Vibration analysis of cycloidal propeller blade during ship maneuvering

Marine cycloidal propeller (MCP) is well known for its maneuvering capability. It has unique kinematics. During operation, for each rotation of the propeller disc, each one of the blades undergoes one oscillation. There is phase angle between the oscillations of different blades. The face and back of the propeller blade interchange during each oscillation. These characteristics distinguish it from a typical screw propeller. In a screw propeller, the face and back of the propeller do not interchange and the blade pitch remains constant during each propeller revolution. Due to above reasons, the blades of cycloidal propellers are subjected to higher fluctuation in the loading. This causes fatigue loading on the blade and load variation on the prime mover. Therefore, during cycloidal propeller design, fatigue and load variation on the blade needs to be investigated. In this paper, structural dynamics of a cycloidal propeller blade during maneuvering conditions is investigated. The maneuvering conditions considered are bollard pull (towing), crash stop, cruising, crabbing, turning and zigzag (Planar Motion Mechanism). For analysis, the blade is considered as a thick plate. Variation of plate thickness and asymmetric support characteristics to account for aerofoil section and stock support are considered. Nonlinear finite element method is used for structural analysis. For computing the hydrodynamic load, a simple model is used. The analysis gives a good insight into the vibration characteristics of the cycloidal propeller blade.