VGOSWEC C++ SEA-Stack Application

Standalone C++ downstream application simulating the model-scale VGOSWEC (Variable-Geometry OSWEC — bottom-hinged flap) using the SEA-Stack framework and Project Chrono for multi-body dynamics.

Overview

• Model: Wave-tank-scale VGOSWEC (~1:40 Froude), hinged flap + fixed base
• Default geometry: geometry/vgm45.obj (flap), geometry/stl_files/center_beam_w_foundation_BEM.STL (base)
• Default hydro data: hydroData/vgoswec_45.h5
• Wave default: Regular waves, H = 0.05 m, T = 1.5 s
• Four pluggable PTO controllers: passive (placeholder — tune with tank data), optimal-passive, complex-conjugate, excitation-FF+PID

Controller / flap-config co-design — three-regime relay

Across the full VGOSWEC flap-vent sweep (VGM-0 = vents closed → VGM-90 = vents fully open), three controllers occupy complementary period bands in a clean relay:

• CC (complex-conjugate) dominates short periods (T ≲ 2 s), tracking the Budal theoretical optimum with up to 2.34 W at T = 1.5 s.
• opt_passive (optimal resistive damping) matches a tuned feedforward controller at each flap's resonance peak with a single tuning-free coefficient. The resonance hump marches across T = 2.5–4.75 s as the flap angle changes.
• ff+PID (excitation-feedforward + PID) carries the long-period tail past resonance with no reactive-power penalty.

The flap angle acts as a co-design knob that shifts the resonance period — and thus the crossover between regimes — across the full T = 2.5–5 s band.

Master operating envelope: upper hull of captured power over all (controller, flap-angle) combinations at every wave period. CC + VGM-0 dominates short T; opt_passive and ff+PID with the T₀-matched flap dominate resonance; ff+PID + VGM-0 dominates the long tail. See analysis/FINDINGS_3REGIME.md for the full findings.

Reproduce all figures from committed CSVs (no solver needed):

python3 scripts/three_regime_comparison.py --plot-only

• Plant-validation foundation: docs/freedecay_validation.md
• Simulation-data regeneration index: docs/REPRODUCTION.md

Repository structure

cpp-vgoswec/
├── CMakeLists.txt          # Top-level CMake
├── README.md
├── LICENSE                 # MIT
├── .gitignore
├── scripts/
│   ├── setup_env.sh        # Source to configure build environment
│   └── *.py                # Sweep / plotting / comparison drivers
├── config/
│   ├── vgoswec_45_passive.yaml         # Linear viscous damper
│   ├── vgoswec_45_opt_passive.yaml     # Optimal passive damping at ω₀
│   ├── vgoswec_45_cc.yaml              # Complex-conjugate reactive control
│   └── vgoswec_45_exc_ff_pid.yaml      # Excitation-FF + PID (active)
│                                       # (same four per flap: 0/10/20/45/90)
├── hydroData/              # BEMIO H5 coefficients, one per flap angle
├── geometry/               # Flap OBJ + base STL meshes
├── src/
│   ├── demo_vgoswec.cpp        # Main simulation entry point
│   ├── active_pto.{h,cpp}      # Four IPTOModel implementations
│   ├── excitation_force_provider.{h,cpp}  # Excitation-force broadcast helper
│   ├── pid_controller.{h,cpp}  # Full PID with anti-windup
│   ├── rsda_pto_functor.{h,cpp}  # Rotational ChLinkRSDA::TorqueFunctor adapter
│   ├── impedance.{h,cpp}       # Impedance / CC-gain free functions
│   ├── config_loader.{h,cpp}   # YAML config loading
├── tests/
│   └── smoke_test.cpp          # Unit smoke tests (BUILD_TESTING)
├── analysis/               # Committed CSVs + figures (see analysis/README.md)
├── output/                 # Run artifacts — gitignored, not reproducible from git
└── docs/
    ├── CONTROLLERS.md          # Controller mathematics and tuning guide
    ├── REPRODUCTION.md         # Repo-wide dataset regeneration index
    ├── freedecay_validation.md # Plant validation vs WEC-Sim
    ├── HIL_MIGRATION.md        # How to drop in a ROS 2 / HIL controller
    ├── MPC_TODO.md             # Future MPC roadmap
    └── EOD_SUMMARY_*.md        # End-of-day phase notes

Note: output/ is gitignored. Only the derived CSVs under analysis/ are committed — raw per-run time series are not recoverable from the repository and must be regenerated by re-running the solver.

Physical properties (model scale, ~1:40 Froude)

Parameter	Value
Flap mass	7.60 kg (neutrally-buoyant assumption)
Flap CoG	(0, 0, −0.2352) m
Flap I_yy	0.15 kg·m² (TODO: bifilar pendulum or ID)
Hinge z	−0.7658 m
Wave tank	H=0.05 m, T=1.5 s (regular default)
Sim duration	60 s, dt=0.005 s

Prerequisites

• SEA-Stack (installed, SEAStack_DIR set)

• Project Chrono ≥ 10.0, installed (not build-tree), with the same -march=native / SIMD settings as everything it shares Eigen objects with

  ABI warning. Chrono v10 exports -march=native to consumers, which sets EIGEN_MAX_ALIGN_BYTES=32. Any downstream code exchanging Eigen objects with Chrono-linked code must match, or Eigen allocates with malloc and frees with handmade_aligned_free → heap-buffer-overflow. This bit us via HydroData::GetInfAddedMassMatrix crossing into cpp-vgoswec.

  Older notes in this repo claimed SEA-Stack requires CH_USE_SIMD=OFF. The current working stack is built with SIMD ON and -march=native, and builds and runs clean. Treat the OFF claim as unverified until confirmed against SEA-Stack's own build configuration.

• yaml-cpp ≥ 0.7

• Eigen3 ≥ 3.4

• For GUI/visualization (optional — headless builds work without these):

  • VulkanSceneGraph (VSG) ≥ 1.1 (vsg::vsg CMake target)
  • vsgXchange ≥ 1.0 (asset loading for VSG; vsgXchange::vsgXchange)
  • vsgImGui ≥ 0.3 (in-scene UI overlay; vsgImGui::vsgImGui)
  • Chrono VSG module built alongside Chrono (Chrono::Chrono_vsg)
  • SEA-Stack GUI helper header present at $HOME/SEA-Stack/apps/seastack/gui/guihelper.h (from the SEA-Stack source tree)
  • libseastack_app_lib available in one of:
    • $HOME/SEA-Stack/build/lib/Release/
    • $HOME/SEA-Stack/build/lib/
    • $HOME/SEA-Stack/install/lib/ When any of the above GUI components are absent CMake automatically falls back to a headless-only build that still compiles and produces CSV output.

Environment

Two equivalent ways to configure the build environment. Both have been verified to produce a clean configure, build, and run.

Option A — repo-local script (self-contained, works on any machine):

source scripts/setup_env.sh

Option B — toolchain aliases (if you maintain ~/env/ toolchain scripts; see ~/TOOLCHAIN.md):

chrono10 && seastack

Either sets Chrono_DIR, SEAStack_DIR, CHRONO_DATA_DIR, VSG_FILE_PATH, CMAKE_PREFIX_PATH, and LD_LIBRARY_PATH. Option B additionally guarantees that only one Chrono flavor is active per shell.

Do not mix the two in one shell. scripts/setup_env.sh sets these variables independently and does not clear a previously-sourced toolchain, so chrono-dev followed by source scripts/setup_env.sh can leave two Chrono installations on LD_LIBRARY_PATH. The dynamic loader then silently picks whichever comes first. Use one mechanism per shell.

VSG_FILE_PATH must point at the Chrono data directory itself, not at data/vsg — VSG resolves assets as vsg/fonts/... relative to that root. One level too deep and the renderer segfaults on the first frame.

Build

# 1. Configure the environment (see above)
source scripts/setup_env.sh      # ...or: chrono10 && seastack

# 2. Configure and build
cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo
cmake --build build -j$(nproc)

# 3. Run (regular waves, passive damper)
./build/demo_vgoswec --config config/vgoswec_45_passive.yaml

# 4. Run with excitation-FF+PID controller
./build/demo_vgoswec --config config/vgoswec_45_exc_ff_pid.yaml

# 5. Run headless
./build/demo_vgoswec --config config/vgoswec_45_passive.yaml --no-viz

Known configure-time warnings (benign)

• CMP0144 / SEASTACK_ROOT, CHRONO_ROOT — CMake < 3.27 policy default ignores upper-case <PACKAGENAME>_ROOT environment variables. Both packages are located via CMAKE_PREFIX_PATH instead, so the warning is informational.
• libyaml-cpp.so.0.8 runtime search path conflict — a system yaml-cpp in /usr/lib/x86_64-linux-gnu may be shadowed by Chrono's bundled copy. Harmless for the current targets.
• Chrono libraries not found for the debug configuration — expected for Release / RelWithDebInfo. A -DCMAKE_BUILD_TYPE=Debug build will fail to link unless Chrono is also built Debug.

Controller selection

Override the controller at runtime:

./build/demo_vgoswec --config config/vgoswec_45_passive.yaml --controller exc_ff_pid

Valid values: passive, opt_passive, cc, exc_ff_pid.

HIL / ROS 2 integration

See docs/HIL_MIGRATION.md. All four controllers implement seastack::pto::IPTOModel, so a future ROS 2 node can drop in a RosPTOModel without modifying the simulation.

License

MIT — see LICENSE.