Port FluidSim core and scenarios to C++20

include/FluidSim/Vehicle.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <array>
+
+namespace fluidsim::port {
+
+// Longitudinal motorcycle model and the friction clutch coupling it to the crank.
+class Vehicle {
+public:
+    int current_gear{};
+    std::array<float, 6> gear_ratios{4.1f, 2.7f, 2.0f, 1.55f, 1.25f, 0.98f};
+    float final_drive_ratio{2.7f}, primary_reduction{1.8f};
+    float clutch_input{1.0f}, clutch_capacity{80.0f}, clutch_engagement_rate{8.0f};
+    float mass{160.0f}, wheel_radius{0.32f}, rotational_inertia{1.2f};
+    float rolling_resistance{0.015f}, drag_coefficient{0.7f}, frontal_area{0.65f};
+    float air_density{1.225f}, gravity{9.80665f};
+    float speed{}, engagement{};
+
+    float total_gear_ratio() const;
+    float kinetic_energy() const;
+    float update(float engine_omega, float engine_inertia, float dt);
+    void shift_up();
+    void shift_down();
+    void set_neutral();
+    void set_first_gear();
+
+private:
+    float shift_cut_timer_{};
+    void apply_road_resistance(float dt);
+};
+
+} // namespace fluidsim::port