Boundary Conditions Tutorial

apps/tutorials/lbm/06_LBBoundaryCondition.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 06_LBBoundaryConditions.cpp
+//! \author Helen Schottenhamml <helen.schottenhamml@fau.de>
+//
+//======================================================================================================================
+
+#include "blockforest/all.h"
+
+#include "core/all.h"
+
+#include "domain_decomposition/all.h"
+
+#include "field/all.h"
+
+#include "geometry/all.h"
+
+#include "gui/all.h"
+
+#include "lbm/all.h"
+
+#include "timeloop/all.h"
+
+namespace walberla
+{
+using LatticeModel_T         = lbm::D2Q9< lbm::collision_model::SRT >;
+using Stencil_T              = LatticeModel_T::Stencil;
+using CommunicationStencil_T = LatticeModel_T::CommunicationStencil;
+
+using PdfField_T = lbm::PdfField< LatticeModel_T >;
+
+using flag_t      = walberla::uint16_t;
+using FlagField_T = FlagField< flag_t >;
+
+//! [variableDefines]
+// number of ghost layers
+const uint_t FieldGhostLayers = uint_t(1);
+
+// unique identifiers for flags
+const FlagUID FluidFlagUID("Fluid Flag");
+const FlagUID NoSlipFlagUID("NoSlip Flag");
+const FlagUID FreeSlipFlagUID("FreeSlip Flag");
+const FlagUID SimpleUBBFlagUID("SimpleUBB Flag");
+const FlagUID UBBFlagUID("UBB Flag");
+const FlagUID DynamicUBBFlagUID("DynamicUBB Flag");
+const FlagUID ParserUBBFlagUID("ParserUBB Flag");
+const FlagUID SimplePressureFlagUID("SimplePressure Flag");
+const FlagUID PressureFlagUID("Pressure Flag");
+const FlagUID OutletFlagUID("Outlet Flag");
+const FlagUID SimplePABFlagUID("SimplePAB Flag");
+//! [variableDefines]
+
+///////////////////////////
+/// PARAMETER STRUCTURE ///
+///////////////////////////
+
+//! [setupStruct]
+struct Setup
+{
+   std::string wallType;
+   std::string inflowType;
+   std::string outflowType;
+
+   Vector3< real_t > inflowVelocity;
+   real_t outflowPressure;
+
+   // DynamicUBB
+   real_t period;
+
+   // ParserUBB
+   Config::BlockHandle parser;
+
+   // SimplePAB
+   real_t omega;
+};
+//! [setupStruct]
+
+////////////////////////////////
+/// CUSTOM BOUNDARY HANDLING ///
+////////////////////////////////
+
+//! [VelocityFunctor]
+class VelocityFunctor
+{
+ public:
+   VelocityFunctor(const Vector3< real_t >& velocity, real_t period, real_t H)
+      : velocity_(velocity), period_(period), H_(H)
+   {
+      constantTerm_ = real_t(4) * velocity_[0] / (H_ * H_);
+   }
+
+   void operator()(const real_t time)
+   {
+      amplitude_ = constantTerm_ * real_t(0.5) * (real_t(1) - std::cos(real_t(2) * math::pi * time / period_));
+   }
+
+   Vector3< real_t > operator()(const Vector3< real_t >& pos, const real_t)
+   {
+      return Vector3< real_t >(amplitude_ * pos[1] * (H_ - pos[1]), real_t(0), real_t(0));
+   }
+
+ private:
+   const Vector3< real_t > velocity_;
+   const real_t period_;
+   const real_t H_;
+
+   real_t constantTerm_; // part of the velocity that is constant in both time and space
+   real_t amplitude_;
+};
+//! [VelocityFunctor]
+
+//! [boundaryTypedefs]
+/// boundary handling
+using NoSlip_T    = lbm::NoSlip< LatticeModel_T, flag_t >;
+using FreeSlip_T  = lbm::FreeSlip< LatticeModel_T, FlagField_T >;
+
+using SimpleUBB_T    = lbm::SimpleUBB< LatticeModel_T, flag_t >;
+using UBB_T          = lbm::UBB< LatticeModel_T, flag_t >;
+using DynamicUBB_T   = lbm::DynamicUBB< LatticeModel_T, flag_t, VelocityFunctor >;
+using ParserUBB_T    = lbm::ParserUBB< LatticeModel_T, flag_t >;
+
+using SimplePressure_T  = lbm::SimplePressure< LatticeModel_T, flag_t >;
+using Pressure_T        = lbm::Pressure< LatticeModel_T, flag_t >;
+using Outlet_T          = lbm::Outlet< LatticeModel_T, FlagField_T >;
+using SimplePAB_T       = lbm::SimplePAB< LatticeModel_T, FlagField_T >;
+
+using BoundaryHandling_T = BoundaryHandling< FlagField_T, Stencil_T, NoSlip_T, FreeSlip_T,
+                                             SimpleUBB_T, UBB_T, DynamicUBB_T, ParserUBB_T,
+                                             SimplePressure_T, Pressure_T, Outlet_T, SimplePAB_T >;
+//! [boundaryTypedefs]
+
+//! [myBoundaryHandlingDeclaration]
+class MyBoundaryHandling
+{
+ public:
+   MyBoundaryHandling(const BlockDataID& flagFieldID, const BlockDataID& pdfFieldID, const Setup & setup,
+                      const std::shared_ptr< lbm::TimeTracker >& timeTracker)
+      : flagFieldID_(flagFieldID), pdfFieldID_(pdfFieldID), setup_(setup), timeTracker_(timeTracker)
+   {}
+
+   BoundaryHandling_T* operator()(IBlock* const block, const StructuredBlockStorage* const storage) const;
+
+ private:
+   const BlockDataID flagFieldID_;
+   const BlockDataID pdfFieldID_;
+
+   Setup setup_;
+   std::shared_ptr< lbm::TimeTracker > timeTracker_;
+
+}; // class MyBoundaryHandling
+//! [myBoundaryHandlingDeclaration]
+
+BoundaryHandling_T* MyBoundaryHandling::operator()(IBlock* const block,
+                                                   const StructuredBlockStorage* const storage) const
+{
+   Vector3< real_t > domainSize(real_c(storage->getNumberOfXCells()), real_c(storage->getNumberOfYCells()),
+                                real_c(storage->getNumberOfZCells()));
+
+   real_t H = domainSize[1];
+
+   VelocityFunctor velocity(setup_.inflowVelocity, setup_.period, H);
+
+   WALBERLA_ASSERT_NOT_NULLPTR(block)
+
+   //! [boundaryHandling_T fields]
+   FlagField_T* flagField = block->getData< FlagField_T >(flagFieldID_);
+   PdfField_T* pdfField   = block->getData< PdfField_T >(pdfFieldID_);
+
+   const auto fluidFlag = flagField->getOrRegisterFlag(FluidFlagUID);
+   //! [boundaryHandling_T fields]
+
+   BoundaryHandling_T* handling = new BoundaryHandling_T(
+      "Boundary Handling", flagField, fluidFlag,
+      //! [handling_NoSlip]
+      NoSlip_T("NoSlip", NoSlipFlagUID, pdfField),
+      //! [handling_NoSlip]
+      //! [handling_FreeSlip]
+      FreeSlip_T("FreeSlip", FreeSlipFlagUID, pdfField, flagField, fluidFlag),
+      //! [handling_FreeSlip]
+      //! [handling_SimpleUBB]
+      SimpleUBB_T("SimpleUBB", SimpleUBBFlagUID, pdfField, setup_.inflowVelocity),
+      //! [handling_SimpleUBB]
+      //! [handling_UBB]
+      UBB_T("UBB", UBBFlagUID, pdfField),
+      //! [handling_UBB]
+      //! [handling_DynamicUBB]
+      DynamicUBB_T("DynamicUBB", DynamicUBBFlagUID, pdfField, timeTracker_, storage->getLevel(*block), velocity,
+                   block->getAABB()),
+      //! [handling_DynamicUBB]
+      //! [handling_ParserUBB]
+      ParserUBB_T("ParserUBB", ParserUBBFlagUID, pdfField, flagField, timeTracker_, storage->getLevel(*block),
+                  block->getAABB()),
+      //! [handling_ParserUBB]
+      //! [handling_SimplePressure]
+      SimplePressure_T("SimplePressure", SimplePressureFlagUID, pdfField, setup_.outflowPressure),
+      //! [handling_SimplePressure]
+      //! [handling_Pressure]
+      Pressure_T("Pressure", PressureFlagUID, pdfField),
+      //! [handling_Pressure]
+      //! [handling_Outlet]
+      Outlet_T("Outlet", OutletFlagUID, pdfField, flagField, fluidFlag),
+      //! [handling_Outlet]
+      //! [handling_SimplePAB]
+      SimplePAB_T("SimplePAB", SimplePABFlagUID, pdfField, flagField, setup_.outflowPressure, setup_.omega,
+                  FluidFlagUID, NoSlipFlagUID));
+      //! [handling_SimplePAB]
+
+   //! [domainBB]
+   CellInterval domainBB = storage->getDomainCellBB();
+   storage->transformGlobalToBlockLocalCellInterval(domainBB, *block);
+   //! [domainBB]
+
+   //! [westBoundary]
+   cell_idx_t ghost = cell_idx_t(FieldGhostLayers);
+
+   domainBB.xMin() -= ghost;
+   domainBB.xMax() += ghost;
+
+   // WEST - Inflow
+   CellInterval west(domainBB.xMin(), domainBB.yMin(),
+                     domainBB.zMin(), domainBB.xMin(),
+                     domainBB.yMax(), domainBB.zMin());
+
+   //! [westBoundary]
+
+   if (setup_.inflowType == "SimpleUBB") {
+      //! [forceBoundary_SimpleUBB]
+      handling->forceBoundary(SimpleUBBFlagUID, west);
+      //! [forceBoundary_SimpleUBB]
+   }
+   else if (setup_.inflowType == "UBB")
+   {
+      //! [forceBoundary_UBB]
+      Cell offset(0, 0, 0);
+      storage->transformBlockLocalToGlobalCell(offset, *block);
+
+      for (auto cellIt = west.begin(); cellIt != west.end(); ++cellIt)
+      {
+         Cell globalCell = *cellIt + offset;
+         const real_t y = real_c(globalCell[1]);
+
+         Vector3< real_t > ubbVel(0);
+         ubbVel[0] = -real_t(4) * y * (y - H) / (H * H) * setup_.inflowVelocity[0];
+
+         handling->forceBoundary(UBBFlagUID, cellIt->x(), cellIt->y(), cellIt->z(), UBB_T::Velocity(ubbVel));
+      }
+      //! [forceBoundary_UBB]
+   }
+   else if (setup_.inflowType == "DynamicUBB")
+   {
+      //! [forceBoundary_DynamicUBB]
+      handling->forceBoundary(DynamicUBBFlagUID, west);
+      //! [forceBoundary_DynamicUBB]
+   }
+   else if (setup_.inflowType == "ParserUBB")
+   {
+      //! [forceBoundary_ParserUBB_eqs]
+      char x_eq[150];
+      sprintf(x_eq, "0.1*4/%f/%f * y * (%f - y) * 0.5 * (1 - cos(2 * 3.1415926538 * t / %f));", H, H, H, setup_.period);
+
+      std::array< std::string, 3 > eqs = { x_eq, "0", "0" };
+      handling->forceBoundary(ParserUBBFlagUID, west, ParserUBB_T::Parser(eqs));
+      //! [forceBoundary_ParserUBB_eqs]
+
+      //! [forceBoundary_ParserUBB_config]
+      handling->forceBoundary(ParserUBBFlagUID, west, ParserUBB_T::Parser(setup_.parser));
+      //! [forceBoundary_ParserUBB_config]
+   }
+   else
+   {
+      WALBERLA_ABORT("Please specify a valid inflow type.")
+   }
+
+   // EAST - outflow
+   CellInterval east(domainBB.xMax(), domainBB.yMin(),
+                     domainBB.zMin(), domainBB.xMax(),
+                     domainBB.yMax(), domainBB.zMin());
+
+   if (setup_.outflowType == "SimplePressure") {
+      //! [forceBoundary_SimplePressure]
+      handling->forceBoundary(SimplePressureFlagUID, east);
+      //! [forceBoundary_SimplePressure]
+   }
+   else if (setup_.outflowType == "Pressure")
+   {
+      //! [forceBoundary_Pressure]
+      Cell offset(0, 0, 0);
+      storage->transformBlockLocalToGlobalCell(offset, *block);
+
+      for (auto cellIt = east.begin(); cellIt != east.end(); ++cellIt)
+      {
+         Cell globalCell = *cellIt + offset;
+         const real_t y = real_c(globalCell[1]);
+
+         real_t local_density =
+            setup_.outflowPressure * (real_t(1.0) + real_t(0.01) * std::sin(real_t(2.0 * 3.1415926538) * y / H));
+
+         handling->forceBoundary(PressureFlagUID, cellIt->x(), cellIt->y(), cellIt->z(),
+                                 Pressure_T::LatticeDensity(local_density));
+      }
+      //! [forceBoundary_Pressure]
+   }
+   else if (setup_.outflowType == "Outlet")
+   {
+      //! [forceBoundary_Outlet]
+      handling->forceBoundary(OutletFlagUID, east);
+      //! [forceBoundary_Outlet]
+   }
+   else if (setup_.outflowType == "SimplePAB")
+   {
+      //! [forceBoundary_SimplePAB]
+      handling->forceBoundary(SimplePABFlagUID, east);
+      //! [forceBoundary_SimplePAB]
+   }
+   else
+   {
+      WALBERLA_ABORT("Please specify a valid outflow type.")
+   }
+
+   domainBB.yMin() -= ghost;
+   domainBB.yMax() += ghost;
+
+   // SOUTH - wall
+   CellInterval south(domainBB.xMin(), domainBB.yMin(),
+                      domainBB.zMin(), domainBB.xMax(),
+                      domainBB.yMin(), domainBB.zMax());
+
+   // NORTH - wall
+   CellInterval north(domainBB.xMin(), domainBB.yMax(),
+                      domainBB.zMin(), domainBB.xMax(),
+                      domainBB.yMax(), domainBB.zMax());
+
+   if (setup_.wallType == "NoSlip")
+   {
+      //! [forceBoundary_NoSlip]
+      handling->forceBoundary(NoSlipFlagUID, south);
+      //! [forceBoundary_NoSlip]
+      handling->forceBoundary(NoSlipFlagUID, north);
+   }
+   else if (setup_.wallType == "FreeSlip")
+   {
+      //! [forceBoundary_FreeSlip]
+      handling->forceBoundary(FreeSlipFlagUID, south);
+      //! [forceBoundary_FreeSlip]
+      handling->forceBoundary(FreeSlipFlagUID, north);
+   }
+   else
+   {
+      WALBERLA_ABORT("Please specify a valid wall type.")
+   }
+
+   //! [fillDomain]
+   handling->fillWithDomain(domainBB);
+   //! [fillDomain]
+
+   return handling;
+}
+
+int main(int argc, char** argv)
+{
+   walberla::Environment walberlaEnv(argc, argv);
+
+   auto blocks = blockforest::createUniformBlockGridFromConfig(walberlaEnv.config());
+
+   // read parameters
+   auto parameters = walberlaEnv.config()->getOneBlock("Parameters");
+
+   const real_t omega = parameters.getParameter< real_t >("omega", real_c(1.4));
+   const Vector3< real_t > initialVelocity =
+      parameters.getParameter< Vector3< real_t > >("initialVelocity", Vector3< real_t >());
+   const uint_t timesteps = parameters.getParameter< uint_t >("timesteps", uint_c(10));
+
+   const double remainingTimeLoggerFrequency =
+      parameters.getParameter< double >("remainingTimeLoggerFrequency", 3.0); // in seconds
+
+   // create fields
+   LatticeModel_T latticeModel = LatticeModel_T(lbm::collision_model::SRT(omega));
+   BlockDataID pdfFieldID  = lbm::addPdfFieldToStorage(blocks, "pdf field", latticeModel, initialVelocity, real_t(1));
+   BlockDataID flagFieldID = field::addFlagFieldToStorage< FlagField_T >(blocks, "flag field", FieldGhostLayers);
+
+   // create and initialize boundary handling
+
+   auto boundariesConfig = walberlaEnv.config()->getOneBlock("Boundaries");
+
+   Setup setup;
+   setup.wallType        = boundariesConfig.getParameter< std::string >("wallType", "NoSlip");
+   setup.inflowType      = boundariesConfig.getParameter< std::string >("inflowType", "SimpleUBB");
+   setup.outflowType     = boundariesConfig.getParameter< std::string >("outflowType", "SimplePressure");
+   setup.inflowVelocity  = boundariesConfig.getParameter< Vector3< real_t > >("inflowVelocity", Vector3< real_t >());
+   setup.outflowPressure = boundariesConfig.getParameter< real_t >("outflowPressure", real_t(1));
+
+   setup.period = boundariesConfig.getParameter< real_t >("period", real_t(100));
+
+   if (setup.inflowType == "ParserUBB") setup.parser = boundariesConfig.getBlock("Parser");
+
+   setup.omega = omega;
+
+   //! [timeTracker]
+   std::shared_ptr< lbm::TimeTracker > timeTracker = std::make_shared< lbm::TimeTracker >();
+   //! [timeTracker]
+
+   //! [boundaryHandlingID]
+   BlockDataID boundaryHandlingID = blocks->addStructuredBlockData< BoundaryHandling_T >(
+      MyBoundaryHandling(flagFieldID, pdfFieldID, setup, timeTracker), "boundary handling");
+   //! [boundaryHandlingID]
+
+   // create time loop
+   SweepTimeloop timeloop(blocks->getBlockStorage(), timesteps);
+
+   // create communication for PdfField
+   blockforest::communication::UniformBufferedScheme< CommunicationStencil_T > communication(blocks);
+   communication.addPackInfo(make_shared< lbm::PdfFieldPackInfo< LatticeModel_T > >(pdfFieldID));
+
+   // add LBM sweep and communication to time loop
+   //! [boundarySweep]
+   timeloop.add() << BeforeFunction(communication, "communication")
+                  << Sweep(BoundaryHandling_T::getBlockSweep(boundaryHandlingID), "boundary handling");
+   //! [boundarySweep]
+   timeloop.add() << Sweep(
+      makeSharedSweep(lbm::makeCellwiseSweep< LatticeModel_T, FlagField_T >(pdfFieldID, flagFieldID, FluidFlagUID)),
+      "LB stream & collide");
+
+   // increment time step counter
+   //! [timeTracker_coupling]
+   timeloop.addFuncAfterTimeStep(makeSharedFunctor(timeTracker), "time tracking");
+   //! [timeTracker_coupling]
+
+   // LBM stability check
+   timeloop.addFuncAfterTimeStep(makeSharedFunctor(field::makeStabilityChecker< PdfField_T, FlagField_T >(
+                                    walberlaEnv.config(), blocks, pdfFieldID, flagFieldID, FluidFlagUID)),
+                                 "LBM stability check");
+
+   // log remaining time
+   timeloop.addFuncAfterTimeStep(timing::RemainingTimeLogger(timeloop.getNrOfTimeSteps(), remainingTimeLoggerFrequency),
+                                 "remaining time logger");
+
+   // add VTK output to time loop
+   //   lbm::VTKOutput< LatticeModel_T, FlagField_T >::addToTimeloop(timeloop, blocks, walberlaEnv.config(), pdfFieldID,
+   //                                                                flagFieldID, FluidFlagUID);
+
+   auto vtkConfig = walberlaEnv.config()->getBlock("VTK");
+
+   uint_t writeFrequency = vtkConfig.getBlock("fluid_field").getParameter< uint_t >("writeFrequency", uint_t(100));
+
+   auto vtkOutput = vtk::createVTKOutput_BlockData(*blocks, "fluid_field", writeFrequency, FieldGhostLayers, false,
+                                                   "vtk_out", "simulation_step", false, true, true, false, 0);
+
+   auto velocityWriter  = std::make_shared< lbm::VelocityVTKWriter< LatticeModel_T, float > >(pdfFieldID, "velocity");
+   auto flagFieldWriter = std::make_shared< field::VTKWriter< FlagField_T > >(flagFieldID, "flag field");
+
+   vtkOutput->addCellDataWriter(velocityWriter);
+   vtkOutput->addCellDataWriter(flagFieldWriter);
+
+   timeloop.addFuncAfterTimeStep(vtk::writeFiles(vtkOutput), "VTKOutput");
+
+   // create adaptors, so that the GUI also displays density and velocity
+   // adaptors are like fields with the difference that they do not store values
+   // but calculate the values based on other fields ( here the PdfField )
+   field::addFieldAdaptor< lbm::Adaptor< LatticeModel_T >::Density >(blocks, pdfFieldID, "DensityAdaptor");
+   field::addFieldAdaptor< lbm::Adaptor< LatticeModel_T >::VelocityVector >(blocks, pdfFieldID, "VelocityAdaptor");
+
+   if (parameters.getParameter< bool >("useGui", false))
+   {
+      GUI gui(timeloop, blocks, argc, argv);
+      lbm::connectToGui< LatticeModel_T >(gui);
+      gui.run();
+   }
+   else
+   {
+      timeloop.run();
+   }
+
+   return EXIT_SUCCESS;
+}
+} // namespace walberla
+
+int main(int argc, char** argv) { walberla::main(argc, argv); }

apps/tutorials/lbm/06_LBBoundaryCondition.prm

+Parameters
+{
+	omega           1.8;
+	initialVelocity < 0.0, 0, 0 >;
+	timesteps       5000;
+
+	useGui 0;
+	remainingTimeLoggerFrequency 3; // in seconds
+}
+
+Boundaries
+{
+
+    wallType        NoSlip;             // `NoSlip`, `FreeSlip` or `Curved`
+    inflowType      SimpleUBB;          // `SimpleUBB`, `UBB`, `DynamicUBB` or `ParserUBB`
+    outflowType     SimplePAB;          // `SimplePressure`, `Pressure`, `Outlet` or `SimplePAB`
+
+	inflowVelocity <0.1, 0, 0>;
+	outflowPressure 1.0;
+
+    period          125;                // number of timesteps per period
+
+    //! [ParserConfig]
+    Parser {
+        x       0.1 * 4 / 80 / 80 * y * (80 - y) * 0.5 * (1 - cos(2 * 3.1415926538 * t / 150));
+        y       0;
+        z       0;
+    }
+    //! [ParserConfig]
+}
+
+//! [domainSetup]
+DomainSetup
+{
+   blocks        <  1,    1, 1 >;
+   cellsPerBlock <  300, 80, 1 >;
+   periodic      <  0,    0, 1 >;
+}
+//! [domainSetup]
+
+StabilityChecker
+{
+   checkFrequency 100;
+   streamOutput   false;
+   vtkOutput      true;
+}
+
+VTK
+{
+   // for parameter documentation see src/vtk/Initialization.cpp
+   fluid_field
+   {
+      writeFrequency 100;
+      ghostLayers    1;
+
+      before_functions {
+         PDFGhostLayerSync;
+      }
+
+      inclusion_filters {
+         DomainFilter;
+      }
+
+      writers {
+         Velocity;
+         Density;
+      }
+   }
+
+   flag_field
+   {
+      writeFrequency 10000000; // write only once
+      ghostLayers    1;
+
+      writers {
+         FlagField;
+      }
+   }
+
+   domain_decomposition
+   {
+      writeFrequency 10000000; // write only once
+      outputDomainDecomposition true;
+   }
+}

apps/tutorials/lbm/CMakeLists.txt

@@ -25,4 +25,8 @@ endif()
 
 waLBerla_add_executable ( NAME 05_BackwardFacingStep
                           FILES 05_BackwardFacingStep.cpp
+                          DEPENDS blockforest boundary core field lbm stencil timeloop vtk )
+
+waLBerla_add_executable ( NAME 06_LBBoundaryCondition
+                          FILES 06_LBBoundaryCondition.cpp
                           DEPENDS blockforest boundary core field lbm stencil timeloop vtk )
\ No newline at end of file

doc/Mainpage.dox

@@ -44,6 +44,8 @@ all the basic data strcutures and concepts of the framework.
   A LBM simulation with complex geometries is built.
 - \ref tutorial_lbm05 \n
   A LBM simulation with a backward-facing step is set up.
+- \ref tutorial_lbm06 \n
+  This tutorial deals with the usage of different LBM boundary conditions.
 
 \subsection codegen Code Generation
 

src/lbm/boundary/ParserUBB.h

@@ -258,9 +258,9 @@ Vector3< real_t > ParserUBB<LatticeModel_T, flag_t, AdaptVelocityToExternalForce