LBMNeumannBC

LBMNeumannBC object

Implements a Neumann boundary condition for Lattice Boltzmann simulations. It enforces a fixed gradient of a microsocpic variable at the boundary.

Overview

This boundary condition enforces a specified gradient at the boundaries. It calculates the required macroscopic value at the boundary to satisfy the gradient condition and then uses the Dirichlet implementation logic to apply it. Note that the gradient specified at the boundary is not the gradient of macroscopic variable. Rather, it is the gradient of distribution fucntions (microscopci variable). This boundary conditions only computes missing directions by applying Non-Equilibrium Boundary Condition (NEBC). This means that the non-equilibirum part of the distribution function is computed from existing values in the current cell and the equilibrium part is computed from the prescribed gradients at the boundary.

It supports domain faces (left, right, top, bottom, front, back) and wall and regional for solid-embedded geometries. For 3D binary media masks, adjacent-to-solid cells are handled by a specialized path. The regional boundary enables users to mark different walls of the domain with different values and apply Neumann condition only in those regions.

Example Input File Syntax

[TensorComputes]
  [Boundary]
    [heat_source]
      type = LBMNeumannBC
      buffer = g
      f_old = gpc
      feq=geq
      velocity = velocity
      rho = T
      gradient = 0.001
      region_id = 3
      boundary = regional
    []
  []
[]
!listing-end

Input Parameters

boundaryEdges/Faces where boundary condition is applied.
C++ Type:MooseEnum
Options:top, bottom, left, right, front, back, wall, regional
Controllable:No
Description:Edges/Faces where boundary condition is applied.
bufferThe buffer this compute is writing to
C++ Type:std::string
Controllable:No
Description:The buffer this compute is writing to
f_oldOld state distribution function
C++ Type:std::string
Controllable:No
Description:Old state distribution function
feqEquilibrium distribution function
C++ Type:std::string
Controllable:No
Description:Equilibrium distribution function
rhoFluid density
C++ Type:std::string
Controllable:No
Description:Fluid density
velocityFluid velocity
C++ Type:std::string
Controllable:No
Description:Fluid velocity

Required Parameters

gradient0.0Gradient at the boundary
C++ Type:double
Unit:(no unit assumed)
Controllable:No
Description:0.0Gradient at the boundary
region_id0Region ID for regional boundary condition
C++ Type:int
Controllable:No
Description:0Region ID for regional boundary condition

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.
enableTrueSet the enabled status of the MooseObject.
Default:True
C++ Type:bool
Controllable:No
Description:Set the enabled status of the MooseObject.

Advanced Parameters

Input Files

(test/tests/lbm/neumann_regional.i)
(test/tests/lbm/neumann_box.i)
(test/tests/lbm/neumann_wall.i)
(examples/lbm/natural_convection_3D/convection.i)

(test/tests/lbm/neumann_regional.i)

[Domain]
  dim = 2
  nx = 11
  ny = 11
  mesh_mode=DUMMY
  parallel_mode = REAL_SPACE
  periodic_directions = 'X Y'
[]

[Stencil]
  [d2q9]
    type = LBMD2Q9
  []
[]

[TensorBuffers]
  [f]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [feq]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [fpc]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [T]
    type=LBMTensorBuffer
    buffer_type = ms
  []
  [velocity]
    type = LBMTensorBuffer
    buffer_type = mv
  []
  [binary_media]
    type = LBMTensorBuffer
    file = binary_regional.h5
    is_integer = true
    buffer_type = ms
  []
[]

[TensorComputes]
  [Initialize]
    [init_T]
      type = LBMConstantTensor
      buffer = T
      constants = 1.0
    []
    [equilibrium]
      type = LBMEquilibrium
      buffer = feq
      bulk = T
      velocity = velocity
    []
    [non_equilibrium]
      type = LBMEquilibrium
      buffer = f
      bulk = T
      velocity = velocity
    []
    [post_collision_equilibrium]
      type = LBMEquilibrium
      buffer = fpc
      bulk = T
      velocity = velocity
    []
  []
  [Solve]
    [T]
      type = LBMComputeDensity
      buffer = T
      f = f
    []
  []
  [Boundary]
    [regional]
      type = LBMNeumannBC
      buffer = f
      f_old = fpc
      feq = feq
      velocity = velocity
      rho = T
      gradient = 0.1
      region_id = 2
      boundary = regional
    []
  []
[]

[Problem]
  type = LatticeBoltzmannProblem
  substeps = 1
  binary_media = binary_media
[]

[Postprocessors]
  [velocity_min]
    type = TensorExtremeValuePostprocessor
    buffer = velocity
    value_type = MIN
  []
  [velocity_max]
    type = TensorExtremeValuePostprocessor
    buffer = velocity
    value_type = MAX
  []
  [density_min]
    type = TensorExtremeValuePostprocessor
    buffer = T
    value_type = MIN
  []
  [densty_max]
    type = TensorExtremeValuePostprocessor
    buffer = T
    value_type = MAX
  []
[]

[Executioner]
  type = Transient
  num_steps = 5
[]

[Outputs]
  file_base = neumann_regional
  csv = true
[]

(test/tests/lbm/neumann_box.i)

[Domain]
  dim = 3
  nx = 5
  ny = 5
  nz = 5
  mesh_mode = DUMMY
  parallel_mode = REAL_SPACE
  periodic_directions = 'X Y Z'
[]

[Stencil]
  [d3q19]
    type = LBMD3Q19
  []
[]

[TensorBuffers]
  [f]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [feq]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [fpc]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [density]
    type=LBMTensorBuffer
    buffer_type = ms
  []
  [velocity]
    type = LBMTensorBuffer
    buffer_type = mv
  []
[]

[TensorComputes]
  [Initialize]
    [init_density]
      type = LBMConstantTensor
      buffer = density
      constants = 1.0
    []
    [equilibrium]
      type = LBMEquilibrium
      buffer = feq
      bulk = density
      velocity = velocity
    []
    [non_equilibrium]
      type = LBMEquilibrium
      buffer = f
      bulk = density
      velocity = velocity
    []
    [post_collision_equilibrium]
      type = LBMEquilibrium
      buffer = fpc
      bulk = density
      velocity = velocity
    []
  []
  [Solve]
    [density]
      type = LBMComputeDensity
      buffer = density
      f = f
    []
  []
  [Boundary]
    [left]
      type = LBMNeumannBC
      buffer = f
      f_old = fpc
      feq = feq
      velocity = velocity
      rho = density
      gradient = 0.001
      boundary = left
    []
    [right]
      type = LBMNeumannBC
      buffer = f
      f_old = fpc
      feq = feq
      velocity = velocity
      rho = density
      gradient = 0.1
      boundary = right
    []
    [top]
      type = LBMNeumannBC
      buffer = f
      f_old = fpc
      feq = feq
      velocity = velocity
      rho = density
      gradient = 0.1
      boundary = top
    []
    [bottom]
      type = LBMNeumannBC
      buffer = f
      f_old = fpc
      feq = feq
      velocity = velocity
      rho = density
      gradient = 0.1
      boundary = bottom
    []
    [front]
      type = LBMNeumannBC
      buffer = f
      f_old = fpc
      feq = feq
      velocity = velocity
      rho = density
      gradient = 0.1
      boundary = front
    []
    [back]
      type = LBMNeumannBC
      buffer = f
      f_old = fpc
      feq = feq
      velocity = velocity
      rho = density
      gradient = 0.1
      boundary = back
    []
  []
[]

[Problem]
  type = LatticeBoltzmannProblem
  substeps = 1
[]

[Postprocessors]
  [velocity_min]
    type = TensorExtremeValuePostprocessor
    buffer = velocity
    value_type = MIN
  []
  [velocity_max]
    type = TensorExtremeValuePostprocessor
    buffer = velocity
    value_type = MAX
  []
  [density_min]
    type = TensorExtremeValuePostprocessor
    buffer = density
    value_type = MIN
  []
  [densty_max]
    type = TensorExtremeValuePostprocessor
    buffer = density
    value_type = MAX
  []
[]

[Executioner]
  type = Transient
  num_steps = 5
[]

[Outputs]
  file_base = neumann_box
  csv = true
[]

(test/tests/lbm/neumann_wall.i)

[Domain]
  dim = 2
  nx = 11
  ny = 11
  mesh_mode=DUMMY
  parallel_mode = REAL_SPACE
  periodic_directions = 'X Y'
[]

[Stencil]
  [d2q9]
    type = LBMD2Q9
  []
[]

[TensorBuffers]
  [f]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [feq]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [fpc]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [T]
    type=LBMTensorBuffer
    buffer_type = ms
  []
  [velocity]
    type = LBMTensorBuffer
    buffer_type = mv
  []
  [binary_media]
    type = LBMTensorBuffer
    file = binary_media.h5
    is_integer = true
    buffer_type = ms
  []
[]

[TensorComputes]
  [Initialize]
    [init_T]
      type = LBMConstantTensor
      buffer = T
      constants = 1.0
    []
    [equilibrium]
      type = LBMEquilibrium
      buffer = feq
      bulk = T
      velocity = velocity
    []
    [non_equilibrium]
      type = LBMEquilibrium
      buffer = f
      bulk = T
      velocity = velocity
    []
    [post_collision_equilibrium]
      type = LBMEquilibrium
      buffer = fpc
      bulk = T
      velocity = velocity
    []
  []
  [Solve]
    [T]
      type = LBMComputeDensity
      buffer = T
      f = f
    []
  []
  [Boundary]
    [wall]
      type = LBMNeumannBC
      buffer = f
      f_old = fpc
      feq = feq
      velocity = velocity
      rho = T
      gradient = 0.1
      boundary = wall
    []
  []
[]

[Problem]
  type = LatticeBoltzmannProblem
  substeps = 1
  binary_media = binary_media
[]

[Postprocessors]
  [velocity_min]
    type = TensorExtremeValuePostprocessor
    buffer = velocity
    value_type = MIN
  []
  [velocity_max]
    type = TensorExtremeValuePostprocessor
    buffer = velocity
    value_type = MAX
  []
  [density_min]
    type = TensorExtremeValuePostprocessor
    buffer = T
    value_type = MIN
  []
  [densty_max]
    type = TensorExtremeValuePostprocessor
    buffer = T
    value_type = MAX
  []
[]

[Executioner]
  type = Transient
  num_steps = 5
[]

[Outputs]
  file_base = neumann_wall
  csv = true
[]

(examples/lbm/natural_convection_3D/convection.i)

[Domain]
  dim = 3
  nx = 270
  ny = 270
  nz = 405
  xmax = 270
  ymax = 270
  zmax = 405
  device_names='cpu'
  parallel_mode = REAL_SPACE
  periodic_directions = 'X Y Z'
  floating_precision=SINGLE
[]

[Stencil]
  [d3q19]
    type = LBMD3Q19
  []
[]

[TensorBuffers]
  # Simulation binary media
  [binary_media]
    type = LBMTensorBuffer
    file = binary_media.h5
    buffer_type = ms
    is_integer = true
  []

  # Density distribution functions
  [f]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [feq]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [fpc]
    type = LBMTensorBuffer
    buffer_type = df
  []
  # Temperature distribution functions
  [g]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [geq]
    type = LBMTensorBuffer
    buffer_type = df
  []
  [gpc]
    type = LBMTensorBuffer
    buffer_type = df
  []
  # Fluid macroscopic variables: density and velocity
  [density]
    type = LBMTensorBuffer
    buffer_type = ms
  []
  [velocity]
    type = LBMTensorBuffer
    buffer_type = mv
  []
  [speed]
    type=LBMTensorBuffer
    buffer_type = ms
  []
  # Temperature macroscpic variables: temperature and 'velocity'
  [T]
    type = LBMTensorBuffer
    buffer_type = ms
  []
  # Forces
  [F]
    type = LBMTensorBuffer
    buffer_type = mv
  []
[]

[TensorComputes]
  [Initialize]
    [density]
      type = LBMConstantTensor
      buffer = density
      constants = 'rho0'
    []
    [velocity]
      type = LBMConstantTensor
      buffer = velocity
      constants = '0.0 0.0 0.0'
    []
    [temperature]
      type = LBMConstantTensor
      buffer = T
      constants = T_C
    []
    [equilibrium_fluid]
      type = LBMEquilibrium
      buffer = feq
      bulk = density
      velocity = velocity
    []
    [equilibrium_fluid_total]
      type = LBMEquilibrium
      buffer = f
      bulk = density
      velocity = velocity
    []
    [equilibrium_fluid_pc]
      type = LBMEquilibrium
      buffer = fpc
      bulk = density
      velocity = velocity
    []
    [equilibrium_temperature]
      type = LBMEquilibrium
      buffer = geq
      bulk = T
      velocity = velocity
    []
    [equilibrium_temperature_total]
      type = LBMEquilibrium
      buffer = g
      bulk = T
      velocity = velocity
    []
    [equilibrium_temperature_pc]
      type = LBMEquilibrium
      buffer = gpc
      bulk = T
      velocity = velocity
    []
  []

  #### Compute ####
  [Solve]

    # For temperature
    [Temperature]
      type = LBMComputeDensity
      buffer = T
      f = g
    []

    # For fluid
    [Fluid_density]
      type = LBMComputeDensity
      buffer = density
      f = f
    []

    [Fluid_velocity]
      type = LBMComputeVelocity
      buffer = velocity
      f = f
      rho = density
      forces = F
      enable_forces = true
    []

    # For temperature
    [Equilibrium_temperature]
      type = LBMEquilibrium
      buffer = geq
      bulk = T
      velocity = velocity
    []

    [Collision_temperature]
      type = LBMBGKCollision
      buffer = gpc
      f = g
      feq = geq
      tau0 = tau_T
    []

    # For fluid
    [Compute_forces]
      type = LBMComputeForces
      buffer = F
      rho0 = 'rho0'
      temperature = T
      T0 = 1.00
      enable_buoyancy = true
      gravity = g
      gravity_direction = 2
    []

    [Equilibrium_fluid]
      type = LBMEquilibrium
      buffer = feq
      bulk = density
      velocity = velocity
    []

    [Collision_fluid]
      type = LBMBGKCollision
      buffer = fpc
      f = f
      feq = feq
      tau0 = tau_f
    []

    [Apply_forces]
      type = LBMApplyForces
      buffer = fpc
      velocity = velocity
      rho = density
      forces = F
      tau0 = tau_f
    []

    [Residual]
      type = LBMComputeResidual
      speed = T
      # TODO this buffer is redundant, but avoids 'missing parameter' error
      buffer = T
    []
  []

  #### Boundary ####
  [Boundary]
    ##### for fluid
    [wall]
      type = LBMBounceBack
      buffer = f
      f_old = fpc
      boundary = wall
    []
    ##### for temperature
    [heat_source]
      type = LBMNeumannBC
      buffer = g
      f_old = gpc
      feq=geq
      velocity = velocity
      rho = T
      gradient = 0.001
      region_id = 3
      boundary = regional
    []
    [walls]
      type = LBMDirichletBC
      buffer = g
      f_old = gpc
      feq=geq
      velocity = velocity
      rho = T
      value = 1.0
      region_id = 2
      boundary = regional
    []
  []
[]

[TensorSolver]
  type = LBMStream
  buffer = 'f g'
  f_old = 'fpc gpc'
  root_compute = Residual
[]

[Problem]
  type = LatticeBoltzmannProblem
  binary_media = binary_media
  scalar_constant_names = 'rho0 T_C T_H tau_f tau_T g'
  scalar_constant_values = '1.0 1.0 1.05 0.55 0.55 0.01'
  substeps = 100
  print_debug_output = true
[]

[Executioner]
  type = Transient
  num_steps = 1000
[]

[TensorOutputs]
  [xdmf2]
    type = XDMFTensorOutput
    buffer = 'T density velocity'
    output_mode = 'Cell Cell Cell'
    enable_hdf5 = true
  []
[]

Overview
Example Input File Syntax
Input Parameters
Input Files