[MPL] New h/cpp files in MPL/Utils containing

getFluidDensity and getFluidDensityAndViscosity for
single phase flow models.

MaterialLib/MPL/Utils/GetFluidDensityAndViscosity.cpp

+/**
+ * \file
+ * \copyright
+ * Copyright (c) 2012-2025, OpenGeoSys Community (http://www.opengeosys.org)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/project/license
+ *
+ * Created on January 21, 2025, 4:10 PM
+ */
+
+#include "GetFluidDensityAndViscosity.h"
+
+#include "MaterialLib/MPL/Phase.h"
+#include "MaterialLib/MPL/VariableType.h"
+#include "ParameterLib/SpatialPosition.h"
+
+namespace MaterialPropertyLib
+{
+
+double getFluidDensity(double const t, double const dt,
+                       ParameterLib::SpatialPosition const& pos,
+                       Phase const& fluid_phase, VariableArray& vars)
+{
+    // Compute density:
+    // Quick workaround: If fluid density is described as ideal gas, then
+    // the molar mass must be passed to the MPL::IdealGasLaw via the
+    // variable_array and the fluid must have the property
+    // MPL::PropertyType::molar_mass. For other density models (e.g.
+    // Constant), it is not mandatory to specify the molar mass.
+    if (fluid_phase.hasProperty(MaterialPropertyLib::PropertyType::molar_mass))
+    {
+        vars.molar_mass =
+            fluid_phase.property(MaterialPropertyLib::PropertyType::molar_mass)
+                .template value<double>(vars, pos, t, dt);
+    }
+
+    return fluid_phase[MaterialPropertyLib::PropertyType::density]
+        .template value<double>(vars, pos, t, dt);
+}
+
+std::tuple<double, double> getFluidDensityAndViscosity(
+    double const t, double const dt, ParameterLib::SpatialPosition const& pos,
+    MaterialPropertyLib::Phase const& fluid_phase,
+    MaterialPropertyLib::VariableArray& vars)
+{
+    auto const fluid_density = getFluidDensity(t, dt, pos, fluid_phase, vars);
+
+    assert(fluid_density > 0.);
+    vars.density = fluid_density;
+
+    auto const viscosity =
+        fluid_phase[MaterialPropertyLib::PropertyType::viscosity]
+            .template value<double>(vars, pos, t, dt);
+
+    return {fluid_density, viscosity};
+}
+
+}  // namespace MaterialPropertyLib

MaterialLib/MPL/Utils/GetFluidDensityAndViscosity.h

+/**
+ * \file
+ * \copyright
+ * Copyright (c) 2012-2025, OpenGeoSys Community (http://www.opengeosys.org)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/project/license
+ *
+ * Created on January 21, 2025, 4:10 PM
+ */
+
+#pragma once
+
+#include <tuple>
+
+namespace ParameterLib
+{
+class SpatialPosition;
+}
+namespace MaterialPropertyLib
+{
+class Phase;
+class VariableArray;
+
+/// It computes fluid density and viscosity for single phase flow model.
+std::tuple<double, double> getFluidDensityAndViscosity(
+    double const t, double const dt, ParameterLib::SpatialPosition const& pos,
+    Phase const& fluid_phase, VariableArray& vars);
+
+/// It computes fluid density for single phase flow model.
+double getFluidDensity(double const t, double const dt,
+                       ParameterLib::SpatialPosition const& pos,
+                       Phase const& fluid_phase, VariableArray& vars);
+}  // namespace MaterialPropertyLib