Tension-Leg Platform (2D): Heave-Surge-Pitch Tendon Dynamics

A Tension-Leg Platform is held against its own excess buoyancy by taut, pre-tensioned tendons running straight down to seabed anchors. This 2D side-view simulation solves an independent, three-degree-of-freedom rigid-body model of that behaviour — coupled heave, surge and pitch — using each tendon's exact Pythagorean geometry rather than a linear approximation, which surfaces the real "set-down" effect: surge motion stretches every tendon a little regardless of direction, pulling the platform's mean heave position downward. Wave forcing is sampled independently at bow and stern stations using linear (Airy) wave theory, which is what actually creates the pitch-exciting moment that a single-point force cannot. Adjust wave height and period, tendon length (water depth) and total pretension to see how they trade off motion amplitude, mean set-down and the risk of a tendon going slack.