Stability analysis

SIMA software includes modelling capabilities that allows building a complete and accurate physical representation of a floater, based on a SIMO model. The static stability of the model can be studied through the calculation of the equilibrium position, GZ-curves or stability maps.

Modelling capabilities

• Non-linear hydrostatic force model

• Ballast tank system
• Position dependent wind and current coefficients
• All other SIMO force models, like anchor lines
• The force models above are also available for time domain simulations.

The force models above are also available for time domain simulations.

Non-linear hydrostatic force model

The model used to compute the exact buoyancy forces and moments acting on the vessel is based on the following:

• Hull geometry is described as a STL file (watertight triangular panel mesh)
• The mesh is cut exactly at the free water surface
• The surface integrals are computed analytically for each wetted panel

Ballast tanks system

Each tank and/or compartment geometry is described as a STL file. Total gravity force and mass matrix are due to fluid in each tank are computed. The following features are included:

• Free-surface effect is included
• Volume of ballast tank can easily be modified
• The mesh is cut exactly at the free fluid surface
• The surface integrals are computed analytically for each panel
• Damaged tank model is available

Position dependent wind and current coefficients

Wind and current force coefficients can be provided by the user as a function of four parameters:

• Relative wind/current direction
• Floater vertical position
• Floater roll angle
• Floater pitch angle

For a given floater position and wind/current direction, the force coefficients are interpolated linearly from the data set.

Calculation possibilities

Different calculation possibilities are available to study the static stability of a system. Advanced post-processing of results, graphics and plots are possible with external python scripts.

• Static equilibrium calculation (with the possibility to restrain desired degrees of freedom)
• Calculation of GZ-curve: equilibrium is computed for each point of the curve. The azimuth angle and the rotation angles are defined by the user.
• Calculation of the stability map (two-dimensional GZ-curve). Equilibrium is computed at each grid point.