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Stability analysis

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.