Sion, Huang and Cheng are developing a dynamic model for white
dwarf-disk interaction in the boundary layers, which is urgently needed
to quantitatively understand the properties of the observed accretion
belts. By applying the energy criteria characterized by the Richardson number, 
, we found that in a differentially
rotating envelope of the white dwarf, the mixing caused by the forced
convection is most efficient on equi-potential surfaces, along
which 
. To simulate these mixing processes, we use
the equipotential surfaces as one family of our coordinate surfaces.
Since the rotational speed distribution as well as the shape of the
surfaces in the white dwarf envelope varies with time, so do our
coordinate surfaces. Further results from our code using this time-dependent zoning technique will be reported in due time.