MoorDyn

The MoorDyn panel configures the mooring line dynamics model for floating offshore turbines. Click MoorDyn under OFFSHORE in the sidebar to open it. MoorDyn is a sub-module and is only active when CompMooring = 3 in the primary .fst file.

What this panel controls

MoorDyn models the quasi-static or dynamic response of mooring lines using a lumped-mass approach. The panel is organised into three tabs: Overview, Solver, and Output.

Solver settings

Setting	Description
dtM	Integration time step for mooring dynamics (s). Rule of thumb: dtM ≤ 0.001 s for typical mooring systems. Values too large relative to line natural periods cause instabilities
kbot	Seabed contact stiffness (N/m per unit area). Controls the restoring force when a mooring line touches the seabed
cbot	Seabed contact damping coefficient (N·s/m per unit area)

Initial condition generation

MoorDyn uses dynamic relaxation to find the static equilibrium before the time-domain simulation begins.

Setting	Description
dtIC	Time step used during the IC analysis interval (s)
TmaxIC	Maximum time allowed for IC convergence (s). If the mooring system has not converged within this time, the simulation proceeds with the current state — check the log for convergence warnings
CdScaleIC	Drag scale factor applied during IC to damp transients. Typically 4–10
threshIC	Convergence threshold — IC analysis stops when line tensions change by less than this fraction between intervals

The Quick Stats panel shows the number of line types, lines, and fairlead points once a .dat file is loaded.

Loading a MoorDyn file

MoorDyn requires a separate .dat input file that defines line types, line geometry, and connection points. Click Open .dat in the panel header to browse to the file, or point the path field to an existing file in your model directory.

Official documentation

For a full description of all MoorDyn parameters, see the OpenFAST MoorDyn User’s Guide.