Add turbocharged twin scenario and cross-platform test harness

include/FluidSim/ReedValve.hpp

@@ -0,0 +1,47 @@
+#pragma once
+#include <algorithm>
+#include <cmath>
+#include <stdexcept>
+
+namespace fluidsim::port {
+// Lumped cantilever-petal model; geometry/material values require calibration.
+class ReedValve {
+public:
+    float length{0.030f}, width{0.016f}, thickness{0.00035f};
+    float youngs_modulus{70e9f}, material_density{1600.0f};
+    float damping_ratio{0.30f}, maximum_lift{0.004f};
+    int petals{4};
+    float lift() const { return lift_; }
+    float step(float dt, float pressure_difference) {
+        if (!std::isfinite(dt) || dt <= 0 || !std::isfinite(pressure_difference))
+            throw std::invalid_argument("invalid reed timestep or pressure");
+        if (!(length > 0 && width > 0 && thickness > 0 && youngs_modulus > 0 && material_density > 0 &&
+              maximum_lift > 0 && petals > 0 && damping_ratio >= 0))
+            throw std::invalid_argument("invalid reed geometry/material");
+        const float mass = .236f * material_density * length * width * thickness * petals;
+        const float stiffness = petals * youngs_modulus * width * thickness * thickness * thickness /
+                                (4 * length * length * length);
+        const float damping = 2 * damping_ratio * std::sqrt(mass * stiffness);
+        const float force = pressure_difference * (3.0f / 8.0f) * length * width * petals;
+        const int steps = std::max(1, int(std::ceil(dt * std::sqrt(stiffness / mass) / .15f)));
+        const float h = dt / steps;
+        for (int i = 0; i < steps; i++) {
+            velocity_ += (force - stiffness * lift_ - damping * velocity_) / mass * h;
+            lift_ += velocity_ * h;
+            if (lift_ < 0) {
+                lift_ = 0;
+                velocity_ = 0;
+            }
+            if (lift_ > maximum_lift) {
+                lift_ = maximum_lift;
+                velocity_ = 0;
+            }
+        }
+        // Front-edge plus triangular side-gap areas for all petals.
+        return petals * (width + length) * lift_;
+    }
+
+private:
+    float lift_{}, velocity_{};
+};
+} // namespace fluidsim::port