Numerical analysis of added mass and damping of elastic hydrofoils

A numerical model is proposed for analyzing the effects of added mass and damping on the dynamic behaviors of hydrofoils. Strongly coupled fluid-structure interactions (FSIs) of hydrofoils are analyzed by using the 3-D panel method for the fluid and the finite element method for the hydrofoils. The added mass and damping matrices due to the external fluid of the hydrofoil are asymmetric and computational inefficient. The computational inefficiencies associated with these asymmetric matrices are overcome by using a modal reduction technique, in which the first several wet mode vectors of the hydrofoil are employed in the analysis of the FSI problem. The discretized system of equations of motion for the hydrofoil are solved using the Wilson-θ method. The present methods are validated by comparing the computed results with those obtained from the finite element analysis. It is found that the stationary flow is sufficient for determining the wet modes of the hydrofoil under the condition of single-phase potential flow and without phase change. In the case of relatively large inflow velocity, the added damping of the fluid can significantly affect the structural responses of the hydrofoil.