An Estimation Method for the Torsional Vibration of the Marine Propulsion System

The paper presents an estimation analysis methopd for the natural mode and frequency of the torsional vibrations of a marine power transmission system. A typical merchantman marine propulsion system is made up of a slow speed main engine connected to a directly driven propeller by a relatively short shaft line. Although all classification societies require calculating the operating parameters of the propulsion system, however, they have no simplified formulas. The torsional vibrations of the marine power transmission system are usually the most dangerous for the shaft line and crankshaft. Numerical algorithms based mostly on the Finite Element Method (FEM) are unobtainable and not useful for a ship crew. The chief of marine engineers should have checked a possibility of the analysis and measurements of torsional vibrations. The authors have investigated an estimation method of the torsional vibrations of the system. The article deals with a simulation method for more difficult parameters of the propulsion system like propeller water added mass moment of inertia. The paper also briefly describes the advantages and disadvantages of the undercritical and overcritical propulsion system and discusses calculation results included in the final part of the work. The introduced calculation method has been verified comparing detailed FEM estimations and the measurements of real ships.