The Micro Modeling Study And The Application Of Granular Material Based On Real Shape

Particulate matter is not only the major part of the geological disasters body,but also the most popular construction materials widely used in lots of engineering projects.Physical and mechanical properties of particulate matter have become an important issue of geotechnical engineering research.The traditional physical tests can only be applied to study macro mechanics of particulate matter.However,numerical method can reveal the micromechanics which can explain the macro mechanics.Therefore,numerical method is the most vital methods in the particulate matter study field.Geotechnical granular particles are the research objects in this paper.This article expounded how to acquire the 3D data of a particle,how to pack lots of particles,how to approximate a particle with several overlapping spheres,and how to conduct triaxial test with both DEM and FEM.This paper designed a 3D scanner with Kinect for Windows.High accuracy,strong portability,high efficiency,economical,fine adaption are the key features of the scanner.The 3D data of 322 particles from Xiaogangjian weir body and 436 particles from Yigong landslide ruins were obtained with this scanner.The statistical analysis revealed that the sphericity,slenderness ratio,volume area ratio are with a strong statistical law.This paper developed a particle packing program with open source software,Chrono::Engine.The results showed that the model are packed tightly.This model can be used as the basic geometric model for the future numerical calculation.The spherical element is the most popular element of particle matter numerical study with DEM.A real particle can be well approximated with fewer overlapping spheres.This paper translated the multi-sphere approximation issue to a setting cover problem.Besides,a modified greedy heuristic algorithm was employed to settle the multi-sphere approximation issue.This algorithm has the following several features.A particle can be approximated with fewer spheres but a fine accuracy.Generally,the number of the spheres will be 20 to 50 and the error will be less than 3%.The complicated particles even the complicatedly connect particles can be approximated bythis algorithm.In addition,the computing time will be just several seconds to tens of seconds.This thesis processed the the angle of repose test with YADE.The occlusion effect between the particles leaded the angle difference between the single sphere model and the multi-sphere approximation model.And this test verified the significance of the multi-sphere approximation in the DEM simulation.For further application of the multi-sphere approximation in more complicated geotechnical engineering problems.This paper realized the coupling of DEM and FEM with LS-DYNA.The rubber membrane of the triaxial tests was simulated by finite elements and the sands of the triaxial tests were simulated by spheres.The continuity of FEM and the discreteness of DEM are well performed in the simulation.The coupling of FEM and DEM can well simulate the contacts of the particles and the rubber membrane.The simulation results are close to the physical triaxial tests with bulging effect.Besides,the stress–strain relationship and the volumetric strain-strain relationship are very similar with the real physical tests.