Simulation of grains in a vibrated U-tube without interstitial fluid
  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. 
J. R. Darias, I. S\'anchez, G. Guti\'errez, R. Paredes
cond-mat.soft