A rational approximation to the evolution of a free surface during fluid withdrawal through a point sink

The time varying flow in which fluid is withdrawn from a reservoir through a point sink of variable strength beneath a free surface is considered. Asymptotic techniques are used to derive an approximate solution to the flow that is valid at intermediate times, giving a simple rational approximation to track changes in the free surface for any temporal variations in the sink strength. Comparisons with numerical simulations are given, showing that the approximation has wide applicability. © Austral. Mathematical Soc. 2010.