Links are simple spring or spring-damper connections linking two points in the model, for example a node on a line to a vessel, or a buoy to an anchor. They pull the two points together, or hold them apart, with a force that depends on their relative positions and velocities.
Links have no mass or hydrodynamic loading and simply apply an equal and opposite force to the two points. They are useful for modelling items such as wires where the mass and hydrodynamic effects are small and can be neglected.
Two types of link are available:
Tethers are simple elastic ties that can take tension but not compression. The unstretched length and stiffness of the tether are specified. If the distance between the ends is less than the unstretched length, the tether falls slack and does not apply a force.
Spring/dampers are combined spring and independent damper units. The spring can take both compression and tension, and may have either a linear or a piecewise-linear length-force relationship. The damper velocity-force relationship may likewise be linear or piecewise-linear.