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. Also, scalar variables that are constant in space but evolve in time can be described by ordinary differential equations.

Documentation on the major classes of variables are presented in:

MooseVariableBase: for typical finite element nonlinear variables and scalar variables
MooseVariableFV: for finite volume variables

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<<<{"href": "index.html"}>>>]
  [convected]
    order<<<{"description": "Specifies the order of the FE shape function to use for this variable (additional orders not listed are allowed)"}>>> = FIRST
    family<<<{"description": "Specifies the family of FE shape functions to use for this variable"}>>> = LAGRANGE
  []
[]

[Kernels<<<{"href": "../Kernels/index.html"}>>>]
  [diff]
    type = Diffusion<<<{"description": "The Laplacian operator ($-\\nabla \\cdot \\nabla u$), with the weak form of $(\\nabla \\phi_i, \\nabla u_h)$.", "href": "../../source/kernels/Diffusion.html"}>>>
    variable<<<{"description": "The name of the variable that this residual object operates on"}>>> = convected
  []

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

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
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, RAVIART_THOMAS, RATIONAL_BERNSTEIN, SIDE_HIERARCHIC, L2_HIERARCHIC_VEC, L2_LAGRANGE_VEC, L2_RAVIART_THOMAS
Controllable:No
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<std::string>
Controllable:No
Description:If specified blocks matching these identifiers will be skipped.
initial_conditionSpecifies a constant initial condition for this variable
C++ Type:std::vector<double>
Unit:(no unit assumed)
Controllable:No
Description:Specifies a constant initial condition for this variable
initial_from_file_varGives the name of a variable for which to read an initial condition from a mesh file
C++ Type:std::string
Controllable:No
Description:Gives the name of a variable for which to read an initial condition from a mesh file
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
Controllable:No
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<double>
Unit:(no unit assumed)
Controllable:No
Description:Specifies a scaling factor to apply to this variable

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

Available Objects

Moose App
ArrayMooseVariableUsed for grouping standard field variables with the same finite element family and order
MFEMVariableClass for adding MFEM variables to the problem (mfem::ParGridFunctions).
MooseLinearVariableFVRealBase class for Moose variables. This should never be the terminal object type
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
MooseVariableFVRealBase class for Moose variables. This should never be the terminal object type
MooseVariableScalarMoose wrapper class around scalar variables
VectorMooseVariableRepresents vector field variables, e.g. Vector Lagrange, Nedelec or Raviart-Thomas
Navier Stokes App
BernoulliPressureVariableBase class for Moose variables. This should never be the terminal object type
INSFVEnergyVariableBase class for Moose variables. This should never be the terminal object type
INSFVPressureVariableBase class for Moose variables. This should never be the terminal object type
INSFVScalarFieldVariableBase class for Moose variables. This should never be the terminal object type
INSFVVelocityVariableBase class for Moose variables. This should never be the terminal object type
PINSFVSuperficialVelocityVariableBase class for Moose variables. This should never be the terminal object type
PiecewiseConstantVariableBase class for Moose variables. This should never be the terminal object type

Available Actions

Moose App
AddVariableActionAdd a non-linear variable to the simulation.
CopyNodalVarsActionCopies variable information from a file.

(examples/ex02_kernel/ex02.i)

[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
[]

Description
Example
Input Parameters
Available Objects
Available Actions