Illustrating example of the possible velocity treatments in case that the integration of the hydrodynamic equation of motions yields a nonmonotonic υ(r) (solid blue curve): in the simple treatment, negative velocity gradients are suppressed during the integration, yielding the blue, dash-dotted curve. In some cases, such as illustrated in this plot, this can spoil the terminal velocity υ_∞. In the more sophisticated treatment, negative gradients are therefore taken into account and υ(r) is modified such that the interpolated solution keeps the obtained υ_∞.