Inverse model for the estimation of ice-induced propeller moments using modal superposition

Abstract

It is necessary to quantify the loads experienced by the propellers of ice-going vessels. Knowledge of these loads will serve to improve propulsion design specifications and maintenance strategies for polar class ships. Recent developments include the inverse solutions of the external ice-induced propeller moments from indirect measurements on the propulsion shaft. These inverse solutions are performed using models that account for the dynamic influence of the shaft. Full-scale propulsion shaft measurements were conducted on board the S.A. Agulhas II, in which the torque and angular velocity were captured, to be transformed into external propeller moments. A new model based on modal superposition for the inverse estimation of propeller moments on ice-going vessels has been developed. This model accounts for the modal inertia in the flexible modes of the shaft, as full-scale data indicated that this was important, and has increased accuracy and efficiency. The model is evaluated using full scale measurements aboard the S.A. Agulhas II, and compared to previous models in literature. The advantages of this model over the state of the art in literature are discussed.