[exercises][ff-pm][interface] Add an extra points task (horizontal velocity BCs)

exercises/exercise-coupling-ff-pm/README.md

@@ -195,6 +195,10 @@ The final result should look something like this:
 
 ![](../extradoc/ex_ff-pm-wave-interface.png)
 
+*Extra Points:*
+Rather than enforcing a pressure difference across the domain, an inflow velocity profile could be set.
+What changes to the boundary conditions in the free-flow domain would you make to introduce this? What conditions can be enforced on the right boundary?
+Hint: A relation between velocity and position is used for the vertical velocity component in the original form of the `initialAtPos` method.
 
 ### 2. Changing the porous medium model
 

exercises/solution/exercise-coupling-ff-pm/interface/CMakeLists.txt

@@ -18,5 +18,10 @@ dumux_add_test(NAME exercise_interface_coupling_ff-pm_c_solution
                LABELS ffpm
                COMPILE_DEFINITIONS EXNUMBER=3)
 
+dumux_add_test(NAME exercise_interface_coupling_ff-pm_extra_solution
+               SOURCES main.cc
+               LABELS ffpm
+               COMPILE_DEFINITIONS EXNUMBER=4)
+
 # add a symlink for each input file
 add_input_file_links()

exercises/solution/exercise-coupling-ff-pm/interface/freeflowsubproblem.hh

@@ -81,7 +81,7 @@ public:
 
         const auto& globalPos = scvf.dofPosition();
 
-#if EXNUMBER == 0 // flow from top to bottom
+#if EXNUMBER == 0  // flow from top to bottom
         if(onUpperBoundary_(globalPos))
         {
             values.setDirichlet(Indices::velocityXIdx);
@@ -93,7 +93,7 @@ public:
             values.setDirichlet(Indices::velocityXIdx);
             values.setDirichlet(Indices::velocityYIdx);
         }
-#else // flow flom left to right
+#elif EXNUMBER < 4 // flow flom left to right
         if(onLeftBoundary_(globalPos) || onRightBoundary_(globalPos))
             values.setDirichlet(Indices::pressureIdx);
         else
@@ -101,6 +101,14 @@ public:
             values.setDirichlet(Indices::velocityXIdx);
             values.setDirichlet(Indices::velocityYIdx);
         }
+#else
+        if (onRightBoundary_(globalPos))
+            values.setDirichlet(Indices::pressureIdx);
+        else
+        {
+            values.setDirichlet(Indices::velocityXIdx);
+            values.setDirichlet(Indices::velocityYIdx);
+        }
 #endif
 
         if(couplingManager().isCoupledEntity(CouplingManager::stokesIdx, scvf))
@@ -199,6 +207,9 @@ public:
         PrimaryVariables values(0.0);
 #if EXNUMBER == 0
         values[Indices::velocityYIdx] = -1e-6 * globalPos[0] * (this->gridGeometry().bBoxMax()[0] - globalPos[0]);
+#elif EXNUMBER == 4
+        values[Indices::velocityXIdx] = 1e-6 * (globalPos[1] - this->gridGeometry().bBoxMin()[1])
+                                      * (this->gridGeometry().bBoxMax()[1] - globalPos[1]);
 #else
         // set fixed pressures on the left and right boundary
         if(onLeftBoundary_(globalPos))
@@ -206,7 +217,6 @@ public:
         if(onRightBoundary_(globalPos))
             values[Indices::pressureIdx] = 0.0;
 #endif
-
         return values;
     }