initial_state_shock_front.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2022 - 2025 by the ryujin authors
//
 
#pragma once
 
#include <compile_time_options.h>
 
#include <initial_state_library.h>
 
namespace ryujin
{
  namespace EulerInitialStates
  {
    template <typename Description, int dim, typename Number>
    class ShockFront : public InitialState<Description, dim, Number>
    {
    public:
      using HyperbolicSystem = typename Description::HyperbolicSystem;
      using View = typename HyperbolicSystem::template View<dim, Number>;
      using state_type = typename View::state_type;
 
      ShockFront(const HyperbolicSystem &hyperbolic_system,
                 const std::string subsection)
          : InitialState<Description, dim, Number>("shock front", subsection)
          , hyperbolic_system_(hyperbolic_system)
      {
        gamma_ = 1.4;
        if constexpr (!View::have_gamma) {
          this->add_parameter("gamma", gamma_, "The ratio of specific heats");
        }
 
        primitive_right_[0] = 1.4;
        primitive_right_[1] = 0.0;
        primitive_right_[2] = 1.;
        this->add_parameter(
            "primitive state",
            primitive_right_,
            "1d primitive state [rho, u, p] (for the Noble-Abel gas EOS) "
            "before the shock (to the right)");
 
        mach_number_ = 2.0;
        this->add_parameter(
            "mach number",
            mach_number_,
            "Mach number of shock front (S1, S3 = mach * a_L/R)");
 
        const auto compute_and_convert_states = [&]() {
          const auto view = hyperbolic_system_.template view<dim, Number>();
 
          if constexpr (View::have_gamma) {
            gamma_ = view.gamma();
          }
 
          /* Compute post-shock state and S3: */
 
          auto b = Number(0.);
          if constexpr (View::have_covolume_constant)
            b = view.eos_covolume_constant();
 
          const auto &rho_R = primitive_right_[0];
          const auto &u_R = primitive_right_[1];
          const auto &p_R = primitive_right_[2];
          /* a_R^2 = gamma * p / rho / (1 - b * rho) */
          const Number a_R = std::sqrt(gamma_ * p_R / rho_R / (1 - b * rho_R));
          const Number mach_R = u_R / a_R;
 
          S3_ = mach_number_ * a_R;
          const Number delta_mach = mach_R - mach_number_;
 
          const Number rho_L =
              rho_R * (gamma_ + Number(1.)) * delta_mach * delta_mach /
              ((gamma_ - Number(1.)) * delta_mach * delta_mach + Number(2.));
          const Number u_L =
              (Number(1.) - rho_R / rho_L) * S3_ + rho_R / rho_L * u_R;
          const Number p_L = p_R *
                             (Number(2.) * gamma_ * delta_mach * delta_mach -
                              (gamma_ - Number(1.))) /
                             (gamma_ + Number(1.));
 
          using state_type_1d =
              typename HyperbolicSystem::template View<1, Number>::state_type;
 
          if constexpr (View::have_energy_equation) {
            state_left_ =
                view.from_initial_state(state_type_1d{{rho_L, u_L, p_L}});
            state_right_ =
                view.from_initial_state(state_type_1d{{rho_R, u_R, p_R}});
          } else {
            state_left_ = view.from_initial_state(state_type_1d{{rho_L, u_L}});
            state_right_ = view.from_initial_state(state_type_1d{{rho_R, u_R}});
          }
        };
 
        this->parse_parameters_call_back.connect(compute_and_convert_states);
        compute_and_convert_states();
      }
 
 
      state_type compute(const dealii::Point<dim> &point, Number t) final
      {
        const Number position_1d = Number(point[0] - S3_ * t);
        return (position_1d > 0. ? state_right_ : state_left_);
      }
 
    private:
      const HyperbolicSystem &hyperbolic_system_;
 
      Number gamma_;
 
      dealii::Tensor<1, 3, Number> primitive_left_;
      dealii::Tensor<1, 3, Number> primitive_right_;
      Number mach_number_;
      Number S3_;
 
      state_type state_left_;
      state_type state_right_;
    };
  } // namespace EulerInitialStates
} // namespace ryujin