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BoundsAux

!syntax description /AuxKernels/BoundsAux

Description

BoundsAux is used for setting bounds on a non-linear variable specified through the parameter bounded_variable. The upper and lower parameters can be used to specify the upper and lower bound respectively. BoundsAux expects a variable parameter to be set (as do all AuxKernels). This can be a dummy AuxVariable; the BoundsAux actually operates on NumericVectors held by the nonlinear system and does nothing but return 0 for the value of the specified variable.

Note that in order for these bounds to have an effect, the user has to specify the PETSc options -snes_type vinewtonssls or -snes_type vinewtonrsls. Both options emply semi-smooth non-linear solution algorithms to solve the variational inequality. However, the vinewtonrsls option employs a reduced space active set method that actually reduces the size of the linear system by the number of active constraints. The PETSc manual pages for the vinewtonssls algorithm can be found here while the manual page for vinewtonrsls can be found here.

MOOSE users can also enforce constraints through MOOSE using UpperBoundNodalKernel and LowerBoundNodalKernel. However, using these objects requires introduction of Lagrange multiplier variables that increase the size of the non-linear system as well as render some preconditioning methods like algebraic multi-grid ineffective. The number of non-linear iterations required to solve a constrained PDE defined by this input file with the various constraint algorithms is summarized below:

  • viewntonrsls and BoundsAux: 22

  • vinewtonssls and BoundsAux: 53

  • UpperBoundNodalKernel and LowerBoundNodalKernel: 25

Example Syntax

[Bounds]
  [bounds]
    type = BoundsAux
    variable = bounds
    bounded_variable = u
    upper = ${l}
    lower = 0
  []
[]
(test/tests/nodalkernels/constraint_enforcement/vi-bounding.i)

Input Parameters

  • bounded_variableThe variable to be bounded

    C++ Type:std::vector

    Options:

    Description:The variable to be bounded

  • variableThe name of the variable that this object applies to

    C++ Type:AuxVariableName

    Options:

    Description:The name of the variable that this object applies to

Required Parameters

  • 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

  • boundaryThe list of boundary IDs from the mesh where this boundary condition applies

    C++ Type:std::vector

    Options:

    Description:The list of boundary IDs from the mesh where this boundary condition applies

  • execute_onLINEAR TIMESTEP_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, PRE_DISPLACE.

    Default:LINEAR TIMESTEP_END

    C++ Type:ExecFlagEnum

    Options:NONE INITIAL LINEAR NONLINEAR TIMESTEP_END TIMESTEP_BEGIN FINAL CUSTOM PRE_DISPLACE

    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, PRE_DISPLACE.

  • lowerThe lower bound for the variable

    C++ Type:double

    Options:

    Description:The lower bound for the variable

  • upperThe upper bound for the variable

    C++ Type:double

    Options:

    Description:The upper bound for the variable

Optional Parameters

  • 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.

  • enableTrueSet the enabled status of the MooseObject.

    Default:True

    C++ Type:bool

    Options:

    Description:Set the enabled status of the MooseObject.

  • seed0The seed for the master random number generator

    Default:0

    C++ Type:unsigned int

    Options:

    Description:The seed for the master random number generator

  • 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.

Advanced Parameters

Input Files