Dynamic Stability Simulation
General information
The computer program FREDYN simulates the dynamic behaviour of a steered ship subjected to waves and wind. FREDYN is to be used in the initial design stage when model test data are not available. The program has been validated against model tests with frigates and containerships. For frigate-type hulls in particular both excitation forces and motion response in waves have been considered in detail, including conditions leading to capsize.

The development of FREDYN was one of projects of the Cooperative Research Navies (CRNAV).

Software tools
FREDYN consists of two parts. In the first part the hydrodynamic coefficients are calculated for six degrees of freedom. From the geometry of the hull, rudders, bilge keels and propeller coefficients (mass, added mass, radii of gyration, damping, retardation functions, buoyancy forces and moments, propeller and rudder forces, bilge keel effects) are determined.
In the second (simulation) part the ship motion components are determined from a set of six coupled different equations of motion. Integration of the calculated accelerations provides the ship velocities and a second integration leads to the ship’s position at each ‘time step’. The total forces are split into the following: diffraction, Froude-Krylov, radiation, viscous damping, buoyancy, rudder, propeller, wave and wind forces. The program can handle regular waves and irregular long-crested seas. Wind can also be taken into account by specifying a constant velocity, or a wind spectrum for modelling wind gustiness. The behaviour of the ship depends on the type of manoeuvre specified and on the characteristics of the automatic pilot or the human helmsman.

FREDYN has been developed for the initial design phase and can be used to analyse the manoeuvrability characteristics in calm water or in waves, as well as the seakeeping performance in moderate to severe seas. The applicability for small vessels depends on the sea state conditions. Shipping of water and breaking waves are not taken into account.

Software Sales
Some software tools are available for commercial use outside MARIN. A complete overview of these software tools for sale can be found under Software Sales.

For more information on Dynamic Stability Simulation, please contact the Ships Seakeeping department .

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