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made the reference to CFD more precise and added the alternatives that are used for solid-like granular behavior. Added damping. |
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The term '''discrete element method''' (DEM) is a family of [[numerical analysis|numerical]] methods for computing the motion of a large number of particles like molecules or grains of sand. The method was originally applied by [[Peter A. Cundall | Cundall]] in [[1971]] to problems in rock mechanics. The theoretical basis of the method was detailed by [[John R. Williams | Williams]], [[Grant Hocking | Hocking]], and [[Graham Mustoe| Mustoe]] in [[1985]] who showed that DEM could be viewed as a generalized finite element method. Its applications to geomechanics problems is described in the book ''Numerical Modeling in Rock Mechanics'', by Pande, G., Beer, G. and Williams, J.R.. Good sources detailing research in the area are to be found in the 1st, 2nd and 3rd International Conferences on Discrete Element Methods. Journal articles reviewing the state of the art have been published by [[John R. Williams | Williams]], and [[Nenad Bicanic| Bicanic]] (see below). A comprehensive treatment of the combined Finite Element-Discrete Element Method is contained in the book ''The Combined Finite-Discrete Element Method'' by [[Ante Munjiza | Munjiza]]. The method is sometimes called ''[[molecular dynamics]]'' (MD), even when the particles are not molecules. However, in contrast to molecular dynamics the method can be used to model particles with non-spherical shape. The various branches of the DEM family are the [[distinct element method]] proposed by [[Peter A. Cundall | Cundall]] in [[1971]], the [[generalized discrete element method]] proposed by [[Grant Hocking | Hocking]], [[John R. Williams | Williams]] and [[Graham Mustoe| Mustoe]] in [[1985]], the [[discontinuous deformation analysis]] (DDA) proposed by [[Gen-hua Shi | Shi]] in [[1988]] and the finite-discrete element method proposed by [[Ante Munjiza| Munjiza]] and [[Roger Owen| Owen]] in [[2004]].
Discrete element methods are processor intensive and this limits either the length of a simulation or the number of particles. Advances in the software are beginning to take advantage of parallel processing capabilities (shared or distributed systems) to scale up the number of particles or length of the simulation. An alternative to treating all particles separately is to average the physics across many particles and thereby treat the material as a [[Continuum mechanics|continuum]]. In the case of [[solid]]-like granular behavior as in soil mechanics, the continuum approach usually treats the material as [[Elasticity (physics)|elastic]] or [[Plasticity (physics)|elasto-plastic]] and models it with the [[finite element method]] or a [[Meshfree methods|mesh free method]]. In the case of liquid-like or gas-like granular flow, the continuum approach may treat the material as a [[fluid]] and use [[computational fluid dynamics]].
==Applications==
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* [[friction]], when two particles touch each other;
* recoil, when two particles collide;
* [[damping]], when energy is lost during the compression and recoil of grains in a collision;
* [[gravity]] (the force of attraction between particles due to their mass), which is only relevant in astronomical simulations.
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