Your seastead design is highly unique. The outward-angled cylindrical floats, counter-tensioned by an underwater cable matrix, act similarly to a hybrid between a semi-submersible offshore oil platform and a tension-leg platform (TLP). Because your design relies heavily on the dynamic tension of cables to hold the 45-degree angled buoyant legs in place, standard boat design software (like Maxsurf) will not be sufficient.
To accurately model the wave interactions, cable tensioning, and the low-speed drag of your submersible mixers, you need Time-Domain Hydrodynamic and Mooring Simulation Software. Below are the best software packages capable of handling your specific geometry and physics.
These programs are used by offshore engineers to design oil rigs, floating wind turbines, and complex mooring systems.
Best for: Cables, moorings, and coupled system dynamics.
OrcaFlex is the industry standard for modeling marine cables, risers, and moorings. It thrives in exactly the kind of setup you described: calculating what happens when one leg wants to float up but is held in tension by a matrix of cables. You can define your 40x16 platform as a 6-DOF (Degrees of Freedom) rigid body, attach the buoyant cylindrical legs, and map out the exact cable routing (including your redundant bottom rectangle). It easily simulates ocean wave states and tracks whether your cables go slack or snap.
Best for: Wave diffraction, radiation, and structural loading.
AQWA is built specifically for offshore floating structures. Because your floats are 4 feet in diameter, they sit right on the edge between needing Morison's equation (for thin objects) and Diffraction theory (for large objects). AQWA handles both seamlessly. You can model the 10 psi pressurized stainless steel legs to ensure wave slamming doesn't fatigue the 1/4" duplex steel.
Best for: Unique marine robotics and tow systems.
ProteusDS is fantastic for testing highly articulated floating objects and complex rigid-body/cable interactions. You can easily drag-and-drop your thruster forces onto the legs to see how your 2.5m propellers at 0.5 MPH will perform against wave drag.
If you don't have the budget for commercial software (which can cost tens of thousands of dollars), the academic and open-source communities have developed incredible tools. However, they require a steep learning curve and usually some programming knowledge (Python, C++, or MATLAB).
Best for: Overall open-source system modeling.
Developed by the US National Renewable Energy Laboratory (NREL), WEC-Sim runs on MATLAB/Simulink. While meant for wave energy converters, it is essentially a multi-body dynamic solver for floating platforms. You can couple it with MoorDyn (an open-source mooring dynamics model) to perfectly simulate your cable connections. You can also program in the thrust vectors of your submersible mixers to simulate your 0.5 to 1 MPH movement through varied sea states.
Best for: Viscous drag and thruster efficiency.
While the tools above are "rigid body" solvers, OpenFOAM is a full Computational Fluid Dynamics (CFD) solver. You would use this to create a virtual wind-tunnel (or water-tunnel) for your seastead. Since your shape is "like a tiny oil platform," estimating drag is difficult without CFD. OpenFOAM will let you accurately map the drag coefficient of those 45-degree legs, and you can model the 2.5m propellers to see if their wake interacts negatively with the cables or the other legs.
To go from your description to a working simulation, you would follow these steps:
If you have access to academic licenses or a budget, OrcaFlex combined with standard Ansys for your structural steel analysis is the safest path for an offshore structure relying so heavily on cables.
If you are bootstrapping, start by learning Rhino3D/Orca3D for basic hydrostatics, and look into WEC-Sim with MoorDyn to simulate the complex way those cables will counter the buoyancy forces of the angled legs.
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