In the present work the analysis of an oscillating wing, located beneath the ship's hull, in random motion, is examined as an unsteady thrust production mechanism, augmenting the overall propulsion system of the ship. The wing undergoes a combined vertical and angular oscillatory motion, while travelling at constant forward speed. The vertical motion is induced by the random motion of the ship in waves, essentially due to ship heave and pitch, while the wing pitching motion is selected as a proper function of wing vertical motion and it is imposed by an external mechanism. Numerical results are presented for the thrust produced by the biomimetic wing as well as the resulting reduction in ship motions over a range of motion parameters. Our calculations indicate that the biomimetic wing is the proper mechanism for transforming the hull kinetic energy to useful thrust, augmenting thus the ship propulsion in rough seas with simultaneous reduction in ship motions. The present method can serve as a useful tool for the assessment and the preliminary design and control of such thrustaugmenting devices, which enhance the overall performance of a ship in a wavy environment.
Biomimetic propulsors is the subject of intensive investigation, since they are ideally suited for converting environmental (sea wave) energy to useful thrust. Recent research and development results concerning flapping foils and wings, supported also by extensive experimental evidence and theoretical analysis, have shown that such systems at optimum conditions could achieve high thrust levels; see, e.g., Triantafyllou et al (2000, 2004), Taylor et al (2010). The contribution of cargo ships in world pollution has been recognised as one of the most important factors (e.g. Colvile 2001, Flannery 2005), taking also into account the bad fuel quality of seagoing vessels in relation to other modes of transport.