Merge pull request #2415 from TomFischer/MPLLinearProperty

[MPL] Change implementation of LinearProperty

CHANGELOG.md

@@ -77,7 +77,8 @@
 - Add MFront/TFEL solid constitutive relation support via.
   MFrontGenericInterfaceSupport library. CMake option `OGS_USE_MFRONT`. [#2259](https://github.com/ufz/ogs/pull/2259)
 - Infrastructure for multi-phase, multi-component material properties library.
-  [#2303](https://github.com/ufz/ogs/pull/2303)
+  [#2303](https://github.com/ufz/ogs/pull/2303),
+  [#2415](https://github.com/ufz/ogs/pull/2415)
 - Anisotropic tensors may now be given in given local coordinate system. [#2370](https://github.com/ufz/ogs/pull/2370)
 - Non-constant density model implementation in HC process. [#2200](https://github.com/ufz/ogs/pull/2200)
 - Add second derivatives of permeability functions in Richards flow. [#2188](https://github.com/ufz/ogs/pull/2188)

Documentation/ProjectFile/properties/property/LinearProperty/c_LinearProperty.md

 Definition of a linear property:
-\f$y(x) = y_{\textrm{ref}} + m (x - x_{\textrm{ref}})\f$
+\f$y(x) = y_{\textrm{ref}} (1 + m (x - x_{\textrm{ref}})\f$
 where
  - \f$y_{\textrm{ref}}\f$ is a reference value, for instance reference density
- - \f$m\f$ is the slope of the linear relationship
+ - \f$m\f$ is a value influencing the slope of the linear relationship
  - \f$x_{\textrm{ref}}\f$ is a reference condition, for instance reference
-   temperatue
+   temperature

Documentation/ProjectFile/properties/property/LinearProperty/independent_variable/t_slope.md

-The slope \f$m\f$ of the linear relation.
+\f$m\f$ is a value influencing the slope of the linear relation. The slope is
+\f$y_{\mathrm{ref}} m.\f$

MaterialLib/MPL/Properties/LinearProperty.cpp

@@ -23,18 +23,20 @@ LinearProperty::LinearProperty(PropertyDataType const& property_reference_value,
 PropertyDataType LinearProperty::value(
     VariableArray const& variable_array) const
 {
-    return boost::get<double>(_value) +
-           boost::get<double>(_independent_variable.slope) *
-               (boost::get<double>(variable_array[static_cast<int>(
-                    _independent_variable.type)]) -
-                boost::get<double>(_independent_variable.reference_condition));
+    return boost::get<double>(_value) *
+           (1 + boost::get<double>(_independent_variable.slope) *
+                    (boost::get<double>(variable_array[static_cast<int>(
+                         _independent_variable.type)]) -
+                     boost::get<double>(
+                         _independent_variable.reference_condition)));
 }
 
 PropertyDataType LinearProperty::dValue(VariableArray const& /*variable_array*/,
                                         Variable const primary_variable) const
 {
     return _independent_variable.type == primary_variable
-               ? _independent_variable.slope
+               ? boost::get<double>(_value) *
+                     boost::get<double>(_independent_variable.slope)
                : decltype(_value){};
 }
 

Tests/MaterialLib/TestMPLLinearProperty.cpp

@@ -24,18 +24,20 @@ TEST(MaterialPropertyLib, LinearProperty)
     MaterialPropertyLib::VariableArray variable_array;
     variable_array[static_cast<int>(
         MaterialPropertyLib::Variable::temperature)] = 303.15;
-    ASSERT_NEAR(boost::get<double>(linear_property.value(variable_array)),
-                y_ref + m * (boost::get<double>(variable_array[static_cast<int>(
-                                 MaterialPropertyLib::Variable::temperature)]) -
-                             x_ref),
-                1.e-10);
+    ASSERT_NEAR(
+        boost::get<double>(linear_property.value(variable_array)),
+        y_ref * (1 + m * (boost::get<double>(variable_array[static_cast<int>(
+                              MaterialPropertyLib::Variable::temperature)]) -
+                          x_ref)),
+        1.e-10);
     ASSERT_EQ(
         boost::get<double>(linear_property.dValue(
             variable_array, MaterialPropertyLib::Variable::phase_pressure)),
         0.0);
-    ASSERT_EQ(boost::get<double>(linear_property.dValue(
-                  variable_array, MaterialPropertyLib::Variable::temperature)),
-              m);
+    ASSERT_NEAR(
+        boost::get<double>(linear_property.dValue(
+            variable_array, MaterialPropertyLib::Variable::temperature)),
+        y_ref * m, 1.e-16);
     ASSERT_EQ(boost::get<double>(linear_property.d2Value(
                   variable_array,
                   MaterialPropertyLib::Variable::temperature,