understanding MultiApps and Transfers Systems.

[zuckarm]

hi all,

i am trying to understand how to set up a coupled problem in MOOSE. for this, i used one of the tutorials in Combined module in MOOSE, and set up the same problem using MultiApps and Transfers.

the main app is solving for displacements, and sub app is solving for temperature. temperature is passed to the main app at the beginning of each timestep.

i getting a difference of values for the temperature using both the above-mentioned methods. also, i have imposed an initial condition of T = 300 in both the methods, but it is not reflected in the postprocesser results.

can anyone please let me know if the problem is set up correctly in both the methods. i am doing this as an exercise to better understand how to set up coupled problems.

thanks.

following is the input file using combined module:

#
# Single block coupled thermal/mechanical
# https://mooseframework.inl.gov/modules/combined/tutorials/introduction/thermoech_step01.html
#

[GlobalParams]
  displacements = 'disp_x disp_y'
[]

[Mesh]
  [generated]
    type = GeneratedMeshGenerator
    dim = 2
    nx = 10
    ny = 10
    xmax = 2
    ymax = 1
  []
  [pin]
    type = ExtraNodesetGenerator
    input = generated
    new_boundary = pin
    coord = '0 0 0'
  []
[]

[Variables]
  [T]
    initial_condition = 300.0
  []
[]

[Kernels]
  [heat_conduction]
    type = HeatConduction
    variable = T
  []
  [time_derivative]
    type = HeatConductionTimeDerivative
    variable = T
  []
  [heat_source]
    type = HeatSource
    variable = T
    value = 5e4
  []
[]

[Physics/SolidMechanics/QuasiStatic]
  [all]
    add_variables = true
    strain = FINITE
    automatic_eigenstrain_names = true
    generate_output = 'vonmises_stress'
  []
[]

[Materials]
  [thermal]
    type = HeatConductionMaterial
    thermal_conductivity = 45.0
    specific_heat = 0.5
  []
  [density]
    type = GenericConstantMaterial
    prop_names = 'density'
    prop_values = 8000.0
  []
  [elasticity]
    type = ComputeIsotropicElasticityTensor
    youngs_modulus = 1e9
    poissons_ratio = 0.3
  []
  [expansion1]
    type = ComputeThermalExpansionEigenstrain
    temperature = T
    thermal_expansion_coeff = 0.001
    stress_free_temperature = 300
    eigenstrain_name = thermal_expansion
  []
  [stress]
    type = ComputeFiniteStrainElasticStress
  []
[]

[BCs]
  [t_left]
    type = DirichletBC
    variable = T
    value = 300
    boundary = 'left'
  []
  [t_right]
    type = FunctionDirichletBC
    variable = T
    function = '300+5*t'
    boundary = 'right'
  []
  [pin_x]
    type = DirichletBC
    variable = disp_x
    boundary = pin
    value = 0
  []
  [bottom_y]
    type = DirichletBC
    variable = disp_y
    boundary = bottom
    value = 0
  []
[]

[Preconditioning]
  [smp]
    type = SMP
    full = true
  []
[]

[Executioner]
  type = Transient
  petsc_options_iname = '-pc_type'
  petsc_options_value = 'lu'
  end_time = 5
  dt = 1
[]

[Postprocessors]
    [temp]
        type = AverageNodalVariableValue
        variable = T
    []
[]

[Outputs]
  exodus = true
    csv = true
[]

and following are the input files using MultiApps and Transfers systems:
main app:

[MultiApps]
  [thermal]
    type        = TransientMultiApp
    input_files = 'thermo_mech_sub.i'
  []
[]

[Transfers]
  [pass_temp_to_main]
    type            = MultiAppCopyTransfer
    source_variable = T
    variable        = T
    from_multi_app  = thermal
    execute_on      = 'TIMESTEP_BEGIN'
  []
[]

[GlobalParams]
  displacements     = 'disp_x disp_y'
  temperature       = T
  eigenstrain_name  = eigenstrain
[]

[Mesh]
  [gen]
    type    = GeneratedMeshGenerator
    dim     = 2
    xmin    = 0
    ymin    = 0
    xmax    = 2
    ymax    = 1
    nx      = 10
    ny      = 10
  []

  [pin]
    type          = ExtraNodesetGenerator
    input         = gen
    new_boundary  = pin
    coord         = '0 0 0'
  []
[]

[Variables]
  [disp_x]
  []

  [disp_y]
  []
[]

[AuxVariables]
  [T]
    initial_condition = 300
  []

  [fx]
  []

  [fy]
  []
[]

[Kernels]
  [static_x]
    type          = StressDivergenceTensors
    variable      = disp_x
    component     = 0
    save_in       = fx
  []

  [static_y]
    type          = StressDivergenceTensors
    variable      = disp_y
    component     = 1
    save_in       = fy
  []
[]

[Materials]
  [mat_props]
    type            = GenericConstantMaterial
    prop_names      = 'density'
    prop_values     = '8000'
  []

  [thermal_props]
    type                  = HeatConductionMaterial
    thermal_conductivity  = 45
    specific_heat         = 0.5
  []

  [elasticity]
    type            = ComputeIsotropicElasticityTensor
    youngs_modulus  = 1e9
    poissons_ratio  = 0.3
  []

  [thermal_strain]
    type                    = ComputeThermalExpansionEigenstrain
    thermal_expansion_coeff = 0.001
    stress_free_temperature = 300
  []

  [total_strain]
    type              = ComputeFiniteStrain
  []

  [total_stress]
    type              = ComputeFiniteStrainElasticStress
    output_properties = 'stress'
    outputs           = exodus
  []
[]

[BCs]
  [pin_x]
    type      = DirichletBC
    variable  = disp_x
    boundary  = pin
    value     = 0
  []

  [bottom_y]
    type      = DirichletBC
    variable  = disp_y
    boundary  = bottom
    value     = 0
  []
[]


[Preconditioning]
  [smp]
    type    = SMP
    full    = true

    petsc_options_iname = '-pc_type'
    petsc_options_value = 'lu'
  []
[]

[Executioner]
  type      = Transient
  dt        = 1
  end_time  = 5

  fixed_point_min_its = 1
  fixed_point_max_its = 5

  nl_rel_tol  = 1e-8
  nl_abs_tol  = 1e-10
[]

[Outputs]
  csv     = true
  exodus  = true
  file_base = outputs/thermo_mech_coupling_main_test_2

  [console]
    type              = Console
    output_linear     = true
    output_nonlinear  = true
  []
[]

[Postprocessors]
  [temp_main]
    type      = AverageNodalVariableValue
    variable  = T
  []

  [sigma_xx]
    type      = ElementAverageValue
    variable  = stress_00
  []

  [sigma_yy]
    type      = ElementAverageValue
    variable  = stress_11
  []

  [sigma_xy]
    type      = ElementAverageValue
    variable  = stress_12
  []
[]

[Debug]
  show_material_props       = true
  #show_action_dependencies  = true
  #show_execution_order      = true
  #show_var_residual_norms   = true
  #output_process_domains    = true
[]

sub app:

[Mesh]
  [gen]
    type    = GeneratedMeshGenerator
    dim     = 2
    xmin    = 0
    ymin    = 0
    xmax    = 2
    ymax    = 1
    nx      = 10
    ny      = 10
  []
[]

[Variables] 
  [T]
    initial_condition = 300
  []
[]

[Kernels]
  [heat_conduction]
    type      = HeatConduction
    variable  = T
  []

  [heat_source]
    type      = HeatSource
    variable  = T
    value     = 5e4
  []

  [time_derivative]
    type      = HeatConductionTimeDerivative
    variable  = T
  []
[]

[BCs]
  [temp_left]
    type      = DirichletBC
    variable  = T
    value     = 300
    boundary  = 'left'
  []

  [temp_right]
    type      = FunctionDirichletBC
    variable  = T
    function  = '300+5*t'
    boundary  = 'right'
  []
[]

[Materials]
  [mat_props]
    type            = GenericConstantMaterial
    prop_names      = 'density'
    prop_values     = '8000'
  []

  [thermal_props]
    type                  = HeatConductionMaterial
    thermal_conductivity  = 45
    specific_heat         = 0.5
  []
[]

[Preconditioning]
  [smp]
    type    = SMP
    full    = true

    petsc_options_iname = '-pc_type'
    petsc_options_value = 'lu'
  []
[]

[Executioner]
  type      = Transient
  dt        = 1
  end_time  = 5

  nl_rel_tol  = 1e-8
  nl_abs_tol  = 1e-10
[]

[Outputs]
  exodus  = true
  
  [console]
    type              = Console
    output_linear     = true
    output_nonlinear  = true
  []
[]
                                                                                 
[Postprocessors]
  [temp_sub]
    type      = AverageNodalVariableValue
    variable  = T
  []
[]

[GiudGiud]

Hello

The problem is that you have set this up for loose coupling using MutlAipps + Transfer, so the equations are solved one after the other but never iterated within a time step.

You need to add fixed point parameters:

[Executioner]
  type = Transient
  petsc_options_iname = '-pc_type'
  petsc_options_value = 'lu'
  end_time = 5
  dt = 1

  fixed_point_max_its = 20
[]

see the fixed point parameters on this page
https://mooseframework.inl.gov/source/executioners/Transient.html
and some discussions on fixed point here
https://mooseframework.inl.gov/syntax/Executioner/FixedPointAlgorithms/index.html

[zuckarm]

hi, i already did that and its giving an error. i mentioned it in earlier reply.

when i add the command eigenstrain_names = eigenstrain in the ComputeFiniteStrain block, it shows me an error:

Solve Did NOT Converge!
Fixed point convergence reason: DIVERGED_NONLINEAR
Aborting as solve did not converge


*** ERROR ***
The following error occurred in the TimeStepper 'ConstantDT' of type ConstantDT.

Solve failed and timestep already at or below dtmin, cannot continue!

[GiudGiud]

This is not an error from the incompatibility of the strain / eigen strain

This is non convergence. It could be a preconditioning issue, it could be from the executioner parameters

[GiudGiud]

https://mooseframework.inl.gov/moose/application_usage/failed_solves.html

[zuckarm]

why is it so that this error shows after the command eigenstrain_names = eigenstrain is added in the ComputeFiniteStrain block?

[GiudGiud]

Because the simulation is no longer converging.

Something about the setup could be wrong elsewhere, or simply the solver cannot solve the problem without modifications to the preconditioning