```html Wave/Motion Simulation Software for a Small “Seastead / Mini-Platform” Concept

Simulation software options for waves + motion + moorings/cables (and possibly thrusters)

For a structure like you describe (a relatively boxy deck + four large inclined cylindrical floats/columns with cable bracing, operating at low speed), you typically want one of these modeling approaches:

Seakeeping/hydrodynamics (frequency-domain or time-domain) for wave loads and motions (heave/pitch/roll, etc.).
Mooring/line dynamics for the cable rectangle and cross-bracing (time-domain line tensions, snap loads).
Low-speed maneuvering + thrusters (optional) for 0.5–1 mph with current/eddy assistance.
High-fidelity CFD only if you need detailed viscous drag, slamming, green water, or complex flow around the legs.

Important practical note: Most wave/motion tools do not accept a pure “text description” and auto-generate a correct model. You almost always need at least a simplified 3D geometry (panels) or a parametric shape, plus mass properties and line properties. The good news is your geometry is simple enough (cylinders + a deck) that building a workable model is usually feasible.

Recommended software (common in offshore/ocean engineering)

Tool	Best for	What you would model	Notes
OrcaFlex (commercial) Orcina Ltd.	Time-domain dynamics of floating systems, cables, moorings, constraints, wave/current/wind loading.	6-DOF floating body (deck + floats as a rigid body or multiple bodies) All cables between float ends (with redundancy rectangle) Environmental: waves (irregular), current, wind Optional: thruster forces as time-varying applied loads	Often the quickest path to “will my cables/geometry survive sea state X?”. Hydrodynamic coefficients may be simplified, or imported from a diffraction tool.
WAMIT (commercial) / NEMOH (open-source) / Capytaine (open-source)	Potential-flow (panel-method) wave-structure interaction: added mass, radiation damping, excitation forces, RAOs.	Panelized wetted surface of your structure (cylinders/legs and any submerged deck parts) Compute RAOs and wave loads vs frequency Export hydrodynamic coefficients for time-domain solvers	Great for wave-induced motions, less direct for cable dynamics unless coupled to another tool. Requires preparing a surface mesh (panels).
OpenFAST + HydroDyn + MoorDyn (open-source, NREL)	Time-domain simulation of floating platforms in waves with moorings (common for floating wind).	Platform hydrodynamics (via HydroDyn; can use potential-flow coefficients) Mooring/cable dynamics (MoorDyn) Add external forces (thrusters) as user-defined loads (more engineering work)	Powerful and free, but not “click-and-run”. Often used with WAMIT/NEMOH-type outputs for hydrodynamics.
ANSYS AQWA (commercial)	Integrated workflow: diffraction/radiation + time-domain + moorings.	3D geometry/meshing Wave load/motion analysis Mooring lines/cables	A common “one suite” solution if you already have ANSYS access.
ProteusDS / SIMO/RIFLEX / MOSES (commercial, various vendors)	Offshore time-domain dynamics, moorings/risers, multi-body.	Similar to OrcaFlex + potential-flow coupling approaches.	Strong but licensing and workflow vary.
CFD (OpenFOAM, STAR-CCM+, ANSYS Fluent)	Detailed viscous drag, slamming, propulsor/thruster flow interaction, highly nonlinear effects.	Full 3D fluid domain with free surface Moving body (6DOF) potentially with overset meshes Propulsors modeled explicitly or as actuator disks	Highest effort and compute cost. Usually not step #1 for concept validation.

What is most realistic for your concept stage?

If your priority is cable/structure dynamics in waves

OrcaFlex is often the most direct way to represent your “four legs + cross cables + perimeter cable” system and get time histories of tensions and motions under irregular waves and current. You can start with simplified hydrodynamics (drag + added mass approximations) and refine later.

If your priority is wave-induced motions (RAOs) and global loads

Use NEMOH/Capytaine (free) or WAMIT (paid) to compute wave excitation and radiation effects. Then couple those coefficients into a time-domain tool (OpenFAST/HydroDyn or OrcaFlex, or AQWA).

How you would “take the description and make a model” (typical inputs)

1) Geometry needed (even simplified)

Deck dimensions and mass properties (mass, CG, inertias).
Four cylindrical legs/floats: diameter, length, orientation (45°), and submergence (half underwater as a start condition).
Connection points: where each leg meets the platform and where each cable attaches at the bottom nodes.

2) Hydrodynamic representation options

Morison-type (drag + inertia) on each cylindrical member (common for “pile-like” elements).
Potential-flow diffraction if the members are large relative to wavelength and you need better accuracy in wave loads/motions.

3) Cables / lines

Diameter, axial stiffness (EA), mass per length, hydrodynamic drag coefficients, and any pretension.
Line layout: two diagonals from each bottom node to adjacent corners, plus perimeter rectangle line (redundant).

4) Environment

Wave spectrum (e.g., JONSWAP / Pierson–Moskowitz), significant wave height (Hs), peak period (Tp), direction spread.
Current profile (surface speed and shear with depth), wind if needed.

5) Thrusters / mixers as propulsion

At concept level, thrusters are often modeled as bounded force actuators applied at known locations/directions.
For 0.5–1 mph, the limiting factor is often drag; CFD or towing-tank style coefficients may be needed for accurate power estimates.

Software selection guidance (quick decision)

Want to learn fastest and get credible “will it survive / what are tensions?” answers: OrcaFlex (paid) or AQWA (paid).
Want free/open-source and you can handle engineering workflow: Capytaine or NEMOH (hydro coeffs) + OpenFAST/MoorDyn (time-domain).
Want detailed drag/power at low speed and thruster interaction: CFD (but expect a steep setup and compute cost).

Modeling caveats specific to your description

Large-diameter legs (4 ft / ~1.22 m) at 45°: in many sea states, wave particle kinematics and member orientation matter. Morison loads can be workable, but choose coefficients carefully and consider model tests or sensitivity studies.
“Half of each column underwater” changes with heave/pitch/roll; the restoring and buoyancy are nonlinear. Time-domain simulation is usually better than only frequency-domain RAOs.
Cable redundancy is good, but snap loads can be severe if any line goes slack then re-tensions. Time-domain line dynamics (not just static catenary) is important.
Internal pressure (10 psi) is more a structural design question; wave simulation tools typically won’t check shell buckling/stress. You’d use FEA (ANSYS, Abaqus) for that, using hydrodynamic loads as inputs.

If you tell me a few details, I can suggest a concrete workflow

Reply with any of the following (even approximate) and I’ll recommend a specific toolchain and the minimal model you need:

Target operating sea state(s): Hs and Tp (or a location with typical wave climate).
Estimated deck + payload CG location and total mass (you mentioned ~36,000 lb).
Whether the legs are sealed buoyancy tanks only, or partially flooded/ballasted.
Cable type (steel wire rope vs synthetic), approximate diameter, and whether you intend pretension.
Whether the “platform” is rigidly connected to the legs (fixed angle) or has hinges/joints.

Links (starting points)

OrcaFlex (Orcina): https://www.orcina.com/orcaflex/
OpenFAST: https://openfast.readthedocs.io/
MoorDyn: https://moordyn.readthedocs.io/
NEMOH: https://lheea.ec-nantes.fr/logiciels-et-brevets/nemoh-presentation-192863.kjsp
Capytaine: https://capytaine.org/
ANSYS AQWA: https://www.ansys.com/products/structures/ansys-aqwa
OpenFOAM: https://www.openfoam.com/

Disclaimer: This is general engineering software guidance, not a certified design review. For safety-critical offshore structures, engage a qualified naval architect/ocean engineer and follow applicable standards (e.g., ABS, DNV).

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