  We propose a derivation of a nonequilibrium Langevin dynamics for a large
particle immersed in a background flow field. A single large particle is placed
in an ideal gas heat bath composed of point particles that are distributed
consistently with the background flow field and that interact with the large
particle through elastic collisions. In the limit of small bath atom mass, the
large particle dynamics converges in law to a stochastic dynamics. This
derivation follows the ideas of [D. D\"urr, S. Goldstein, and J. L. Lebowitz,
1981 and 1983; P. Calderoni, D. D\"urr, and S. Kusuoka, 1989] and provides
extensions to handle the nonzero background flow. The derived nonequilibrium
Langevin dynamics is similar to the dynamics in [M. McPhie, et al., 2001]. Some
numerical experiments illustrate the use of the obtained dynamic to simulate
homogeneous liquid materials under flow.
