Two dimension porous media reconstruction using granular model under   influence of gravity
  Modeling of pores generation in 2-D with granular grains using molecular dynamics method is reported in this work. Grains with certain diameter distribution are let falling due to gravity. Three configurations (larger diameter on top, smaller diameter on top, and mixed) and two kinds of mixture (same grains density and same grains mass) are used in the simulation. Mixture with heterogen density gives higher porosity than the homogen one for higher initial height, but change into opposite condition for lower initial height. 
Pury Sundari, Umar Fauzi, Zaroh Irayani, Sparisoma Viridi
cond-mat.soft