  The stresses produced by magnetorotational turbulence can provide effective
angular momentum transport in accretion disks. However, questions remain about
the ability of simulated disks to reproduce observationally inferred
stress-to-gas-pressure ratios. In this paper we present a set of high
resolution global magnetohydrodynamic disk simulations which are initialised
with different field configurations: purely toroidal, vertical field lines, and
nested poloidal loops. A mass source term is included which allows the total
disk mass to equilibrate in simulations with long run times, and also enables
the impact of rapid mass injection to be explored. Notably different levels of
angular momentum transport are observed during the early-time transient disk
evolution. However, given sufficient time to relax, the different models evolve
to a statistically similar quasi-steady state with a stress-to-gas-pressure
ratio, $\alpha \sim 0.032-0.036$.
  The indication from our results is that {\it steady, isolated} disks may be
unable to maintain a large-scale magnetic field or produce values for the
stress-to-gas-pressure ratio implied by some observations. Supplementary
simulations exploring the influence of trapping magnetic field, injecting
vertical field, and rapidly injecting additional mass into the disk show that
large stresses ($\alpha \sim 0.1-0.25$) can be induced by these mechanisms. The
simulations highlight the common late-time evolution and characteristics of
turbulent disks for which the magnetic field is allowed to evolve freely. If
the boundaries of the disk, the rate of injection of magnetic field, or the
rate of mass replenishment are modified to mimic astrophysical disks, markedly
different disk evolution occurs.
