Validation of analytical methods for the estimation of the torsional vibrations of ship power transmission systems.

The propulsion system is one of the main sources of ship vibrations. A typical propulsion system consists of an engine, a shaft line and a propeller. In order to estimate the vibration levels of a ship propulsion system, analytical methods are still relevant in the preliminary ship design stage. In this paper, three analytical procedures for the vibration analysis of a ship shafting system are presented. The shafting system dynamic behaviour is simulated by reducing the problem to two-, three-, and multi-mass models. Propeller and engine damping is taken into account. Differential equations of motion for the two- and the three-mass models are solved analytically. In the case of the multi-mass model, Rayleigh's quotient and the Galerkin method are used for free and forced vibration analysis, respectively. Since the first natural mode of the shaft line is dominant, the problem can be reduced to a single d.o.f. in the modal space and solved analytically. For all three models, relatively simple formulae for the engine torque transfer factor to the intermediate shaft are derived. The presented procedures are validated by a comparison with measurements. The comparison indicates the high accuracy of the proposed procedures. [ABSTRACT FROM AUTHOR]