Thus, the VOF method provides a simple and economical way to track free boun-
daries in two- or three-dimensional meshes. In principle, the method could be used to track surfaces of discontinuity in material properties, in tangential velocity, or any other property. The particular case being represented determines the specific boundary condition that must be applied at the location of the boundary. For situations where the surface does not remain fixed in the fluid, but has some additional relative motion, the equation of motion, Eq. (2), must be modified