From 0ef0eb1e6a555cd154f0d0642778cde25c763235 Mon Sep 17 00:00:00 2001
From: Hrvoje Jasak <h.jasak@wikki.co.uk>
Date: Fri, 25 May 2018 10:11:29 +0100
Subject: [PATCH] Robustness improvement on top AMG level

---
 .../amg/amgPolicy/clusterAmgPolicy.C          |  3 +++
 src/lduSolvers/amg/coarseAmgLevel.C           | 20 +++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/lduSolvers/amg/amgPolicy/clusterAmgPolicy.C b/src/lduSolvers/amg/amgPolicy/clusterAmgPolicy.C
index 26c6e50fb..18d778652 100644
--- a/src/lduSolvers/amg/amgPolicy/clusterAmgPolicy.C
+++ b/src/lduSolvers/amg/amgPolicy/clusterAmgPolicy.C
@@ -525,6 +525,9 @@ Foam::clusterAmgPolicy::clusterAmgPolicy
             "clusterAmgPolicy::clusterAmgPolicy\n"
             "(\n"
             "    const lduMatrix& matrix,\n"
+            "    const FieldField<Field, scalar>& bouCoeffs,\n"
+            "    const FieldField<Field, scalar>& intCoeffs,\n"
+            "    const lduInterfaceFieldPtrsList& interfaceFields,\n"
             "    const label groupSize,\n"
             "    const label minCoarseEqns\n"
             ")"
diff --git a/src/lduSolvers/amg/coarseAmgLevel.C b/src/lduSolvers/amg/coarseAmgLevel.C
index 57c9b167f..5e25384dc 100644
--- a/src/lduSolvers/amg/coarseAmgLevel.C
+++ b/src/lduSolvers/amg/coarseAmgLevel.C
@@ -193,11 +193,9 @@ void Foam::coarseAmgLevel::solve
 {
     lduSolverPerformance coarseSolverPerf;
 
-    label maxIter = Foam::min(2*policyPtr_->minCoarseEqns(), 1000);
-
     dictionary topLevelDict;
     topLevelDict.add("minIter", 1);
-    topLevelDict.add("maxIter", maxIter);
+    topLevelDict.add("maxIter", 500);
     topLevelDict.add("tolerance", tolerance);
     topLevelDict.add("relTol", relTol);
 
@@ -220,7 +218,6 @@ void Foam::coarseAmgLevel::solve
     if (matrixPtr_->matrix().symmetric())
     {
         // Note: must change preconditioner to C0.  HJ. 10/Oct/2017
-        // topLevelDict.add("preconditioner", "Cholesky");
         topLevelDict.add("preconditioner", "ILUC0");
 
         coarseSolverPerf = cgSolver
@@ -248,6 +245,21 @@ void Foam::coarseAmgLevel::solve
         ).solve(x, b, cmpt);
     }
 
+    // Check for convergence
+    const scalar magInitialRes = mag(coarseSolverPerf.initialResidual());
+    const scalar magFinalRes = mag(coarseSolverPerf.finalResidual());
+
+    if (magFinalRes > magInitialRes && magInitialRes > SMALL)
+    {
+        if (blockLduMatrix::debug)
+        {
+            Info<< "Divergence in top AMG level" << endl;
+            coarseSolverPerf.print();
+        }
+
+        x = 0;
+    }
+
     // Restore debug
     blockLduMatrix::debug = oldDebug;