Equation and boundary condition

[lecopivo]

I have a question about the equation you used.

All the waves travels downward so I guess you added a convection term into the wave equation, to make this happen. But what boggles me is, what are the boundary conditions? It seams to me, that the waves does not bounce of the edge of the screen, I find this very strange.

What equation exactly do you calculate and what are the boundary conditions?

Thank you, Tomas