Fillingasilowithamixtureofgrains: Friction-inducedsegregation

Westudythe llingprocessofatwo-dimensionalsilowithinelasticparticlesby simulationofagranular-medialatticegas(GMLG)model. Wecalculatethesurfaceshapeand o wprol esforamonodispersesystemandweintroduceanovelgeneralizationoftheGMLG modelforabinarymixtureofparticlesofdi erentfrictionpropertieswhere,forthe rsttime, wemeasure thesegregation processonthesurface. Theresultsareingoodagreementwitha recenttheory,andweexplaintheobservedsmalldeviationsbythenonuniformvelocityprol e. Mixturesofgrainstendtoseparateasaresponsetovirtuallyanytypeofexternalpertur- bation(1),ane ectthatcanbeamajorprobleminsomepracticalsituations,andusefulin others. Indeed,understandingtheunderlyingprocessesofsegregationphenomenaingranular mixturesisanintriguingproblemofinteresttoscientistsfromawiderangeofdisciplines. Segregationoccurswhenamixtureispouredontoahorizontalbaseandapilebuildsup. Whenthegrainsofthemixturedi erinsize,thelargegrainstendtogatheratthebottom ofthepile(2),whilewhenthegrainshavedi erentshapes,themorefacetedgrainsarefound preferentiallynearthetop. Anevenmoresurprisinge ectcanbeobservedwhenamixtureof smallroundedandlargefacetedgrainsispouredbetweentwoparallelplates: stratication is observed|i.e.,thegrainsorganizespontaneouslyintostripes(3). Particlesizedistributioncruciallyinuences segregation. However,theparticlesgenerally di ernotonlyinsizebutalsoinotherproperties,suchasfrictionalones. Frictionale ectsplay arelevantroleinbandformationin3-Drotatingdrums,insegregationinthinrotatingdrums, and also segregation and strati cation in 2-D silos. Thus the study of the particular case