computes the dt
C++ Type:PostprocessorName
Controllable:No
Description:The name of the postprocessor that computes the dt

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.
dtInitial value of dt
C++ Type:double
Controllable:No
Description:Initial value of dt
offset0Add an offset to the supplied postprocessor value.
Default:0
C++ Type:double
Controllable:No
Description:Add an offset to the supplied postprocessor value.
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.
scale1Multiple scale and supplied postprocessor value.
Default:1
C++ Type:double
Controllable:No
Description:Multiple scale and supplied postprocessor value.

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/modules/navier_stokes/test/tests/finite_volume/cns/shock_tube_2D_cavity/hllc_sod_shocktube_2D.i)

rho_left = 1
E_left = 2.501505578
u_left = 1e-15

rho_right = 0.125
E_right = 1.999770935
u_right = 1e-15

x_sep = 35

[GlobalParams]
  fp = fp
[]

[Mesh]
  [./cartesian]
    type = CartesianMeshGenerator
    dim = 2
    dx = '40 20'
    ix = '200 100'
    dy = '1 20  2  20 1'
    iy = '4 100 10 100 4'
    subdomain_id = '0 0
                    0 1
                    1 1
                    0 1
                    0 0'
  [../]

  [./wall]
    type = SideSetsBetweenSubdomainsGenerator
    input = cartesian
    primary_block = 1
    paired_block = 0
    new_boundary = 'wall'
  [../]

  [./delete]
    type = BlockDeletionGenerator
    input = wall
    block = 0
  [../]
[]

[FluidProperties]
  [./fp]
    type = IdealGasFluidProperties
    allow_imperfect_jacobians = true
  [../]
[]

[Variables]
  [./rho]
    order = CONSTANT
    family = MONOMIAL
    fv = true
  [../]
  [./rho_u]
    order = CONSTANT
    family = MONOMIAL
    fv = true
  [../]
  [./rho_v]
    order = CONSTANT
    family = MONOMIAL
    fv = true
  [../]
  [./rho_E]
    order = CONSTANT
    family = MONOMIAL
    fv = true
  [../]
[]

[AuxVariables]
  [./Ma]
    order = CONSTANT
    family = MONOMIAL
  [../]

  [./p]
    order = CONSTANT
    family = MONOMIAL
  [../]

  [./v_norm]
    order = CONSTANT
    family = MONOMIAL
  [../]

  [./temperature]
    order = CONSTANT
    family = MONOMIAL
  [../]
[]

[AuxKernels]
  [./Ma_aux]
    type = NSMachAux
    variable = Ma
    fluid_properties = fp
    use_material_properties = true
  [../]

  [./p_aux]
    type = ADMaterialRealAux
    variable = p
    property = pressure
  [../]

  [./v_norm_aux]
    type = ADMaterialRealAux
    variable = v_norm
    property = speed
  [../]

  [./temperature_aux]
    type = ADMaterialRealAux
    variable = temperature
    property = T_fluid
  [../]
[]

[FVKernels]
  [./mass_time]
    type = FVTimeKernel
    variable = rho
  [../]

  [./mass_advection]
    type = CNSFVMassHLLC
    variable = rho
  [../]

  [./momentum_x_time]
    type = FVTimeKernel
    variable = rho_u
  [../]

  [./momentum_x_advection]
    type = CNSFVMomentumHLLC
    variable = rho_u
    momentum_component = x
  [../]

  [./momentum_y_time]
    type = FVTimeKernel
    variable = rho_v
  [../]

  [./momentum_y_advection]
    type = CNSFVMomentumHLLC
    variable = rho_v
    momentum_component = y
  [../]

  [./fluid_energy_time]
    type = FVTimeKernel
    variable = rho_E
  [../]

  [./fluid_energy_advection]
    type = CNSFVFluidEnergyHLLC
    variable = rho_E
  [../]
[]

[FVBCs]
  [./mom_x_pressure]
    type = CNSFVMomImplicitPressureBC
    variable = rho_u
    momentum_component = x
    boundary = 'left right wall'
  [../]

  [./mom_y_pressure]
    type = CNSFVMomImplicitPressureBC
    variable = rho_v
    momentum_component = y
    boundary = 'wall'
  [../]
[]

[ICs]
  [./rho_ic]
    type = FunctionIC
    variable = rho
    function = 'if (x < ${x_sep}, ${rho_left}, ${rho_right})'
  [../]

  [./rho_u_ic]
    type = FunctionIC
    variable = rho_u
    function = 'if (x < ${x_sep}, ${fparse rho_left * u_left}, ${fparse rho_right * u_right})'
  [../]

  [./rho_E_ic]
    type = FunctionIC
    variable = rho_E
    function = 'if (x < ${x_sep}, ${fparse E_left * rho_left}, ${fparse E_right * rho_right})'
  [../]
[]

[Materials]
  [./var_mat]
    type = ConservedVarValuesMaterial
    rho = rho
    rhou = rho_u
    rhov = rho_v
    rho_et = rho_E
    fp = fp
  [../]
  [./sound_speed]
    type = SoundspeedMat
    fp = fp
  [../]
[]

[Preconditioning]
  [./smp]
    type = SMP
    full = true
    petsc_options_iname = '-pc_type'
    petsc_options_value = 'lu'
  [../]
[]

[Postprocessors]
  [./cfl_dt]
    type = ADCFLTimeStepSize
    c_names = 'sound_speed'
    vel_names = 'speed'
  [../]
[]

[Executioner]
  type = Transient
  end_time = 100
  [TimeIntegrator]
    type = ExplicitSSPRungeKutta
    order = 2
  []
  l_tol = 1e-8

  [./TimeStepper]
    type = PostprocessorDT
    postprocessor = cfl_dt
  [../]
[]