Add source for LinearFVTimeDerivative. (#29149)

framework/src/linearfvkernels/LinearFVElementalKernel.C

@@ -29,15 +29,20 @@ LinearFVElementalKernel::addMatrixContribution()
 {
   // These only contribute to the diagonal of the matrix, so we just get
   // the contribution and insert it immediately.
-  const auto dof_id = _current_elem_info->dofIndices()[_sys_num][_var_num];
-  (*_linear_system.matrix).add(dof_id, dof_id, computeMatrixContribution());
+  (*_linear_system.matrix).add(_dof_id, _dof_id, computeMatrixContribution());
 }
 
 void
 LinearFVElementalKernel::addRightHandSideContribution()
 {
   // These only contribute to one entry of the right hand side, so we just get
   // the contribution and insert it immediately.
-  const auto dof_id = _current_elem_info->dofIndices()[_sys_num][_var_num];
-  (*_linear_system.rhs).add(dof_id, computeRightHandSideContribution());
+  (*_linear_system.rhs).add(_dof_id, computeRightHandSideContribution());
+}
+
+void
+LinearFVElementalKernel::setCurrentElemInfo(const ElemInfo * elem_info)
+{
+  _current_elem_info = elem_info;
+  _dof_id = _current_elem_info->dofIndices()[_sys_num][_var_num];
 }

framework/src/linearfvkernels/LinearFVTimeDerivative.C

@@ -0,0 +1,59 @@
+//* 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 "LinearFVTimeDerivative.h"
+
+registerMooseObject("MooseApp", LinearFVTimeDerivative);
+
+InputParameters
+LinearFVTimeDerivative::validParams()
+{
+  InputParameters params = LinearFVElementalKernel::validParams();
+  params.addClassDescription("Represents the matrix and right hand side contributions of a "
+                             "time derivative term in a partial differential equation.");
+  params.addParam<MooseFunctorName>(
+      "factor", 1.0, "A multiplier on the variable within the time derivative.");
+  return params;
+}
+
+LinearFVTimeDerivative::LinearFVTimeDerivative(const InputParameters & params)
+  : LinearFVElementalKernel(params),
+    _factor(getFunctor<Real>("factor")),
+    _time_integrator(_sys.getTimeIntegrator(_var_num)),
+    _factor_history(_time_integrator.numStatesRequired(), 0.0),
+    _state_args(_time_integrator.numStatesRequired(), determineState())
+{
+  // In case we need older states
+  for (const auto i : index_range(_state_args))
+    _state_args[i] = Moose::StateArg(i, Moose::SolutionIterationType::Time);
+}
+
+Real
+LinearFVTimeDerivative::computeMatrixContribution()
+{
+  const auto elem_arg = makeElemArg(_current_elem_info->elem());
+  return _factor(elem_arg, _state_args[0]) * /*_time_integrator.matrixContribution() */
+         _current_elem_volume;
+}
+
+Real
+LinearFVTimeDerivative::computeRightHandSideContribution()
+{
+  return /*_time_integrator.rhsContribution(_dof_id, _factor_history) */ _current_elem_volume;
+}
+
+void
+LinearFVTimeDerivative::setCurrentElemInfo(const ElemInfo * elem_info)
+{
+  LinearFVElementalKernel::setCurrentElemInfo(elem_info);
+
+  const auto elem_arg = makeElemArg(_current_elem_info->elem());
+  for (const auto i : index_range(_factor_history))
+    _factor_history[i] = _factor(elem_arg, _state_args[i]);
+}