\ddot\alpha(t) + a \dot\alpha(t) + b^2 \alpha(t) = F + A\omega(t) + B\epsilon(t/\tau).$$ For both models of athermal noise $\epsilon(t/\tau)$ mentioned above, the macroscopic limit of the right-hand side of [Eq. (\[eq:lgv2\])]{} yields $f = F + B/\tau$; cf. [Eq. (\[eq:mac1\])]{} and Refs. [@PRE2016II; @PRE2016III]. The necessity of the constant term $F$ in [Eq. (\[eq:lgv2\])]{} is demonstrated in [Sec. \[sec:mic\]]{}, where we study in detail nonequilibrium aspects of the fluctuations of $\alpha(t)$.

The purpose of this paper is to demonstrate a complete Langevin representation of a nonequilibrium physical system. To do this, in [Sec. \[sec:mic\]]{} we first determine all the parameters of [Eq. (\[eq:lgv2\])]{} for the microscopic model of a shear flow in a simple fluid, which was already studied in [Ref. [@PRE2016III]]{}. Then, in [Sec. \[sec:mes\]]{} we perform simulations of the Langevin dynamics and compare their results with the original system.

In our computational study, the two models of athermal noise, discussed earlier, are treated separately. They generate qualitatively very similar trajectories of $\alpha(t)$, as observed in stochastic simulations of [Sec. \[sec:mes\]]{}. Although exponential shot noise [@MorgadoQ2016] has discrete singularities, which make its physical interpretation distinct from simple exponential noise [@PRE2016II], in the second-order Langevin dynamics this affects only 