{"157211":{"#nid":"157211","#data":{"type":"event","title":"Toward a Precise Continuum Model for Dense Granular Flows","body":[{"value":"\u003Ch5\u003ESchool of Physics Soft Condensed Matter and Biophysics Seminar: Presenting\u0026nbsp;Ken Kamrin, MIT\u003C\/h5\u003E\u003Cp\u003EThe challenge of predicting velocity and stress fields in any flowing granular material has proven to be a difficult one, from both computational and theoretical perspectives.\u0026nbsp; Indeed, researchers are still in search of the ``Navier-Stokes\u0022-equivalent for flowing granular materials.\u0026nbsp;\u0026nbsp; Granular flows can be adequately predicted using grain-by-grain discrete element methods (DEM), but these approaches become computationally unrealistic for large bodies of material and long times.\u0026nbsp;\u0026nbsp; A robust continuum model, once identified, would have the practical benefit that it could be implemented at a meso-scale saving many orders of magnitude in computation time compared to DEM.\u003C\/p\u003E\u003Cp\u003EHere, we begin by synthesizing a 3D elasto-viscoplastic law for steady granular flow, merging an existing \u0022frictional fluid\u0022 relation with a nonlinear granular elasticity relation to close the system.\u0026nbsp; The flow rate vanishes within a frictional (Drucker-Prager) yield surface and the elastic response is based on a mean-field model generalizing Hertz\u0027s contact law. The resulting form is general, able to produce flow and stress predictions\u0026nbsp; in any well-posed boundary value problem.\u0026nbsp; We implement it using ABAQUS\/Explicit finite-element package and run test simulations in multiple geometries. The solutions are shown to compare favorably against a number of experiments and DEM simulations.\u003C\/p\u003E\u003Cp\u003EWhile this relation appears to function well for rapid flows, experimental results can often differ from the predictions in regions of slower flows.\u0026nbsp; We have been able to attribute many of these phenomena to nonlocal effects stemming from the finite-ness of the grain size.\u0026nbsp; To correct this, we consider the addition of a simple nonlocal term to the rheology in a fashion similar to recent nonlocal flow models in the emulsions community.\u0026nbsp; The results of this extended model are compared against many DEM steady-flow simulations in three different 2D geometries.\u0026nbsp; Quantitative agreement is found for all geometries and over various geometrical\/loading parameters.\u0026nbsp; By natural extension, the nonlocal model is then converted to three dimensions with minimal changes, and is implemented numerically as a User-Element in the ABAQUS package.\u0026nbsp; We show that a single calibration of the 3D model quantitatively predicts hundreds of experimental flows in different geometries, including, for the first time, the wide-shear zones observed in the split-bottom annular couette cell, a geometry made infamous for resisting a theoretical treatment for almost a decade.\u003C\/p\u003E\u003Cp\u003E\u0026nbsp;\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003ESchool of Physics Soft Condensed Matter and Biophysics Seminar: Presenting\u0026nbsp;Ken Kamrin, MIT\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"School of Physics Soft Condensed Matter and Biophysics Seminar: Presenting Ken Kamrin, MIT"}],"uid":"27664","created_gmt":"2012-09-26 15:44:36","changed_gmt":"2016-10-08 02:00:10","author":"Alison Morain","boilerplate_text":"","field_publication":"","field_article_url":"","field_event_time":{"event_time_start":"2012-10-16T16:00:00-04:00","event_time_end":"2012-10-16T17:00:00-04:00","event_time_end_last":"2012-10-16T17:00:00-04:00","gmt_time_start":"2012-10-16 20:00:00","gmt_time_end":"2012-10-16 21:00:00","gmt_time_end_last":"2012-10-16 21:00:00","rrule":null,"timezone":"America\/New_York"},"extras":[],"related_links":[{"url":"http:\/\/web.mit.edu\/kkamrin\/www\/","title":"http:\/\/web.mit.edu\/kkamrin\/www\/"},{"url":"https:\/\/www.physics.gatech.edu\/seminars-colloquia\/series\/soft-condensed-matter-and-biophysics\/ken-kamrin-20121016","title":"https:\/\/www.physics.gatech.edu\/seminars-colloquia\/series\/soft-condensed-mat..."}],"groups":[{"id":"126011","name":"School of Physics"}],"categories":[],"keywords":[{"id":"44941","name":"Ken Kamrin"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[{"id":"1795","name":"Seminar\/Lecture\/Colloquium"}],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003E\u003Ca href=\u0022mailto:alison.morain@physics.gatech.edu\u0022\u003Ealison.morain@physics.gatech.edu\u003C\/a\u003E\u003C\/p\u003E","format":"limited_html"}],"email":[],"slides":[],"orientation":[],"userdata":""}}}