Wave Feed-Forward as a Means to Improve Dynamic Positioning

Existing dynamic positioning systems for ships depend mainly on a feed-back control using the position error as input, supplemented by a feed-forward control signal based on the instantaneous wind speed and direction. This paper explores the possibility of creating a feed-forward control signal which can reduce the horizontal motions of the vessel which are caused by the low frequency second order wave drifting forces in irregular waves. Results of model tests are presented which indicate that the relative wave height measured directly alongside and from the vessel can be used to create a wave-feed-forward control signal which reduces significantly the low frequency wave induced surge, sway and yaw motions of a vessel moored in irregular waves.

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