initial_state_function.h

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//
// SPDX-License-Identifier: Apache-2.0
// [LANL Copyright Statement]
// Copyright (C) 2023 - 2024 by the ryujin authors
// Copyright (C) 2023 - 2024 by Triad National Security, LLC
//
 
#pragma once
 
#include <compile_time_options.h>
 
#include <initial_state_library.h>
 
#include <deal.II/base/function_parser.h>
 
namespace ryujin
{
  namespace ShallowWaterInitialStates
  {
    template <typename Description, int dim, typename Number>
    class Function : public InitialState<Description, dim, Number>
    {
    public:
      using HyperbolicSystem = typename Description::HyperbolicSystem;
      using View =
          typename Description::template HyperbolicSystemView<dim, Number>;
      using state_type = typename View::state_type;
 
      Function(const HyperbolicSystem &hyperbolic_system,
               const std::string subsection)
          : InitialState<Description, dim, Number>("function", subsection)
          , hyperbolic_system_(hyperbolic_system)
      {
 
        depth_expression_ = "1.4";
        this->add_parameter(
            "water elevation expression",
            depth_expression_,
            "A function expression describing the water elevation. When "
            "bathymetry is 0, this reduces to the water depth.");
 
        bathymetry_expression_ = "0.";
        this->add_parameter("bathymetry expression",
                            bathymetry_expression_,
                            "A function expression describing the bathymetry");
 
 
        velocity_x_expression_ = "3.0";
        this->add_parameter(
            "velocity x expression",
            velocity_x_expression_,
            "A function expression describing the x-component of the velocity");
 
        if constexpr (dim > 1) {
          velocity_y_expression_ = "0.0";
          this->add_parameter("velocity y expression",
                              velocity_y_expression_,
                              "A function expression describing the "
                              "y-component of the velocity");
        }
 
        /*
         * Set up the muparser object with the final flux description from
         * the parameter file:
         */
        const auto set_up_muparser = [this] {
          using FP = dealii::FunctionParser<dim>;
          /*
           * This variant of the constructor initializes the function
           * parser with support for a time-dependent description involving
           * a variable »t«:
           */
          depth_function_ = std::make_unique<FP>(depth_expression_);
          velocity_x_function_ = std::make_unique<FP>(velocity_x_expression_);
          if constexpr (dim > 1)
            velocity_y_function_ = std::make_unique<FP>(velocity_y_expression_);
          bathymetry_function_ = std::make_unique<FP>(bathymetry_expression_);
        };
 
        set_up_muparser();
        this->parse_parameters_call_back.connect(set_up_muparser);
      }
 
      state_type compute(const dealii::Point<dim> &point, Number t) final
      {
        const auto view = hyperbolic_system_.template view<dim, Number>();
        state_type full_primitive;
 
        /* Compute bathymetry */
        const Number z = compute_bathymetry(point);
 
        depth_function_->set_time(t);
        full_primitive[0] =
            std::max(Number(depth_function_->value(point)) - z, Number(0.));
 
        velocity_x_function_->set_time(t);
        full_primitive[1] = velocity_x_function_->value(point);
 
        if constexpr (dim > 1) {
          velocity_y_function_->set_time(t);
          full_primitive[2] = velocity_y_function_->value(point);
        }
 
        return view.from_primitive_state(full_primitive);
      }
 
      auto initial_precomputations(const dealii::Point<dim> &point) ->
          typename InitialState<Description, dim, Number>::
              initial_precomputed_type final
      {
        /* Compute bathymetry: */
        return {compute_bathymetry(point)};
      }
 
    private:
      const HyperbolicSystem &hyperbolic_system_;
 
      std::string depth_expression_;
      std::string velocity_x_expression_;
      std::string velocity_y_expression_;
      std::string bathymetry_expression_;
 
      std::unique_ptr<dealii::FunctionParser<dim>> depth_function_;
      std::unique_ptr<dealii::FunctionParser<dim>> velocity_x_function_;
      std::unique_ptr<dealii::FunctionParser<dim>> velocity_y_function_;
      std::unique_ptr<dealii::FunctionParser<dim>> bathymetry_function_;
 
      DEAL_II_ALWAYS_INLINE inline Number
      compute_bathymetry(const dealii::Point<dim> &point) const
      {
        bathymetry_function_->set_time(0.);
        return bathymetry_function_->value(point);
      }
    };
  } // namespace ShallowWaterInitialStates
} // namespace ryujin