feat(shell-surface-pressure-load): step 3 - evaluate-shell-pressure-kernel

include/fesa/loads/shell_surface_pressure.h

@@ -0,0 +1,44 @@
+#ifndef FESA_LOADS_SHELL_SURFACE_PRESSURE_H_
+#define FESA_LOADS_SHELL_SURFACE_PRESSURE_H_
+
+#include <array>
+#include <string>
+
+#include "fesa/core/status.h"
+#include "fesa/math/vector3.h"
+#include "fesa/model/model_types.h"
+
+namespace fesa {
+
+/// @brief Selects the surface geometry used to evaluate uniform pressure.
+enum class SurfacePressureConfiguration { kReference, kCurrent };
+
+/// @brief Supplies one four-node shell facet pressure evaluation.
+struct ShellSurfacePressureInput {
+  std::array<Vector3, 4> reference_coordinates;
+  std::array<Vector3, 4> translational_displacements;
+  ShellSurfaceSide side;
+  double pressure_magnitude;
+  double load_factor;
+  SurfacePressureConfiguration configuration;
+  SourceLocation location;
+  std::string entity_identity;
+};
+
+/// @brief Stores one fixed-order pressure force and external tangent.
+struct ShellSurfacePressureContribution {
+  std::array<double, 24> force;
+  std::array<double, 24 * 24> external_tangent;
+};
+
+/// @brief Evaluates one four-node reference or follower surface pressure.
+/// @param input Geometry, pressure, side, load factor, and diagnostic identity.
+/// @return A finite 24-DOF force and external tangent or a structured failure.
+/// @note Translation DOFs occupy components zero through two of each node.
+/// @warning The returned tangent is the positive derivative of external force.
+Result<ShellSurfacePressureContribution> EvaluateShellSurfacePressure(
+    const ShellSurfacePressureInput& input);
+
+}  // namespace fesa
+
+#endif  // FESA_LOADS_SHELL_SURFACE_PRESSURE_H_