Refactor cell diameter computation to utilities (#1265)

Description
The cell diameter calculation was repeated in every scratch data. This PR refactors it in an inline function in the utilities.

Testing
No impact on current tests.

Co-authored-by: Bruno Blais <blais.bruno@gmail.com>

CHANGELOG.md

@@ -3,6 +3,12 @@
 All notable changes to the Lethe project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/).
 
+## [Master] - 2024-08-27
+
+### Changed
+
+- MINOR Refactored cell diameter computation as an inline function in the utilities. [#1265](https://github.com/chaos-polymtl/lethe/pull/1265)
+
 ## [Master] - 2024-08-23
 
 ### Added

include/core/utilities.h

@@ -585,4 +585,34 @@ value_string_to_tensor(const std::string &value_string_0,
   return output_tensor;
 }
 
+/**
+ * @brief Computes equivalent cell diameter by comparing the area to a disk (2D)
+ * or the volume to a sphere (3D).
+ *
+ * @tparam dim Number of spatial dimensions (2D or 3D).
+ *
+ * @param[in] cell_measure Area (2D) or volume (3D) of the cell.
+ *
+ * @param[in] fe_degree Polynomial degree of the shape function.
+ *
+ * @return Cell diameter value.
+ */
+template <int dim>
+inline double
+compute_cell_diameter(const double cell_measure, const unsigned int fe_degree)
+{
+  double h;
+  if constexpr (dim == 2)
+    h = std::sqrt(4. * cell_measure / numbers::PI) / fe_degree;
+  else if constexpr (dim == 3)
+    h = std::cbrt(6. * cell_measure / numbers::PI) / fe_degree;
+  else
+    Assert(
+      false,
+      ExcMessage(std::string(
+        "'dim' should have a value of either 2 or 3. Only 2D and 3D simulations "
+        "are supported.")));
+  return h;
+}
+
 #endif

include/solvers/cahn_hilliard_scratch_data.h

@@ -189,13 +189,9 @@ class CahnHilliardScratchData
                                 source_chemical_potential,
                                 1);
 
-
-    if (dim == 2)
-      this->cell_size =
-        std::sqrt(4. * cell->measure() / M_PI) / fe_cahn_hilliard.degree;
-    else if (dim == 3)
-      this->cell_size =
-        pow(6 * cell->measure() / M_PI, 1. / 3.) / fe_cahn_hilliard.degree;
+    // Compute cell diameter
+    this->cell_size =
+      compute_cell_diameter<dim>(cell->measure(), fe_cahn_hilliard.degree);
 
     // Gather Phi and eta (values, gradient and laplacian)
     this->fe_values_cahn_hilliard[phase_order].get_function_values(

include/solvers/heat_transfer_scratch_data.h

@@ -209,10 +209,8 @@ class HeatTransferScratchData
 
     source_function->value_list(quadrature_points, source);
 
-    if (dim == 2)
-      this->cell_size = std::sqrt(4. * cell->measure() / M_PI) / fe_T.degree;
-    else if (dim == 3)
-      this->cell_size = pow(6 * cell->measure() / M_PI, 1. / 3.) / fe_T.degree;
+    // Compute cell diameter
+    this->cell_size = compute_cell_diameter<dim>(cell->measure(), fe_T.degree);
 
     // Gather temperature (values, gradient and laplacian)
     this->fe_values_T.get_function_values(current_solution,

include/solvers/navier_stokes_scratch_data.h

@@ -270,10 +270,8 @@ class NavierStokesScratchData
         components[k] = fe.system_to_component_index(k).first;
       }
 
-    if (dim == 2)
-      this->cell_size = std::sqrt(4. * cell->measure() / M_PI) / fe.degree;
-    else if (dim == 3)
-      this->cell_size = pow(6 * cell->measure() / M_PI, 1. / 3.) / fe.degree;
+    // Compute cell diameter
+    this->cell_size = compute_cell_diameter<dim>(cell->measure(), fe.degree);
 
     // Gather velocity (values, gradient and laplacian)
     this->fe_values[velocities].get_function_values(current_solution,

include/solvers/tracer_scratch_data.h

@@ -170,12 +170,9 @@ class TracerScratchData
         levelset_function->value_list(quadrature_points, sdf_values);
       }
 
-    if (dim == 2)
-      this->cell_size =
-        std::sqrt(4. * cell->measure() / M_PI) / fe_tracer.degree;
-    else if (dim == 3)
-      this->cell_size =
-        pow(6 * cell->measure() / M_PI, 1. / 3.) / fe_tracer.degree;
+    // Compute cell diameter
+    this->cell_size =
+      compute_cell_diameter<dim>(cell->measure(), fe_tracer.degree);
 
     // Gather tracer (values, gradient and laplacian)
     this->fe_values_tracer.get_function_values(current_solution,

include/solvers/vof_scratch_data.h

@@ -161,11 +161,9 @@ class VOFScratchData
     this->quadrature_points = fe_values_vof.get_quadrature_points();
     auto &fe_vof            = fe_values_vof.get_fe();
 
-    if (dim == 2)
-      this->cell_size = std::sqrt(4. * cell->measure() / M_PI) / fe_vof.degree;
-    else if (dim == 3)
-      this->cell_size =
-        pow(6 * cell->measure() / M_PI, 1. / 3.) / fe_vof.degree;
+    // Compute cell diameter
+    this->cell_size =
+      compute_cell_diameter<dim>(cell->measure(), fe_vof.degree);
 
     fe_values_vof.get_function_values(current_solution,
                                       this->present_phase_values);

source/solvers/fluid_dynamics_nitsche.cc

@@ -109,15 +109,9 @@ FluidDynamicsNitsche<dim, spacedim>::assemble_nitsche_restriction()
           local_matrix = 0;
           local_rhs    = 0;
 
-
-          const auto &cell   = particle->get_surrounding_cell();
-          double      h_cell = 0;
-          if (dim == 2)
-            h_cell = std::sqrt(4. * cell->measure() / M_PI) /
-                     this->velocity_fem_degree;
-          else if (dim == 3)
-            h_cell = pow(6 * cell->measure() / M_PI, 1. / 3.) /
-                     this->velocity_fem_degree;
+          const auto  &cell   = particle->get_surrounding_cell();
+          double       h_cell = compute_cell_diameter<dim>(cell->measure(),
+                                                     this->velocity_fem_degree);
           const double penalty_parameter =
             1. / std::pow(h_cell * h_cell, double(dim) / double(spacedim));
           const auto &dh_cell =
@@ -362,13 +356,8 @@ FluidDynamicsNitsche<dim, spacedim>::calculate_forces_on_solid(
 #else
       const auto &cell = particle->get_surrounding_cell();
 #endif
-      double h_cell = 0;
-      if (dim == 2)
-        h_cell =
-          std::sqrt(4. * cell->measure() / M_PI) / this->velocity_fem_degree;
-      else if (dim == 3)
-        h_cell =
-          pow(6 * cell->measure() / M_PI, 1. / 3.) / this->velocity_fem_degree;
+      double h_cell =
+        compute_cell_diameter<dim>(cell->measure(), this->velocity_fem_degree);
       const double penalty_parameter =
         1. / std::pow(h_cell * h_cell, double(dim) / double(spacedim));
       const auto &dh_cell =
@@ -451,13 +440,8 @@ FluidDynamicsNitsche<dim, spacedim>::calculate_torque_on_solid(
 #else
       const auto &cell = particle->get_surrounding_cell();
 #endif
-      double h_cell = 0;
-      if (dim == 2)
-        h_cell =
-          std::sqrt(4. * cell->measure() / M_PI) / this->velocity_fem_degree;
-      else if (dim == 3)
-        h_cell =
-          pow(6 * cell->measure() / M_PI, 1. / 3.) / this->velocity_fem_degree;
+      double h_cell =
+        compute_cell_diameter<dim>(cell->measure(), this->velocity_fem_degree);
       const double penalty_parameter =
         1. / std::pow(h_cell * h_cell, double(dim) / double(spacedim));
       const auto &dh_cell =

source/solvers/postprocessing_cfd.cc

@@ -260,10 +260,7 @@ calculate_CFL(const DoFHandler<dim> &dof_handler,
     {
       if (cell->is_locally_owned())
         {
-          if (dim == 2)
-            h = std::sqrt(4. * cell->measure() / M_PI) / degree;
-          else if (dim == 3)
-            h = pow(6 * cell->measure() / M_PI, 1. / 3.) / degree;
+          h = compute_cell_diameter<dim>(cell->measure(), degree);
           fe_values.reinit(cell);
           fe_values[velocities].get_function_values(evaluation_point,
                                                     present_velocity_values);

source/solvers/vof.cc

@@ -1437,10 +1437,8 @@ VolumeOfFluid<dim>::assemble_projection_phase_fraction(
           fe_values_phase_fraction.reinit(cell);
 
           cell_volume = cell->measure();
-          if (dim == 2)
-            h = std::sqrt(4. * cell_volume / M_PI) / fe->degree;
-          else if (dim == 3)
-            h = pow(6 * cell_volume / M_PI, 1. / 3.) / fe->degree;
+
+          h = compute_cell_diameter<dim>(cell_volume, fe->degree);
 
           local_matrix_phase_fraction = 0;
           local_rhs_phase_fraction    = 0;
@@ -1624,17 +1622,9 @@ VolumeOfFluid<dim>::assemble_projected_phase_fraction_gradient_matrix_and_rhs(
           auto &fe_filtered_phase_fraction =
             fe_values_projected_phase_fraction_gradient.get_fe();
 
-          if (dim == 2)
-            h =
-              std::sqrt(4. * projected_phase_fraction_gradient_cell->measure() /
-                        M_PI) /
-              fe_filtered_phase_fraction.degree;
-          else if (dim == 3)
-            h =
-              pow(6 * projected_phase_fraction_gradient_cell->measure() / M_PI,
-                  1. / 3.) /
-              fe_filtered_phase_fraction.degree;
-
+          h = compute_cell_diameter<dim>(
+            projected_phase_fraction_gradient_cell->measure(),
+            fe_filtered_phase_fraction.degree);
 
           local_matrix_projected_phase_fraction_gradient = 0;
           local_rhs_projected_phase_fraction_gradient    = 0;
@@ -1831,12 +1821,8 @@ VolumeOfFluid<dim>::assemble_curvature_matrix_and_rhs(
 
           auto &fe_curvature = fe_values_curvature.get_fe();
 
-          if (dim == 2)
-            h = std::sqrt(4. * curvature_cell->measure() / M_PI) /
-                fe_curvature.degree;
-          else if (dim == 3)
-            h = pow(6 * curvature_cell->measure() / M_PI, 1. / 3.) /
-                fe_curvature.degree;
+          h = compute_cell_diameter<dim>(curvature_cell->measure(),
+                                         fe_curvature.degree);
 
           // Get pfg values, curvature values and gradients
           fe_values_projected_phase_fraction_gradient[pfg].get_function_values(