ICs System

Description

The ICs block within an input file is utilized to define the initial (starting) conditions for the variables within your simulation. Initial conditions may be applied to both the "unknowns" (nonlinear or scalar variables) or auxiliary variables. The interface for defining an Initial Condition is to support a function that returns a value at a "Point", and optionally higher order derivatives at that point (e.g. Gradient, Second).

ICs Block

The preferred syntax is to create a top-level "ICs" block with subblocks defining the initial conditions for one or more variables.

[ICs<<<{"href": "index.html"}>>>]
  [u_ic]
    type = FunctionIC<<<{"description": "An initial condition that uses a normal function of x, y, z to produce values (and optionally gradients) for a field variable.", "href": "../../source/ics/FunctionIC.html"}>>>
    variable<<<{"description": "The variable this initial condition is supposed to provide values for."}>>> = 'u'
    function<<<{"description": "The initial condition function."}>>> = parsed_function
  []
[]

ICs from an Exodus File

MOOSE contains a shortcut syntax for reading solutions from an Exodus file for the initial condition from right within the Variables. The name of the variable and the time step from which to read the solution must be supplied.

[Variables<<<{"href": "../Variables/index.html"}>>>]
  active<<<{"description": "If specified only the blocks named will be visited and made active"}>>> = 'u v'

  [u]
    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
    initial_from_file_var<<<{"description": "Gives the name of a variable for which to read an initial condition from a mesh file"}>>> = u
    initial_from_file_timestep<<<{"description": "Gives the timestep (or \"LATEST\") for which to read a solution from a file for a given variable. (Default: LATEST)"}>>> = 6
  []

  [v]
    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
    [InitialCondition]
      type = BoundingBoxIC
      x1 = 0.0
      x2 = 1.0
      y1 = 0.0
      y2 = 1.0
      inside = 3.0
      outside = 1.0
    []
  []
[]

Initial Condition Coupling

Initial Conditions objects in MOOSE can couple to other variables in the system. When this occurs MOOSE will automatically evaluate dependencies and evaluate initial conditions in an order that supports the valid inspection of variables when computing initial conditions for other variables.

Gradients

Some shape function families support gradient degrees of freedom (Hermite). To properly initialize these DOFs, the initial condition system has an optional override for supplying gradient values.

Inspecting Current Node or Element Pointers

The initial condition system uses a generic projection algorithm for setting the initial condition for each supported discretization scheme. In the general case, the projection system may choose to sample anywhere within the domain and not necessarily right on a mesh node or at an element center position. However, for common FE discretizations such as Lagrange, all of the initial condition samples are taken at nodes. To support these common cases, InitialCondition derived objects have access to pointers to both current nodes and current elements. These will be non-null when samples are taken at the corresponding mesh entity and null otherwise.

Sanity checks on ICs

Multiple initial conditions may not be applied to the same variable on the same block
Multiple initial conditions may not be applied to the same variable on the same boundary
Global initial conditions will conflict with subdomain or boundary restricted ICs on the same variable

Block/Boundary Restrictions

The ICs system support both the BlockRestrictable Interface and BoundaryRestrictable Interface interfaces. When using nodal variables with block restriction, there is an ambiguity that can occur at inter-block interfaces where a node sits in elements of two or more different blocks. To resolve this ambiguity on multi-block nodes, MOOSE chooses the IC object defined on the lowest block ID for a node to "win" along the interface; the winning object's variable must be defined on the block - otherwise the IC for the next lowest block ID for the node is used - and so forth until one has the variable defined.

Old and Older ICs

The ICs system supports the ability to set ICs on old and older states. This can be useful for initializing old and older states of variables needed for various time integration schemes. It can be set with the "state" parameter and specifying OLD or OLDER.

Available Objects

Moose App
ArrayConstantICSets constant component values for an array field variable.
ArrayFunctionICAn initial condition that uses a normal function of x, y, z to produce values (and optionally gradients) for a field variable.
BoundingBoxICBoundingBoxIC allows setting the initial condition of a value inside and outside of a specified box. The box is aligned with the x, y, z axes
ConstantICSets a constant field value.
FunctionICAn initial condition that uses a normal function of x, y, z to produce values (and optionally gradients) for a field variable.
FunctionScalarICInitializes a scalar variable using a function.
FunctorICAn initial condition that uses a normal function of x, y, z to produce values (and optionally gradients) for a field variable.
IntegralPreservingFunctionICFunction initial condition that preserves an integral
MFEMScalarICSets the initial values of an MFEM scalar variable from a user-specified scalar coefficient.
MFEMVectorICSets the initial values of an MFEM vector variable from a user-specified vector coefficient.
RandomICInitialize a variable with randomly generated numbers following either a uniform distribution or a user-defined distribution
ScalarComponentICInitial condition to set different values on each component of scalar variable.
ScalarConstantICInitalize a scalar variable with a constant value prescribed by an input parameter.
ScalarSolutionICSets the initial condition from a scalar variable stored in an Exodus file, retrieved by a SolutionUserObject
ScalarSolutionInitialConditionSets the initial condition from a scalar variable stored in an Exodus file, retrieved by a SolutionUserObject
SolutionICSets the initial condition from a field variable stored in an Exodus file, retrieved by a SolutionUserObject
SolutionInitialConditionSets the initial condition from a field variable stored in an Exodus file, retrieved by a SolutionUserObject
VectorConstantICSets constant component values for a vector field variable.
VectorFunctionICSets component values for a vector field variable based on a vector function.
Thermal Hydraulics App
FlowModelGasMixICIC for the solution variables of FlowModelGasMix.
FunctionNodalAverageICInitial conditions for an elemental variable from a function using nodal average.
RhoEAFromPressureTemperatureFunctionVelocityICSet the initial condition for rho*E*A from pressure and temperature variables and a velocity scalar function
RhoEAFromPressureTemperatureVelocityICSet the initial condition for rho*E*A from pressure, temperature and a scalarfield velocity variable
SpecificInternalEnergyICSets the initial condition for the specific internal energy of a phase
SpecificTotalEnthalpyICSets the initial condition for the special total enthalpy of a phase
SpecificVolumeICSets an initial condition for the specific volume of a phase
SumICSets the initial condition as the sum of other variables
VariableFunctionProductICSets the initial condition as the product of a variable and a function
VariableProductICSets the initial condition as the product of several variables
VectorVelocityICComputes velocity in the direction of a 1-D element from a vector velocity function
VolumeJunction1PhaseICIC for junction variables in VolumeJunction1Phase.
Porous Flow App
PorousFlowFluidPropertyICAn initial condition to calculate one fluid property (such as enthalpy) from pressure and temperature
PorousFlowFluidStateICAn initial condition to calculate z from saturation
Phase Field App
BimodalInverseSuperellipsoidsICBimodal size distribution of large particles (specified in input file, value invalue) and small particles (placed randomly inside the larger particles, value outvalue)
BimodalSuperellipsoidsICBimodal size distribution of large particles (specified in input file) and small particles (placed randomly outside the larger particles)
BndsCalcICInitialize the location of grain boundaries in a polycrystalline sample
ClosePackICClose packed arrangement of smooth circles
CoupledValueFunctionICInitialize the variable from a lookup function
CrossICCross-shaped initial condition
IsolatedBoundingBoxICSpecify variable values inside and outside a list of isolated boxes shaped axis-aligned regions defined by pairs of opposing corners
LatticeSmoothCircleICPerturbed square lattice of smooth circles
MultiBoundingBoxICAllows setting the initial condition of a value of a field inside and outside multiple bounding boxes.
MultiSmoothCircleICRandom distribution of smooth circles with given minimum spacing
MultiSmoothSuperellipsoidICRandom distribution of smooth ellipse with given minimum spacing
NestedBoundingBoxICSpecify variable values inside a list of nested boxes shaped axis-aligned regions defined by pairs of opposing corners
PFCFreezingICBase class for generating a random field for a variable.
PolycrystalColoringICRandom Voronoi tesselation polycrystal (used by PolycrystalVoronoiICAction)
PolycrystalColoringICLinearizedInterfaceSets up polycrystal initial conditions from user objects for transformed linearized interface
PolycrystalRandomICRandom initial condition for a polycrystalline material
PolycrystalVoronoiVoidICRandom distribution of smooth circles with given minimum spacing
RampICLinear ramp along the x-axis with given values at the left and right extreme points.
ReconPhaseVarICSets the initial condition of the phase weights from the EBSD reader
RndBoundingBoxICRandom noise with different min/max inside/outside of a bounding box
RndSmoothCircleICRandom noise with different min/max inside/outside of a smooth circle
SmoothCircleFromFileICMultiple smooth circles read from a text file
SmoothCircleICCircle with a smooth interface
SmoothCircleICLinearizedInterfaceCircle with a smooth interface transformed using the linearized interface function
SmoothSuperellipsoidICSuperellipsoid with a smooth interface
SpecifiedSmoothCircleICMultiple smooth circles with manually specified radii and center points
SpecifiedSmoothSuperellipsoidICMultiple smooth superellipsoids with manually specified center points; semiaxes a,b,c; and exponents n
ThumbICThumb shaped bicrystal for grain boundary mobility tests
Tricrystal2CircleGrainsICTricrystal with two circles/bubbles
TricrystalTripleJunctionICTricrystal with a triple junction
Solid Mechanics App
VolumeWeightedWeibullInitialize a variable with randomly generated numbers following a volume-weighted Weibull distribution
Sub Channel App
FCTFdisplacementICThis class calculates the displacement of the duct for the areva FCTF
MarvelTriFlowAreaICComputes flow area of subchannels in a triangular lattice arrangement in a MARVEL-type micro-reactor
MarvelTriWettedPerimICComputes wetted perimeter of subchannels in a triangular lattice arrangement in a MARVEL-type micro-reactor
MassFlowRateICComputes mass float rate from specified mass flux and cross-sectional area
QuadFlowAreaICComputes subchannel flow area in the square lattice subchannel arrangement
QuadInterWrapperFlowAreaICComputes cross-sectional area for inter-wrapper cells in a square lattice subchannel arrangement
QuadInterWrapperPowerICComputes axial power rate, W/m that goes into the inter-wrapper cells in a square lattice subchannel arrangement
QuadInterWrapperWettedPerimICComputes wetted perimeter of inter-wrapper cells in the square lattice subchannel arrangement
QuadPowerICComputes axial heat rate (W/m) that goes into the subchannel cells or is assigned to the fuel pins, in a square lattice arrangement
QuadWettedPerimICComputes wetted perimeter of subchannels in a square lattice arrangement
SCMMassFlowRateICComputes mass float rate from specified mass flux and cross-sectional area
SCMQuadFlowAreaICComputes subchannel flow area in the square lattice subchannel arrangement
SCMQuadPowerICComputes axial heat rate (W/m) that goes into the subchannel cells or is assigned to the fuel pins, in a square lattice arrangement
SCMQuadWettedPerimICComputes wetted perimeter of subchannels in a square lattice arrangement
SCMTriFlowAreaICComputes flow area of subchannels in a triangular lattice arrangement
SCMTriPowerICComputes axial power rate (W/m) that goes into the subchannel cells or is assigned to the fuel pins, in a triangular lattice arrangement
SCMTriWettedPerimICComputes wetted perimeter of subchannels in a triangular lattice arrangement
TriFlowAreaICComputes flow area of subchannels in a triangular lattice arrangement
TriInterWrapperFlowAreaICComputes flow area of inter-wrapper cells in a triangualar subchannel lattice
TriInterWrapperPowerICComputes linear power rate (W/m) that goes into interwrapper cells in a triangular subchannel lattice
TriInterWrapperWettedPerimICComputes wetted perimeter of inter-wrapper cells in a triangular subchannel lattice
TriPowerICComputes axial power rate (W/m) that goes into the subchannel cells or is assigned to the fuel pins, in a triangular lattice arrangement
TriWettedPerimICComputes wetted perimeter of subchannels in a triangular lattice arrangement
ViscosityICComputes viscosity from specified pressure and temperature
Navier Stokes App
NSFunctionInitialConditionSets intial values for all variables.
NSInitialConditionNSInitialCondition sets intial constant values for all variables.
PNSInitialConditionPNSInitialCondition sets intial constant values for any porous flow variable.
Fluid Properties App
RhoFromPressureTemperatureICComputes the density from pressure and temperature.
RhoVaporMixtureFromPressureTemperatureICComputes the density of a vapor mixture from pressure and temperature.
SpecificEnthalpyFromPressureTemperatureICComputes the specific enthalpy from pressure and temperature.

Available Subsystems

Phase Field App
PolycrystalICs

Available Actions

Moose App
AddInitialConditionActionAdd an InitialCondition object to the simulation.

(test/tests/ics/function_ic/parsed_function.i)

#
# Test the automatically generated gradients in ParsedFunction and the gradient pass-through in FunctionIC
# OLD MOOSE behavior was for parsed_function to behave the same as parsed_zerograd_function
# NEW MOOSE behavior is for parsed_function to behave the same as parsed_grad_function
#

[Mesh]
  type = GeneratedMesh
  dim = 2
  xmin = 0
  xmax = 3.141
  ymin = 0
  ymax = 3.141
  nx = 10
  ny = 10
[]

[Variables]
  [u]
    order = THIRD
    family = HERMITE
  []
[]

[Functions]
  [parsed_function]
    type = ParsedFunction
    expression = 'sin(x)-cos(y/2)'
  []
  [parsed_grad_function]
    type = ParsedGradFunction
    expression = 'sin(x)-cos(y/2)'
    grad_x = 'cos(x)'
    grad_y = 'sin(y/2)/2'
  []
  [parsed_zerograd_function]
    type = ParsedGradFunction
    expression = 'sin(x)-cos(y/2)'
    grad_x = '0'
    grad_y = '0'
  []
[]

[ICs]
  [u_ic]
    type = FunctionIC
    variable = 'u'
    function = parsed_function
  []
[]

[Executioner]
  type = Steady
[]

[Problem]
  solve = false
[]

[Outputs]
  file_base = parsed
  [OverSampling]
    type = Exodus
    refinements = 3
  []
[]

(test/tests/ics/from_exodus_solution/nodal_part2.i)

# Use the exodus file for restarting the problem:
# - restart one variable
# - and have one extra variable with IC
#

[Mesh]
  file = out_nodal_part1.e
[]

[Functions]
  [exact_fn]
    type = ParsedFunction
    expression = ((x*x)+(y*y))
  []

  [forcing_fn]
    type = ParsedFunction
    expression = -4
  []
[]

[Variables]
  active = 'u v'

  [u]
    order = FIRST
    family = LAGRANGE
    initial_from_file_var = u
    initial_from_file_timestep = 6
  []

  [v]
    order = FIRST
    family = LAGRANGE
    [InitialCondition]
      type = BoundingBoxIC
      x1 = 0.0
      x2 = 1.0
      y1 = 0.0
      y2 = 1.0
      inside = 3.0
      outside = 1.0
    []
  []
[]

[Problem]
  allow_initial_conditions_with_restart = true
[]

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

  [ffn]
    type = BodyForce
    variable = u
    function = forcing_fn
  []

  [diff_v]
    type = Diffusion
    variable = v
  []
[]

[BCs]
  [all]
    type = FunctionDirichletBC
    variable = u
    boundary = '0 1 2 3'
    function = exact_fn
  []

  [left_v]
    type = DirichletBC
    variable = v
    boundary = '3'
    value = 0
  []

  [right_v]
    type = DirichletBC
    variable = v
    boundary = '1'
    value = 1
  []
[]

[Executioner]
  type = Steady

  solve_type = 'PJFNK'
[]

[Outputs]
  file_base = out_nodal_var_restart
  exodus = true
[]

Description
ICs Block
ICs from an Exodus File
Initial Condition Coupling
Gradients
Inspecting Current Node or Element Pointers
Sanity checks on ICs
Block / Boundary Restrictions
Old and Older ICs
Available Objects
Available Subsystems
Available Actions