T. Watanabe et H. Kaburaki, INCREASE IN CHAOTIC MOTIONS OF ATOMS IN A LARGE-SCALE SELF-ORGANIZED MOTION, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 54(2), 1996, pp. 1504-1509
The macroscopic flow transition between heat conduction and convection
in the two-dimensional Rayleigh-Benard system is simulated using the
molecular-dynamics method. The heat conduction state, in which motions
of atoms are random and a large-scale flow does not appear, is establ
ished when the temperature difference between the top and bottom walls
is small. It is shown, when the temperature difference is large, that
macroscopic convection rolls appear and the trajectories of atoms are
along the rolls. The degree of the chaotic motions of atoms is observ
ed in terms of the Lyapunov exponent. In the heat conduction state, th
e Lyapunov exponent is shown to increase with the average temperature
and the temperature difference. It is found that the Lyapunov exponent
depends not only on the temperatures but also on the macroscopic flow
velocity when the how field shows the convecting state. The chaotic m
otions of atoms are shown to increase in the large-scale self-organize
d motion.