Dynamic Loads on Fast Ferry Hull Structures Induced by the Engine-Propeller Coupling

In this paper the problem of the vibrations induced on the hull by the propulsion system is considered. Although the problem has been widely studied in the technical literature, some new aspects concerning the propulsion system model are here investigated. In particular the engine is modelled taking into account its exact crankshaft dynamics, leading to variable inertia effects and parametric excitation. The pulsating propeller torque in the hull wake is studied as well, by solving the flow about the propeller by a boundary element technique. The derived model allows an accurate calculation of the reaction forces transmitted by the engine-propeller system to the ship structures; in this way the characteristic time history of the vibrational motion of important parts of the ships can be predicted. The attention is focused on a typical fast passenger ship, the finite element model of which is developed. Preliminary test results are shown and the performed numerical simulations suggest that the global propeller-engine-structure model could be a useful tool in the frame of the optimization of the vibrational ship design.