Dynamic Positioning Using Model Predictive Control With Short-Term Wave Prediction

Remotely operated vehicle (ROV) operations are today typically supported by large designated vessels. New emerging concepts aim to streamline ROV operations by utilizing unmanned surface vessels of a smaller size. Reduction in size may result in first-order wave induced motion being more significant. This motivates the use of dynamic positioning control using thrusters to actively compensate for first-order wave-driven horizontal-plane motion in order to maximize operability. This article proposes a controller for dynamic positioning based on model predictive control and short-term wave motion prediction intended to actively compensate for first-order waves. By considering the full dynamic sea environment, the controller is able to dampen out some of the oscillatory motion caused by first-order waves. The controller is able reduce the average deviation from the set-point with up to 65% for a variety of sea conditions. The maximum distance error to the reference point is reduced by up to 65% depending on sea state. The dynamics of the thrusters is a limiting factor when counteracting first-order waves and fast thrusters are therefore crucial in achieving best possible positioning. The cost of the wave-compensated positioning is a more dynamic consumption of power.