  We study a particular generalisation of the classical Kramers model
describing Brownian particles in the external potential. The generalised model
includes the stochastic force which is modelled as an additive random noise
that depends upon the position of the particle, as well as time. The stationary
solution of the Fokker-Planck equation is analysed in two limits: weak external
forcing, where the solution is equivalent to the increase of the potential
compared to the classical model, and strong external forcing, where the
solution yields a non-zero probability flux for the motion in a periodic
potential with a broken reflection symmetry.
