Variables System

Description

The Variables block within an input file is utilized to define the unknowns within a system of partial differential equations. These unknowns are often referred to as nonlinear variables within documentation. The nonlinear variables defined within this block are used by Kernel objects to define the equations for a simulation.

Example

The following input file snippet demonstrates the creation of a single nonlinear variable that is used by two Kernel objects, refer to Example 2 for more details.

[Variables]
  [convected]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff]
    type = Diffusion
    variable = convected
  []

  [conv]
    type = ExampleConvection
    variable = convected
    velocity = '0.0 0.0 1.0'
  []
[]

[Mesh]
  file = mug.e
[]

[Variables]
  [convected]
    order = FIRST
    family = LAGRANGE
  []
[]

[Kernels]
  [diff]
    type = Diffusion
    variable = convected
  []

  [conv]
    type = ExampleConvection
    variable = convected
    velocity = '0.0 0.0 1.0'
  []
[]

[BCs]
  [bottom]
    type = DirichletBC
    variable = convected
    boundary = 'bottom'
    value = 1
  []

  [top]
    type = DirichletBC
    variable = convected
    boundary = 'top'
    value = 0
  []
[]

[Executioner]
  type = Steady
  solve_type = 'PJFNK'
[]

[Outputs]
  execute_on = 'timestep_end'
  exodus = true
[]

Input Parameters

• active__all__ If specified only the blocks named will be visited and made active

  Default:__all__

  C++ Type:std::vector

  Options:

  Description:If specified only the blocks named will be visited and made active

• familyLAGRANGESpecifies the family of FE shape functions to use for this variable

  Default:LAGRANGE

  C++ Type:MooseEnum

  Options:LAGRANGE MONOMIAL HERMITE SCALAR HIERARCHIC CLOUGH XYZ SZABAB BERNSTEIN L2_LAGRANGE L2_HIERARCHIC NEDELEC_ONE LAGRANGE_VEC MONOMIAL_VEC

  Description:Specifies the family of FE shape functions to use for this variable

• inactiveIf specified blocks matching these identifiers will be skipped.

  C++ Type:std::vector

  Options:

  Description:If specified blocks matching these identifiers will be skipped.

• isObjectActionTrueIndicates that this is a MooseObjectAction.

  Default:True

  C++ Type:bool

  Options:

  Description:Indicates that this is a MooseObjectAction.

• orderFIRSTSpecifies the order of the FE shape function to use for this variable (additional orders not listed are allowed)

  Default:FIRST

  C++ Type:MooseEnum

  Options:CONSTANT FIRST SECOND THIRD FOURTH

  Description:Specifies the order of the FE shape function to use for this variable (additional orders not listed are allowed)

• scalingSpecifies a scaling factor to apply to this variable

  C++ Type:std::vector

  Options:

  Description:Specifies a scaling factor to apply to this variable

Available Objects

• Moose App
• ArrayMooseVariableUsed for grouping standard field variables with the same finite element family and order
• MooseVariableRepresents standard field variables, e.g. Lagrange, Hermite, or non-constant Monomials
• MooseVariableBaseBase class for Moose variables. This should never be the terminal object type
• MooseVariableConstMonomialSpecialization for constant monomials that avoids unnecessary loops
• MooseVariableScalarMoose wrapper class around scalar variables
• VectorMooseVariableRepresents vector field variables, e.g. Vector Lagrange or Nedelec

Available Subsystems

• Phase Field App
• CHPFCRFFSplitVariables
• HHPFCRFFSplitVariables
• PFCRFFVariables
• PolycrystalVariables

Available Actions

• Moose App
• AddVariableAction
• CopyNodalVarsAction