“…However, there are many cases in which the flow is self-similar. When gravity is ignored under the condition of W/g T, where W is the impact speed, g the acceleration due to gravity and T the time that the impact has lasted, well-known examples in two dimensions include those studied by Cumberbatch (1960) for a liquid wedge impacting on a flat wall and Dobrovol'skaya (1969) and Zhao & Faltinsen (1993) include the papers by Semenov & Iafrati (2006) for water entry of an asymmetric wedge, Xu, Duan & Wu (2008) for oblique water entry of an asymmetric wedge, Wu (2007) and Duan, Xu & Wu (2009) for impact between a liquid wedge and a solid wedge, and Semenov, Wu & Oliver (2013) on the impact of two liquid wedges. A related self-similar 2D problem is the one investigated by Keller, Milewski & Vanden-Broeck (2002), which involves the merging of two liquid wedges with the surface-tension effect.…”