Development of ice class calculation tool and process sensitivity analysis
Permanent address of the item is
Jääluokkalaskentatyökalun kehittäminen ja laskentaprosessin herkkyysanalyysi
The main focus of the study is in transient torque vibration due to ice excitation on propulsion machinery components but some background for ice class rules is also presented generally. It is studied how the ice classification calculation process for propeller units could be done more automatically and how sensitive the process is to different parameters. Additionally aspects of the upcoming rule updates are discussed. These updates try to harmonize the ice class calculations internationally and bring out alternatives for the calculation process. As a part of this study partly automated calculation process was developed with Matlab as a sales team tool to ease the preliminary calculations that have to be made during the sales offer. The program includes simulation of a thruster unit and gear calculations based on the given input parameters. This kind of a tool is needed because the offered thruster needs to be classified accordingly and on the current rules this is the safest way to ensure that the offered values can be achieved. The program was developed for a single thruster unit using Finnish-Swedish ice class rules and marine gear rating rules. First in the program ice class excitation loads are calculated and simulated. Then the gears are evaluated to find out validity of power for the chosen thruster unit. This program can be applied to other units as well by making the necessary changes to the propeller unit’s simulation model and by changing the mass-elastic data. Sensitivity analysis was also conducted for Rolls-Royce US 305 azimuthing thruster unit. The results showed that the most critical factor is the gear design itself because it needs to be optimized for heavy loads and the current designs are based on the free running conditions. Other design factors influence the resulting maximum power as well and may have significance cumulatively but otherwise their effect is minimal compared to the gears. Flexible coupling is also quite critical component because of the damping properties and its effect on systems nominal frequencies. Higher power can be achieved by choosing a lower inertia engine or motor and choosing a lower input speed. Additionally propeller design parameters like pitch have some effects but the most important factor is the choice between open and ducted propeller. Open propellers have notably higher loads than ducted in the rules. Other important factor in the design is the propeller diameter, bigger diameter increases the ice load.