김경종
111 lines
3.6 KiB
Markdown
111 lines
3.6 KiB
Markdown
# Step 7: local-stiffness-kernel
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## Read These Files First
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Read the following files before editing:
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- `/AGENTS.md`
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- `/docs/ARCHITECTURE.md`
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- `/docs/ADR.md`
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- `/docs/formulations/euler-beam-3d-formulation.md`
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- `/docs/numerical-reviews/euler-beam-3d-review.md`
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- `/docs/implementation-plans/euler-beam-3d-implementation-plan.md`
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Also read any files created by previous steps in this phase.
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## Task
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Use TDD to create the local 12x12 stiffness kernel for the 3D Euler-Bernoulli beam.
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Create:
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- `/src/fesa/elements/euler_beam_3d.hpp`
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- `/src/fesa/elements/euler_beam_3d.cpp`
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- `/tests/unit/euler_beam_3d_local_stiffness_test.cpp`
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Required API:
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```cpp
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namespace fesa::elements {
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using Vector12 = std::array<double, 12>;
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using Matrix12 = std::array<double, 144>;
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struct EulerBeam3DSection {
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double young_modulus;
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double shear_modulus;
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double area;
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double torsion_constant;
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double second_moment_y;
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double second_moment_z;
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};
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Matrix12 euler_beam_3d_local_stiffness(double length, const EulerBeam3DSection& section);
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Vector12 euler_beam_3d_local_end_forces(double length,
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const EulerBeam3DSection& section,
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const Vector12& local_displacements);
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} // namespace fesa::elements
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```
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Implementation rules:
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- Matrix storage is row-major: index `(row, col)` is `row * 12 + col`.
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- Validate `length > 0` and all section constants are positive; throw `std::invalid_argument` otherwise.
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- Use only C++17 standard library.
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- Do not introduce an external linear algebra dependency.
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- Do not edit CMake files; source and test globs should pick up new files.
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## Tests To Write First
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Create `/tests/unit/euler_beam_3d_local_stiffness_test.cpp` before production code.
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Test behavior:
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- For `L = 2.0`, `E = 210.0`, `G = 80.0`, `A = 3.0`, `J = 4.0`, `Iy = 5.0`, `Iz = 6.0`, verify representative matrix entries:
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- axial: `K(0,0) = EA/L`, `K(0,6) = -EA/L`, `K(6,6) = EA/L`
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- torsion: `K(3,3) = GJ/L`, `K(3,9) = -GJ/L`, `K(9,9) = GJ/L`
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- local `x-y` bending uses `EIz`: `K(1,1) = 12*E*Iz/L^3`, `K(1,5) = 6*E*Iz/L^2`, `K(5,5) = 4*E*Iz/L`
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- local `x-z` bending uses `EIy`: `K(2,2) = 12*E*Iy/L^3`, `K(2,4) = -6*E*Iy/L^2`, `K(4,4) = 4*E*Iy/L`
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- Verify all entries are symmetric within `1.0e-10`.
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- Verify `euler_beam_3d_local_end_forces` returns `K * u` for a displacement vector with at least three nonzero components.
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- Verify invalid length and nonpositive section constants throw `std::invalid_argument`.
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RED command:
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```powershell
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ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_local_stiffness_test
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```
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Expected RED: test executable missing or compile failure because the header/API does not exist.
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Then implement the minimal API.
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GREEN command:
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```powershell
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ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_local_stiffness_test
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```
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## Acceptance Criteria
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```powershell
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ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_local_stiffness_test
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python -m unittest discover -s scripts -p "test_*.py"
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python scripts/validate_workspace.py
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```
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## Verification Notes
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1. Confirm RED failed before production code was added.
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2. Confirm no parser, assembly, or results writer code was changed.
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3. Update `phases/euler-beam-3d/index.json` step 7:
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- success: `"status": "completed"`, `"summary": "local 3D Euler beam stiffness and local end-force kernel added"`
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- failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
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- blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
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## Forbidden
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- Do not add shear deformation or Timoshenko terms.
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- Do not modify reference artifacts.
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