The Research Of A Method For Representing Boundaries Of DEM Based On 2D CAD Model

There are lots of granular materials in the nature, and the traditional continuum mechanics method (CMM), which is applied to research the interaction between granular materials and related mechanical parts, can only consider the granular colony as a whole, and it is unable to analyze the movement course of each granular particle and the interaction among the colony. As a result, it cannot resolve the problem very well. Recently when designing the related mechanical parts, the experience and experimentation methods are depended on mostly, and it takes both time and stamina a lot and cannot achieve the expected designing purpose. It is estimated that the abrasion loss of related equipments during the carrying course of granular materials costs 40%, and the demand of optimized design and energy saving is far away from satisfaction.In seventies of the 20th century, Cundall et al. put forward the DEM primarily. The basic thought is to simplify granular colony as a set of particles with a certain kind of shape and mass, and endues the particle-particle and particle-boundary relationship with a certain kind of contact mechanics model and some parameters. The DEM is applied to research the contact effects, which influence the particle-particle and particle-boundary relationship, and the different physical and mechanical characteristics between particle and contacted boundary. The dynamic laxity method, the Newton's Second Law and time step iteration are introduced in DEM to calculate the movement and displacement of each particle, and thus it is especially compatible to resolve the nonlinear problem. Because of these virtues mentioned above, DEM has become a popular method on studying the kinetic problem of granular colony, and it is widely applied in the field of rock engineering and sands flowing; the transportation, mixing, classification of granular materials; the agglomeration and collision of granular materials; the interaction between granular materials and related mechanical parts; the equipment of chemical industry and mine engineering.With the extensive application of DEM, it becomes an emphasis and difficulty in the research of boundary modeling of DEM and the development of the software of DEM that how to build up an analysis of boundary model of DEM with the complicated structure and the style of movement. This paper is based on the present status of the research of DEM and the summary of the current boundary modeling of DEM. I put forward a method of building up an analysis of boundary model of DEM from the CAD model of 2D mechanical. Also it can implement the integration of the software of AutoCAD and the software of 3D DEM analysis and simulation, thereby we develop the general system of the design of structure and the analysis of performance in the integrated analysis and design of mechanical. We also proved the feasibility of the method through lots of calculation and simulation experiment of DEM.Since DEM proposed in the past, the main boundary modeling method on roughly have been divided into two directions: One method is compiles the boundary through the computer program; Another method is use general modeling software, establishes the boundary model, then through the computer secondary development, obtain the boundary information which is needed and join into the DEM software. The merit of modeling through the computer program is through this method, the boundary model is closely related to the DEM. In the realization process, the operation should quite be strong regarding the boundary. But this method has very big drawbacks. The main drawback is that the index relations with the workload.Therefore although the mentality of this method is quite clear, regarding the actual application, the significance is not very big. Use general modeling software can easily establish complex boundary model, and there is also quite splendid modeling software in the market that already has successfully demonstrated in the direction of 2D boundary modeling. But in the 3D direction, there is not a very unified method. At present, there are two main solutions. One is use 3D drawing software draws up the boundary, then read the information through the computer; The other is use 2D drawing software draws up 2D graph, then through the matching arithmetic, obtain the 3D geometric information and establish the 3D DEM modelAt present, the method of building 3D model from 2D model presented by internal or abroad divided into several categories:â‘ The method use tensile approach. The advantage of using this method is that can be understanded easily. To build a 3D model by adding depth property. This method regarding the simple standard position graph may the quite easy realization, but regarding complex combination entity reconstruction on comparison difficulty.â‘¡Based on 2D three views model establishment three-dimensional model. Between these methods main mentality is the basis 3D entity projecting three mutually perpendicular projection planes the relations, using the 2D information of three views to gain 3D information of the projection entity. This method merit lies inwith the production practice relation is close, may describe the quite complex boundary model.According to the analysis of AutoCAD inner data's storage pattern, and the summary of the three-dimensional rebuild's ideology, we use the three view of planar projection to rebuild the object of three-dimensional. First, we build a planar identification coordinate correspond to the three-dimensional coordinate, second, we rebuild the object and acquire the geometrical parameters, the method used in this articles include top to bottom and bottom to top, and we mixed up the method to use it, and put forward a universal method to acquire the information of conicoid, face the regular object in the same circle, take some special algorithm to acquire all the object's geometrical parameters from an example. When we got all object's geometrical parameters, we need combine the type of movement, and set the information of movement and material, the real and virtual attribute of object and the object to adhere up to the 3D mechanical. Then, we transfer the information of topology, geometry, movement and material, and real and virtual attribute to external user's database. The software of 3D DEM analysis and simulation obtain the primitive record, including the geometric information of boundary (type of primitive topology, feature parameter of boundary), the information of movement (movement attribute parameter of primitive), the information of material (material parameter of primitive). It need build up the instance of the class of primitive of DEM, and then store all the primitive instance. These can be provided in the process of the calculation and simulation of DEM. As a result, it builds up an analysis of boundary model of DEM, including the model of topology and geometry of 3D boundary, the model of movement and the attribute of material, the real and virtual attribute of object.Our workgroup have finished the method of 2D modeling and software, add some fuction, such as adding the particle's entrance, acquire the information of ellipse and NURBS lines, etc. Perfect the 2D boundaries modeling and the software. To take this integrated software by lots of boundary's 2D CAD models building 3D DEM analytical models, and do some emulator to the tangency between the particle and the boundary. The models and analycal prove the right and validity of the boundary's modeling and the software.The advantage of building up an analysis of boundary model of DEM from the CAD model of 2D mechanical:â‘ we reduce the requirement of drawing table, when we design the component of machine, we can draw any component of machine in the CAD that we familiar with, and at present the 3D drawing is not so mature, we did not have a good development kit to redevelop.â‘¡when we use the CAD drawing system to set the component of machine, the user can adjust the drawing position, size and shape conveniently, to bring more convenience for user, the lot of attribute of the object added by user prepare the DEM software emulator abundantly.â‘¢in the course of object's modeling, we do lots of work to the data, satisfy the requirement the component's emulator, and this method connect with practice tight, and can describe the complex object model.