The Improvement Of Boundary Modeling Method Of3D DEM

China is a large agricultural country. With the development of science andtechnology in agricultural production, the utilization rate of agricultural machinery isincreasing. In the case of large-scale use of agricultural machinery, designing efficientmechanical components is particularly important. After completing the design ofmechanical parts, need to experiment to determine the feasibility of mechanicaldesign, the use of computer simulation technology in the pilot phase, to replace thetraditional test procedure can significantly improve the design efficiency ofmechanical components.During the simulation of agricultural machinery components, need to calculatethe mechanics relationship between granular objects such as soil, seeds andmechanical components. DEM(Discrete element method) is a common method ofparticle object simulation, the basic idea is: divide the research objects intoindependent elements, each elements has the size, quality and other physicalproperties, set the mechanics relationship between element and element or boundaryobject, analyze each element’s mechanical state can give the movement state of theresearch object in a time step, the whole movement can calculated by analyzing themovement state of the research object in continuous time steps.When simulating the movement of mechanical components by DEM, inaddition to build particle object analytical model, but also need to build models ofmechanical components, namely boundary modeling process. Agricultural machinerycomponent with complex structures, in order to be modeled accurately, our group usesecondary development method based on Pro/E software to build boundary models.To optimize the software, add automatic extraction of boundary features and adaptivemesh generation capabilities. In order to solve the versatility problem of the programbased on CAD software, proposed the boundary modeling method based on STL files.In this paper, the research group developed boundary modeling software has beenoptimized, the software can automatically recognizes all the surface of a solid model,and then mesh all surfaces to complete the solid model meshing process. After this,you may also need to set the motion properties or material properties of the part, the software automatically recognizes all the parts contained in assembly for user tochoose and set properties. After completing the above steps, save the results into adatabase for simulation program. The optimized software decrease the interactionwith user, and improve the user experience of the software.The quantity and quality of grid will affect the computing speed and accuracy ofsimulation. When using the uniform grid to represent a surface and the current surfacehas small part need detail description. In order to ensure accuracy, it is necessary touse small size grid to represent the surface, which increases the number of grid anddecrease the computing speed. Adaptive mesh generation method can decide the meshsize depends on the surface features, it generate small size grid at feature point andnormal size grid in other parts, thus reducing the grid number without sacrificing theaccuracy.CAD-based modeling software highly integrated with CAD software, it candirectly access the underlying data of the solid. However, this method is highlydependent on CAD software, the need for different CAD software to develop differentsoftware, making the software development and maintenance difficult. STL file is acommon file format to represent a CAD model and almost all CAD software canexport the model as an STL file format. Boundary modeling method based on STLfiles solves this versatility problem.After the completion of the improvement to the software, need to test thesoftware to ensure the correctness of the result. Test results show that the software cancorrectly identify all surfaces in the model and mesh all the surfaces. After settingmovement properties for the component, part can move correctly. Software also canadaptively determine the gird size according to the geometric features of surface whilemeshing the surface. To test the meshing function based on STL file, the test resultswere compared with the origin CAD model, the test results show that the generationmesh can accurately restore feature CAD models. In summary, the boundarymodeling software can generate boundary grid of the modeled correctly.