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.
