functionObject: Added executeAtStart

By default most functionObjects now execute and write at the start-time except
those that perform averaging (fieldAverage, dsmcFields) which cannot be executed
until the end of the first time-step.  There is also a new optional
functionObject dictionary entry "executeAtStart" which defaults to true but can
be set false if the execution and results of the functionObject are not required
or appropriate at the start-time.

A result of this change is that time logs of forces, sampling etc. now include a
values for time 0.

src/functionObjects/field/fieldAverage/fieldAverage.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2011-2018 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2019 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -151,7 +151,7 @@ void Foam::functionObjects::fieldAverage::calcAverages()
         periodIndex_++;
     }
 
-    Log << type() << " " << name() << " write:" << nl
+    Log << type() << " " << name() << nl
         << "    Calculating averages" << nl;
 
     addMeanSqrToPrime2Mean<scalar, scalar>();

src/functionObjects/field/fieldAverage/fieldAverage.H

@@ -286,6 +286,12 @@ public:
         //- Read the field average data
         virtual bool read(const dictionary&);
 
+        //- Do not average at the start of the run
+        virtual bool executeAtStart() const
+        {
+            return false;
+        }
+
         //- Calculate the field averages
         virtual bool execute();
 

src/functionObjects/lagrangian/dsmcFields/dsmcFields.H

@@ -89,6 +89,12 @@ public:
         //- Read the dsmcFields data
         virtual bool read(const dictionary&);
 
+        //- Do not evaluate the state at the start of the run
+        virtual bool executeAtStart() const
+        {
+            return false;
+        }
+
         //- Do nothing
         virtual bool execute();