Open‑Source Seastead Wave‑Simulation Tools – Comparison

This page compares free / open‑source packages that can simulate a small floating platform (seastead) with legs, cables, and wave loading. The goal is to see when cables go slack or experience snap (snatch) loads, and to produce visual videos of the motion.

Quick‑look table

*Time to first simple model assumes you are comfortable writing Python scripts and have an AI assistant (Claude Code / Cursor.ai) to generate scaffold code. Times are order‑of‑magnitude estimates; actual effort depends on your prior experience.

Which tool is best for the “brain‑storming” stage?

• If you want a quick, visual, all‑in‑one simulation that can already show cable tension spikes and slack, Project Chrono (with HydroChrono) is the most practical. You can model the platform, legs, and cables in one Python script, apply wave forcing, and record the motion. The built‑in “distance constraint” lets you watch tension values in real time.
• If you need high‑fidelity wave diffraction (e.g., you plan to test very steep waves where the platform’s shape matters) you can later feed Capyatine’s coefficients into Chrono, but that adds a week or two of work.
• If you have lots of GPU compute and want to study splash‑up, splash‑down, and wave breaking around the legs, DualSPHysics is powerful, but you’ll need to couple it with a multi‑body solver (again, Chrono is a good candidate).
• All the other tools (OpenFOAM, OpenFAST) are great for detailed engineering, but they are far more time‑consuming and may be overkill for early brainstorming.

Typical workflow with Project Chrono (recommended)

1. Install – pip install pychrono (or build from source for the newest HydroChrono).
2. Create geometry – Use simple cylinders for the four legs and a box for the living area. Export as a .obj or create directly in PyChrono (e.g., ChBodyEasyCylinder).
3. Add buoyancy – Use the built‑in ChBuoyancy (or the newer HydroChrono helper) that computes force based on submerged volume. It accepts a wave height & period.
4. Add cables – Create ChLinkDistance or a chain of point‑masses to represent flexible cables. Measure the link’s tension with link.GetReaction().
5. Run simulation – Set a time step (e.g., 1 ms), run for several wave periods, and record position / tension.
6. Visualize – Use the built‑in Irrlicht viewer (or export to VTK and render with ParaView). You can capture a screen‑record for a video.
7. Detect snap loads – Plot the tension time‑history; look for sudden spikes when a cable goes slack and then re‑tensions.

A minimal script (≈ 50 lines) can be generated by an AI assistant. Below is a rough sketch (Python):

# PyChrono example (pseudo‑code)
import pychrono as chrono
import math

sys = chrono.ChSystemSMC()
# Wave parameters
wave_height = 1.0  # m
wave_period = 5.0  # s

# Platform (box)
platform = chrono.ChBodyEasyBox(12.192, 4.877, 1.0, 1500, True)
sys.AddBody(platform)

# Legs (cylinders) – 4 legs, each 1.22 m dia, 7.32 m long
leg_dim = chrono.ChDimensionConstants()
for (x, y) in [(-6.1,-2.44), (6.1,-2.44), (-6.1,2.44), (6.1,2.44)]:
    leg = chrono.ChBodyEasyCylinder(0.61, 7.32, 1500, True)
    leg.SetPos(chrono.ChVector(x, y, -3.66))   # half submerged
    sys.AddBody(leg)
    # Attach leg to platform with a revolute joint (pivot)
    joint = chrono.ChLinkRevolute()
    joint.Initialize(platform, leg, chrono.ChFrame(chrono.ChVector(x, y, 0)))
    sys.AddLink(joint)

# Simple cable (distance constraint) between leg bottoms
cable = chrono.ChLinkDistance()
cable.Initialize(leg1, leg2, False)   # you would list the two leg bodies
sys.AddLink(cable)

# Buoyancy – use built‑in simple buoyancy (no diffraction)
buoy = chrono.ChBuoyancy()
buoy.SetWaterDensity(1025)
buoy.SetWaveHeight(wave_height)
buoy.SetWavePeriod(wave_period)
# Attach to each body
for body in [platform] + legs:
    body.AddBuoyancyForce(buoy)

# Run
ts = 0.001
duration = 30.0
while sys.GetChTime() < duration:
    sys.DoStepDynamics(ts)
    # monitor tension (cable.GetReaction()[0])
    pass

You can replace the simple buoyancy with a HydroChrono “ChHydroWave” for more realistic sinusoidal wave forcing. The script will run on a laptop in a few minutes, giving you a video of the platform bobbing and cables tensioning.

Workflow with Capyatine + MoorDyn (if you need higher fidelity)

1. Create a “mesh” of the platform (e.g., in Gmsh) and run Capyatine to obtain added‑mass, damping, and excitation matrices.
2. Use those matrices in your own time‑domain integration (or couple to Chrono via Python‑CTypes). This step provides accurate wave forces.
3. Set up MoorDyn input files for each cable – you can specify the unstretched length, stiffness, and damping.
4. Run the coupled simulation (you will write a loop that updates the platform’s motion, computes wave forces from Capyatine, and passes the motion to MoorDyn for cable tension).
5. Record tension and produce a video (e.g., via Matplotlib animation or by exporting to VTK).

This path is more work but yields engineering‑grade data for snap loads.

Summary recommendation

• Start with Project Chrono (PyChrono + HydroChrono) – you can have a working simulation in a day or two, see cable slack/tension, and generate a video that clearly shows how the platform moves in waves.
• If the results feel “too optimistic” or you need precise diffraction for large wave heights, then move to a Capyatine + MoorDyn coupling (a week or two of extra work).
• Use Blender only for artistic renders; do not rely on its physics for engineering.
• DualSPHysics, OpenFOAM, and OpenFAST are excellent for final detailed analysis, but they demand far more time and expertise.

Links & resources

• Project Chrono: https://projectchrono.org/
• PyChrono (Python wrapper): https://www.projectchrono.org/pychrono
• HydroChrono (wave loading): https://www.projectchrono.org/hydrochrono
• Capyatine (diffraction): https://github.com/mmntb/capyatine
• MoorDyn (mooring lines): https://www.matt-hall.org/moordyn
• DualSPHysics: https://dualsphysics.org/
• OpenFOAM: https://www.openfoam.org/
• OpenFAST: https://openfast.readthedocs.io/

All of the above packages run on Linux and Windows. They are free (no licence fee), and you can ask Claude Code or Cursor.ai to help write the Python glue code.

Prepared for the seastead brainstorming team – feel free to copy this HTML onto your site.