||Carlos Guedes Soares, Fernando Lopez Pena
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In the last period, requirements and intergovernmental regulations related to vehicle technology for reduced pollution and environmental impact have become strict, and response to the demand of greening of transport has been recognized to be an important factor concerning global warming and climatic change. Thus, environmentally friendly technical solutions offering reduction of exhaust gases are requested. Additionally, the increased competition in the field of maritime technology requires even more economical vessels. Therefore, minimization of ship resistance/drag has become a central issue. On the other hand, the superior swimming and manoeuvring capabilities of aquatic animals has motivated research on fish-like propulsion for many years in the past. Important reviews addressing various aspects of fish undulatory propulsion have been presented by a number of authors. In particular, experimental and theoretical work identifying the principal mechanism for producing propulsive and transient forces in oscillating flexible bodies and fins in water, in connection also with the formation and control of large-scale vortices, is reviewed in Triantafyllou et al. (2000). A survey of experimental hydro-dynamic data concerning undulatory locomotion in fishes, providing as background a general description of the major theoretical model of undulatory propulsion has been presented by Lauder & Tyttel (2006). Also, research and development of flapping-wing propulsors and results concerning marine vehicles equipped with such systems is reviewed and discussed in Rozhdestvensky & Ryzhov (2003). and state-of-the-art in experimental research on the physics of swimming and flying animals in Taylor et al. (2010). Biomimetic propulsors could be found quite exploitable for converting environmental (sea wave) energy to useful thrust; see also Triantafyllou et al. (2004). A main difference between a flapping propulsor and a conventional propeller is that the former absorbs its energy by two independent motions: the heaving motion and the pitching motion, while for the propeller there is only rotational power feeding. In real sea conditions, the ship undergoes moderate or higher-amplitude oscillatory motions, due to waves, and the vertical ship motion could be exploited for providing one of the modes of combined/complex oscillatory motion of a biomimetic propulsion system free of cost...