Impact of different characteristics of the ice–propeller interaction torque on the torsional vibration response of a Polar-Class shaftline

Abstract

During navigation in Polar regions, ice-induced torque excitation endangers the operation and integrity of ship propulsion systems. Predicting these dynamic phenomena through proper numerical models is therefore essential. This paper studies the influence of different properties of the ice–propeller torque on the transient torsional dynamics of a Polar-Class shafting system. We initially considered the ice torque defined by the current regulatory framework. Hence, we examined variants of four ice impact properties—(i) rise shape; (ii) angular span; (iii) ramps up–down feature; (iv) number of ice impacts—to study the transient and steady-state conditions induced by the ice–propeller excitation. We performed a series of torsional vibration analyses using the numerical model of the shaftline of the Canadian Coast Guard (CCG) icebreaker Terry Fox. Furthermore, we tested the system with Diesel engine and electric motor excitation models interchangeably; the electric drive solution proved to counter ice-induced transient perturbations more effectively. The results indicate that the ice impact span, the ramps up–down application, and the number of impacts are the most important factors to affect the shaftline’s rotational speed drop and response torque. In particular, the significance of the ice impact ramps is such that it might entail a review of the in-force regulatory guidelines.