  We present a computational study using Molecular Dynamics of the development
of an accumulation of grains in one side of a two dimensional U-tube under
vertical vibrations. Studying the evolution of the height difference between
the centers of mass of the branches of the tube, we found that it reaches a
saturation value after vibrating for some time. We obtain that this saturation
value is the same if the simulation start with the arms leveled or with a large
initial height difference. We explore the effect of the width of the tube, the
density of the grains and the coefficient of restitution between the grains and
the wall on the value of the saturation. We obtain a value of the width of the
tube for which the saturation value reaches a maximum, and show that the
transport of grains between arms is favored for low grain densities and high
grain-wall restitution coefficient.
