Clear up old moving boundary

framework/include/userobject/ElementSubdomainModifier.h

@@ -90,6 +90,9 @@ class ElementSubdomainModifier : public ElementUserObject
   // Change the subdomain ID of all ancestor elements
   void setAncestorsSubdomainIDs(const SubdomainID & subdomain_id, const dof_id_type & elem_id);
 
+  // Clear old moving boundaries
+  void clearOldMovingBoundary(MooseMesh & mesh);
+
   // Elements on the undisplaced mesh whose subdomain IDs have changed
   std::vector<const Elem *> _moved_elems;
 

framework/src/userobject/ElementSubdomainModifier.C

@@ -136,6 +136,11 @@ ElementSubdomainModifier::finalize()
     updateBoundaryInfo(_displaced_problem->mesh(), _moved_displaced_elems);
   }
 
+  clearOldMovingBoundary(_mesh);
+
+  if (_displaced_problem)
+    clearOldMovingBoundary(_displaced_problem->mesh());
+
   // Reinit equation systems
   _fe_problem.meshChanged();
 
@@ -159,6 +164,30 @@ ElementSubdomainModifier::finalize()
   _fe_problem.initElementStatefulProps(movedElemsRange());
 }
 
+void
+ElementSubdomainModifier::clearOldMovingBoundary(MooseMesh & mesh)
+{
+  std::vector<std::pair<Elem *, unsigned int>> to_be_cleared;
+  //auto & elem_side_bnd_ids = _mesh.getMesh().get_sideset_map();
+  BoundaryInfo & bnd_info = mesh.getMesh().get_boundary_info();
+  auto & elem_side_bnd_ids = bnd_info.get_sideset_map();
+  for (const auto & pr : elem_side_bnd_ids)
+  {
+    if (pr.second.second == _moving_boundary_id)
+    {
+      Elem * elem = _mesh.elemPtr(pr.first->id());
+      const Elem * neighbor = elem->neighbor_ptr(pr.second.first);
+      if (elem->subdomain_id() == neighbor->subdomain_id())
+        to_be_cleared.emplace_back(elem, pr.second.first);
+    }
+  }
+
+  for (auto & elem_side: to_be_cleared)
+  {
+    bnd_info.remove_side(elem_side.first, elem_side.second);
+  }
+}
+
 void
 ElementSubdomainModifier::updateBoundaryInfo(MooseMesh & mesh,
                                              const std::vector<const Elem *> & moved_elems)