From c66ebe7b9150df759cc464a611ab1386773f08b0 Mon Sep 17 00:00:00 2001
From: Hrvoje Jasak <h.jasak@wikki.co.uk>
Date: Thu, 30 Mar 2017 10:35:36 +0100
Subject: [PATCH] Bugfix: surface stability deltaT control.  Dirk Grunding

---
 .../setSurfaceStabilityDeltaT.H               | 55 +++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 applications/solvers/surfaceTracking/interTrackFoam/setSurfaceStabilityDeltaT.H

diff --git a/applications/solvers/surfaceTracking/interTrackFoam/setSurfaceStabilityDeltaT.H b/applications/solvers/surfaceTracking/interTrackFoam/setSurfaceStabilityDeltaT.H
new file mode 100644
index 000000000..818a0cdea
--- /dev/null
+++ b/applications/solvers/surfaceTracking/interTrackFoam/setSurfaceStabilityDeltaT.H
@@ -0,0 +1,55 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | foam-extend: Open Source CFD
+   \\    /   O peration     | Version:     4.0
+    \\  /    A nd           | Web:         http://www.foam-extend.org
+     \\/     M anipulation  | For copyright notice see file Copyright
+-------------------------------------------------------------------------------
+License
+    This file is part of foam-extend.
+
+    foam-extend is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by the
+    Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    foam-extend is distributed in the hope that it will be useful, but
+    WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+    General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with foam-extend.  If not, see <http://www.gnu.org/licenses/>.
+
+Global
+    setSurfaceStabilityDeltaT
+
+Description
+    Reset the timestep to maintain a constant maximum courant Number.
+    Reduction of time-step is immediate, but increase is damped to avoid
+    unstable oscillations.
+
+\*---------------------------------------------------------------------------*/
+
+if (adjustTimeStep)
+{
+    scalar maxDeltaTFact = maxCo/(CoNum + SMALL);
+    scalar deltaTFact = min(min(maxDeltaTFact, 1.0 + 0.1*maxDeltaTFact), 1.2);
+
+    runTime.setDeltaT
+    (
+        Foam::min
+        (
+            interface.surfStabCrit().value(),
+            Foam::min
+            (
+                deltaTFact*runTime.deltaT().value(),
+                maxDeltaT
+            )
+        )
+    );
+
+    Info<< "deltaT = " <<  runTime.deltaT().value() << endl;
+}
+
+// ************************************************************************* //