ADV-1: Contact problem

Note

Prerequisites of this tutorial include VEC-0: Linear elasticity

Note

Intended learning outcome:

• general structure of a program developed using MoFEM
• idea of Simple Interface in MoFEM and how to use it
• idea of Domain element in MoFEM and how to use it
• Use default Forms Integrals
• how to push the developed UDOs to the Pipeline
• utilisation of tools to convert outputs (MOAB) and visualise them (Paraview)

/**
 * \file contact.cpp
 * \example contact.cpp
 *
 * Example of contact problem
 *
 */
 
/* This file is part of MoFEM.
 * MoFEM is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * MoFEM 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 Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with MoFEM. If not, see <http://www.gnu.org/licenses/>. */
 
#ifndef EXECUTABLE_DIMENSION
#define EXECUTABLE_DIMENSION 3
#endif
 
#include <MoFEM.hpp>
#include <MatrixFunction.hpp>
 
using namespace MoFEM;
 
template <int DIM> struct ElementsAndOps {};
 
template <> struct ElementsAndOps<2> {
  static constexpr FieldSpace CONTACT_SPACE = HCURL;
  using DomainEle = PipelineManager::FaceEle;
  using DomainEleOp = DomainEle::UserDataOperator;
  using BoundaryEle = PipelineManager::EdgeEle;
  using BoundaryEleOp = BoundaryEle::UserDataOperator;
  using PostProcEle = PostProcFaceOnRefinedMesh;
  using OpSetPiolaTransformOnBoundary =
      OpSetContravariantPiolaTransformOnEdge2D;
};
 
template <> struct ElementsAndOps<3> {
  static constexpr FieldSpace CONTACT_SPACE = HDIV;
  using DomainEle = VolumeElementForcesAndSourcesCore;
  using DomainEleOp = DomainEle::UserDataOperator;
  using BoundaryEle = FaceElementForcesAndSourcesCore;
  using BoundaryEleOp = BoundaryEle::UserDataOperator;
  using PostProcEle = PostProcVolumeOnRefinedMesh;
  using OpSetPiolaTransformOnBoundary =
      OpHOSetContravariantPiolaTransformOnFace3D;
};
 
constexpr FieldSpace ElementsAndOps<2>::CONTACT_SPACE;
constexpr FieldSpace ElementsAndOps<3>::CONTACT_SPACE;
 
constexpr int SPACE_DIM =
    EXECUTABLE_DIMENSION; //< Space dimension of problem, mesh
 
constexpr EntityType boundary_ent = SPACE_DIM == 3 ? MBTRI : MBEDGE;
using EntData = EntitiesFieldData::EntData;
using DomainEle = ElementsAndOps<SPACE_DIM>::DomainEle;
using DomainEleOp = ElementsAndOps<SPACE_DIM>::DomainEleOp;
using BoundaryEle = ElementsAndOps<SPACE_DIM>::BoundaryEle;
using BoundaryEleOp = ElementsAndOps<SPACE_DIM>::BoundaryEleOp;
using PostProcEle = ElementsAndOps<SPACE_DIM>::PostProcEle;
 
using AssemblyDomainEleOp =
    FormsIntegrators<DomainEleOp>::Assembly<PETSC>::OpBase;
using AssemblyBoundaryEleOp =
    FormsIntegrators<BoundaryEleOp>::Assembly<PETSC>::OpBase;
using OpSetPiolaTransformOnBoundary =
    ElementsAndOps<SPACE_DIM>::OpSetPiolaTransformOnBoundary;
constexpr FieldSpace CONTACT_SPACE = ElementsAndOps<SPACE_DIM>::CONTACT_SPACE;
 
//! [Operators used for contact]
using OpMixDivULhs = FormsIntegrators<DomainEleOp>::Assembly<
    PETSC>::BiLinearForm<GAUSS>::OpMixDivTimesVec<SPACE_DIM>;
using OpLambdaGraULhs = FormsIntegrators<DomainEleOp>::Assembly<
    PETSC>::BiLinearForm<GAUSS>::OpMixTensorTimesGrad<SPACE_DIM>;
using OpMixDivURhs = FormsIntegrators<DomainEleOp>::Assembly<PETSC>::LinearForm<
    GAUSS>::OpMixDivTimesU<3, SPACE_DIM, SPACE_DIM>;
using OpMixLambdaGradURhs = FormsIntegrators<DomainEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpMixTensorTimesGradU<SPACE_DIM>;
using OpMixUTimesDivLambdaRhs = FormsIntegrators<DomainEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpMixVecTimesDivLambda<SPACE_DIM>;
using OpMixUTimesLambdaRhs = FormsIntegrators<DomainEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpGradTimesTensor<1, SPACE_DIM, SPACE_DIM>;
using OpSpringLhs = FormsIntegrators<BoundaryEleOp>::Assembly<
    PETSC>::BiLinearForm<GAUSS>::OpMass<1, SPACE_DIM>;
using OpSpringRhs = FormsIntegrators<BoundaryEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpBaseTimesVector<1, SPACE_DIM, 1>;
//! [Operators used for contact]
 
//! [Body force]
using OpBodyForce = FormsIntegrators<DomainEleOp>::Assembly<PETSC>::LinearForm<
    GAUSS>::OpSource<1, SPACE_DIM>;
//! [Body force]
 
//! [Only used with Hooke equation (linear material model)]
using OpKCauchy = FormsIntegrators<DomainEleOp>::Assembly<PETSC>::BiLinearForm<
    GAUSS>::OpGradSymTensorGrad<1, SPACE_DIM, SPACE_DIM, 0>;
using OpInternalForceCauchy = FormsIntegrators<DomainEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpGradTimesSymTensor<1, SPACE_DIM, SPACE_DIM>;
//! [Only used with Hooke equation (linear material model)]
 
//! [Only used for dynamics]
using OpMass = FormsIntegrators<DomainEleOp>::Assembly<PETSC>::BiLinearForm<
    GAUSS>::OpMass<1, SPACE_DIM>;
using OpInertiaForce = FormsIntegrators<DomainEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpBaseTimesVector<1, SPACE_DIM, 1>;
//! [Only used for dynamics]
 
//! [Essential boundary conditions]
using OpBoundaryMass = FormsIntegrators<BoundaryEleOp>::Assembly<
    PETSC>::BiLinearForm<GAUSS>::OpMass<1, SPACE_DIM>;
using OpBoundaryVec = FormsIntegrators<BoundaryEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpBaseTimesVector<1, SPACE_DIM, 0>;
using OpBoundaryInternal = FormsIntegrators<BoundaryEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpBaseTimesVector<1, SPACE_DIM, 1>;
//! [Essential boundary conditions]
 
// Only used with Hencky/nonlinear material
using OpKPiola = FormsIntegrators<DomainEleOp>::Assembly<PETSC>::BiLinearForm<
    GAUSS>::OpGradTensorGrad<1, SPACE_DIM, SPACE_DIM, 1>;
using OpInternalForcePiola = FormsIntegrators<DomainEleOp>::Assembly<
    PETSC>::LinearForm<GAUSS>::OpGradTimesTensor<1, SPACE_DIM, SPACE_DIM>;
 
constexpr bool is_quasi_static = true;
constexpr bool is_large_strains = true;
 
constexpr int order = 2;
constexpr double young_modulus = 100;
constexpr double poisson_ratio = 0.25;
constexpr double rho = 0;
constexpr double cn = 0.01;
constexpr double spring_stiffness = 0.1;
 
#include <OpPostProcElastic.hpp>
#include <ContactOps.hpp>
#include <HenckyOps.hpp>
#include <PostProcContact.hpp>
using namespace ContactOps;
using namespace HenckyOps;
 
struct Example {
 
  Example(MoFEM::Interface &m_field) : mField(m_field) {}
 
  MoFEMErrorCode runProblem();
 
private:
  MoFEM::Interface &mField;
 
  MoFEMErrorCode setupProblem();
  MoFEMErrorCode createCommonData();
  MoFEMErrorCode bC();
  MoFEMErrorCode OPs();
  MoFEMErrorCode tsSolve();
  MoFEMErrorCode postProcess();
  MoFEMErrorCode checkResults();
 
  boost::shared_ptr<ContactOps::CommonData> commonDataPtr;
  boost::shared_ptr<PostProcEle> postProcFe;
  std::tuple<SmartPetscObj<Vec>, SmartPetscObj<VecScatter>> uXScatter;
  std::tuple<SmartPetscObj<Vec>, SmartPetscObj<VecScatter>> uYScatter;
  std::tuple<SmartPetscObj<Vec>, SmartPetscObj<VecScatter>> uZScatter;
 
  boost::shared_ptr<std::vector<unsigned char>> boundaryMarker;
 
  template <int DIM> Range getEntsOnMeshSkin();
};
 
//! [Run problem]
MoFEMErrorCode Example::runProblem() {
  MoFEMFunctionBegin;
  CHKERR setupProblem();
  CHKERR createCommonData();
  CHKERR bC();
  CHKERR OPs();
  CHKERR tsSolve();
  CHKERR postProcess();
  CHKERR checkResults();
  MoFEMFunctionReturn(0);
}
//! [Run problem]
 
//! [Set up problem]
MoFEMErrorCode Example::setupProblem() {
  MoFEMFunctionBegin;
  Simple *simple = mField.getInterface<Simple>();
 
  // Select base
  enum bases { AINSWORTH, DEMKOWICZ, LASBASETOPT };
  const char *list_bases[LASBASETOPT] = {"ainsworth", "demkowicz"};
  PetscInt choice_base_value = AINSWORTH;
  CHKERR PetscOptionsGetEList(PETSC_NULL, NULL, "-base", list_bases,
                              LASBASETOPT, &choice_base_value, PETSC_NULL);
 
  FieldApproximationBase base;
  switch (choice_base_value) {
  case AINSWORTH:
    base = AINSWORTH_LEGENDRE_BASE;
    MOFEM_LOG("EXAMPLE", Sev::inform)
        << "Set AINSWORTH_LEGENDRE_BASE for displacements";
    break;
  case DEMKOWICZ:
    base = DEMKOWICZ_JACOBI_BASE;
    MOFEM_LOG("EXAMPLE", Sev::inform)
        << "Set DEMKOWICZ_JACOBI_BASE for displacents";
    break;
  default:
    base = LASTBASE;
    break;
  }
 
  // Note: For tets we have only H1 Ainsworth base, for Hex we have only H1
  // Demkowicz base. We need to implement Demkowicz H1 base on tet.
  CHKERR simple->addDomainField("U", H1, base, SPACE_DIM);
  CHKERR simple->addBoundaryField("U", H1, base, SPACE_DIM);
 
  CHKERR simple->addDomainField("SIGMA", CONTACT_SPACE, DEMKOWICZ_JACOBI_BASE,
                                SPACE_DIM);
  CHKERR simple->addBoundaryField("SIGMA", CONTACT_SPACE, DEMKOWICZ_JACOBI_BASE,
                                  SPACE_DIM);
 
  CHKERR simple->setFieldOrder("U", order);
  CHKERR simple->setFieldOrder("SIGMA", 0);
 
  auto skin_edges = getEntsOnMeshSkin<SPACE_DIM>();
 
  // filter not owned entities, those are not on boundary
  Range boundary_ents;
  ParallelComm *pcomm =
      ParallelComm::get_pcomm(&mField.get_moab(), MYPCOMM_INDEX);
  if (pcomm == NULL) {
    SETERRQ(PETSC_COMM_WORLD, MOFEM_DATA_INCONSISTENCY,
            "Communicator not created");
  }
 
  CHKERR pcomm->filter_pstatus(skin_edges, PSTATUS_SHARED | PSTATUS_MULTISHARED,
                               PSTATUS_NOT, -1, &boundary_ents);
 
  CHKERR simple->setFieldOrder("SIGMA", order - 1, &boundary_ents);
  // Range adj_edges;
  // CHKERR mField.get_moab().get_adjacencies(boundary_ents, 1, false,
  // adj_edges,
  //                                          moab::Interface::UNION);
  // adj_edges.merge(boundary_ents);
  // CHKERR simple->setFieldOrder("U", order, &adj_edges);
 
  CHKERR simple->setUp();
  MoFEMFunctionReturn(0);
}
//! [Set up problem]
 
//! [Create common data]
MoFEMErrorCode Example::createCommonData() {
  MoFEMFunctionBegin;
 
  auto set_matrial_stiffness = [&]() {
    MoFEMFunctionBegin;
    FTensor::Index<'i', SPACE_DIM> i;
    FTensor::Index<'j', SPACE_DIM> j;
    FTensor::Index<'k', SPACE_DIM> k;
    FTensor::Index<'l', SPACE_DIM> l;
    constexpr auto t_kd = FTensor::Kronecker_Delta_symmetric<int>();
    constexpr double bulk_modulus_K =
        young_modulus / (3 * (1 - 2 * poisson_ratio));
    constexpr double shear_modulus_G =
        young_modulus / (2 * (1 + poisson_ratio));
    constexpr double A =
        (SPACE_DIM == 2) ? 2 * shear_modulus_G /
                               (bulk_modulus_K + (4. / 3.) * shear_modulus_G)
                         : 1;
    auto t_D =
        getFTensor4DdgFromMat<SPACE_DIM, SPACE_DIM, 0>(*commonDataPtr->mDPtr);
    t_D(i, j, k, l) = 2 * shear_modulus_G * ((t_kd(i, k) ^ t_kd(j, l)) / 4.) +
                      A * (bulk_modulus_K - (2. / 3.) * shear_modulus_G) *
                          t_kd(i, j) * t_kd(k, l);
    MoFEMFunctionReturn(0);
  };
 
  commonDataPtr = boost::make_shared<ContactOps::CommonData>();
 
  commonDataPtr->mGradPtr = boost::make_shared<MatrixDouble>();
  commonDataPtr->mStrainPtr = boost::make_shared<MatrixDouble>();
  commonDataPtr->mStressPtr = boost::make_shared<MatrixDouble>();
  commonDataPtr->contactStressPtr = boost::make_shared<MatrixDouble>();
  commonDataPtr->contactStressDivergencePtr =
      boost::make_shared<MatrixDouble>();
  commonDataPtr->contactTractionPtr = boost::make_shared<MatrixDouble>();
  commonDataPtr->contactDispPtr = boost::make_shared<MatrixDouble>();
  commonDataPtr->curlContactStressPtr = boost::make_shared<MatrixDouble>();
 
  constexpr auto size_symm = (SPACE_DIM * (SPACE_DIM + 1)) / 2;
 
  commonDataPtr->mDPtr = boost::make_shared<MatrixDouble>();
  commonDataPtr->mDPtr->resize(size_symm * size_symm, 1);
 
  CHKERR set_matrial_stiffness();
  MoFEMFunctionReturn(0);
}
//! [Create common data]
 
//! [Boundary condition]
MoFEMErrorCode Example::bC() {
  MoFEMFunctionBegin;
  auto bc_mng = mField.getInterface<BcManager>();
  auto simple = mField.getInterface<Simple>();
 
  CHKERR bc_mng->removeBlockDOFsOnEntities(simple->getProblemName(),
                                           "NO_CONTACT", "SIGMA", 0, 3);
 
  CHKERR bc_mng->removeBlockDOFsOnEntities(simple->getProblemName(), "REMOVE_X",
                                           "U", 0, 0);
  CHKERR bc_mng->removeBlockDOFsOnEntities(simple->getProblemName(), "REMOVE_Y",
                                           "U", 1, 1);
  CHKERR bc_mng->removeBlockDOFsOnEntities(simple->getProblemName(), "REMOVE_Z",
                                           "U", 2, 2);
  CHKERR bc_mng->removeBlockDOFsOnEntities(simple->getProblemName(),
                                           "REMOVE_ALL", "U", 0, 3);
 
  CHKERR bc_mng->pushMarkDOFsOnEntities(simple->getProblemName(), "FIX_X", "U",
                                        0, 0);
  CHKERR bc_mng->pushMarkDOFsOnEntities(simple->getProblemName(), "FIX_Y", "U",
                                        1, 1);
  CHKERR bc_mng->pushMarkDOFsOnEntities(simple->getProblemName(), "FIX_Z", "U",
                                        2, 2);
  CHKERR bc_mng->pushMarkDOFsOnEntities(simple->getProblemName(), "FIX_ALL",
                                        "U", 0, 3);
 
  boundaryMarker = bc_mng->getMergedBlocksMarker(vector<string>{"FIX_"});
 
  MoFEMFunctionReturn(0);
}
//! [Boundary condition]
 
//! [Push operators to pipeline]
MoFEMErrorCode Example::OPs() {
  MoFEMFunctionBegin;
  PipelineManager *pipeline_mng = mField.getInterface<PipelineManager>();
  auto bc_mng = mField.getInterface<BcManager>();
 
  auto add_domain_base_ops = [&](auto &pipeline) {
    auto det_ptr = boost::make_shared<VectorDouble>();
    auto jac_ptr = boost::make_shared<MatrixDouble>();
    auto inv_jac_ptr = boost::make_shared<MatrixDouble>();
    if (SPACE_DIM == 2) {
      pipeline.push_back(new OpCalculateHOJacForFace(jac_ptr));
      pipeline.push_back(new OpInvertMatrix<2>(jac_ptr, det_ptr, inv_jac_ptr));
      pipeline.push_back(new OpSetInvJacH1ForFace(inv_jac_ptr));
      pipeline.push_back(new OpMakeHdivFromHcurl());
      pipeline.push_back(new OpSetContravariantPiolaTransformOnFace2D(jac_ptr));
      pipeline.push_back(new OpSetInvJacHcurlFace(inv_jac_ptr));
      pipeline.push_back(new OpSetHOWeightsOnFace());
    } else {
      pipeline.push_back(new OpCalculateHOJacVolume(jac_ptr));
      pipeline.push_back(new OpInvertMatrix<3>(jac_ptr, det_ptr, inv_jac_ptr));
      pipeline.push_back(
          new OpSetHOContravariantPiolaTransform(HDIV, det_ptr, jac_ptr));
      pipeline.push_back(new OpSetHOInvJacVectorBase(HDIV, inv_jac_ptr));
      pipeline.push_back(new OpSetHOInvJacToScalarBases(H1, inv_jac_ptr));
      pipeline.push_back(new OpSetHOWeights(det_ptr));
    }
  };
 
  auto henky_common_data_ptr = boost::make_shared<HenckyOps::CommonData>();
  henky_common_data_ptr->matGradPtr = commonDataPtr->mGradPtr;
  henky_common_data_ptr->matDPtr = commonDataPtr->mDPtr;
 
  auto add_domain_ops_lhs = [&](auto &pipeline) {
    pipeline.push_back(new OpSetBc("U", true, boundaryMarker));
 
    if (is_large_strains) {
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpCalculateVectorFieldGradient<SPACE_DIM, SPACE_DIM>(
              "U", commonDataPtr->mGradPtr));
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpCalculateEigenVals<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpCalculateLogC<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpCalculateLogC_dC<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpCalculateHenckyStress<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpCalculatePiolaStress<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpHenckyTangent<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpKPiola("U", "U", henky_common_data_ptr->getMatTangent()));
    } else {
      pipeline.push_back(new OpKCauchy("U", "U", commonDataPtr->mDPtr));
    }
 
    if (!is_quasi_static) {
      // Get pointer to U_tt shift in domain element
      auto get_rho = [this](const double, const double, const double) {
        auto *pipeline_mng = mField.getInterface<PipelineManager>();
        auto &fe_domain_lhs = pipeline_mng->getDomainLhsFE();
        return rho * fe_domain_lhs->ts_aa;
      };
      pipeline_mng->getOpDomainLhsPipeline().push_back(
          new OpMass("U", "U", get_rho));
    }
 
    auto unity = []() { return 1; };
    pipeline.push_back(new OpMixDivULhs("SIGMA", "U", unity, true));
    pipeline.push_back(new OpLambdaGraULhs("SIGMA", "U", unity, true));
 
    pipeline.push_back(new OpUnSetBc("U"));
  };
 
  auto add_domain_ops_rhs = [&](auto &pipeline) {
    auto get_body_force = [this](const double, const double, const double) {
      auto *pipeline_mng = mField.getInterface<PipelineManager>();
      FTensor::Index<'i', SPACE_DIM> i;
      FTensor::Tensor1<double, SPACE_DIM> t_source;
      auto fe_domain_rhs = pipeline_mng->getDomainRhsFE();
      const auto time = fe_domain_rhs->ts_t;
 
      // hardcoded gravity load
      t_source(i) = 0;
      t_source(1) = 1.0 * time;
      return t_source;
    };
 
    pipeline.push_back(new OpSetBc("U", true, boundaryMarker));
 
    pipeline.push_back(new OpBodyForce("U", get_body_force));
    pipeline.push_back(new OpCalculateVectorFieldGradient<SPACE_DIM, SPACE_DIM>(
        "U", commonDataPtr->mGradPtr));
 
    if (is_large_strains) {
      pipeline_mng->getOpDomainRhsPipeline().push_back(
          new OpCalculateEigenVals<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainRhsPipeline().push_back(
          new OpCalculateLogC<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainRhsPipeline().push_back(
          new OpCalculateLogC_dC<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainRhsPipeline().push_back(
          new OpCalculateHenckyStress<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainRhsPipeline().push_back(
          new OpCalculatePiolaStress<SPACE_DIM>("U", henky_common_data_ptr));
      pipeline_mng->getOpDomainRhsPipeline().push_back(new OpInternalForcePiola(
          "U", henky_common_data_ptr->getMatFirstPiolaStress()));
    } else {
      pipeline.push_back(new OpSymmetrizeTensor<SPACE_DIM>(
          "U", commonDataPtr->mGradPtr, commonDataPtr->mStrainPtr));
      pipeline.push_back(new OpTensorTimesSymmetricTensor<SPACE_DIM, SPACE_DIM>(
          "U", commonDataPtr->mStrainPtr, commonDataPtr->mStressPtr,
          commonDataPtr->mDPtr));
      pipeline.push_back(
          new OpInternalForceCauchy("U", commonDataPtr->mStressPtr));
    }
 
    pipeline.push_back(new OpCalculateVectorFieldValues<SPACE_DIM>(
        "U", commonDataPtr->contactDispPtr));
 
    pipeline.push_back(new OpCalculateHVecTensorField<SPACE_DIM, SPACE_DIM>(
        "SIGMA", commonDataPtr->contactStressPtr));
    pipeline.push_back(
        new OpCalculateHVecTensorDivergence<SPACE_DIM, SPACE_DIM>(
            "SIGMA", commonDataPtr->contactStressDivergencePtr));
 
    pipeline.push_back(
        new OpMixDivURhs("SIGMA", commonDataPtr->contactDispPtr,
                         [](double, double, double) { return 1; }));
    pipeline.push_back(
        new OpMixLambdaGradURhs("SIGMA", commonDataPtr->mGradPtr));
 
    pipeline.push_back(new OpMixUTimesDivLambdaRhs(
        "U", commonDataPtr->contactStressDivergencePtr));
    pipeline.push_back(
        new OpMixUTimesLambdaRhs("U", commonDataPtr->contactStressPtr));
 
    // only in case of dynamics
    if (!is_quasi_static) {
      auto mat_acceleration = boost::make_shared<MatrixDouble>();
      pipeline_mng->getOpDomainRhsPipeline().push_back(
          new OpCalculateVectorFieldValuesDotDot<SPACE_DIM>("U",
                                                            mat_acceleration));
      pipeline_mng->getOpDomainRhsPipeline().push_back(new OpInertiaForce(
          "U", mat_acceleration, [](double, double, double) { return rho; }));
    }
 
    pipeline.push_back(new OpUnSetBc("U"));
  };
 
  auto add_boundary_base_ops = [&](auto &pipeline) {
    pipeline.push_back(new OpSetPiolaTransformOnBoundary(CONTACT_SPACE));
    if (SPACE_DIM == 3)
      pipeline.push_back(new OpSetHOWeightsOnFace());
    pipeline.push_back(new OpCalculateVectorFieldValues<SPACE_DIM>(
        "U", commonDataPtr->contactDispPtr));
    pipeline.push_back(new OpCalculateHVecTensorTrace<SPACE_DIM, BoundaryEleOp>(
        "SIGMA", commonDataPtr->contactTractionPtr));
  };
 
  auto add_boundary_ops_lhs = [&](auto &pipeline) {
    MoFEMFunctionBegin;
    auto &bc_map = bc_mng->getBcMapByBlockName();
    for (auto bc : bc_map) {
      if (bc_mng->checkBlock(bc, "FIX_")) {
        MOFEM_LOG("EXAMPLE", Sev::inform)
            << "Set boundary matrix for " << bc.first;
        pipeline.push_back(
            new OpSetBc("U", false, bc.second->getBcMarkersPtr()));
        pipeline.push_back(new OpBoundaryMass(
            "U", "U", [](double, double, double) { return 1.; },
            bc.second->getBcEntsPtr()));
        pipeline.push_back(new OpUnSetBc("U"));
      }
    }
 
    pipeline.push_back(new OpSetBc("U", true, boundaryMarker));
    pipeline.push_back(
        new OpConstrainBoundaryLhs_dU("SIGMA", "U", commonDataPtr));
    pipeline.push_back(
        new OpConstrainBoundaryLhs_dTraction("SIGMA", "SIGMA", commonDataPtr));
    pipeline.push_back(new OpSpringLhs(
        "U", "U",
 
        [this](double, double, double) { return spring_stiffness; }
 
        ));
    if (boundaryMarker)
      pipeline.push_back(new OpUnSetBc("U"));
    MoFEMFunctionReturn(0);
  };
 
  auto time_scaled = [&](double, double, double) {
    auto *pipeline_mng = mField.getInterface<PipelineManager>();
    auto &fe_domain_rhs = pipeline_mng->getDomainRhsFE();
    return -fe_domain_rhs->ts_t;
  };
 
  auto add_boundary_ops_rhs = [&](auto &pipeline) {
    MoFEMFunctionBegin;
    for (auto &bc : mField.getInterface<BcManager>()->getBcMapByBlockName()) {
      if (bc_mng->checkBlock(bc, "FIX_")) {
        MOFEM_LOG("EXAMPLE", Sev::inform)
            << "Set boundary residual for " << bc.first;
        pipeline.push_back(
            new OpSetBc("U", false, bc.second->getBcMarkersPtr()));
        auto attr_vec = boost::make_shared<MatrixDouble>(SPACE_DIM, 1);
        attr_vec->clear();
        if (bc.second->bcAttributes.size() != SPACE_DIM)
          SETERRQ1(PETSC_COMM_WORLD, MOFEM_DATA_INCONSISTENCY,
                   "Wrong size of boundary attributes vector. Set right block "
                   "size attributes. Size of attributes %d",
                   bc.second->bcAttributes.size());
        std::copy(&bc.second->bcAttributes[0],
                  &bc.second->bcAttributes[SPACE_DIM],
                  attr_vec->data().begin());
 
        pipeline.push_back(new OpBoundaryVec("U", attr_vec, time_scaled,
                                             bc.second->getBcEntsPtr()));
        pipeline.push_back(new OpBoundaryInternal(
            "U", commonDataPtr->contactDispPtr,
            [](double, double, double) { return 1.; },
            bc.second->getBcEntsPtr()));
 
        pipeline.push_back(new OpUnSetBc("U"));
      }
    }
 
    pipeline.push_back(new OpSetBc("U", true, boundaryMarker));
    pipeline.push_back(new OpConstrainBoundaryRhs("SIGMA", commonDataPtr));
    pipeline.push_back(new OpSpringRhs(
        "U", commonDataPtr->contactDispPtr,
        [this](double, double, double) { return spring_stiffness; }));
    pipeline.push_back(new OpUnSetBc("U"));
    MoFEMFunctionReturn(0);
  };
 
  add_domain_base_ops(pipeline_mng->getOpDomainLhsPipeline());
  add_domain_base_ops(pipeline_mng->getOpDomainRhsPipeline());
  add_domain_ops_lhs(pipeline_mng->getOpDomainLhsPipeline());
  add_domain_ops_rhs(pipeline_mng->getOpDomainRhsPipeline());
 
  add_boundary_base_ops(pipeline_mng->getOpBoundaryLhsPipeline());
  add_boundary_base_ops(pipeline_mng->getOpBoundaryRhsPipeline());
  CHKERR add_boundary_ops_lhs(pipeline_mng->getOpBoundaryLhsPipeline());
  CHKERR add_boundary_ops_rhs(pipeline_mng->getOpBoundaryRhsPipeline());
 
  auto integration_rule_vol = [](int, int, int approx_order) {
    return 3 * order;
  };
  CHKERR pipeline_mng->setDomainRhsIntegrationRule(integration_rule_vol);
  CHKERR pipeline_mng->setDomainLhsIntegrationRule(integration_rule_vol);
  auto integration_rule_boundary = [](int, int, int approx_order) {
    return 3 * order;
  };
  CHKERR pipeline_mng->setBoundaryRhsIntegrationRule(integration_rule_boundary);
  CHKERR pipeline_mng->setBoundaryLhsIntegrationRule(integration_rule_boundary);
 
  MoFEMFunctionReturn(0);
}
//! [Push operators to pipeline]
 
//! [Solve]
MoFEMErrorCode Example::tsSolve() {
  MoFEMFunctionBegin;
 
  Simple *simple = mField.getInterface<Simple>();
  PipelineManager *pipeline_mng = mField.getInterface<PipelineManager>();
  ISManager *is_manager = mField.getInterface<ISManager>();
 
  auto set_section_monitor = [&](auto solver) {
    MoFEMFunctionBegin;
    SNES snes;
    CHKERR TSGetSNES(solver, &snes);
    PetscViewerAndFormat *vf;
    CHKERR PetscViewerAndFormatCreate(PETSC_VIEWER_STDOUT_WORLD,
                                      PETSC_VIEWER_DEFAULT, &vf);
    CHKERR SNESMonitorSet(
        snes,
        (MoFEMErrorCode(*)(SNES, PetscInt, PetscReal, void *))SNESMonitorFields,
        vf, (MoFEMErrorCode(*)(void **))PetscViewerAndFormatDestroy);
    MoFEMFunctionReturn(0);
  };
 
  auto scatter_create = [&](auto D, auto coeff) {
    SmartPetscObj<IS> is;
    CHKERR is_manager->isCreateProblemFieldAndRank(simple->getProblemName(),
                                                   ROW, "U", coeff, coeff, is);
    int loc_size;
    CHKERR ISGetLocalSize(is, &loc_size);
    Vec v;
    CHKERR VecCreateMPI(mField.get_comm(), loc_size, PETSC_DETERMINE, &v);
    VecScatter scatter;
    CHKERR VecScatterCreate(D, is, v, PETSC_NULL, &scatter);
    return std::make_tuple(SmartPetscObj<Vec>(v),
                           SmartPetscObj<VecScatter>(scatter));
  };
 
  auto set_time_monitor = [&](auto dm, auto solver) {
    MoFEMFunctionBegin;
    boost::shared_ptr<Monitor> monitor_ptr(
        new Monitor(dm, commonDataPtr, uXScatter, uYScatter, uZScatter));
    boost::shared_ptr<ForcesAndSourcesCore> null;
    CHKERR DMMoFEMTSSetMonitor(dm, solver, simple->getDomainFEName(),
                               monitor_ptr, null, null);
    MoFEMFunctionReturn(0);
  };
 
  auto dm = simple->getDM();
  auto D = smartCreateDMVector(dm);
  uXScatter = scatter_create(D, 0);
  uYScatter = scatter_create(D, 1);
  if (SPACE_DIM == 3)
    uZScatter = scatter_create(D, 2);
 
  if (is_quasi_static) {
    auto solver = pipeline_mng->createTSIM();
    auto D = smartCreateDMVector(dm);
    CHKERR set_section_monitor(solver);
    CHKERR set_time_monitor(dm, solver);
    CHKERR TSSetSolution(solver, D);
    CHKERR TSSetFromOptions(solver);
    CHKERR TSSetUp(solver);
    CHKERR TSSolve(solver, NULL);
  } else {
    auto solver = pipeline_mng->createTSIM2();
    auto dm = simple->getDM();
    auto D = smartCreateDMVector(dm);
    auto DD = smartVectorDuplicate(D);
    CHKERR set_section_monitor(solver);
    CHKERR set_time_monitor(dm, solver);
    CHKERR TS2SetSolution(solver, D, DD);
    CHKERR TSSetFromOptions(solver);
    CHKERR TSSetUp(solver);
    CHKERR TSSolve(solver, NULL);
  }
 
  CHKERR VecGhostUpdateBegin(D, INSERT_VALUES, SCATTER_FORWARD);
  CHKERR VecGhostUpdateEnd(D, INSERT_VALUES, SCATTER_FORWARD);
  CHKERR DMoFEMMeshToLocalVector(dm, D, INSERT_VALUES, SCATTER_REVERSE);
 
  MoFEMFunctionReturn(0);
}
//! [Solve]
 
//! [Postprocess results]
MoFEMErrorCode Example::postProcess() { return 0; }
//! [Postprocess results]
 
//! [Check]
MoFEMErrorCode Example::checkResults() { return 0; }
//! [Check]
 
template <int DIM> Range Example::getEntsOnMeshSkin() {
  Range body_ents;
  CHKERR mField.get_moab().get_entities_by_dimension(0, DIM, body_ents);
  Skinner skin(&mField.get_moab());
  Range skin_ents;
  CHKERR skin.find_skin(0, body_ents, false, skin_ents);
 
  return skin_ents;
};
 
static char help[] = "...\n\n";
 
int main(int argc, char *argv[]) {
 
  // Initialisation of MoFEM/PETSc and MOAB data structures
  const char param_file[] = "param_file.petsc";
  MoFEM::Core::Initialize(&argc, &argv, param_file, help);
 
  // Add logging channel for example
  auto core_log = logging::core::get();
  core_log->add_sink(
      LogManager::createSink(LogManager::getStrmWorld(), "EXAMPLE"));
  LogManager::setLog("EXAMPLE");
  MOFEM_LOG_TAG("EXAMPLE", "example");
 
  try {
 
    //! [Register MoFEM discrete manager in PETSc]
    DMType dm_name = "DMMOFEM";
    CHKERR DMRegister_MoFEM(dm_name);
    //! [Register MoFEM discrete manager in PETSc
 
    //! [Create MoAB]
    moab::Core mb_instance;              ///< mesh database
    moab::Interface &moab = mb_instance; ///< mesh database interface
    //! [Create MoAB]
 
    //! [Create MoFEM]
    MoFEM::Core core(moab);           ///< finite element database
    MoFEM::Interface &m_field = core; ///< finite element database insterface
    //! [Create MoFEM]
 
    //! [Load mesh]
    Simple *simple = m_field.getInterface<Simple>();
    CHKERR simple->getOptions();
    CHKERR simple->loadFile("");
    //! [Load mesh]
 
    //! [Example]
    Example ex(m_field);
    CHKERR ex.runProblem();
    //! [Example]
  }
  CATCH_ERRORS;
 
  CHKERR MoFEM::Core::Finalize();
}

/* This file is part of MoFEM.
 * MoFEM is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * MoFEM 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 Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with MoFEM. If not, see <http://www.gnu.org/licenses/>. */
 
/**
 * \file ContactOps.hpp
 * \example ContactOps.hpp
 */
 
namespace ContactOps {
 
 
//! [Common data]
struct CommonData {
  boost::shared_ptr<MatrixDouble> mDPtr;
  boost::shared_ptr<MatrixDouble> mGradPtr;
  boost::shared_ptr<MatrixDouble> mStrainPtr;
  boost::shared_ptr<MatrixDouble> mStressPtr;
 
  boost::shared_ptr<MatrixDouble> contactStressPtr;
  boost::shared_ptr<MatrixDouble> contactStressDivergencePtr;
  boost::shared_ptr<MatrixDouble> contactTractionPtr;
  boost::shared_ptr<MatrixDouble> contactDispPtr;
 
  boost::shared_ptr<MatrixDouble> curlContactStressPtr;
};
//! [Common data]
 
FTensor::Index<'i', SPACE_DIM> i;
FTensor::Index<'j', SPACE_DIM> j;
FTensor::Index<'k', SPACE_DIM> k;
FTensor::Index<'l', SPACE_DIM> l;
 
struct OpConstrainBoundaryRhs : public AssemblyBoundaryEleOp {
  OpConstrainBoundaryRhs(const std::string field_name,
                         boost::shared_ptr<CommonData> common_data_ptr);
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &data);
 
private:
  boost::shared_ptr<CommonData> commonDataPtr;
};
 
struct OpConstrainBoundaryLhs_dU : public AssemblyBoundaryEleOp {
  OpConstrainBoundaryLhs_dU(const std::string row_field_name,
                            const std::string col_field_name,
                            boost::shared_ptr<CommonData> common_data_ptr);
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
 
private:
  boost::shared_ptr<CommonData> commonDataPtr;
};
 
struct OpConstrainBoundaryLhs_dTraction : public AssemblyBoundaryEleOp {
  OpConstrainBoundaryLhs_dTraction(
      const std::string row_field_name, const std::string col_field_name,
      boost::shared_ptr<CommonData> common_data_ptr);
  MoFEMErrorCode iNtegrate(EntitiesFieldData::EntData &row_data,
                           EntitiesFieldData::EntData &col_data);
 
private:
  boost::shared_ptr<CommonData> commonDataPtr;
};
 
template <typename T1, typename T2>
inline FTensor::Tensor1<double, SPACE_DIM>
normal(FTensor::Tensor1<T1, 3> &t_coords,
       FTensor::Tensor1<T2, SPACE_DIM> &t_disp) {
  FTensor::Tensor1<double, SPACE_DIM> t_normal;
  t_normal(i) = 0;
  t_normal(1) = 1.;
  return t_normal;
}
 
template <typename T>
inline double gap0(FTensor::Tensor1<T, 3> &t_coords,
                   FTensor::Tensor1<double, SPACE_DIM> &t_normal) {
  return (-0.5 - t_coords(1)) * t_normal(1);
}
 
template <typename T>
inline double gap(FTensor::Tensor1<T, SPACE_DIM> &t_disp,
                  FTensor::Tensor1<double, SPACE_DIM> &t_normal) {
  return t_disp(i) * t_normal(i);
}
 
template <typename T>
inline double normal_traction(FTensor::Tensor1<T, SPACE_DIM> &t_traction,
                              FTensor::Tensor1<double, SPACE_DIM> &t_normal) {
  return -t_traction(i) * t_normal(i);
}
 
inline double sign(double x) {
  if (x == 0)
    return 0;
  else if (x > 0)
    return 1;
  else
    return -1;
};
 
inline double w(const double g, const double t) { return g - cn * t; }
 
inline double constrian(double &&g0, double &&g, double &&t) {
  return (w(g - g0, t) + std::abs(w(g - g0, t))) / 2 + g0;
};
 
inline double diff_constrains_dtraction(double &&g0, double &&g, double &&t) {
  return -cn * (1 + sign(w(g - g0, t))) / 2;
}
 
inline double diff_constrains_dgap(double &&g0, double &&g, double &&t) {
  return (1 + sign(w(g - g0, t))) / 2;
}
 
OpConstrainBoundaryRhs::OpConstrainBoundaryRhs(
    const std::string field_name, boost::shared_ptr<CommonData> common_data_ptr)
    : AssemblyBoundaryEleOp(field_name, field_name, DomainEleOp::OPROW),
      commonDataPtr(common_data_ptr) {}
 
MoFEMErrorCode
OpConstrainBoundaryRhs::iNtegrate(EntitiesFieldData::EntData &data) {
  MoFEMFunctionBegin;
 
  const size_t nb_gauss_pts = AssemblyBoundaryEleOp::getGaussPts().size2();
 
  auto &nf = AssemblyBoundaryEleOp::locF;
 
  auto t_normal = getFTensor1Normal();
  t_normal(i) /= sqrt(t_normal(j) * t_normal(j));
 
  auto t_w = getFTensor0IntegrationWeight();
  auto t_disp = getFTensor1FromMat<SPACE_DIM>(*(commonDataPtr->contactDispPtr));
  auto t_traction =
      getFTensor1FromMat<SPACE_DIM>(*(commonDataPtr->contactTractionPtr));
  auto t_coords = getFTensor1CoordsAtGaussPts();
 
  size_t nb_base_functions = data.getN().size2() / 3;
  auto t_base = data.getFTensor1N<3>();
  for (size_t gg = 0; gg != nb_gauss_pts; ++gg) {
 
    auto t_nf = getFTensor1FromPtr<SPACE_DIM>(&nf[0]);
 
    const double alpha = t_w * getMeasure();
 
    auto t_contact_normal = normal(t_coords, t_disp);
    FTensor::Tensor2<double, SPACE_DIM, SPACE_DIM> t_P;
    t_P(i, j) = t_contact_normal(i) * t_contact_normal(j);
 
    FTensor::Tensor2<double, SPACE_DIM, SPACE_DIM> t_Q;
    t_Q(i, j) = kronecker_delta(i, j) - t_P(i, j);
 
    FTensor::Tensor1<double, SPACE_DIM> t_rhs_constrains;
 
    t_rhs_constrains(i) =
        t_contact_normal(i) *
        constrian(gap0(t_coords, t_contact_normal),
                  gap(t_disp, t_contact_normal),
                  normal_traction(t_traction, t_contact_normal));
 
    FTensor::Tensor1<double, SPACE_DIM> t_rhs_tangent_disp,
        t_rhs_tangent_traction;
    t_rhs_tangent_disp(i) = t_Q(i, j) * t_disp(j);
    t_rhs_tangent_traction(i) = cn * t_Q(i, j) * t_traction(j);
 
    size_t bb = 0;
    for (; bb != AssemblyBoundaryEleOp::nbRows / SPACE_DIM; ++bb) {
      const double beta = alpha * (t_base(i) * t_normal(i));
 
      t_nf(i) -= beta * t_rhs_constrains(i);
      t_nf(i) -= beta * t_rhs_tangent_disp(i);
      t_nf(i) += beta * t_rhs_tangent_traction(i);
 
      ++t_nf;
      ++t_base;
    }
    for (; bb < nb_base_functions; ++bb)
      ++t_base;
 
    ++t_disp;
    ++t_traction;
    ++t_coords;
    ++t_w;
  }
 
  MoFEMFunctionReturn(0);
}
 
OpConstrainBoundaryLhs_dU::OpConstrainBoundaryLhs_dU(
    const std::string row_field_name, const std::string col_field_name,
    boost::shared_ptr<CommonData> common_data_ptr)
    : AssemblyBoundaryEleOp(row_field_name, col_field_name,
                            DomainEleOp::OPROWCOL),
      commonDataPtr(common_data_ptr) {
  sYmm = false;
}
 
MoFEMErrorCode OpConstrainBoundaryLhs_dU::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  const size_t nb_gauss_pts = getGaussPts().size2();
  auto &locMat = AssemblyBoundaryEleOp::locMat;
 
  auto t_normal = getFTensor1Normal();
  t_normal(i) /= sqrt(t_normal(j) * t_normal(j));
 
  auto t_disp = getFTensor1FromMat<SPACE_DIM>(*(commonDataPtr->contactDispPtr));
  auto t_traction =
      getFTensor1FromMat<SPACE_DIM>(*(commonDataPtr->contactTractionPtr));
  auto t_coords = getFTensor1CoordsAtGaussPts();
 
  auto t_w = getFTensor0IntegrationWeight();
  auto t_row_base = row_data.getFTensor1N<3>();
  size_t nb_face_functions = row_data.getN().size2() / 3;
 
  for (size_t gg = 0; gg != nb_gauss_pts; ++gg) {
 
    const double alpha = t_w * getMeasure();
 
    auto t_contact_normal = normal(t_coords, t_disp);
    FTensor::Tensor2<double, SPACE_DIM, SPACE_DIM> t_P;
    t_P(i, j) = t_contact_normal(i) * t_contact_normal(j);
 
    FTensor::Tensor2<double, SPACE_DIM, SPACE_DIM> t_Q;
    t_Q(i, j) = kronecker_delta(i, j) - t_P(i, j);
 
    auto diff_constrain = diff_constrains_dgap(
        gap0(t_coords, t_contact_normal), gap(t_disp, t_contact_normal),
        normal_traction(t_traction, t_contact_normal));
 
    size_t rr = 0;
    for (; rr != AssemblyBoundaryEleOp::nbRows / SPACE_DIM; ++rr) {
 
      auto t_mat = getFTensor2FromArray<SPACE_DIM, SPACE_DIM, SPACE_DIM>(
          locMat, SPACE_DIM * rr);
 
      const double row_base = t_row_base(i) * t_normal(i);
 
      auto t_col_base = col_data.getFTensor0N(gg, 0);
      for (size_t cc = 0; cc != AssemblyBoundaryEleOp::nbCols / SPACE_DIM;
           ++cc) {
        const double beta = alpha * row_base * t_col_base;
 
        t_mat(i, j) -= (beta * diff_constrain) * t_P(i, j);
        t_mat(i, j) -= beta * t_Q(i, j);
 
        ++t_col_base;
        ++t_mat;
      }
 
      ++t_row_base;
    }
    for (; rr < nb_face_functions; ++rr)
      ++t_row_base;
 
    ++t_disp;
    ++t_traction;
    ++t_coords;
    ++t_w;
  }
 
  MoFEMFunctionReturn(0);
}
 
OpConstrainBoundaryLhs_dTraction::OpConstrainBoundaryLhs_dTraction(
    const std::string row_field_name, const std::string col_field_name,
    boost::shared_ptr<CommonData> common_data_ptr)
    : AssemblyBoundaryEleOp(row_field_name, col_field_name,
                            DomainEleOp::OPROWCOL),
      commonDataPtr(common_data_ptr) {
  sYmm = false;
}
 
MoFEMErrorCode OpConstrainBoundaryLhs_dTraction::iNtegrate(
    EntitiesFieldData::EntData &row_data,
    EntitiesFieldData::EntData &col_data) {
  MoFEMFunctionBegin;
 
  const size_t nb_gauss_pts = getGaussPts().size2();
  auto &locMat = AssemblyBoundaryEleOp::locMat;
 
  auto t_normal = getFTensor1Normal();
  t_normal(i) /= sqrt(t_normal(j) * t_normal(j));
 
  auto t_disp = getFTensor1FromMat<SPACE_DIM>(*(commonDataPtr->contactDispPtr));
  auto t_traction =
      getFTensor1FromMat<SPACE_DIM>(*(commonDataPtr->contactTractionPtr));
  auto t_coords = getFTensor1CoordsAtGaussPts();
 
  auto t_w = getFTensor0IntegrationWeight();
  auto t_row_base = row_data.getFTensor1N<3>();
  size_t nb_face_functions = row_data.getN().size2() / 3;
 
  for (size_t gg = 0; gg != nb_gauss_pts; ++gg) {
 
    const double alpha = t_w * getMeasure();
 
    auto t_contact_normal = normal(t_coords, t_disp);
    FTensor::Tensor2<double, SPACE_DIM, SPACE_DIM> t_P;
    t_P(i, j) = t_contact_normal(i) * t_contact_normal(j);
 
    FTensor::Tensor2<double, SPACE_DIM, SPACE_DIM> t_Q;
    t_Q(i, j) = kronecker_delta(i, j) - t_P(i, j);
 
    const double diff_traction = diff_constrains_dtraction(
        gap0(t_coords, t_contact_normal), gap(t_disp, t_contact_normal),
        normal_traction(t_traction, t_contact_normal));
 
    size_t rr = 0;
    for (; rr != AssemblyBoundaryEleOp::nbRows / SPACE_DIM; ++rr) {
 
      auto t_mat = getFTensor2FromArray<SPACE_DIM, SPACE_DIM, SPACE_DIM>(
          locMat, SPACE_DIM * rr);
      const double row_base = t_row_base(i) * t_normal(i);
 
      auto t_col_base = col_data.getFTensor1N<3>(gg, 0);
      for (size_t cc = 0; cc != AssemblyBoundaryEleOp::nbCols / SPACE_DIM;
           ++cc) {
        const double col_base = t_col_base(i) * t_normal(i);
        const double beta = alpha * row_base * col_base;
 
        t_mat(i, j) += (beta * diff_traction) * t_P(i, j);
        t_mat(i, j) += beta * cn * t_Q(i, j);
 
        ++t_col_base;
        ++t_mat;
      }
 
      ++t_row_base;
    }
    for (; rr < nb_face_functions; ++rr)
      ++t_row_base;
 
    ++t_disp;
    ++t_traction;
    ++t_coords;
    ++t_w;
  }
 
  MoFEMFunctionReturn(0);
}
 
}; // namespace ContactOps