Publisher DOI: 10.5957/JOSR.09180055
Title: Steady and Unsteady Hydrodynamic Loads on the Azimuth Bearing of a POD during a Crash-Stop Maneuver
Language: English
Authors: Neitzel-Petersen, Jan Clemens  
Stutz, Sophie Juliane 
Abdel-Maksoud, Moustafa  
Issue Date: Mar-2021
Publisher: The Society of Naval Architects and Marine Engineers
Source: Journal of ship research 65 (1): 25-40 (2021-03)
Journal: Journal of ship research 
Abstract (english): 
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 profileshaped 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.

Crash-stop maneuvers must be carried out during sea trials and regular mandatory class surveys to demonstrate compliance with safety requirements for the ship, crew, and passengers in an emergency situation. In the case of ships equipped with podded propulsion devices, these maneuvers often result in the maximum azimuth bearing load that can occur in a ship's lifetime. The stopping maneuver for ships with a conventional twin-screw propeller shaft drive arrangement is performed by turning the sense of propeller rotation into the opposite direction. By contrast, for ships equipped with podded propulsion devices, the whole unit of the podded propulsor turns around its azimuth axis until the propeller produces thrust opposite to the ship's heading direction, while the propeller turning direction remains unchanged. During the crash-stop maneuver, the lateral surface of the pod is for a short period of time almost perpendicular to the incoming flow, and consequently, the exposed surface of the pod housing to the inflow reaches a maximum value. Because the crash-stop maneuvers must be carried out at maximum ship speed, the podded drive must operate under the most severe loads during these trials. Large steering moments are required to turn the pod under these conditions, and extreme loads must be held by the azimuth bearing and then transferred to the ship structure. These loads are the design loads for the bearing and the structural components of the pod housing.
Conference: Journal of Ship Research 
ISSN: 0022-4502
Institute: Fluiddynamik und Schiffstheorie M-8 
Document Type: Article
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