Nonlinear Hydrostatics

The Nonlinear Hydrostatics model computes buoyancy forces by volume integration based on hull geometry.

The geometry file should be of type STL (STereoLithography).

The position and orientation of the geometry given in the body coordinate system:

  • X: X-position of the geometry, \(\mathrm {[m]}\)

  • Y: Y-position of the geometry, \(\mathrm {[m]}\)

  • Z: Z-position of the geometry, \(\mathrm {[m]}\)

  • Roll: Roll angle of the geometry, \(\mathrm {[deg]}\)

  • Pitch: Pitch angle of the geometry, \(\mathrm {[deg]}\)

  • Yaw: Yaw angle of the geometry, \(\mathrm {[deg]}\)

The hydrostatic force model will only return the buoyancy force when using this formulation. It is therefore often relevant to include the gravity forces for the body in that case (see Gravity force).

Nonlinear hydrostatic stiffness is primarily intended for hydrostatic analysis with large body motions (e.g. stability calculations, calculations and installation analysis) in calm conditions, where integration over the domain Z<0 is sufficient. It should be used with care in conditions with waves. In conditions with waves, using a linear hydrostatic stiffness is often more accurate.