Merge pull request #20120 from laagesen/intfunction_20065

Add ForcingFunctionAux AuxKernel

framework/doc/content/source/auxkernels/ForcingFunctionAux.md

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+# ForcingFunctionAux
+
+!syntax description /AuxKernels/ForcingFunctionAux
+
+This `AuxKernel` adds a forcing function to the value of an `AuxVariable` from the previous
+time step. For each time step $\delta t$, the value of the `AuxVariable` is computed as
+\begin{equation}
+V(t + \Delta t) = V(t) + f \Delta t
+\end{equation}
+where $V$ is the `AuxVariable` and $f$ is the forcing function. $f$ is a MOOSE `function`
+that is specified as an input parameter.
+
+## Example Input File Syntax
+
+In this example, value of a postprocessor is supplied to the forcing function f used by the `ForcingFunctionAux` `AuxKernel`, which increments the `AuxVariable` T.
+
+!listing /test/tests/auxkernels/forcing_function_aux/forcing_function_aux.i block=AuxKernels
+
+!syntax parameters /AuxKernels/ForcingFunctionAux
+
+!syntax inputs /AuxKernels/ForcingFunctionAux
+
+!syntax children /AuxKernels/ForcingFunctionAux

framework/include/auxkernels/ForcingFunctionAux.h

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+//* This file is part of the MOOSE framework
+//* https://www.mooseframework.org
+//*
+//* All rights reserved, see COPYRIGHT for full restrictions
+//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
+//*
+//* Licensed under LGPL 2.1, please see LICENSE for details
+//* https://www.gnu.org/licenses/lgpl-2.1.html
+
+#pragma once
+
+#include "FunctionAux.h"
+
+/**
+ * Add a forcing function to the previous time step value of an AuxVariable
+ */
+class ForcingFunctionAux : public FunctionAux
+{
+public:
+  static InputParameters validParams();
+
+  ForcingFunctionAux(const InputParameters & parameters);
+
+protected:
+  virtual Real computeValue() override;
+
+  /// AuxVariable value at previous time step
+  const VariableValue & _u_old;
+};

framework/src/auxkernels/ForcingFunctionAux.C

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+//* This file is part of the MOOSE framework
+//* https://www.mooseframework.org
+//*
+//* All rights reserved, see COPYRIGHT for full restrictions
+//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
+//*
+//* Licensed under LGPL 2.1, please see LICENSE for details
+//* https://www.gnu.org/licenses/lgpl-2.1.html
+
+#include "ForcingFunctionAux.h"
+#include "Function.h"
+
+registerMooseObject("MooseApp", ForcingFunctionAux);
+
+InputParameters
+ForcingFunctionAux::validParams()
+{
+  InputParameters params = FunctionAux::validParams();
+  params.addClassDescription("Auxiliary Kernel that adds a forcing function to the value of an "
+                             "AuxVariable from the previous time step.");
+  return params;
+}
+
+ForcingFunctionAux::ForcingFunctionAux(const InputParameters & parameters)
+  : FunctionAux(parameters), _u_old(uOld())
+{
+  if (isNodal())
+    paramError("variable", "The variable must be elemental");
+}
+
+Real
+ForcingFunctionAux::computeValue()
+{
+  return _u_old[_qp] + _dt * _func.value(_t, _q_point[_qp]);
+}

test/tests/auxkernels/forcing_function_aux/forcing_function_aux.i

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+# This is a test of the ForcingFunctionAux AuxKernel.
+# The diffusion equation for u is solved with boundary conditions to force a gradient
+# du/dx = 2, which is constant in time.
+# du/dx is integrated over the unit square domain using a postprocessor, resulting in 2.
+# The value of this postprocessor is supplied to the forcing function f used by
+# the ForcingFunctionAux AuxKernel, which increments the AuxVariable T.
+# Since the time step is 1, the value of T increases by 2 for each time step.
+
+[Mesh]
+  type = GeneratedMesh
+  dim = 2
+  nx = 10
+  ny = 10
+[]
+
+[Variables]
+  [./u]
+  [../]
+[]
+
+[AuxVariables]
+  [./grad_u_x]
+    order = CONSTANT
+    family = MONOMIAL
+    initial_condition = 2
+  [../]
+  [./T]
+    order = CONSTANT
+    family = MONOMIAL
+    initial_condition = 100
+  [../]
+[]
+
+[Functions]
+  [./u_ic_func]
+    type = ParsedFunction
+    value = '2*x'
+  [../]
+  [./f]
+    type = ParsedFunction
+    vars = f
+    vals = grad_int
+    value = f
+  [../]
+[]
+
+[ICs]
+  [./u_ic]
+    type = FunctionIC
+    variable = u
+    function = u_ic_func
+  [../]
+[]
+
+[Kernels]
+  [./dudt]
+    type = TimeDerivative
+    variable = u
+  [../]
+  [./diff]
+    type = Diffusion
+    variable = u
+  [../]
+[]
+
+[AuxKernels]
+  [./grad_u_x_aux]
+    type = VariableGradientComponent
+    variable = grad_u_x
+    component = x
+    gradient_variable = u
+  [../]
+  [./T_increment]
+    type = ForcingFunctionAux
+    variable = T
+    function = f
+  [../]
+[]
+
+[Postprocessors]
+  [./grad_int]
+    type = ElementIntegralVariablePostprocessor
+    variable = grad_u_x
+    execute_on = 'INITIAL TIMESTEP_END'
+  [../]
+[]
+
+[BCs]
+  [./left]
+    type = DirichletBC
+    variable = u
+    boundary = left
+    value = 0
+  [../]
+  [./right]
+    type = DirichletBC
+    variable = u
+    boundary = right
+    value = 2
+  [../]
+[]
+
+[Executioner]
+  type = Transient
+  scheme = bdf2
+  solve_type = PJFNK
+  petsc_options_iname = '-pc_type -pc_hypre_type'
+  petsc_options_value = 'hypre boomeramg'
+  nl_abs_tol = 1e-10
+  num_steps = 2
+  dt = 1
+[]
+
+[Outputs]
+  exodus = true
+[]
+

test/tests/auxkernels/forcing_function_aux/tests

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+[Tests]
+  issues = '#20065'
+  design = 'auxkernels/ForcingFunctionAux.md'
+  [./forcing_function_aux]
+    type = 'Exodiff'
+    input = 'forcing_function_aux.i'
+    exodiff = 'forcing_function_aux_out.e'
+    requirement = "MOOSE shall include the ability to increase the value of an AuxVariable from the previous time step using a forcing function."
+  [../]
+[]