Ship Motion Compensation Platform for High Payloads; Dynamic Analysis and Control

Abstract

When a ship motion compensation system carries very high payloads, in the size order of the displacement of the ship, the load dynamics and ship dynamics influence each other.What are these dynamics and how can an actuation system counteract or even benefit from it.Foundations to answer these questions are laid with a selection of literature focusing on non linear model predictive control, time domain hydrodynamics and motion compensation or generation mechanisms primarily of parallel robotic platform type.Next a physical scale experiment in which a heavy hexapod with quasi-static control is placed a ship is investigated.The instability shown in the experiments shows the severity and justify the topic.A planar model is estimated that quantifies sources of instability and shows that there are configurations of system parameters that result in instable behavior.Finally a new conceptual 3 degree of freedom platform mechanism is developed, and for the first time in literature a 3D coupled parallel robotic platform -ship dynamic simulation is derived.Two control techniques are applied, an unsophisticated quasi-static approach and a nonlinear model predictive control approach.Where for the latter real time capability with true online nonlinear optimization is achieved, which is also a first for this kind of systems.This model based approach outperforms the more nave actuation scheme in stability and energy efficiency.