Shaft Response as a Propulsion Machinery Design Load

A vessel navigating in ice-covered waters experiences an additional ice-related load that acts on the propulsion machinery. Thus, the influence of this load on the propulsion machinery must be known, because it affects the safety and efficiency of the design and operation of the ice-going vessel. The ice-related load, in full-scale trials and model-scale tests, is typically measured at the shaft line between the propeller and diesel engine. Hence, the measured load includes a dynamic response of all elements in the mechanical transmission line. Therefore, this paper describes an approach to link the measured ice-related response of the shaft with the ice-propeller load. Therein, the rule-based DNV ice-propeller load is implemented in a bond graph model of the propulsion machinery system, which is used to obtain the dynamic response of all elements of the machinery system from the propeller to a diesel engine. The obtained shaft response is collected, filtered with different sampling frequency and converted to the ice-propeller load using a developed reverse model of the propulsion machinery. Furthermore, two different models of the shaft line: a rigid and a first order flexible are developed and verified. As a result, the converted ice-propeller load is compared with the rule-based DNV ice-propeller load and the influence of the sampling frequency and shaft models on the converted ice-propeller load is presented.