SEA-Stack

A unified platform for WEC simulation

David Ogden (Simocean)

Collaborators:

NLR · UW–Madison

May 2026

Motivation — one modelling framework for WECs

One system description, several fidelity paths

  • One WEC system description.
  • Multiple fidelity paths.
  • The device should evolve across tools — not be rebuilt for each one.
  • Adapters connect the solver paths.

Why this matters for WEC design

  • WEC design remains highly exploratory
  • Broad exploration requires fast iteration across large design spaces
  • Survivability and nonlinear loads demand targeted higher fidelity
  • Switching tools forces you to re-enter the same device instead of evolving one definition
  • SEA-Stack is being developed around that problem

Wide variety of WEC concepts under exploration

Composite of diverse WEC concepts: tank arrays, attenuators, internal PTO, novel buoys, platforms, flexible bodies, linkages, point absorber diagram

Many concepts and topologies; whichever you pursue, you still need broad sweeps across geometry, PTO, mooring, control, and sea states, not a single nominal design.

Low- and mid-fidelity modelling is what makes broad exploration and optimization practical across many cases.

High fidelity for loads and survivability

https://www.youtube.com/watch?v=ARIg3oQtZ0w

Extreme loads often occur in operational sea states — not only in rare storm conditions.

What the platform actually needs to support

Open-ended innovation

  • rigid / flexible systems
  • novel PTOs
  • closed loops
  • unusual topologies

Broad exploration

  • sweeps
  • optimization
  • many sea states
  • parametric studies

Early de-risking

  • impulsive loads
  • survivability
  • nonlinear events
  • targeted high fidelity

The software environment should not unnecessarily constrain the design space.

The workflow should evolve with the research question — not restart from scratch.

Architecture — preserving the system definition

Integrated workflow vs siloed tools

workflow_seastack_vs_siloed.png

WECs are fundamentally coupled systems

Credible WEC models carry hydrodynamics, structures, mooring, PTO, and control together — coupled, not independent silos.

wec_anatomy.svg

Workflow requirements shape the architecture

Workflow need Architectural response Supporting tools
Explore unusual WEC concepts Flexible multibody foundation Project Chrono — native C++ multibody, constraints, joints, contact, FEA-capable host
Short turnaround in interactive use Interactive visual workflows VSG GUI + packaged demos
Run large campaigns and optimization studies Headless scalable workflows YAML / CLI / HDF5 — reproducible study automation and batch I/O; native C++ underneath
Carry the same system definition across fidelities Solver-independent domain models Thin adapter layers — same YAML/device definition when hydro engine changes
Extend physics over time Modular explicit interfaces Chrono-free domain libraries
Integrate external ecosystems Native interoperability paths Chrono · MoorDyn · OpenFOAM · DualSPHysics — same native C++ ecosystem for clean adapters

Architecture — domain, adapters, and external solvers

architecture_tikz_monthly_report.png

User-facing model definition — YAML, assets, outputs

example.setup.yaml

setup.yaml wires the case together

model_file: example.model.yaml
simulation_file: example.simulation.yaml
hydro_file: example.hydro.yaml

output_directory: outputs

example.model.yaml

One segment + one universal joint (excerpts) · TSDAs omitted on slide

chrono-version: 10.0

model:
  name: "example_model"
  angle_degrees: false

  data_path:
    type: RELATIVE
    root: "."

  bodies:
    # Segment 1 (Nose)
    - name: body1
      location: [18.0, 0.0, -1.8]
      mass: 438293
      fixed: false
      inertia:
        moments: [876585.0, 47773884.0, 47773884.0]

  joints:
    - name: joint_12
      type: UNIVERSAL
      body1: body1
      body2: body2
      location: [36.0, 0.0, -1.8]
      axis1: [0, 1, 0]
      axis2: [0, 0, 1]

example.hydro.yaml

Waves, spreading, excitation, MoorDyn · H5 from shared BEM data

hydrodynamics:
  bodies:
    - name: body1
      h5_file: ../assets/hydroData/example_directional.h5

  waves:
    type: irregular
    height: 3.0
    period: 10.0
    spectrum: jonswap
    spreading:
      type: cos2s
      s: 12

  moordyn:
    enabled: true
    input_file: mooring/lines_example.txt
    bodies: [body1, body3]

example.simulation.yaml

Chrono time step, integrator, linear solver

chrono-version: 10.0

simulation:
  time_step: 0.02
  end_time: 600.0
  integrator:
    type: HHT
    use_stepsize_control: true
  solver:
    type: SPARSE_LU

One system definition, multiple fidelity paths

fidelity.svg

Capabilities today

System dynamics

  • rigid multibody hydrodynamics
  • wide range of joints and constraints
  • closed kinematic loops
  • dry FEA bodies / flexible members

Hydrodynamics and waves

  • first-order potential-flow forces
  • radiation damping via convolution or state-space
  • regular, irregular, directional, and bimodal seas
  • nonlinear hydrostatics from submerged volume

Subsystems and workflows

  • MoorDyn coupling
  • linear and hydraulic PTO components
  • PI control and scalar control interfaces
  • YAML / CLI / HDF5 campaign workflows

Verification and release philosophy

Verification is treated as part of the release process — verification reports are packaged alongside public releases.

Verified today

  • linear hydrodynamics
  • multibody hydrodynamic coupling
  • MoorDyn integration
  • state-space radiation-force models
  • irregular, directional, and bimodal sea-state workflows

Current expansion areas

  • hydraulic PTO verification against WEC-Sim / PTO-Sim
  • higher-fidelity comparison workflows
  • verification of new features before public release

SEA-Stack in use

SEA-Stack modes

Interactive

Interactive use: try layouts, debug topology, inspect coupled motion.

Headless

Run sweeps, campaigns, optimization, and reproducible studies.

Higher fidelity

Higher-fidelity studies for nonlinear loads, structural detail, and survivability questions.

Interactive use — topology and qualitative checks

Interactive use: quick qualitative checks on how a concept behaves before committing to large parametric runs.

  • Novel topologies · joints · mooring · sea states
  • Qualitative dynamics, debugging, “does this behave?”

Five-segment attenuator — directional spreading, MoorDyn (illustrative run)

Headless runs — parametric studies and campaigns

design_exploration_loop.svg

Same system definition, headless execution: parametric sweeps, optimization, and campaign studies without rebuilding the model per design point. Example: TEAMER TALOS taper-draft sweep — see Current studies and collaborations later in this deck.

Targeted higher fidelity — nonlinear wave interaction and loads

Use higher-fidelity SPH/CFD-style models where needed for slamming, survivability, complex free-surface behaviour, and detailed load assessment — without redefining the device from scratch.

https://www.youtube.com/watch?v=ebtOX1pSci4

RM3 — nonlinear PTO behaviour

Two-body Reference Model 3 with rectified hydraulic PTO, regular waves.

Trimaran — flexible structural representation

Three-hull trimaran with Euler-beam FEA cross-arms under irregular wave loading.

Current studies and collaborations

Overview — TALOS, WITT, and VLFP

Current studies already using SEA-Stack span headlessdesign exploration campaigns, interactive modelling and experimental validation.

TALOS

TEAMER design-exploration study; report under TSR (Lancaster) review. Used for multi-configuration response and performance sweeps.

PNNL WITT

Two-body model with MoorDyn rope / connection modelling; ProteusDS decay-test verification; PTO subsystem next.

VLFP

Very large floating platform collaboration with Strathclyde and Oxford; conference paper coming next month.

TALOS — taper-draft design sweep

fig_talos_phase10_taper_draft_sweep.png

Same system definition in YAML — hull taper draft swept with other parameters held fixed; regular-wave period on the horizontal axis; headings by line style; six-DOF response (top) and capture-width performance (bottom).

VLFP (very large floating platform) — experimental validation

Collaboration with University of Strathclyde and University of Oxford on very large floating platforms (VLFP); full benchmark discussion in a conference paper to be presented next month.

VLFP simulation: segmented platform
HYEL benchmark: heave and flex upstream RAO versus experiment and CFD

HYEL case: heave and flex-upstream RAOs — SEA-Stack configurations compared with hydroelastic model, CFD, and experiment.

PNNL WITT — two-body model (MoorDyn tether)

SEA-Stack YAML viewer: PNNL WITT two-body model with MoorDyn tether coloured by tension

Two rigid bodies with rope / connection modelling in MoorDyn; decay-test verification against ProteusDS data in progress.

PTO subsystem — next development step.

Roadmap and summary

Roadmap — extending the same architecture

roadmap.svg

Summary

  • Motivation — one modelling framework for WECs: one system description across fidelities; why that matters for design; concept diversity; operational-load illustration; what the platform needs to support.
  • Architecture — preserving the system definition: integrated vs siloed workflows; coupled physics; requirements vs architecture; stack diagram; YAML / assets / outputs and fidelity paths; capabilities today; verification tied to releases.
  • SEA-Stack in use: interactive use, headless runs, and higher-fidelity studies; packaged examples (RM3, trimaran).
  • Current studies and collaborations: TALOS, VLFP (HYEL), and PNNL WITT.
  • Roadmap: planned extensions on the same architecture (preceding slide).