Smooth taper
the parameters :
cfg.get<bool>("Disk.Smoothing.Change", false),
cfg.get<real>("Disk.Smoothing.Taper", real(1e-7)),
seem not to be used in the code, we should reintroduce the possibility of changing the smoothing lenght with a taper function like what is done for the mass in:
applyMassTapper(real physicalTime)