Steady and Unsteady Hydrodynamic Loads on the Azimuth Bearing of a POD during a Crash-Stop Maneuver

The crash-stop maneuver of a ship equipped with two pods produces the largest loads that the structure and azimuth bearing can possibly experience. For design purposes, a sufficiently fast and accurate determination of the loads is thus critically important. This study examines load estimation during crash-stop maneuvers based on model tests and numerical methods. Forces and moments are compared to determine the influence of different control parameters (azimuth rate, propeller number of revolution, etc.). In addition, the results of numerical simulations carried out in model- and full-scale are used to analyze the influence of the Reynolds number on the flow behavior. Results show a significant influence of the azimuth rate on the maximum forces and moments. The numerical calculations indicate a strong dependency of the flow stall behavior on the azimuth rate. The dynamic stall effect on the profile-shaped parts, such as the pod strut, is shifted to a larger angle of attack compared with a steady angular position. This phenomenon is also observed during the model tests. The full-scale simulations show up to a 23% increase of the forces compared with the model-scale simulations. Thus, a detailed and careful handling of the results considered in the design process is required for the load estimation.