We (Hsien
Shang together with research assistant Mei-Yin Chou and
Anthony Allen) are carrying out studies of MHD flows by
Zeus2D. Simulations of wide-angle winds are done on their
asymptotic regime and for long-term evolution to achieve
time-steady state, and to further investigate the implications
on the formation of outflows by interacting these wide-angle
winds with ambient media. They adopted analytic construction
for the MHD wind where the density, poloidal and toroidal
velocity, and toroidal magnetic fields follow a simple power-law
relationship from Li & Shu (1996). Due to the sharp
drop-off in density and magnetic field strengths characterized
by such winds, and large spatial coverage in the computational
domains, establishing robust numerical results has been
a challenging task. The numerical boundary and reflection
effects arise very easily. To establish robust runs and
performances based on local resources, they first established
benchmark tests on various platforms of locally accessible
ASIAA machines and with the use of a variety of optimization
flags, the benchmark is summarized in Allen, Chou, and Shang
(2002). Steady-state runs have also been established for
super-Alfv\'enic winds running into vacuum from a narrow
launch sphere of hidden zones in the hope to mimic the x-winds.
On the effects
of wide-angle winds interacting with ambient environment,
in progress are the simulations of winds running into surrounding
medium of constant density, and later on more realistic
configurations from Li and Shu (1997) toroid model sequences
may be implemented. In the figures are simulations of winds
of terminal speed of 300 km/s (~ 3 Va) and ambient densities
from 10-16 and 10-19g/cm3. These results are plotted on
four-panels to illustrate selected time frames of 100, 400,
700, and 1000 years of evolution. The appearance of the
resultant density structures and shapes of shock fronts
suggests strong connections to the lobe shapes of molecular
outflows. Further work will continue to investigate such
connections.
