SMARTEST 
(Fairlead pulley spring system)

A single spring through a fairlead pulley simulates the three components of the nonlinear restoring mooring force. The fairlead pulley is free to rotate (3D) around the fairlead point. There are two anchor points per line. The anchor points (100 LB weights) are positioned in the basin with the towing truss by using the truss position for the X-coordinate and a ruler at the back truss edge for the Y coordinate. Six parameters (X,Y for 2 anchor points; spring stiffness; and the initial stretch) are calculated by a least squares fit, assuming that the restoring force acts in the bisect direction of the space angle at the fairlead pulley.

The offset here is given in model scale.

The following plots show how the simulation works for a single mooring line. The numbers are given in full scale.

Another  advantage of the new system is that it matches automatically the vertical stiffness  of the mooring lines within 1 % accuracy.

The next picture shows the position of  4 mooring lines in the basin. Note that the system can represent SCRs, if the simulation of their inertia is not required.

An alternative approach with two anchor pulleys (no fairlead pulley).
This simulation produces the same triangle geometry/forces.

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