ENH: additional feedback about controlled mesh motion update type

- ensure that the updateControl is "non-sticky" on re-read,
  even if we do not support runtime-modifiable here

STYLE: add syntax example (wingMotion), but with updateInterval 1

src/dynamicFvMesh/dynamicFvMesh/dynamicFvMesh.C

@@ -41,9 +41,7 @@ namespace Foam
 
 void Foam::dynamicFvMesh::readDict()
 {
-    IOdictionary dict
+    IOobject dictHeader
-    (
-        IOobject
     (
         "dynamicMeshDict",
         thisDb().time().constant(),
@@ -51,10 +49,25 @@ void Foam::dynamicFvMesh::readDict()
         IOobject::MUST_READ_IF_MODIFIED,
         IOobject::NO_WRITE,
         false // Do not register
-        )
     );
 
+    if (dictHeader.typeHeaderOk<IOdictionary>(false, false))
+    {
+        IOdictionary dict(dictHeader);
         timeControl_.read(dict);
+
+        if (!timeControl_.always())
+        {
+            // Feedback about the trigger mechanism
+            Info<< "Controlled mesh update triggered on "
+                << timeControl_.type() << nl;
+        }
+    }
+    else
+    {
+        // Ensure it is pass-through
+        timeControl_.clear();
+    }
 }
 
 
@@ -138,7 +151,8 @@ bool Foam::dynamicFvMesh::controlledUpdate()
         if (!timeControl_.always())
         {
             // Feedback that update has been triggered
-            Info<< "Mesh update triggered based on " << timeControl_.name() << nl;
+            Info<< "Mesh update triggered based on "
+                << timeControl_.type() << nl;
         }
 
         return this->update();

tutorials/incompressible/pimpleFoam/RAS/wingMotion/wingMotion2D_pimpleFoam/constant/dynamicMeshDict

@@ -20,6 +20,11 @@ motionSolverLibs (sixDoFRigidBodyMotion);
 
 motionSolver    sixDoFRigidBodyMotion;
 
+// Not necessarily useful here, but can have different motion updates types
+updateControl   timeStep;
+updateInterval  1;
+
+
 patches         (wing);
 innerDistance   0.3;
 outerDistance   1;