CableDyn

CableDyn is an open-source finite-element solver for the static and dynamic analysis of offshore mooring lines and dynamic power cables. It is written in Fortran 2018 and runs as a standalone program, as a mooring module of OpenFAST, maintained by NLR (National Laboratory of the Rockies, formerly NREL) (CompMooring = 5), through a C interface, or from Python. It reads input decks in the MoorDyn v2 format and solves them with two line formulations:

• Tension-only lines (EI = 0): chains, wire ropes, and synthetic-fibre moorings.
• Finite-bending lines (finite-EI): cubic-Hermite elements for dynamic power cables, including lazy-wave configurations, with continuous centreline curvature.

The current stable release is v0.1.0, the first public release. Interfaces are versioned and may change before 1.0.0.

Capabilities

Area	Features
Statics	Catenary seeding, Newton solution, load continuation, mesh sequencing, adaptive meshing
Dynamics	Implicit generalised-alpha integration, prescribed support motion, consistent mass, automatic step subdivision
Environment	Buoyancy, Morison drag, added mass, Froude–Krylov loading, regular and irregular waves, current profiles, seabed contact with friction
Materials	Linear axial stiffness, Kelvin–Voigt damping, viscoelastic (series-Kelvin; MoorDyn ElasticMod 2/3), Syrope polyester model
Topology	Fixed, coupled, free, and connected points; clump weights; rigid bodies and rods; end rotational stiffness; active line-length control; line failure
Outputs	Effective tension, position, velocity, acceleration, curvature, bending moment, end angles, contact response, solver diagnostics
Interfaces	Standalone driver, OpenFAST and FAST.Farm, C ABI, Python package

Section and keyword names follow MoorDyn v2; unsupported combinations stop with a named error rather than running approximately.

Quick start

1. Download from the latest release:

   Asset	Contents
   CableDyn_driver.exe	Standalone solver for Windows x64
   openfast.exe	OpenFAST with CableDyn available as CompMooring = 5
   cabledyn-0.1.0-py3-none-any.whl	Python package (pre- and post-processing, batch runs)
   cabledyn-0.1.0.tar.gz	Python source distribution
   SHA256SUMS.txt	Checksums for the assets above

   Both executables are statically linked, need no installer, compiler, or runtime DLLs, and run on Windows 10 (version 1903 or later) and Windows 11, from folders named in any script. A turbine controller used by an OpenFAST model still needs its own DISCON.dll. The example decks are in the examples folder of the release's Source code (zip) archive: unzip it and copy examples next to the executables.

2. Verify the download (compare with SHA256SUMS.txt):

   Get-FileHash CableDyn_driver.exe -Algorithm SHA256

3. Solve an example deck. The driver finds the static equilibrium, then runs the dynamics when the deck sets dtM and TMax:

   .\CableDyn_driver.exe examples\wd0050_chain.dat wd0050

   Results are written to wd0050.out and related tables in the current folder. The driver does not create folders: an output root such as results\wd0050 needs New-Item -ItemType Directory -Force results | Out-Null first.

4. Optionally, script runs from Python. cabledyn-run needs to find the driver: pass --executable, set the CABLEDYN_DRIVER environment variable, or put the driver on PATH. A relative output root is resolved against the deck's folder, so this run writes examples\wd0050.out:

   python -m pip install "cabledyn-0.1.0-py3-none-any.whl[post]"
   cabledyn-run examples\wd0050_chain.dat wd0050 --executable .\CableDyn_driver.exe

   A source build names the driver cabledyn (see Build from source); the release executable is CableDyn_driver.exe.

For OpenFAST, set CompMooring = 5 in the .fst file and point MooringFile at a CableDyn deck; ready-to-run cases are in examples/openfast. Every shipped deck is listed in examples/.

Documentation

The manual at https://cabledyn.readthedocs.io covers installation, tutorials, the deck format, options, outputs, theory, OpenFAST coupling, the C API, Python, validation, and troubleshooting.

Build from source

conda env create -f environment.yml
conda activate cabledyn
cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build --parallel
ctest --test-dir build -L fortran -LE slow --output-on-failure

The driver is build/cabledyn (build\bin\cabledyn.exe with the conda toolchain on Windows); the release ships the same program as CableDyn_driver.exe.

See DEVELOPMENT.md for the full test suite, the Python package, and the OpenFAST build, and ARCHITECTURE.md for the source layout.

Validation

CableDyn is verified against analytical solutions and compared with MoorDyn, OrcaFlex, two physical experiments (Holcombe lazy-wave, Bergdahl dynamic chain), the IEA 15 MW VolturnUS-S reference systems, and coupled OpenFAST runs. Results, acceptance criteria, and reproduction commands are in VALIDATION.md; data and scripts are in validation/.

Repository layout

Directory	Contents
app/	Standalone driver (CableDyn_driver.exe)
src/	Solver core, C interface, OpenFAST module
python/	Python package
tests/	CTest unit, integration, and validation tests
doc/	Sphinx manual
examples/	Standalone and OpenFAST input decks
integration/openfast/	OpenFAST patch series and build scripts
release/	Release checks and the static Windows build
validation/	Validation records, reference data, and scripts

Citation

If you use CableDyn in academic work, please cite:

J. H. Seo, J. Lim, K. Shim, J. Song. CableDyn: Curvature-resolving implicit finite-element analysis of mooring lines and dynamic power cables for floating offshore wind. Ocean Engineering 368 (Part 2), 128332, 2026. https://doi.org/10.1016/j.oceaneng.2026.128332

To identify the software version, also cite the release (CableDyn 0.1.0). CITATION.cff contains both entries (GitHub Cite this repository); BibTeX is on the manual's How to cite page.

Contributing and support

Questions, bug reports, and feature requests are welcome in GitHub Issues; see SUPPORT.md for where each belongs. Read CONTRIBUTING.md before opening a pull request. Everyone taking part is expected to follow the Code of Conduct. Report security issues privately as described in SECURITY.md.

If you extend or fix CableDyn in your own copy, please consider contributing the change here, so that every user benefits and the validation record stays in one place.

CableDyn is research software. Users are responsible for model selection, convergence checks, and compliance with the design codes that govern their work.

Maintainer: Prof. Jae Hoon Seo, Department of Naval Architecture and Ocean Engineering, Inha University, Republic of Korea, jaehoon.seo@inha.ac.kr

Acknowledgements

CableDyn builds on the work of others, and we are grateful to the developers and maintainers of MoorDyn (Hall et al.), whose open input format CableDyn reads and which serves as a comparison reference; of OpenFAST (NLR), which hosts CableDyn as a mooring module; and of OrcaFlex, the industry reference used for many of the comparisons in VALIDATION.md. OrcaFlex is a product of Orcina Ltd.

License and name

CableDyn is distributed under the Apache License 2.0. See LICENSE and NOTICE.

"CableDyn" identifies the official project in this repository. Modified versions are welcome under the licence, but, as Section 6 of the Apache License 2.0 provides, they may not use the name in a way that implies they are the official CableDyn or endorsed by its maintainers; describing a work as "based on CableDyn" is fine.