From 35439753ef974131328ace4fcc1a39aa0bd331eb Mon Sep 17 00:00:00 2001
From: Henry Weller <http://cfd.direct>
Date: Sat, 12 Dec 2015 09:00:42 +0000
Subject: [PATCH] PairCollision: stabilize normalization of the force direction
 for low force Resolves bug-report
 http://www.openfoam.org/mantisbt/view.php?id=1948

---
 .../Kinematic/CollisionModel/PairCollision/PairCollision.C      | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairCollision.C b/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairCollision.C
index 185bfb2f52..54131aa829 100644
--- a/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairCollision.C
+++ b/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairCollision.C
@@ -246,7 +246,7 @@ void Foam::PairCollision<CloudType>::wallInteraction()
 
                     vector pW = nearPt - pos;
 
-                    scalar normalAlignment = normal & pW/mag(pW);
+                    scalar normalAlignment = normal & pW/(mag(pW) + ROOTSMALL);
 
                     // Find the patchIndex and wallData for WallSiteData object
                     label patchI = patchID[realFaceI - mesh.nInternalFaces()];