The calculation of a normal force between multiparticle contacts using   fractional operators
  This paper deals with the complex problem of how to simulate multiparticle contacts. The collision process is responsible for the transfer and dissipation of energy in granular media. A novel model of the interaction force between particles has been proposed and tested. Such model allows us to simulate multiparticle collisions and granular cohesion dynamics. 
Leszczynski Jacek