Hydrodynamic performance of flapping wings for augmenting ship propulsion in waves

The present work deals with the hydrodynamic analysis of flapping wings located beneath the hull of the ship and operating in random waves, while travelling at constant forward speed. The system is investigated as an unsteady thrust production mechanism, augmenting the overall ship propulsion. The main arrangement consists of a horizontal wing in vertical motion induced by ship heave and pitch, while pitching about its own pivot axis that is actively set. A vertical oscillating wing-keel is also considered in transverse oscillatory motion, which is induced by ship rolling and swaying. Ship flow hydrodynamics are modeled in the framework of linear theory and ship responses are calculated taking into account the additional forces and moments due to the above unsteady propulsion systems. Subsequently, a non-linear 3D panel method including free wake analysis is applied to obtain the detailed characteristics of the unsteady flow around the flapping wing. Results presented illustrate significant thrust production, reduction of ship responses and generation of anti-rolling moment for ship stabilization, over a range of motion parameters. Present method can serve as a useful tool for assessment, preliminary design and control of the examined thrust-augmenting devices, enhancing the overall performance of a ship in waves.