  High-resolution spectroscopy has revealed large concentrations of CNO and
sometimes other intermediate-mass elements in the shells ejected during nova
outbursts, suggesting that the solar composition material transferred from the
secondary mixes with the outermost layers of the underlying white dwarf during
the thermonuclear runaway. Multidimensional simulations have shown that
Kelvin-Helmholtz instabilities provide self-enrichment of the accreted envelope
with material from the outermost layers of the white dwarf, at levels that
agree with observations. However, the Eulerian and time-explicit nature of most
multidimensional codes used to date and the overwhelming computational load
have limited their applicability, and no multidimensional simulation has been
conducted for a full nova cycle. This paper explores a new methodology that
combines 1-D and 3-D simulations. The early stages of the explosion (i.e.,
mass-accretion and initiation of the runaway) have been computed with the 1-D
hydrodynamic code SHIVA. When convection extends throughout the entire
envelope, the structures for each model were mapped into 3-D Cartesian grids
and were subsequently followed with the multidimensional code FLASH. Two key
physical quantities were extracted from the 3-D simulations and subsequently
implemented into SHIVA, which was used to complete the simulation through the
late expansion and ejection stages: the time-dependent amount of mass
dredged-up from the outer white dwarf layers, and the time-dependent convective
velocity profile throughout the envelope. More massive envelopes than those
reported from previous models with pre-enrichment have been found. This results
in more violent outbursts, characterized by higher peak temperatures and
greater ejected masses, with metallicity enhancements in agreement with
observations.
