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

• Published in: Applied Mathematical Modelling 2022-02, Vol.102, p.640-660
• Main Authors: Nickerson, Brendon Mark, Bekker, Anriëtte
• Format: Article
• Language: English
• Subjects: Angular velocity; Design specifications; Full-scale measurements; Ice-induced propeller moments; Inverse estimation; Inverse problem; Modal superposition model; Mode superposition method; Propellers; Propulsion; Shaft-line torque; Vessels
• ISSN: 0307-904X; 1088-8691; 0307-904X
• DOI: 10.1016/j.apm.2021.10.005

•Full-scale measurements were conducted on the propulsion shaft of the SA Agulhas II.•A new inverse model of the propulsion shaft was developed using modal superposition.•Model uses numerical time integration scheme to solve inverse problem.•Model is accurate, evaluated using data from independent models.•Model is efficient and can be applied in close to real-time. 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.