A method was developed for predicting the dynamic stress field in marine propeller blades rotating through a non-uniform ship wake. For this analysis, the propeller geometric characteristics, operating conditions, and the ship wake are assumed to be known in advance.; The basic ingredients in the fluid-structural interaction problem are the applications of the Green's function method on the fluid domain and finite element method on the structural domain of the propeller blades. Two models were developed. The hydrodynamic model, which employs potential theory, represents the blades and their wakes as overlays of advancing and rotating source and dipole patches. The structural model uses three dimensional 8-node isoparametric elements for the propeller blades. The hydrodynamic and structural models are coupled through the linear equations of motion.; The hydroelastic interaction enters into the analysis by way of the unknown hydrodynamic forces. These are represented as the hydrodynamic added mass and damping matrices, which are associated with the unknown nodal point vibratory accelerations and velocities, respectively.; The added mass and damping matrices are unsymmetric and fully populated by this theory. The numerical difficulties associated with these characteristics make the direct applications of these matrices prohibitive. A systematic compaction procedure was developed for reducing these matrices. The procedure was developed as an iteration based upon the normalization of the blade first mode shape for each nodal degree of freedom. The blade fundamental natural frequency and mode shape, both in air and in water, were calculated from this iterative process.; A series of propellers, with 0-deg, 36-deg, 72-deg, and 108-deg skew, were chosen for the purpose of studying the propeller blade dynamic stress behavior versus skew.
展开▼
