The viscosity correction of symmetrical model lines for wave-resistance analysis

Abstract

It is known that improved correlation between experimental and computed wave resistance can be obtained by taking into account various effects, such as nonlinearity (fullness) of the model, the free-surface wave, and viscosity, in the theory of wave resistance. This paper concerns only the viscosity effect and the resulting virtual modification of the model lines. It is shown here that the modifications because of viscosity effect can be computed rationally from the performance of the boundary layer. The thickness of the layer and especially the size of the separated region in the cases where separation occurs determine the magnitude of virtual modification of a body shape as a function of model speed. These speeds are divided into low- and high-speed ranges with the introduction of the concept of limiting speed. At speeds lower than the limiting speed, the boundary layer is laminar and it separates from the hull in the region of sufficient adverse pressure gradient. At higher speeds, it is partly or fully turbulent and it may separate from the hull, depending upon the shape of the model. It is shown that no separation occurs if the model is basically similar to the one treated in this paper.