From f05ab894d36c03ec322b422dbf813e36c823b361 Mon Sep 17 00:00:00 2001
From: Henry Weller <http://cfd.direct>
Date: Fri, 26 May 2023 15:25:01 +0100
Subject: [PATCH] waveForcing: Added optional lambdaBoundary specification

which allows lambda to set higher in the cells adjacent to the boundary which is
particularly useful when solving for waves in a domain with no mean-flow and
wave BCs to avoid numerical stability problems where the specified wave flow
reverses into the domain.  The alternative is to use symmetry rather than wave
BCs on the side patches which is stable without using lambdaBoundary but there
is modest distortion of the wave profile adjacent to the side patches which does
not propagate into the domain due to the wave forcing.
---
 src/waves/fvModels/forcing/forcing.C          | 25 +++++++++++++++++++
 src/waves/fvModels/forcing/forcing.H          |  3 +++
 src/waves/fvModels/waveForcing/waveForcing.H  |  4 +++
 .../floatingObjectWaves/constant/fvModels     |  3 ++-
 .../floatingObjectWaves/system/controlDict    |  2 +-
 5 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/src/waves/fvModels/forcing/forcing.C b/src/waves/fvModels/forcing/forcing.C
index a51c5bc5af..895fd55258 100644
--- a/src/waves/fvModels/forcing/forcing.C
+++ b/src/waves/fvModels/forcing/forcing.C
@@ -50,6 +50,14 @@ void Foam::fv::forcing::readCoeffs()
             coeffs().lookup(lambda_.name())
         );
 
+    lambdaBoundary_ =
+        dimensionedScalar
+        (
+            lambdaBoundary_.name(),
+            lambdaBoundary_.dimensions(),
+            coeffs().lookupOrDefault(lambdaBoundary_.name(), 0)
+        );
+
     const bool foundScale = coeffs().found("scale");
     const bool foundOgn = coeffs().found("origin");
     const bool foundDir = coeffs().found("direction");
@@ -157,6 +165,22 @@ Foam::tmp<Foam::volScalarField::Internal> Foam::fv::forcing::forceCoeff
         volScalarField::Internal::New(typedName("forceCoeff"), lambda_*scale)
     );
 
+    // Damp the cells adjacent to the boundary with lambdaBoundary if specified
+    if (lambdaBoundary_.value() > 0)
+    {
+        const fvBoundaryMesh& bm = mesh().boundary();
+
+        forAll(bm, patchi)
+        {
+            if (!bm[patchi].coupled())
+            {
+                UIndirectList<scalar>(tforceCoeff.ref(), bm[patchi].faceCells())
+              = lambdaBoundary_.value()
+               *Field<scalar>(scale, bm[patchi].faceCells());
+            }
+        }
+    }
+
     // Write out the force coefficient for debugging
     if (debug && mesh().time().writeTime())
     {
@@ -185,6 +209,7 @@ Foam::fv::forcing::forcing
 :
     fvModel(name, modelType, mesh, dict),
     lambda_("lambda", dimless/dimTime, NaN),
+    lambdaBoundary_("lambdaBoundary", dimless/dimTime, 0),
     scale_(nullptr),
     origins_(),
     directions_()
diff --git a/src/waves/fvModels/forcing/forcing.H b/src/waves/fvModels/forcing/forcing.H
index fb918a8d30..989d18de82 100644
--- a/src/waves/fvModels/forcing/forcing.H
+++ b/src/waves/fvModels/forcing/forcing.H
@@ -65,6 +65,9 @@ protected:
         //- Damping coefficient [1/s]
         dimensionedScalar lambda_;
 
+        //- Optional boundary damping coefficient [1/s]
+        dimensionedScalar lambdaBoundary_;
+
         //- The scaling function
         autoPtr<Function1<scalar>> scale_;
 
diff --git a/src/waves/fvModels/waveForcing/waveForcing.H b/src/waves/fvModels/waveForcing/waveForcing.H
index 12c4e63477..304dcce003 100644
--- a/src/waves/fvModels/waveForcing/waveForcing.H
+++ b/src/waves/fvModels/waveForcing/waveForcing.H
@@ -63,6 +63,10 @@ Usage
         }
 
         lambda          0.5; // Forcing coefficient
+
+     // lambda          2;   // Optional boundary forcing coefficient
+                             // Useful when wave BCs are specified
+                             // without mean flow
     }
     \endverbatim
 
diff --git a/tutorials/incompressibleVoF/floatingObjectWaves/constant/fvModels b/tutorials/incompressibleVoF/floatingObjectWaves/constant/fvModels
index 24ad7bfbe6..870980f48d 100644
--- a/tutorials/incompressibleVoF/floatingObjectWaves/constant/fvModels
+++ b/tutorials/incompressibleVoF/floatingObjectWaves/constant/fvModels
@@ -45,7 +45,8 @@ forcing
         duration    0.5;
     }
 
-    lambda      25;
+    lambda          5;
+    lambdaBoundary  25;
 }
 
 
diff --git a/tutorials/incompressibleVoF/floatingObjectWaves/system/controlDict b/tutorials/incompressibleVoF/floatingObjectWaves/system/controlDict
index edf8b160fa..c3dac56239 100644
--- a/tutorials/incompressibleVoF/floatingObjectWaves/system/controlDict
+++ b/tutorials/incompressibleVoF/floatingObjectWaves/system/controlDict
@@ -65,7 +65,7 @@ functions0
 DebugSwitches
 {
     // Write the forcing and damping scale and force fields
-    // forcing   1;
+    forcing   1;
 }
 
 // ************************************************************************* //