Adding check for density < VSMALL to avoid FPE.

Modifying nanoNozzle tutorial to shorten the run and increase the density.

src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloud.C

@@ -548,6 +548,15 @@ void Foam::moleculeCloud::initialiseMolecules
                         zoneDict.lookup("numberDensity")
                     );
 
+                    if (numberDensity < VSMALL)
+                    {
+                        WarningIn("moleculeCloud::initialiseMolecules")
+                            << "numberDensity too small, not filling zone "
+                            << zone.name() << endl;
+
+                        continue;
+                    }
+
                     latticeCellScale = pow
                     (
                         latticeIds.size()/(det(latticeCellShape)*numberDensity),
@@ -572,6 +581,16 @@ void Foam::moleculeCloud::initialiseMolecules
                         zoneDict.lookup("massDensity")
                     );
 
+                    if (massDensity < VSMALL)
+                    {
+                        WarningIn("moleculeCloud::initialiseMolecules")
+                            << "massDensity too small, not filling zone "
+                            << zone.name() << endl;
+
+                        continue;
+                    }
+
+
                     latticeCellScale = pow
                     (
                         unitCellMass/(det(latticeCellShape)*massDensity),

tutorials/discreteMethods/molecularDynamics/mdFoam/nanoNozzle/system/controlDict

@@ -20,7 +20,7 @@ startTime       0;
 
 stopAt          endTime;
 
-endTime         1e-10;
+endTime         5e-12;
 
 deltaT          1e-15;
 

tutorials/discreteMethods/molecularDynamics/mdFoam/nanoNozzle/system/mdInitialiseDict

@@ -27,7 +27,7 @@ FoamFile
 
 sectionA
 {
-    massDensity             980;
+    massDensity             1004;
     temperature             298;
     bulkVelocity            (0.0 0.0 0.0);
     latticeIds
@@ -46,7 +46,7 @@ sectionA
 
 sectionB
 {
-    massDensity             980;
+    massDensity             1004;
     temperature             298;
     bulkVelocity            (0.0 0.0 0.0);
     latticeIds
@@ -65,7 +65,7 @@ sectionB
 
 sectionC
 {
-    massDensity             980;
+    massDensity             1004;
     temperature             298;
     bulkVelocity            (0.0 0.0 0.0);
     latticeIds