volume.hh

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// SPDX-FileCopyrightText: 2021-2025 The Ikarus Developers mueller@ibb.uni-stuttgart.de
// SPDX-License-Identifier: LGPL-3.0-or-later
 
#pragma once
 
#include <dune/localfefunctions/derivativetransformators.hh>
#include <dune/localfefunctions/meta.hh>
 
#include <ikarus/finiteelements/ferequirements.hh>
#include <ikarus/utils/concepts.hh>
#include <ikarus/utils/traits.hh>
 
namespace Ikarus {
 
template <typename PreFE, typename FE>
class VolumeLoad;
 
template <int wd>
struct VolumeLoadPre
{
  static constexpr int worldDim = wd;
  std::function<Eigen::Vector<double, worldDim>(const Dune::FieldVector<double, worldDim>&, const double&)> volumeLoad;
 
  template <typename PreFE, typename FE>
  using Skill = VolumeLoad<PreFE, FE>;
};
 
// Deduction guide
template <class F>
VolumeLoadPre(F f) -> VolumeLoadPre<traits::FunctionTraits<F>::return_type::RowsAtCompileTime>;
 
template <typename PreFE, typename FE>
class VolumeLoad
{
public:
  using Traits                  = PreFE::Traits;
  using Requirement             = FERequirements<FESolutions::displacement, FEParameter::loadfactor>;
  static constexpr int worldDim = Traits::worlddim;
  using Pre                     = VolumeLoadPre<worldDim>;
 
  explicit VolumeLoad(const Pre& pre = {})
      : volumeLoad_{pre.volumeLoad} {}
 
protected:
  template <template <typename, int, int> class RT>
  requires Dune::AlwaysFalse<RT<double, 1, 1>>::value
  auto calculateAtImpl(const Requirement& req, const Dune::FieldVector<double, Traits::mydim>& local,
                       Dune::PriorityTag<0>) const {}
 
  template <typename ST>
  auto calculateScalarImpl(
      const Requirement& par, ScalarAffordance affordance,
      const std::optional<std::reference_wrapper<const Eigen::VectorX<ST>>>& dx = std::nullopt) const -> ST {
    if (not volumeLoad_)
      return 0.0;
    ST energy            = 0.0;
    const auto uFunction = underlying().displacementFunction(par, dx);
    const auto geo       = underlying().geometry();
    const auto& lambda   = par.parameter();
 
    for (const auto& [gpIndex, gp] : uFunction.viewOverIntegrationPoints()) {
      const auto uVal                      = uFunction.evaluate(gpIndex);
      Eigen::Vector<double, worldDim> fext = volumeLoad_(geo.global(gp.position()), lambda);
      energy -= uVal.dot(fext) * geo.integrationElement(gp.position()) * gp.weight();
    }
    return energy;
  }
 
  template <typename ST>
  void calculateVectorImpl(
      const Requirement& par, VectorAffordance affordance, typename Traits::template VectorType<ST> force,
      const std::optional<std::reference_wrapper<const Eigen::VectorX<ST>>>& dx = std::nullopt) const {
    if (not volumeLoad_)
      return;
    using namespace Dune::DerivativeDirections;
    using namespace Dune;
    const auto uFunction = underlying().displacementFunction(par, dx);
    const auto geo       = underlying().geometry();
    const auto& lambda   = par.parameter();
 
    for (const auto& [gpIndex, gp] : uFunction.viewOverIntegrationPoints()) {
      const Eigen::Vector<double, worldDim> fext = volumeLoad_(geo.global(gp.position()), lambda);
      const double intElement                    = geo.integrationElement(gp.position()) * gp.weight();
      for (size_t i = 0; i < underlying().numberOfNodes(); ++i) {
        const auto udCi = uFunction.evaluateDerivative(gpIndex, wrt(coeff(i)));
        force.template segment<worldDim>(worldDim * i) -= udCi * fext * intElement;
      }
    }
  }
 
  template <typename ST>
  void calculateMatrixImpl(
      const Requirement& par, MatrixAffordance, typename Traits::template MatrixType<> K,
      const std::optional<std::reference_wrapper<const Eigen::VectorX<ST>>>& dx = std::nullopt) const {}
 
private:
  std::function<Eigen::Vector<double, worldDim>(const Dune::FieldVector<double, worldDim>&, const double&)> volumeLoad_;
  //> CRTP
  const auto& underlying() const { return static_cast<const FE&>(*this); }
  auto& underlying() { return static_cast<FE&>(*this); }
};
 
template <int worldDim>
auto volumeLoad(const std::function<Eigen::Vector<double, worldDim>(const Dune::FieldVector<double, worldDim>&,
                                                                    const double&)>& f) {
  VolumeLoadPre pre(f);
  return pre;
}
 
template <typename F>
auto volumeLoad(F&& f) {
  VolumeLoadPre pre(f);
  return pre;
}
 
} // namespace Ikarus