Unsteady Lift of an Oscillating Wing below Free-Surface

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A new numerical method has been developed to analyze unsteady hydrodynamic forces of 3D lifting surface of arbitrary plan form in infinite flow, in which velocity potential is expressed by the doublet distribution over wing and the wake. The results by this method show good agreement with existing theories and experiments for some rectangular and triangular wings in steady and unsteady problems.For 2D wings below free-surface, an integral equation method which includes the free-surface effects and the thickness of the wing exactly is developed. Following conclusions are obtained from numerical calculations and experiments.1) There is non-zero attack angles where the lift of the wing becomes zero.2) Thickness of the wing section does not affect hydrodynamic forces so much that thin wing would give good approximation.3) Free-surface effects on hydrodynamic forces appear at the ratio of the oscillating frequency to the uniform flow velocity takes some values.