Lift line coupling
The Lift Line coupling is a single line model, which includes the following features in a simplified way:

Drag forces on the line.

Static line weight.

Longitudinal inertia forces due to vertical acceleration at both ends.
The Lift Line model gives fast and quite accurate model for prediction of the total static and
dynamic line end forces, and load offset. This coupling type requires that the line is mainly
vertical. The net weight of the body at the lower end of the line will be applied as a force and it is
therefore not possible to have two coupling lines down to the same body.
The simplified Lift Line is modeled by nominal Emodule, diameter, transverse and longitudinal drag
coefficient, and mass per meter length. The model gives zero compressive forces. The basic model
is a straight line. A modification to the straightline assumption is made to take into account the
transition of horizontal motion and forces from the crane to the lifted body due to WF motion, LF
motion and transient motions (moving vessel).
Current forces and the damping forces of the line acting on the body and the load are calculated
along a straight line. The line weight and buoyancy and the dynamic line mass forces are also
calculated along the same line.