pyBmodes

A pure-Python finite-element library for wind-turbine blade and tower modal analysis — coupled flap–lag–torsion–axial vibration modes from a 15-DOF Bernoulli-Euler beam element, with first-class support for the OpenFAST / BModes / WISDEM-WindIO ecosystem.

Highlights

  • Reads what the wind-energy field uses. OpenFAST decks (ElastoDyn / SubDyn / HydroDyn / MoorDyn), BModes .bmi, and the WISDEM / WindIO ontology .yaml are all first-class inputs. Mooring (Jonkman 2007 catenary), hydrodynamics (WAMIT / HydroDyn .1 / .hst), and composite-layup blade reductions (PreComp-class, BeamDyn-validated) come built in. No wrapper around a Fortran binary — pure Python, numpy + scipy runtime.

  • Cross-validated to better than 0.01 % on every benchmark case. Six independent verifications against the BModes Fortran reference solver (NREL 5MW land / OC3 monopile / OC3 Hywind floating spar + IEA-3.4-130-RWT + BModes CertTest Test03 / Test04) plus three closed-form analytical references (Wright 1982 rotating blade, Bir 2009 pinned-free cable, Blevins tip-mass tower). The validation matrix is mechanically audited by scripts/audit_validation_claims.py in CI — claims cannot drift ahead of tests.

  • ElastoDyn-compatible polynomial round-trip. Solve modes, fit the constrained 6th-order polynomial ansatz with design-matrix condition-number reporting, then write the coefficients straight back into the input deck via pybmodes patch (with safety modes: --dry-run / --diff / --backup / --output-dir). Six pre-patched reference decks ship in the wheel — three fixed-base, three floating.

  • Engineering-report-quality Campbell diagrams. Rotor-speed sweeps with Hungarian MAC-based mode tracking; floating platforms get six rigid-body modes named natively (surge / sway / heave / roll / pitch / yaw). Operating-window shading, per-rev excitation rays (1P / 3P / 6P / 9P), inline family labels, and explicit log-frequency support.

  • One-click WISDEM / WindIO pipeline. pybmodes windio ontology.yaml discovers companion HydroDyn / MoorDyn / ElastoDyn decks scoped to the turbine root, then solves the composite-layup blade, the tubular tower, and (if present) the coupled floating platform — with an optional Campbell sweep and a bundled Markdown / HTML / CSV report.

30-second tour

from pybmodes.models import Tower
from pybmodes.elastodyn import compute_tower_params, patch_dat

# ElastoDyn main + tower files read from one path; rotor mass lumped.
tower = Tower.from_elastodyn("NRELOffshrBsline5MW_Onshore_ElastoDyn.dat")
modal = tower.run(n_modes=4)

# Constrained 6th-order fit; FA/SS family selection with
# torsion-contamination filter.
params = compute_tower_params(modal)
patch_dat("NRELOffshrBsline5MW_Onshore_ElastoDyn.dat", params)

The user guide takes it from there:

User guide

Reference

Developer guide

What this project is not

  • Not a multi-body dynamics solver. Use OpenFAST + ElastoDyn for time-domain simulation.

  • Not a CFD code. Hydrodynamics come in as 6 × 6 matrices from WAMIT / HydroDyn potential-flow output.

  • Not a structural design tool. The supported workflow is analysis of a defined structure, not optimisation of one. Use WISDEM for design.

See Limitations for the full scope statement.

Status

Stable 1.x baseline. The public API surface enumerated in API contract is semver-frozen across 1.x minor releases. Numerical outputs may still shift between minor releases when validation tightens or a modelling correction lands; every such shift is called out in Changelog under Fixed / Changed with magnitude and affected case.

Citation

If you use pyBmodes in academic work, please cite it via the CITATION.cff file in the repository root. GitHub’s “Cite this repository” widget, Zenodo, and most reference managers read it automatically.

License

Apache 2.0 — see LICENSE.

Copyright 2024-2026 Jae Hoon Seo, Marine Structural Mechanics and Integrity Lab (SMI Lab), Inha University.

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