ENH: use lerp for valueFraction (mixed BCs) and field relaxation

Note:
  in some borderline cases (eg, PDRFoam) the multiplication order
  and rounding imposed by the lerp function may affect the
  results slightly.

  eg,  (valueFraction_ * this->patch().deltaCoeffs()*refValue_)
  vs.  (valueFraction_ * (this->patch().deltaCoeffs()*refValue_))

src/finiteArea/fields/faPatchFields/basic/mixed/mixedFaPatchField.C

@@ -198,12 +198,11 @@ void Foam::mixedFaPatchField<Type>::evaluate(const Pstream::commsTypes)
 
     Field<Type>::operator=
     (
-        valueFraction_*refValue_
-      +
-        (1.0 - valueFraction_)*
+        lerp
         (
-            this->patchInternalField()
-          + refGrad_/this->patch().deltaCoeffs()
+            this->patchInternalField() + refGrad_/this->patch().deltaCoeffs(),
+            refValue_,
+            valueFraction_
         )
     );
 
@@ -214,11 +213,12 @@ void Foam::mixedFaPatchField<Type>::evaluate(const Pstream::commsTypes)
 template<class Type>
 Foam::tmp<Foam::Field<Type>> Foam::mixedFaPatchField<Type>::snGrad() const
 {
-    return
+    return lerp
+    (
+        refGrad_,
+        (refValue_ - this->patchInternalField())*this->patch().deltaCoeffs(),
         valueFraction_
-       *(refValue_ - this->patchInternalField())
-       *this->patch().deltaCoeffs()
-      + (1.0 - valueFraction_)*refGrad_;
+    );
 }
 
 
@@ -238,9 +238,12 @@ Foam::tmp<Foam::Field<Type>> Foam::mixedFaPatchField<Type>::valueBoundaryCoeffs
     const tmp<scalarField>&
 ) const
 {
-    return
-         valueFraction_*refValue_
-       + (1.0 - valueFraction_)*refGrad_/this->patch().deltaCoeffs();
+    return lerp
+    (
+        refGrad_/this->patch().deltaCoeffs(),
+        refValue_,
+        valueFraction_
+    );
 }
 
 
@@ -256,9 +259,12 @@ template<class Type>
 Foam::tmp<Foam::Field<Type>>
 Foam::mixedFaPatchField<Type>::gradientBoundaryCoeffs() const
 {
-    return
-        valueFraction_*this->patch().deltaCoeffs()*refValue_
-      + (1.0 - valueFraction_)*refGrad_;
+    return lerp
+    (
+        refGrad_,
+        this->patch().deltaCoeffs()*refValue_,
+        valueFraction_
+    );
 }
 
 

src/finiteVolume/expressions/fields/fvPatchFields/exprMixedFvPatchField.C

@@ -234,25 +234,14 @@ Foam::exprMixedFvPatchField<Type>::exprMixedFvPatchField
     }
     else
     {
-        // Emulate mixedFvPatchField<Type>::evaluate,
+        // Like mixedFvPatchField<Type>::evaluate()
         // but avoid our own updateCoeffs
         if (!this->updated())
         {
-            this->parent_bctype::updateCoeffs();
+            mixedFvPatchField<Type>::updateCoeffs();
         }
 
-        Field<Type>::operator=
-        (
-            this->valueFraction()*this->refValue()
-          +
-            (1.0 - this->valueFraction())*
-            (
-                this->patchInternalField()
-              + this->refGrad()/this->patch().deltaCoeffs()
-            )
-        );
-
-        fvPatchField<Type>::evaluate();
+        mixedFvPatchField<Type>::evaluate();
     }
 }
 

src/finiteVolume/fields/fvPatchFields/basic/mixed/mixedFvPatchField.C

@@ -209,7 +209,6 @@ void Foam::mixedFvPatchField<Type>::rmap
 template<class Type>
 void Foam::mixedFvPatchField<Type>::evaluate(const Pstream::commsTypes)
 {
-
     if (!this->updated())
     {
         this->updateCoeffs();
@@ -217,11 +216,11 @@ void Foam::mixedFvPatchField<Type>::evaluate(const Pstream::commsTypes)
 
     Field<Type>::operator=
     (
-        valueFraction_*refValue_
-      + (1.0 - valueFraction_)
-       *(
-            this->patchInternalField()
-          + refGrad_/this->patch().deltaCoeffs()
+        lerp
+        (
+            this->patchInternalField() + refGrad_/this->patch().deltaCoeffs(),
+            refValue_,
+            valueFraction_
         )
     );
 
@@ -233,11 +232,12 @@ template<class Type>
 Foam::tmp<Foam::Field<Type>>
 Foam::mixedFvPatchField<Type>::snGrad() const
 {
-    return
+    return lerp
+    (
+        refGrad_,
+        (refValue_ - this->patchInternalField())*this->patch().deltaCoeffs(),
         valueFraction_
-       *(refValue_ - this->patchInternalField())
-       *this->patch().deltaCoeffs()
-      + (1.0 - valueFraction_)*refGrad_;
+    );
 }
 
 
@@ -259,9 +259,12 @@ Foam::mixedFvPatchField<Type>::valueBoundaryCoeffs
     const tmp<scalarField>&
 ) const
 {
-    return
-        valueFraction_*refValue_
-      + (1.0 - valueFraction_)*refGrad_/this->patch().deltaCoeffs();
+    return lerp
+    (
+        refGrad_/this->patch().deltaCoeffs(),
+        refValue_,
+        valueFraction_
+    );
 }
 
 
@@ -277,9 +280,12 @@ template<class Type>
 Foam::tmp<Foam::Field<Type>>
 Foam::mixedFvPatchField<Type>::gradientBoundaryCoeffs() const
 {
-    return
-        valueFraction_*this->patch().deltaCoeffs()*refValue_
-      + (1.0 - valueFraction_)*refGrad_;
+    return lerp
+    (
+        refGrad_,
+        this->patch().deltaCoeffs()*refValue_,
+        valueFraction_
+    );
 }
 
 

src/finiteVolume/fields/fvPatchFields/derived/fixedJump/fixedJumpFvPatchField.C

@@ -212,7 +212,7 @@ void Foam::fixedJumpFvPatchField<Type>::relax()
         return;
     }
 
-    jump_ = relaxFactor_*jump_ + (1 - relaxFactor_)*jump0_;
+    jump_ = lerp(jump0_, jump_, relaxFactor_);
 
     if (timeIndex_ != this->db().time().timeIndex())
     {

src/finiteVolume/fields/fvPatchFields/derived/partialSlip/partialSlipFvPatchField.C

@@ -153,8 +153,12 @@ Foam::partialSlipFvPatchField<Type>::snGrad() const
 
     return
     (
-        valueFraction_*refValue_
-      + (1.0 - valueFraction_)*transform(I - sqr(nHat), pif) - pif
+        lerp
+        (
+            transform(I - sqr(nHat), pif),
+            refValue_,
+            valueFraction_
+        ) - pif
     )*this->patch().deltaCoeffs();
 }
 
@@ -174,10 +178,12 @@ void Foam::partialSlipFvPatchField<Type>::evaluate
 
     Field<Type>::operator=
     (
-        valueFraction_*refValue_
-      +
-        (1.0 - valueFraction_)
-       *transform(I - sqr(nHat), this->patchInternalField())
+        lerp
+        (
+            transform(I - sqr(nHat), this->patchInternalField()),
+            refValue_,
+            valueFraction_
+        )
     );
 
     parent_bctype::evaluate();

src/finiteVolume/fields/fvPatchFields/derived/phaseHydrostaticPressure/phaseHydrostaticPressureFvPatchScalarField.C

@@ -180,7 +180,7 @@ void Foam::phaseHydrostaticPressureFvPatchScalarField::operator=
 {
     fvPatchScalarField::operator=
     (
-        valueFraction()*refValue() + (1 - valueFraction())*ptf
+        lerp(ptf, refValue(), valueFraction())
     );
 }
 

src/finiteVolume/fields/fvPatchFields/derived/pressureDirectedInletOutletVelocity/pressureDirectedInletOutletVelocityFvPatchVectorField.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -204,8 +204,7 @@ void Foam::pressureDirectedInletOutletVelocityFvPatchVectorField::operator=
 {
     fvPatchField<vector>::operator=
     (
-        valueFraction()*(inletDir_*(inletDir_ & pvf))
-      + (1 - valueFraction())*pvf
+        lerp(pvf, inletDir_*(inletDir_ & pvf), valueFraction())
     );
 }
 

src/finiteVolume/fields/fvPatchFields/derived/pressureNormalInletOutletVelocity/pressureNormalInletOutletVelocityFvPatchVectorField.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -171,10 +171,11 @@ void Foam::pressureNormalInletOutletVelocityFvPatchVectorField::operator=
     const fvPatchField<vector>& pvf
 )
 {
+    tmp<vectorField> n = patch().nf();
+
     fvPatchField<vector>::operator=
     (
-        valueFraction()*(patch().nf()*(patch().nf() & pvf))
-      + (1 - valueFraction())*pvf
+        lerp(pvf, n()*(n() & pvf), valueFraction())
     );
 }
 

src/finiteVolume/fields/fvPatchFields/derived/pressurePermeableAlphaInletOutletVelocity/pressurePermeableAlphaInletOutletVelocityFvPatchVectorField.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -202,8 +202,7 @@ void Foam::pressurePermeableAlphaInletOutletVelocityFvPatchVectorField
 
     fvPatchField<vector>::operator=
     (
-        valueFraction()*(n()*(n() & pvf))
-      + (1 - valueFraction())*pvf
+        lerp(pvf, n()*(n() & pvf), valueFraction())
     );
 }
 

src/thermoTools/derivedFvPatchFields/externalWallHeatFluxTemperature/externalWallHeatFluxTemperatureFvPatchScalarField.C

@@ -317,11 +317,12 @@ void Foam::externalWallHeatFluxTemperatureFvPatchScalarField::updateCoeffs()
     scalarField qr(Tp.size(), Zero);
     if (qrName_ != "none")
     {
-        qr =
+        qr = lerp
+        (
+            qrPrevious_,
+            patch().lookupPatchField<volScalarField>(qrName_),
             qrRelaxation_
-           *patch().lookupPatchField<volScalarField>(qrName_)
-          + (1 - qrRelaxation_)*qrPrevious_;
-
+        );
         qrPrevious_ = qr;
     }
 
@@ -454,9 +455,8 @@ void Foam::externalWallHeatFluxTemperatureFvPatchScalarField::updateCoeffs()
         }
     }
 
-    valueFraction() =
-        relaxation_*valueFraction() + (1 - relaxation_)*valueFraction0;
-    refValue() = relaxation_*refValue() + (1 - relaxation_)*refValue0;
+    valueFraction() = lerp(valueFraction0, valueFraction(), relaxation_);
+    refValue() = lerp(refValue0, refValue(), relaxation_);
 
     mixedFvPatchScalarField::updateCoeffs();