title: Onset of fluidization in vertically shaken granular material
abstract: When granular material is shaken vertically one observes convection, surface fluidization, spontaneous heap formation, and other effects. There is a controversial discussion in the literature as to whether there exists a threshold for the Froude number Gamma=A(0)omega(2)(0)/g, below which these effects cannot be observed anymore. By means of theoretical analysis and computer simulation we find that there is no such single threshold. Instead, we propose a modified criterion that coincides with the critical Froude number Gamma(c)=1 for small driving frequency omega(0).
authors.affiliation: ICA 1, Universitat Stuttgart, Pfaffenwaldring 27, D-70569 Stuttgart, Germany and Institut fur Physik, Humboldt-Universitat zu Berlin, Invalidenstrasse 110, D-10115 Berlin, Germany.
authors.initials: T
authors.lastname: Poschel
authors.initials: T
authors.lastname: Schwager
authors.initials: C
authors.lastname: Saluena