ENH: support multiple weights on some field function objects (#1930)

- weight fields are combined by multiplication

  - volFieldValue:
    * 0-N scalar fields

  - surfaceFieldValue:
    * 0-N scalar fields
    * 0-1 vector fields

  In some cases this can be used to avoid creating additional
  fields.

      weightFields  (rho U);
  vs.
      derivedFields (rhoU);
      weightField   rhoU;

src/functionObjects/field/fieldValues/surfaceFieldValue/surfaceFieldValue.C

@@ -645,9 +645,14 @@ void Foam::functionObjects::fieldValues::surfaceFieldValue::writeFileHeader
         writeHeaderValue(os, "Area", totalArea_);
         writeHeaderValue(os, "Scale factor", scaleFactor_);
 
-        if (weightFieldName_ != "none")
+        if (weightFieldNames_.size())
         {
-            writeHeaderValue(os, "Weight field", weightFieldName_);
+            writeHeaderValue
+            (
+                os,
+                "Weight field",
+                flatOutput(weightFieldNames_, FlatOutput::BareComma{})
+            );
         }
 
         writeCommented(os, "Time");
@@ -915,7 +920,7 @@ Foam::functionObjects::fieldValues::surfaceFieldValue::surfaceFieldValue
     needsUpdate_(true),
     writeArea_(false),
     selectionNames_(),
-    weightFieldName_("none"),
+    weightFieldNames_(),
     totalArea_(0),
     nFaces_(0),
     faceId_(),
@@ -949,7 +954,7 @@ Foam::functionObjects::fieldValues::surfaceFieldValue::surfaceFieldValue
     needsUpdate_(true),
     writeArea_(false),
     selectionNames_(),
-    weightFieldName_("none"),
+    weightFieldNames_(),
     totalArea_(0),
     nFaces_(0),
     faceId_(),
@@ -971,7 +976,8 @@ bool Foam::functionObjects::fieldValues::surfaceFieldValue::read
 
     needsUpdate_ = true;
     writeArea_ = dict.getOrDefault("writeArea", false);
-    weightFieldName_ = "none";
+    weightFieldNames_.clear();
+
     totalArea_ = 0;
     nFaces_ = 0;
     faceId_.clear();
@@ -1054,11 +1060,29 @@ bool Foam::functionObjects::fieldValues::surfaceFieldValue::read
                 << exit(FatalIOError);
         }
 
-        if (dict.readIfPresent("weightField", weightFieldName_))
+        // Can have "weightFields" or "weightField"
+
+        bool missing = true;
+        if (dict.readIfPresent("weightFields", weightFieldNames_))
         {
-            Info<< "    weight field  = " << weightFieldName_ << nl;
+            missing = false;
         }
         else
+        {
+            weightFieldNames_.resize(1);
+
+            if (dict.readIfPresent("weightField", weightFieldNames_.first()))
+            {
+                missing = false;
+                if ("none" == weightFieldNames_.first())
+                {
+                    // "none" == no weighting
+                    weightFieldNames_.clear();
+                }
+            }
+        }
+
+        if (missing)
         {
             // Suggest possible alternative unweighted operation?
             FatalIOErrorInFunction(dict)
@@ -1069,6 +1093,16 @@ bool Foam::functionObjects::fieldValues::surfaceFieldValue::read
                 << "or use a different operation."
                 << exit(FatalIOError);
         }
+
+        Info<< "    weight field  = ";
+        if (weightFieldNames_.empty())
+        {
+            Info<< "none" << nl;
+        }
+        else
+        {
+            Info<< flatOutput(weightFieldNames_) << nl;
+        }
     }
 
     // Backwards compatibility for v1612 and older
@@ -1177,46 +1211,79 @@ bool Foam::functionObjects::fieldValues::surfaceFieldValue::write()
         }
     }
 
-    // Only a few weight types (scalar, vector)
+
-    if (weightFieldName_ != "none")
+    // Check availability and type of weight field
+    // Only support a few weight types:
+    // scalar: 0-N fields
+    // vector: 0-1 fields
+
+    // Default is a zero-size scalar weight field (ie, weight = 1)
+    scalarField scalarWeights;
+    vectorField vectorWeights;
+
+    for (const word& weightName : weightFieldNames_)
     {
-        if (validField<scalar>(weightFieldName_))
+        if (validField<scalar>(weightName))
         {
-            scalarField weightField
+            tmp<scalarField> tfld = getFieldValues<scalar>(weightName, true);
-            (
-                getFieldValues<scalar>(weightFieldName_, true)
-            );
 
-            // Process the fields
+            if (scalarWeights.empty())
-            writeAll(Sf, weightField, points, faces);
+            {
+                scalarWeights = tfld;
+            }
+            else
+            {
+                scalarWeights *= tfld;
+            }
         }
-        else if (validField<vector>(weightFieldName_))
+        else if (validField<vector>(weightName))
         {
-            vectorField weightField
+            tmp<vectorField> tfld = getFieldValues<vector>(weightName, true);
-            (
-                getFieldValues<vector>(weightFieldName_, true)
-            );
 
-            // Process the fields
+            if (vectorWeights.empty())
-            writeAll(Sf, weightField, points, faces);
+            {
+                vectorWeights = tfld;
+            }
+            else
+            {
+                FatalErrorInFunction
+                    << "weightField " << weightName
+                    << " - only one vector weight field allowed. " << nl
+                    << "weights: " << flatOutput(weightFieldNames_) << nl
+                    << abort(FatalError);
+            }
         }
-        else
+        else if (weightName != "none")
         {
+            // Silently ignore "none", flag everything else as an error
+
+            // TBD: treat missing "rho" like incompressible with rho = 1
+            // and/or provided rhoRef value
+
             FatalErrorInFunction
-                << "weightField " << weightFieldName_
+                << "weightField " << weightName
-                << " not found or an unsupported type"
+                << " not found or an unsupported type" << nl
                 << abort(FatalError);
         }
     }
+
+
+    // Process the fields
+    if (vectorWeights.size())
+    {
+        if (scalarWeights.size())
+        {
+            vectorWeights *= scalarWeights;
+        }
+
+        writeAll(Sf, vectorWeights, points, faces);
+    }
     else
     {
-        // Default is a zero-size scalar weight field (ie, weight = 1)
+        writeAll(Sf, scalarWeights, points, faces);
-        scalarField weightField;
-
-        // Process the fields
-        writeAll(Sf, weightField, points, faces);
     }
 
+
     if (operation_ != opNone)
     {
         file() << endl;

src/functionObjects/field/fieldValues/surfaceFieldValue/surfaceFieldValue.H

@@ -84,7 +84,7 @@ Usage
         names           (<zone-name> <zone-regex>);
 
         postOperation   none;
-        weightField     alpha1;
+        weightFields    (rho U);
         scaleFactor     1.0;
         writeArea       false;
         surfaceFormat   none;
@@ -105,7 +105,8 @@ Usage
       names        | Extended selection                 | word/regex list | no | -
       operation    | Operation type: see below          | word |  yes  | -
       postOperation | Post-operation type: see below    | word |  no   | none
-      weightField  | Name of field to apply weighting   | word |  no   | none
+      weightField   | Name of field to apply weighting   | word |  maybe |
+      weightFields  | Names of fields to apply weighting | wordList | maybe |
       scaleFactor  | Output value scaling factor        | scalar |  no  | 1.0
       writeArea    | Write the surface area             | bool |  no   | false
       surfaceFormat | Output value format               | word <!--
@@ -403,8 +404,8 @@ protected:
         //- Extended selections
         wordRes selectionNames_;
 
-        //- Weight field name - optional
+        //- Weight field name(s) - optional
-        word weightFieldName_;
+        wordList weightFieldNames_;
 
         //- Total area of the surfaceFieldValue
         scalar totalArea_;

src/functionObjects/field/fieldValues/surfaceFieldValue/surfaceFieldValueTemplates.C

@@ -118,7 +118,7 @@ Foam::functionObjects::fieldValues::surfaceFieldValue::getFieldValues
     if (mandatory)
     {
         FatalErrorInFunction
-            << "Field " << fieldName << " not found in database"
+            << "Field " << fieldName << " not found in database" << nl
             << abort(FatalError);
     }
 

src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.C

@@ -135,9 +135,15 @@ void Foam::functionObjects::fieldValues::volFieldValue::writeFileHeader
 ) const
 {
     volRegion::writeFileHeader(*this, os);
-    if (weightFieldName_ != "none")
+
+    if (weightFieldNames_.size())
     {
-        writeHeaderValue(os, "Weight field", weightFieldName_);
+        writeHeaderValue
+        (
+            os,
+            "Weight field",
+            flatOutput(weightFieldNames_, FlatOutput::BareComma{})
+        );
     }
 
     writeCommented(os, "Time");
@@ -210,7 +216,7 @@ Foam::functionObjects::fieldValues::volFieldValue::volFieldValue
             true  // Failsafe behaviour
         )
     ),
-    weightFieldName_("none")
+    weightFieldNames_()
 {
     read(dict);
     writeFileHeader(file());
@@ -237,7 +243,7 @@ Foam::functionObjects::fieldValues::volFieldValue::volFieldValue
             true  // Failsafe behaviour
         )
     ),
-    weightFieldName_("none")
+    weightFieldNames_()
 {
     read(dict);
 }
@@ -252,15 +258,33 @@ bool Foam::functionObjects::fieldValues::volFieldValue::read
 {
     fieldValue::read(dict);
 
-    weightFieldName_ = "none";
+    weightFieldNames_.clear();
 
     if (usesWeight())
     {
-        if (dict.readIfPresent("weightField", weightFieldName_))
+        // Can have "weightFields" or "weightField"
+
+        bool missing = true;
+        if (dict.readIfPresent("weightFields", weightFieldNames_))
         {
-            Info<< "    weight field = " << weightFieldName_;
+            missing = false;
         }
         else
+        {
+            weightFieldNames_.resize(1);
+
+            if (dict.readIfPresent("weightField", weightFieldNames_.first()))
+            {
+                missing = false;
+                if ("none" == weightFieldNames_.first())
+                {
+                    // "none" == no weighting
+                    weightFieldNames_.clear();
+                }
+            }
+        }
+
+        if (missing)
         {
             // Suggest possible alternative unweighted operation?
             FatalIOErrorInFunction(dict)
@@ -271,6 +295,16 @@ bool Foam::functionObjects::fieldValues::volFieldValue::read
                 << "or use a different operation."
                 << exit(FatalIOError);
         }
+
+        Info<< "    weight field  = ";
+        if (weightFieldNames_.empty())
+        {
+            Info<< "none" << nl;
+        }
+        else
+        {
+            Info<< flatOutput(weightFieldNames_) << nl;
+        }
     }
 
     Info<< nl << endl;
@@ -297,14 +331,45 @@ bool Foam::functionObjects::fieldValues::volFieldValue::write()
         V = filterField(fieldValue::mesh_.V());
     }
 
-    // Weight field - zero-size means weight = 1
+    // Check availability and type of weight field
-    scalarField weightField;
+    // Only support a few weight types:
-    if (weightFieldName_ != "none")
+    // scalar: 0-N fields
+
+    // Default is a zero-size scalar weight field (ie, weight = 1)
+    scalarField scalarWeights;
+
+    for (const word& weightName : weightFieldNames_)
     {
-        weightField = getFieldValues<scalar>(weightFieldName_, true);
+        if (validField<scalar>(weightName))
+        {
+            tmp<scalarField> tfld = getFieldValues<scalar>(weightName, true);
+
+            if (scalarWeights.empty())
+            {
+                scalarWeights = tfld;
+            }
+            else
+            {
+                scalarWeights *= tfld;
+            }
+        }
+        else if (weightName != "none")
+        {
+            // Silently ignore "none", flag everything else as an error
+
+            // TBD: treat missing "rho" like incompressible with rho = 1
+            // and/or provided rhoRef value
+
+            FatalErrorInFunction
+                << "weightField " << weightName
+                << " not found or an unsupported type" << nl
+                << abort(FatalError);
+        }
     }
 
-    writeAll(V, weightField);
+
+    // Process the fields
+    writeAll(V, scalarWeights);
 
     if (Pstream::master())
     {

src/functionObjects/field/fieldValues/volFieldValue/volFieldValue.H

@@ -69,7 +69,8 @@ Usage
       name         | Name for regionType                | word |  yes  | -
       operation    | Operation type: see below          | word |  yes  | -
       postOperation | Post-operation type: see below    | word |  no   | none
-      weightField  | Name of field to apply weighting   | word |  no   | none
+      weightField   | Name of field to apply weighting   | word |  maybe |
+      weightFields  | Names of fields to apply weighting | wordList | maybe |
     \endtable
 
     The inherited entries are elaborated in:
@@ -214,8 +215,8 @@ protected:
         //- Optional post-evaluation operation
         postOperationType postOperation_;
 
-        //- Weight field name - only used for weighted modes
+        //- Weight field name(s) - optional
-        word weightFieldName_;
+        wordList weightFieldNames_;
 
 
     // Protected Member Functions
@@ -233,7 +234,7 @@ protected:
         //  Checks for availability on any processor.
         inline bool canWeight(const scalarField& weightField) const;
 
-        //- True if the field name is valid (exists, and a supported type)
+        //- Return true if the field name is valid
         template<class Type>
         bool validField(const word& fieldName) const;
 

src/functionObjects/field/fieldValues/volFieldValue/volFieldValueTemplates.C

@@ -71,7 +71,7 @@ Foam::functionObjects::fieldValues::volFieldValue::getFieldValues
     if (mandatory)
     {
         FatalErrorInFunction
-            << "Field " << fieldName << " not found in database"
+            << "Field " << fieldName << " not found in database" << nl
             << abort(FatalError);
     }
 

tutorials/compressible/rhoSimpleFoam/squareBend/system/sampling

@@ -182,6 +182,7 @@ areaAverage
 
     operation       weightedAreaAverage;
     weightField     rhoU;
+    weightFields    ( rho U none );  // 2012 and later
     fields          ( p pTotal );
 }
 
@@ -194,6 +195,7 @@ areaIntegrate
 
     operation       weightedAreaIntegrate;
     weightField     rhoU;
+    weightFields    ( rho U );  // 2012 and later
     fields          ( T );
 }