Research Of Three-Dimensional Discrete Element Method Based On Combination Ellipsoid Particle Model

Most of the materials existing in nature are granular materials,such as sands,soil and dust in the air.Common agricultural products like soy,wheat,corn,salt and the powder that are used in the field of medicine and chemical like fertilizers,cements and medicines are alos granular materails.Broadly speaking, granular materials are composed by liquid and gas.They are called liquid particles and gaseous particles,such as raindrops and droplets are the liquid particles in the air;liquid bubbles,tiny bubbles in the hydraulic propulsion are the the gaseous particles in the liquid.For this reason,our world is composed of particles at the macroscopical viewpoint.Therefore,simulating and analyzing natural phenomenons and social productions by particles is making more and more concern.Particle materials have two properties,discreteness and fluidity.Such as the natural phenomenons of landslides and avalanches are caused by the movement of soil particles in internal and external force.But particle materials'movement properties are different from the mechanical properties of solid and fluid,that is why the study of particle meterials can not be used by traditional solid or fluid mechanical methods.Currently,the research of discrete particles is divided into two basic methods,continuum mechanics method(CMM)and discrete element method(DEM).We consider the discrete particles as one continuum in CMM,and then analyze and computer the situation with continuum mechanics theory such as the elastic model,rigid body model and sticky plastic model.The typical methods based on CMM are the finite element method and boundary element method.on the other hand,time-driven discrete element is widely used in current research and application.DEM is proposed firstly in 1971 by Prof.Cundall,and in the late 70s Prof.Cundall in collaboration with Prof.Strack had presented the discrete element method for soil.The idea of DEM is from earlier molecular dynamics theory.The principle of DEM is to track and evaluate elements position and orientation,and then calculate the interactions between the elements themselves and between the elements and their environment by Newton's second law and the dynamic relaxation method.In DEM,we consider the collection of particles as elements. CMM is highly dependent on simple and fixed equations, ignoring particlar characteristics of the object ,and not meeting the assumption of continuity properties.For the reasons above,the simulation results by CMM are imprecise.Compared with CMM,DEM builds numerical model by particlar characteristics of the elements.In simulation,DEM takes each particle as one element,and tracks their movements and force,and then analyzes element movement discipline.At last,DEM has a big advantage in analyzing and simulating the discrete world. After years of concentrated efforts, we finally put the DEM into practices.Our researches about DEM calculations and DEM simulation applications have made much progress and have accumulated lots of valuable experiences.We conclude DEM research achievements of theory research,algorithm optimization and program design at home and abroad.To combine the design requirements in agricultural production,we independently develop one DEM software with calculation,simulation and performance analysis models.Spherial particles are usually used as particle model in early DEM softwares.It's easy to calculate the results,but great differences between particles in reality.The defcet affects the fidelity of simulation results.Afer the research of three-dimensional spherical particles,we design the particle model with spherial combination style.The new statagy can design particle model with complex shapes.thereby,it is enhancing the similarity and fidelity between the simulation and reality.In this paper,based on early three-dimensional DEM software ,we design and create one three-dimensional DEM software based on new combination ellipsoid particle model. In addition,we append some new function modules,such as normal distribution,uniform distribution methods in particle generation module,the boundary force analysis module,elastic boundary module and single-particle tracking module.In the end,we modify the double buffer display method in OpenGL,that improve the simulation display.I have systematically studied on the basic theory of three-dimensional combination ellipsoid particle models includes four-spheres combination ellipsoid particle model and multi-spheres combination ellipsoid particle model.I create combination ellipsoid particle models with object-oriented method,designing geometric modeling,particle group generation methods,OpenGL display methods,collision detection methods between particles and between particles and boundary,calculation on contact point and composite volume,contact force calculation methods,and particle move and update methods.I have made a general and specific design for DEM simulation software based on combination ellipsoid particle model.and have analyzed some critical techonologies methodically.Introducing new features and modules of the software.First of all,I analyze two distribution generation method of combination ellipsoid particle model,normal distribution and uniform distribution.Secondly,I design and implement tracking module between two special points.This module will help us analyze particle movement and force state in a period of time.Thirdly,I design and develop the boundary force analysis module,which not only display one single boundary force ,but also multi-boundaries.It can help us improve the design of the boundary models.Finally,Introducing the elastic boundary module,which is divided into two parts,translational and rotational movement.Elastic boundaries are similar to the role of spring which is the common tool in actual production.One combination of black-box testing and white-box testing methods has been carried out in testing the three-dimensional DEM software.Testing new features and modules such as normal distribution,uniform distribution on generation module,the boundary force analysis module,elastic boundary module and single-particle tracking module.Through above tests,DEM software based on combination ellipsoid particle model works well,calculation results are accurate and correct.DEM software is running available and stable .