[PL] add integral measure term to natural BCs

ProcessLib/BoundaryCondition/NeumannBoundaryConditionLocalAssembler.h

@@ -59,7 +59,8 @@ public:
             auto const& sm = Base::_shape_matrices[ip];
             auto const& wp = Base::_integration_method.getWeightedPoint(ip);
             _local_rhs.noalias() += sm.N * _neumann_bc_parameter(t, pos)[0] *
-                                    sm.detJ * wp.getWeight();
+                                    sm.detJ * wp.getWeight() *
+                                    sm.integralMeasure;
         }
 
         auto const indices = NumLib::getIndices(id, dof_table_boundary);

ProcessLib/BoundaryCondition/RobinBoundaryConditionLocalAssembler.h

@@ -71,9 +71,9 @@ public:
             // adding a alpha term to the diagonal of the stiffness matrix
             // and a alpha * u_0 term to the rhs vector
             _local_K.diagonal().noalias() +=
-                sm.N * alpha * sm.detJ * wp.getWeight();
-            _local_rhs.noalias() +=
-                sm.N * alpha * u_0 * sm.detJ * wp.getWeight();
+                sm.N * alpha * sm.detJ * wp.getWeight() * sm.integralMeasure;
+            _local_rhs.noalias() += sm.N * alpha * u_0 * sm.detJ *
+                                    wp.getWeight() * sm.integralMeasure;
         }
 
         auto const indices = NumLib::getIndices(id, dof_table_boundary);