Hydroelastic analysis of underwater rotating propellers based on different boundary conditions

The knowledge of the added mass and damping characteristics induced by the vibration of the propeller in water is important to predict the hydroelastic behavior of the propulsion system. A three-dimensional panel method combined with the finite element method is conducted to analyze the properties of wet modes and added dampings of marine propellers by imposing three different non-penetration boundary conditions. One is imposed on the blade surface of the equilibrium position. The other is named a partly non-penetration boundary condition, which is imposed on the blade surface of real-time vibration position. Only the corrections of the flow velocities that are exerted on the blade surface by the real-time vibration and the equilibrium positions are considered. The third one takes both the correction of the normal vectors and the flow velocities enforced on the blade surface of the real-time vibration and the equilibrium positions into account, and is termed as a completely non-penetration boundary condition. It is observed that the third boundary condition must be applied for analyzing the wet mode frequencies of lightweight propellers, especially for those which have a small blade number. In addition, the added damping is overestimated by applying the first and second boundary conditions.