Dynamic Transom Foil

Motion and Resistance Reduction

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Two important performance parameters of a ship are fuel consumption and motions in a seaway. Besides a well-designed hull, several appendages can be used to increase the performance. One of these is a resistance reducing fixed foil behind the transom of the ship. This wing has the potential to create large lift forces near the aft of the ship, thereby changing the resistance and dynamic position of the vessel.
In this thesis an algorithm is designed that controls the pitch angle and thus lift of this foil. The goal is to investigate the potential of such a dynamic foil for further reduction of (added) resistance and ship motions. The resistance reduction is investigated by creating thrust on the foil trough an oscillating foil principle (i.e. vertically moving the foil to create propulsion). The research is done with the use of the FINE/Marine CFD package. A model from the AMECRC OPV series is used for analysis, in combination with a foil optimized in earlier research.
From the literature review can be concluded that a dynamic, rotating foil behind a ship will not generate thrust in the same manner as an oscillating foil does. Furthermore, an initial CFD study showed that the pitching velocity of the ship has the greatest influence on the changing angle of attack on the foil. Additionally a study into basic wing theory showed that the foil would produce the most thrust at low angles of attack.
With the use of this information, four algorithms were developed. Two of these algorithms focused on reducing the overall resistance by increasing the generated thrust on the foil. The results showed that the generated thrust cannot be significantly increased in comparison to a static foil. Two other algorithms were designed with the goal to reduce the pitching motion of the vessel. These two algorithms both achieved a significant reduction of the pitching motion, which also lead to a reduction in added wave resistance. Although the foil dampened the pitch motion, the generated thrust was found to be less than for the case with a static foil. The reduction in thrust was similar in size to the reduction in added wave resistance. It can be concluded that the rotating foil was able to provide similar resistance reduction as a static foil, with the added benefit of a significant reduction in pitch motion.