Augmenting Ship Propulsion in Waves Using Flapping Foils Initially Designed for Roll Stabilization

Biomimetic flapping foils attached on ship hull are studied for wave-energy extraction, stored in ship motions, and direct conversion to propulsive power. We examine a pair of roll-stabilization wings located at the side of the hull, in horizontal arrangement. The fins gain their linear oscillation (heaving) from ship pitching and heaving responses in irregular waves, while wing's rotation (pitching) is properly controlled with respect to its vertical motion history. A method, developed in our previous works, is applied for that purpose. The system operates in realistic sea conditions modeled by using parametric spectra, taking into account the coupling between ship responses and the hydrodynamics of the lifting appendages. We present numerical calculations concerning the operation of the augmenting system indicating that, although the present arrangement is designed for roll reduction purposes it can obtain significant amount of thrust. Also it is illustrated that, after reposition of the fins near the bow, the performance of the system can be further enhanced.