Description of Brownian motion including both kinetic and hydrodynamic effects

Abstract: It is known that a full description of Brownian motion in the entire course of time should incorporate both kinetic and hydrodynamic effects, but a formula accounts for both effects has been established only in three dimension and only for the limiting case when Brownian particles are much bigger and heavier than fluid particles. Nevertheless, for applications, it is important to consider small Brownian particles (sometimes even smaller than fluid particles). In these cases, unfortunately, only formulae in the short (long) time limit considering exclusively kinetic (hydrodynamic) effect are available. Here we derive a general solution to both two- and three-dimensional Brownian motion. Our solution is applicable to a wide spectrum of suspended particles from being smaller than the fluid particles to usual Brownian particles. Our analytical results are well corroborated by the numerical simulations.