Evaluation of a Finite Difference Helicoidal Shell Analysis by Comparison with Test Results for a Marine Propeller

The ability to predict the blade natural frequencies and the stresses under operating conditions is a necessary requirement of the blade design process. This requires an accurate definition of the steady and cyclic pressure loads over the blade surface. It also requires an appropriate structural model and analytic procedure for solving the structural response of the blade. This paper presents the results achieved by application of a finite difference helicoidal shell analysis computer program to a supercavitating marine propeller blade. The natural frequencies, mode shapes, steady stress and cyclic stress are evaluated, and the results are compared to measured values. Comparison with test results is made using both analytically derived and measured pressure distributions. Correlation of measured and calculated "in air" natural frequencies and mode shapes is quite good particularly for the higher modes. The calculated stresses agree well when compared to calculations based upon measured pressures.