Evaluation, design and optimization for strength and integrity of polar class propellers

An advanced 3D unsteady panel method was developed for the design and optimization of the strength and integrity of polar class propellers. Blade ice loading specification in both milling and impact cases, under the Unified Polar Class Rules (URI3), by the International Association of Classification Societies (IACS), was implemented. An optimization example and analysis were given for an R-class propeller. The strength of the R-class propeller was assessed for all 7 polar classes and 5 loading cases. Comparison was also made for all polar classes and ice loading cases. As the blade has little skew with a wide chord, both the spindle torque and the in-plane bending moment are small, so only out-of-plane bending failure is the key factor for strength. It was also found that by URI3, there is little difference in strength requirement between polar classes 1 (strongest requirement) and 7 (the weakest). An integrity design and optimization example showed a saving of 1.4 tonnes of blade material (22% saving) by decreasing the safety factor to 1.51 (the minimum safety factor under URI3 is 1.5), for which case the blade thickness is about 80% of the existing design.