Basic Theories And Research Of Algorithms For DEM Based On Elliptical Particles Model

There are lots of flows of granular materials (such as granulated fertilizer, soil, leechdom, coal and rock) and actions between granular materials and working parts of machinery in industrial and agricultural production. For example, there are also have the flows of granular materials among the agricultural product planting, harvesting, transportation, graduation, processing, packing and so on. In the industrial production, such as pharmacy, metallurgy, energy sources and mine, there are also lots of flows of granular materials.The flows of granular materials have the relations not only with itself mechanical properties but also with the farm machinery's working part structural style, size parameter, movement parameter and so on. A good farm machinery design should make granular materials to flow according to the expectation way, so as to reduce the unnecessary damage. For example, when sowing seeds, the seeds'flowing should reduce the damage of the seeds and it should save the mechanical power consumption, when farming the land, it should consider the mutual function and its dynamics question between the farm machinery's working part and granular materials.Granular materials have the property between the solid and the fluid, although its structure is simple, they have the complex mechanics characteristic. 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 materials as a whole, and it is unable to analyze the movement course of each particle and the interaction among the colony, and it also can not analyze the situation of the contact and the separation among the granular materials. As a result, it can not resolve the problem very well. Recently when designing the related mechanical parts, designers mostly depended on their experience and experimentation methods, and it takes both time and stamina a lot and can not 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 are far away from satisfaction.In seventies of the 20th century, Cundall et al. put forward the DEM (Discrete Element Method) primarily. The basic thought is to simplify granular materials as a set of particles with a certain kind of shape and mass, and endue 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 particles and contacted boundaries. The dynamic laxity method, the Newton's Second Law and time step iteration are introduced into DEM to calculate the movement and displacement of each particle, and thus it is especially compatible to resolve the nonlinear problem. It can analyze particle lumping, destruction of the whole material, flowing heterogeneously, chemical reaction and heat transfer, when adopting different dynamics equations. It can analyze not only the interaction among various granular materials and different border but also the influence on the motion of granular materials, according to changing the model of particle, the model of border, dynamics equations and parameters in Discrete Element Method. Because of these virtues mentioned above, DEM has become a popular method on studying the kinetic problem of granular materials, and it is widely applied in the fields 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.Therefore, according to the characteristics and design requirements of working parts of machinery, our teamwork present a novel method to establish a 2D DEM to analyze model of machine's parts based on their CAD model. And then we implement the integration of CAD software and the DEM analyzing software by self-development for analyzing the performance of machine's parts which are contacted with granular materiels at working, thereby establish a novel universal digital design method and integrated software for designing and analyzing the mechanical parts. The software will offer a new method and new tool for optimal design of the mechanical parts.Based on the computing theory of DEM methodology, arithmetic and the production of programming, with the characteristic and design requirement interrelated mechanical parts. This paper uses ellipse equation to build the 2D DEM analytic models of ellipse particles, puting forward to adopt ellipse particles exterior circles to process preliminary contact inspections, adopts the method of geometric potential with ellipse equation to process contact inspections, contact overlaps calculation, contact strength, particles's velocity and displacement between particles and boudaries, it also presents the thought of modeling DEM computing course.Based on the methodology and theory above, this paper uses C++ developed the 2D ellipse particles DEM simulation software with VC++6.0 development platform. This paper introduces the requirement, framework, primary functions of the software and the key techniques of realizing the software, perfects and appends the functions of the 2D DEM simulation software, including ameliorating the arithmetic of Bresenham about the arc boundary in the field of proximity query, distinguishing the entry of particles from CAD, and appending the entry of particles sports attributes, also realizing computational process of 2D DEM, simulating multi-shapes and multi-particles, displaying the simple polygon entry and generating points in the simple polygon and so on.This paper adopts black testing and white testing to analyze circle DEM system and ellipse DEM system. Contrast analyzing the change of dynamics, displacement, velocity based on the circle particles model and the ellipse particles model in the computing process. Through analyzing the some different shapes of ellipse particles, we can know that the effective of 2D-DEM compute software is not influence on the shape of ellipse particles. Test results prove the feasibility and usability of the 2D-DEM compute software. And this paper also provides a new method and new tool for researching the DEM.The virtues of this 2D design-analysis software are as follows,①It can establish the analyse model based on the 2D CAD model of related mechanism directly, and then can implement the integration between CAD software and the DEM analysis software, thereby can integrate the CAD design and DEM performance analysis of related mechanism.②I t can analyze realize the simulation of the working process of mechanical parts by modifying the mechanical model parameters, such as the density and the friction coefficient of the particles and the normal and tangential stiffness coefficient, and so on.③It can carry through a dynamic simulation for the working process of mechanical parts based on the CAD model, therefore it can analyze the working mechanism and give some changes of dynamics, displacement and velocity.④It can build the particle's model by generic ellipse equation. This realizes the generalization of the particles modeling and the DEM of the ellipse particles. It also develops and realizes the 2D ellipse particles DEM simulation software, thus extends the using scope of this software.