A Dynamic Allocation Strategy for Voith Schneider Propeller

Abstract

To ensure a ship’s capability of Dynamic Positioning, the propulsion system of the vessel is usually designed over-actuated, meaning the ship has more control inputs than degrees of freedom. The distribution of thrust demands of some higher-level controller onto the available thrusters, the thrust allocation, is an essential problem and due to the over-actuated problem not trivial. Furthermore, the thrust should be delivered fast and precisely to achieve good positioning results. The usage of a Voith Schneider Propeller allows thrust generation with these properties but spans a new problem due to complex modeling and increased number of control variables. The paper on hand presents a thrust allocation algorithm which utilizes the dynamic advantages of Voith Schneider Propeller. The algorithm uses a two-step approach consisting of Quadratic Programming optimization and external tracking algorithms for calculation of power-optimal propulsion control. The proposed strategy is compared to a non-linear, multi-criteria optimization which is based on high quality open-water characteristics. The results show strong similarities though the computational time can be significantly reduced by usage of the proposed allocation.