Preliminary study on a concept of wave propulsion by an active pitch-oscillating fin

Rising fuel prices and regulations to reduce CO₂ emission have become a strong driving force to push shipyards and ship owners to build and operate energy saving ships. To meet these increasing demands, many novel designs and devices have been developed for reducing drag or for improving propulsion efficiency of a ship in seaway. Furthermore, several approaches using passive or active oscillating fin to extract wave power to assist ship propulsion have also been explored. The objective of the present study is to investigate the feasibility of a concept using an active pitch-oscillating fin to harness wave power for propulsion enhancement of merchant ships. Experimental data of the NACA 0012 oscillating foil are adopted to validate the present CFD simulation. Dependence of propulsion performance on Reynolds number and submerged depth are investigated. It has been confirmed that thrust of a flapping fin increases but efficiency decreases with larger Reynolds number, and shallower submerged depth of fin has negative effect for propulsion. Through simulations, thrust and propulsion efficiency of a flapping fin equipped at bow in full-scale ship are assessed. An active pitch-oscillating fin together with heave motion driven by ship vertical response to waves may generate significant amount of thrust with relatively high efficiency. As an example shown in the paper, for a VLCC of 321 meter long, a bow fin with projected area to waterline area ratio of 1/143, pitching actively around its pivot axis, may save energy about 3.1%~9.5% in the ship speed ranges of 12~16.5 knot.