```html Seastead Wave Simulation Software Guide

🌊 Seastead Wave Simulation Software Guide

Comprehensive analysis tools for your semi-submersible platform design

📋 Your Seastead Design Specifications

Living Area: 40' × 16' (640 sq ft)
Leg Configuration: 4 columns at 45° angle
Column Dimensions: 4' diameter × 24' length
Material: Duplex Stainless Steel (¼" sides, ½" ends)
Waterplane Footprint: 50' × 74'
Total Weight: ~36,000 lbs
Propulsion: 4× submersible mixers (2.5m props)
Target Speed: 0.5-1 MPH
Internal Pressure: 10 psi
Design Type: Semi-submersible (mini oil platform style)

🏆 Professional Industry-Standard Software

ANSYS AQWA

ANSYS Inc.

Professional Industry Standard
  • Hydrodynamic diffraction and radiation analysis
  • Wave loading on floating and fixed structures
  • Mooring system analysis (perfect for your cable system)
  • Time-domain simulation in irregular seas
  • Motion response in 6 degrees of freedom
  • Coupled analysis with structural mechanics

Suitability for Your Design: ⭐⭐⭐⭐⭐

Excellent choice for semi-submersible platforms. Can model your angled columns, cable mooring system, and thruster forces. Industry standard for offshore structures.

OrcaFlex

Orcina Ltd.

Professional Industry Standard
  • Dynamic analysis of offshore marine systems
  • Excellent mooring and cable modeling
  • Real-time 3D visualization
  • Vessel hydrodynamics with imported RAOs
  • Multiple line types (chains, ropes, cables)
  • Python scripting for automation

Suitability for Your Design: ⭐⭐⭐⭐⭐

Outstanding for modeling your cross-bracing cable system with redundancy analysis. Great visualization to understand failure scenarios when one cable breaks.

WAMIT

WAMIT Inc. (MIT spinoff)

Professional Research Standard
  • Boundary element method for wave-body interaction
  • Computes added mass, damping, and exciting forces
  • Multi-body interactions
  • Higher-order panel methods available
  • Well-documented theory manual
  • Outputs can feed into other simulation tools

Suitability for Your Design: ⭐⭐⭐⭐

Excellent for computing the hydrodynamic coefficients of your unique geometry. Often used alongside time-domain tools like OrcaFlex.

SESAM (GeniE, HydroD, SIMA)

DNV (Det Norske Veritas)

Professional Classification Society
  • Complete offshore structure design suite
  • Integrated structural and hydrodynamic analysis
  • Time-domain simulation with SIMA
  • Fatigue and ultimate strength analysis
  • Direct link to classification requirements
  • Wave spectrum library included

Suitability for Your Design: ⭐⭐⭐⭐⭐

If you ever need classification or insurance approval, DNV's SESAM suite provides direct compliance checking. Excellent for your semi-submersible configuration.

💰 Open Source & Lower Cost Options

OpenFAST

National Renewable Energy Laboratory (NREL)

Free/Open Source Government Funded
  • Originally for floating wind turbines
  • HydroDyn module for platform hydrodynamics
  • MoorDyn module for mooring dynamics
  • Coupled aero-hydro-servo-elastic simulation
  • Active development community
  • Well-documented with tutorials

Suitability for Your Design: ⭐⭐⭐⭐

Excellent free option. Your semi-submersible is similar to floating wind turbine platforms. MoorDyn can model your cable system. May require some adaptation for your specific geometry.

Capytaine

Open Source (Python)

Free/Open Source Python-based
  • Python BEM solver for wave-body interaction
  • Based on Nemoh (see below)
  • Easy integration with Python workflows
  • Good documentation and examples
  • Can compute hydrodynamic coefficients
  • Meshio support for geometry import

Suitability for Your Design: ⭐⭐⭐

Good for computing wave forces on your platform. Would need to couple with another tool for time-domain mooring simulation. Python integration is very convenient.

Nemoh

École Centrale de Nantes

Free/Open Source Academic
  • BEM solver for first-order wave forces
  • Computes RAOs (Response Amplitude Operators)
  • Added mass and damping matrices
  • Fortran-based with pre/post processors
  • Can handle multiple bodies
  • Output compatible with other tools

Suitability for Your Design: ⭐⭐⭐

Good starting point for understanding your platform's wave response characteristics. Outputs can be used in time-domain simulations.

OpenFOAM with waves2Foam

Open Source CFD

Free/Open Source CFD-based
  • Full CFD simulation with free surface
  • Can capture nonlinear wave effects
  • Arbitrary geometry support
  • 6-DOF rigid body motion
  • High fidelity but computationally expensive
  • Large user community

Suitability for Your Design: ⭐⭐⭐

Overkill for routine analysis but excellent for detailed studies of wave impacts on your columns or validating simpler models. Very computationally intensive.

MoorDyn (Standalone)

NREL / Matt Hall

Free/Open Source Specialized
  • Lumped-mass mooring dynamics model
  • Can run standalone or coupled
  • Handles complex line configurations
  • C++ with Python bindings available
  • Relatively easy to set up
  • Good for cable failure scenarios

Suitability for Your Design: ⭐⭐⭐⭐

Perfect for analyzing your cross-cable system and testing redundancy when one cable fails. Can be coupled with hydrodynamic tools.

📊 Software Comparison Table

Software Cost Learning Curve Mooring Semi-Sub Best For
ANSYS AQWA $$$$$ Medium ✅ Excellent ✅ Excellent Full professional analysis
OrcaFlex $$$$ Medium ✅ Excellent ✅ Excellent Cable system dynamics
WAMIT $$$ High ❌ Limited ✅ Excellent Hydrodynamic coefficients
SESAM Suite $$$$$ High ✅ Excellent ✅ Excellent Classification compliance
OpenFAST Free Medium-High ✅ Good ✅ Good Free comprehensive tool
Capytaine Free Medium ❌ No ✅ Good Python-based analysis
Nemoh Free Medium ❌ No ✅ Good Computing RAOs
OpenFOAM Free Very High ⚠️ Complex ✅ Excellent Detailed CFD studies
MoorDyn Free Low-Medium ✅ Excellent ❌ Needs coupling Cable system only

🎯 Recommended Approach for Your Seastead

  1. Start with OpenFAST (Free)

    Use this to get initial motion responses and understand your platform's behavior in waves. The HydroDyn + MoorDyn combination can model your semi-submersible with cables.

  2. Model Your Geometry

    Create a mesh of your 4 angled columns in a CAD tool (FreeCAD, Blender, or Rhino) and export to formats these tools can read (.stl, .gdf, etc.).

  3. Test Cable Failure Scenarios

    Use MoorDyn (within OpenFAST or standalone) to simulate what happens when one of your 8+ cables fails. Your rectangular cable provides redundancy - verify it works!

  4. Consider OrcaFlex for Final Design

    If budget allows, OrcaFlex provides excellent visualization and is industry-trusted. They offer educational licenses.

  5. Validate with Physical Model

    Consider building a small-scale model for wave tank testing to validate your simulations.

📐 Typical Simulation Workflow

1 CAD Geometry
2 Mesh Generation
3 Hydro Coefficients
4 Define Moorings
5 Wave Conditions
6 Time Simulation
7 Results Analysis

💻 Example: OpenFAST Input Structure

Here's a simplified example of how you might define your platform in OpenFAST:

--- HYDRODYN INPUT FILE (simplified) --- WaveMod 2 ! Irregular waves (JONSWAP) WaveHs 2.5 ! Significant wave height (m) WaveTp 8.0 ! Peak period (s) WaveDir 0.0 ! Wave direction (deg) --- PLATFORM PROPERTIES --- PtfmMass 16329 ! Platform mass (kg) ~36000 lbs PtfmRIner 1.0E7 ! Roll inertia (kg-m^2) PtfmPIner 1.0E7 ! Pitch inertia (kg-m^2) PtfmYIner 2.0E7 ! Yaw inertia (kg-m^2) --- MEMBER DATA (4 angled columns) --- ! JointID X(m) Y(m) Z(m) 1 7.62 2.44 2.0 ! Top of column 1 2 11.28 6.10 -3.66 ! Bottom of column 1 ! ... repeat for columns 2, 3, 4 --- MOORDYN LINES (8 cables + 4 perimeter) --- NLines 12 ! Total number of mooring lines LineType 1 ! Steel cable UnstrLen 15.0 ! Unstretched length (m)

📝 Important Modeling Considerations for Your Design

1. Hydrodynamic Modeling

  • Your 4' diameter columns are small enough that Morison equation may be sufficient (potential flow for larger members)
  • The 45° angle creates interesting wave loading - horizontal and vertical components both matter
  • Half-submerged columns mean variable waterplane area as platform moves
  • Small waterplane area = low hydrostatic stiffness = longer natural periods

2. Cable System Modeling

  • Your cross-bracing + perimeter cables create a statically indeterminate system (good for redundancy!)
  • Model cables as tension-only elements
  • Include cable stretch (stiffness) for dynamic response
  • Simulate single cable failure scenarios to verify redundancy
  • Consider snap loads when slack cables become taut

3. Thruster Modeling

  • 2.5m propellers provide significant thrust at low speed
  • Model as constant or controllable forces
  • Consider thrust vectoring if props can rotate
  • At 0.5-1 MPH, wave drift forces will likely dominate

4. Wave Conditions to Simulate

  • Operational: Hs = 1-2m, Tp = 5-8s (typical conditions)
  • Design: Hs = 3-4m, Tp = 8-12s (moderate storms)
  • Survival: Hs = 6-8m, Tp = 10-14s (severe conditions)
  • Consider your intended operating area's wave statistics

⚠️ Important Caveats

  • Simulation results should be validated against physical model tests when possible
  • These tools require proper training to use effectively
  • Input garbage = output garbage - geometry and conditions must be accurate
  • For insurance or classification, professional engineering review is typically required
  • Second-order wave forces (drift) are important for station-keeping analysis

🔗 Resources & Links

Software Website Documentation
OpenFAST github.com/OpenFAST/openfast openfast.readthedocs.io
Capytaine github.com/capytaine/capytaine capytaine.github.io
MoorDyn github.com/mattEhall/MoorDyn moordyn.readthedocs.io
Nemoh ec-nantes.fr/nemoh Included with download
OpenFOAM openfoam.com Documentation
OrcaFlex orcina.com/orcaflex With license
ANSYS AQWA ansys.com/aqwa With license
SESAM dnv.com/sesam With license
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