A moving hydrofoil close to the water surface creates waves. These waves may have steady or unsteady forms, resulting in steady or unsteady forces on the hydrofoil. In the unsteady case, waves grow to the point of wave breaking in certain conditions. There is not any analytical solution for this case and numerical modeling is the only tool (besides model tests) to investigate the hydrofoil performance. For the steady case, Vladimirov (1937) presented a method based on potential flow. Then Kotchin (1951), Wadlin et al.(1955) and Ducane (1972) added the image technique to the method and analyzed steady motion of hydrofoil. Sutherland (1951) and Payne (1996) used concept of added mass to discuss the effects of free surface on hydrofoil performance. For the unsteady case, Duncan (1983) investigated wave breaking due to a moving hydrofoil close to free surface. Azcueta et al. (2000) studied the issue using CFD modeling. They pointed out that the wave breaking changes the lift force of hydrofoil considerably.
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