Abstract
Unsteady lift acting on an oscillating wing below a free-surface is studied in two dimensional problem. Unsteady velocity potential is expressed by the distribution of singularities over the wing and the wake. A set of integral equations in terms of the forward speed Green function is solved numerically for a thick wing of arbitrary section. Hydrodynamic forces are obtained by integrating the pressure on wing surface.
Numerical calculations for a wing with several Froude numbers and the submergences are demonstrated and the results such as the pressure distribution and the hydrodynamic force coefficients are presented graphically. It is found that unsteady lift on an oscillating wing at shallow submergence shows abrupt change near the characteristic number, τ takes 0.25, which is determined by the forward speed and the oscillating frequency. This could be explained by the fact that one of four surface wave systems is possible to propagate forward for τ≤0.25.
Experimental results carried out for two wings in heaving oscillation show good agreement with the present calculations.
