feat(thermal): add local shell kernel and time grid

include/fesa/analysis/thermal_time_grid.h

@@ -0,0 +1,11 @@
+#ifndef FESA_ANALYSIS_THERMAL_TIME_GRID_H_
+#define FESA_ANALYSIS_THERMAL_TIME_GRID_H_
+#include <cstdint>
+#include "fesa/core/status.h"
+namespace fesa {
+class ThermalTimeGrid final { public:
+ static Result<ThermalTimeGrid> Create(double period,double increment,std::uint32_t maximum);
+ std::uint32_t Count() const noexcept; double Time(std::uint32_t index) const noexcept; double Delta(std::uint32_t index) const noexcept;
+ private: ThermalTimeGrid(double p,double d,std::uint32_t n,bool close):period_(p),increment_(d),count_(n),close_(close){} double period_,increment_; std::uint32_t count_; bool close_; };
+}
+#endif

include/fesa/elements/thermal_shell.h

@@ -0,0 +1,28 @@
+#ifndef FESA_ELEMENTS_THERMAL_SHELL_H_
+#define FESA_ELEMENTS_THERMAL_SHELL_H_
+
+#include <array>
+#include <cstddef>
+
+#include "fesa/math/matrix.h"
+#include "fesa/math/vector3.h"
+
+namespace fesa {
+
+/// @brief Local Q4 times two-segment P2 transient-heat shell kernel.
+class ThermalShell final {
+ public:
+  ThermalShell(std::array<std::size_t, 4> node_indices,
+               std::array<Vector3, 4> coordinates, double conductivity,
+               double density, double specific_heat, double thickness);
+  const std::array<std::size_t, 4>& NodeIndices() const noexcept;
+  const Matrix& Conductivity() const noexcept;
+  const Matrix& Capacity() const noexcept;
+ private:
+  std::array<std::size_t, 4> node_indices_;
+  Matrix conductivity_{20U, 20U};
+  Matrix capacity_{20U, 20U};
+};
+
+}  // namespace fesa
+#endif  // FESA_ELEMENTS_THERMAL_SHELL_H_