Prediction Method of the Unsteady Lift Acting on an Oscillating Three Dimensional Hydrofoil Submerged Under a Free Surface

Abstract

Hydrofoil vessels, which are supported partially or totally by the foil lift, have been widely investigated. Accurate estimate of the unsteady lift acting on the foil is important to predict vessel's motion on the wave. This paper presents the theory of the unsteady lift acting on oscillating three dimensional hydrofoil submerged under a free surface and the numerical calculation results. The method of images is employed to account for the free surface and a formula is derived on the assumption that ratio of span to average chord (aspect ratio) is not too small. The validity of this theory is confirmed on account of good agreement of experimental values and theoretical ones. As a result of calculating the unsteady lift of the three dimensional hydrofoil in various conditions, the relations between the characteristics of the lift and the submerged depth, aspect ratio, and reduced frequency respectively are made clear.