  Two commonly accepted approaches for simulations of thermally-activated
vortex motion in superconductors are compared. These are (i) the so-called flux
creep approach based on the expression E=vB relating the electric field E to
the velocity v of the thermally-activated flux motion and the local flux
density B, and (ii) the approach employing a phenomenological nonlinear
current-voltage curve, E(j). Our results show that the two approaches give
similar but also distinctly different behaviors for the distributions of
current and flux density in both a long slab and thin strip geometry. The
differences are most pronounced where the local B is small. Magneto-optical
imaging of a YBaCuO thin film carrying a transport current was performed to
compare the simulations with experimental behavior. It is shown that the flux
creep approach describes the experiments far better than simulations based on
the E(j) approach.
