| There are lots of flows of granular materials and actions between granularmaterials and working parts of machinery in industrial and agricultural production.For example,when sowing seeds, this course has the seed, the fertilizer and soilflowing; when farming the land, this course has the soil flowing; agricultural productharvest, transportation, graduation, processing, packing and so on, they also have theflowsofgranularmaterials.The flows of granular materials have the relation with not onlyitself mechanicalproperties but also the farm machinery's workingpart structural style, size parameter,movement parameter and so on. A good farm machinery design should make it toflow according to the expectation way, for example, when sowing seeds, the seed'sflowing should reduce the unnecessary damage, when sowing seeds, it should savethe mechanical power consumption, when farming the land, it should consider themutual function and its dynamics question between the farm machinery's workingpartwithgranularmaterials.Granularmaterialshavethepropertybetweenthesolidandthefluid,althoughitsstructure is simple, but they have the complex mechanics characteristic. Thetraditional continuum mechanics method (CMM), which is applied to research theinteraction between granular materials and related mechanical parts, can onlyconsider the granular materials as a whole, and it is unable to analyze the movementcourse of each particle and the interaction among the colony. As a result, it cannotresolvethe problem verywell.Recentlywhendesigningthe related mechanical parts,the experience and experimentation methods are depended on mostly, and it takesboth time and stamina a lot and cannot achieve the expected designing purpose. It isestimated that the abrasion loss of related equipments during the carrying course ofgranular materials costs 40%, and the demand of optimized design and energysavingisfarawayfromsatisfaction.In seventies of the 20th century, Cundall et al. put forward the DEM (DiscreteElement Method) primarily. The basic thought is to simplify granular materials as aset of particles with a certain kind of shape and mass, and endue the particle-particleand particle-boundary relationship with a certain kind of contact mechanics modeland some parameters. The DEM is applied to research the contact effects, whichinfluence the particle-particle and particle-boundary relationship, and the differentphysical and mechanical characteristics between particles and contacted boundaries.The dynamic laxity method, the Newton's Second Law and time step iteration areintroduced into DEM to calculate the movement and displacement of each particle,and thus it is especially compatible to resolve the nonlinear problem. It can analyzeparticle lumping, destruction of the whole material, flowing heterogeneously,chemical reaction and heat transfer, when adopting different dynamics equations. Itcan analyze not only the interaction between various granular materials and differentborder but also the influence on the motion of granular materials, according tochanging the model of particle, the model of border, dynamics equations andparameters in Discrete Element Method. Because of these virtues mentioned above,DEM has become a popular method on studying the kinetic problem of granularmaterials,anditiswidelyappliedinthefieldsofrockengineeringandsandsflowing,the transportation, mixing, classification of granular materials, the agglomeration andcollision of granular materials, the interaction between granular materials and relatedmechanicalparts,theequipmentofchemicalindustryandmineengineering.Therefore,relatedthecharacteristics anddesignrequirements ofworkingparts ofmachinery, our teamwork presents a novel method to establish a 2D DEM to analyzemodel of machine's parts based on their CAD model. And then we implement theintegration of CAD software and the DEM analyzing software by self-developmentfor analyzing the performance of machine's parts which are contacted with granularmateriel at working, thereby establish a novel universal digital design method andintegrated software for designing and analyzing the machine's parts. The softwarewillofferanewmethodandnewtoolforoptimaldesignofthemachine'sparts.During the process of developing two-dimension integrated design analysesoftware, one of the important questions that influence the analyse precision andefficiencyis howtobuildtheDEM modelsofcomplicatedshapeparticles.This paperuses superquadratics equation to build the 2D DEM analyse models of complicatedparticles , puts forward to adopting exterior rectangles to process preliminary contactinspections , adopts the method of Newton downhill to process accurate contactinspections,contactpointssolvingandcontactoverlapscalculation.In order to realize 2D DEM analyzingmodel built byboundary2D CAD model(CADsoftwareplan),itadoptsBresenhamarithmetictosetboundarygraphicelementinformation so as to process proximity query, utilizes geometrical and numericalmethod to process the calculation of contact-detection, contact-points solution andcontact-overlaps between particles and boundaries, it also presents the thought ofmodeling DEM computing courses. The DEM computing model is composed of thecontacting model, dynamic equation, searching algorithm and methodology andtheoryofDEMcomputing.Based on the methodology and theory above, the DEM simulation software isdeveloped with VC++6.0 platform. This paper introduces the framework, function ofthe software and the key techniques to realize the software, including generatingparticles, detecting method for the contact of particles and the boundary, thecomputational process of DEM, description of object classes, etc. It uses the objectoriented method to analyze the software demand analysis, software method ofexploitation, software system structure, software data communication so on, it alsoaims at simulation software which develops, using white box test and the black boxtest to carryon the test analysis for this integrated software, confirmed the software'saccuracy and validity, this also provides the method and the reference for the similarsoftware research. Above this foundation, this paper but also has carried on thesimulation test to several complex structures precision seed metering devices'workprocess, compares the analytic result and the experimental result, further hasconfirmedthesoftware'saccuracyandvalidity.Test results prove the correctness and validityof the algorithm, theyalso provideaviablemethodforsimulationanalyseofthecomplicatedparticles'DEMmovement.The virtues of this 2D design-analysis software are:â‘ It can establish theanalyse model based on the 2D CAD model of related mechanism directly, and thencanimplementtheintegrationbetweenCADsoftwareandtheDEManalysissoftware,thereby can integrate the CAD design and DEM performance analysis of relatedmechanism.â‘¡It can analyze and evaluate the performance of boundary withdifferent structure and accessional parameters through modifying the CAD model indesigning period, and can realize the optimization of structure scheme and sizeparameter of related mechanism or make the decision according to the requirementfor designing .â‘¢It can carry through a dynamic simulation for the working processof mechanical parts based on the CAD model, therefore can analyze the workingmechanism and invent the mechanical parts with new mechanism. These cannot beimplemented by current design methods and technique of mechanical parts that arerelative to granular materials.â‘£It can build the particle's model by superquadraticsequation. This establishes the generalization for the particles modeling and makesDEMcomputingforparticleswhichcanbeanycomplicatedshape. |
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