In this section, we will consider the hypothesis that the finiteness of is induced by the presence of container walls. If we are able to simulate a system of the same size as used in the experiment we use solid walls in all directions perpendicular to gravity to match the conditions of the experiments as close as possible and thus avoid effects from the absence of the walls.
Gravity points in direction.
The boundary conditions in the simulations are periodic parallel to gravity and rigid wall perpendicular to it. With this experimental setup, they found velocity fluctuations and . The velocity fluctuations do not depend on the depth of the vessel and the ratio of the fluctuations . In the measurements of Nicolai and Guazzelli the motion of the particles is projected onto the optical apparatus in direction. Thus, they do not report the components of velocities and fluctuations.