Roberto Žigulić

The paper describes a coupled torsional-bending model of ship propulsion system vibrations. The developed model is based on the modified model of the Jeffcott rotor. In order to test the model and determine the coupled torsional-bending vibrations, several cases were analyzed. First, a reference case corresponding to a fully axisymmetric ship propulsion system is set up. Then, the influence of the constant radial force in the vertical direction at the position of the stern bearing was analyzed, such as the conditions of navigation of the ship at calm sea under partial or fully loaded hull. Finally, the case of sailing on rough sea is analyzed, when the propeller racing occurs due to the stern lifting out of the sea. For simplicity, the harmonic law of amplitude changing of the vertical radial force on the stern tube bearing as well as of the propeller load was adopted. Based on the results of numerical analysis, it was found that the proposed model well describes the case of coupling of torsional and bending vibrations of the propulsion system.