The reformulation of one-phase Stefan problems, by use of a Baiocchi-type transformation, as ‘oxygen-diffusion’ problems, makes it possible to compare different solutions. The comparison extends to ‘zero-specific-heat’ cases, which are better known, in two dimensions, as Hele-Shaw problems. Known solutions of Hele-Shaw problems can be used to bound and estimate asymptotic behaviour of solutions to Stefan problems. The use of similar techniques gives rise to some exact solutions of ‘squeeze-film’ problems and some limited results concerning continuity.

In this work exact upper bounds of the drag force are found for curved plates of fixed total arc-length in flow with a wake, which forms according to the Joukowsky-Roshko-Eppler model. The shapes of maximum drag are determined in an explicit analytical form and can be interpreted as those of ideal parachutes.

Using the theory of conformal mappings, we show that two-dimensional quasi-static moving boundary problems can be described by a non-linear Löwner-Kufarev equation and a functional relation ℱ between the shape of the boundary and the velocity at the boundary. Together with the initial data, this leads to an initial value problem. Assuming that ℱ satisfies certain conditions, we prove a theorem stating that this initial value problem has a local solution in time. The proof is based on some straightforward estimates on solutions of Löwner-Kufarev equations and an iteration technique.

Recently, the free boundary problem of quasistationary Stokes flow of a mass of viscous liquid under the action of surface tension forces has been considered by R. W. Hopper, L. K. Antanovskii, and others. The solution of the Stokes equations is represented by analytic functions, and a time dependent conformal mapping onto the flow domain is applied for the transformation of the problem to the unit disk. Two coupled Hilbert problems have to be solved there, which leads to a Fredholm boundary integral equation. The solution of this equation determines the time evolution of the conformal mapping. The question of the existence of a solution to this evolution problem for arbitrary (smooth) initial data has not yet been answered completely. In this paper, local existence in time is proved using a theorem of Ovsiannikov on Cauchy problems in an appropriate scale of Banach spaces. The necessary estimates are obtained in a way that is oriented at the a priori estimates for the solution given by Antanovskii. In the case of small deviations from the stationary solution represented by a circle, these a priori estimates, together with the local results, are used to prove even global existence of the solution in time.