# LevelSetCFLCondition

Computes the minimum timestep based on the Courant-Friedrichs-Lewy (CFL) condition. The CFL condition, is defined as

(1) where is the Courant number, is the maximum allowed Courant number, is the magnitude of the velocity, is the time step, and is the interval distance, and , in three dimensions, represents the index for the , , and components.

The LevelSetCFLCondition postprocessor estimates by using the the magnitude of the maximum velocity across quadrature points of an element () and computing the minimum element length for all elements in the finite element mesh ():

(2)

Finally, assuming that the maximum allowable Courant number, the maximum allowable timestep is computed as:

(3)

## Example Syntax

The LevelSetCFLCondition is added to the input file in the [Postprocessors] block as follows.


[./cfl]
type = LevelSetCFLCondition
velocity_x = vel_x
velocity_y = vel_y
execute_on = 'initial'
[../]
(modules/level_set/test/tests/reinitialization/master.i)

and it is designed to work to set the timestep within the TimeStepper block. Also, notice that at this point is possible to apply a "scaling" factor to the computed timestep to allow the simulation to operate at some level below the timestep limitation.


[Executioner]
type = Transient
solve_type = PJFNK
start_time = 0
end_time = 1
nl_rel_tol = 1e-12
scheme = crank-nicolson
petsc_options_iname = '-pc_type -pc_sub_type'
petsc_options_value = 'asm      ilu'
[./TimeStepper]
type = PostprocessorDT
postprocessor = cfl
scale = 1
[../]

[]
(modules/level_set/test/tests/reinitialization/master.i)

## Input Parameters

• execute_onTIMESTEP_ENDThe list of flag(s) indicating when this object should be executed, the available options include NONE, INITIAL, LINEAR, NONLINEAR, TIMESTEP_END, TIMESTEP_BEGIN, FINAL, CUSTOM.

Default:TIMESTEP_END

C++ Type:ExecFlagEnum

Options:NONE INITIAL LINEAR NONLINEAR TIMESTEP_END TIMESTEP_BEGIN FINAL CUSTOM

Description:The list of flag(s) indicating when this object should be executed, the available options include NONE, INITIAL, LINEAR, NONLINEAR, TIMESTEP_END, TIMESTEP_BEGIN, FINAL, CUSTOM.

• velocity_zThe variable containing the z-component of the velocity front.

C++ Type:std::vector

Options:

Description:The variable containing the z-component of the velocity front.

• velocity_xThe variable containing the x-component of the velocity front.

C++ Type:std::vector

Options:

Description:The variable containing the x-component of the velocity front.

• blockThe list of block ids (SubdomainID) that this object will be applied

C++ Type:std::vector

Options:

Description:The list of block ids (SubdomainID) that this object will be applied

• velocity_yThe variable containing the y-component of the velocity front.

C++ Type:std::vector

Options:

Description:The variable containing the y-component of the velocity front.

### Optional Parameters

• enableTrueSet the enabled status of the MooseObject.

Default:True

C++ Type:bool

Options:

Description:Set the enabled status of the MooseObject.

• use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

Default:False

C++ Type:bool

Options:

Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

• outputsVector of output names were you would like to restrict the output of variables(s) associated with this object

C++ Type:std::vector

Options:

Description:Vector of output names were you would like to restrict the output of variables(s) associated with this object

• control_tagsAdds user-defined labels for accessing object parameters via control logic.

C++ Type:std::vector

Options:

Description:Adds user-defined labels for accessing object parameters via control logic.

• allow_duplicate_execution_on_initialFalseIn the case where this UserObject is depended upon by an initial condition, allow it to be executed twice during the initial setup (once before the IC and again after mesh adaptivity (if applicable).

Default:False

C++ Type:bool

Options:

Description:In the case where this UserObject is depended upon by an initial condition, allow it to be executed twice during the initial setup (once before the IC and again after mesh adaptivity (if applicable).

• seed0The seed for the master random number generator

Default:0

C++ Type:unsigned int

Options:

Description:The seed for the master random number generator

• implicitTrueDetermines whether this object is calculated using an implicit or explicit form

Default:True

C++ Type:bool

Options:

Description:Determines whether this object is calculated using an implicit or explicit form