Add free-surface LBM showcase: Zalesak's rotating disk

apps/showcases/FreeSurface/CMakeLists.txt

@@ -46,3 +46,7 @@ waLBerla_add_executable(NAME    RisingBubble
 waLBerla_add_executable(NAME    TaylorBubble
                         FILES   TaylorBubble.cpp
                         DEPENDS blockforest boundary core domain_decomposition field lbm postprocessing timeloop vtk)
+
+waLBerla_add_executable(NAME    ZalesakDisk
+                        FILES   ZalesakDisk.cpp
+                        DEPENDS blockforest boundary core domain_decomposition field lbm postprocessing timeloop vtk)
\ No newline at end of file

apps/showcases/FreeSurface/ZalesakDisk.cpp

+//======================================================================================================================
+//
+//  This file is part of waLBerla. waLBerla is free software: you can
+//  redistribute it and/or modify it under the terms of the GNU General Public
+//  License as published by the Free Software Foundation, either version 3 of
+//  the License, or (at your option) any later version.
+//
+//  waLBerla is distributed in the hope that it will be useful, but WITHOUT
+//  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+//  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+//  for more details.
+//
+//  You should have received a copy of the GNU General Public License along
+//  with waLBerla (see COPYING.txt). If not, see <http://www.gnu.org/licenses/>.
+//
+//! \file ZalesakDisk.cpp
+//! \author Christoph Schwarzmeier <christoph.schwarzmeier@fau.de>
+//
+// This showcase simulates a slotted disk of gas in a constant rotating velocity field. This benchmark is commonly
+// referred to as Zalesak's rotating disk (see doi: 10.1016/0021-9991(79)90051-2).
+//======================================================================================================================
+
+#include "blockforest/Initialization.h"
+
+#include "core/Environment.h"
+
+#include "field/Gather.h"
+
+#include "lbm/PerformanceLogger.h"
+#include "lbm/field/AddToStorage.h"
+#include "lbm/free_surface/LoadBalancing.h"
+#include "lbm/free_surface/SurfaceMeshWriter.h"
+#include "lbm/free_surface/TotalMassComputer.h"
+#include "lbm/free_surface/VtkWriter.h"
+#include "lbm/free_surface/bubble_model/Geometry.h"
+#include "lbm/free_surface/dynamics/SurfaceDynamicsHandler.h"
+#include "lbm/free_surface/surface_geometry/SurfaceGeometryHandler.h"
+#include "lbm/free_surface/surface_geometry/Utility.h"
+#include "lbm/lattice_model/D2Q9.h"
+
+namespace walberla
+{
+namespace free_surface
+{
+namespace ZalesakDisk
+{
+using ScalarField_T = GhostLayerField< real_t, 1 >;
+using VectorField_T = GhostLayerField< Vector3< real_t >, 1 >;
+
+using CollisionModel_T      = lbm::collision_model::SRT;
+using ForceModel_T          = lbm::force_model::GuoField< VectorField_T >;
+using LatticeModel_T        = lbm::D2Q9< CollisionModel_T, true, ForceModel_T, 2 >;
+using LatticeModelStencil_T = LatticeModel_T::Stencil;
+using PdfField_T            = lbm::PdfField< LatticeModel_T >;
+using PdfCommunication_T    = blockforest::SimpleCommunication< LatticeModelStencil_T >;
+
+// the geometry computations in SurfaceGeometryHandler require meaningful values in the ghost layers in corner
+// directions (flag field and fill level field); this holds, even if the lattice model uses a D3Q19 stencil
+using CommunicationStencil_T =
+   typename std::conditional< LatticeModel_T::Stencil::D == uint_t(2), stencil::D2Q9, stencil::D3Q27 >::type;
+using Communication_T = blockforest::SimpleCommunication< CommunicationStencil_T >;
+
+using flag_t                        = uint32_t;
+using FlagField_T                   = FlagField< flag_t >;
+using FreeSurfaceBoundaryHandling_T = FreeSurfaceBoundaryHandling< LatticeModel_T, FlagField_T, ScalarField_T >;
+
+// function describing the initialization velocity profile (in global cell coordinates)
+inline Vector3< real_t > velocityProfile(real_t angularVelocity, Cell globalCell, Vector3< real_t > domainCenter)
+{
+   // add 0.5 to get Cell's center
+   const real_t velocityX = -angularVelocity * ((real_c(globalCell.y()) + real_c(0.5)) - domainCenter[0]);
+   const real_t velocityY = angularVelocity * ((real_c(globalCell.x()) + real_c(0.5)) - domainCenter[1]);
+
+   return Vector3< real_t >(velocityX, velocityY, real_c(0));
+}
+
+int main(int argc, char** argv)
+{
+   Environment walberlaEnv(argc, argv);
+
+   if (argc < 2) { WALBERLA_ABORT("Please specify a parameter file as input argument.") }
+
+   // print content of parameter file
+   WALBERLA_LOG_INFO_ON_ROOT(*walberlaEnv.config());
+
+   // get block forest parameters from parameter file
+   auto blockForestParameters              = walberlaEnv.config()->getOneBlock("BlockForestParameters");
+   const Vector3< uint_t > cellsPerBlock   = blockForestParameters.getParameter< Vector3< uint_t > >("cellsPerBlock");
+   const Vector3< bool > periodicity       = blockForestParameters.getParameter< Vector3< bool > >("periodicity");
+   const uint_t loadBalancingFrequency     = blockForestParameters.getParameter< uint_t >("loadBalancingFrequency");
+   const bool printLoadBalancingStatistics = blockForestParameters.getParameter< bool >("printLoadBalancingStatistics");
+
+   // get domain parameters from parameter file
+   auto domainParameters    = walberlaEnv.config()->getOneBlock("DomainParameters");
+   const uint_t domainWidth = domainParameters.getParameter< uint_t >("domainWidth");
+
+   const real_t diskRadius = real_c(domainWidth) * real_c(0.15);
+   const Vector3< real_t > diskCenter =
+      Vector3< real_t >(real_c(domainWidth) * real_c(0.5), real_c(domainWidth) * real_c(0.75), real_c(0.5));
+   const real_t diskSlotLength = real_c(0.25) * real_c(domainWidth);
+   const real_t diskSlotWidth  = real_c(0.05) * real_c(domainWidth);
+
+   // define domain size
+   Vector3< uint_t > domainSize;
+   domainSize[0] = domainWidth;
+   domainSize[1] = domainWidth;
+   domainSize[2] = uint_c(1);
+   const Vector3< real_t > domainCenter =
+      real_c(0.5) * Vector3< real_t >(real_c(domainSize[0]), real_c(domainSize[1]), real_c(domainSize[2]));
+
+   // compute number of blocks as defined by domainSize and cellsPerBlock
+   Vector3< uint_t > numBlocks;
+   numBlocks[0] = uint_c(std::ceil(real_c(domainSize[0]) / real_c(cellsPerBlock[0])));
+   numBlocks[1] = uint_c(std::ceil(real_c(domainSize[1]) / real_c(cellsPerBlock[1])));
+   numBlocks[2] = uint_c(std::ceil(real_c(domainSize[2]) / real_c(cellsPerBlock[2])));
+
+   // get number of (MPI) processes
+   uint_t numProcesses = uint_c(MPIManager::instance()->numProcesses());
+   WALBERLA_CHECK_LESS_EQUAL(numProcesses, numBlocks[0] * numBlocks[1] * numBlocks[2],
+                             "The number of MPI processes is greater than the number of blocks as defined by "
+                             "\"domainSize/cellsPerBlock\". This would result in unused MPI processes. Either decrease "
+                             "the number of MPI processes or increase \"cellsPerBlock\".")
+
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(numProcesses);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(cellsPerBlock);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(domainSize);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(numBlocks);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(domainWidth);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(periodicity);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(loadBalancingFrequency);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(printLoadBalancingStatistics);
+
+   // get physics parameters from parameter file
+   auto physicsParameters = walberlaEnv.config()->getOneBlock("PhysicsParameters");
+   const uint_t timesteps = physicsParameters.getParameter< uint_t >("timesteps");
+
+   const real_t relaxationRate           = physicsParameters.getParameter< real_t >("relaxationRate");
+   const CollisionModel_T collisionModel = CollisionModel_T(relaxationRate);
+   const real_t viscosity                = collisionModel.viscosity();
+
+   const real_t reynoldsNumber = physicsParameters.getParameter< real_t >("reynoldsNumber");
+   const real_t angularVelocity =
+      reynoldsNumber * viscosity / (real_c(0.5) * real_c(domainWidth) * real_c(domainWidth));
+   const Vector3< real_t > force(real_c(0), real_c(0), real_c(0));
+
+   const bool enableWetting  = physicsParameters.getParameter< bool >("enableWetting");
+   const real_t contactAngle = physicsParameters.getParameter< real_t >("contactAngle");
+
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(reynoldsNumber);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(relaxationRate);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(enableWetting);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(contactAngle);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(timesteps);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(viscosity);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(force);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(angularVelocity);
+   WALBERLA_LOG_DEVEL_ON_ROOT("Timesteps for full rotation " << real_c(2) * math::pi / angularVelocity);
+
+   // read model parameters from parameter file
+   const auto modelParameters               = walberlaEnv.config()->getOneBlock("ModelParameters");
+   const std::string pdfReconstructionModel = modelParameters.getParameter< std::string >("pdfReconstructionModel");
+   const std::string pdfRefillingModel      = modelParameters.getParameter< std::string >("pdfRefillingModel");
+   const std::string excessMassDistributionModel =
+      modelParameters.getParameter< std::string >("excessMassDistributionModel");
+   const std::string curvatureModel          = modelParameters.getParameter< std::string >("curvatureModel");
+   const bool enableForceWeighting           = modelParameters.getParameter< bool >("enableForceWeighting");
+   const bool useSimpleMassExchange          = modelParameters.getParameter< bool >("useSimpleMassExchange");
+   const real_t cellConversionThreshold      = modelParameters.getParameter< real_t >("cellConversionThreshold");
+   const real_t cellConversionForceThreshold = modelParameters.getParameter< real_t >("cellConversionForceThreshold");
+   const bool enableBubbleModel              = modelParameters.getParameter< bool >("enableBubbleModel");
+   const bool enableBubbleSplits             = modelParameters.getParameter< bool >("enableBubbleSplits");
+
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(pdfReconstructionModel);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(pdfRefillingModel);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(excessMassDistributionModel);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(curvatureModel);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(enableForceWeighting);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(useSimpleMassExchange);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(cellConversionThreshold);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(cellConversionForceThreshold);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(enableBubbleModel);
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(enableBubbleSplits);
+
+   // read evaluation parameters from parameter file
+   const auto evaluationParameters      = walberlaEnv.config()->getOneBlock("EvaluationParameters");
+   const uint_t performanceLogFrequency = evaluationParameters.getParameter< uint_t >("performanceLogFrequency");
+
+   WALBERLA_LOG_DEVEL_VAR_ON_ROOT(performanceLogFrequency);
+
+   // create non-uniform block forest (non-uniformity required for load balancing)
+   const std::shared_ptr< StructuredBlockForest > blockForest =
+      createNonUniformBlockForest(domainSize, cellsPerBlock, numBlocks, periodicity);
+
+   // add force field
+   const BlockDataID forceFieldID =
+      field::addToStorage< VectorField_T >(blockForest, "Force field", force, field::fzyx, uint_c(1));
+
+   // create lattice model
+   const LatticeModel_T latticeModel = LatticeModel_T(collisionModel, ForceModel_T(forceFieldID));
+
+   // add pdf field
+   const BlockDataID pdfFieldID = lbm::addPdfFieldToStorage(blockForest, "PDF field", latticeModel, field::fzyx);
+
+   // add fill level field (initialized with 0, i.e., gas everywhere)
+   const BlockDataID fillFieldID =
+      field::addToStorage< ScalarField_T >(blockForest, "Fill level field", real_c(1.0), field::fzyx, uint_c(2));
+
+   // add boundary handling
+   const std::shared_ptr< FreeSurfaceBoundaryHandling_T > freeSurfaceBoundaryHandling =
+      std::make_shared< FreeSurfaceBoundaryHandling_T >(blockForest, pdfFieldID, fillFieldID);
+   const BlockDataID flagFieldID                                      = freeSurfaceBoundaryHandling->getFlagFieldID();
+   const typename FreeSurfaceBoundaryHandling_T::FlagInfo_T& flagInfo = freeSurfaceBoundaryHandling->getFlagInfo();
+
+   // initialize the velocity profile
+   for (auto blockIt = blockForest->begin(); blockIt != blockForest->end(); ++blockIt)
+   {
+      PdfField_T* const pdfField   = blockIt->getData< PdfField_T >(pdfFieldID);
+      FlagField_T* const flagField = blockIt->getData< FlagField_T >(flagFieldID);
+
+      WALBERLA_FOR_ALL_CELLS(pdfFieldIt, pdfField, flagFieldIt, flagField, {
+         //  cell in block-local coordinates
+         const Cell localCell = pdfFieldIt.cell();
+
+         // get cell in global coordinates
+         Cell globalCell = pdfFieldIt.cell();
+         blockForest->transformBlockLocalToGlobalCell(globalCell, *blockIt, localCell);
+
+         // set velocity profile
+         const Vector3< real_t > initialVelocity = velocityProfile(angularVelocity, globalCell, domainCenter);
+         pdfField->setDensityAndVelocity(localCell, initialVelocity, real_c(1));
+      }) // WALBERLA_FOR_ALL_CELLS
+   }
+
+   // create the disk
+   const Vector3< real_t > diskBottomEnd = diskCenter - Vector3< real_t >(real_c(0), real_c(0), -real_c(domainSize[2]));
+   const Vector3< real_t > diskTopEnd    = diskCenter - Vector3< real_t >(real_c(0), real_c(0), real_c(domainSize[2]));
+   const geometry::Cylinder disk(diskBottomEnd, diskTopEnd, diskRadius);
+   bubble_model::addBodyToFillLevelField< geometry::Cylinder >(*blockForest, fillFieldID, disk, true);
+
+   // create the disk's slot
+   const Vector3< real_t > slotMinCorner = Vector3< real_t >(diskCenter[0] - diskSlotWidth * real_c(0.5),
+                                                             diskCenter[1] - diskRadius, -real_c(domainSize[2]));
+   const Vector3< real_t > slotMaxCorner = Vector3< real_t >(
+      diskCenter[0] + diskSlotWidth * real_c(0.5), diskCenter[1] - diskRadius + diskSlotLength, real_c(domainSize[2]));
+   AABB slotAABB(slotMinCorner, slotMaxCorner);
+   bubble_model::addBodyToFillLevelField< AABB >(*blockForest, fillFieldID, slotAABB, false);
+
+   // initialize domain boundary conditions from config file
+   const auto boundaryParameters = walberlaEnv.config()->getOneBlock("BoundaryParameters");
+   freeSurfaceBoundaryHandling->initFromConfig(boundaryParameters);
+
+   // IMPORTANT REMARK: this must be called only after every solid flag has been set; otherwise, the boundary handling
+   // might not detect solid flags correctly
+   freeSurfaceBoundaryHandling->initFlagsFromFillLevel();
+
+   // communication after initialization
+   Communication_T communication(blockForest, flagFieldID, fillFieldID, forceFieldID);
+   communication();
+
+   PdfCommunication_T pdfCommunication(blockForest, pdfFieldID);
+   pdfCommunication();
+
+   // add bubble model
+   std::shared_ptr< bubble_model::BubbleModelBase > bubbleModel = nullptr;
+   if (enableBubbleModel)
+   {
+      const std::shared_ptr< bubble_model::BubbleModel< LatticeModelStencil_T > > bubbleModelDerived =
+         std::make_shared< bubble_model::BubbleModel< LatticeModelStencil_T > >(blockForest, enableBubbleSplits);
+      bubbleModelDerived->initFromFillLevelField(fillFieldID);
+
+      bubbleModel = std::static_pointer_cast< bubble_model::BubbleModelBase >(bubbleModelDerived);
+   }
+   else { bubbleModel = std::make_shared< bubble_model::BubbleModelConstantPressure >(real_c(1)); }
+
+   // set density in non-liquid or non-interface cells to one (after initializing with hydrostatic pressure)
+   setDensityInNonFluidCellsToOne< FlagField_T, PdfField_T >(blockForest, flagInfo, flagFieldID, pdfFieldID);
+
+   // create timeloop
+   SweepTimeloop timeloop(blockForest, timesteps);
+
+   const real_t surfaceTension = real_c(0);
+
+   // Laplace pressure = 2 * surface tension * curvature; curvature computation is not necessary with zero surface
+   // tension
+   bool computeCurvature = false;
+   if (!realIsEqual(surfaceTension, real_c(0), real_c(1e-14))) { computeCurvature = true; }
+
+   // add surface geometry handler
+   const SurfaceGeometryHandler< LatticeModel_T, FlagField_T, ScalarField_T, VectorField_T > geometryHandler(
+      blockForest, freeSurfaceBoundaryHandling, fillFieldID, curvatureModel, computeCurvature, enableWetting,
+      contactAngle);
+
+   geometryHandler.addSweeps(timeloop);
+
+   // get fields created by surface geometry handler
+   const ConstBlockDataID curvatureFieldID = geometryHandler.getConstCurvatureFieldID();
+   const ConstBlockDataID normalFieldID    = geometryHandler.getConstNormalFieldID();
+
+   // add boundary handling for standard boundaries and free surface boundaries
+   const SurfaceDynamicsHandler< LatticeModel_T, FlagField_T, ScalarField_T, VectorField_T > dynamicsHandler(
+      blockForest, pdfFieldID, flagFieldID, fillFieldID, forceFieldID, normalFieldID, curvatureFieldID,
+      freeSurfaceBoundaryHandling, bubbleModel, pdfReconstructionModel, pdfRefillingModel, excessMassDistributionModel,
+      relaxationRate, force, surfaceTension, enableForceWeighting, useSimpleMassExchange, cellConversionThreshold,
+      cellConversionForceThreshold);
+
+   dynamicsHandler.addSweeps(timeloop);
+
+   // add load balancing
+   const LoadBalancer< FlagField_T, CommunicationStencil_T, LatticeModelStencil_T > loadBalancer(
+      blockForest, communication, pdfCommunication, bubbleModel, uint_c(50), uint_c(10), uint_c(5),
+      loadBalancingFrequency, printLoadBalancingStatistics);
+   timeloop.addFuncAfterTimeStep(loadBalancer, "Sweep: load balancing");
+
+   // add VTK output
+   addVTKOutput< LatticeModel_T, FreeSurfaceBoundaryHandling_T, PdfField_T, FlagField_T, ScalarField_T, VectorField_T >(
+      blockForest, timeloop, walberlaEnv.config(), flagInfo, pdfFieldID, flagFieldID, fillFieldID, forceFieldID,
+      geometryHandler.getCurvatureFieldID(), geometryHandler.getNormalFieldID(),
+      geometryHandler.getObstNormalFieldID());
+
+   // add triangle mesh output of free surface
+   SurfaceMeshWriter< ScalarField_T, FlagField_T > surfaceMeshWriter(
+      blockForest, fillFieldID, flagFieldID, flagIDs::liquidInterfaceGasFlagIDs, real_c(0), walberlaEnv.config());
+   surfaceMeshWriter(); // write initial mesh
+   timeloop.addFuncAfterTimeStep(surfaceMeshWriter, "Writer: surface mesh");
+
+   // add logging for computational performance
+   const lbm::PerformanceLogger< FlagField_T > performanceLogger(
+      blockForest, flagFieldID, flagIDs::liquidInterfaceFlagIDs, performanceLogFrequency);
+   timeloop.addFuncAfterTimeStep(performanceLogger, "Evaluator: performance logging");
+
+   WcTimingPool timingPool;
+
+   for (uint_t t = uint_c(0); t != timesteps; ++t)
+   {
+      timeloop.singleStep(timingPool, true);
+
+      // set the constant velocity profile
+      for (auto blockIt = blockForest->begin(); blockIt != blockForest->end(); ++blockIt)
+      {
+         PdfField_T* const pdfField   = blockIt->getData< PdfField_T >(pdfFieldID);
+         FlagField_T* const flagField = blockIt->getData< FlagField_T >(flagFieldID);
+
+         WALBERLA_FOR_ALL_CELLS(pdfFieldIt, pdfField, flagFieldIt, flagField, {
+            if (flagInfo.isInterface(flagFieldIt) || flagInfo.isLiquid(flagFieldIt))
+            {
+               //  cell in block-local coordinates
+               const Cell localCell = pdfFieldIt.cell();
+
+               // get cell in global coordinates
+               Cell globalCell = pdfFieldIt.cell();
+               blockForest->transformBlockLocalToGlobalCell(globalCell, *blockIt, localCell);
+
+               // set velocity profile
+               const Vector3< real_t > initialVelocity = velocityProfile(angularVelocity, globalCell, domainCenter);
+               pdfField->setDensityAndVelocity(localCell, initialVelocity, real_c(1));
+            }
+         }) // WALBERLA_FOR_ALL_CELLS
+      }
+
+      if (t % performanceLogFrequency == uint_c(0) && t > uint_c(0)) { timingPool.logResultOnRoot(); }
+   }
+
+   return EXIT_SUCCESS;
+}
+
+} // namespace ZalesakDisk
+} // namespace free_surface
+} // namespace walberla
+
+int main(int argc, char** argv) { return walberla::free_surface::ZalesakDisk::main(argc, argv); }
\ No newline at end of file

apps/showcases/FreeSurface/ZalesakDisk.prm

+BlockForestParameters
+{
+   cellsPerBlock                 < 50, 50, 1 >;
+   periodicity                   < 0, 0, 1 >;
+   loadBalancingFrequency        0;
+   printLoadBalancingStatistics  false;
+}
+
+DomainParameters
+{
+   domainWidth       100;
+}
+
+PhysicsParameters
+{
+   reynoldsNumber    100; // Re = angularVelocity * domainWidth * 0.5 * domainWidth / kin. viscosity
+   relaxationRate    1.8;
+   enableWetting     false;
+   contactAngle      0; // only used if enableWetting=true
+   timesteps         1000000;
+}
+
+ModelParameters
+{
+   pdfReconstructionModel        OnlyMissing;
+   pdfRefillingModel             EquilibriumRefilling;
+   excessMassDistributionModel   EvenlyAllInterface;
+   curvatureModel                FiniteDifferenceMethod;
+   enableForceWeighting          false;
+   useSimpleMassExchange         false;
+   cellConversionThreshold       1e-2;
+   cellConversionForceThreshold  1e-1;
+
+   enableBubbleModel             True;
+   enableBubbleSplits            false; // only used if enableBubbleModel=true
+}
+
+EvaluationParameters
+{
+   performanceLogFrequency 10000;
+}
+
+BoundaryParameters
+{
+   // X
+   Border { direction W;  walldistance -1; FreeSlip{} }
+   Border { direction E;  walldistance -1; FreeSlip{} }
+
+   // Y
+   Border { direction N;  walldistance -1; FreeSlip{} }
+   Border { direction S;  walldistance -1; FreeSlip{} }
+
+   // Z
+   //Border { direction T;  walldistance -1; FreeSlip{} }
+   //Border { direction B;  walldistance -1; FreeSlip{} }
+}
+
+MeshOutputParameters
+{
+   writeFrequency 0;
+   baseFolder     mesh-out;
+}
+
+VTK
+{
+   fluid_field
+   {
+      writeFrequency       4241;
+      ghostLayers          0;
+      baseFolder           vtk-out;
+      samplingResolution   1;
+
+      writers
+      {
+         fill_level;
+         mapped_flag;
+         velocity;
+         density;
+         //curvature;
+         //normal;
+         //obstacle_normal;
+         //pdf;
+         //flag;
+         //force;
+      }
+
+      inclusion_filters
+      {
+         //liquidInterfaceFilter; // only include liquid and interface cells in VTK output
+      }
+
+      before_functions
+      {
+         //ghost_layer_synchronization;   // only needed if writing the ghost layer
+         gas_cell_zero_setter;            // sets velocity=0 and density=1 all gas cells before writing VTK output
+      }
+   }
+
+   domain_decomposition
+   {
+      writeFrequency             0;
+      baseFolder                 vtk-out;
+      outputDomainDecomposition  true;
+   }
+}
\ No newline at end of file