Fig. 2.

Sketch of the inflated ring with the definition of the parameters and coordinates, where $R+r$ is the radial distance to the axis of symmetry, $z$ is the height, $s$ is the curvilinear coordinate along the membrane in the $\left({\mathbf{e}}_{\mathbf{r}},{\mathbf{e}}_{\mathbf{z}}\right)$ plane, and $\tan \phi$ is the local slope of the profile.