Since January 2011, when calculations of shafting transient torsional vibrations caused by ice impacts became mandatory, numerous modeling-based analyses have been carried out for the ice class ships. However, their number is still not sufficient to learn from the experience and draw general conclusions about the shafting response in ice conditions. The major reasons of this could be summarized as follows. First of all, lack of an effective and physically meaningful tool for the prediction of transient vibrations makes the analysis rather difficult. Secondly, some simplifying assumptions about the response of the propulsion system in ice conditions are to be made because the consideration and addressing the complex nature of a propulsion system in practical design are impossible for many reasons. Third of all, various underlying uncertainties in the input data put a shaft designer in situation when he needs to make a choice. This paper is an attempt to make some contributions to the presentation and analysis of the propulsion shafting torsional vibration induced by propeller-ice interaction. Two practical examples: one - for a polar class ship with direct coupled diesel engine and another one - for the case of a geared propulsion unit are considered. Some uncertainties in analysis of the induced ice-related torques are considered and assessed.

Since 1869 the main goal of whirling vibration calculations of rotating machinery was to determine critical speeds. Currently, all Classification Societies require a propulsion shafting whirling vibration calculation (also named bending or lateral vibration calculation) in the scope of the critical speeds i.e. free whirling vibration calculation. However, fatigue failure of the bracket and aft stern tube bearings, destruction of high-speed shafts with universal joints, noise and hull vibrations, generated by shafting, indicate the importance and inevitability of forced whirling vibration calculations. This paper presents some latest results of free and forced whirling vibration calculations obtained using the software intended for shaft design.

No abstract

No abstract