Torsional vibration analysis of diesel driven propulsion systems: The case of a polar-class vessel

Abstract

The reliability of marine propulsion plants of ice-going vessels is essential in preserving ship safety during ice navigation. Therefore, the development of reliable design tools of the transmission shafting systems is fundamental to simulate ice–propeller interaction processes correctly. This paper outlines a methodology to model the torsional dynamics of fully-geared, Diesel-driven propulsion systems; specifically, a novel analytical model to simulate the dynamic Diesel engine torque is described. We consider the Canadian Coast Guard heavy icebreaker Terry Fox as a case study, whose propulsion plant includes two shaftlines driven by two 4-stroke Diesel engines each and equipped with controllable pitch propellers (CPP). On this vessel, we performed full-scale measurements during open-water sea trials to: (i) validate the Diesel-drive mathematical model; (ii) update the numerical eigenfrequencies of the system; (iii) determine the curve of the propeller-absorbed hydrodynamic torque. Finally, we simulate the dynamic response of the shaftline’s model by applying an ice–propeller transient excitation. The results indicate the effectiveness of the proposed methodology to simulate the Diesel engine torque, and the significance of considering the CPP pitch variation in transient-state conditions when ice-induced loads are concerned.